Light weight nuclear reactor, updating Mars Direct

Tom Kalbfus · 2014-06-28 15:34:30

Would you want to have that double wheel space station as shown in 2001 A Space Odyssey and attach a rocket to that for travel to Mars?

Last edited by Tom Kalbfus (2014-06-28 15:34:46)

JoshNH4H · 2014-06-28 16:53:42

It's always easy to argue for why spending more money will make something better. In fact, it's about as close as you can get to a fact of life, especially in engineering. But just as much as it's a fact that a 200 billion dollar returns more, and more useful, information than a 100 billion dollar mission, it's also a fact that that is a hell of a lot of money. Almost a quarter trillion dollars. To use scientific notation, it's 2e11 dollars. It's about the size of Connecticut or Colorado's economy. Done over 10 years, it's like having every employed person in Vermont working on the Space program. It corresponds to about 120% of NASA's annual budget, which typically gets split a lot of ways.

A mission like this would presumably have to be funded by the government, because it seems like an enterprise too large in scale and too risky for capitalism to undertake. It would probably have to be an American exercise, because we alone have the infrastructure, economy, technology base, and know-how that would be needed to do such a thing. Does anyone who's been watching the US government lately think that anyone has the vision and power to make that happen? I don't.

So we need to ask ourselves: What do we want from a Mars mission? What is it specifically that people will be able to do that we can't do with robots that will get cheaper and more reliable every year? How, once there, can we leverage the crew's capabilities to do everything that needs to get done on as low a budget as possible?

Your primary claim has been that the purpose of a human mission is to do prospecting to validate potential colony locations. It may be helpful in this respect to think of Earth, or even the United States. Let's say you are going to immigrate from somewhere to the United States. The US is a big country, and there are lots of different places where you could live. It would definitely be possible to spend a couple years travelling from city to city, trying to pick out the best one based on a list of criteria. But nobody really has the time or money for that. More often, using a more limited dataset, people pick a city where they think they could live, and make a life there, perhaps moving later on if it becomes necessary or desirable.

There are corresponding truths for the establishment of new towns: When North America was being colonized by the Europeans, they didn't carefully survey the entire coast to find the best place to colonize. In fact, the first colony was placed in an extraordinarily bad place; The second was better, but presumably not the "best" place.

I propose that the fundamental basis of colony location is this: It is physically possible to place a colony at every location on the surface of the planet. There are going to be multiple sources for every resource of importance, and at least some travel will be necessary, from any colony location, to obtain these. Furthermore, it will be necessary for the colony to rely on reserves for a time while things are being finalized, meaning that there will be a transition from outpost/base to colony.

The cost, both in mass and dollars, required to keep a base supplied is going to be much less than the cost of setting the base up to begin with.

There are three resources that can't be obtained from the air [and are therefore not universally available at low altitudes] that are vital to the function and growth of a colony. These are Water, Sunlight, and Iron.

The second limits the colony's location to within 10 or 15 degrees of the equator. Glaciers can be found farther than about 30 degrees from the equator, which is 1800 kilometers from the equator or 900 kilometers (560 miles, the distance from Washington, DC to Boston, MA on the highway), but there is also some evidence of a huge frozen sea near Elysium, at 5 degrees North, and I would be quite surprised if there were not geologically small but on a human scale plenty big deposits of ice or icy regolith pretty much everywhere on the planet. Based on this map 4-6% water (or at least an equivalent amount of Hydrogen, so possibly in the form of Hydroxide minerals) is the norm across Mars, and above 60 degrees North and South it seems that there are actually significant concentrations of ice, basically everywhere.

It is my claim that, in this environment, it is reasonable to find a useful concentration of water within 50 kilometers of any well-selected site. A useful amount of water might be regolith that is 25% water ice or more, for a total amount of ten tonnes of water. Given water recycling, I would imagine that 10 tonnes of water would be enough to handle the life support needs of lots of people for quite a while. Industrial uses will follow, of course, and by then larger sources of water should have been located and extracted.

Iron is much more common on Mars than on Earth, about twice as much by weight in Martian dirt. This image show that there is a patch of land near Elysium where the dirt is 20% Iron by mass. Wikipedia suggests that on Earth we sometimes mine where there is just 15% Iron by mass, so this is a huge find (One that is actually, coincidentally, nearly colocated with the frozen sea). Wikipedia also mentions that Iron ores can be concentrated both with water and vulcanism, and both of these have happened on Mars. Given that we have a virgin planet, there is no doubt in my mind that there are mine-able iron deposits there.

Silica is needed for glassmaking. While its existence on Mars is poorly documented, it should be possible to turn Iron ore into glass once the Iron has been smelted out of it, using "decolorizers", which was a technology known to the Romans. This will be necessary for various other applications.

I propose that sending a constellation of MER (Mars Exploration Rover, e.g. Spirit and Opportunity) class rovers-- With emphasis on deeper drilling and long range, but less fine-grain scientific capabilities and definitely solar powered-- to Mars, perhaps 10 or 15 of them, to various promising locations. Pick the most promising of these for a mission or two, which will prove basic technologies and locate the best local resource concentrations, and then follow up with a colony.

Other important resources include Bauxite (Aluminium), Basalt (Bricks, cast Basalt, Basalt Fiber), Sulfur/Sulfates (Can be extracted from dirt), Salt (Ditto), Phosphorous-- unknown but probably possible to find. Chromium, Manganese, and Vanadium (For Stainless Steel-- perhaps in volcanic outflows).

