Living on Mars

Chipper Q
Chipper Q
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RE: But Chipper, what about

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But Chipper, what about the dynamics of a manned mission to Mars? I read that Von Braun calculated in 370000 metric tons the payload to be lifted into Earth orbit in order to assemble a Mars vehicle capable of going there and getting back with its crew. Has anybody redone this calculation?


Good point, Tullio. Perhaps not all that mass needs to get there at once; maybe in lots of smaller stages, but regarding the calculations, please have a look at the lecture, "Shane Ross: The Interplanetary Transport Network," that you can find a link to on this page. Fascinating ways to get around the solar system effeciently!

Mike, when you mentioned pizza and beer earlier, I saw a niche for providing a service at L1; thanks! :)

tullio
tullio
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RE: Good point, Tullio.

Message 26493 in response to message 26492

Quote:

Good point, Tullio. Perhaps not all that mass needs to get there at once; maybe in lots of smaller stages, but regarding the calculations, please have a look at the lecture, "Shane Ross: The Interplanetary Transport Network," that you can find a link to on this page. Fascinating ways to get around the solar system effeciently!


Thanks Chipper, I enjoyed the lecture. I had a brief introduction to the Lagrange points many years ago, when I translated "The high frontier. Colonies in space" by Gerald K.O'Neill. It is good to know that they can be used to travel efficiently. By the way, I think the Genesis spacecraft had a hard landing due to a non functioning parachute, but its scientific results were saved. Cheers.
Tullio

ghstwolf
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RE: But Chipper, what

Message 26494 in response to message 26490

Quote:
But Chipper, what about the dynamics of a manned mission to Mars? I read that Von Braun calculated in 370000 metric tons the payload to be lifted into Earth orbit in order to assemble a Mars vehicle capable of going there and getting back with its crew. Has anybody redone this calculation?

I'm sure the calculations have been done many times since. What little references to this plan I've found, suggest this was a far bigger project than we're really discussing. His plan involves something like a dozen ships, which makes sense of the weight (for scale, 370,000 metric tons is roughly 4 aircraft carriers). It also seems to be formulated just after WWII (1946-1948 published around 1952). Even keeping the scale, we could easily lower that weight.

To the rest of the post, are you actually suggesting that the Mars Reconnaissance Orbiter is using the only profile (or as you used Dynamic) that can be used? Sorry I don't buy that, but even if that was the case, as long as the exposure issue is well addressed (specificly for the in-flight portion), adding 6 months in orbit is not a deal breaker. That would still leave 12 months on the surface, assuming the same mission length cap of 2 1/2 years.


tullio
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RE: I'm sure the

Message 26495 in response to message 26494

Quote:
I'm sure the calculations have been done many times since. What little references to this plan I've found, suggest this was a far bigger project than we're really discussing. His plan involves something like a dozen ships, which makes sense of the weight (for scale, 370,000 metric tons is roughly 4 aircraft carriers). It also seems to be formulated just after WWII (1946-1948 published around 1952). Even keeping the scale, we could easily lower that weight.


One wonders why such as hard-headed person as Von Braun would send so many ships to Mars. Redundancy? It makes me think of Columbus'caravels. One of three came back. Will it be the same from Mars?
Tullio

Mike Hewson
Mike Hewson
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RE: One wonders why such as

Message 26496 in response to message 26495

Quote:
One wonders why such as hard-headed person as Von Braun would send so many ships to Mars. Redundancy? It makes me think of Columbus'caravels. One of three came back. Will it be the same from Mars?
Tullio


If he estimated just post WWII he'll be using fuel characteristics and engine designs and efficiencies known at that time. Both have improved to the extent that the 'specific impulse' or thrust per weight of fuel has significantly improved. Bear in mind that any fuel required from a given point onwards in a mission has to be carried to that position by the burning of other fuel. Thus a large fraction of liftoff weight is in fact fuel simply present to be used to lift other fuel. For instance the space shuttle uses half of it's pre-launch fuel just to get to the sound barrier!! The calculations have an exponential character so that a small gain in specific impulse has a far greater effect on lowering fuel requirements or increasing payload ( essentially the non fuel weight ) than you would expect from simple proportion. I don't really know the exact magnitudes, but it would not be unreasonable to expect only about two aircraft carriers worth!
Also the vast bulk of the fuel is used to get out of the local gravity well. If the mission payload could be mated to fueled components already in Earth orbit then that is a real win for Mars transfer. Now of course you have to get those fueled components to Earth orbit presumably by stepwise or incremental addition to stores over many launches rather than one big heave upwards. So you can divide total fuel costs into installments. In near Earth orbit we have significant radiation protection from the magnetic field.
For the transfer between planets it all depends on timing, timing and timing.
- The timing with respect to relative positions of Earth and Mars at transfer is the dominant one. You aim your craft toward a position where Mars will be when you get there too.
- The second timing is how long you want to take to get there. A shorter time requires a higher velocity, and thus higher fuel costs to speed up at the start, and slowing down at the other end. You can take longer and use less fuel by going slower. With living people on board a shorter trip uses less consumables, a longer trip more. Clearly anything that is already on Mars that can be used doesn't have to be taken and is a bonus. Radiation exposure time and associated mass/fuel cost of desired protection elements affects fuel etc calculations. Aerobraking or whatever non-fuel methods of slowing at destination clearly are good also.
- The last timing is how long to stay and thus when to come back home. Assuming we have to take everything we need to use when we stay there, obviously even a slightly longer stay can dramatically up the fuel costs ( fuel lifting fuel etc ). Alas the planets won't pause in their orbits, so you come home partly by waiting for the Solar System merry-go-round to evolve and then you leave Mars. But the longer you stay the more you need to take to stay alive.......etc
Clearly all these factors interact in a complex manner. The Apollo missions were in fact planned backwards by first deciding exactly what was going to be bobbing up and down in the ocean at final touchdown. You then reverse time a few minutes to determine what then needs to be present at say 'chute opening time higher up in order to get to touchdown. Go back some more and elaborate on what is needed prior to say re-entry in order to get to the 'chute opening moment. Iterate right back to the pad and you now have a launch specification.
That assumes you are going to use the 'one big stack' method of delivery. Why not build up a number of assets on Mars prior to the final delivery of humans? Not all the humans need go at once either. This will take longer, and probably be more expensive overall. But it has the advantage of more options during the unfolding of the program. You learn and get better as you go. There are fewer critical paths or timelines through your overall program.
For me the mission specs must include beer and pizza rations even if it turns out to be the last thing I ate or drank!! :-)
Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

