The Mars Underground

[CaptainArchmage]

So it's normal specific impulse. And it is one weird way to measure the effectiveness if ISRU. One that sounds wrong. Sone other number. Maybe the ratio you described earlier. Mass advantage that ISRU provides.

I think this is about correct. Jet engines don't use an internal oxidiser supply, so an "effective ISP" seems to be used for some of them.

In other news, you could use other methods to get the fuel as well from ISRU. Technically an electrolysis system with enough power to back it up could use the water present to make liquid hydrogen and liquid oxygen, or liquid methane and liquid oxygen (using the Mars atmosphere).

[Kulebron]

It relies on ISRU, which is great as a long term goal, but not mature enough

Personally, I don't get the point of a manned expedition on Mars at this stage. The technology is simply not mature enough, and it will take decades to develop and bring up to a usable TRL. During those decades, we would be doing nothing.

Didn't they make a working prototype? NASA has a test stand that imitates low pressure and low temperature. There's no problem to test the prototype there and then do a reentry survival + work after reentry test on Earth.

The only problem that stops this from happening is the lack of political will. I agree with Zubrin that should there be a program to do this in 10 years, things that have to be done would start to be done.

I think a big problem with NASA is that the "big challenge organization" can't live further after the goal is completed, and NASA is doing a different thing, it does many long-term low-profile and quite lean missions like rovers. So it just should be another organization to do manned Mars mission, and NASA should not do big missions like constellation at 1/10th effort. The way it goes now, it will take forever to do any big mission, even to the Moon.

If I were US tax payer, I'd vote to reduce NASA budget, make it focus on long small missions, stop programs like Orion, and create a new organization to do the big mission.

Edited January 2, 2015 by Kulebron

[Nibb31]

ISRU requires mining equipment, extraction equipment, crushing equipment, processing equipment, tankage and refueling equipment... All of this is heavy machinery that has to be rad-hardened, vacuum hardened, temperature tolerant, automated, and zero-maintenance. A test stand with the theoretical processes is a great first step. Automating those processes in a package that can work autonomously on another planet with life-depending reliability is a huge technical challenge. You need to get everything right the first time. We are talking about a level of magnitude more complexity than the wheels of Curiosity for example.

The TRL for ISRU as around 2 or 3 at this stage. For humans to be able to solely depend on it to return from a real expedition, it needs to be TRL 8 or 9, and it needs some form of redundancy. To get there will take many years of engineering and precursor missions to validate the technology.

Edited January 2, 2015 by Nibb31

[Bill Phil]

I think the ISRU for Mars, with Metholox, uses the Sabatier Reaction. Taking advantage of the CO2 in the atmosphere, not the ground, plus hydrogen brought along.

And that's still complicated equipment. Although, self maintenance of a probe would be interesting...

Edited January 2, 2015 by Bill Phil
Phone, Can't use the keyboard on it

[Torquemadus]

Zubrin has already tested the ISRU technology needed for the mission. He considers it to be the lowest tech and lowest risk aspect of the mission. It would be a simple enough matter to demonstrate ISRU ahead of time as part of an unmanned sample return mission.

Zubrin checked with the engineers at Martin to see if the relatively small amount of cryogenic hydrogen needed could be properly insulated and stored for the trip to Mars. There would be some boil off, which is accounted for. The hydrogen is only needed for the earlier flights, when a permanent base has not yet been established and a supply of Martian water is not yet available.

In Zubrin's book, The Case For Mars, he explains and de-bunks the various "dragons" which supposedly require that a manned mission to Mars be put off until the distant future. Factions within NASA use these "dragons" to justify enormous spending on zero gravity research, radiation effects, human factors research, and advanced propulsion. Each of these different factions are keen to justify their budget, and don't want NASA's main goal to be a manned Mars mission that doesn't depend on them for success.

The overriding reason why we haven't sent humans anywhere beyond low Earth orbit since the Apollo Programme, is that there hasn't been a heavy lift rocket available to send them there.

[Bill Phil]

No. The primary reason is... Why? We have plenty if RC cars! We don't need people.

Hmm... When you think about it: Curiosity is just a glorified RC Car with a ton of experiments. ( Hyberbole, booyah!)

[ndiver]

Zubrin has already tested the ISRU technology needed for the mission. He considers it to be the lowest tech and lowest risk aspect of the mission. It would be a simple enough matter to demonstrate ISRU ahead of time as part of an unmanned sample return mission.