The basic point is that we know that this stuff is somewhere, and a lot of prospecting is going to have to be done to find it. I would expect this prospecting to be directed by humans but strongly aided by robots. I would also expect that much of this can happen on a first mission, once a location has been identified, and also after the establishment of a small base. The second mission can, after all, be Mars' first permanent residents, even if they are not independent of Earth from the get-go.

A note on radiation: I don't think that the crew needs so much water for life support that there can be 20 cm of it used as a shield around the habitat. Let's say you have a crew of 4 in a cylindrical habitat with 80 m^3 per person and three floors, each of which is 2.5 m tall, you end up talking about carrying 18 tonnes of water with you, which is way more than anyone's claiming that people need. A much better idea is to try to do intelligent placing of cargo so as to shield that way. Based on my analysis in this post the half-value-thickness for regolith against cosmic rays is .45 m, after radiation peaks at .1 m below the surface. This corresponds to a HVT of 1,260 kg/m^2 or 126 g/cm^2, which is bad news because it's a lot. However, it is my understanding that using lighter elements enables better shielding, and we really don't need more than one HVT. Once on Mars, piled regolith ought to do the trick.

I've written this post not because I disagree with you, necessarily, but rather because this is a discussion that needs to be had, and I'm more than willing to step up to the plate and be the advocate for a much smaller, Zubrinesque mission.

GW Johnson · 2014-06-28 17:00:27

A powered version of the "2001 A Space Odyssey" space station? No, something that big is not required to send 6-12 people to Mars. Not at all.

The orbit to orbit ship is a long skinny thing sort of like the "Discovery" from that same movie, except not as big, and except that you deliberately spin it nose-over-tail, the way it was found in the second movie "2010 Odyssey 2".

That means the habitat module at one end is not a sphere with a centrifuge inside, it's a simple cylinder (or cylinders) with decks perpendicular to the ship's long axis. You set the spin rate for 1 full gee on the deck furthest from the center of gravity. If the ship is 100 to 150 m long at 150 to 400 tons, it's really easy to get 1 full gee at 56 m radius, and a spin rate of 4 rpm, easily tolerable even by untrained civilians.

Most of the long journey is spent coasting. You spin for gravity during those phases, which greatly simplifies life support, waste control and processing, cooking, and a whole host of daily living needs. You de-spin for a few days only for major maneuvers, living on astronaut food and using zero-gee toilets only for those short periods.

Put your daily work shift stations on the far deck at 1 full gee. Put the sleeping quarters at the lowest-gee deck, because gravity provides little health benefit when prone while sleeping (otherwise bed rest studies would not be in least useful for understanding microgravity effects). Recreation and storage can be in-between.

You put your main engines at the other end of the baton-shaped ship, so that the center of gravity is nearer the geometric middle. The length in between is docked-together propellant tankage. You stage off empties and reconfigure to the same long baton shape after each burn, and then spin-up again for gravity. How easy is that? How reliable, too? No cables to break, causing loss of vehicle and crew.

Propellant is the cheapest of all commodities to be launched. I'd make the ship maximally reusable, meaning minimum number of empty tanks to be jettisoned, and reuse it for multiple missions. That just means a bit bigger departure mass.

I'd reuse it to visit any and all of several destinations. The same ship could take human crews anywhere from Mercury out to the main asteroid belt. It could serve for decades with periodic propulsion and subsystem upgrades, as they become available.

If you add electric propulsion mounted at the spin center 90 degrees to the spin plane, you could use that to cut travel time, without incurring the spiral-out/spiral-in time (and delta-vee) penalties associated with super low-thrust electric propulsion as we know it.

GW

Last edited by GW Johnson (2014-06-28 17:06:03)

RobertDyck · 2014-06-28 19:28:34

JoshNH4H wrote:

Other important resources include Bauxite (Aluminium), Basalt (Bricks, cast Basalt, Basalt Fiber), Sulfur/Sulfates (Can be extracted from dirt), Salt (Ditto), Phosphorous-- unknown but probably possible to find. Chromium, Manganese, and Vanadium (For Stainless Steel-- perhaps in volcanic outflows).

At the 2005 Mars Society convention, I presented a paper about mining aluminum. I still argue for that approach. Since then I discovered that a company in Sweden is already doing it, but they don't have my idea to recycle carbon anodes. The point is Mars does not have bauxite. That mineral is the result of a rain forest depleting all nutrients from soil. Volcanic minerals are weathered to clay, plants convert clay to soil, then millions of years of action by a rain forest depletes nutrients useful to plants. What's left is aluminum oxide, iron oxide, silicon dioxide, and some soil. Mars never had a rain forest; it did have running water, but no rain forest. So no bauxite. It does have bytownite, which is a form of plagioclase feldspar that will dissolve in hydrochloric acid. Anorthite is the most pure form that will dissolve, but bytownite will dissolve too and that's what orbiters have detected on Mars. The mining company in Sweden found a deposit of pure anorthite. Good for them; use what you have. The process reverses pH to extract aluminia (aluminum oxide) from ore. Then next step is the same as bauxite: alumina is smelted via electrolysis.

The other point is silica gel will be a by-product of extracting alumina. That silica gel can be desiccated to form pure silica. Melt that and add soda & lye to make glass. Pure white silica sand is the traditional ore to make glass on Earth, but the only deposit of silica sand they found on Mars so far is just a few inches long. Not enough for even a single window. So glass as a by-product of smelting aluminum?

