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New Proposed Path for Manned Trips to Mars: Let Mars' Gravity Capture Spacecraft
As illustrated in this article at io9.com, the conventional method considered for launching a manned craft to Mars might make less sense, even if it takes less time, than a more complicated but more efficient means akin to a method that's been already been successfully used to minimize the amount of fuel used in exploring both within and beyond the solar system.
Known as the "Hohmann Transfer" method, this type of maneuver is known to be effective. But it is also quite expensive and relies very heavily on timing. Hence why a new idea is being proposed which would involve sending the spacecraft out ahead of Mars' orbital path and then waiting for Mars to come on by and scoop it up.
This is what is known as "Ballistic Capture", a new technique proposed by Professor Francesco Topputo of the Polytechnic Institute of Milan and Edward Belbruno, a visiting associated researcher at Princeton University and former member of NASA's Jet Propulsion Laboratory.
In their research paper, which was published in arXiv Astrophysics in late October, they outlined the benefits of this method versus traditional ones. In addition to cutting fuel costs, ballistic capture would also provide some flexibility when it comes to launch windows.
It's an interesting idea, but getting *TO* Mars isn't the real problem. The biggest problem, that nobody is talking about (because they have no idea how to solve it), is *LANDING* on Mars.
http://www.universetoday.com/7...
The real problem is the combination of Mars’ atmosphere and the size of spacecraft needed for human missions. While the Apollo lunar lander weighed approximately 10 metric tons, a human mission to Mars will require three to six times that mass, given the restraints of staying on the planet for a year. Landing a payload that heavy on Mars is currently impossible, using our existing capabilities. "It’s this ugly, grey zone. There’s too much atmosphere on Mars to land heavy vehicles like we do on the moon, using propulsive technology, and there’s too little atmosphere to land like we do on Earth. Until we come up with a whole new system, landing humans on Mars will be an ugly and scary proposition."
That article is from 2007. Since then a Sky Crane was used to land the 1 ton Curiosity rover on Mars. I think it's pretty clear that we simply may not land an entire 100 ton payload as a single vessel, but would instead land the various supplies, habitats, and people as separate payloads. Perhaps they all come on a single ship (unlikely), but there's no reason with our current technology that we couldn't land the pieces separately. Worst case would be the humans don't land close enough to the supplies to be able to survive long-term, in which case Plan B is to explore similar to how the Apollo Lunar program did, and head back after several days. Then a later mission would bring another set of people to use the supplies already delivered.
Better known as 318230.
Why send/land everything at once anyway? Send living/experimentation modules and any needed non-perishable supplies or equipment such as vehicles on previous missions. Then send in a manned mission with perishable supplies/experiment subjects (seeds, plants, animals, whatever) afterwards. This allows for smaller payloads that can land easier, and has the added benefit of being easier to launch from Earth. It also gives you the chance to resend any critical supplies should one of the landings go wrong or land really off course.
The only thing necessary for evil to triumph is for it to be pitted against a slightly greater evil
There's perhaps an even more compelling argument why the atmosphere is good for us if we intend to land on Mars AND launch again: ISRU and the Sabatier reaction could be a huge win. If you plan to spend a few months on the surface, you can generate a ton of methalox fuel using the local atmosphere and only half a ton of water. Even if you needed to bring the water with you (which would be the safe option, I guess), it would effectively double your engine's Isp! You could even produce fuel for the trans-Earth injection this way, further saving the total Martian payload you'd need to launch. Without the atmosphere, none of this would be possible.
Ezekiel 23:20
Unless you do ISRU, of course. At that point, you'll be sending at most a lot of water (but much less then the fuel extracted this way).
Ezekiel 23:20
This has been standard NASA thinking for decades, that it was too hard to start an engine in the supersonic regime, hard to control flight, and therefor too risky to incorporate into any mission. However, SpaceX has shown that you can relight an engine pointed into a supersonic flow, and maintain control of the vehicle with the engine pointed into the supersonic flow. It's not without flaws, but it works. There are groups inside NASA that are beginning to rethink the old arguments and investigate this for use in future applications.
Yeah, but experience with gigantic hypersonic parachutes is also rather limited.
Again, it's really doubtful that there's any show stoppers here. But there's a lot that needs to be done before you can bet a whole mission on these sort of things. There's many thousands of little details that could kill the crew if they go wrong, so the odds of any one doing so must be kept to the tiniest fraction of a percent.
I am a proud traitor to my species in alliance with my mother the Earth in opposition to those who would destroy her.
I think you could decelerate to subsonic velocities at the proper moment
The "proper moment" is before you enter the atmosphere. So no. As soon as you enter the atmosphere, you can't do a retro-burn until you are subsonic, and you can't slow to subsonic without multiple hypersonic and supersonic parachutes. (Terminal velocity for a capsule on Mars is supersonic. You would hit the ground before you slowed enough to be able to fire retro-rockets.)
The only alternative is to have enough fuel in Mars orbit to do a retro-burn that virtually zeros the orbital velocity before you enter the atmosphere. And, by definition, that takes as much fuel as it does to launch from the surface into orbit.
Have a look at the entry sequence for MSL-Curiosity, hypersonic heat shield, supersonic drag-chutes, huge subsonic parachutes, and retrorockets, because the parachutes aren't enough to let you land on the surface. And every stage pushed the state of the art to the limits of current technology. All that just to land 900kg.
Now imagine what you'd have to add to land a multi-ton human-scale capsule...
Oh, did I say capsule? No. You have to get back home, so you need to land an entire launch vehicle on the surface of Mars. Plus all the infrastructure necessary to refuel and launch that vehicle.
under much worse conditions then in the Martian landing scenario
Earth reentry is much easier than Mars. A nice fat atmosphere to bleed off all your velocity, down to subsonic, before you even worry about parachutes or retro-rockets. Mars' atmosphere is just awful. Too thick to be ignored, too thin to be useful. Exactly, precisely wrong.
Science is all about firing a drunk pig out of a cannon just to see what happens.
The best idea I've heard is to make use of aerodynamic lift for that, so instead of falling down on a purely ballistic trajectory you make large enough surfaces to actually _fly_.
You won't be able land like airplanes (or Space Shuttles) do on Earth, but you'll be able to use the lift to cause a stall. If you are careful then you can make your vertical speed to be zero at that moment and your horizontal speed will just be subsonic (I remember reading calculations proving that) for a reasonably shaped airfoil. Then you can use retro rockets to bleed away the remaining speed.
It's complicated, but we have some experience with Space Shuttles that we might be able to reuse.