“I think Buzz is saying put a human crew in orbit around Mars, and then use robotic explorers with a minimal delay.”

You may be right. That makes perfect sense now that you point it out.

Okay, but the whole point of the article is the landing issue. The article was about why landing is not as simple as people think, and outlining the challenges of why that is so. Yet you came in and blanket dismissed the landing challenges in order to talk about return. It sounded like you weren’t paying attention, because the article was not about all the challenges or even the most severe challenge, just the unexpected challenges on the one aspect, landing.

> Assuming the landing issues can be solved, we still have a retrieval problem.

True, solving the landing problem does not address the relaunch problem. But if you can blindly dismiss the landing problem as “solvable”, then why isn’t the relaunch problem equally as easily dismissed as “solvable”? Both are technical engineering challenges that will require much effort.

> It would be no good sending Astronauts to Mars, if having successfully landed them on the planet, we can’t get them back.

While it would be a difficult political sell, several people have commented (here and elsewhere) that a one-way trip would not be a deterrent. As long as we’re talking sending supplies and equipment to keep them alive indefinitely (barring natural life span, illness, injury, etc), they’d be the first colonists.

Mark Martin said:
> Buzz Parsec: “Wouldn’t robot explorers be much more flexible and useful and capable if the speed-of-light delay was a fraction of a second instead of 20 minutes?”

Yes. This is an argument of the form “if p, then q”. But p is not true, so q also is not true.

I think Buzz is saying put a human crew in orbit around Mars, and then use robotic explorers with a minimal delay.

MichaelS said:
> I am curious about several statements they made in the article. For one, they say that an airbag landing subjects the occupants to 10-20 g’s of force. What if you slow the thing down with something before you hit, and just use the airbags to cover the last bit of deceleration?

That’s what they already do. The MERs used a heat shield to dump orbital velocity, a parachute to slow in atmosphere, retrorockets to slow the payload, and then dropped in airbags to the ground. The people who have been doing it (i.e. Rob Manning) say that the solution does not scale up.

> Second, since when could humans not survive 10-20 g’s? … If you place the crew members face-up (like in the shuttle), on springy seats with good cushioning, I don’t see any reason why they wouldn’t easily survive 20 g’s of non-sustained acceleration.

I’d like to see some numbers on the effects of a 10 – 20 g shock load on the human body. But you seem to think the springy seats and good cushioning would help. Well, if they help, they help by reducing the shock load. But I think that is already being included in the estimate to get the shock down to 10-20 g’s.

> Next, why is Mach 2 the magical number for parachutes? Top fuel drag cars use parachutes in Earth atmosphere at around Mach 0.45. 4 times the speed squared is 16 times more force, but divide by 100 because of the low-density atmosphere. So Mach 2 should produce about 16% of the force that drag racing chutes are designed to handle. 100 / 16% is 6.25, and the square root is 2.5, so you should be able to go Mach 5 and deploy drag chutes without a problem.

Mach 1 is not an absolute velocity, but rather is relative to the air density. Mach 1 on the ground is a different velocity than Mach 1 at 30,000 ft. Also, supersonic speeds produce shock that is not a part of subsonic velocities. I think the difference in the dynamics makes extrapolating from half Mach to twice Mach a bit improper.

> Using multi-stage chutes, you could start with lots of little chutes to bleed off large amounts of speed, then release those and deploy a couple of huge chutes for lower speeds.

Except there isn’t enough atmosphere. No, not density, but altitude. You have competing needs between surface area to create drag, time to inflate the parachute, and velocity both before and after deployment. The low density of the atmosphere means the surface area must be significantly greater to get reasonable drag, but the more surface area means more inflation time, and even afterwards the velocity is higher than on Earth. The combination of parachute size vs. terminal velocity means either a chute the size of the Rose Bowl (or the equivalent in lots of chutes) to get Earth-like velocities, or a reasonable sized chute and a velocity too high to withstand the impact. Combining smaller chutes doesn’t necessarily help, as you have to deploy and keep them from tangling.