My response to mission architecture is here: Yet another Mars architecture

JoshNH4H · 2014-06-28 20:12:29

I very much like that solution for Aluminium production, and I would say it goes to reinforce my point. Do you know why the bayer process doesn't work on non-Bauxite ores? And do you know how high quality the bauxite has to be for the bayer process to work?

Writing up a response now.

idiom · 2014-06-29 23:18:28

JoshNH4H wrote:

It's always easy to argue for why spending more money will make something better. In fact, it's about as close as you can get to a fact of life, especially in engineering.

I would completely disagree with that.

Limitless resources lead to lazy engineering.

Figuring out how to do more with less is how we got Mars Direct in the first place, easily a much better return on resources than the 90-day plan model.

JoshNH4H · 2014-07-01 11:26:55

But then look at we would have gotten for the 90 day report mission-- A large space infrastructure with fuel production capability, and a whole bunch else.

There's a lot to be said for "less is more", but brute force will always get the job done if you can afford it.

GW Johnson · 2014-07-01 16:56:05

Deep space mission design with people on board is a severely-constrained optimization problem. The best result is constraint-driven among several constraint-driven choices, somewhat like linear programming, except this is very non-linear. It will never be "truly optimal" in terms of weight or dollars. It may not resemble the expected notions going in, not at all.

With humans to support, these constraints are very severe, more so than any other kind of mission, and violating them risks the most expensive thing we know of: loss of a crew.

A lot of the vehicle and mission design concepts I have seen on these forums are quite innovative and interesting. Some include features I would never have thought of by myself. My trouble with most of them is that I cannot see how the microgravity disease and radiation-exposure risks can be addressed in vehicles that small. We can argue about living space requirements, another serious shortfall (in my opinion) with smallish vehicles. But the need for shielding and spin gravity looks to be fairly absolute.

This may just be me, but I also have a hard time with cable-connected spin designs. Not with steady-state spin, but with the transient dynamics of spin-up and spin-down, required for every maneuver and all dockings. Further, a cable seems to me susceptible to severing by meteor impact or other accident, admittedly low probability, but nonzero. There seems in most cable-connected designs no way to recover from a parted cable, which event then leads to loss-of-crew, unless you use multiple cables, which is heavier and risks entanglement.

Solid structures can be designed to be more failure-tolerant and simultaneously have fewer failure modes to begin with. That being said, I'm no fan of trusses either, that being a really fast way to gain inert weight that only serves a single purpose. I'd rather use my propellant tankage as my rigid spin structure, weight I have to carry anyway. At least it would serve two purposes.

Just food for thought in these discussions.

GW

JoshNH4H · 2014-07-01 17:24:59

GW, I'm writing up a reply to you in the "yet another mission architecture" thread, but I'm very interested in hearing a more extensive response to my post in this thread on the twenty eighth.

JoshNH4H · 2014-07-07 09:14:53

GW Johnson wrote:

Deep space mission design with people on board is a severely-constrained optimization problem. The best result is constraint-driven among several constraint-driven choices, somewhat like linear programming, except this is very non-linear. It will never be "truly optimal" in terms of weight or dollars. It may not resemble the expected notions going in, not at all.
With humans to support, these constraints are very severe, more so than any other kind of mission, and violating them risks the most expensive thing we know of: loss of a crew.
A lot of the vehicle and mission design concepts I have seen on these forums are quite innovative and interesting. Some include features I would never have thought of by myself. My trouble with most of them is that I cannot see how the microgravity disease and radiation-exposure risks can be addressed in vehicles that small. We can argue about living space requirements, another serious shortfall (in my opinion) with smallish vehicles. But the need for shielding and spin gravity looks to be fairly absolute.
This may just be me, but I also have a hard time with cable-connected spin designs. Not with steady-state spin, but with the transient dynamics of spin-up and spin-down, required for every maneuver and all dockings. Further, a cable seems to me susceptible to severing by meteor impact or other accident, admittedly low probability, but nonzero. There seems in most cable-connected designs no way to recover from a parted cable, which event then leads to loss-of-crew, unless you use multiple cables, which is heavier and risks entanglement.
Solid structures can be designed to be more failure-tolerant and simultaneously have fewer failure modes to begin with. That being said, I'm no fan of trusses either, that being a really fast way to gain inert weight that only serves a single purpose. I'd rather use my propellant tankage as my rigid spin structure, weight I have to carry anyway. At least it would serve two purposes.
Just food for thought in these discussions.
GW

Regarding cable-connected spin designs, I think I have a design that you might like. It consists of eight cables attached in the following pattern:

This design has several failsafes. Firstly, all equipment with any moving parts at all is located on top of the crew capsule. This means that, if a spacewalk/repair is necessary, the crew can do repairs in a gravity field with something to stand on. The cables can have a lot of extra strength engineered into them and still be quite light.

The red cables are designed to to be the primary weight bearing cables. There are five of these so that any cable can snap and the structure will still be stable. So long as they are not adjacent, two cables can snap and the system will remain stable. Should two, or even three, adjacent cables snap, the torque bearing cables will prevent the system from becoming unbalanced. Because they are much farther from the center than the load bearing cables, they do not need to be nearly as strong.

Each cable is attached to the dead mass through simple bolts, presumably redundant ones. However, the system on the crew side is a bit more complex. Each load bearing cable is attached to a winch attached to a platform on a spring. Attached to the roof of the crew cabin are magnetic dampeners, which use eddy currents induced either in the wire itself or metal pieces attached to it to take energy out of any oscillations.