tullio
tullio
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RE: That assumes you are

Message 26497 in response to message 26496

Quote:
That assumes you are going to use the 'one big stack' method of delivery. Why not build up a number of assets on Mars prior to the final delivery of humans? Not all the humans need go at once either. This will take longer, and probably be more expensive overall. But it has the advantage of more options during the unfolding of the program. You learn and get better as you go. There are fewer critical paths or timelines through your overall program.
For me the mission specs must include beer and pizza rations even if it turns out to be the last thing I ate or drank!! :-)
Cheers, Mike.


This reminds me of a book I read in my youth. It was "Rockets, missiles and space travel" by Willy Ley, a member of the original Von Braun group, with the beautiful paintings by Chesley Bonestell. Unfortunately I lost in the travesties of married life, along with many youth dreams. But I still remember the encouragement given by Columbus to his doubting crews: "Adelante las naves!".
Tullio

hockeyguy
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Maybe that space elevator can

Message 26498 in response to message 26497

Maybe that space elevator can reduce the costs of a mission to mars. google it theres lots of results.

ghstwolf
ghstwolf
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RE: Maybe that space

Message 26499 in response to message 26498

Quote:
Maybe that space elevator can reduce the costs of a mission to mars. google it theres lots of results.

If the project was 100 tons, and assuming we were stuck using the shuttle (with a cost of $25000/lb), that would be 5 billion dollars. I don't see anyway to cut this mission's weight down to that and keep it meaningful. Using that same cost meteric, the breakeven point using a $200/lb cost for the elevator, is about 101 tons.

And that assumes we never use it again (that we charge the whole expense of construction to the Mars base project). If we are serious about a moon base or mining asteroids, those too can benefit from drasticly reduced costs. It also dispurses the costs.

So in a single word, Yes.


tullio
tullio
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RE: If the project was 100

Message 26500 in response to message 26499

Quote:
If the project was 100 tons, and assuming we were stuck using the shuttle (with a cost of $25000/lb), that would be 5 billion dollars. I don't see anyway to cut this mission's weight down to that and keep it meaningful. Using that same cost meteric, the breakeven point using a $200/lb cost for the elevator, is about 101 tons.


NASA seems to think of an antimatter-powered spacecraft. Here is an excerpt taken from www.nasa.gov:
A rough estimate to produce the 10 milligrams of positrons needed for a human Mars mission is about 250 million dollars using technology that is currently under development," said Smith. This cost might seem high, but it has to be considered against the extra cost to launch a heavier chemical rocket (current launch costs are about $10,000 per pound) or the cost to fuel and make safe a nuclear reactor. "Based on the experience with nuclear technology, it seems reasonable to expect positron production cost to go down with more research," added Smith.
Tullio

ghstwolf
ghstwolf
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RE: NASA seems to think of

Message 26501 in response to message 26500

Quote:
NASA seems to think of an antimatter-powered spacecraft. Here is an excerpt taken from www.nasa.gov:
A rough estimate to produce the 10 milligrams of positrons needed for a human Mars mission is about 250 million dollars using technology that is currently under development," said Smith. This cost might seem high, but it has to be considered against the extra cost to launch a heavier chemical rocket (current launch costs are about $10,000 per pound) or the cost to fuel and make safe a nuclear reactor. "Based on the experience with nuclear technology, it seems reasonable to expect positron production cost to go down with more research," added Smith.
Tullio

Even if we don't add fuel, the mission will still require more than 100 tons. Hell the ISS weights 50 tons, and doesn't need the bulky radiation sheilding or a full 2 1/2 years worth of supplies. That with the stipulation that this is at least a 6-10 man crew and a mission that is more than go there and come home alive. If it is a mission to prep a permanent base, it might take more than 100 tons of equipment for the mission (not including the vehicle to get there and back).

Launch costs range from $10K/lb for the smallest (and least versitile) rockets to $14K/lb for some of the bigger ones. The current shuttle is not a great choice, but for many of the sections the shuttle is the only option (at its $25K/lb), maybe the next generation platform is better.


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