What we need to go to Mars - short term projects

RobertDyck · 2016-07-01 13:46:57

I've posted in various threads before, but let's separate into a separate thread.

fix the urine processing assembly on ISS
We can use ISS life support for Mars. So let's get the damn thing to work. The urine processor got clogged with calcium deposits. Long term exposure to zero-G is known to cause bone decalcification, so this is dissolved astronaut bones. NASA is aware of this and working on it. Get it done!
recover moisture from feces
I suggested a reality show competition: Russia vs NASA. The reality TV show could pay for the entire project. At the 2004 Mars Society Convention in Chicago, some NASA officials said current law prohibits NASA from accepting advertising funding so this would require Congressional approval. It's now 2016 and it's still not done. Get it done! Astronauts say the question they're asked most often is how do they go to the bathroom in space. So there is interest, this could work. But if Congress refuses to authorize the reality TV show competition, then fund the damn thing. Get it done!
direct CO2 electrolysis to recover O2 from CO2 currently dumped in space
This won't replace the current life support system, it will augment it. Currently 50% of CO2 recovered from cabin air is dumped in space. The other 50% goes to the Sabatier reactor. Direct CO2 electrolysis only recovers 40% of O2 contained in the CO2, but 40% is better than 0%. This could replenish recycling losses.
sink and shower on ISS
These were planned for the US Habitation module, but that module was cancelled. The hull became Node 3. Most of the life support equipment planned for the Hab module are now in Node 3. The water processing assembly is capable of handling wash water, all that's needed is a way to collect it. The shower was to be based on the one from Skylab. The "sink" would look like a glove box, so water doesn't get out in zero-G. Get it done!
operate ISS without resupply for duration of a Mars mission
ISS gets frequent cargo resupply. A mission to Mars won't. Crew on a Mars mission won't experience zero-G for the entire duration; at least while on Mars they will have Mars gravity. So changing crew on ISS for this simulation is Ok. But no cargo resupply for the full duration of a Mars mission. The purpose is to prove life support can operate that long.
MCP spacesuit
Dava Newman is now deputy administrator for NASA. Before working for NASA, she was the last researcher actively working on MCP. Others are retired or died of old age. Get it done!
manoeuvring while rotating in tethered flight
Attach a Dragon cargo ship to a Dragon V2 crew capsule. Or Cygnus cargo ship to CST-100 Starliner. Or Russian Progress cargo ship to Soyuz capsule. The idea is to produce artificial gravity by rotation, and change orbit while rotating. Don't stop to change orbit, that would defeat the point. Manoeuvre while rotating in tethered flight. This can be done by timing, fire thrusters in the direction you want to go, and time it so the capsule or cargo ship pulls on the tether. Cargo ships are filled with garbage from ISS after their cargo is off-loaded. So if something goes wrong and controllers have to decide which ship to sacrifice, it's trivial. One has astronauts and the other has garbage? Can you say "no-brainer"? The point is to simulate mid-course correction for a habitat enroute to Mars. This was done in 1966 by Gemini 11 with an Agena target vehicle, but they didn't manoeuvre while rotating, and only produced micro-gravity. This is the next step.
ISPP demonstrator
NASA project managers have repeatedly stated they don't want ISPP on their project, because it hasn't been demonstrated to be reliable. Every technology was tested first sometime. This technology is long overdue. A Scout class mission can do it in one mission: land on Mars, a rover the size of Sojourner can collect samples, a small rocket can leave the surface of Mars to return to Earth, and a capsule similar to Genesis or Star Dust can re-enter Earth's atmosphere.

IanM · 2016-07-01 18:37:08

Here are some thoughts:
-URINE: In addition to clogging the urinary disposal systems, calcium also contributes to the formation of Kidney stones, which are by no means pleasant to deal with it, especially on somewhere such as Mars. While my gut feeling would be to somehow collect the calcium from the urine to try absorption by the bones, perhaps it would be better to prevent absorption loss in the first place. Dealing with it directly is unfortunately outside of my knowledge
-FECES: This is very risky, but also worthwhile: unlike fresh urine, which is for all intents and purposes sterile, feces is loaded with a lot of unsavory things such as E. Coli, which while belonging in the digestive system is bad in the bloodstream. I do know that people have historically dried dung for use as fuel - perhaps the water lost by such a process could be collected and purified to remove bacteria and other pathogens. As for the reality show aspect, I remember that Mars One tried raising funds by featuring their first astronauts on Television, but from I've read that plan ultimately fell through.
-ELECTROLYSIS: Perhaps the CO2 could be concentrated to make the process more efficient.
-SINK AND SHOWER: After researching it a little bit, I am surprised that having rinsing shampoo hasn't happened yet. For medium- and long-term goals, we could have a partial-G space transport instead of zero-G, which would make rinsing at least a bit easier.

