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Moon Is Stepping Stone, Not Alternative to Mars, NASA Chief Says

scientificamerican.com

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Re: Moon Is Stepping Stone, Not Alternative to Mars, NASA Chief Says

#51

Post by stcredzero »

aaron_m04 wrote: post #48
stcredzero wrote: post #13

Earlier quoted context omitted.

"Braking," not breaking. Some of the most difficult challenges have to do with maintaining life support long term. The Moon isn't a bad place for that. If we're able to deal with operations in conditions dealing with vacuum, that experience is still applicable. Also, the human side of the procedures for preventing lunar dust and grit from entering the living space will be important and applicable to Mars. Mars soil i…

> Mars soil isn't as bad, but some of it you don't want in your living space either. It's probably worse, since Martian soil has perchlorates, which are toxic and cause thyroid problems at low concentrations.

Some Martian soil may have hexavalent chromium, which can cause cancer and birth defects at low concentrations.

Re: Moon Is Stepping Stone, Not Alternative to Mars, NASA Chief Says

#52

Post by cuboidGoat »

chr1 wrote: post #42
cuboidGoat wrote: post #19

Earlier quoted context omitted.

By the end of this century I suspect there will be more than a million people living off earth, with the majority in orbitals. In about 200 years or so, I wouldn't be at all surprised if there were more people off earth than on it.

What would be the incentive for living off earth for such a large number of people? I really wish for you to be right, but with population growth slowing down, and possibility of building floating cities or terraforming Sahara, building large orbital stations or going to mars in large numbers may be economically not viable, unless we invent something radically new.

I think there will be two things. One is economics, fetching asteroids could be very big business, and the other is political, space will be viewed as freedom of a sort, given the kind of restrictions that may be in place on Earth by then, with the climate transforming alongside having a lot more people than we do today, even if growth slows down, which is far from certain. We could easily be in the age of what Bruce Sterling refers to as the Khaki Greens, aka, militarised enforcement of ecological protection.

Re: Moon Is Stepping Stone, Not Alternative to Mars, NASA Chief Says

#53

Post by logfromblammo »

Nomentatus wrote: post #45
logfromblammo wrote: post #36

Earlier quoted context omitted.

Transport between bodies in space is measured by kilometers per second as delta-V, not kilometers. Earth LEO 9.3 km/s LEO escape 3.22 km/s escape MTO 0.6 km/s MTO MCO 0.9 km/s MCO LMO 1.4 km/s LMO Mars 4.1 km/s ----- 19.5 Earth LEO 9.3 km/s LEO LLO 4.04 km/s LLO Moon 1.87 km/s ----- 15.2 Moon LLO 1.87 km/s LLO escape 1.40 km/s escape MTO 0.6 km/s MTO MCO 0.9 km/s MCO LMO 1.4 km/s LMO Mars 4.1 km/s ----- 10.3 (Earth -…

Thanks for the numbers. 30% of delta-V but much more than 30% more fuel used (etc) since "compound interest" applies as you're using fuel to ship fuel out of orbit and then much of that fuel again to change your orbit to mars, etc. Similarly, Napoleon came up against the limits of using horses to pack hay for horses invading Russia - compound interest; you can only do so much. PS - that 30% assumes a path that I don'…

Going directly from low orbit to a transfer orbit to the second body will usually save some delta-V over going to escape orbit first and then going to transfer orbit. I didn't have the numbers for low lunar orbit to Mars transfer orbit, so I changed the Earth to Mars path for a fairer comparison.

I didn't forget the Lagrange libration points, but decided not to include them because they were not relevant to the parent comment, and they would still require some mechanism to get propellant mass up to them. They're currently almost empty, and won't be very useful until the Moon itself has launch capacity to get water up there. Again, I was mainly responding to the parent post.

The rocket equation is indeed a bear. As delta-V scales linearly, fuel requirements scale up exponentially. One way to manage it is to use stages. Another is to refuel and assemble vehicles higher up in the gravity well. As it happens, shipping tanks of fuel and propellant up to LEO separately means that missions to Mars starting fully fueled from LEO would require only 0.9 km/s more than missions starting from the lunar surface. Measuring by delta-V, LEO is at about the halfway point for an Earth-Mars mission.

But it's also worth noting that the surface of the Moon is closer to LEO than the surface of the Earth. Shipping fuel and propellant from the Moon to LEO, to rendezvous with and refuel a vehicle coming up from Earth, is even cheaper than shipping up the resupply mass from Earth.

