Yet another Mars architecture

GW Johnson · 2013-11-22 10:29:09

Josh:

Relative to your question in post 142 above, there are multiple points in a trip where a spinning vehicle must be stopped in order to maneuver effectively. Every arrival and any any dockings, for example. Plus any mid-course corrections. With a spinning baton, this is simple thrusters (or even just reaction wheels) acting upon a semi-rigid body structurally sized for the loads. Because there are many thrusters, an accidental single "stuck" thruster can be managed (Armstrong's Gemini-Agena near-disaster is the first example of such an incident).

A cable-connected assembly is dynamically very "soft", and limited in its structural strength to the cable tensile strength, and to the strength of the attach fittings. It's a lot more cumbersome to spin up and down with thrusters (you have to coordinate at least pairs of thrusters, assuming two modules), and I cannot even imagine how to do that with reaction wheels. One stuck thruster, and this thing starts bouncing around like one of those paddle things with the ball on a rubber band. That's a recipe for an unrecoverable disaster, and it's a single-point failure mode that the baton doesn't have.

The baton is bigger and heavier, but simply easier and safer. IMHO.

GW

RobertDyck · 2013-11-22 10:30:07

This article was posted to the Washington DC chapter email list. The person who posted it gave the subject line "The Pruning Shears are Being Sharpened..."

This option would terminate NASA’s human space exploration and space operations programs, except for those necessary to meet space communications needs (such as communication with the Hubble Space Telescope). The agency’s science and aeronautics programs and robotic space missions would continue. Eliminating those human space programs would save $73 billion between 2015 and 2023, the Congressional Budget Office estimates.

http://www.transterrestrial.com/?p=52265

Continue to push for gobs of cash, and this is what you get.

::Edit:: I just plugged $450 billion into a US dollar inflation calculator, for 1989 to 2013. The result was $847.55 billion. Subtract just under $100 billion for ISS, and you get roughly $750 billion. That's what you're asking for, what military contractors such as Boeing, Lockheed-Marting, and ATK would charge, and what Congress sees.

Last edited by RobertDyck (2013-11-22 10:51:44)

GW Johnson · 2013-11-22 10:59:40

I agree with Josh in post 150, although Mars Direct might not in itself be the best way, but something relatively-small sort of like it might be.

I am unconvinced that betting lives on in-situ propellant production is consistent with a decent chance of returning the crew safely. Every site is different, what if the site you choose turns out to be unsuitable for unforseen reasons, and you cannot make your return propellant? Until you do know, it's a very bad bet on that very first trip.

One of the things NASA has learned to its chagrin is that there is nothing as expensive as a dead crew. Space travel has extreme dangers, they've learned that lesson 3 times now. And it applies to the commercial folks, too. No one is immune to that fact of life.

That first trip needs to explore deeply enough to find that now-unknown "thing" that provides us a compelling reason to return. Period.

The best way to do that is make multiple landings, once you have gone to all the trouble to send men all that way. That's how you play the odds: no one site is likely to provide that compelling discovery. But out of many, the odds are much better that one will.

Lesson: maximize the number of landings at different sites all over the planet in that first trip. You are looking for stuff the robots cannot find.

Myself, I don't think we ought to bet lives with in-situ return propellant, which will still be "experimental" on that very first trip. You experiment with it (and all the other in-situ technologies) on that trip, yes, but you have to assure the return, even if all your in-situ experiments fail.

Just my opinions, and they would apply to both government or commercial missions.

GW

Tom Kalbfus · 2013-11-22 11:46:21

Why not just have NASA subsidize private missions conducted for profit?

GW Johnson · 2013-11-22 12:24:06

NASA will never subsidize anything they do not (over-) control. What's required is a plan based on tinkertoys that NASA can be convinced to subsidize, and which will not be killed by NASA over-control. Schedule is far slower that way, but the job gets done. Example: manned Dragon, for which there is no logical reason it could not fly in a year, instead of waiting till 2017.

Commercial guys are better off with private financing, except that the price tags are generally too high for private financing. It's a price tag vs how-fast-can-we-do-this question. There are not sufficient billionaires with vision. I'm surprised there are as many as there are.