RobertDyck · 2016-07-01 20:15:08

Thanks IanM.

FECES: Before the first module was launched for ISS, Russia had planned to replace the Mir space station with Mir2. They built a core module for Mir2. This core module was an upgrade from the core module for Mir, which was an upgrade from Salyut 7, which was an upgrade from Salyut 6, etc. The thing they changed for Mir2 was a vacuum desiccator toilet, to recover moisture from feces. When ISS was built, Russian modules for Mir2 became modules for ISS. That core module became Zvezda, sometimes called the Russia service module. But NASA was concerned the plumbing for the new toilet was too complicated, so insisted the Russians use their old design.

The Johnson Space Agency built an advanced life support project. On the ground, but with a volunteer living in it. It included an incinerating toilet. That's the word they used in documents published on the internet, and several people I spoke with assume the word "incinerating" means burning something. Anything deployed in space would not burn anything, it would use an electro-resistive oven to bake-out moisture. If this is an "incinerating" toilet, then it would bake feces at the temperature of a self-cleaning oven.

I'm suggesting build both. Install the Russian one on the Russian side of ISS, and the American one on the American side. Let's see which works best. Obviously moisture recovered would have to be filtered. Reverse osmosis will remove any bacteria.

ELECTROLYSIS: The process starts with 100% CO2. This is described in Robert Zubrin's book "The Case for Mars". He wants to use it to make additional oxygen to top-up the tanks for the Earth Return Vehicle. NASA learned of Sabatier from "Mars Direct", but instead of using it to make methane fuel, they're using it to make water for life support. So I suggest taking another component of ISPP and using it for life support. According to Robert Zubrin's book, only 80% of CO2 gets converted to CO. And since CO still has one of the atoms of oxygen, that means 40% of oxygen contained in CO2 gets recovered. But 40% is better than 0%.

URINE: If you want to reduce calcium bone loss, the best way is artificial gravity. The tether experiment addresses that. NASA has been looking for decades for a medical means to slow or prevent bone decalcification in zero-G. They haven't found one. I doubt they will within the foreseeable future.

Last edited by RobertDyck (2016-07-03 01:32:28)

IanM · 2016-07-01 20:51:47

If we were to use an incinerating toilet to dry feces, I would assume the high temperatures might require some more space to cool down and condense the water compared to the Russian version. That being said, I'm assuming NASA has already thought of that, and perhaps the temperatures might also quasi-pasteurize the water, making filtration slightly easier. In any case, I agree that both methods should be simultaneously tested and compared.

For electrolysis, assuming that this is a simple 2CO2 --> O2 + 2CO reaction, the Carbon Monoxide could be used for some other purpose; perhaps it could be further broken down into graphite and Oxygen, but I have a feeling that that will be a highly energetically unfavorable reaction.

Unfortunately, I could not find anything about bone growth in merely partial gravity, like on Mars, so I can't say anything about the decrease of bone calcium and the increase of urine calcium.

RobertDyck · 2016-07-03 02:05:17

Partial gravity was supposed to be tested in the centrifuge on ISS. The Centrifuge Accommodation Module was cancelled. When NASA cancelled it the first time, Italy paid for it, and Japan built it. It was sitting in the staging building at KSC waiting for Shuttle to launch it. But President Obama cancelled Shuttle before it could be launched. Some people at NASA campaigned to launch it, and there was one more external tank available, but president Obama did not authorize it. That module is now sitting out doors as a display in Japan. After exposure to the elements, it may not be in any condition to fly.

Here on Earth we can test hypergravity with a centrifuge. But 1G will always be the minimum. We can produce partial gravity for a couple minutes with an aircraft flying parabolic arcs. It's 25 to 30 seconds for zero-G, longer for Moon gravity, more yet for Mars gravity. But you won't get any data about bone decalcification from just a couple minutes. ISS has microgravity, technically the station is so big there's a tiny difference between the portion closest to Earth vs the portion farthest away. Engineers have to worry about that, but to astronauts it feels like zero-G. A centrifuge can add acceleration, so starting with zero allows reduced gravity.

Apollo astronauts did walk on the Moon. But I talked to a NASA flight surgeon who told me the data is useless because it's contaminated. Those astronauts experienced high-G during launch, then zero-G during the flight to the Moon, zero-G again on return, and very high-G during atmospheric re-entry. That makes an difference in astronaut bodies before and after flight completely useless.

