Mars Moon Return Mission

Phobos and Deimos (mars's moons) are the last achievements listed in the free version of the application, and one of the easiest after earth orbit and moon return mission.

## Rocket

Only one rocket is necessary for a single return mission to both Phobos and Deimos at once, this rocket is shown in the picture below:

From top to bottom, this rocket is composed of: parachute, capsule, heat shield, stage separator, with two RCS thrusters mounted on it, 5t fuel tank with two docking ports on it, stage separator, 20t fuel tank with two rovers mounted on it with side separators, 10t fuel tank with two landing legs, stage separator, probe, 10t fuel tank with, on each side of it: 15t fuel tank with on its side a booster made of 15t, 20t and 10t fuel tanks with aerodynamic nose cone, Hawk engine and RCS thrusters. The one of the 15t fuel tanks on the side of the center 10t fuel tank have a docking port at its bottom, hidden in the stage separator. This docking port is required during return trip to host the capsule with putting the main spacecraft out of balance during powered phase. All the elements described above compose the main spacecraft.

The main spacecraft is linked to the second stage with three stage separators. The second stage is made of, from top to bottom: one center 20t tank with a 20t tank and two 10t tanks on each side of it. The outermost 10t tank have an aerodynamic nose cone above it. Below theses seven tanks, there is seven 20t tanks and seven hawk engines below them.seven

Below the second stage there is the first stage connected to it with seven stage separators. It is made of seven 20t tanks with a Hawk engine on each of them.

One big specificity of the spacecraft carried by this rocket is that the Phobos and Deimos descent stage don't have main engine, but only RCS. The reason is the very low gravity of Phobos and Deimos, much smaller than earth's moon, which allows landing and take off with RCS thrusters alone.

Photos and Deimos descent spacecraft have some other specificities:

Its height is not at all due to its fuel needs, but only because if the many elements it has to be equipped with: landing legs, rovers, docking ports, RCS thrusters. Because of this, RCS thrusters are very close to the capsule stage separator, and **great caution shall be used when activating or deactivating its RCS**, in order to not jettison its capsule unintentionally. For this reason, frequent Quicksave are highly recommended when using this spacecraft.

As we can see, this Phobos and Deimos spacecraft carries two rovers: one for Phobos, and one for Deimos.

## Mission

Photos and Deimos return mission start like a Mars mission, except that only one launch is required.

### Mars's moons transfer

Once existing earth sphere of influence, when performing the trajectory correction for Mars flyby, take care to do it on the correct side in order to orbit the same direction as Phobos and Deimos, otherwise a rendezvous would be impossible, because the spacecraft would fly against meaning regarding Mars's moons. Tune this flyby to orbit Mars a little higher than Deimos. When at the periapsis of this flyby, burn retrograde to enter circular Mars orbit little higher than Deimos.

From this, speed up time until flying very close to Deimos, and then use "Navigate To" functionality to reach Deimos encounter performing a flyby of it at 1100m. The reason of this altitude is that time speeding is impossible above x3 when lower than 1000m, and rendezvous procedure would be far too long at x3 time speed. Once at 1100m of Deimos, burn retrograde at 0.1% to enter circular orbit at this altitude.

### Deimos descent and landing

From this point, descent spacecraft can be separated to start the descent : burn retrograde with RCS to get an orbit with very low periapsis, as shown on the picture below:

During the descent at x3 time speed maximum, exist Map view and zoom out to see the ground. Deploy landing legs, make them face the ground regarding closest point to Deimos and wait for the flyby of this point. When at the lower altitude, burn retrograde to cancel horizontal speed and a little bit upgrade to move down the ground.

As Deimos has a very small gravity, the game may not detect landing upon both landing legs touchdown. In such case, burn upgrade to push the spacecraft towards the ground and pitch it to make both landing legs touch the ground if they don't. This may be sufficient to let the game detect the landing and print it on the screen.

Deimos has such small gravity that rovers can barely drive on them, and if they are deployed the same way as on Mars, the side separator will throw them into orbit instead letting them reach the ground. For this reason, rover deployment on Phobos and Deimos needs to first take off, pitch the spacecraft to rover side, burn upgrade to make the rover touch the ground, and then detonate the side separator. This will make the rover being pushed to the ground and the spacecraft rised up into space, as shown on the picture below, with only one rover because the first one has already been deployed on the other Mars moon.

   Once the rover has been deployed, use RCS to rise apoapside to a little bit more than 1000m (you'll see that RCS are more powerful and less accurate than an Hawk engine at 0.1% thrust).

When at this apoapside higher than 1000m, use RCS again to circularized the orbit a little bit higher than 1000m, and switch to the main spacecraft to perform the rendezvous (even without "Navigate To" functionality), because its Hawk engine is much more accurate for a rendezvous. As orbits are very close to each other over Mars moons, rendezvous can only consist in speeding time until the spacecraft are close, and the use RCS for approach and docking.

The main spacecraft shown on this page have 3 docking ports: one on each side and a third at the bottom. The ones on the sides are intended to be used during Deimos to Phobos transfer, because the unbalance won't be a problem as long as Hawk engines thrust are low. The docking port at the bottom is intended to be used for transfer to earth, once the lower part of the descent spacecraft has been jettison, in order to let it fit between the engines of the main spacecraft.

### Deimos to Phobos transfer

    Once docked back on Deimos orbit, simply burn prograde to exist Deimos influence sphere and then burn retrograde to lower the periapsis a little bit higher than Phobos orbit. Once there, burn retrograde again to circularized the orbit.

From this, the procedure is exactly the same as for Deimos: speed time until being close to Phobos, use "Navigate To" to enter Phobos influence sphere and perform 1100m flyby, circularize the orbit at this altitude, undock, descent, land, takeoff and deploy the rover, get back on 1100m orbit, rendezvous and dock.

### Return to Earth

As told in the rocket description, the size of the descent stage is not due to its fuel needs, so it will still have fuel once back from Deimos and Phobos. before jettison of the descent stage lower part, transfer all the remaining fuel to the main stage. Once jettison, undock the upper part of the descent stage from the side of the main stage and dock it on the bottom port. Transfer all the fuel of this stage to the main one, and then use "Navigate To" functionality to go back to earth (exiting Phobos influence sphere may be necessary first).

Once outside Mars influence sphere, correct the trajectory at 0.1% thrust to enter earth atmosphere. Before this entering, separate the capsule and make it heat shield face moving direction. Open parachute at 1000m altitude.

Once landed, click on "Recover", you'll get the two Phobos and Deimos achievements.