Space_is_hard - Mars Ascent

#Space_is_hard - Mars Ascent

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##Overall Methodology

I believe we can treat Mars Ascent much like an Earth Ascent; that is, a single burn to orbit should be possible due to Mars's thin atmosphere relative to its orbital velocity. Unlike Kerbin's stock configuration, where the atmosphere height is very tall in proportion to the orbital velocity, most of the Mars ascent delta-v budget can be directed towards horizontal accelleration instead of requiring massive amounts of altitude gain to escape a thick atmosphere.

What this means for us is that, after a short vertical hop from the surface, we can pitch over quite a bit, probably 45 degrees or more. A continuous surface prograde burn should ideally net us orbital velocity as we approach horizontal, however this will probably end up being a very low orbit and circularizing after apoapsis is probably dangerous due to the risk of terrain. For that reason, we'll probably have to do a constant-altitude circularization until our orbit circularizes and our apoapsis gets to the target altitude.

##Things we need to know

* Is the ascent vehicle a separate stage from the descent vehicle? (I assume so)

* What kind of TWR profile will our ascent vehicle have?

* How much disk space can we allot towards the ascent script?

* Will there be staging events during ascent, or is the ascent vehicle an SSTO? Will there be drop tanks?

* Will we be rendezvousing with an orbiter or proceeding directly to Earth from the parking orbit?

* If redezvous with an orbiter is required, what kind of parking orbit will the orbiter be in? Circular? Elliptical and synchronous? Will it be inclined to the equator? Inclined to the ecleptic?

* What is the latitude and elevation of our landing site?

* What is our delta-v budget for ascent?

* Will we be using hypergolic fuels? Or will a cryogenic be involved, such as from Sabatier-produced LOX/Methane?

* Will we be required to ensure plane alignment with the orbiter? Will we be given a launch time or are we required to determine that ourselves?

* Will our ascent vehicle have an offset center-of-mass from EDL?

##Challenges we may face

* If we're rendezvousing with an orbiter in an eccentric synchronous orbit, this will complicate rendezvous quite a bit. Most rendezvous methods and scripts assume two nearly-circular orbits.

* The ascent profile is not something that we're going to be familiar with as players, and will certainly require a good bit of experimentation to get the pitchover altitude and amount tuned.

##Emergency Abort

I don't anticipate mechanical failures to be simulated, but it's been expressed that we should have an abort contingency anyways. We will require some very different abort methods as compared to an Earth ascent, due to:

* Our ascent vehicle will most likely have its propulsion system permanently attached to the crew capsule. If something were to go wrong with the engines or tankage, we would most likely be stuck with it the rest of the way down.

* I doubt that the ascent vehicle will be equipped with landing equipment such as landing legs. Should we require an emergency landing on the surface, we're going to have to set it down on the engine bell.

* We most likely won't be equipped with solid escape motors. Any "GTFO" thrusting will have to be done with the ascent engine, if it's still working.

* The farther through the ascent we go, the farther forward our center of mass will go. Late-ascent abort may mean we'll be stuck with a vehicle that's only aerodynamically stable when flying forwards. A lack of heatshield, combined with near-orbital velocity reentry heating, may mean that a late-ascent abort may not be possible.

We do have one thing going for us, though, and that is that we'll probably still have the decent chutes attached to the capsule. Those would be designed to stop a more massive descent vehicle and therefore would probably allow us to decelerate quite a bit, leaving much less work for the ascent engine to do as we approach touchdown. We would have to communicate to the mission planners that the decent chutes would need to be repacked before ascent.