Governments (at all levels and in all places) drag things out by worrying way too much about yearly budgets, all the while increasing total integrated program costs just to hold down peak cost in any given year. This generally causes technical problems as well as high integrated costs. Example: space shuttle's vulnerable cluster vehicle. Another example: that's why the typical highway construction job takes 2-5 years per mile of freeway, when concrete cures in 30 days. Ridiculous.

GW

JoshNH4H · 2013-11-22 14:34:17

Tom Kalbfus wrote:

Why not just have NASA subsidize private missions conducted for profit?

What would the parameters be for such a mission? How would you do oversight in order to make sure that crew didn't die (remembering that this would be just as bad for public relations as if NASA were running the program)? How would you define the objectives of the mission? How would you make it so that the companies that attempt the mission would have access to all of the different technologies that would be required to make it workable?

GW Johnson wrote:

One of the things NASA has learned to its chagrin is that there is nothing as expensive as a dead crew. Space travel has extreme dangers, they've learned that lesson 3 times now. And it applies to the commercial folks, too. No one is immune to that fact of life.

I agree, and that has been added to my sig

Regarding spinning habs, with a dead mass attached to them:

I'll do my calculations for 1g and .4g, representing the gravitational accelerations at the surface of the Earth and Mars, respectively. This paper suggests that 2 RPM is the maximum allowable acceleration. I'll go with it, because I'm lacking better information. This is something that we should be experimenting with on ISS, but unfortunately are not. Maybe SpaceX will get on it at some point; somebody certainly ought to.

Anyway, for 1g and 2 RPM, the radius required is 223 m. This means that the speed will be 47 m/s. Each spin-up, spin-down will be 94 m/s. If 4 RPM is acceptable, the required radius falls to 56 m and the velocity falls to 24 m/s (47 m/s for spin-up, spin-down). If we find that 8 RPM is acceptable (I've seen studies that suggest that if you spin up slowly enough it will be fine), these numbers fall even farther to 14 m radius and a velocity of 12 m/s (24 m/s spin-up, spin-down).

If .4 g is acceptable but only 2 RPM, the radius needs to be 90 m, and the velocity is 19 m/s (38 m/s spin-up, spin-down). For 4 RPM, it's 23 m, and 10 m/s (19 m/s spin-up, spin-down). For 8 RPM it's 6 m and 5 m/s (10 m/s spin-up, spin-down).

I don't know what's typically required in terms of course correction, but let's say it will be necessary to stop the rotation four times during transit. In addition to initial spin up and spin down, this implies a total delta-V between 50 m/s and 470 m/s. Using storable hypergolics with an Isp of 315 s (See: Space Shuttle OMS), this implies a mass ratio of 1.17, which really isn't too bad. Maybe a couple tonnes of fuel.

Having said that, it should be possible to do course correction burns without spinning down. Here's how:

Let's say your spacecraft has two sets of rocket engines, one whose thrust would increase the angular velocity and one whose thrust would decrease it. Let's say, for the sake of calculations, that your system consists of one 10 tonne body and one one tonne body. Let's say that the ten tonne body rotates about the barycenter of the two masses with a radius of 10 m. This means that the one tonne mass must rotate about this center with a radius of 100 m, for a total cable length of 110 m. Let's say that the gravitational acceleration experienced by the 10 tonne mass is 1 m/s^2. This means that the rotation velocity will be 3.2 m/s, and the angular velocity just a hair over 3 RPM.

Let's say that the total course correction maneuver is split up into smaller chunks. Let's say that you want to add a delta-V in an arbitrary direction x which lies on the plane of rotation of the system. When the larger mass (this corresponds to the habitation module, where you want to have all your equipment so that you can do something if possible if anything goes wrong). When your "hab" module is traveling in the opposite of direction x, you fire your engine. For the purposes of this thought experiment, I'll ignore the mass loss from doing this, but let's say it adds -10,000 Newton-seconds to the momentum of the hab module, thus decelerating it by 1 m/s in direction x.

