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

[HopDavid]

"You can't do Mars cuz the launch window is too small"

What I actually said is the moon is a more plausible near term goal. One of the lunar advantages is more frequent launch windows.

I didn't say we can't do Mars.

[Betruger]

Maybe you can actually write what someone was getting at when you quote them.

[HopDavid]

That is what I said in the completion of the sentance.

TDPerk said there's no station keeping needed. You tell GIThruster no one is talking about thrusters. Then you talk about Hall Thrusters to do station keeping.

The disconnect is yours.

Which is why I recommended parking it on L4 or L5.

From LEO to EML5 is 3.9 km/s. From LEO Trans Mars Insertion is 3.6 km/s

EML4 and 5 are 380,000 kilometers from the moon.

In a number of ways EML1 and 2 are better locations for depots.

But this only applies if someone INSISTS on chemical rockets. Not my prefered method, but if you MUST...

This thread is about Musks' kerosene rockets. I happen to agree chemical rockets alone aren't the best solution. Momentum exchange tethers could be a game changers. But these aren't on Musk's radar (so far as I can tell).

However even with tethers, there'd be a use for propellant in LEO.

Oh, and by the way, I suspect it would be easier and cheaper with acceptable losses to just store the fuels cryogenically. But if not, and you must...

The most credible and detailed propellant depot proposals I've seen come from United Launch Alliance.

Realistic Near-Term Propellant Depots
Oddly enough the proposed ACES depots store cryogenic oxygen and hydrogen. These aerospace engineers are obviously unaware that thermal cracking of water with light weight mirrors is so easy. And I also remain unaware it's so easy. You consistently fail to provide numbers or well thought out models.

A Commercially Based Lunar Architecture
A ULA lunar architecture using the proposed ACES propellant depots. On page 17 they note a high throughput mitigates LEO boil off losses. And the frequency of lunar launch windows allows high throughput. Not true for a Mars architecture. They also propose propellant depots at EML2. For several reasons. It's the most benign thermal environment for cryogens. It also is closer to the moon in terms of distance and delta V. It is closer to the earth in terms of delta V. EML1 and EML2 have received much more interest for staging platforms in recent architecture proposals. Much less so than EML4 and EML5. We are no longer in the 70's.

Evolving to a Depot-Based Space Transportation Architecture
If ULA's lunar architecture comes to pass, we would have an excellent platform for deep space missions. This would be especially true if we managed to make use of lunar volatiles. These volatiles are 2.5 km/s from EML2. Besides hydrogen and oxygen for propellant, lunar volatiles could provide water for radiation shielding, water to drink and air to breathe. All this would be mass that doesn't have to be lifted from the bottom of an 11.2 km/s gravity well.

And again, the region of interest is EML2. Not EML4 or 5.

[Aero]

Check this out.

http://www.pureenergysystems.com/news/2 ... _Hydrogen/

The ideal temperature for the SHEC reaction is 850 degrees Celsius, which is what the present array is designed to deliver. However, the process will separate hydrogen at temperatures as low as 400 degrees Celsius.

[GIThruster]

It would be interesting to see an apples for apples comparison of the costs to launch H2 and 02 from the Earth and the Moon. Launching from the Moon you need a large fission reactor to melt, gather and form the <6% water from polar craters into ice pellets and a sling to launch them. Then some way to retrieve them and mirrors to remelt and crack them. Given all that expense, it's probably easier to crack them with another reactor rather than a mirror.

From Earth you need more energy for the launches, but people don't need to live and work in space. That's a pretty huge expense that I'd guess is not justified, especially when you note Musk isn't looking at H2 rockets.

It happens pretty often these schemes get popular support only by ignoring the economics and viability of the scheme and once reality dawns, they die pretty quickly. When they don't die, we all get stuck with stuff like shuttle.

[KitemanSA]

"You can't do Mars cuz the launch window is too small"

What I actually said is the moon is a more plausible near term goal. One of the lunar advantages is more frequent launch windows.

I didn't say we can't do Mars.

• Someone said that Musk wanted to send huge numbers of people to Mars.
  Someone said that the launch window wouldn't support that plan.
  Someone said that the launches into LEO could be staged over the ~two years between optimum Mars transits.
  Someone said that the propellant would undergo too high a loss rate.
  I said, not if it were stored as water ice.
  AND THE RACE WAS OFF!

After that is seems there were three or four folks talking past each other with different sets of assumptions: Electrolytic dissociation is too slow; thermal cracking could be quite fast; thermal dissociation rockets would be good; yada, yada, yada.

Who the heck knows what anyone was talking about.

[HopDavid]

Someone said that Musk wanted to send huge numbers of people to Mars.
Someone said that the launch window wouldn't support that plan.

So far as I know, I'm the only one pointing to biannual Martian launch windows.

