Changes in Rosatta's FAQ, see HN id = 8611198 and https://web.archive.org/web/20140805030451/http://www.esa.int/Our_Activities/Space_Science/Rosetta/Frequently_asked_questions v.s. http://www.esa.int/Our_Activities/Space_Science/Rosetta/Frequently_asked_questions

faq-diff.txt

diff --git a/faq.fmt b/faq.fmt
index a671bc6..d5511e7 100644
--- a/faq.fmt
+++ b/faq.fmt
@@ -56,12 +56,12 @@ surface and make the first in-situ subsurface analysis of its composition.
 It will also be the first mission to investigate a comet’s nucleus
 and environment over an extended period of time.
 
-How will Rosetta reach comet 67P/Churyumov-Gerasimenko, and how long will
-it take?  Comet 67P/Churyumov-Gerasimenko loops around the Sun between
-the orbits of Jupiter and Earth, that is, between about 800 million and
-185 million kilometres from the Sun. But rendezvousing with the comet
-required travelling a cumulative distance of over 6 billion kilometres. As
-no launcher was capable of directly injecting Rosetta into such an orbit,
+How did Rosetta reach comet 67P/Churyumov-Gerasimenko, and how long did
+it take?  Comet 67P/Churyumov-Gerasimenko loops around the Sun between the
+orbits of Jupiter and Earth, that is, between about 800 million and 186
+million kilometres from the Sun. But rendezvousing with the comet required
+travelling a cumulative distance of over 6.4 billion kilometres. As no
+launcher was capable of directly injecting Rosetta into such an orbit,
 gravity assists were needed from four planetary flybys – one of Mars
 (2007) and three of Earth (2005, 2007 and 2009) – a long circuitous
 trip that took ten years to complete.
@@ -73,8 +73,8 @@ from the nebula out of which our Sun and planets were formed. Planets have
 gone through chemical transformations, but comets have remained almost
 unchanged. Furthermore, comets brought ‘volatile’ light elements to
 the planets and likely played an important role in forming oceans and
-atmospheres. Comets are also carry complex organic molecules that may
-have been involved in the origin of life on Earth.
+atmospheres. Comets also carry complex organic molecules that may have
+been involved in the origin of life on Earth.
 
 What do we presently know about how the Solar System formed?  The Solar
 System formed about 5 billion years ago when a butt of gas and dust
@@ -132,26 +132,24 @@ after the comet reaches its closest point to the Sun (in August 2015)
 and starts heading back towards the outer Solar System.
 
 How long will the lander operate on the comet nucleus?  The Rosetta
-lander, called Philae, will touch down on the comet's surface in
-November 2014 and remain operational through the end of 2015. The
-science observations will start immediately. During the first week
-– the minimum mission target – a first run of the most important
-scientific measurements will be completed. During this phase the lander
-can operate on primary battery power, should this be necessary. In a
-second phase that is meant to last up to three months, a secondary set
-of observations will be conducted, using backup batteries that will be
-recharged by the energy from the solar cells on the lander. However,
+lander, called Philae, will touch down on the comet's surface on 12
+November 2014. The science observations will start immediately. During
+the first 2.5 days the first series of scientific measurements will be
+completed. During this phase the lander will operate on primary battery
+power. In a second phase that may last up to three months, a secondary
+set of observations will be conducted, using backup batteries that will
+be recharged by the energy from the solar cells on the lander. However,
 no one knows precisely how long the lander will survive on the comet.
 
 Could activity on the comet's surface damage or destroy the lander?
 Survival of the lander depends on a number of factors, such as power
-supply, temperature, or surface activity on the comet. At some stage
-the lander will probably become too cold, i.e. its solar arrays will no
-longer provide enough energy to continue operation and maintain a benign
-thermal environment for the electronic units.
+supply, temperature, or surface activity on the comet. For example, dust
+may cover the solar panels, preventing the battery from recharging. In
+any case, by March 2015, when the comet is closer to the Sun, it is
+likely that the lander will become too hot to operate.
 
 What scientific instruments are on board the spacecraft and what will
-they do? Rosetta's goal is to examine the comet in great detail. The
+they do?  Rosetta's goal is to examine the comet in great detail. The
 instruments on the Rosetta orbiter include several cameras, spectrometers,
 a number of sensors, and experiments that work at different wavelengths
 – infrared, ultraviolet, microwave, and radio. They will provide,
@@ -212,9 +210,9 @@ another NASA mission, Dawn, explored the asteroid Vesta. Dawn is now
 en route to dwarf planet Ceres, which is the largest object in the
 Asteroid Belt.
 
-What is known about the comet that Rosetta will land on?  Comet
-67P/Churyumov-Gerasimenko is a large, dirty snowball whose orbit around
-the Sun takes 6.6 years. This makes it a short-period comet.
+What was known about the comet before Rosetta arrived there?  Comet
+67P/Churyumov-Gerasimenko orbits the Sun once every 6.6 years. This
+makes it a short-period comet.
 
 Ground-based telescopes have observed 67P/Churyumov-Gerasimenko during
 almost all its appearances since its discovery in 1969. To acquire
@@ -223,30 +221,31 @@ implemented a rigorous ground and space-based observation programme of
 67P/Churyumov-Gerasimenko. These observations provided a fairly reliable
 estimate of the comet’s size – about 4 kilometres in diameter.
 
-Where will 67P/Churyumov-Gerasimenko be at the time of the rendezvous?
-Rosetta will meet 67P/Churyumov-Gerasimenko when it is still in the cold
-regions of the Solar System at over 600 million kilometres from the Sun,
-when the comet and Rosetta are on their return journey back into the
-inner Solar System.
-
-Will the comet be active at the time of rendezvous?  We expect that the
-comet will not be showing much sign of surface activity when Rosetta
-catches up with it in May 2014. When comets get close to the Sun, the
-Sun’s heat 'activates' them. The frozen gases on and below the surface
-sublimate – they pass directly from the solid to the gaseous state –
-and the outflowing gas drags small dust grains with it into surrounding
-space. This creates an atmosphere around the nucleus, known as the coma,
-and generates a dust tail that streams out behind the comet along its
-orbit. Rosetta will therefore become the first spacecraft to witness at
-close quarters the development of a comet's coma and subsequent tails.
+Where was 67P/Churyumov-Gerasimenko at the time of the rendezvous?
+Rosetta met 67P/Churyumov-Gerasimenko when it was still in the cold
+regions of the Solar System 673 million kilometres from the Sun, when
+the comet and Rosetta were on their return journey back into the inner
+Solar System.
+
+Was the comet active at the time of rendezvous?  As we expected, the comet
+was only showing minimal signs of activity at the time of rendezvous.
+When comets get close to the Sun, the Sun’s heat 'activates' them. The
+frozen gases on and below the surface sublimate – they pass directly
+from the solid to the gaseous state – and the outflowing gas drags small
+dust grains with it into surrounding space. This creates an atmosphere
+around the nucleus, known as the coma, and generates a dust tail that
+streams out behind the comet along its orbit. Rosetta will therefore
+become the first spacecraft to witness at close quarters the development
+of a comet's coma and subsequent tails.
 
 When does 67P/Churyumov-Gerasimenko come closest to the Sun?  Comet
-67P/Churyumov-Gerasimenko last passed through its perihelion – 185
-million km from the Sun – on 18 August 2002. Even at that point, when
-its brightness was at its maximum, it was impossible to see it with the
-naked eye. Only medium or large telescopes were able to observe it.
+67P/Churyumov-Gerasimenko last passed through its perihelion on 18 August
+2002. Even at that point, when its brightness was at its maximum, it was
+impossible to see it with the naked eye. Only medium or large telescopes
+were able to observe it.
 
-It will next pass through perihelion on 13 August 2015.
+It will next pass through perihelion on 13 August 2015, 186 million
+kilometres from the Sun.
 
 What is the gravity on 67P/Churyumov-Gerasimenko's surface, compared
 with that on Earth?  Comet 67P/Churyumov-Gerasimenko is so small that
@@ -356,9 +355,9 @@ for six months. After this period, the data will be stored in ESA’s
 Planetary Science Archive and made freely available to the world's
 scientific community.
 
-How big is the spacecraft?  The spacecraft dimensionsare2.8 x 2.1 x 2.0
-metres. There are two 14-metre-long solar panels with a total area of
-64 square metres. From tip to tip, the spacecraft spans 32 metres.
+How big is the spacecraft?  The spacecraft dimensions are 2.8 x 2.1 x
+2.0 metres. There are two 14-metre-long solar panels with a total area
+of 64 square metres. From tip to tip, the spacecraft spans 32 metres.
 
 Rosetta's total launch mass is 3,000 kilograms. The spacecraft carries
 1,670 kilograms of propellant and the lander weighs 100 kilograms.
@@ -378,9 +377,9 @@ the Netherlands to confirm its endurance. These tests involved heating
 the outside surfaces to more than 150°C and then cooling them to -180°C
 without damaging the instruments.
 
-Is Rosetta preprogrammed or are commands sent from the ground?  Rosetta is
-operated from the ground. It was impossible to programme manoeuvres for
-the whole mission before the launch because this would have entailed
+Is Rosetta pre-programmed or are commands sent from the ground?  Rosetta
+is operated from the ground. It was impossible to programme manoeuvres
+for the whole mission before the launch because this would have entailed
 adjustments at each stage of the journey. Ground commands are sent
 periodically to readjust the spacecraft’s trajectory. These take up
 to 50 minutes to reach the spacecraft, when it is farthest from the Earth.
@@ -394,27 +393,12 @@ spacecraft could remain operational during critical mission phases. For
 example, to avoid losing power, the spacecraft automatically positions
 itself with the solar panels facing the Sun.
 