So the reason you haven't been able to find data on partial gravity is there isn't any.

Last edited by RobertDyck (2016-07-03 09:28:54)

Terraformer · 2016-07-03 06:58:06

Well, we can at least get data for engineering systems under partial gravity. Like toilets, or showers. That has to be worth something, even if it's just used to tell us what we can do when we finally launch a centrifuge space station.

IanM · 2016-07-03 07:18:39

RobertDyck wrote:

So the reason you haven't been able to find data on partial gravity is there isn't any.

That is quite surprising and disappointing. That and finding out ground conditions on Mars are I think the most important short-term science, as opposed to engineering, projects. Though Terraformer is right, in that we at least know somewhat how to set up such experiments properly.

Tom Kalbfus · 2016-07-03 08:04:13

RobertDyck wrote:

Partial gravity was supposed to be tested in the centrifuge on ISS. The Centrifuge Accommodation Module was cancelled. When NASA cancelled it the first time, Italy paid for it, and Japan built it. It was sitting in the staging building at KSC waiting for Shuttle to launch it. But President Obama cancelled Shuttle before it could be launched. Some people at NASA campaigned to launch it, and there was one more external tank available, but president Obama did not authorize it. That module is not sitting out doors as a display in Japan. After exposure to the elements, it may not be in any condition to fly.
https://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Centrifuge_%28ISS%29_in_TKSC-01.jpg/220px-Centrifuge_%28ISS%29_in_TKSC-01.jpg
Here on Earth we can test hypergravity with a centrifuge. But 1G will always be the minimum. We can produce partial gravity for a couple minutes with an aircraft flying parabolic arcs. It's 25 to 30 seconds for zero-G, longer for Moon gravity, more yet for Mars gravity. But you won't get any data about bone decalcification from just a couple minutes. ISS has microgravity, technically the station is so big there's a tiny difference between the portion closed to Earth vs the portion farthest away. Engineers have to worry about that, but to astronauts it feels like zero-G. A centrifuge can add acceleration, so starting with zero allows reduced gravity.
Apollo astronauts did walk on the Moon. But I talked to a NASA flight surgeon who told me the data is useless because it's contaminated. Those astronauts experienced high-G during launch, then zero-G during the flight to the Moon, zero-G again on return, and very high-G during atmospheric re-entry. That makes an difference in astronaut bodies before and after flight completely useless.
So the reason you haven't been able to find data on partial gravity is there isn't any.

Well you know, we can send astronauts back to the Moon and have them stay there for months at a time, and on the Moon's surface, we can simulate Martian gravity with a centrifuge. I think a centrifuge on Earth can simulate Jovian gravity, it would be a long time before we have any prospects of sending humans into Jupiter's atmosphere, much less of bringing them back, but perhaps we can test out an exoskeleton that would help such a person move about under Jovian gravity. I think 2.51-G is tolerable for people sitting in acceleration couches, but not for much else.

RobertDyck · 2016-07-03 09:45:44

YouTube video from 2010: Raytheon XOS 2 exoskeleton

But this is the Mars Society. And I could give you a long diatribe why Mars is far better than Jupiter.

Last edited by RobertDyck (2016-07-03 11:32:36)

GW Johnson · 2016-07-03 13:44:16

Actually, we could have gone to Mars when first planned in 1983-1987 time frame. We likely would have lost the crews to microgravity diseases or solar flare radiation, however. All the rest of what is being discussed here is just gravy. There are even significant mass ratio advantages to imperfect life support recycling, as long as waste is jettisoned between burns.

Knowing what we know now, about microgravity diseases and space radiation, we could go to Mars at any time we summon the political (or commercial) will to go. You simply do 1 gee spin gravity, and you provide a radiation shelter against solar flare events. All the other things are just gravy, as I said. There still isn't much we can really do about galactic cosmic radiation, but that threat is low enough that we just don't let the same crew fly interplanetary twice.

The thing is, if you do those two required things in order to go without killing your crew, your mission designs and vehicle designs do not look very much like SLS/Orion at all, and certainly nothing like Apollo. This also looks very unlike most of today's mission plans. If you add in some real cost-effectiveness, your mission and vehicle designs start looking more and more like the old 1950's proposals, just updated for how technology actually turned out between then and now.

Those old guys back then were actually quite knowledgeable and talented, as it turns out.

