Elon Musk says he will put millions of people on Mars.

[HopDavid]

Tens of dollars per pound is exceedingly optimistic even if Musk does achieve reusable rockets to LEO.
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The energy used to get to Sydney from the States is greater than that needed to get to orbit. And most anyone can fly to Sydney for less than $10 per pound. Get the flight rate up and the same will apply to orbit.

10 hour 747 flight uses ~ 150,000 litres of fuel. And carries ~100,000kg load That is an FMR of ~ 1:1

Realistic FMR for LEO is 16:1.

Maybe Sydney/US needs two 10 hour flights? But even so it looks like LEO is 10X more expensive (in fuel weight) than travel to Sydney?

Add to this that rocket fuel is more expensive than jet fuel.

of course, fuel cost is still insignificant compared with other stuff.

A 16:1 FMR does boost fuel costs. But this is indeed insignificant compared to the other problems it causes.

Given FMR 16:1 vs 1:1, the 747 can have a much more robust structure. The tinier the mass fraction the more tenuous the structure. Whittle down the mass fraction and the craft becomes more fragile.

The SpaceX Grasshopper video seems to indicate the first and second stages will use propellant to shed re-entry velocity in addition to the usual aerobraking. This would make an even more difficult mass fraction.

A two stage Falcon plus a Dragon are three components that must be recovered and re-assembled. The maintenance costs of a 747 would be higher if it split into three parts each trip.

Unlike the Falcon stages and Dragon, a 747 doesn't endure a high speed re-entry. Given a 16:1 FMR (or greater, depending on how much propellant is used to shed re-entry velocity), making a craft robust enough to endure re-entry is even more difficult.

[HopDavid]

Just how quickly would boil off of propellant O2 & H2 occur?

Store it as solid water and I'd say "not quickly at all"!

How many joules does it take to crack a tonne of water into H2 and O2?

What are the watts per kilogram of plausible orbital power sources?

Given a LEO power source of plausible mass, how long would it take to crack a tonne of water?

Do these numbers and you may find storing orbital propellant in the form of water isn't the panacea some believe it is.

[kunkmiester]

Light lag to the Moon: 3 seconds
Light lag to Mars: ten to fifty minutes.

Another thing you need for telerobots is lots of bandwidth. Since signal strength falls with inverse square of distance, high lunar bandwidth is less challenging than high band width to Mars telerobots.

We have CNC machines that can be left over a weekend without trouble, and the sensors to work outdoors aren't that big of a deal anymore, the construction industry has been working on that.

You wouldn't do the whole base from earth anyway--you'd do your basic earth moving with mostly autonomous robots, and get machines sent from earth put in place and tunnels sealed. As your first mission approaches Mars, and the time lag drops, you have them start supervisign the robots in more detailed tasks, and only the final touches would remain for humans to do.

Mars launch windows are also for optimum use of propellant and time. With cheaper propellant from cheaper transport and/or lunar origin, more energy is available on your budget, and if I'm not worried about it taking even longer for my robots to get there, I get even more.

[KitemanSA]

The energy used to get to Sydney from the States is greater than that needed to get to orbit. And most anyone can fly to Sydney for less than $10 per pound. Get the flight rate up and the same will apply to orbit.

10 hour 747 flight uses ~ 150,000 litres of fuel. And carries ~100,000kg load That is an FMR of ~ 1:1

Realistic FMR for LEO is 16:1.

Maybe Sydney/US needs two 10 hour flights? But even so it looks like LEO is 10X more expensive (in fuel weight) than travel to Sydney?

I said energy, not fuel. Get the rate up and more energy efficient ways will be found (or maybe it will be the reverse).

The ENERGY cost / kilogram is ~$1. The rest of the $21 should cover the operational cost.

[KitemanSA]

Just how quickly would boil off of propellant O2 & H2 occur?

Store it as solid water and I'd say "not quickly at all"!

How many joules does it take to crack a tonne of water into H2 and O2?

What are the watts per kilogram of plausible orbital power sources?

Given a LEO power source of plausible mass, how long would it take to crack a tonne of water?

Do these numbers and you may find storing orbital propellant in the form of water isn't the panacea some believe it is.

Try figuring the cost/rate via THERMAL cracking using a light weight mirror in VERY strong/steady sunlight. The values aren't so bad after all.

Hey, maybe the staging area could be L4 or L5, then sunlight is there 24/363:23+/2.

[HopDavid]

We have CNC machines that can be left over a weekend

I thought we were talking about time between launch windows. Try years, not a weekend.

without trouble,

Manufacturing on factory floors is a very controlled environment and the machines do predictable repetitive, tasks.

Civil engineering in a wilderness is a completely different matter. The unexpected can and will happen.

You wouldn't do the whole base from earth anyway--you'd do your basic earth moving with mostly autonomous robots, and get machines sent from earth put in place and tunnels sealed.

Autonomous robots that dig and seal tunnels? This sort of A.I. is still far beyond the state of the art.

Mars launch windows are also for optimum use of propellant and time. With cheaper propellant from cheaper transport and/or lunar origin,

I agree propellant from lunar origin could be a game changer.

But I entered the conversation when someone said Mars is a better near term goal than the moon.

If the moon is skipped for Mars, lunar propellant wouldn't be avaiable.

more energy is available on your budget, and if I'm not worried about it taking even longer for my robots to get there, I get even more.

Hohmann routes are the lowest delta V routes I know of. Taking a slower route to Mars will not save delta V.

As for time not being an issue, that's just wishful thinking.

If the program is government funded, a long term project is difficult to sustain through many election cycles.