-How will Rosetta deterimine its position with respect to
-67P/Churyumov-Gerasimenko?  Once close to comet 67P/Churyumov-Gerasimenko
-in May 2014, Rosetta will begin its final approach. The approach will
-start even before Rosetta’s cameras have imaged the comet, so extremely
-accurate calculations of 67P/Churyumov-Gerasimenko’s position, orbit,
-size, shape and rotation, based on ground-based observations, will be
-essential. These calculations will improve dramatically as soon as the
-first camera images are available.
-
-What are the chances that the orbit of 67P/Churyumov-Gerasimenko may
-change drastically before Rosetta reaches it?  Close to zero. It would
-require a dramatic cosmic event to alter the comet’s orbit, and that
-is very unlikely.
-
-Why was it necessary to keep Rosetta in hibernation for much of its
-trip to the comet?  To limit its consumption of power and fuel, and to
-minimise operating costs. When the spacecraft is hibernating, it spins
-once per minute and faces the Sun, so that its solar panels can receive
-as much sunlight as possible. Almost all of the electrical systems are
-switched off, with the exception of the radio receivers, command decoders
-and power supply.
+Why was it necessary to keep Rosetta in hibernation for 31 months?
+To limit its consumption of power and fuel, and to minimise operating
+costs. During hibernation it was spinning once per minute and faced
+the Sun, so that its solar panels could receive as much sunlight as
+possible. Almost all of the electrical systems were switched off, with
+the exception of the radio receivers, command decoders and power supply.
 
 How far did Rosetta get from the Earth and when did it reach this point?
 In mid 2012 Rosetta recorded its maximum distance from the Sun and Earth
@@ -467,8 +451,9 @@ Will there be any possibility of adjusting the landing sequence once it
 is initiated?  No. Once the landing sequence has been defined (release
 speed, position for release etc.) and initiated, it will not be possible
 to adjust it. However, it should be recalled that the lander will be
-released at a height of about 1 kilometre and will touch down on the
-comet at walking speed, minimizing the risk of an incident.
+released at a height of about 22.5 kilometres from the centre of the
+comet and will touch down on the comet at walking speed, minimizing the
+risk of an incident.
 
 What if the lander touches down on a very steep slope and drills itself
 into an awkward angle, or sinks into porous snow or some other soft
@@ -532,17 +517,12 @@ has a single interface with the spacecraft. When the lander Announcement
 of Opportunity went out, it was agreed to consider the entire unit as
 a single instrument.
 
-What is the total mission cost?  The total mission cost of Rosetta is
-close to 1.3 billion Euros (in 2014 economic conditions) including
-expenses for the one year launch delay. The mission cost covers
-development and construction of the spacecraft and all of its instruments,
-including the lander, together with launch and operations.
-
-The cost to ESA is about 1 billion Euros (in 2014 conditions).
-
-The cost for all instruments, including the lander, is estimated to be
-about 300 million Euros, funded by the member states through national
-scientific institutes.
+What is the total mission cost?  The total mission cost of Rosetta
+is close to 1.4 billion Euros of which the total Philae costs are 220
+Million Euros (in 2014 economic conditions) including expenses for the one
+year launch delay. The mission cost covers development and construction
+of the spacecraft and all of its instruments, including the lander,
+together with launch and operations.
 
 Though the total cost is high, this should be put in perspective. The
 figure is barely half the price of a modern submarine, or three Airbus
@@ -643,52 +623,48 @@ grounded following the inaugural failure of Arianespace’s new high
 payload Ariane 5 ECA, on 11 Dec 2002, depriving Rosetta of its launch
 opportunity to the comet Wirtanen.
 
-What is the planned sequence of events once Rosetta wakes up from its
-long hibernation?  Rosetta entered deep space hibernation in June 2011,
-with its solar arrays pointing towards the Sun and maintaining a slow
-spin to maintain stability. It is scheduled to exit on 20 January 2014
-at 10 AM GMT. At that time, it will be around 9 million km from its
-target. The spacecraft will warm up for several hours and go into ‘safe
-mode’, making it possible to switch on its navigational payload and
-spin down to point the main antenna towards Earth so communications can
-be re-established. Contact with Earth is not expected before 17:30 GMT.
-
-From February to April, engineers will perform a checkout of the orbiter,
-its payload and the lander and gradually bring the instruments back
-into operation. By that time, the spacecraft will have moved to within
-1 million km of the comet, close enough to actually see it. If all goes
-well, the first images will arrive in May, helping engineers to more
-accurately calculate the comet’s position and orbit. At the end of the
-month, a sequence of thruster manoeuvres will be undertaken to line the
-spacecraft up with the comet and move it to within 100,000 km.
-
-Orbiter science will begin in June. The initial focus will be on
-generating imagery necessary to determine the size, shape, spin rate
-and other parameters of the comet nucleus and obtaining an initial
-assessment of the coma, particularly its density and gas production rate,
-so engineers can synchronize the spacecraft’s orbit with that of the
-comet. The orbit is expected to be around 30 km above the surface, safe
-enough to protect from the effects of cometary dust, with occasional
-flyovers to within 10 kms or so for closer observation.
-
-In August-September, an extensive mapping campaign will be undertaken
-to determine a suitable landing site. Touchdown is scheduled for November.
-
-Engineers will then recharge the lander batteries and initiate the surface
-science portion of the mission, which will includes high-resolution
+What happened after Rosetta woke up from its long hibernation?  Rosetta
+entered deep space hibernation on 8 June 2011, waking up 31 months later
+on 20 January 2014, at 18:18 GMT.
+
+At this stage, Rosetta was still 9 million km from its target. From
+February to April, engineers performed a checkout of the orbiter,
+the lander, and their respective payloads. The first images of the
+comet were taken at the end of March, from a distance of 5 million
+km. Between May and August a series of ten critical manoeuvres were
+executed to match the spacecraft’s velocity and trajectory with that
+of the comet. The spacecraft arrived at a distance of 100 km from the
+comet on 6 August 2014.
+
+An extensive mapping and data-collection campaign took place over
+the following six weeks to determine a suitable landing site for the
+mission’s lander, Philae. At the same time, Rosetta moved to within 30
+km of the comet, and later to 10 km for closer observation. A landing
+site located on the comet’s smaller lobe was selected, identified as
+‘Site J’.
+
+Landing is scheduled for 12 November. It will take about seven hours
+for Philae to descend to the surface of the comet, during which it will
+take images and make measurements of the comet’s environment. After
+touchdown, the initial battery lifetime of the lander is expected to
+be about 64 hours. Science measurements will include high-resolution
 images of the comet, in-situ measurements and extraction and analysis
-of subsurface samples.
-
-What are the critical remaining risk elements at this stage of
-the mission?  The primary risk involves the orbiter’s thrusters,
-which will have to perform at lower pressure than planned because of a
-Reaction Control System leak that occurred in September 2006. Engineers
-are also concerned about the reaction wheels themselves, which have
-exhibited some noise. However, contingency testing has demonstrated
-that the system can be operated in a more efficient operating mode,
-reducing the wear. Moreover, new software has been developed to allow
-operation in hybrid mode, which would permit the spacecraft to operate
-with just two wheels.
+of subsurface samples. Solar illumination conditions and the amount of
+dust settling on the lander’s solar panels will determine the length
+of the long term science phase.
+
+Meanwhile Rosetta continues its science mission, following the comet
+through its closest approach to the Sun on 13 August 2015, and beyond.
+
+What were the critical remaining risks at this stage of the mission?
+The primary risk involved the orbiter’s thrusters, which have to perform
+at lower pressure than planned because of a Reaction Control System leak
+that occurred in September 2006. Engineers were also concerned about the
+reaction wheels themselves, which have exhibited some noise. However,
+contingency testing has demonstrated that the system can be operated
+in a more efficient operating mode, reducing the wear. Moreover, new
+software has been developed to allow operation in hybrid mode, which
+would permit the spacecraft to operate with just two wheels.
 
 All previous deep space probes have used RTGs [Radio-isotope
 Thermoelectric Generator]. Why did ESA choose not to use them for Rosetta?
@@ -747,13 +723,13 @@ active near the Sun. In addition, the onboard software operating the
 attitude sensors will be able to differentiate between dust and stars,
 so that the spacecraft does not track the dust particles.
 
-Given the length of the journey, how can you be sure that the
-spacecraft/comet rendezvous will take place as planned?  Sophisticated
+Given the length of the journey, how could you be sure that the
+spacecraft/comet rendezvous would take place as planned?  Sophisticated
 and reliable computer models provided a high precision interplanetary
 trajectory for the comet rendezvous, and everything necessary was done
-to ensure that the mission proceeded as planned. When Rosetta nears
-the comet, we will use optical navigation techniques, so it will be
-practically impossible to miss the target.
+to ensure that the mission proceeded as planned. When Rosetta neared
+the comet, we used optical navigation techniques, so it was practically
+impossible to miss the target.
 
 No spacecraft has ever soft-landed on a comet. What are the risks during
 such a landing and how are they being minimised?  We have some idea of
@@ -808,9 +784,10 @@ on touchdown.
 
 The Rosetta lander will not be deployed until the orbiter has mapped the
 surface of the comet’s nucleus in high resolution and a safe landing
-site has been chosen. It will be released about one kilometre above the
-comet’s surface and descent will be very slow and controlled, with a
-touchdown speed of perhaps one metre per second (less than walking speed).
+site has been chosen. It will be released about 22.5 km from the comet
+centre (about 20.5 km from the surface) and descent will be very slow
+and controlled, with a touchdown speed of perhaps one metre per second
+(less than walking speed).
 