What's happened here is that the velocity of the barycenter has increased by about .91 m/s, and the angular speed has decreased by about .86 RPM. You then allow the system to rotate by 180 degrees so that the hab module is moving in the positive direction x. Now, you repeat the maneuver, except you fire the set of rocket engines on the other side of the hab, to increase the angular velocity by that same .86 RPM.

What you end up with is that you used 2 m/s of delta-V capacity to increase the velocity of the barycenter by 1.82 m/s. In this case, the delta-V was increased by 10%. More generally, the delta-V will increase by the ratio of the mass of the body without an engine to the mass of the body with the engine.

Now, where does the rest of this delta-V go? Energy is conserved, after all. What happens is that it goes, at first, to pendular motion between the two objects. This is undesirable, but manageable: By having multiple cables between the two bodies, the pendular motion can be eliminated by turning the whole thing into a damped oscillator. This works best if you have multiple cables connected symmetrically, but not at the center of, the hab.

It's not the most graceful system but it would work.

Terraformer · 2013-11-22 15:08:22

No, I'm not stuck in a circle. People who are relying on Congress are stuck in a circle. I've given up on getting anyone else to do what I want done.

Any Mars mission where the focus is on simply getting to Mars, rather than creating the infrastructure needed to sustain colonisation, *is* flags and footprints.

So yes, I'm a Lunie. Because we need Lunar resources if we want to settle the solar system, unless we're allowed to use Orion. Because Luna is the most profitable option.

RobertDyck · 2013-11-22 15:29:22

1989: 90-Day report
Cancelled by Congress due to cost
Bill Clinton & Al Gore: VentureStar
Lock-Mart refuses to share cost of overrun
cancelled by George W. due to cost
George W: Constellation
Stalled due to cost
Cancelled by Obama due to cost
Restored by Republican Congress because it's "their's"
Boeing dawdles on Orion in order to increase cost
Dragon successful, Cygnus successful
Congress considers cancelling all human spaceflight, due to cost

Are we seeing a pattern here?

JoshNH4H · 2013-11-22 16:05:51

Terraformer wrote:

Any Mars mission where the focus is on simply getting to Mars, rather than creating the infrastructure needed to sustain colonisation, *is* flags and footprints.

That's categorically false. It's entirely possible for a mission to be both low-cost (In the way that Mars Direct is low cost, i.e., could be funded within NASA's current budget if it were reallocated a bit) and still lay important foundations for the settlement of Mars, for example by locating colony sites, demonstrating technologies, proving resources, and doing science and areology that will tell us more about the planet and allow us to locate resources better.

With regards to ISPP (In Situ Propellant Production), because the resource in question is the atmosphere, we can be fairly certain that it will be the same more or less everywhere on the planet, admittedly with variations in temperature and pressure based on location. The atmosphere can be simulated on Earth by using a chamber with the same pressure, temperature, and gas composition. From there the only really difference would be gravity. I think that ISPP is a good technology to start with in terms of ISRU (In Situ Resource Utilization), and we can expand from there when it comes to making real colonies.

GW Johnson · 2013-11-22 17:22:10

I have to question ISPP schemes based on the atmosphere due to the compression problem: 6-7 mbar is next-of-kin to vacuum. You only have a 1 year stay on Mars to make the 100's of tons of propellant required to return. And you need some hydrogen.

It can come from soil ice, but you have to process millions of tons to get hundreds or thousands of tons of water, unless you just happen (I repeat JUST HAPPEN) to land almost on top of a huge near-surface buried glacier, and not a bunch of small scattered lenses plus interstitial ice. And, Mars Direct-style minimalist mission plans don't call for landing the equivalent of a D-8 or D-9 Caterpillar bulldozer to dig it out. Those weigh dozens of tons, and they're not the only heavy equipment you are going to need.

If you have massive ice available, and you have a mining machinery (in the dozens of tons class), then you can make LOX-LH2, with all the evaporative problems involved with LH2, and also providing our solutions here for the para vs ortho form also work on Mars (NOT a foregone conclusion).

