27 thoughts on “The Problem With Landing On Mars”

  2. If the supersonice retropropulsion bugaboo is real, you’d need to spend a lot of propellant to burn your engines all the way down keeping yourself subsonic. Could you even ‘stop’ yourself in orbit that way? Assuming I understand your proposal, Rand.

    1. You can do most of the braking outside the atmosphere, coming to a dead stop and then descending vertically in the easily analysed but suboptimal limit case. The likeliest solution is a combination of as much propulsion as necessary, but as much aerodynamic deceleration as possible.

    2. A paper I was reading a few years ago (coauthored I think by Bobby Braun himself back before becoming NASA’s chief techologist) talked a bit about the problem of supersonic retrobraking. It turns out that most of the early Viking-era research on the topic assumed the engines were all located right in the center of the aeroshell. When you go with multiple engines out near the periphery of the aeroshell, there were early suggestions that the plumes would enhance instead of reduce the aerodynamic braking effect. Needs more work, but not that expensive of work (compared to building a big HLV like SLS).

  3. I often wonder why NASA engineers have so little imagination. It would appear that the idea of refueling in orbit or on a moon requires so little of it. Don’t these guys ever read any SF?

    1. Well, propulsive descent is a brute force solution, so it would be nice to find something more advanced eventually. However, with ISRU and / or RLVs and considering we already have SEP it is not at all urgent. In fact using lots of propellant is an interesting possibility if you want to fund commercial RLVs. We could start doing that essentially now. Let’s land something heavy on Olympus Mons and start returning scientifically valuable data ASAP.

    2. Also, don’t forget that R&D guys have an obvious conflict of interests that makes them favour getting funding for R&D straight from Uncle Sam instead of using brute force and leaving R&D to market forces.

  4. I Am Not A Chemist, but what resource on Phobos could you make propellants from? The oxidizer sounds doable, but what for fuel?

    1. Spectroscopy indicates that it’s a probably a captured carbonaceous chondritic asteroid, which means that a high percentage of it (~20%) is water. It also has a lot of carbon if you want to make methane or some other hydrocarbon.

  5. There’s the old joke that according to Lawrence Livermore Labs, the right way to land on another body is to aerobrake. If it doesn’t have enough atmosphere for that, nuke it until it does, then aerobrake. Problem solved.

  6. Paul, it’s pretty likely that Phobos and Deimos have carbonaceous chondrite composition, and so should have up to 20% volatiles. This isn’t proven, though, and Phobos-Grunt was, alas, supposed to return a sample that would have let us know for sure.

  8. It would take an ascent stage of about 1000 kg to get an astronaut back into orbit from the surface of Mars, which sounds about like the weight limit they’re talking about for a lander. At a 0.75G acceleration, max Q occurs about 90 seconds after liftoff, with a dynamic pressure equivalent to going 75 mph on a motorcycle. The astronaut doesn’t even need a capsule, just a seat.

    A powered descent would be similar, with a similar mass requirement, so I don’t think NASA’s complaint is a show stopper. If we can land lots of small payloads accurately, it accomplishes the same thing as landing one big payload. Additionally, you gain redundancy, versatility, and can incrementally test.

    1. At a 0.75G acceleration, max Q occurs about 90 seconds after liftoff, with a dynamic pressure equivalent to going 75 mph on a motorcycle. The astronaut doesn’t even need a capsule, just a seat.

      That would be one crazy amusement park ride.

    2. If we can land lots of small payloads accurately, it accomplishes the same thing as landing one big payload.

      That’s the trade-off, isn’t it? Landing everything the crew will need at one time seems safer because (assuming the landing is successful), everything is guaranteed to be in the same place. With multiple landings, there’s the chance that critical supplies will be too far away to retrieve. Some form of the old Mars Internet idea would be helpful because it would allow you to have a communications and navigation infrastructure in place, making multiple landings more accurate.

      Multiple landings increases the likelihood that at least one will fail but proper distribution of your payloads reduces the consequences of failure. You could likely greatly reduce you landing mass considerably if you sent an in-situ propellant production facility ahead by a couple years and let it make the propellant for the return trip. I like your idea of small landers and return vehicles, especially since they could be made reusable for multiple trips.

      It seems the linked article assumed a manned mission would do a direct entry to Mars like we do with unmanned landers (and Apollo did on return from the moon). Personally, I’d prefer to leave the vehicle for the return trip in Mars orbit to minimize weight brought down to the surface. You could enter orbit around Mars first before letting the crew land or you could have the crew landers separate and do a direct entry while the unmanned return vehicle enters orbit around the planet.

  11. Simplest solution of all – why bother going down the gravity well? Nothing will be produced on Mars and sold for a profit on Earth, short of 50 years of space infrastructure development and resource exploitation. Free and inexhaustible, energy and resources just the other side of GEO. Mars is a dead end, for now.

  13. NASA currently estimates it will require bringing anywhere from 40 to 80 tons of stuff to the surface of Mars to keep humans alive for even a day.

    Bald face lying. It’s not just for politicians anymore.

    SpaceX is planning to send about ten tons with each Dragon lander; each should keep a person alive for more than two years assuming no ISRU.

    While not a simple mission, it is both doable and affordable to put a dozen ISRU researchers for the first mission with supplies for over two years waiting for them on the surface. The landers get sent to mars orbit fully fueled before the two gas and go spaceships arrive with a dozen new martian. All for less than the SLS or the Webb scope.

    No guts no glory.

    These guys would be saying it’s impossible to land on the moon if we hadn’t already done it… with vacuum tubes.

    Include some nuclear engineers and some tiny lasers so they can get lots of heat from local thorium.

    1. Nonsense on its face. The Apollo 17 LM weighed nearly 38,000 pounds at launch, and about 17,000 pounds after expending its descent stage propellants. And it kept a crew of 2 alive on the moon for a little over 4 days.

  14. There is an even easier solution.

    “We’re not going to sent 80 spacecraft to Mars,” said engineer Bobby Braun

    See the problem ? This is an engineer speaking. An economist would say, thats precisely we would want to do, because cranking out 80 identical 1-ton landers could easily work out to be much cheaper than megaengineering unobtainium projects.

  15. Given the challenges of landing on Mars it makes you appreciate the skills of the Apollo era engineers who designed the Viking landers 🙂

    1. This is going off topic here but .. have you seen Fanwing ? Seems like a promising way to accomplish the same without rockets.

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