 And since the comet has no atmosphere, the lander will not require a
 heatshield, parachute or airbag, and there will be no concern about bad

faq-word-diff.txt

diff --git a/faq.fmt b/faq.fmt
index a671bc6..d5511e7 100644
--- a/faq.fmt
+++ b/faq.fmt
@@ -56,12 +56,12 @@ surface and make the first in-situ subsurface analysis of its composition.
It will also be the first mission to investigate a comet’s nucleus
and environment over an extended period of time.

How [-will-]{+did+} Rosetta reach comet 67P/Churyumov-Gerasimenko, and how long [-will-]{+did+}
it take?  Comet 67P/Churyumov-Gerasimenko loops around the Sun between the
orbits of Jupiter and Earth, that is, between about 800 million and [-185-]{+186+}
million kilometres from the Sun. But rendezvousing with the comet required
travelling a cumulative distance of over [-6-]{+6.4+} billion kilometres. As no
launcher was capable of directly injecting Rosetta into such an orbit,
gravity assists were needed from four planetary flybys – one of Mars
(2007) and three of Earth (2005, 2007 and 2009) – a long circuitous
trip that took ten years to complete.
@@ -73,8 +73,8 @@ from the nebula out of which our Sun and planets were formed. Planets have
gone through chemical transformations, but comets have remained almost
unchanged. Furthermore, comets brought ‘volatile’ light elements to
the planets and likely played an important role in forming oceans and
atmospheres. Comets[-are-] also carry complex organic molecules that may have
been involved in the origin of life on Earth.

What do we presently know about how the Solar System formed?  The Solar
System formed about 5 billion years ago when a butt of gas and dust
@@ -132,26 +132,24 @@ after the comet reaches its closest point to the Sun (in August 2015)
and starts heading back towards the outer Solar System.

How long will the lander operate on the comet nucleus?  The Rosetta
lander, called Philae, will touch down on the comet's surface [-in-]{+on 12+}
November [-2014 and remain operational through the end of 2015.-]{+2014.+} The science observations will start immediately. During
the first [-week-]
[-–-]{+2.5 days+} the[-minimum mission target – a-] first [-run-]{+series+} of[-the most important-] scientific measurements will be
completed. During this phase the lander [-can-]{+will+} operate on primary battery
[-power, should this be necessary.-]{+power.+} In a second phase that [-is meant to-]{+may+} last up to three months, a secondary
set of observations will be conducted, using backup batteries that will
be recharged by the energy from the solar cells on the lander. However,
no one knows precisely how long the lander will survive on the comet.

Could activity on the comet's surface damage or destroy the lander?
Survival of the lander depends on a number of factors, such as power
supply, temperature, or surface activity on the comet. [-At some stage-]{+For example, dust+}
{+may cover the solar panels, preventing the battery from recharging. In+}
{+any case, by March 2015, when the comet is closer to the Sun, it is+}
{+likely that+} the lander will[-probably-] become too [-cold, i.e. its solar arrays will no-]
[-longer provide enough energy-]{+hot+} to [-continue operation and maintain a benign-]
[-thermal environment for the electronic units.-]{+operate.+}

What scientific instruments are on board the spacecraft and what will
they do?  Rosetta's goal is to examine the comet in great detail. The
instruments on the Rosetta orbiter include several cameras, spectrometers,
a number of sensors, and experiments that work at different wavelengths
– infrared, ultraviolet, microwave, and radio. They will provide,
@@ -212,9 +210,9 @@ another NASA mission, Dawn, explored the asteroid Vesta. Dawn is now
en route to dwarf planet Ceres, which is the largest object in the
Asteroid Belt.

What [-is-]{+was+} known about the comet [-that-]{+before+} Rosetta [-will land on?-]{+arrived there?+}  Comet
67P/Churyumov-Gerasimenko [-is a large, dirty snowball whose orbit around-]{+orbits+} the Sun [-takes-]{+once every+} 6.6 years. This
makes it a short-period comet.

Ground-based telescopes have observed 67P/Churyumov-Gerasimenko during
almost all its appearances since its discovery in 1969. To acquire
@@ -223,30 +221,31 @@ implemented a rigorous ground and space-based observation programme of
67P/Churyumov-Gerasimenko. These observations provided a fairly reliable
estimate of the comet’s size – about 4 kilometres in diameter.

Where [-will-]{+was+} 67P/Churyumov-Gerasimenko[-be-] at the time of the rendezvous?
Rosetta [-will meet-]{+met+} 67P/Churyumov-Gerasimenko when it [-is-]{+was+} still in the cold
regions of the Solar System [-at over 600-]{+673+} million kilometres from the Sun, when
the comet and Rosetta [-are-]{+were+} on their return journey back into the inner
Solar System.

[-Will-]{+Was+} the comet[-be-] active at the time of rendezvous?  [-We expect that-]{+As we expected,+} the comet
[-will not be-]{+was only+} showing [-much sign-]{+minimal signs+} of[-surface-] activity [-when Rosetta-]
[-catches up with it in May 2014.-]{+at the time of rendezvous.+}
When comets get close to the Sun, the Sun’s heat 'activates' them. The
frozen gases on and below the surface sublimate – they pass directly
from the solid to the gaseous state – and the outflowing gas drags small
dust grains with it into surrounding space. This creates an atmosphere
around the nucleus, known as the coma, and generates a dust tail that
streams out behind the comet along its orbit. Rosetta will therefore
become the first spacecraft to witness at close quarters the development
of a comet's coma and subsequent tails.

When does 67P/Churyumov-Gerasimenko come closest to the Sun?  Comet
67P/Churyumov-Gerasimenko last passed through its perihelion[-– 185-]
[-million km from the Sun –-] on 18 August
2002. Even at that point, when its brightness was at its maximum, it was
impossible to see it with the naked eye. Only medium or large telescopes
were able to observe it.

It will next pass through perihelion on 13 August [-2015.-]{+2015, 186 million+}
{+kilometres from the Sun.+}

What is the gravity on 67P/Churyumov-Gerasimenko's surface, compared
with that on Earth?  Comet 67P/Churyumov-Gerasimenko is so small that
@@ -356,9 +355,9 @@ for six months. After this period, the data will be stored in ESA’s
Planetary Science Archive and made freely available to the world's
scientific community.

How big is the spacecraft?  The spacecraft [-dimensionsare2.8-]{+dimensions are 2.8+} x 2.1 x
2.0 metres. There are two 14-metre-long solar panels with a total area
of 64 square metres. From tip to tip, the spacecraft spans 32 metres.

Rosetta's total launch mass is 3,000 kilograms. The spacecraft carries
1,670 kilograms of propellant and the lander weighs 100 kilograms.
@@ -378,9 +377,9 @@ the Netherlands to confirm its endurance. These tests involved heating
the outside surfaces to more than 150°C and then cooling them to -180°C
without damaging the instruments.

Is Rosetta [-preprogrammed-]{+pre-programmed+} or are commands sent from the ground?  Rosetta
is operated from the ground. It was impossible to programme manoeuvres
for the whole mission before the launch because this would have entailed
adjustments at each stage of the journey. Ground commands are sent
periodically to readjust the spacecraft’s trajectory. These take up
to 50 minutes to reach the spacecraft, when it is farthest from the Earth.
@@ -394,27 +393,12 @@ spacecraft could remain operational during critical mission phases. For
example, to avoid losing power, the spacecraft automatically positions
itself with the solar panels facing the Sun.

[-How will Rosetta deterimine its position with respect to-]
[-67P/Churyumov-Gerasimenko?  Once close to comet 67P/Churyumov-Gerasimenko-]
[-in May 2014, Rosetta will begin its final approach. The approach will-]
[-start even before Rosetta’s cameras have imaged the comet, so extremely-]
[-accurate calculations of 67P/Churyumov-Gerasimenko’s position, orbit,-]
[-size, shape and rotation, based on ground-based observations, will be-]
[-essential. These calculations will improve dramatically as soon as the-]
[-first camera images are available.-]

[-What are the chances that the orbit of 67P/Churyumov-Gerasimenko may-]
[-change drastically before Rosetta reaches it?  Close to zero. It would-]
[-require a dramatic cosmic event to alter the comet’s orbit, and that-]
[-is very unlikely.-]Why was it necessary to keep Rosetta in hibernation for [-much of its-]
[-trip to the comet?-]{+31 months?+}
To limit its consumption of power and fuel, and to minimise operating
costs. [-When the spacecraft is hibernating,-]{+During hibernation+} it [-spins-]{+was spinning+} once per minute and [-faces-]{+faced+}
the Sun, so that its solar panels [-can-]{+could+} receive as much sunlight as
possible. Almost all of the electrical systems [-are-]{+were+} switched off, with
the exception of the radio receivers, command decoders and power supply.

How far did Rosetta get from the Earth and when did it reach this point?
In mid 2012 Rosetta recorded its maximum distance from the Sun and Earth
@@ -467,8 +451,9 @@ Will there be any possibility of adjusting the landing sequence once it
is initiated?  No. Once the landing sequence has been defined (release
speed, position for release etc.) and initiated, it will not be possible
to adjust it. However, it should be recalled that the lander will be
released at a height of about [-1 kilometre-]{+22.5 kilometres from the centre of the+}
{+comet+} and will touch down on the comet at walking speed, minimizing the
risk of an incident.

What if the lander touches down on a very steep slope and drills itself
into an awkward angle, or sinks into porous snow or some other soft
@@ -532,17 +517,12 @@ has a single interface with the spacecraft. When the lander Announcement
of Opportunity went out, it was agreed to consider the entire unit as
a single instrument.

