Gilly

Gilly/Data

Gilly is a tiny asteroid, the only natural satellite of Eve, and the smallest celestial body in the Kerbol system. Landing on Gilly is challenging due to its very low mass, steep slopes, and highly eccentric orbit, making it very easy to overthrust engines or send a spacecraft tumbling. Gilly's odd shape and fast rotation give the surface near the peaks an apparent velocity near 5 m/s. The navball of a lander securely parked on the surface may still display "Orbit" and a small non-zero lateral speed. To prevent tumbling upon landing, the final velocity trim may need to be performed by eye.

Escaping Gilly is much easier — the EVA jetpack can easily put a lone Kerbal into orbit or set him on an escape trajectory. In fact, it's possible to deploy a Kerbal from a spacecraft in orbit around Gilly, send him down to the surface, and land him without using any other fuel source. Albeit with some difficulty due to the lack of a navball, the Kerbal can even return to orbit, rendezvous with the spacecraft, and still have just a bit less than 50% pack fuel left.

Gilly has the least gravity of all bodies in the Kerbol system, with half of that possessed by Jool's moon Pol, due to its extremely low mass and small size. A Kerbal can jump over 1000 meters on this moon. Gilly's gravity makes it ideal for very low fuel interplanetary missions; however, its eccentric and inclined orbit may make encounters more difficult and fuel-costly.

An unplanned encounter with Gilly is unlikely when approaching Eve, even if player's trajectory is near the plane of Gilly's orbit. This is because Gilly's mass is very small relative to Eve's mass, resulting in a very small sphere of influence compared to the semi-major axis of its orbit. In fact, no other moon in the game has a smaller mass ratio.

Gilly was once even more dangerous to land on due to a clipping bug with the collision mesh. This problem was fixed in version 0.17.1.

Topography

A topographic map of Gilly.

The surface of Gilly is extremely dynamic and uneven, with many steep slopes and smooth areas. This moon is considered a captured asteroid. Gilly has the lowest mass and gravitational force of any body in the Kerbol system. Due to its minuscule mass and gravitational force, it does not have an atmosphere.

Gilly's color might come from a high content of solid carbon. When terrain scatters are enabled in the settings menu, small rocks show up on the surface.

Gravity

The gravity of Gilly is extremely low, with only 0.5% of Kerbin's surface gravity. Because of this, it is very impractical to walk on Gilly; each step will launch a Kerbal several meters into the air, and a jumping Kerbal will usually take around 200 seconds to return to the surface. This makes jetpacks a necessity to move around the moon practically. The low gravity also makes it very difficult to get into an encounter since it makes the sphere of influence so miniscule. On the other hand, starting a craft is very easy to accomplish as they weigh far less than usual.

Landing

Landing's difficulty is ambiguous and mixed - a major pro is that you don't need to do much to slow down to land safely, but the con is that due to Gilly's extremely low gravity, landing can be actually challenging, because of the lack of any "grip" (you can easily bounce off the terrain), extremely uneven terrain and relatively fast rotation (when compared to its size) of the satellite (navball indications are simply fallacious and it is adviced to actually keep the prograde tilted a little bit sideways to counter the Coriolis effect if you are landing close to the equator). It is adviced to be adept in manually using RCS thrusters and to have SAS active on the lander.

Reference Frames

Gilly/RefFrames

Gallery

An unsuccessful touchdown attempt in 0.17. Note the landing legs clipping through terrain.
Topographical image of Gilly.
Screenshot123.png

A successful EVA landing.
A topographic height map of Gilly as of Version 0.18.2. Made with the ISA MapSat plugin.
A successful probe landing. Small rocks are visible on the surface in the background.
A successful scientific, electrically powered probe landed on Gilly. The probe's small mass combined with Gilly's low gravity makes ionic engines feasible, as shown here.
Successful EVA landing with a fuel check to show usage.
Return to Gilly orbit and the spacecraft via EVA.
A successful, if rushed, rendezvous with the orbiting spacecraft with just an EVA pack and some pluck.
If done right, one could probably land, take off, and rendezvous with an orbiting spacecraft with over 3 units of monoprop.