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This has come up as a topic of discussion on our mailing list, so I was curious what the space heads here think.
We are developing a Mars Direct addon to the freeware Orbiter Spaceflight Simulator. We're trying to stick to Dr. Zubrin's plan as much as is practical. Mars direct calls for two types of manned launches with the Ares HLV; one with a manned ERV for a lunar mission, and one with a manned hab module for Mars missions.
If you have to abort during the Trans Mars Insertion burn, you can always use the aerobrake to bring yourself back into a LEO and have someone come pick up the crew. There's no rush since there's three years worth of food, oxy and water on board.
But what happens if you have to abort before LEO is established? I suppose with the ERV you could supposedly land in the Atlantic, the same way as an Apollo capsule would. The hab module on the other hand, is a lot bigger. Would it be effective to fit the Hab with some kind of flotation device? And would the heatshield/aerobrake, designed for Mars, hold up in Earth's atmosphere?
We are considering wiether or not we should launch the Hab module unmanned, and then rendevous with it in LEO before the Trans Mars Insertion.
For our website see:
http://barnstormer.home.mindspring.com/ … ...ect.htm
For Orbiter:
http://www.medphys.ucl.ac.uk/~martins/o … orbit.html
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Mars or Bust! Easy to say... a lot heavier if you actually start to apply it to design.
I think the easiest way around the diffculty is a rendevous in orbit. To design to survive the abort severly compromises the ability to function without an abort. The Apollo lander and Command Service Module were expendable in an abort.
Come on to the Future
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I believe that Zubrin had the idea to make the Hab's heat shield strong enough for Earth entry. This would give a good margin of safety when landing at Mars and it would be testable in Earth's atmosphere.
As for the landing -- why not launch over land? The Hab is designed to land on solid ground. And, it has parachutes to slow its decent. Since the gravity is stronger on Earth, the landing rocket burn would simply have to be shorter and stronger. Or, more fuel could be put in the tanks. This would also give an extra margin of safety upon arriving at Mars.
Another thought -- if abort to ocean splashdown is used, then an inflatable ring could be put around the first floor of the Hab. In a splashdown abort it would serve as a flotation device for the Hab. On a normal mission it would be used as extra living area once the Hab has landed.
Another Idea -- Don't do any modifications to the hab. When the Hab parachutes into the Atlantic, just keep the hatch closed and use the natural boyancy to stay afloat. It might not be very stable but it won't sink. Just sit tight until a helicopter or ship can come pick you up.
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More weight on the shield or fuel in bigger tanks all adds weight that detracts from consumables etc.
However it might be worth it. The inflatable ring is a decent idea even without looking to bouyancy.
I am not up to scratch on parachute theory... Could the same parachutes be used?
Also what if the abort occurs with a full stack 10ft of the pad... or 500ft or 2000ft while you still have all that booster below. Can the whole hab emergeny abort?
Come on to the Future
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Nah...it'll probably just explode. If it could uncouple from the booster maybe the heat sheild would absorb the blast though. But now I'm stepping out of my area of expertise.
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More weight on the shield or fuel in bigger tanks all adds weight that detracts from consumables etc.
However it might be worth it. The inflatable ring is a decent idea even without looking to bouyancy.
I am not up to scratch on parachute theory... Could the same parachutes be used?
Also what if the abort occurs with a full stack 10ft of the pad... or 500ft or 2000ft while you still have all that booster below. Can the whole hab emergeny abort?
An abort of the hab:
Launch-escape-system: Soyuz and Apollo had a rescue system for emergency just after or during launch or preparations. This was jettisoned after 2nd stage ignition. In case of a hab, such a device should be mounted on top and it would be pretty heavy to be able to detract that hab from the HLLV.
Heath-shields: When during launch something fails, the 'mission' turns out to be a parabolic flight. This means that the velocity is not larger than 7.5 km/s. The entry velocity of the hab in Mars atmosphere is about the same value. It can be a kilometer a second lower. This depends on the precise trajectory choice.
At Mars, the hab cannot slow down as low as is possible in Earth's atmosphere, because of the density of the atmosphere. So an abort on Earth will last more from the Heath-Shield than on Mars. Beside that: Earth's atmosphere is corrosive, Mars' is not. I don''t know if this matters, but it could be.
Parachutes: No problem. Because of the density of Earth's atmosphere is much bigger than that of Mars on Earth the parachute's can be much smaller than on Mars and even than decelerate more.
Landing rockets: Again no problem. Less velocity remains in case of an Earth-abotrt than on a landing on Mars. I think these rockets don't need to burn (as was the case with Apollo).
Land or Water: A launch on Earth has to be eastward. Beside that, the surface of Earth East of the launch-site should be nearly uncrowded. That's why it's easy to launch at a east-coast. The Russians and Chinese have desert east of their launch sites. When we want to launch from KSC or Kourou, inflatable swimming-stuff has to be attached on the hab. Eventually it could be jettisoned after safe launch.
But all this said, I think an unmanned hab-launch, by a non-man-rated HLLV, and a rendez-vous in LEO is preferable.
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