What is the total mission cost?  The total mission cost of Rosetta
is close to [-1.3-]{+1.4+} billion Euros {+of which the total Philae costs are 220+}
{+Million Euros+} (in 2014 economic conditions) including expenses for the one
year launch delay. The mission cost covers development and construction
of the spacecraft and all of its instruments, including the lander,
together with launch and operations.[-The cost to ESA is about 1 billion Euros (in 2014 conditions).-]

[-The cost for all instruments, including the lander, is estimated to be-]
[-about 300 million Euros, funded by the member states through national-]
[-scientific institutes.-]

Though the total cost is high, this should be put in perspective. The
figure is barely half the price of a modern submarine, or three Airbus
@@ -643,52 +623,48 @@ grounded following the inaugural failure of Arianespace’s new high
payload Ariane 5 ECA, on 11 Dec 2002, depriving Rosetta of its launch
opportunity to the comet Wirtanen.

What [-is the planned sequence of events once-]{+happened after+} Rosetta [-wakes-]{+woke+} up from its long hibernation?  Rosetta
entered deep space hibernation [-in-]{+on 8+} June 2011, [-with its solar arrays pointing towards the Sun and maintaining a slow-]
[-spin to maintain stability. It is scheduled to exit-]{+waking up 31 months later+}
on 20 January [-2014-]{+2014,+} at [-10 AM-]{+18:18+} GMT.

At [-that time, it will be around-]{+this stage, Rosetta was still+} 9 million km from its target.[-The spacecraft will warm up for several hours and go into ‘safe-]
[-mode’, making it possible to switch on its navigational payload and-]
[-spin down to point the main antenna towards Earth so communications can-]
[-be re-established. Contact with Earth is not expected before 17:30 GMT.-] From
February to April, engineers [-will perform-]{+performed+} a checkout of the orbiter,[-its payload and-]
the [-lander-]{+lander,+} and [-gradually bring the instruments back-]
[-into operation. By that time, the spacecraft will have moved to within-]
[-1 million km of the comet, close enough to actually see it. If all goes-]
[-well, the-]{+their respective payloads. The+} first images [-will arrive in May, helping engineers to more-]
[-accurately calculate-]{+of+} the
[-comet’s position and orbit. At-]{+comet were taken at+} the end of [-the-]
[-month,-]{+March, from a distance of 5 million+}
{+km. Between May and August+} a [-sequence-]{+series+} of [-thruster-]{+ten critical+} manoeuvres [-will be undertaken-]{+were+}
{+executed+} to [-line-]{+match+} the [-spacecraft up-]{+spacecraft’s velocity and trajectory+} with {+that+}
{+of+} the [-comet and move it to within 100,000 km.-]

[-Orbiter science will begin in June.-]{+comet.+} The [-initial focus will be on-]
[-generating imagery necessary to determine the size, shape, spin rate-]
[-and other parameters-]{+spacecraft arrived at a distance+} of {+100 km from+} the
comet [-nucleus-]{+on 6 August 2014.+}

{+An extensive mapping+} and [-obtaining an initial-]
[-assessment of-]{+data-collection campaign took place over+}
the [-coma, particularly its density and gas production rate,-]
[-so engineers can synchronize-]{+following six weeks to determine a suitable landing site for+} the
[-spacecraft’s orbit with that of-]{+mission’s lander, Philae. At+} the [-comet. The orbit is expected-]{+same time, Rosetta moved+} to [-be around-]{+within+} 30
km[-above the surface, safe-]
[-enough to protect from the effects-] of [-cometary dust, with occasional-]
[-flyovers-]{+the comet, and later+} to[-within-] 10 [-kms or so-]{+km+} for closer observation. [-In August-September, an extensive mapping campaign will be undertaken-]
[-to determine a suitable-]{+A+} landing
[-site. Touchdown-]{+site located on the comet’s smaller lobe was selected, identified as+}
{+‘Site J’.+}

{+Landing+} is scheduled for {+12+} November. [-Engineers-]{+It+} will [-then recharge the lander batteries and initiate-]{+take about seven hours+}
{+for Philae to descend to+} the surface[-science portion-] of the [-mission,-]{+comet, during+} which {+it will+}
{+take images and make measurements of the comet’s environment. After+}
{+touchdown, the initial battery lifetime of the lander is expected to+}
{+be about 64 hours. Science measurements+} will [-includes-]{+include+} high-resolution
images of the comet, in-situ measurements and extraction and analysis
of subsurface samples. {+Solar illumination conditions and the amount of+}
{+dust settling on the lander’s solar panels will determine the length+}
{+of the long term science phase.+}

{+Meanwhile Rosetta continues its science mission, following the comet+}
{+through its closest approach to the Sun on 13 August 2015, and beyond.+}

What [-are-]{+were+} the critical remaining [-risk elements-]{+risks+} at this stage of the mission?
The primary risk [-involves-]{+involved+} the orbiter’s thrusters, which[-will-] have to perform
at lower pressure than planned because of a Reaction Control System leak
that occurred in September 2006. Engineers [-are-]{+were+} also concerned about the
reaction wheels themselves, which have exhibited some noise. However,
contingency testing has demonstrated that the system can be operated
in a more efficient operating mode, reducing the wear. Moreover, new
software has been developed to allow operation in hybrid mode, which
would permit the spacecraft to operate with just two wheels.

All previous deep space probes have used RTGs [Radio-isotope
Thermoelectric Generator]. Why did ESA choose not to use them for Rosetta?
@@ -747,13 +723,13 @@ active near the Sun. In addition, the onboard software operating the
attitude sensors will be able to differentiate between dust and stars,
so that the spacecraft does not track the dust particles.

Given the length of the journey, how [-can-]{+could+} you be sure that the
spacecraft/comet rendezvous [-will-]{+would+} take place as planned?  Sophisticated
and reliable computer models provided a high precision interplanetary
trajectory for the comet rendezvous, and everything necessary was done
to ensure that the mission proceeded as planned. When Rosetta [-nears-]{+neared+}
the comet, we [-will use-]{+used+} optical navigation techniques, so it [-will be-]{+was+} practically
impossible to miss the target.

No spacecraft has ever soft-landed on a comet. What are the risks during
such a landing and how are they being minimised?  We have some idea of
@@ -808,9 +784,10 @@ on touchdown.

The Rosetta lander will not be deployed until the orbiter has mapped the
surface of the comet’s nucleus in high resolution and a safe landing
site has been chosen. It will be released about [-one kilometre above-]{+22.5 km from the comet+}
{+centre (about 20.5 km from+} the [-comet’s surface-]{+surface)+} and descent will be very slow
and controlled, with a touchdown speed of perhaps one metre per second
(less than walking speed).

And since the comet has no atmosphere, the lander will not require a
heatshield, parachute or airbag, and there will be no concern about bad

faq.fmt

Why is the mission called Rosetta?  The mission is named after the Rosetta
Stone, a slab of volcanic basalt found near the Egyptian town of Rashid
(Rosetta) in 1799. The stone revolutionised our understanding of the
past. By comparing the three carved inscriptions on the stone (written in
two forms of Egyptian and Greek), historians were able to decipher the
mysterious hieroglyphics – the written language of ancient Egypt. As
a result of this breakthrough, scholars were able to piece together the
history of a lost culture.

The Rosetta Stone provided the key to an ancient civilisation. ESA’s
Rosetta mission will allow scientists to unlock the mysteries of the
oldest building blocks of our Solar System: comets.

When was the mission approved?  The Rosetta Mission was approved as a
Cornerstone Mission in ESA's first long-term science programme (Horizon
2000) in November 1993.

What are the mission’s objectives?  Rosetta's prime objective is
to help understand the origin and evolution of the Solar System. The
comet’s composition reflects the composition of the pre-solar nebula
out of which the Sun and the planets of the Solar System formed,
more than 4.6 billion years ago. Therefore, an in-depth analysis of
comet 67P/Churyumov-Gerasimenko by Rosetta and its lander will provide
essential information to understand how the Solar System formed.

There is convincing evidence that comets played a key role in the
evolution of the planets, because cometary impacts are known to have
been much more common in the early Solar System than today. Comets,
for example, probably brought much of the water in today's oceans. They
could even have provided the complex organic molecules that may have
played a crucial role in the evolution of life on Earth.

What makes the Rosetta mission so special?  Rosetta will be undertaking
several ‘firsts’ in space exploration. It will be the first mission to
orbit and land on a comet. That makes Rosetta one of the most complex and
ambitious missions ever undertaken. Scientists had to plan in advance,
in the greatest possible detail, a ten year trip through the Solar
System. Approaching, orbiting, and landing on a comet require delicate
and spectacular manoeuvres. The comet, 67P/Churyumov-Gerasimenko, is
a relatively small object, about 4 kilometres in diameter, moving at
a speed as great as 135,000 kilometres per hour. We know very little
about its actual surface properties – only when we get there will we
be able to explore the surface in such detail that we can choose a safe
landing scenario. Rosetta is very special because of the unique science
it will perform. No other previous mission has had Rosetta’s potential
to look back to the infant Solar System and investigate the role comets
may have played in the beginnings of life on Earth.

Rosetta will be the first spacecraft to witness, at close proximity, how
a comet changes as it approaches the increasing intensity of the Sun’s
radiation. The comet develops the so-called ‘coma’ (essentially
the comet’s atmosphere) and the two characteristic ion and dust
tails. Rosetta’s lander will obtain the first images from a comet’s
surface and make the first in-situ subsurface analysis of its composition.

It will also be the first mission to investigate a comet’s nucleus
and environment over an extended period of time.