If you add in a workable compression scheme, then you can use local atmosphere to make LOX and LCH4, instead of LOX-LH2. That combo will store easier and longer with lower losses. Bit lower Isp, but OK.

That's a lot of if's, either way. Which is why I hold the unpopular opinions that I hold.

GW "dead crew" Johnson

RobertDyck · 2013-11-22 17:38:55

Mars Direct brings hydrogen from Earth. Each tonne of hydrogen becomes 18 tonnes of liquid methane and liquid oxygen. No need to rely on insitu water ice. There's lots of atmosphere, that's all it counts on. Simple. Reliable.

As for compression, you don't use a pump. Every night, ambient temperature drops to just a few degrees above freezing for dry ice. So use a refrigerator to drop that last couple degree, accumulate a chunk of dry ice. The coils would be inside a container, with a valves to let atmosphere in. At dawn, close the valves, then reverse the heat pump to warm the dry ice. Result is phase change to self pressurize. It greatly concentrates CO2. Sufficient concentration to directly feed a Sabatier. Let chemical engineers argue whether convection is sufficient to circulate Mars atmosphere into the coils, or whether a fan is necessary. I suspect a fan won't be needed.

Some people have suggest a special condensation surface could accumulate dry ice without the need for active refrigeration. Again, I leave that detail to chemical engineers.

Fancy bulldozer? Just don't need it. Send a drilling rig to take core samples. First mission will determine what the resource is. Only after that is documented would you even consider sending heavy equipment. Again, the first mission will not make use of local ice at all. That way there is absolutely no risk. But you do want to land where there is ice. First explore, measure, document. Then send equipment to utilize it. What we have measured and documented now is atmosphere, so use that.

GW Johnson · 2013-11-22 20:56:25

I quite agree that conventional compression makes no sense on Mars. The compression scheme you describe is pretty much the only practical thing we could do. What I question is throughput per unit mass for the combined compression and reactor machine you describe. And, throughput per unit electrical power that must be supplied.

This thing you describe has to be big enough to make dozens to hundreds of tons of propellant in only a year (less per year if pre-positioned years ahead, but it has to run unattended by men in that case). Between it and its power supply, we might has well have shipped a bulldozer and an electrolysis plant, I fear.

I've seen some lab experiment results, including Zubrin's. But those are not prototypes of realistic equipment, not yet. Has anybody built a real prototype of what we might send to Mars? Tested it at simulated Martian conditions? Not to my knowledge, they haven't.

It better be much further along in the development and test process, than a prototype tested a few times at simulated conditions, before we bet lives on it. I would not yet risk my life on it, which is a powerful statement, when you consider my first career choices in the 1960's were aimed at being an astronaut for the then-planned Mars mission of 1983. That was long before we understood all the risks of 2.5 years in space.

GW

JoshNH4H · 2013-11-22 22:22:56

A couple things I'd like to add to Robertdyck's post, which for the most part I agree with emphatically:

1: Based on the Mars direct mission, the ISPP plant would be sent and landed the orbital cycle before people are sent. This means that Mission Control will know if the fuel has been produced before the humans even launch from Earth. If not, (for example, if the ISPP unit breaks or otherwise malfunctions) another unit can be landed with the crew. This also means that the ISPP plant will have not one year, but 26 months, more even than a Martian year (22 1/2 months). 26 months is a lot of time. 26 months ago was September 22, 2011.

2: I don't think pumps are quite as hard as you make them out to be. The Martian atmosphere (5 torr) is considered a medium grade vacuum. We definitely have pumps now that can compress things. I know the turbopumps in the SSME increase the pressure acting on the Hydrogen and Oxygen by a similar proportion. You can google pumps that do this kind of pressurization; They don't look tooo heavy. Even if we don't go for refrigeration, which is more logical.

GW Johnson · 2013-11-23 10:24:00

Josh:

Relative to your point 1 in the last post, what happens when the pre-landed ISPP device fails to produce enough propellant (or even any at all) by the time the launch window rolls around to send the men? This is a nonzero probability, after all is said and done. At least there will be months of warning, as the device falls further and further behind its quota. So, what's the backup plan? Carry return propellant, or don't go? That's one of a zillion failures we have to be prepared to deal with.