The torque bearing cables are the same, but they lack the magnetic dampeners. Put together, the system acts like a mass-spring-dampener system that is stable with respect to forces or moments applied in any direction. It is massively fail-safe and low-mass (more on this later), and uses simple, well-established technologies.

Now, what about course corrections? These are a necessary part of any mission and one simply has to be able to do them. It might be possible to minimize their number, though. It looks like Curiosity had up to six planned and used 4, while Mariner 9 had two, and MRO had 6 planned and used 4. So I'll plan for 6, but assume that 3 are to occur after the final spin-down, in the approach to Mars. This means that the crew will be subject to approximately 1-2 weeks of weightlessness, which shouldn't be a big health concern.

The first possibility is that it won't be necessary to spin down to accomplish a Trajectory Correction Maneuver (TCM, in NASA-speak). This would involve maneuvering thrusters on two sides of the craft, and firing one in the desired direction when the craft is facing that way, and then waiting till it has completed a 180 degree rotation to cancel out that angular momentum. In this way, 100% of the firing energy can go towards firing in the correct direction. However, it depends on precise firing times and in general I really don't favor this approach.

A better approach is to consider just how much impulse is required for spin-up and spin-down. The rotation speed of the craft for various rotation rates and gravity levels is as follows:

The formula used here is v=a/w, where v is the rotation velocity, a is the acceleration, and w (omega) is the rotation rate, expressed in radians per second, where there are 2*pi radians per rotation. For the mission I've suggested, 4 spin-up/spin-down maneuvers would have to be done, meaning that you would need a delta-V eight times the rotation velocity. For low rotation rates and high gravities, this can result in some relatively onerous requirements, for example 750 m/s for 1 Earth gravity at 1 RPM [Using 300 s hypergolics, this results in fuel equal to about 22% of your dry mass]. The jury is out regarding what really constitutes an acceptable rotation rate, or an acceptable gravity level for long-term spaceflight.

Note that holding gravity constant, the velocity goes up as the rotation rate goes down because the radius of rotation gets bigger.

My take: In keeping with the Mars Direct mission plan, most Mars missions are currently planned to be 910 days, of which 550 are spent on the Martian surface and 360 spent in space. Heavier g-loading will be experienced on Mars entry, while launching from Mars, and on Earth entry.

The two issues with spin gravity are, of course, acceptable rotation rate and acceptable gravity levels. I'll deal with the latter first.

Current tours of duty on the ISS are 6 months. For those 180 days (1/5 of a Mars mission) astronauts are in 0 g. The record for a manned spaceflight is 437.7 days, a bit less than half of our mission. It is unknown what the effects of fractional g's are, but we do know that the biggest problems are bone and muscle loss. Muscle loss can be prevented with a healthy exercise regimen, but is somewhat less troublesome because it's possible to regrow muscles. Bone loss is an issue, all the more over an extended period of time in space. But I've read some articles suggesting that NASA is experimenting with the use of osteoporosis medicines to prevent bone loss, and preliminary results look good. Source, Related Bed Rest Study. We'll find out more about this soon, I hope. I'd also like to see some experiments with fractional gravities, at least on animals, but who knows if that will ever happen.

Anyway, it is my opinion that a Martian level of gravity in combination with drug therapies will be sufficient to eliminate the worst effects of microgravity and thus make a full-duration Mars mission safe for people. Disagreement is by no means a mission killer, but it will increase the delta-v requirement for spin-up and spin-down proportionally.

The rotation rate is even more murky, IMO, than the effects of fractional gravity. Study results are fractious and confusing, often mutually exclusive and contradictory, and to claim that we know any value for a rotation rate that is "comfortable" would probably be a lie.

However, I will say this:

The uncomfortableness coming from high rotation rates comes from the same system as the uncomfortableness from microgravity, and the vomit comet, and seasickness, and amusement park rides. There is, fortunately, medicine that can reduce this effect, and therefore I would be comfortable with relatively high rotation rates. I don't know about anyone else, but I was a fan of the carnival ride known as the "gravitron", which spins you at approximately 20 RPM to generate maybe 2-3 g (I estimate a radius of 4 m, so that would be about 2 g) against the wall, and I wasn't dizzy until I got off.

I take no issue with conservatively low rotation rates, but really rotation is not something that is a mission killer, and in the end it's probably easier to get people acclimated to than microgravity-- Just take them to the amusement park, over and over again until they don't puke

I also propose that acclimatization be slow, and therefore spin-up happens over the course of a day or even two days. To have a crew cabin with a gravity of 1 Mars g, at 3 RPM, requires a spin-up delta V of 11.8 m/s. Over the course of a day this is an acceleration of just 14 micrometers/s^2. As an aside, this is about twice as much as the Dawn spacecraft with its ion drive running. I'm thinking that an arcjet might be worthwhile, if we find that the delta-V requirements are significant (In the example of the Earth g, 1 RPM case, it could reduce the fuel fraction from 22% to about 9%) it would probably be a good choice, especially because an arcjet can run on Hydrazine, which is also likely to be a component of the TCM fuel.

