Mars Aeroentry - How do we get out of Mars orbit?

Mark S · 2002-07-26 14:52:33

One of the least well-defined aspects of Mars Direct, at least from what I've read in "Case for Mars," is the descent to the Martian surface from orbit. I'm assuming that it will follow the same profile as all previous Mars landers: retro-rocket fires and falls away. Spacecraft enters Mars's atmosphere, protected by heatshield. Parachute deploys, heat shield is released. Braking engine fires just prior to landing.

This would all be fine, except that the aerobrake (assuming an unfurling, hemispherical shield) would have to protect the retro-rocket during aerocapture. Of course, other designs such as the NASA DRM have integrated the aerobrake with the lander's skin. Stil, I think that this expendable stack of heat shields and engines is inefficient.

I'm imagining an alternative lander shaped similarly to the McDonnell Douglas Delta Clipper (or a missile re-entry vehicle, for that matter.) it would enter the Martian atmosphere nose-first, before re-orienting itself using RCS thrusters and making a powered landing on the same engines used for the retro-fire burn.

I think that this approach is elegant, but it is untested. Before it can be added to Mars Direct, a sub-orbital demonstration of this type of lander must be made on earth. It would go one step beyond the DC-X test flights. My hope is that the Mars Society will recognize the need for this landing system and form a partnership with somebody to carry out these tests.

Phobos · 2002-07-26 17:27:23

I'm imagining an alternative lander shaped similarly to the McDonnell Douglas Delta Clipper (or a missile re-entry vehicle, for that matter.) it would enter the Martian atmosphere nose-first, before re-orienting itself using RCS thrusters and making a powered landing on the same engines used for the retro-fire burn.

Wouldn't it add mission risk though if you were to require the lander to flip right-side up in the middle of entry? The aerobrake shield might add more mass but it seems like it would be a safer alternative to flipping the spacecraft around using thrusters. Or did I misunderstand something here?

mfrieden · 2002-07-26 19:07:32

Well, you'd still be screwed if your thrusters failed to fire, aerobrake or not. Seems like the same risk to me.

Phobos · 2002-07-27 11:07:49

But adding that extra maneuver would make the mission that much more risky just to save a little weight. Your asking a lot of your systems to be able to flip the spacecraft over when it's rushing at a great speed toward the Martian surface. You'll have virtually no time to correct any errors should one occur. I think it would be better to leave such risky maneuvers out of the first Mars missions.

Mark S · 2002-08-01 08:23:02

I've also thought about a plug-nozzle for the hab lander that will serve as de-orbit engine, heat shield, and landing engine. The plug nozzle was a concept that was tested in the 1960's and featued prominently in Phillip Bono's designs for single stage rockets. It was also known as an annular aerospike.

Lockheed Martin and Boeing resurrected the idea for the X-33 as the linear aerospike. They did away with the heat shield requirements and arranged the combustion chamber in two rows rather than a ring. Work on this engine has stopped, so it doesn't look good for using an aerospike for the first trip to Mars.

Mark S · 2002-08-09 12:09:30

In NASA's design reference missions, the landers make a direct entry into Mars's atmosphere instead of aerobraking into orbit. The landers have been redesigned into conical shapes with a higher lift-drag ratio than the disk-shaped aerobrake.

This approach raises many design challenges. The entry profile has to be stretched out so that the g-forces don't kill the astronauts. It also requires a great deal of precision when determining the point of entry, which dictates some kind of guidance computer on board the ship. Tail-first landing will also require a moderate re-orientation maneuver near the end of descent, although the lifting entry does eliminate the need for parachutes.

If this approach is what NASA goes with, I hope that this maneuver is rehearsed somehow before the first humans arrive. It seems a bit risky compared with the original Mars Direct approach.

Nirgal82 · 2002-08-09 16:38:54

I thought the the heat shield was deployed for the duration of the trip out in Zubrin's Mars Direct. At least thats the way it looked in the diagrams, heh.
But then again, it does have to fit in the nosecone of a rocket.
I imagine unfurling would be a very critical process carried out in the first hour outside of the Terran atmosphere, I mean, If you can't get that sucker out and ready, you die, or at best you wait the long wait involved in free return trajectories.
On the other hand, who says a complicated unfulring process needs to be done. Perhaps, speaking from a Mars Direct point of view, you could fit the shield, "unfurled" (actually solid, as in this scenario it would never have to be folded into a compact space) to the side of the rocket stage that contains the hab. Of course this would produce extra drag but I'm sure this can be minimized by strapping it in the lowest drag configuration. Once en route to Mars you could perform an Apollo style docking manuver; jettison the heat shield prior to extending the cable and tether, maneuver the hab to dock with the shield, then release the tether and "put that sucker on spin cycle" {; ) (I like the way you put that as well Phobos)
Of course I don't know how well attached things can be when they've been put together in this manner, I mean its not like the LM and CM had to go through aerobraking manuevers together.
So depending on that factor, and if this idea be used, the only technology needing R&D is strong docking couplings...

Your friendly neighborhood Martian...
-Matt

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#1 2002-07-26 14:52:33

Re: Mars Aeroentry - How do we get out of Mars orbit?

#2 2002-07-26 17:27:23

Re: Mars Aeroentry - How do we get out of Mars orbit?

#3 2002-07-26 19:07:32

Re: Mars Aeroentry - How do we get out of Mars orbit?

#4 2002-07-27 11:07:49

Re: Mars Aeroentry - How do we get out of Mars orbit?

#5 2002-08-01 08:23:02

Re: Mars Aeroentry - How do we get out of Mars orbit?

#6 2002-08-09 12:09:30

Re: Mars Aeroentry - How do we get out of Mars orbit?

#7 2002-08-09 16:38:54

Re: Mars Aeroentry - How do we get out of Mars orbit?

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