As for what the failure-to-produce might trace to, without men there to observe and diagnose what the robots were not programmed to recognize, it could be difficult (or even impossible) to figure out whether the fault lies somewhere in the machine, or with something peculiar about the site. That's why I keep saying the first manned trip ought to try this stuff out, but not bet lives on it. To check it out properly in time for a manned mission in the 2030's, we ought to have experiments like this already on Mars. We need at the very least a decade's experience (preferably more) with these devices, in multiple sites, before betting lives on them. There's very little time left to get that job done. And I don't see any credible efforts started yet.

Relative to point 2, I quite agree that the freeze-out and sublimation-compression scheme offers lighter weight and simpler machinery for the same massflow throughput, even if it's an average for batch production. That's definitely the way to go. It's not that piston or turbine pumps won't work, it's just that they'll be heavy and consume a lot of power for the same massflow throughput. And, it's mass that we must accumulate to return.

Conventional compression machines' mass, and to some extent power requirement, are more or less proportional to their volume throughput (piston machines are absolutely constant volume per cycle of rotation, and most turbomachines are close to that), while the mass throughput is directly proportional to inlet density. That's why looking at them on the internet, as designed for 1 atm ambient here, is quite misleading regarding their sizing for 0.007 atm ambient there.

To zeroth order, you're factor 140 down in massflow for the same volume, same machine mass, and some intermediate level of power. You can cut machine mass by a factor of 2 to 5 for flightweight vs commercial/industrial, but you'll never cut it by anything close to that factor of 140 imposed by low inlet density. I dunno what the factor on power will be, but it's likely bigger than the 2-5 factor for flightweight machine mass.

GW

RobertDyck · 2013-11-23 10:45:57

I have said before, we need to demonstrate key technologies with unmanned missions before sending humans. That means a robotic sample return mission to demonstrate ISPP.

I have to mention, the "freeze-out and sublimation-compression" idea is not my idea. Robert Zubrin and his team developed the Mars Atmosphere Carbon Dioxide Freezer. The link is to an abstract on the website for Robert Zubrin's company. Unfortunately the full paper is no longer available. I also have a paper on ISPP, published through AIAA, dated 1994. Robert Zubrin is one of the four authors, all from Martin Marietta Astronautics. This is all very old.

GW Johnson · 2013-11-23 10:58:03

I've seen the Zubrin paper with the freezer and the sabatier (sp?) reactor. It's a nice device. It's also a laboratory environment device. Not yet ready for prime time on Mars. But it could be made ready.

The point I am trying to make is that one test on one probe mission (and it doesn't need to be a sample return, any of the landers we have sent could have served) is not enough experience with it to justify betting lives on this technology. You need at least about half a dozen to a dozen such tests, all at different sites. Dozens (plural) would be better, but not practical to accomplish. One or two? Nowhere near enough.

Weather is different at every site every day all around the calendar and the globe, and varies strongly on short time scales with the passage of weather systems. The device will respond differently as weather changes. Saying the atmosphere is the same might be technically true in the sense of its chemical composition, but that ignores the very important fact that the climate and weather is always different and always changing.

GW

RobertDyck · 2013-11-23 12:37:23

Dozens? Then you argue to never go. I said sample return because it won't just demonstrate ISPP. It will demonstrate a complete system: launch from Earth, land on Mars, make fuel, launch from Mars, land back on Earth. It needs to be done successfully once before sending humans.

I still argue to start construction of the permanent base with the first human mission. If you wanted human exploration by direct landing, rather than exploration from a base, then it should have been done in the late 1990s. It's far overdue.

Last edited by RobertDyck (2013-11-23 22:03:48)

JoshNH4H · 2013-11-23 17:23:46

GW: What do you think about the possibility of a complete systems test within a "Mars Jar", so to speak, on Earth? The laws of physics are the same, after all.