GW

Last edited by GW Johnson (2016-07-03 13:47:25)

Tom Kalbfus · 2016-07-03 20:44:23

RobertDyck wrote:

YouTube video from 2010: Raytheon XOS 2 exoskeleton
https://i.ytimg.com/vi/-UpxsrlLbpU/hqdefault.jpg?custom=true&w=320&h=180&stc=true&jpg444=true&jpgq=90&sp=68&sigh=fqSEgG9rx-6BXvTrHlAHDaO__uo
But this is the Mars Society. And I could give you a long diatribe why Mars is far better than Jupiter.

Mars is a symbol, it is a destination among many, it is low hanging fruit, it has characteristics similar to Earth in its day length which makes some adjustments easier.

Jupiter looks harder than it is, because of its high gravity. I believe an exoskeleton could be made which could give humans the freedom of movement they need in a Jovian environment, the "habitable" zone of Jupiter is around 3 atmospheres of pressure, I think I heard, where the temperature is around room temperature among the water clouds.
https://en.wikipedia.org/wiki/Atmosphere_of_Jupiter

Jupiter's troposphere contains a complicated cloud structure.[18] The upper clouds, located in the pressure range 0.6–0.9 bar, are made of ammonia ice.[19] Below these ammonia ice clouds, denser clouds made of ammonium hydrosulfide or ammonium sulfide (between 1–2 bar) and water (3–7 bar) are thought to exist

3 to 7 bars of atmosphere isn't too bad, divers have survived that by breathing a mixture of helium, nitrogen, and oxygen. We would want to be at the water cloud level where the temperature is close to comfortable to minimize climate control requirements.

So imagine an existence where you have to wear an exoskeleton all the time, I think a person can lie down on a contoured couch, one could also immerse oneself in a bathtub and the water would distribute the weight. Things would fall faster under this high gravity, humans would have to get used to that!

RobertDyck · 2016-07-03 22:50:36

This discussion thread is "short term projects". Colonizing Jupiter is a long way off, Mars can be done now. I believe NASA should do all these. And they can, they aren't multi-billion dollar mega-projects.

Tom Kalbfus · 2016-07-04 05:30:40

Colonizing Mars is at least a decade off, that is not short term, the longer we wait, other technologies will develop, including artificial intelligence and nanotechnology which opens up other possibilities. Zubrin had other ideas, but what if the tide of nanotech and AI robotics over takes us before we get to Mars? Politically, as its a government decision right now, our government keeps putting it off. Do you think the developers of nanotech and AI will say, "Wait, we haven't gone to Mars yet, we have to stop what were doing until after we've sent humans to Mars." Zubrin's vision if it were to occur as he envisioned was to take place in the early 2000s, that decade has come and gone, technology has advanced, the window for sending humans to Mars is closing, I think if we wait long enough, machines will do it for us, they will be just as intelligent as humans, and be rapidly getting more so.

I think our strategy thus far has been to wait for a tidal wave of nanotechnology and AI to flood the Solar System if it doesn't destroy us first! I notice the people trying to develop those technologies aren't waiting. Computer technology isn't a slow technology laden with pork barrel projects designed to give people jobs, it is profitable and unregulated, if we try to regulate it, other countries won't, they will move ahead of us and we'll be at their mercy! Space technology, unfortunately is a slow technology, the government has made it that way, as the only way to advance is with nuclear rocketry, and governments won't permit that, there has been some tinkering at the other end, ion and plasma drives, those are nice, but they only work after achieving orbit, and achieving orbit with chemical rockets is the most expensive thing. If we can't go half the distance to the planets, we don't get to employ those other technologies to go the other half, as there is no money left after launching those chemical rockets. SpaceX is trying to correct this, relying on computer technology to precisely land rockets on pads, ironically its the computer that makes this work with the same old clunky rocket technology.

Space Travel has been a spectator experience for all of the Space Age, as it has remained forbiddingly expensive. Perhaps nanotechnology developments can build a space elevator, they say in 20 years, we may have materials strong enough to do the job, so maybe we're waiting on that, hopefully runaway nanotech devices of another sort don't destroy us first, or maybe artificial intelligence will breakout first and accelerate things on the space elevator front. Who knows?

Meanwhile a manned Mars Mission before that will cost billions of dollars, hopefully in the low billions. It will be something to watch and read about, a nice change of pace from the Space Station. Regarding its importance to humanity, that depends on whether we survive the Singularity or not, I think a post-Singularity Mars colony or a colony anywhere else in the Solar System will be easy, assuming we survive it, before the singularity its going to be a lot of hard work and money spent, but seeing how we don't know whether we'll survive the singularity, we might as well enjoy life until then.

