kRPC hover script

hover.py

import krpc
import time

conn = krpc.connect()
vessel = conn.space_center.active_vessel
control = vessel.control
flight = vessel.flight(vessel.orbit.body.reference_frame)

target = 15 # target altitude above the surface, in meters
g = 9.81
while True:

    alt_error = target - flight.surface_altitude

    # compute the desired acceleration:
    #   g   to counteract gravity
    #   -v  to push the vertical speed towards 0
    #   e   to push the altitude error towards 0
    a = g - flight.vertical_speed + alt_error

    # Compute throttle setting using newton's law F=ma
    F = vessel.mass * a
    control.throttle = F / vessel.available_thrust

    time.sleep(0.01)

Wow, thank you for posting this! This is such an elegant solution that it makes you feel dumb.

I first tried the naive solution of incrementing and decrementing the vessel.control.throttle by 0.1 based on flight.mean_altitude. Then when it was just bouncing back and forth I tried to limit the flight.vertical_speed for a smoother flight. And then I started looking into approximating the total distance based on the past N velocities, almost like an approximated integral. Never thought to use one of the first formulas you learn in Physics class.