> Finally, a horribly inefficient, but seemingly plausible method for fuel delivery: since we need fuel to take off, then fuel to land using rockets, send a couple extra ships carrying extra fuel. On Mars orbit, dock the ships together to re-fuel the primary before landing. This would lower the weight of the landing craft by only requiring capacity for as much fuel as needed to take off or land (whichever is higher), not the amount needed to take off and land plus the amount of extra to accomodate this during takeoff. By lowering the vehicle weight, you’d make slowing down easier.

This is already being considered, as well as manufacturing fuel on the ground.

Second: Why Mars now? We still don’t have space colonies, which as far as being livable are much easier to create than terraforming MArs and a LOT easier to get to,,,

I expect The Flaming Bush was just trying to leave the next president a political headache to deal with. In other words, no matter what that Pres. does,(continue the program or redirect those funds) he’s going to receive flak. It’s a no-win political situation. Good for Republicans, bad for Democrats. Just what any incompetant politico would want to leave his successor, to deflect attention from the Bush Fiasco,,,

Space Colonies now, dang it!

GAry 7

“Wouldn’t robot explorers be much more flexible and useful and capable if the speed-of-light delay was a fraction of a second instead of 20 minutes?”

Yes. This is an argument of the form “if p, then q”. But p is not true, so q also is not true.

It’s not strictly true that *no* technology exists for zero-g fuel transfers. After all, any restartable rocket in space effectively uses some system of pumping liquids in zero-g. That system is typically compressed inert gas, such as helium or nitrogen, to push the propellants through their conduits. This of course is only used for a brief time, just long enough to start the engine, at which the acceleration feeds the propellants.

Nevertheless, it is a system in principle. On STS-41G there was an experiment with orbital refueling in which nitrogen pressed a rocket fuel from one reservoir to another, and it was [considered to be] successful.

Another approach to consider is swapping propellant tanks. Jettison the empty one and replace it with the waiting replacement. This too will have its engineering challenges, but I think it is a plausible enough system to warrant study.

That fuel has to get down to the surface,
before it can be used to launch a ship back into space.

Whether the Astronaut’s landing craft carries the fuel or
even if there is a fuel drop in advance,
the fuel still has to get there.

Most fuels in current use tend to be volatile.
Getting the fuel to the surface of Mars,
so it can be used to re-launch the Astronauts back into space,
is going to be really, really tricky.
Kind of like landing a rather large unstable bomb on the planets surface.

Can we make rocket fuel from the resources available on Mars?
Big unknown.

Getting the Astronauts back is going to be very hard,
even if we can get them to the surface to start with.

Anyone got a stargate?

Folcrom.

If we are going to do this (and I think we should) we need to find innovative uses of reliable, existing technology wherever possible.

I read the article. I ignored the landing issues, as I consider all the problems of landing as “solvable”. It will eventually be attempted and achieved. Don’t make assumptions about what people have or have not read.

What concerns me more, is not the landing, but getting the Astronauts back.

Assuming the landing issues can be solved, we still have a retrieval problem.

It would be no good sending Astronauts to Mars, if having successfully landed them on the planet, we can’t get them back.

Both landing and retrieval have to be solved. Personally, I believe retrieval will be the harder of the two.

It might be better to set up bases on the Martian moons in orbit, until such problems as landing and retrieval can be solved. Something mentioned in an earlier blog as being “cool”. To me, the idea of using Martian moons as a base, would be not only cool, but also essential.

Build up infrastructure in Mars orbit first. Use Mars orbit to send down lots more robotic missions. At some point in the future, when all problems with landing and retrieval are solved, then and only then consider human landings on Mars.

Folcrom.

And that is something that we are going to have to accept if we are to become a true spacefaring species. If we’re doing enough missions, then people are going to die on a regular basis, in a multitude of horrible ways. And it is going to become so commonplace that it barely merits a mention in the affected person’s hometown newspaper, next to the traffic accident reports.