Zubrin checked with the engineers at Martin to see if the relatively small amount of cryogenic hydrogen needed could be properly insulated and stored for the trip to Mars. There would be some boil off, which is accounted for. The hydrogen is only needed for the earlier flights, when a permanent base has not yet been established and a supply of Martian water is not yet available.

He tested it with a funding of 44 000$ from the NASA, and as explained, he assumes his system to not be as effective as it can be if optimized (they did not had any chemist in their team, when they built the prototype).

Here is a photo of the prototype they made:

This ISRU system requested for the manned mission can easily be tested and validated with a Mars sample return mission.

For the hydrogen during the travel, Zubrin mentions that the spaceship would leave Earth with 117% of the hydrogen required for the ISRU to compensate the boiling, but that this boiling hydrogen can be used to make water.

Edited January 2, 2015 by ndiver

[Kulebron]

As for equipment to live off the ground, I think the best way is to get a minimum viable base there, either robotic or this very manned mission, with a 3D printer, and try using materials from there. Print parts for mining equipment, get it to work, print processing equipment, and so on. Manned mission has a great advantage there, because trial-error cycle is much faster than if you send a complete machine from Earth.

I'm still wondering what valuable things can you get there on Mars and how to make a base self-sustainable at least economically or at least biologically.

[meve12]

At first I thought it wouldn't make a difference, but then I found this http://www.grc.nasa.gov/WWW/Fuels-And-Space-Propellants/GELLED.htm

Apparently the boil off rate can be decreased by just mixing liquid hydrogen with liquid methane, although it doesn't say by how much. Let's stipulate that a 50% mixture would be enough to prevent boil off on the 6 month transit, and you then took the hydrogen and turned it into methane on Mars. You would have two and a half times more methane that if you brought only methane. Thus the effective ISP would increase to...

...almost 3200 seconds. So now the MAV is effectively at the performance level of electric propulsion, but at the TWR of chemical.

http://www.zingerbug.com/Comments/glitter_graphics/100_percent_fabulous_rainbow.gif

That cannot possibly be right. Bringing along more methane just means you've brought along more fuel, not that your engine has suddenly gotten more efficient.

[Northstar1989]

That cannot possibly be right. Bringing along more methane just means you've brought along more fuel, not that your engine has suddenly gotten more efficient.

I don't think you understand the point he is making. He is talking about mass-leveraging: using mass you bring to a destination (such as Mars) to make an even greater mass of fuel (or anything else, for that matter).

If you bring along 4 tons of Hydrogen to Mars, you can convert it into 16 tons of Methane (the mass-leveraging factor is approximately 1:4) using the Sabatier Reaction with CO2 readily-available in the Martian atmosphere. Combine that with the fact that 80% of the mass of a Meth/LOX fuel mixture is Oxygen (more if you burn oxygen-rich), which can be electrolyzed from Martian CO2, and you end up with a 1:20 mass-leveraging ratio.

All this is why he used the term "effective ISP" rather than the actual ISP on any engine you'd be utilziing.

For what it's worth, Mars' atmosphere is also significantly rich in Argon- which could be utilized to run a VASIMR engine. If you wanted to get REALLY ambitious, you could start collecting THAT from the Martian atmosphere, and use it for your return-journey to Earth (of course, running a sufficiently powerful VASIMR thruster for a manned mission would almost certainly require an onboard nuclear reactor or Microwave Beamed Power).

Regards,

Northstar

Edited January 5, 2015 by Northstar1989

[Dkmdlb]

However, Zubrin's Mars Direct is more minimalistic and a bit reckless. It relies on ISRU, which is great as a long term goal, but not mature enough to risk astronauts lives on. It also implies tether-based artificial gravity, which adds unnecessary complexity.

Astronaut's lives aren't at risk with the Mars Direct ISRU plan. All the ISRU is finished well before the astronauts go down to the surface. If there are any problems, they just wait in Mars orbit for a return window.

Also the tether isn't mission critical.

*EDIT* - Having just checked my sources, it appears that the ISRU might actually be finished before the astronauts even launch.

Edited January 5, 2015 by Dkmdlb

[Bill Phil]

Just wait? Assuming they have enough life support, sure. But who's to say they will?

[Dkmdlb]

The people in charge of planning the mission?

[billbobjebkirk]

I wonder, would it be possible to compensate for boil-off by splitting water in Martian soil?

EDIT: also, with regards to safety, once the ISRU is done, which has two seperate chances to occure, one of them before the mission even starts, the safest place to be is the surface, which has free water and low level radiation protection.

EDIT2: although, I do think that Semi-Direct, as outloned in DRM 3.0, is our best plan.

Edited January 5, 2015 by billbobjebkirk