Here is Lockheed Martin's concept design for its Mars lander.
And here is an illustration from the talk Elon Musk recently gave about his Mars plans.
I looked at these and thought, those look like the cover illustrations from paperback sci-fi of the 50s and 60s.
So I'm wondering, are Elon Musk and Lockheed's designers being influenced by all the illustrations they saw as kids? Or is this actually a very sensible to design planetary landers that was just lost in the Apollo era?
How feasible is it to actually land a rocket like that, so to speak bottom-down? Would it enter the atmosphere bottom-down like that? Pivot close to the ground? How much propellant would that take? Or is the idea that you land it like a space shuttle, say, and then somehow set it up again as a vertical rocket?
ReplyDeleteWell, Space-X just landed their reusable booster that way, so it is possible even in earth atmosphere. But I don't know why it would be the best approach.
ReplyDelete@David
ReplyDeleteIt's actually pretty feasible to land a rocket bottom-down, in the appropriate conditions.
That's how the lunar lander worked, after all. It descended backwards, and as it did so the rocket fired against the direction of motion to slow the descent, and the inherent nature of the physics involved caused the lander to "even out" and land upright automatically. Then when they were ready, they just blasted off again.
Pivoting in the atmosphere is pretty tricky, since it works against the aerodynamics of the classic "cigar" shape of most rockets, so typically you pivot before entering the atmosphere, in the vacuum of space, to aim the bottom of the ship downward. The problem with that is then you need to worry about friction from the atmosphere, and it's hard to properly heat shield the bottom of a ship.
One way to get around this is to enter the atmosphere facing forward, bleed off a lot of speed from the friction of the air, and then manage the landing via parachute. That's how the lunar lander made it back to earth. This wasn't necessary when landing on the moon, because its atmosphere was so much thinner that it not only wouldn't cause much heat from friction, but it also wouldn't allow parachutes to function regardless.
Another option is to use a space plane design, like the shuttle. This limits you to landing on planets with sufficient atmospheres to allow you to fly and land like a plane, however, so that wouldn't work on the moon.
The question of how much propellant it takes is probably the single biggest problem for all of space travel. The short answer is: it depends. The heavier your ship, the stronger the gravity of the planet, and the denser the atmosphere all mean you'll require more and more fuel to get you off and back onto a given planet.
The lunar lander had all of these qualities working for it - very little atmosphere, very low gravity, and a very small craft. But to get the lander off the earth in the first place, it had to be placed atop those gigantic booster rockets, to overcome the extra gravity and atmosphere.
Landing on Mars is a lot like landing on the moon, except harder. It has only a bit more of an atmosphere to content with, but lot more gravity, so that's more fuel to begin with. But one of the big hurdles of a Martian mission is carrying all the stuff you'd need to survive the trip there and establish a sustainable base, so you need a bigger ship to carry a bigger payload and the much larger amount of fuel necessary to even lift that payload. So more propellant all around, and ideally more efficient too.
If you're building your craft with the intent of it not making a return trip, then that cuts down a lot of the need for fuel. I imagine that makes the idea of not using detachable booster rockets much more viable. Instead of needing multiple different rocket motors which you discard in flight to make later stages lighter to allow them to not just land but also launch again, you can just use a single engine system that spreads it's fuel usage between launch and landing.
One big thing which I'm led to believe is very different today compared to the lunar landings is the rocket fuel itself. The Apollo missions used solid rocket fuel boosters, which have the benefit of being simple, stable, and powerful, but the downside of burning continuously until exhausted, with no means of stopping it. I would assume these Martian landers will employ liquid fuel, which allows you to burn off only as much as you need at any given time.
someone educate me, please. what's the draw for going to a planet on a one-way ticket, to get there and realize that yep it indeed has a toxic atmosphere of perchlorates, high radiation, no protective ionosphere, very little water, and you're there doing what machines do yet cost far less to operate remotely than keep you alive. i know of more hospitable sand-burials in the utah desert.
ReplyDeletei've read (and agree with) statements that sending humans into space is not an act of science but one of politics. help me understand how this is untrue.