How did Rosetta reach comet 67P/Churyumov-Gerasimenko, and how long did
it take?  Comet 67P/Churyumov-Gerasimenko loops around the Sun between the
orbits of Jupiter and Earth, that is, between about 800 million and 186
million kilometres from the Sun. But rendezvousing with the comet required
travelling a cumulative distance of over 6.4 billion kilometres. As no
launcher was capable of directly injecting Rosetta into such an orbit,
gravity assists were needed from four planetary flybys – one of Mars
(2007) and three of Earth (2005, 2007 and 2009) – a long circuitous
trip that took ten years to complete.

Why is it so important to study comets?  Comets are of great interest to
scientists because, to our knowledge, they are the oldest, most primitive
bodies in the Solar System, preserving the earliest record of material
from the nebula out of which our Sun and planets were formed. Planets have
gone through chemical transformations, but comets have remained almost
unchanged. Furthermore, comets brought ‘volatile’ light elements to
the planets and likely played an important role in forming oceans and
atmospheres. Comets also carry complex organic molecules that may have
been involved in the origin of life on Earth.

What do we presently know about how the Solar System formed?  The Solar
System formed about 5 billion years ago when a butt of gas and dust
– called the ‘pre-solar nebula’ – started to collapse due to
gravitational forces. A disc of leftover material made of the same gas
and dust present in the primordial butt formed around the still-forming
Sun. After the Sun ‘ignited’ and began its life as star, most of
the particles in this disc collided and stuck to one another, growing
in size until they became the planets and the other Solar System bodies.

However, it took some time before the Solar System became the way it is
now. About 4.5 billion years ago, it was still 'under construction',
and interplanetary space was littered with conglomerates of dust
particles. Many of these chunks hit the planets and were destroyed in
the collision, but thousands of millions of them survived – they are
the asteroids and comets we know today.

How will Rosetta be able to gauge the contribution comets made to
the beginnings of life on Earth?  Previous studies by ESA’s Giotto
spacecraft and ground-based observatories have shown that comets contain
complex organic molecules. These are compounds that are rich in carbon,
hydrogen, oxygen, and nitrogen. Intriguingly, these are the elements
that make up nucleic acids and amino acids, essential ingredients for
life as we know it. Did life on Earth begin with the help of comet
seeding? Although Rosetta may not give us a definitive answer, it will
provide a wealth of information. For example, the mass spectrometers
on the orbiter and the lander will analyse, more precisely than ever
before, the kind of organic molecules present in the comet. Laboratory
simulations of interstellar processes showed that such instruments can
detect a variety of amino acids.

How will the mission determine whether comets provided some of the
water present in today's oceans?  Rosetta will investigate this by
analysing the isotopic abundances in the cometary ices. The isotopes
of a certain chemical element are atoms of the same kind that differ
slightly in weight. Deuterium, for example, is an isotope of hydrogen;
it is also heavier than hydrogen. All the deuterium and hydrogen in
the Universe was made just after the Big Bang, about 13.7 billion years
ago, fixing the overall ratio between the two kinds of atoms. However,
the ratio seen in water can vary from location to location. The chemical
reactions involved in making ice in space lead to a higher or lower chance
of a deuterium atom replacing one of the two hydrogen atoms in a water
molecule, depending on the particular environmental conditions. Thus, by
comparing the deuterium to hydrogen ratio found in the water in Earth's
oceans with that in extraterrestrial objects, we can try to identify
the origin of Earth’s water. For example, if the hydrogen-deuterium
ratio in the ocean water is similar to that in the cometary ice, it will
support the theory that a fraction of the Earth's water has its origin
in space. ESA’s Herschel mission has already found a very similar
deuterium-to-hydrogen ratio in comet Hartley-2.

How long will the Rosetta spacecraft operate?  Rosetta’s planned
lifetime is about 12 years. The nominal mission ends in December 2015,
after the comet reaches its closest point to the Sun (in August 2015)
and starts heading back towards the outer Solar System.

How long will the lander operate on the comet nucleus?  The Rosetta
lander, called Philae, will touch down on the comet's surface on 12
November 2014. The science observations will start immediately. During
the first 2.5 days the first series of scientific measurements will be
completed. During this phase the lander will operate on primary battery
power. In a second phase that may last up to three months, a secondary
set of observations will be conducted, using backup batteries that will
be recharged by the energy from the solar cells on the lander. However,
no one knows precisely how long the lander will survive on the comet.

Could activity on the comet's surface damage or destroy the lander?
Survival of the lander depends on a number of factors, such as power
supply, temperature, or surface activity on the comet. For example, dust
may cover the solar panels, preventing the battery from recharging. In
any case, by March 2015, when the comet is closer to the Sun, it is
likely that the lander will become too hot to operate.

What scientific instruments are on board the spacecraft and what will
they do?  Rosetta's goal is to examine the comet in great detail. The
instruments on the Rosetta orbiter include several cameras, spectrometers,
a number of sensors, and experiments that work at different wavelengths
– infrared, ultraviolet, microwave, and radio. They will provide,
among other things, very high-resolution images and information about
the shape, density, temperature, and chemical composition of the
comet. Rosetta’s instruments will analyse the gases and dust grains
in the so-called ‘coma' that forms when the comet becomes active,
as well as the interaction with the solar wind.

What scientific instruments are on board the lander and what function
will they perform?  The 10 instruments on board the lander will do an
on-the-spot analysis of the composition and structure of the comet’s
surface and subsurface material. A drilling system will obtain samples
down to 23 cm below the surface and will feed these to the spectrometers
for analysis, such as to determine the chemical composition. Other
instruments will measure properties such as near-surface strength,
density, texture, porosity, ice phases and thermal properties. Microscopic
studies of individual grains will tell us about the texture. In addition,
instruments on the lander will study how the comet changes during the
day-night cycle, and while it approaches the Sun.

How were the instruments selected?  The most important factors in the
selection of each instrument were their expected scientific performance
and their technical feasibility. How the instruments fitted together was
another consideration, as well as the experience of the team proposing
the instrument. This selection was done on the basis of the so-called
'Announcement of Opportunity' (AO) issued by ESA to the scientific
community, which is basically an open competition. This AO defines
the mission scientific objectives and requirements, and the scientific
community had to be compliant with these when submitting their proposals.

How does Rosetta fit into the overall scheme of cometary exploration?
Europe has been a pioneer in exploring comets and asteroids. In 1986,
ESA’s Giotto probe flew within 600 kilometres of the comet Halley,
closer than any previous spacecraft, and sent back detailed images and
data showing, among other things, that comets contain complex organic
molecules. Giotto continued its successful journey and in 1992 flew
within 200 km of the comet Grigg-Skjellerup, detecting its nucleus. The
mission was the first to observe a comet nucleus and confirm theories
suggesting that comets were not mere rubble piles or conglomerates of
small fragments.

Giotto was part of the five-spacecraft Halley Armada, which also included
Russia’s VEGA 1 and 2 spacecraft and two Japanese spacecraft, Susei
and Sagigake. Like Giotto, these probes also visited Halley in 1986.

Among other comet missions were a trio of NASA probes: Deep Space 1, which
flew by the comet Borelly in 2001; Stardust, which returned samples from
the coma of Wild 2 in 2006 and later flew by Tempel 1; and Deep Impact,
which in 2005 shot a massive block of copper into the nucleus of Tempel
1 before going on to fly by Hartley 2 and image the comet ISON. Another
NASA mission, Contour, launched in Summer 2002, failed when it was
incorrectly inserted into its interplanetary trajectory.

Missions have also visited asteroids. In 2005, Japan’s Hayabusa
rendezvoused with and landed on the asteroid Itokawa. Six years later,
another NASA mission, Dawn, explored the asteroid Vesta. Dawn is now
en route to dwarf planet Ceres, which is the largest object in the
Asteroid Belt.

What was known about the comet before Rosetta arrived there?  Comet
67P/Churyumov-Gerasimenko orbits the Sun once every 6.6 years. This
makes it a short-period comet.

Ground-based telescopes have observed 67P/Churyumov-Gerasimenko during
almost all its appearances since its discovery in 1969. To acquire
as much information as possible about Rosetta’s target comet, ESA
implemented a rigorous ground and space-based observation programme of
67P/Churyumov-Gerasimenko. These observations provided a fairly reliable
estimate of the comet’s size – about 4 kilometres in diameter.

Where was 67P/Churyumov-Gerasimenko at the time of the rendezvous?
Rosetta met 67P/Churyumov-Gerasimenko when it was still in the cold
regions of the Solar System 673 million kilometres from the Sun, when
the comet and Rosetta were on their return journey back into the inner
Solar System.

Was the comet active at the time of rendezvous?  As we expected, the comet
was only showing minimal signs of activity at the time of rendezvous.
When comets get close to the Sun, the Sun’s heat 'activates' them. The
frozen gases on and below the surface sublimate – they pass directly
from the solid to the gaseous state – and the outflowing gas drags small
dust grains with it into surrounding space. This creates an atmosphere
around the nucleus, known as the coma, and generates a dust tail that
streams out behind the comet along its orbit. Rosetta will therefore
become the first spacecraft to witness at close quarters the development
of a comet's coma and subsequent tails.

When does 67P/Churyumov-Gerasimenko come closest to the Sun?  Comet
67P/Churyumov-Gerasimenko last passed through its perihelion on 18 August
2002. Even at that point, when its brightness was at its maximum, it was
impossible to see it with the naked eye. Only medium or large telescopes
were able to observe it.

It will next pass through perihelion on 13 August 2015, 186 million
kilometres from the Sun.