Not neccessarily; the orbital mechanics don’t really like that approach. Zubrin’s book goes through the details, but I don’t have it with me so I’m going by memory. If you go for a “get there and back again” mission, you need to spend around 9 months each way, and swing by Venus for a speed boost. You then have a few days in orbit, before leaving for the return trip. If you’re going for a long-term mission, you take the direct 6-month route (no Venus fly-by), but you need to spend a year at Mars before your return window opens up. Different mission, different radiation requirements, different supply requirements–I don’t know that the fast mission would be a very good test bed for the slow one.

Next, why is Mach 2 the magical number for parachutes? Top fuel drag cars use parachutes in Earth atmosphere at around Mach 0.45. 4 times the speed squared is 16 times more force, but divide by 100 because of the low-density atmosphere. So Mach 2 should produce about 16% of the force that drag racing chutes are designed to handle. 100 / 16% is 6.25, and the square root is 2.5, so you should be able to go Mach 5 and deploy drag chutes without a problem. Using multi-stage chutes, you could start with lots of little chutes to bleed off large amounts of speed, then release those and deploy a couple of huge chutes for lower speeds.

Finally, a horribly inefficient, but seemingly plausible method for fuel delivery: since we need fuel to take off, then fuel to land using rockets, send a couple extra ships carrying extra fuel. On Mars orbit, dock the ships together to re-fuel the primary before landing. This would lower the weight of the landing craft by only requiring capacity for as much fuel as needed to take off or land (whichever is higher), not the amount needed to take off and land plus the amount of extra to accomodate this during takeoff. By lowering the vehicle weight, you’d make slowing down easier.

The Apollo mission reports are good as well to understand the many many problem sof operating on the moon. This stuff is difficult.

The MERs are 175 kg (~385 lbs) each. You can barely get one person with life support equipment in that package, and airbags aren’t a fun way to land (20 g bump). Anyway, suppose you want to land all your supplies that way. How much supplies? Like your new habitat, food, water, power stations, rovers, etc. The article says 30 metric tons is a low estimate, ~66,000 lbs (rounded down). That means 171 landers all hitting the same square kilometer, and then you have to assemble everything before you can use it. Lots of hiking and hauling and lifting and what not, and no rover to get you around because that’s in pieces, too. No tent to crawl into for a nap, that hasn’t been found and set up yet. Need a snack? How do you get it into your suit? No habitat/airlock to open the helmet.

You want to be able to land large items as single items.

Paul said:
> I don’t know that it’s landing on Mars that’s the problem. NASA and the Russian space agency have been landing on Earth for years. It’s landing on Mars and retaining an ability to leave again that’s the problem.

No, it’s landing on Mars and being able to walk away from the landing that is the problem. You could try lithobraking, but creating craters isn’t conducive to continuing your mission.

Folcrom said:
>Landing on Mars shouldn’t be a problem.
We land Astrononauts back on Earth after sending them into space afterall.

As slang said, did you read the article? There is extensive discussion about how airbags won’t work, retrothrusters won’t work, heat shields won’t work, lifting bodies won’t work, parachutes won’t work, and combinations of those systems won’t work. As was stated, there’s just enough atmosphere to make thrusters dangerous but not enough atmosphere for heat shields, parachutes, and lifting bodies to work.

You are correct about one thing – assuming the landing problem is solved, that does not address the additional challenges of the relaunch problem, which is also significantly more difficult than Apollo.

The dinosaurs didn’t have a space program either.
(A paraphrase of something Larry Niven pointed out.)

I assume we would have to use some in-space thursters and then aerobraking with a large (probably folding) heat shield. At that point, getting the primates onto the planet is the tough part. My first thought would be to reduce the mass by breaking it up into manageable pieces, landing each of your primates individually so you could use existing methodology with the lower mass – some kind of personal lander-pod each astronaut would pilot to planetfall. Each pod could use a skycrane, parachute, thrusters, or whatever will work for the small mass. Trouble is, then you’re stuck where you land and need to rendezvous with your habitat. But once everybody is landed, you could remotely pilot the original ship down without having to worry about the humans, so you could use it to supply anybody who landed off-course in an emergency.