While weather conditions on Mars do vary, both seasonally and daily, the variation isn't so large as to make designing around it impossible. I'd say about the biggest variation would come froma prolonged global dust storm. However, it's not that complicated to design a wind shield and a dust shield. Admittedly, it would be nice if we could play around with some dust samples to see how they affect things, but I'd think we could design around them. Certainly it's not a mission killer or an insurmountable challenge.

RGClark · 2013-11-23 18:03:48

JoshNH4H wrote:

Terraformer and Bob-
I'm not arguing that fuel depots are a bad choice when it comes to colonization. What I am saying is that it's nonsensical to argue that it makes sense to build an extensive lunar infrastructure as a prerequisite to a Mars mission. The initial mission should be cheap and fairly quick; infrastructure comes later, once feasibility has been proven.
Lunar ISRU is not a prereq for martin ISRU. The technologies and environments are very different. As Zubrin likes to say, if you want to go to Mars, go to Mars.

Lunar ISRU is not a prerequisite for Martian ISRU if you use atmospheric ISRU on Mars for propellant production. But when you consider the recent evidence of large amounts of near surface ice even at mid-latitudes on Mars, the same type of ISRU you would use on the Moon also becomes possible on Mars.
Doing the ISRU to turn ice into hydrolox is fairly easy. It's a debatable point which of the surface or atmospheric ISRU methods would be easier.

Here's an article by return-to-the-Moon propellant Dr. Paul Spudis that argues testing ISRU on the Moon should be done as a precursor to a Mars flight:

The Road to Mars Is Paved in Lunar Rock (Op-Ed).
By Paul D. Spudis | June 25, 2013 02:39pm ET

In effect, these lunar properties mean that a complete, end-to-end systems test of all the pieces of a Mars Direct-style architecture could be performed in cislunar space, overcoming the most critical obstacle: the "risk" of requiring ISRU in the critical path.
In my opinion, ISRU is the most important and game-changing technology for future spaceflight. I will go so far as to say that a human Mars mission is inconceivable without incorporating ISRU in some form, most likely as a source of propellant but also for other potential uses (e.g., shielding, oxygen and water). And, such ISRU will not occur until it is proven in space, most easily and usefully on the moon.

http://www.space.com/21713-mining-moon-resources.html

Bob Clark

Last edited by RGClark (2013-11-23 18:36:00)

JoshNH4H · 2013-11-24 00:37:18

RGClark wrote:

Lunar ISRU is not a prerequisite for Martian ISRU if you use atmospheric ISRU on Mars for propellant production. But when you consider the recent evidence of large amounts of near surface ice even at mid-latitudes on Mars, the same type of ISRU you would use on the Moon also becomes possible on Mars.
Doing the ISRU to turn ice into hydrolox is fairly easy. It's a debatable point which of the surface or atmospheric ISRU methods would be easier.

I disagree, actually. Our missions are almost guaranteed to be more-or-less equatorial, because higher local temperatures and higher insolation mean that equatorial regions are more amenable to habitation and colonization (This is even leaving the nuclear vs. solar debate aside, because once the colony starts building their power systems on their own I think pretty much everyone agrees they're going to be concentrated solar power). There is water there but as GW said we can't count on it; it could be variable in composition and depth, it could have disappeared, or maybe we misread the geographical hints. The water ice at mid-latitudes in particular is mostly inferred from pictures taken from orbit rather than satellite imagery (which doesn't show water content getting into the 30% range, e.g. unmistakeably water ice as opposed to hydrates) until above 60 degrees latitude.

On Earth, 60 degrees latitude is the approximate location of Oslo and Helsinki. It's not uninhabitable, but it sure is cold; Now, when we're talking about a place where the mean temperature at the equator is significantly below zero; Why in Heinlein's name would you go somewhere less hospitable?

Now, I'll say it again, that the systems needed for atmosphere-based ISRU on Mars can be tested in the proper environment, right here on Earth; there's no need to take this detour to the Moon. As Zubrin says: "If you want to go to Mars, go to Mars."