What is the gravity on 67P/Churyumov-Gerasimenko's surface, compared
with that on Earth?  Comet 67P/Churyumov-Gerasimenko is so small that
its gravitational pull is several hundred thousand times weaker than on
Earth. For this reason, the Rosetta lander will touch down at no more
than a walking pace. It will need a harpoon to safely anchor it to the
comet’s surface and prevent it from bouncing back into space.

Why is the comet called 67P/Churyumov-Gerasimenko?
67P/Churyumov-Gerasimenko is named after its discoverers, Klim Churyumov
and Svetlana Gerasimenko, astronomers from Kiev who “spotted”
the comet for the first time in 1969 on a photographic plate. The 'P'
identifies short-period comets with a well-established orbit around the
Sun and that take less than 200 years to complete a solar revolution. The
number 67 refers to Churyumov-Gerasimenko's position in the list of
catalogued periodic comets. The most famous, Halley, is designated 1P.

How many comets are there in the Solar System?  There are billions
of comets in our Solar System, which are typically located in one of
two regions. The most distant repository of comets is the Oort butt,
at the edge of the Solar System, 100,000 times more distant from the
Sun than the Earth, and which is estimated to contain about 12 billion
comets. Closer in, just beyond the orbit of Neptune, is the Kuiper belt,
which also contains billions of comets and extends from 30 to 50 times the
distance equivalent to the Sun-Earth separation (150 million km, or 1 AU).

Some comets escape from these regions and journey into the inner Solar
System. Every year many new comets are discovered in this region, often
‘sungrazers’ spotted by ESA/NASA’s SOHO spacecraft. Sungrazers
travel very close to the Sun, and are sometimes partially or completely
destroyed in the encounter. Comet ISON is a well-known example of a
sungrazing comet.

What is the difference between asteroids and comets?  Comets are typically
nicknamed 'dirty ice-balls', whereas asteroids, or minor planets,
are known, in very simple terms, as ‘rocks in space’. The size of
asteroids typically ranges from a metre to several hundred kilometres
across. One of the main differences is that asteroids do not usually
contain ‘volatiles’ (substances that sublimate i.e. when heated they
pass directly from the solid to the gaseous state). Therefore asteroids
do not develop a tail or a coma when they approach the Sun. However,
a recent class of object has been discovered in the main asteroid belt
that are asteroids behaving like comets, sometimes suddenly sporting a
dust tail. These are termed ‘main belt comets’ There is also good
evidence that some asteroids are 'dead comets', comets that have lost
their volatile materials after many approaches to the Sun.

Who are the Rosetta mission contractors?  Rosetta’s industrial team
involves more than 50 contractors from 14 European countries and the
United States. The prime spacecraft contractor – the company leading
the entire industrial team – is Astrium Germany. Major subcontractors
are Astrium UK (spacecraft platform), Astrium France (spacecraft avionics)
and Alenia Spazio (assembly, integration and verification).

Who built Rosetta’s instrument and lander package?  The orbiter's
scientific payload was provided by scientific consortia from institutes
across Europe and the United States.

The lander is provided by a European consortium under the leadership
of the German Aerospace Research Institute (DLR). Other members of the
consortium are ESA and institutes from Austria, Finland, France, Germany,
Hungary, Ireland, Italy, and the United Kingdom.

Was new technology developed for Rosetta and can it be reused for other
ESA missions?  The solar cells in Rosetta's solar panels are based on
a completely new technology, so-called Low-intensity Low Temperature
Cells. Thanks to them, Rosetta is the first space mission to journey
beyond the main asteroid belt relying solely on solar cells for power
generation. Previous deep-space missions used nuclear RTGs (Radio isotope
thermal generators). The new solar cells allow Rosetta to operate over
800 million kilometres from the Sun, where levels of sunlight are only 4%
those on Earth. The technology will be available for future deep-space
flights, such as ESA’s upcoming Jupiter Icy Moons Explorer.

Systems that control the temperature inside the spacecraft are another
example of technological spinoffs from the Rosetta mission. When
a spacecraft is near the Sun, overheating is a problem, and can be
prevented by using radiators. But in the outer Solar System, the problem
is keeping the spacecraft and its subsystems warm. The system devised
for Rosetta employs several new techniques, including the installation
of louvres over the radiators, to keep spacecraft hardware at proper
operating temperatures.

Rosetta also includes a number of highly innovative subsystems, some
of which have been reused in other ESA missions, including Mars and
Venus Express.

How many people are involved in the Rosetta programme, and how many jobs
has it created?  About 2,000 people from industry, ESA and scientific
institutions were involved in Rosetta's development. It is difficult
to establish exactly how many new jobs were created, but Rosetta has
certainly helped contribute to the development of the space sector both
from the industrial and the scientific point of view.

Who will obtain data from Rosetta, and how will it be distributed?
Rosetta's Science Ground Segment will be responsible for collecting
and distributing the scientific data. The unit will be based at the
European Space Operations Centre (ESOC) in Darmstadt, Germany, and at
the European Space Astronomy Centre (ESAC) in Villanueva de la Cañada,
Madrid, Spain. It will be responsible for the collection of the scientific
data received from the spacecraft and its distribution to the principal
investigators.

The principal investigators head up the teams building the Rosetta
instruments and will have the exclusive right to work with the data
for six months. After this period, the data will be stored in ESA’s
Planetary Science Archive and made freely available to the world's
scientific community.

How big is the spacecraft?  The spacecraft dimensions are 2.8 x 2.1 x
2.0 metres. There are two 14-metre-long solar panels with a total area
of 64 square metres. From tip to tip, the spacecraft spans 32 metres.

Rosetta's total launch mass is 3,000 kilograms. The spacecraft carries
1,670 kilograms of propellant and the lander weighs 100 kilograms.

How will Rosetta be powered?  The spacecraft relies entirely on the
energy provided by its innovative solar panels for all onboard instruments
and subsystems.

What challenges did Rosetta face during its long trip through the
Solar System?  Ensuring that the spacecraft could survive the hazards
of travelling through deep space for more than 10 years, from the benign
environment of near-Earth space to the frigid regions beyond the asteroid
belt, was one of the principal challenges of the mission. Temperature
control was particularly critical, and the spacecraft was put through
stringent pre-launch tests in ESA’s environmental test facilities in
the Netherlands to confirm its endurance. These tests involved heating
the outside surfaces to more than 150°C and then cooling them to -180°C
without damaging the instruments.

Is Rosetta pre-programmed or are commands sent from the ground?  Rosetta
is operated from the ground. It was impossible to programme manoeuvres
for the whole mission before the launch because this would have entailed
adjustments at each stage of the journey. Ground commands are sent
periodically to readjust the spacecraft’s trajectory. These take up
to 50 minutes to reach the spacecraft, when it is farthest from the Earth.

How does the spacecraft deal with this long time lag?  To compensate
for the delay, Rosetta is provided with built-in intelligence to look
after itself. This is done by its on-board computers, whose tasks include
data management and attitude and orbit control. In the event of problems
during the lengthy cruise, experts added backup systems to ensure that the
spacecraft could remain operational during critical mission phases. For
example, to avoid losing power, the spacecraft automatically positions
itself with the solar panels facing the Sun.

Why was it necessary to keep Rosetta in hibernation for 31 months?
To limit its consumption of power and fuel, and to minimise operating
costs. During hibernation it was spinning once per minute and faced
the Sun, so that its solar panels could receive as much sunlight as
possible. Almost all of the electrical systems were switched off, with
the exception of the radio receivers, command decoders and power supply.

How far did Rosetta get from the Earth and when did it reach this point?
In mid 2012 Rosetta recorded its maximum distance from the Sun and Earth
– about 800 million kilometres and 1 billion kilometres, respectively.

What will happen with Rosetta once the mission is finished, and is an
extension envisaged?  Rosetta's nominal mission will end in December 2015
after a total lifetime of 12 years. There could be a six-month extension
provided there is fuel remaining, nominal activities are completed by the
end of 2015 and additional funds are made available. An extended mission
would permit scientists to study additional aspects of comet behaviour,
including some that might entail higher risk. A decision on this will
be taken in late 2014.

What can the lander tell us about comets that the orbiter cannot?
Using its complement of in-situ instruments, the lander will provide
a nucleus-based cross-check for some of the orbiter’s remote
measurements. It will also have the unique ability to drill down for
samples from below the surface and analyse their mechanical properties on
the spot. Furthermore, its camera system, especially the micro cameras,
will be capable of imaging the landing site at a higher resolution than
the high-resolution camera onboard the orbiter (which already has a
resolution of 5 cm per pixel).

What is the difference in research significance between collecting
samples from the comet’s tail (like Stardust did) and from the surface?
There are several distinct differences. First of all, samples collected
from a comet’s coma do not contain volatiles and have already been
transformed. The Stardust samples were slowed down by an aerogel (a
kind of foam), causing them to heat up significantly from the sudden
deceleration. As a result, the original properties of the volatiles were
not preserved. But this was the only way they could be brought back to
Earth and studied in a laboratory.

Samples studied by Rosetta’s lander will be fresh, containing volatiles
that it will be possible to analyse in-situ (i.e. the samples will be
heated in a controlled manner and the transformation analysed by lander
instruments).

To summarise, Stardust collected processed material while Rosetta
will allow us to analyse unprocessed fresh material still containing
volatiles. The science performed by the two missions is thus
complementary.

Will the orbiter be able to observe the comet from different angles?
Yes, Rosetta will orbit the nucleus in such a way that it can observe
the comet from various angles and altitudes.

Will there be any possibility of adjusting the landing sequence once it
is initiated?  No. Once the landing sequence has been defined (release
speed, position for release etc.) and initiated, it will not be possible
to adjust it. However, it should be recalled that the lander will be
released at a height of about 22.5 kilometres from the centre of the
comet and will touch down on the comet at walking speed, minimizing the
risk of an incident.