Spin up and spin down will happen as follows:

At first the crew cabin will be tightly mated to the ballast. Then, one of the spin-up engines will impart the system with some angular momentum. From there, the winches will slowly winch the system down to full extension with either continuous firing (in the case of the arcjet) or intermittent bursts (in the case of normal rocket engines). The de-spin process involves doing this in reverse. If one or more than one of the winches fails, it's not a big issue. Because of the slow de-spin speed, a slight electric charge imparted to the cables ought to be sufficient to make them repel each other and not become tangled even if one or more winches does fail. In this case, the system has the same tolerance to winch failure as it does to cable snapping.

Anything of importance should be located with the crew, that way in the case of complete failure the ballast can simply be jettisoned and an attempt made to either complete the mission or return to Earth while under zero g conditions. I would propose that completing the mission would be a better option under these circumstances, because then zero-g time would be limited to 180 consecutive days, separated by some time spent in a gravity field, rather than 720 consecutive days as in the case of the free return.

So: A completely stable, massively redundant, and highly failure tolerant spin-cable system. What do you think?

By the way, cable radii are as follows:

This is the radius of rotation of the crew cabin. Assuming that the mass of ballast is going to be much less than that, its radius will be much larger. Zubrin called for Mars gravity at 1 RPM, and a cable that totaled 1500 m. This implies a ballast with a mass about 25% as large as the crew cabin. Roughly speaking, multiply the radius given by 5 for total cable length. It'll be more if you're trying to use your tankage as ballast without cables. I just don't think it's feasible, no matter how big your mission is.

tl;dr: Cables are safe, good, necessary

JoshNH4H · 2014-07-07 10:15:07

Regarding radiation, the effects of radiation are fairly well known and well characterized. In interplanetary space, radiation totals about 50 rem per year, unshielded. At the Martian surface, radiation totals 10-20 rem per year, also unshielded. 50 rem per year happens to be NASA's limit for radiation, and career limits, depending on age and sex, are between 90 and 300 rem for reasonable crew ages. The astronauts are likely to get a good bit of shielding from the design of the hab, so they will most likely take less than this. The big worry is a solar flare. These flares can hit you with X-rays and fast-moving proton radiation (with a smaller amount of heavier nuclei dominated by Helium), which are actually not really so hard to shield from. I propose that each person's bunk be a fully shielded radiation shelter, or rather that they are in the radiation shelter with removable partitions between, and that the craft be spun such that the feet are always pointing towards the Sun.

GW Johnson · 2014-07-08 17:45:52

Well, 8 cables certainly has some redundancy. Am I correct in surmising that we start and stop the spin when pulled together, with the spin slowing to design values as you pay out to the design radius? Otherwise, I have no sense of how to spin this up and down without tumbling and tangling things. You can't push on a string, after all.

Between the structure of the habitat module, and whatever water and wastewater is on board, I don't see that solar flare shielding is that big a problem. Even if there's not 20 cm of water available. Sounds like there's probably not, especially for the smaller mission and vehicle designs. (GCR simply isn't a problem, as long as the crew doesn't do this trip twice.) Stored foodstuffs, stored clothing and bedding items, and stored equipment can also serve as shielding. As can any tanks of thruster or main-engine propellants. But, I think water supply estimates should expanded some: with spin gravity, you can do real cooking with real free-surface liquids in real pots and pans, and, you can use real frozen food (another potential radiation shield, and a very good one, too).

From a spacecraft designer's safety-first standpoint, I'd still recommend the flight control station be the radiation shelter for solar flares, not the sleeping quarters. That way, critical maneuvers can be conducted regardless of the solar "weather" outside. Those events are at most a handful of hours long. But at peak, the worst ones are every bit as lethal as the fallout right after a nuke weapon surface blast. Up to around 4000 rem/hour.

I would also recommend that habitat module interior layout be designed around the notion that access must be had to the pressure shell in seconds, in order to repair meteor/space junk punctures before the module can depressurize. It's another safety-first thing. That does not seem to be the custom yet, but that design practice is long overdue adoption. It means you do not mount any equipment at all, of any kind, on the pressure shell wall. Period. Everything needs to go on a central core structure. And you need a repair kit in every single compartment. No exceptions. The upside is more emotionally-spacious living spaces, and the opportunity to have lots of windows.

GW

Mark Friedenbach · 2014-07-08 18:25:57

That's why you don't have eight cables, you have one cable with eight threads.

JoshNH4H · 2014-07-08 21:18:41

GW-

Rather than starting and stopping the spin at any one time, I propose to increase it gradually. You could, for example, endeavor to obtain an approximately constant rotation rate by doing small firings every couple hours, thus preventing your crew from being subject to excessive gravity forces before the cables are reeled out.

I don't know about windows-- that's radiation again-- but the idea of keeping the outside wall clear is a good one. Perhaps make it a corridor. IMO it's actually a good idea to make the floor plan of the hab as illogical as possible, thus giving the illusion of there being more space than there is. I would also make the architecture as varied as possible, the lighting high-intensity and multicolored, and the hallways lit as bright as day during the daytime hours and have a real sunrise and sunset. Perhaps make the hallways mirrored on both sides, or at least shiny if not perfectly reflective to give the illusion of very large hallways.

Edit: The Atomic Rockets website has a good discussion of what happens in the case of a hull breach here.

RobertDyck · 2014-07-31 10:32:45

BUMP

This year's Mars Society Convention is one week from today. The purpose of this discussion thread was to update Mars Direct. Not redesign it, not address the fact the ERV does not have artificial gravity. Just update with modern equipment. I would like this discussed at the Convention. My sister is getting married, her second marriage. Her wedding day is Saturday, August 9. So I'll be there instead of the Convention. Besides, I'm still unemployed, surviving with a home business repairing computers. I don't have funds to go to the Convention. So I won't be there.