If the program is privately funded, a long term project is difficult to sustain past an investor's working lifetime.

[HopDavid]

Try figuring the cost/rate via THERMAL cracking using a light weight mirror in VERY strong/steady sunlight. The values aren't so bad after all.

How would I know if the values aren't so bad? You've provided no numbers and no cites.

[HopDavid]

I said energy, not fuel. Get the rate up and more energy efficient ways will be found (or maybe it will be the reverse).

Merlin engines are basically old school kerosene rocket engines. Musk hasn't developed any oogie boogie science that enables us to circumvent the rocket equation.

[williatw]

But I entered the conversation when someone said Mars is a better near term goal than the moon.
If the moon is skipped for Mars, lunar propellant wouldn't be avaiable.
If the program is government funded, a long term project is difficult to sustain through many election cycles.
If the program is privately funded, a long term project is difficult to sustain past an investor's working lifetime.

Lets see now...I started the thread based on Musk's statement in the link on the 1st page about his desire to see millions on Mars. I said nothing about "skipping the moon". Far as I am concerned you can do both concurrently. And when/if lunar propellant becomes available sure it will be used by those going to Mars as well. I saw it is privately funded, as for how the investors would get their money back plus profit, see earlier post: viewtopic.php?t=3383
The one thing Mars would have to trade on would be its location beyond earth laws/regs. It would not take years and years after the colony was started to set up the bank of Mars. Obviously this would probably only work if the facility was private in nature. A NASA/US gov base on Mars the moon or anywhere else would by definition subject to US laws/regs/taxes. Reusable rockets and Bigelow modules bought off the shelf would suggest startup cost for a Mars colony of low billions, as opposed to the 100's if not 1000's of billions NASA says it would cost.

[williatw]

A launch window is determined by the capabilities of the vehicle compared to the optimal flight path. The more extra performance the vehicle is capable of, the "wider" the launch window can be and still successfully reach the intended target.
I see no reason why the plan of launching numerous rockets into earth orbit, and then firing them all off into a Mars Transfer Orbit during the launch window wouldn't work. Complex, but getting the rockets working in the first place is complex ...

To anyone who can answer a related question. Suppose the mars colony takes off, & you can re-fuel at the mars end as well as the earth end from propellant depots. Further suppose you have NTR like the TRITON. Launch windows from earth to mars occur every 2.14yrs(781days). With chemical round trip approx(180days out +18mts[for earth return window]+180days back=907days). You return to earth 127 days to late back for our NTR to catch the next window back to mars. My Question: Could the NTR save enough time on the round trip time to get back prior to the next window from earth to mars opening up? Lets further add another 60 days to get it ready before window opens up. So I am asking whether (127+60=187days) could be shaved off of the chemical roundtrip time (907-187=720day round trip time)? Anyone know if that would be doable with a relatively near term NTR like the Triton?

[KitemanSA]

Try figuring the cost/rate via THERMAL cracking using a light weight mirror in VERY strong/steady sunlight. The values aren't so bad after all.

How would I know if the values aren't so bad? You've provided no numbers and no cites.

That means YOU try figuring. Until you do, you won't accept others statements. Try it and see.

[Skipjack]

Here is a study by ULA (Lockheed/Boeing) on how to do a lunar architecture entirely using commercial LVs and propellant depots.
http://www.ulalaunch.com/site/docs/publ ... re2009.pdf

There is more to this. Dana Rohrbacher recently brought an internal study conducted by NASA to the light. This study was held back to no endanger funding for the SLS (fuel depots would be cheaper and sooner).
http://images.spaceref.com/news/2011/21jul2011.pdf
http://satellite.tmcnet.com/topics/sate ... y-lift.htm

If you dont want to use cryogenics, one could also use Hydrogenperoxide which is split up by a cathalyst. The Isp is slightly lower than for H2 LOX, but it is much easier to handle.
If the price to LEO is low enough, it does not matter whether you loose a bit of Isp. Of course if you were to use an electric propulsion or sorts, things would be different yet again.
Hypergolics could also be an interesting alternative for in space propulsion. We have lots of experience with storing those already.

[GIThruster]

Woah, is there evidence that this report was held back specifically so it could not be used to sell SLS? I was under the impression that NASA doesn't much want SLS. OBama didn't want it. It's Senator Nelson who wants it, and everyone else who doesn't know what's going on.

One would think the press would have a field day with stuff like this and it's not on any of the network news. One would think at least Fox would pick up the story if for no other reason than to call OBama a wimp.

[KitemanSA]

I said energy, not fuel. Get the rate up and more energy efficient ways will be found (or maybe it will be the reverse).

Merlin engines are basically old school kerosene rocket engines. Musk hasn't developed any oogie boogie science that enables us to circumvent the rocket equation.

True, but Tethers Unlimited has.

Before we get into TOO much of an argument, I have to accede to your original statement about $10/pound being questionable IF one limits oneself to ROCKETS only. I never do. The best launch method short of a space elevator (in my mind) is a combination Kite Launch, Rocket, Rotovator system where very stage is optimized: ~2km/s on each end by tether and ~3.5 in the middle by rocket. As materials improve, the two ends take up more and more of the total delta V and the rocket gets minimized.

Should be interesting what DARPA's ALASA project comes up with. The originator of the "Black Horse" project is running it.

[Roger]

This months SKy & Telescope has short blurb about Mars, 4 million years ago Mars was 64 degrees Fahrenheit.

IIRC AS it is now, in the summer, along the equator Mars can approach 32 F at mid day.