RGClark · 2013-11-24 09:04:22

RobertDyck wrote:

This article was posted to the Washington DC chapter email list. The person who posted it gave the subject line "The Pruning Shears are Being Sharpened..."
This option would terminate NASA’s human space exploration and space operations programs, except for those necessary to meet space communications needs (such as communication with the Hubble Space Telescope). The agency’s science and aeronautics programs and robotic space missions would continue. Eliminating those human space programs would save $73 billion between 2015 and 2023, the Congressional Budget Office estimates.
http://www.transterrestrial.com/?p=52265
Continue to push for gobs of cash, and this is what you get.
::Edit:: I just plugged $450 billion into a US dollar inflation calculator, for 1989 to 2013. The result was $847.55 billion. Subtract just under $100 billion for ISS, and you get roughly $750 billion. That's what you're asking for, what military contractors such as Boeing, Lockheed-Marting, and ATK would charge, and what Congress sees.

I don't think it is likely human spaceflight will be cancelled entirely due to the political importance applied to human spaceflight in relation to other nations space programs. What I do think and hope is that a more commercial approach will be taken once it is discussed openly the savings possible in development costs under this approach, perhaps 90%(!)

I found this on NasaWatch that shows this is being discussed in Congress, though not yet by the leaders of the committees deciding funding for NASA:

Is House Leadership Dropping Hints on Space Policy?
By Keith Cowing on November 20, 2013 10:35 PM.
http://nasawatch.com/archives/2013/11/i … eader.html

Bob Clark

RGClark · 2013-11-24 10:38:30

GW, I agree with you multiple robotic ISRU missions need to be sent to Mars first before we do a manned mission using ISRU. But you don't seem too optimistic about either surface or atmospheric ISRU being doable in the near term. Do you think a mission that does not use ISRU will be doable?

Bob Clark

GW Johnson · 2013-11-24 11:02:28

Bob:

I do think a mission not depending upon ISRU is possible, although it is inherently more expensive. You have to send the return propellant, as we all know, which makes your vehicle or vehicles much larger. We now know how to do this with on-orbit assembly, and our commercial rockets are big enough to do it, and 10 times cheaper than the shuttle was. ISS taught us a lot about this.

I think Josh is correct, we can test ISRU and ISPP equipment in chambers here on Earth, and to a point, we can send small versions on landers to Mars between now and the time the men go. It may prove reliable enough to bet lives on it, and it may not. My money is on "not", especially if the government does it. It takes them 25 years to build a jet fighter now. There's only 15-20 years left to get this job done on NASA's schedule, shorter yet if commercial entities take the lead.

There's a reason for that very first expedition to bring their return propellant: exploration. Which is answering the deceptively-simple questions (1) what all is there? and (2) where exactly is it? Robots can only partially answer these, remote sensing the same. Until men can react to what the robots were not programmed for, and until men can drill a km or two down, you simply cannot answer those questions.

Because every site is different in what it offers, and what it conceals (just like here), you have to explore at more than one site. As many as possible makes a great deal of basic common sense. To incorporate multiple landing sites into one mission requires on-orbit basing with multiple (or better yet reusable) landers, and also perhaps with pre-landed supplies at those sites. It makes sense because it is (and will be for some time yet) so difficult to safely make a manned trip that far and that long. Why go to all that trouble and just land at one (likely unrepresentative) place? That's flag-and-footprints nonsense. We've been there.

What you do is test out all that ISRU and ISPP stuff "for real" as you explore. If it works, and you have reusable landers, use the propellants you made to explore more sites yet. More bang for the buck. An even better chance of finding what is needed for a base.

Pick the most promising site while you're there for such a base, and put it together, operating robotically, and ready for the second mission, which will base there, not in orbit. Once you have that target base, the commercial folks will likely mount that second mission. That is the seed from which a colony grows.

I dunno what combination of resources and profit opportunities will justify that base. No one knew details like that when they started sailing from Europe to the Americas. They just knew they would find something, and that they would know it when they saw it. So will we.