Last edited by Tom Kalbfus (2016-07-04 07:13:04)

GW Johnson · 2016-07-04 13:03:31

I think the list in post #1 is a pretty good list to start with. Of those the truly crucial items are a supple space suit and some sort of experimentation with spin gravity. The critical missing item is likely the pacing item for Musk's 2025 plans: being able to land in a vehicle that can take off again, whether from orbit or direct from interplanetary flight.

The spin gravity thing enables all sorts of bathing, laundry, and cooking items that are very difficult to impossible in weightlessness. The same techniques we use here at home become feasible. That includes wastewater management. Astronauts can easily cope with weightlessness for a day or two while making maneuvers, as long as the vehicle spins for gravity during the long periods in coast.

I'm not a fan of cable-connected approaches to spin gravity. There are too many failure modes (no matter how many redundant cables) and some really non-intuitive dynamical responses because you "cannot push on a string". Nor am I fan of truss-connected approaches, because those just add inert weight, something quickly lethal in terms of mass ratio. I prefer using what I already have to have anyway to comprise the radius for my spin, as long as the components are nominally rigid. This can be achieved by docking things together into the right shapes.

As I have posted elsewhere on these forums, Musk's MCT plans are yet unclear, but perhaps should become a little clearer after the September meeting. His MCT is supposed to land on Mars and be refueled by ISPP for the trip home, as near as I can tell. At his projected flight rate of 1 or more every 2 years, my guess is that his ISPP must be "complete" in the sense of not depending upon hydrogen shipped from Earth, and with oxygen production as well. That is the nature of the landing problem Musk faces. For that kind of mission, there are two missing enabling items: (1) a suitable vehicle design, and (2) full-capability ISPP (fuel and oxidizer).

His picture does differ from the schemes I have seen from NASA, and from a lot of other sources, including here on these forums. I am unsure how Musk intends to reconcile the seriously-conflicting design requirements for long-duration interplanetary flight with those of a Mars lander, all in the one vehicle. He probably doesn't yet really know, himself.

The old 1950's concepts sidestepped this conflict as an orbit-to-orbit transport that never lands anywhere, and a separate vehicle explicitly designed to be a lander. There is actually a lot of wisdom in that.

GW

Last edited by GW Johnson (2016-07-04 13:10:50)

RobertDyck · 2016-07-04 13:23:33

The main reason for cancelling Shuttle was cost. The cost had increased exponentially in the 1980s, and continued to increase until it was cancelled. But cancelling Shuttle means all those workers out of a job, Congress doesn't like losing that many good paying jobs in their districts. So they created SLS and Orion to keep those NASA centers, contractors, and NASA employees working. One argument for Mars it is that it will cost the same price, but instead of a make-work project that produces no results, this will actually accomplish something. When voters cheer, Congress men and women get to take credit.

The reason for Mars instead of the Moon, is that equipment for Mars can be used on the Moon. Or an asteroid. Equipment design for the Moon cannot be used for Mars or an asteroid. Same time, same cost, greater utility. Congress has already mandated development of a Deep Space Habitat. One argument Robert Zubrin made in 1990 is that his (and his partner's) Mars surface habitat could be used as that Deep Space Habitat. New buzzwords today, but same idea. My mission plan is a tweak of Robert Zubrin's, but I continue to argue for the same principles. I argue for a separate Deep Space Habitat and surface habitat. A mission to the Moon would use the same surface habitat, but not the DSH. An asteroid mission would use the DSH, but not the surface hab. All would require a light-weight capsule for return to Earth. Orion is just not light enough, Dragon is.

But we could argue about mission architecture later. First is technology in the initial post of this discussion thread.

RobertDyck · 2016-07-04 13:29:48

GW Johnson wrote:

The old 1950's concepts sidestepped this conflict as an orbit-to-orbit transport that never lands anywhere, and a separate vehicle explicitly designed to be a lander. There is actually a lot of wisdom in that.

In 1960/1961, NASA debated Earth orbit assembly or direct launch. The latter would land an Apollo CSM on the surface of the Moon. The problem is even a Saturn V couldn't launch it. Earth orbit assembly could be done with Saturn 1B rockets, but required as much work to assemble as building ISS. In 1960/'61 they didn't have confidence that could be done before the Russians landed. One American company pushed the idea of Lunar orbit rendezvous, and one of their engineers showed total launch mass was much less than direct launch. In fact launch mass was low enough to fit on a Saturn C5 (later to become Saturn V), and at that point NASA had already selected Saturn C5.