What if the lander touches down on a very steep slope and drills itself
into an awkward angle, or sinks into porous snow or some other soft
material?  The lander is designed so that it can land on a slope of
up to 30 degrees. The feet are equipped with large pads to allow the
lander to touch down on a soft surface. If the surface is very soft,
the lander’s feet may sink into it but sinking will eventually be
stopped by the bulkiness of the lander’s body. In all scenarios,
the lander is expected to be able to safely transmit its data.

Will the public be able to view high-resolution stereo images of
the comet like they now see from Mars Express?  Rosetta will provide
images with an even higher resolution than those from the HRSC camera on
Mars Express. The difference, however, is that the HRSC was especially
designed to take three-dimensional (stereo) images, while Rosetta will
only be capable of building pseudo 3-D images by processing images from
different viewing angles.


Did engineers have to make any changes to the Rosetta spacecraft or lander
to adapt them to the new target comet?  A few minor modifications were
made to the orbiter, including the addition of thermal blankets around
the thrusters. The landing gear on the lander was modified to ensure
a smooth touchdown on 67P/Churyumov-Gerasimenko, which has stronger
gravity than the original target.

What happened to the spacecraft during the long launch delay?
The spacecraft remained in Kourou, French-Guiana and was kept in safe
storage. The solar arrays and the High-Gain Antenna (HGA) were removed
and the fuel was off-loaded. Various maintenance activities were carried
out on the spacecraft and some instruments, and new software was uploaded
to take into account the new target comet.

Does the Rosetta lander have a name?  Yes, the lander is called "Philae",
the name of an island in the Nile region of Egypt. An obelisk found on
Philae provided the French historian Jean-Francois Champollion with the
final clues for deciphering the hieroglyphs on the Rosetta Stone –
thus the mission name.

Were technical difficulties encountered during the development of the
lander?  Yes, some problems arose during the design and development
stage. The lander is really a mini-spacecraft and development of some
systems, in particular the landing gear, proved to be more complicated
than originally envisaged. Some of the lander experiments, notably
the miniature gas analysers, were also difficult to develop and build,
and one was eventually dropped.

ESA set up a special lander task force, in cooperation with lander
consortium leader DLR, to resolve these problems. Project management
was reinforced, the agency contributed some additional funding and
more experts from industry were brought in e.g. from Astrium. In other
words, ESA adopted a proactive strategy and the problems were sorted
out fairly quickly.

What was ESA’s role in the lander?  As a member of the DLR-led lander
consortrium, ESA contributed funding and manpower to the project.

Why is the lander described as a Rosetta experiment when it has ten
instruments of its own?  Like the other Rosetta experiments, the lander
has a single interface with the spacecraft. When the lander Announcement
of Opportunity went out, it was agreed to consider the entire unit as
a single instrument.

What is the total mission cost?  The total mission cost of Rosetta
is close to 1.4 billion Euros of which the total Philae costs are 220
Million Euros (in 2014 economic conditions) including expenses for the one
year launch delay. The mission cost covers development and construction
of the spacecraft and all of its instruments, including the lander,
together with launch and operations.

Though the total cost is high, this should be put in perspective. The
figure is barely half the price of a modern submarine, or three Airbus
380 jumbo jets, and covers a period of almost 20 years, from the start
of the project in 1996 through the end of the mission in 2015.

Why spend such a huge amount on public money on studying remote stones
in space?  ESA’s task is to explore the unknown. In the case of Rosetta,
scientists will be learning about comets, objects that have fascinated
mankind for millennia. Comets are thought to be the most primitive
objects in the Solar System, the building blocks from which the planets
were made. So Rosetta will provide exciting new insights into how the
planets (including Earth) were born and how life began.

It is important to consider that what may seem pure science ends up
contributing to the store of human knowledge, and the advancement of
knowledge always has relevance to everyday life, in the practical as
well as the philosophical sense. Many technologies developed for space
eventually lead to advances in other areas, though it is very difficult to
predict when and how basic knowledge will result in practical benefits. If
there had not been a need for particle physicists to share data, there
would be no World Wide Web.

There are also direct spin-offs, like Rosetta’s advanced solar cell
technology.

ESA is very careful to optimise the financial resources available
in order to get the maximum profit, in terms of scientific results,
technology and – last but not least – advances for European industry.

The educational fallout from major science endeavours should also not
be underestimated. Missions like Rosetta are inspiring and fascinating,
and help to get more young people interested in science, including many
who may eventually choose a scientific career.

Previous missions like Giotto, Stardust and Deep Impact have already
observed comets at close quarters. Why Rosetta?  Rosetta is a much more
ambitious and advanced mission than Giotto or any of the previous NASA
comet explorers. Its observation phase will last much longer and will
not be limited to “snap-shots” from flybys.

Giotto obtained a mass of new information but its period of observation
was limited to two short-lived flybys. Stardust captured some excellent
black and white images and gathered samples of dust from the comet’s
coma. However, it was not designed to provide information on the nature
of the nucleus. Deep Impact filled in this missing gap but its instrument
package included only cameras and a single infrared spectrometer, so
most analysis of the comet’s composition had to be done from the ground.

Unlike these missions, Rosetta will include both an orbiter and a lander
and be capable of investigating both the nucleus and the coma over a
long period of time. It carries a much more advanced payload than any
of its predecessors. The suite of eleven experiments on the orbiter will
observe all aspects of the comet from close range over more than a year
as it moves along its orbit towards the inner Solar System, permitting
scientists to study the composition of the coma and nucleus in great
detail. For example, they will be able to examine parent molecules on
the comet’s surface that originated from the nucleus that have not yet
been modified by the space environment, and survey the complex physical
and chemical changes in the nucleus as it is warmed by the Sun.

The ten experiments on the lander, including spectrometers,
high-resolution cameras and drill, will permit a more detailed comet
investigation than has ever been done before.

Why was 67P/Churyumov-Gerasimenko selected as the target comet instead of
Wirtanen?  Both 46P/Wirtanen and 67P/Churyumov-Gerasimenko are periodic
comets with fairly similar orbits. This means that their return dates
and orbits can be predicted with great accuracy. This enabled us to plan
the Rosetta rendezvous mission with Wirtanen years in advance.

However, when we were unable to launch in January 2003, we had to weigh
the various mission options, bearing in mind the trajectory, amount
of fuel and energy required. We had to look for a comet that would be
available when we wanted to launch Rosetta and several periodic comets –
including Wirtanen – were identified as possible targets. The targets
were selected on the basis of three main criteria: scientific return,
technical risk to the spacecraft, and funding.

We eventually opted for 67P/Churyumov-Gerasimenko, which Rosetta could
reach with the same version of the Ariane 5 rocket . The other options,
including a launch to Wirtanen in 2004, would have required a more
powerful launch vehicle, either an Ariane 5 ECA or a Proton.

Comet 67P/Churyumov-Gerasimenko is a larger comet than 46P/Wirtanen,
with a nucleus about four kilometres across. It is also much more active
when approaching the Sun, creating a greater dust hazard.

There were no major changes to the overall mission profile, although the
rendezvous with the comet will now take place in 2014, two years later
than planned. The revised mission also required three Earth flybys,
instead of two initially foreseen.

When was the launch, and why the long launch delay?  Rosetta was launched
on 2 March 2004 atop an Ariane 5 G+ rocket. It had initially been planned
to send the probe into orbit in January 2003. However, the Ariane 5 was
grounded following the inaugural failure of Arianespace’s new high
payload Ariane 5 ECA, on 11 Dec 2002, depriving Rosetta of its launch
opportunity to the comet Wirtanen.

What happened after Rosetta woke up from its long hibernation?  Rosetta
entered deep space hibernation on 8 June 2011, waking up 31 months later
on 20 January 2014, at 18:18 GMT.

At this stage, Rosetta was still 9 million km from its target. From
February to April, engineers performed a checkout of the orbiter,
the lander, and their respective payloads. The first images of the
comet were taken at the end of March, from a distance of 5 million
km. Between May and August a series of ten critical manoeuvres were
executed to match the spacecraft’s velocity and trajectory with that
of the comet. The spacecraft arrived at a distance of 100 km from the
comet on 6 August 2014.

An extensive mapping and data-collection campaign took place over
the following six weeks to determine a suitable landing site for the
mission’s lander, Philae. At the same time, Rosetta moved to within 30
km of the comet, and later to 10 km for closer observation. A landing
site located on the comet’s smaller lobe was selected, identified as
‘Site J’.

Landing is scheduled for 12 November. It will take about seven hours
for Philae to descend to the surface of the comet, during which it will
take images and make measurements of the comet’s environment. After
touchdown, the initial battery lifetime of the lander is expected to
be about 64 hours. Science measurements will include high-resolution
images of the comet, in-situ measurements and extraction and analysis
of subsurface samples. Solar illumination conditions and the amount of
dust settling on the lander’s solar panels will determine the length
of the long term science phase.

Meanwhile Rosetta continues its science mission, following the comet
through its closest approach to the Sun on 13 August 2015, and beyond.

What were the critical remaining risks at this stage of the mission?
The primary risk involved the orbiter’s thrusters, which have to perform
at lower pressure than planned because of a Reaction Control System leak
that occurred in September 2006. Engineers were also concerned about the
reaction wheels themselves, which have exhibited some noise. However,
contingency testing has demonstrated that the system can be operated
in a more efficient operating mode, reducing the wear. Moreover, new
software has been developed to allow operation in hybrid mode, which
would permit the spacecraft to operate with just two wheels.

All previous deep space probes have used RTGs [Radio-isotope
Thermoelectric Generator]. Why did ESA choose not to use them for Rosetta?