GW

Last edited by GW Johnson (2013-11-24 11:09:19)

RGClark · 2013-11-24 20:58:21

JoshNH4H wrote:

...The water ice at mid-latitudes in particular is mostly inferred from pictures taken from orbit rather than satellite imagery (which doesn't show water content getting into the 30% range, e.g. unmistakeably water ice as opposed to hydrates) until above 60 degrees latitude.
On Earth, 60 degrees latitude is the approximate location of Oslo and Helsinki. It's not uninhabitable, but it sure is cold; Now, when we're talking about a place where the mean temperature at the equator is significantly below zero; Why in Heinlein's name would you go somewhere less hospitable?
Now, I'll say it again, that the systems needed for atmosphere-based ISRU on Mars can be tested in the proper environment, right here on Earth; there's no need to take this detour to the Moon. As Zubrin says: "If you want to go to Mars, go to Mars."

I don't understand the distinction you are making between "pictures" and satellite imagery. Perhaps you were referring to the instruments that detected high hydrogen amounts from which it was derived indirectly the amounts of water ice. But I think one of the key discoveries of Mars Reconnaissance Orbiter is the finding of large ice deposits within centimeters of the surface at about 40 degrees latitude and above.
This did come from actual imaging. What was found was recent meteor impacts uncovered pure ice beneath just centimeters of soil. Note this was at the latitude of a former lander mission, the Viking 2 landing site. This corresponds to a latitude of New York City on Earth.
I'm actually not opposed to atmospheric ISRU for propellant for the return mission. What is driving my favoring using lunar propellant for Mars missions is that I really, really do not like the 6 to 8 month travel times proposed for Mars missions. Shortening this has required nuclear propulsion which still results in months long travel times. Evidence from ISS missions suggests this will result in at least some of the astronauts being incapacitated for days, in addition to the radiation and eye damage problems now revealed.
Using lunar propellant would allow huge rockets to be used to cut the travel time to weeks.

Bob Clark

GW Johnson · 2013-11-24 22:39:29

Hi Bob:

I rather like the idea of flying faster myself. There are two things that could make it possible that I am familiar with, one speculative, one very sure. Those are open-cycle gas core nuclear thermal rockets (speculative), and nuclear pulse propulsion (a sure thing). I'm not so familiar with propellants made on the moon, though it seems like it could be done, so I put that somewhere in between speculative and a sure thing.

Failing faster trips, you avoid the microgravity diseases with spin gravity. So months in space need not be a health problem. Doesn't take building Battlestar Galacticas, doesn't take building Rube Goldberg cable contraptions. It does require on-orbit assembly from docked modules of a baton-shaped vehicle of significant dimensions. This is not something even SLS could fling up there, even if it ever does fly. At 4 rpm, for one full gee you only need a 56 m radius from the center of gravity to the habitat module. It's simply not outlandish to contemplate building a thing like that.

Imaging and remote sensing often get it right, sometimes get it wrong. It's a lot better now than when we first started using these technologies, when our results were most often quite wrong. Even so, there is still nothing like ground truth. That's the gold standard upon which you can ethically bet lives. To this day I'm not very confident that high hydrogen content should equate to abundant water. Lots of minerals have hydrogen in them, and not just hydrates. We are talking an alien world here, after all.

I really do worry about a radiation shelter. Not enough folks do, yet. The GCR issue doesn't worry me, a 2.5 year mission would only violate the astronaut annual exposure limits in a solar max year, and then not by very much at all, even if the vehicle had zero shielding effect. It's solar flares that worry me. But, 20 cm of water works even for the worst of those. Any life support system we build will have water and wastewater tanks. Just wrap them around your designated shelter.

I have seen no showstoppers for going to Mars since the 1990's, when we got the microgravity disease results from ISS, Mir, and Salyut all digested. We've known what to do about radiation even longer than that. And ever since Atlas-5 and Delta-4 became inexpensive commercial launchers capable of flinging 15+ tons to LEO, we've had the means to go, a whole lot more cheaply than we could have done in the 1990's.

The problems are not technical, they are idiotic politics (especially politics-of-money), and a lack of demand from a public swamped with economic troubles and wars, focused everywhere else but space. As I said in another thread, I think the Tito fly-by stunt is meant to shame NASA, ESA, and the rest into actually doing something. I dunno whether that stunt will actually accomplish that result. But at least he is trying.

GW

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