So my architecture learns from this lesson.

GW Johnson · 2016-07-08 10:37:29

Assembly in LEO with two Saturn-5's per moon mission was NASA's baseline. I remember a delay due to not-invented-here attitude. But, finally accepting the lunar orbit rendezvous required splitting of Apollo into a lander and a CSM. The numbers were just too good: only one Saturn-5 per mission.

I see you noticed that everything about Apollo could have been done with Saturn-1B's, at the cost of doing a lot of assembly and refueling in LEO. That's still true today, and is in fact exactly how we built ISS. We just used a very expensive vehicle to send the modules up there.

Sending a 100 ton spaceplane up there with a 15 ton deliverable payload cost around $1.5 B per launch, or about $100M per delivered ton. If you just send the 15 ton payload, you get to launch something 6 times smaller, at 6 times less cost, all else equal. ISS's $110B could have been closer to $20-30B if the items had been launched with early-vintage expendable rockets. 20-20 hindsight, but true, nonetheless.

Today, with commercial rockets that operate competitively, launch costs are lower still, even expendable. They did it by simplifying and reducing the supporting logistical "tail". With Atlas-5, you're looking at something in the neighborhood of $150M per launch with 15 tons to LEO. That's $10M per delivered ton, factor 10 less than with shuttle. That would certainly allow a $20B ISS if built today. Ariane, Proton, and some others are similar.

Spacex does even better, even as all-expendable. It's around $90M to send 13 tons with Falcon-9. That's $7M per delivered ton. It's projected to be around $120M to send 54 tons with Falcon-Heavy. That's around $2.2M per delivered ton!! There is a beneficial scale effect here with large sizes.

Now, NASA projects SLS Block 1 capable of send 70 tons to LEO for about $500M per launch. (Critics say it will cost at least twice that.) That's $7M/ton if you believe NASA, $14M/ton if you believe the critics. If you believe in beneficial scale effects, this number should be nearer $1-2M/ton delivered! Which just goes to prove that NASA still knows nothing about how to launch things inexpensively, and so they specified the expensive way to their "big space" contractors for SLS. (No different for Orion.)

Unless you really have to have the 8 m shroud diameter, why would you ever launch anything with SLS, when orbital assembly by docking is so very feasible today? The only things we really need are (1) a relocatable on-orbit assembly facility and (2) ability to do propellant transfers on orbit to complete our capabilities.

BTW, most of my reusable Mars lander designs have nominally-10 m diameter heat shields. They wouldn't really fit SLS, need to be assembled in LEO anyway. Unless SLS can be qualified to fly with a hammerhead payload shape.

GW

Last edited by GW Johnson (2016-07-08 10:54:25)

RobertDyck · 2016-07-08 12:13:06

What you say about Apollo is true.

An 8-metre diameter payload is not the constraint for SLS. According to someone on another forum, Falcon 9 could be modified to fly an 8-metre (or 8.4m) diameter fairing. It would require first stage engine gimbals that can swivel farther from axial than they can now. The reason for SLS is payload mass.

SLS block 1 can lift 70 metric tonnes to LEO. SLS block 2 was supposed to lift 130t. Various other configurations have intermediate lift. Falcon Heavy can lift 54t.

I noticed Saturn 1 was able to lift 9t; it was upgraded to Saturn 1B able to lift 20t. That was simply by replacing the upper stage with the 3rd stage from Saturn V. Could the Falcon Heavy upper stage be replaced with a LOX/LH2 larger stage?

But all this is getting off-topic.

GW Johnson · 2016-07-09 13:54:06

I based my shroud diameter estimate on the illustrations I have seen. The shroud looks to be the same diameter or not much bigger than the "exploration upper stage", which is listed as 8.4 m diameter. They'll still be using 5-segment SRB's on Block 1B, which limits the core stage gimballing control available, at least in the plane of the SRB's. So a shroud diameter in the 8.4 to at most 10 m range seems reasonable for Block 1B and Block 2. It's smaller on Block 1, whose second stage is only 5 m diameter.

The reason this is an important item is the size and shape of whatever lander we decide to use at Mars. Whatever those vehicles are, they must have an entry heat shield of some diameter, and they will have some length. There must be some sort of landing legs that fold out, and the span of these needs to be comparable to the vehicle length for stability landing on rough ground. Almost no matter what kind of design one attempts, these requirements tend to drive larger heat shield diameters, perhaps exceeding 10 m.