Points for ERV:
• Dragon v2 for capsule
• SAFE-400 reactor
• mobility from Curiosity rover to transport reactor
• life support from ISS
• module on nose for life support, similar to Cygnus but smaller
• ADEPT heat shield
• lower row of seats in Dragon replaces with ISS toilet, one exercycle (or other exercise equipment), and storage for food and Mars samples

RobertDyck · 2014-08-09 02:27:28

Going through the document for the nuclear reactor. The same document linked in the first postof this discussion.

The SAFE-400 space fission reactor (Safe Affordable Fission Engine) is a 400 kWt HPS producing 100 kWe to power a space vehicle using two Brayton power systems – gas turbines driven directly by the hot gas from the reactor. Heat exchanger outlet temperature is 880°C. The reactor has 127 identical heatpipe modules made of molybdenum, or niobium with 1% zirconium. Each has three fuel pins 1 cm diameter, nesting together into a compact hexagonal core 25 cm across. The fuel pins are 70 cm long (fuelled length 56 cm), the total heatpipe length is 145 cm, extending 75 cm above the core, where they are coupled with the heat exchangers. The core with reflector has a 51 cm diameter. The mass of the core is about 512 kg and each heat exchanger is 72 kg.

The chart that document provides says "512kg". However, this paragraph shows more: 512kg for the core + 72kg for each "heat exchanger". That paragraph says it has "127 identical heatpipe modules". Please tell me that isn't 72kg per heat pipe. That would total 512kg + 127 * 72kg = 9,656kg. The paragrph also says "two Brayton power systems"; does that mean 72kg for each "power system"? So is that 512kg + 2 * 72kg = 656kg. That doesn't include radiation shielding, but the ERV uses a "light truck" to park the reactor in the bottom of a crater.

Last edited by RobertDyck (2014-08-09 10:40:31)

RobertDyck · 2014-08-19 15:39:37

I emailed Dr Zubrin after the Mars Society convention, about the SAFE-400 reactor. I requested he calculate electric propulsion using this reactor, stating that Franklin Chang Díaz probably will argue for it. I expected the result to show electric propulsion *STILL* would not get you to Mars faster than LOX/LH2. However, his response was that this is not a complete reactor: no radiation shielding, and no radiator. I knew about the shielding, but hadn't realized the radiator. Anybody able to determine mass of a radiator for the surface of Mars?

RobertDyck · 2014-12-25 14:29:54

I found some more detail. The CST-100 is smaller, lighter weight. Orion capsule + service module + propellant has a total mass of 21.25 metric tonnes, making it way to heavy for a Mars ERV. CST-100 is reported to mass approximately 10 metric tonnes. Capsule diameter is 15.0 feet diameter instead of 16.5 feet. Service module is smaller. And service module main engines are used for launch escape instead of a separate launch abort rocket. Abort from Mars is stupid, because you can't abort to Mars surface. The 21.25 metric tonnes for Orion does not include the launch abort system. So CST-100 could be used for the Mars Direct ERV instead of Dragon.

https://www.aiaa.org/uploadedFiles/Abou … Reiley.pdf

GW Johnson · 2014-12-26 16:20:51

You can abort to Mars's surface if you have a spare lander, and you base from low Mars orbit.

GW

RobertDyck · 2014-12-28 15:17:10

ERV engines

According to mass estimates in the first post of this thread, and the book "The Case For Mars" paper back edition, published 1997, page 93. The ERV will convert 6.3 tonnes of hydrogen feedstock into 94 tonnes of methane/oxygen propellant and 9 tonnes of water. Of that, 82 tonnes will be used to return to Earth, the rest for ground vehicles. I have recommend replacing the light truck described in Mars Direct with mobility components from the Curiosity rover. That uses electricity to run electric motors, and since mobility will be attached directly to the reactor, it won't be usable for anything after that. And can be run by power from the nuclear reactor itself. The hab will bring at least one ground vehicle, fuel could be used for that. And water for the hab. So this reduces mass of the ERV. At launch, the ERV will not carry that water or fuel for ground vehicles, won't carry the reactor or light truck, won't carry the propellant production plant, will have consumed hydrogen feed stock, and expended/ejected the aeroshell. This will reduce ERV total mass from 28.6 tonnes to 16.0 tonnes. Then add 82 tonnes of propellant for a new total of 98 tonnes. So we need an ascent engine that can lift more than that mass from Mars. But Mars has 38% gravity, so it requires 82 * 0.38 = 31.16 tonnes force. And Mars Direct calls for an engine with Isp = 380 seconds. Do any engines exist that can do that?

Looking through Astronautix.com, only two American LOX/LCH4 engines. One was developed by Orion Propulsion Inc for Orion, currently owned by Dynetics who now working with Aerojet Rocketdyne. But they only developed an RCS thruster, capable of 100 pounds (45kgf) thrust. The other was developed by Orbital Technologies Corporation, also tested 2005, but it was also an RCS thruster: 133 Newton thrust (29 pounds). The only other engines were developed by Russia in the 1990s. Mars Direct was based on Isp of 380 seconds, but the engines designed by Russia for ground launch produce 309 to 316 seconds at sea level, or 351 to 353 seconds in vacuum. Russian engines designed for vacuum only produce better Isp:
RD-160: 2,000 kgf, Isp 381s
RD-185: 18,250 kgf, Isp 378s
RD-167: 36,000 kgf, Isp 379s
RD-192S: 217,000 kgf, Isp 372s
And some others with poor Isp.
RD-190 is a 6 chamber engine, each is an RD-169. It has same Isp as RD-169: 351s in vacuum.
Ok, then we have a few choices. 8 x RD-160, or 2 x RD-185, or one RD-167.
Interesting trivia: RD-167 is 4 chambers with one common turbopump. RD-185 is single chamber, based on RD-120 but modified for liquid methane and larger exhaust cone. RD-120 is used for the second stage of Zenit.