That was done in response to Betruger saying Moon and Mars were a toss up.

I was saying the moon a more plausible near term goal, not that Mars isn't doable.

Someone said that the launches into LEO could be staged over the ~two years between optimum Mars transits.
Someone said that the propellant would undergo too high a loss rate.
I said, not if it were stored as water ice.

And so far you still haven't made this case.

After that is seems there were three or four folks talking past each other with different sets of assumptions: Electrolytic dissociation is too slow; thermal cracking could be quite fast;

You still haven't given any numbers for thermal cracking. Nor have you given any numbers for your seran wrap mirror positioned by 1000s of Hall Thrusters.

[HopDavid]

Check this out.

http://www.pureenergysystems.com/news/2 ... _Hydrogen/

The ideal temperature for the SHEC reaction is 850 degrees Celsius, which is what the present array is designed to deliver. However, the process will separate hydrogen at temperatures as low as 400 degrees Celsius.

No numbers.

How many thermal joules?

How much propellant would be made?

What's the mass of the catalytic bed reactor?

The oxygen is sequestered as an oxide compound. Thus the oxygen wouldn't be usable as propellant.

Does this process rely on gravity?

[HopDavid]

It would be interesting to see an apples for apples comparison of the costs to launch H2 and 02 from the Earth and the Moon. Launching from the Moon you need a large fission reactor to melt, gather and form the <6% water

The deposits found by Chandrayaan 1 are evidently richer than 6%. Sheets of ice two meters thick.

But you're correct energy density of power sources is an issue. Lunar propellant schemes need a low mass high watt power source. This is one of the big show stoppers.

So my ears prick up when someone talks about a power source with lots of watts per kilogram. Or ways to crack water with less power.

Sadly in this forum the argument has gone like this: "Why do stooopid ULA engineers talk about cryogenic depots? Me know mirrors and thermal water cracking million times better. Me no have to give cites or numbers. Cuz it so obvious to anyone who not stoooopid. Duh!"

[GIThruster]

So far as I know, I'm the only one pointing to biannual Martian launch windows.

if you watch the vid I posted the link to, Musk believes they can open a window for 6 months out of every 2 years. That's not terrible.

[GIThruster]

The 2 meter ice thickness is just an interpretation and everyone involved wants to find ice. The <6% figure comes from actual analysis of debris thrown up from an impact. Until we have much better data, I would not be making any plans on the expectation of finding 2 meter thick sheets of water ice.

[kunkmiester]

I wouldn't use fission power on the lunar poles. Plenty of sun.

[KitemanSA]

Sadly in this forum the argument has gone like this: "Why do stooopid ULA engineers talk about cryogenic depots? Me know mirrors and thermal water cracking million times better. Me no have to give cites or numbers. Cuz it so obvious to anyone who not stoooopid. Duh!"

You certainly missed the development of the issue.
SOMEONE said depots were a bad idea. They said it would lose too much. "Me" said not if it were stored as ice. "Me never said it was a million times better that cryo-storage, just that is was a solution to the POSSIBLE loss issue with cryo.

YOU (IIRC) made the ridiculous strawman about cracking it with photo-voltaic electricity.
"Me" merely noted that given HIS numbers for a one sqare meter mirror, the equivilent weight (as the values provided by YOU for the ISS PVA) of mirror could crack a lot more H2O. I did give numbers. If it wasn't obvious that the PVE method wasn't as effective, maybe "YOU" are "stoopid".

[GIThruster]

Well if we look at the big picture as regards Mars, it's pretty unlikely more than footprints and flagpoles could be placed there without a reactor--fission or fusion. If you have to have one on Mars, there's little to be gained by not having them at all your fuel depots, wherever you might have them.

Apparently, NASA and DOE are working together to produce a suitcase sized reactor this year. I'm sure that's just the reactor chamber but still, that would be an impressive feat:

http://news.discovery.com/space/mars-co ... 10830.html

Anyone who could take such a small reactor and turn it into a tiny TRITON like thruster that burns ice would surely have a market for Lunar and Mars hoppers, where the low gravity means the thrust/weight disadvantage of fission as compared to chemical is not such an issue. Fact is, tiny TRITONs could work for everything but Earth launch. Just needs someone to spend a few billion dollars on the right thing.

[williatw]

So far as I know, I'm the only one pointing to biannual Martian launch windows.

if you watch the vid I posted the link to, Musk believes they can open a window for 6 months out of every 2 years. That's not terrible.

I watch part four he does lightly touch on nuclear rockets and seems receptive to the questioner in the audience who brings them up. Haven't gotten to the part where he talks about launch windows to mars being 6months long every two years. That sounds like you would need something with greater deltaV than a chemcial rocket even with propellant depots for refueling.