Re: Moon Is Stepping Stone, Not Alternative to Mars, NASA Chief Says

#54

Post by Recurecur »

davedx wrote: post #20

Ugh. Zubrin's 'The Case For Mars' (which on reading, it's obvious SpaceX have based a lot of their strategy on) is categorically against going back to the Moon and using it as a 'stepping stone'. Zubrin's 'Mars Direct' architecture shows quite plainly that it is possible using current technology readiness levels and funding to send a significant scientific mission to Mars directly , without the need for huge orbital…

"We've been to the Moon. We don't need to go back. We need to aim higher."

In an absolute sense, we don't need to do either.

I believe the Moon will support the first permanent population of humans outside Earth.

It remains to be seen if there is any meaningful physiological difference between 1/6 G and 1/3 G. If not, the experience of living on either will be more similar than not. My gut feeling is that there will have to be centrifugal "gravity" available on both the Moon and Mars.

I think the Moon has one thing that Mars does not - it is an attractive spot for heavy industry producing goods shipped to Earth, with abundant solar energy to boot. There is no issue with nuclear power there either.

Re: Moon Is Stepping Stone, Not Alternative to Mars, NASA Chief Says

#55

Post by Kim_Bruning »

zwieback wrote: post #16

Human space flight - what a waste of resources. Send robots for the next 100 years.

Human beings with their millennia of evolution still have quite the edge over any robot ;)

But launching a human is still more expensive than launching several robots.

Right now, launching humans is getting cheaper every year. Space missions are projected to become more profitable over time as people start space mining and later space fabrication.

So I agree with you that launching robots right now has a higher ROI than launching robots.

I think we also agree there's a crossover point.

Where I think we disagree on is when that crossover point might. You say 100 years; I think with current trends it could be under 50 years, maybe under 25 years.

Why do you think it'll take 100 years to hit crossover?

Re: Moon Is Stepping Stone, Not Alternative to Mars, NASA Chief Says

#56

Post by Kim_Bruning »

chr1 wrote: post #42
cuboidGoat wrote: post #19

Earlier quoted context omitted.

By the end of this century I suspect there will be more than a million people living off earth, with the majority in orbitals. In about 200 years or so, I wouldn't be at all surprised if there were more people off earth than on it.

What would be the incentive for living off earth for such a large number of people? I really wish for you to be right, but with population growth slowing down, and possibility of building floating cities or terraforming Sahara, building large orbital stations or going to mars in large numbers may be economically not viable, unless we invent something radically new.

Same incentive as everywhere. They get paid. ;-)

Even the most automated of robotic factories on earth still have a number of humans in an oversight role, where they make themselves quite useful.

The same would be true of any space industry. People would be hired on for a tour in space, and they'd be paid sufficient salary to make it worth their while.

Re: Moon Is Stepping Stone, Not Alternative to Mars, NASA Chief Says

#57

Post by Kim_Bruning »

yazr wrote: post #28

How "self sustaining" will a Mars base ever be ? So let assume they can make oxygen, water, maybe even calories. Great. Self supporting base. But other than that. Everything will have to be trucked in. Pipes, electrical wires, valves, medical supplies, antennas, plastics, etc. Will any of these be manufactured on-site in say 2050 ?!

Mars is a large world. It's not as big as earth, but there's also no oceans, so the exploitable land area is roughly the same. And it is pristine; no one has ever exploited any of it.

With plenty of space and plenty of resources at hand, long term there's no reason a mars colony could not be self sustaining.

Whether that could be true as early as 2050 would depend, of course!

Re: Moon Is Stepping Stone, Not Alternative to Mars, NASA Chief Says

#58

Post by cuboidGoat »

Kim_Bruning wrote: post #56
chr1 wrote: post #42

Earlier quoted context omitted.

What would be the incentive for living off earth for such a large number of people? I really wish for you to be right, but with population growth slowing down, and possibility of building floating cities or terraforming Sahara, building large orbital stations or going to mars in large numbers may be economically not viable, unless we invent something radically new.

Same incentive as everywhere. They get paid. ;-) Even the most automated of robotic factories on earth still have a number of humans in an oversight role, where they make themselves quite useful. The same would be true of any space industry. People would be hired on for a tour in space, and they'd be paid sufficient salary to make it worth their while.

And when you are up there, you will want to stay up if you can, as each dip into the well costs you a ton of money.
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