“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.