So, we either need a way to launch larger diameter objects that we build on the ground, or we find some way to assemble these vehicles in Earth orbit from smaller components. But, we need a lander we can test in space, and we need it in time to make Musk's trip to Mars about 2025. That's not much time to develop such a vehicle.

Musk I think wants to land the MCT directly on Mars. No one yet knows what shape this thing will have, but it must be a compromise between the seriously-conflicting design requirements of a deep space transport and a Mars surface lander. I rather doubt his concept meets the landing leg spacing vs length needed for rough-ground stability. Being nothing yet but a concept, I rather doubt he and his team have thought this through as thoroughly yet as they need to.

My guess is that the the MCT should be developed as an orbit-to-orbit transport, and that the lander should be a separate type of vehicle. But that's just my guess.

GW

Last edited by GW Johnson (2016-07-09 13:54:27)

RobertDyck · 2016-07-09 14:25:09

I should have mentioned, when Robert Zubrin and his partner David Baker created Mars Direct, they included a heat shield that can expand like an umbrella. If you read "The Case for Mars", Zubrin says they got that from a device that a NASA researcher was already working on. Today it's called ADEPT. A carbon fibre fabric heat shield with metal ribs that open like an umbrella. That allows a heat shield diameter larger than the pressurized lander. Important because an aeroshell is subject to the cube-square rule. I'm sure you're familiar with that: an object's volume hence it's mass increases as the cube of it's diameter or radius, while surface area increases as the square. So increasing a aeroshell will eventually have problems slowing through atmospheric drag. You don't want to crash into the ground before parachutes open. The umbrella heat shield changes the rules, completely bypasses the cube-square rule. It also avoids fairing limit.

Last edited by RobertDyck (2016-07-12 13:55:03)

GW Johnson · 2016-07-12 09:46:13

I looked at the entry deceleration problem parametrically with a crude tool originally used for estimating warhead entry. I got roughly the same thing that JPL gets in its probe designs, both of us assuming shallow entry angles. Up to about a ton at entry, you come out of hypersonics at an altitude high enough to deploy a supersonic-capable chute and have it actually slow you down to subsonic. Heavier than that, your altitude is just too low and time to impact just too short for a chute to do any good.

What ADEPT, and the heat-protected ballutes, do is lower the ballistic coefficient at higher masses toward that obtained with lower masses, raising the altitude back up to something where a chute might have the capability to help. But this is the net of two competing effects. My hunch is that there are still size limits for chute effectiveness, just at a higher entry mass. Murphy's Law says that limit is still too low to land really big things like we'd like to.

There is another effect intervening here: the terminal velocity of the chute. These things can only be so big, and they must have the right mass/area "loading", or they will not open. We are pretty much restricted to ringsail or ribbon designs, in order to get supersonic opening speeds. These things would be very difficult to design-in inflatable forced opening features, because they are objects with big holes, or lots of small holes, through them. About the max is Mach 2.5, and it get "iffier and iffier" the closer you demand to Mach 2.5 opening speed. That's limited by material stress capabilities, not geometry. Opening shock is just too much.

As you increase the mass at constant mass loading, you can maintain the same terminal speed. But if practical size limits intervene (Murphy's Law says they will), then mass loading and terminal speed go up as your landed mass increases. Very quickly you have a chute with a supersonic terminal speed. It really doesn't do you much good toward landing. Sort of a "more trouble than it's worth" situation.

That's why I tend to favor the supersonic retropropulsion approach: come out of hypersonics and immediately fire up the retro engines, direct to propulsive landing. Avoid all the failure modes of deploying aerodecelerators of any type, either during or immediately after entry. You pay for it with extra mass (propellant for landing), but there's no inherent size limit with this approach. How many hundreds of tons would you like to land? Doesn't matter, it can be done.

I think that's what Musk has in mind for his MCT, which will be on the order of a couple of hundreds of tons at entry. Things like that will come out of hypersonics at local Mach 3 (about 0.7 km/s) at something like 5 km altitude, and a steep downward path angle. You'll need something like 2-to-4 gee thrust levels to get it slowed to a stop at touchdown, even from LMO. Entry angles will be really shallow, like 1 degree or less.

This sort of thing is far easier to control precisely from an LMO entry than it is for entry direct from interplanetary trajectories. Which is one reason why I like sortie-ing from LMO instead of direct landing. I differ from Musk, and from Zubrin, and NASA, there. The other reason is that if you stage from LMO, you can visit more than one site, if you bring enough landers, or re-use them. That is a huge mission adaptability/flexibility advantage (to adapt to unexpected ground truth conditions) that the direct landing approach can never have.