Of course Russian engines are blocked by the Ukraine thing.

Last edited by RobertDyck (2014-12-28 15:36:57)

SpaceNut · 2014-12-28 21:27:30

I recall a methane engine discussion in Mars Colonial Transporter

http://en.wikipedia.org/wiki/Raptor_(rocket_engine)

SpaceX advances drive for Mars rocket via Raptor power

RobertDyck · 2015-09-08 09:43:25

If NASA launched Mars Direct, that means astronauts would ride in the hab from launch pad 39B at KSC all the way to Mars surface. What is its launch escape system?

RobertDyck · 2015-12-09 00:05:20

I've tried coming up with some analogies. Some people claimed Mars Direct is too spartan. It really isn't. I try to put this in terms that people can relate to in every day life, to illustrate just how big it is.

The SLS core stage is 27.6 feet (8.4 metres) diameter. SLS block 2 is basically the Ares launch vehicle with main engines moved directly beneath the core stage, instead of to one side like Shuttle. The Mars Direct habitat was designed to have the same diameter as the core stage. The Mars Direct habitat outer diameter is therefore 8.4 metres. Assume 20 centimetre thick walls including thermal insulation, you get 8 metre inside diameter. Area = πR² (Pi * Radius ^ 2), you get 50.265 square metres = 541 square feet.

I have said before the upper floor alone is as large as a 60 foot class A motorhome with slide-outs. In most states the largest motorhome you can get is 45 feet long. To fit on the road it's 8.5 feet wide. After subtracting for bumpers, dashboard, etc., interior living space is typically 8 feet wide by 40 feet long. That's only 320 square feet. With slide-outs they can get up to 400 square feet. I read an internet post from Wyoming that said by law an RV can be no larger than 400 square feet. Any larger and they're considered a mobile home, not an RV. But a few states allow the big ones. Class A are the ones that look like a highway bus. The ones 40 to 45 feet long have dual rear axle. The only 60 foot motorhomes are articulated, they're 2 segments with an accordion joint in the middle. Typically they have 2 axles in the front, and another 2 axles at the back of the front segment. The rear segment has another axle.

attachment.php?attachmentid=20217&stc=1&d=1334967754

Analog research states FMARS and MDRS both fully use both floors. But a real Mars mission will not have access to most of the lower floor. It will be filled with rocket engines to land on Mars, propellant tanks to feed those engines, landing legs and their mechanism, RCS thrusters to manoeuvre in space, propellant thanks for the thrusters, and life support equipment. We saw on ISS that life support is the size of 5 full size refrigerators. And that doesn't include the direct CO2 electrolysis unit that I want to add to increase recycling efficiency. Solar panels for power, that have to be stowed during launch, and deployed in space. Those solar panels have to be retracted and protected during atmospheric entry at Mars. You really want a fairing to cover the solar panels during atmospheric entry, so the fairing for launch is not discarded. And Mars has day and night, so you need a battery for life support. Even using lithium ion, it will have to be as large as a bar fridge. And an airlock. You also need storage for the rover. Remember Mars Direct included a rover capable of carrying all crew up to 1,000km one way to reach the ERV in case they land that far away. It will require a door that folds down to form a ramp, to get the rover out and down to the ground. So storage will be as large as a single car garage. Packed around the rover will be surface science equipment; and an inflatable greenhouse, deflated and folded. So the lower deck will be completely unusable during transit from Earth to Mars.

Once on Mars, the rover will be deployed outside. As will surface science instruments. The greenhouse will be taken outside, unfolded, inflated, and set up for use. Once outside, all that stuff will never come back in. So you will have a space the size of a single car garage, usable as a workshop or lab. The garage must be able to depressurize, so the rover can get out. Probably life support will be in pressurized compartments, with a door to each unit in the garage wall. We have seen on ISS that life support requires continual maintenance.

The greenhouse depicted for Mars Direct is about 6 metres wide, by 12 meters long, and squashed with hold-down straps to be only 3 metres high. This is as wide as a double car garage, and twice as long.

To summarize: the upper floor alone is as large as a 60-foot class A motorhome with slide-outs, and once on Mars the lower deck is equivalent to a single car garage, plus an inflatable greenhouse twice as large as a double car garage. For anyone who claims this is spartan, try saying that to an Apollo astronaut. They only had a Lunar Module.

Here is an image of the inside of a Lunar Module. This is from the movie "Apollo 18", which depicted a mission that never happened. The image is a set, but it's built from spec's of the real Apollo LM.

Of course the Achilles heel of Mars Direct is the return vehicle. It's just a capsule, but larger than the Apollo Command Module. The size is equal to the Dragon capsule. Again, I'll put this in terms of every day experiences. The Mercury capsule was just one seat. Gemini was as large as a 2-seat sports car. The Apollo Command Module had interior volume equal to a modern mini-van. Dragon has an interior volume equal to a modern cargo van. It's larger, but it's still just seats.

