Phobos

Phobos
Base Data
Radius	1126.67 meters
Gravity	0.0057 m/s2
Timewarp Height	1000 meters
Color	RGB: 91, 79, 73 HEX: #5B4F49
Orbit Data
Semi-major axis	468.8 kilometers
SOI radius	2440 meters

Phobos is one of the two Martian moons, the other being Deimos. It's the larger one of the two, and it orbits closer to Mars. Its low gravity makes landing on it relatively easy. The surface of Phobos is porous.

Phobos is the key for the exploration of Mars, so many players build bases/colonies on Phobos. They also land a lot of landers on this celestial body.

Terrain

A section of the surface of Phobos, taken by a lander.

The terrain is very porous. Its porosity might dislocate rockets when landing on these pores. When rocket lands on one of the pores, it may stay upright. It is covered in some craters and high mountains. The high mountains are a place where the gravity is lowest.

Some areas of the surface are very rough; that's why rockets that landed there after touchdown tip over, due to the low gravity and the irregularity and porosity of the surface. Some landers tip over to the side, or land in different directions and/or angles, but when they stay on the surface for a long time, the other part that has not touched the surface touches the surface of the moon.

The bigger pores can be used for landing on a big flat surface (like probes); the smaller ones can be used for landers with landing legs and landing in between them. The best place to land on the moon is a place where it's relatively flat.

Moving on Phobos

Driving rovers on the surface may be difficult, due to the extremely low gravity and the porous terrain. Wheels do not have enough grip to stay on the ground and may lift the rocket off of the surface. The gravity may be enough to make the rover orbit Phobos and in some cases escape Phobos' gravity and orbit Mars. Rovers are meant to explore the ground, not to be a satellite with wheels that are useless and drives around nothing but space.

To counteract this, it is recommended to use (clipped) Ion Engines to push the rover down while using wheels to move horizontally (though the wheels would have to be manually enabled, and couldn't with RCS Thrusters). or use rotation if you don't have the part expansion DLC. (Since the gravity is too weak to even hold torque of a rover.). Finally, making a hopping with some structural parts and probes is another effective way to move.

Reaching orbit from Phobos is simple. RCS Thrusters are powerful enough to reach orbit, and adjust, possibly to the extent of leaving the sphere of influence. Ion thrusters is another option, since it has the same thrust as the thrusters, and they have a very high specific impulse (I_sp) of 1200s.

What to do on Phobos?

Phobos has a very small sphere of influence and low gravity. Engines that have miniscule thrust or operating at a very low throttle is enough for the spacecraft to escape Phobos, then orbit it on Mars. RCS thrusters thrust is too high to even modify the orbit with precision. The orbit insertion is easy, because Phobos is small, so short engine burns must be conducted. In some cases, the rocket comes into a high speed, and long engine burns must be conducted at full throttle. It is recommended to start decelerating to orbit on Phobos on Mars even before entering Phobos SOI.

A Mars space station can be built on Phobos. But due to the small size, docking maneuvers must be done carefully. The other building spaces for a Mars space station are Deimos and in high Mars orbit (usually between the orbits of Phobos and Deimos).

A Phobian base can be built on Phobos. But, bases on Phobos must be small enough, to fit the size of Phobos. The maximum number of bases on Phobos is around 5–8.

A Phobos Space Elevator can be built on Phobos, but in the simulator, it is very complex. First, multiple segments and the main elevator must be built. Then, some support structures must be built around the elevator to keep it stable. Sometimes, the elevator topples even the structures are in place, due to the low gravity.

Phobos is the key of exploring Mars. So, landers would land in the planet, usually in the bases, then they would be refueled, then sent back to Mars or Earth.

Trivia

• Unlike the rest of the celestial bodies, Phobos has its size roughly 10 times smaller than the real-life Phobos; the same applies to Deimos. For others, their size is 20 times smaller than that of their real-life counterpart.
• Phobos is one of the perfect places to experiment on orbital physics due to its low gravity.
• The porosity of Phobos is caused by being a rubble pile, or it had been formed irregularly.
• Due to the low gravity of Mars and its moons and the low difficulty to get there, players often extend Mars missions to include landing on the moons of Mars before returning home.
• Some players practice docking on Phobos, since it is small. Small bodies are easy to dock rockets on.
• If you jump on Phobos, you would never return back to the surface and forever orbit Mars, unless if Phobos catches you up in its orbit.
• In real life, Phobos will drop pass Mars's Roche limit around 40 million years from now and disintegrate, giving Mars a ring. In a few hundred million years, the ring will have fallen to Mars' equator, creating craters on it and heating up the atmosphere.
• Phobos has no sphere of influence in real life because its mass is too small to support one, and it is too close to Mars.
• Phobos is named after the son of Ares (Mars) and Aphrodite (Venus) and twin brother of Deimos. Phobos was the god and personification of fear and panic (cf. phobia).
• In 1.5.5 update its orbit was lowered from 1340 km to 468.8 km. This change is due to rescaling.
• The exploration of Phobos in real-life is extremely difficult and is part of the so called "Mars Curse". Mostly those attempts are from the former Soviet Union and modern day Russia. These are Phobos 1 and 2 and Fobos-Grunt which could have made observations and deploy a small probe onto its surface, and return back samples to Earth.
• Although exploring Phobos is difficult, there is a mission proposed by JAXA and European Countries (i.e MMX).
• There is a glitch when escaping Phobos' SOI by accelerating, your spacecraft would become stuck.
• It might have been used to be an asteroid but was captured by Mars' gravity because of Jupiter's gravity pulling Phobos towards Mars, eventually capturing it. It was possibly captured 2–4 billion years ago.
  • However, it’s more likely that it was formed from a collision with a large object billions of years ago, explaining the close & stable orbit. In addition, it also explains the similar composition.