GW
"suspenders, belt, and armored codpiece, always"

Last edited by GW Johnson (2016-07-12 10:02:13)

RobertDyck · 2016-07-12 14:04:02

I posted figures from a study by NASA's ADEPT team. They ran the numbers for 40 metric tonne landed mass. They found total launch mass is still lowest using heat shield, parachute, and subsonic retropropulsion for landing. Sure, there's probably a mass limit, but ADEPT works for landed mass slightly larger than a Mars Direct habitat. Good enough.

SpaceNut · 2016-07-12 17:55:21

OK so lets say we do fix the list

1. •fix the urine processing assembly on ISS
2. •recover moisture from feces
3. •direct CO2 electrolysis to recover O2 from CO2 currently dumped in space
4. •sink and shower on ISS
5. •operate ISS without resupply for duration of a Mars mission
6. •MCP spacesuit
7. •manoeuvring while rotating in tethered flight
8. •ISPP demonstrator

of which most are not really that hard to accomplish but its the funding that is not there for the work to be done.

I would say that items 1-4 are very much related to how we handle recycling. Item 5 is its own seperate test of how to handle the outbound or return leg of any mars mission. This one is conditional for the test perameters of the test such as how much power, quantity of water ect...and food of course.....items 7, 8 and 9 are all seperate missions of test to prove out how to do each and while the moon might be a good testing area for some the conditions for mars are quite different.

GW Johnson · 2016-07-15 09:34:56

The astronaut food problem is a killer for item 5 in your list. Last I heard, that freeze-dried stuff they do lasts about a year, year-and-a-half at the most, before it gets too unpalatable to eat. There's civilian camp food stuff that lasts a lot longer, but NASA seems to have had a serious not-invented-here attitude about using it.

You're really limited if you insist on only foods that can be wet down and heated in a microwave in zero-gee. If you have artificial gravity, you can use frozen foods and free-surface water cooking. Save the freeze-dried stuff for those few days when you quit spinning to maneuver. Otherwise, keep your freeze-dried stuff frozen to slow its degradation with time. Or use the civilian camping stuff.

But having frozen food adds weight for the refrigerators/freezers, and bulk (not in the form of liquid water in a tank somewhere) for the volume of the frozen foods. This affects considerably mission launched weight and size-of-spacecraft. The estimating relations based on astronaut food are just wrong for this scenario.

I'm not sure we can really simulate a Mars mission duration successfully at all on ISS, because you cannot do spin gravity there, and we already know we need it for a variety of other reasons besides just food. I think in hindsight we might have spent $110B on the wrong space station design, at least one supposedly suitable for getting ready for interplanetary flight. Unless somebody adds a spinning annex to the thing. Or sends one up to its own orbit. These need not be 1% as expensive as ISS was.

Item 7 should be expanded to include things other than cable-connected. I think when we actually get around to experimenting with it, we're going to find out that the transient dynamics of cable-connected things are really complicated by "you cannot push on a string" effects, to the point of introducing some failure modes we cannot really deal with.

We'll end up having to experiment with other ideas. But it makes sense to use common sense to screen out the ridiculous ones (like giant truss-connected structures that add huge amounts of inert mass, or things that have to spin way too fast). There's a well known limit of about an 8 rpm limit for long term adaptation of the balance organs, and I'm estimating about a 12 rpm limit for blood pressure gradient effects that cause fainting.

The scope of the ISPP demonstrator item needs to be defined. The main questions are (1) "will we produce LCH4 only or will we produce both LCH4 and LOX, since both are really needed?", (2) "if we produce LOX, how will we do it (from what I've read here, there's two ways)?", and (3) "how fast can we accumulate many, many tons of the produced propellants?".

A corollary is "how many tons do we need/what are we going to do with it?" The other corollary is "what do we do if it doesn't produce as much as we wanted?" That last is a Murphy's Law problem, which makes it more likely to happen, than we'd like to admit.

GW

Last edited by GW Johnson (2016-07-15 09:58:28)

GW Johnson · 2016-07-15 10:03:40

Here's an odd thought: if Musk is going to Mars to build a city/colony, he is going to need organic matter in quantity to turn regolith into farmable soil. Why improve the efficiency of the life support system?

We're going to need that sewage down on Mars to use for a fertilizer source. That muck is a precious commodity for any colony. So, pack the extra food and water for a lower-efficiency life support system, and leave the resulting sewage generated during the flight, on Mars.

GW

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