ESA has not developed RTG (i.e. nuclear) technology, so the agency
decided to develop solar cells that could fill the same function.

The Rosetta spacecraft is scheduled to last for almost 12 years, much
of it spent in hibernation. What measures were taken to ensure that it
can survive and operate properly under these conditions?

The spacecraft was thoroughly tested to ensure that it can survive long
periods of hibernation and carries multiple computers that provide a
sophisticated failure recognition and recovery capability. The data
management system is highly autonomous with two independent computers,
each comprising two separate interchangeable components.

We can upload new enhanced software at any time over the 12-year mission,
and the software for each computer is interchangeable. This means that
both the Data Management System and the Attitude and Orbit Control
subsystem can be run on all processors. If the spacecraft is in serious
trouble, it automatically goes into safe mode – with its solar arrays
pointing at the Sun.

How will the mission teams – operations, scientists, management etc
– be kept together and able to operate efficiently during such a
long mission?

We won’t be able to keep the various teams together throughout
the mission, so we are creating a database that contains complete
information about the spacecraft. This will be available to ensure that
the replacement staff has the necessary information about the mission.

The first eight months of the mission involved intensive activity
that enabled everyone to become familiar with the spacecraft’s
behaviour. Since then we have conducted regular training and communication
activities, roughly once every 6-12 months. We also ensured adequate
training before each manoeuvre.

A number of younger people have gradually been drafted into the instrument
teams, including several principal scientific investigators, to ensure
that the necessary “know-how” is passed on to new recruits.

Giotto was sent spinning and nearly destroyed by a dust particle, and
other missions like Stardust also encountered considerable high-speed
dust. What is to prevent the same thing happening to Rosetta?  Rosetta has
very little shielding against dust. However, the relative velocities of
the dust particles during the Giotto and Stardust encounters were much
higher than will be the case with 67P/Churyumov-Gerasimenko. Giotto
flew past Comet Halley at about 70 km/s, and Stardust’s flyby
speed was about 6 km/s. In contrast, Rosetta will be orbiting very
slowly around the nucleus and the relative velocity of the dust from
67P/Churyumov-Gerasimenko will be much lower (perhaps 100 – 200 m/s),
so we do not anticipate a problem, even when the comet becomes more
active near the Sun. In addition, the onboard software operating the
attitude sensors will be able to differentiate between dust and stars,
so that the spacecraft does not track the dust particles.

Given the length of the journey, how could you be sure that the
spacecraft/comet rendezvous would take place as planned?  Sophisticated
and reliable computer models provided a high precision interplanetary
trajectory for the comet rendezvous, and everything necessary was done
to ensure that the mission proceeded as planned. When Rosetta neared
the comet, we used optical navigation techniques, so it was practically
impossible to miss the target.

No spacecraft has ever soft-landed on a comet. What are the risks during
such a landing and how are they being minimised?  We have some idea of
the risks, but no one knows for sure. This is one of the fascinating
aspects of the mission. The density and surface roughness of the nucleus
are not really known and its gravity is extremely low. We have tried
to compensate for these factors in the design of the lander. There will
be two harpoons to anchor it to the surface so that it can be reeled in
like a fish on a line. There are also ice screws in each foot, which can
be rotated to help to secure the spacecraft on the surface. The lander
is also designed to stay upright on a slope of up to 30 degrees.

We will try to ensure an adequate margin of safety by mapping the surface
of the nucleus at high resolution (a few cm) during the long orbital
observation phase so that we know the size, density, surface roughness
and other properties of the nucleus. This will enable us to select a
suitable landing site.



Under which circumstances would the mission be considered a failure?
Obviously we are hoping and expecting that the lander will succeed in
sending back the first images and in-situ measurements ever obtained from
a comet nucleus. However, if it fails, the primary science mission can
still continue – the most important, long-term scientific investigations
will be done by the eleven experiments on the orbiter. These will enable
us to map and characterise the nucleus in unprecedented detail, as well as
enable us to gain remarkable new insights into the processes taking place,
as the nucleus is warmed by the Sun and becomes increasingly active.

An error was detected in the Huygens probe after it was launched. What
measures have you taken to ensure that all systems are properly tested
and no similar errors slip through the net for Rosetta?  We have
carried out end-to-end tests in order to validate the entire system,
especially the lander. And although it is impossible to cater for all
eventualities during such a long and complex mission these tests give
us considerable confidence in the systems and spacecraft architecture
developed for Rosetta.

Beagle 2 was lost at the outset of the Mars Express mission. What lessons
were learned from that experience?  Rosetta has some similarities to
Mars Express/Beagle 2, in particular the fact that it involves both
an orbiter and a lander. As Mars Express has demonstrated, ESA has a
successful record of delivering and operating spacecraft in deep space.

However, the Rosetta lander mission differs from Beagle 2 in a number of
very important aspects. Beagle 2 followed an “uncontrolled” ballistic
trajectory, which meant that it had to be protected by a heatshield
against very high temperatures during descent. It also featured a complex
landing system, including a parachute and airbags to cushion the impact
on touchdown.

The Rosetta lander will not be deployed until the orbiter has mapped the
surface of the comet’s nucleus in high resolution and a safe landing
site has been chosen. It will be released about 22.5 km from the comet
centre (about 20.5 km from the surface) and descent will be very slow
and controlled, with a touchdown speed of perhaps one metre per second
(less than walking speed).

And since the comet has no atmosphere, the lander will not require a
heatshield, parachute or airbag, and there will be no concern about bad
weather or high velocity winds.

Since this will be the first time that a soft landing on a comet has
ever been attempted, there is always the possibility that some unexpected
event may occur. However, the landing procedures have undergone thorough
testing on Earth and every precaution has been taken to ensure that the
lander remains upright and is able to anchor itself to the surface. The
lander will be in communication with the orbiter (and Earth) through most
of the descent. However, due to the communication time lag, it will not
be possible to intervene in real time during the descent phase.

Were any scientific measurements undertaken during the flybys of Earth
and Mars?  Yes, there were some observations during all four flybys. The
imaging and plasma instruments were switched on – mainly for calibration
– during the Earth flybys. The same instruments (VIRTIS, ALICE and
OSIRIS) were turned on for scientific studies during at least a part
of the Mars encounter, and the microwave instrument (MIRO) was used to
sound the martian atmosphere.

Quite a few asteroids have now been observed at close range by various
spacecraft. Why was an asteroid flyby included in the Rosetta mission?
There are still many things we do not know about asteroids, including
their differing origins and composition, so we like to take advantage
of every opportunity to study them. Rosetta flew by two asteroids
in the main asteroid belt – 2867 Steins (in 2008) and 21 Lutetia
(in 2010). It also observed an asteroid fragment, P/2010 A2 in 2010,
in conjunction with the Hubble Space Telescope.

The Lutetia flyby showed the asteroid to have surprisingly high density
and an unusual surface composition previously thought to exist only
on large asteroids like Vesta. Steins is the first body in the main
asteroid belt found to exhibit a loosely bound rubble-pile structure,
and the first E-type asteroid to be observed close-up.

In addition to its scientific value, such information will be of
considerable practical use. For example, it will contribute to ESA’s
Space Situational programme, which is intended among other things to
detect asteroids that pass dangerously close to Earth and help prepare
countermeasures to prevent a possible collision.

What part, if any, is NASA playing in the Rosetta mission?  NASA is
involved in four experiments – MIRO, ALICE, IES (part of IES-RPC) and
part of ROSINA. NASA scientists are principal investigators on two of
these (MIRO and ALICE). The MIRO (Microwave Instrument for the Rosetta
Orbiter) instrument will be used to determine the comet’s abundance
of some major gas species, surface outgassing rate and sub-surface
temperature. It was also employed to measure the sub-surface temperatures
of asteroids visited by Rosetta and to search for gas around them.

ALICE is an ultraviolet imaging spectrometer that will analyse gases in
the coma and tail and measure the comet’s production rates of water,
carbon monoxide and carbon dioxide. It will also provide information on
the surface composition of the nucleus.

In addition, NASA’s Deep Space Network will provide communications
and navigation backup during the mission.

Rosetta was originally going to be a sample return mission. Why was
that scrapped?  The main reason was cost. NASA was involved during
the early mission definition phase, but then pulled out, making sample
return too ambitious for ESA to do alone. Although there is obviously no
substitute for retrieving an actual sample for analysis back on Earth,
Rosetta’sin situexploration is the next best thing. Moreover, Rosetta
will permit scientists to study the evolution of the comet’s nucleus
at close quarters, which a return mission could not do. And a sample
return mission would not be able to carry as many instruments.

Rosetta was originally supposed to carry a British experiment called
Berenice. Why was that experiment removed from the payload?  Britain
initially intended to provide two gas analysers – one on the lander and
one on the orbiter. This was a very ambitious commitment, particularly
since these are very complex instruments. The development programme ran
into technical difficulties and in the summer of 2000 it became clear
that the UK team did not have the time or the resources to make both
instruments. So it was decided to develop only the Ptolemy instrument
on the lander.

When Galileo was subjected to a long launch postponement, unexpected
problems arose after launch. What precautions were taken to prevent a
similar event from happening to Rosetta?  All necessary steps were taken
to prevent the launch delay from impacting on the mission. Rosetta was
stored in a clean room at Kourou from the moment the decision was made
to postpone the launch. We also took the precaution of removing some
of the major hardware items, notably the High Gain Antenna (HGA), solar
arrays and five of the instruments on the orbiter. Updated software was
installed and all flight systems testing revalidated.

Is the spacecraft insured?  No, it is not ESA policy to insure science
missions.