In this discussion thread I described a module docked to the nose of Dragon with the same recycling life support as ISS. That module would be a cylinder packed with equipment, and just barely enough room in the centre for a single astronaut to enter to perform maintenance. On approach to Earth, that module would be discarded. I said the module could be similar to the Cygnus cargo ship. After further research, it's exactly the same size as the pressurized cargo compartment of a standard Cygnus, without service module.

I have come up with an alternate mission architecture. My approach was to take lessons learned from Apollo, and apply to Mars Direct. Specifically, NASA initially wanted to land the Apollo Command and Service Module on the surface of the Moon, and return directly to Earth. But it was so heavy even a Saturn V couldn't lift it. Then one engineer proposed splitting it into mother ship and Lunar Module. The mother ship would consist of the Command Module NASA was already working on, but the Service Module would be substantially smaller. The total stack was light enough to fit on a Saturn V. So my idea was to do the same thing, do not drop the return capsule on Mars just to lift it off again. Instead park a vehicle optimized for interplanetary travel in Mars orbit, together with the return capsule. The Mars ascent vehicle would be light weight, like the Lunar Module. And since Mars Direct dropped a separate habitat, that ascent vehicle could be even lighter. Astronauts could ride in their spacesuits, so the MAV would not require any life support or pressurization.

But, this discussion thread is about updating Mars Direct. And my goal is to debunk claims that Mars Direct is too spartan. So I have to point out that Apollo astronauts used Apollo equipment to go to the Moon. Are modern astronauts too wimpy? I doubt that; it's more likely contractor executives trying to maximize profit. Can we go now?

GW Johnson · 2015-12-09 14:25:49

It is only my opinion, but I fear we will kill the crew if we do not supply some level of artificial gravity approaching 1 full gee during the transit to Mars, and more especially the transit from Mars. There is no data to suggest that a year at Mars at 0.38 gee is enough to be therapeutic. The free-return entry at Earth is likely to be 15 gees. Currently, one cosmonauts barely survived a 3-4 gee return from a 400-day stay in LEO. None of the variations on Mars Direct I ever heard of address this lethal issue.

Plus, there is the issue of crew confinement during the 6-9 month voyage home. You cramp them up in a space capsule that long, and they will kill each other. That (crew insanity) is precisely why Gemini 7 went only 2 weeks, not the intended 3 weeks, in LEO back in the mid 1960's. Admittedly, those conditions were more rugged ("doing in the suit"), but we're still talking weeks, not months, no matter what.

When you start talking about splitting the architecture into stuff left in Mars orbit vs stuff you take down with you, and add into the mix the need for artificial gravity plus real living space, you might as well built an orbit-to-orbit transport and some landing boats of some kind. Which puts us right back to a 1950's mission architecture, just with better technology than they had back then.

It makes real sense to recover the orbit-to-orbit transport back in LEO when the crew comes home, so you can re-use it (or most of it) for other missions. That amortizes the cost of the thing out over a much larger community that it eventually serves. Plus, you avoid the 15-gee free-return ride that is so risky, except as a last-ditch emergency backup.

GW

SpaceNut · 2015-12-10 10:56:36

Mini-nuclear plants the next frontier of US power supply -- or the next Solyndra?

The technology, called "small modular reactors," will be the centerpiece of an entirely new way of thinking about nuclear power. They are much smaller than what traditionally has been built in this country -- producing about one-sixth the power. They'll also cost less -- about $1 billion-2 billion apiece, compared with $10 billion-$15 billion for a large plant.
Typical nuclear units produce between 1,000 and 1,400 megawatts of electricity. SMRs, as they're called, top out at about 180 megawatts. The plan is to build them in two-packs, for a total of 360 megawatts, which is right around the output of a coal-fired unit.
B&W has taken the lead in the development of SMRs with its mPower design. Eighty-five feet tall and 13 feet wide, it incorporates several systems into one unit. The unit is built in a factory, instead of in the field, and then shipped to the site on a truck.

Big dollars....

Small Nuclear Power Reactors
(Updated November 2015)

As nuclear power generation has become established since the 1950s, the size of reactor units has grown from 60 MWe to more than 1600 MWe, with corresponding economies of scale in operation. At the same time there have been many hundreds of smaller power reactors built for naval use (up to 190 MW thermal) and as neutron sourcesa, yielding enormous expertise in the engineering of small power units. The International Atomic Energy Agency (IAEA) defines 'small' as under 300 MWe, and up to about 700 MWe as 'medium' – including many operational units from 20th century. Together they are now referred to by IAEA as small and medium reactors (SMRs). However, 'SMR' is used more commonly as an acronym for 'small modular reactor', designed for serial construction and collectively to comprise a large nuclear power plant. (In this paper the use of diverse pre-fabricated modules to expedite the construction of a single large reactor is not relevant.) A subcategory of very small reactors – vSMRs – is proposed for units under about 15 MWe, especially for remote communities.

very big article with a list of reactors and descriptions of each.

New Mars Forums

Announcement

#101 2014-06-28 15:34:30

Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

#117 2014-08-19 15:39:37

Re: Light weight nuclear reactor, updating Mars Direct

#118 2014-12-25 14:29:54

Re: Light weight nuclear reactor, updating Mars Direct

#119 2014-12-26 16:20:51

Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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Re: Light weight nuclear reactor, updating Mars Direct

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