The Case for a Small CEV

TwinBeam · 2005-08-24 12:00:10

Why would the lunar lander need to be pressurized, or even enclosed? Astronauts could land in their suits, on an open framework lander. Set up an inflatable shelter when you get down, or just land near a pressurized hab.

Ad Astra · 2005-08-24 18:16:09

The thing I like about the enclosed lander is that it's an extra level of safety. A micrometeoroid strike would be a disaster for astronauts in suits, but the thin skin of the LSAM would be enough to slow it down. If the suits lost pressure, the LSAM would be a redundant pressure vessel.

That's not to say that an enclosed lander would necessarily be a pressurized lander. But this is the design solution I prefer because it gives the biggest safety margin.

GCNRevenger · 2005-08-25 17:03:32

Now that the first week of classes is about over...

Placing a small fleet of fuel tankers into orbit around the Earth and Moon is a horrible idea any which way, for a number of reasons:
~Numerous long-life nav/maneuvering systems and cryocoolers on each one, with additional landers needed per-mission, in addition to the nav/maneuvering systems for CEV capsule and landers. Expensive and heavy!
~Size or granularity of fuel tanks required causes tankage duplicity since tanks must be fairly large on the ships, decreasing payload substantially. Also requires tricky cryogenic fuel transfers.
~Requires additional docking operations, increasing mission complexity while decreasing flexibility and unessesarrily lengthening mission time (rendezvous can take days).

Flexibility is the last thing we need right now, because that means developing more vehicles, which is expensive and time consuming. Don't waste money designing smaller vehicles! Thats money that can be spent on actually building and flying to the Moon instead. We know what size we need, a capsule with room for up to six that has its own Earth-return rocket, and a lander with room for four with supplies for ~10 days or six with fewer days plus several tonnes of payload. This very same lander, the exact kind, minus the crew cabin/acent vehicle will serve as heavy cargo landers and both will be launched by the same rocket.

I repeat, putting fuel in tankers doesn't change the amount of fuel you need for a mission. It really doesn't, in fact it increases it. It just changes how it gets there... The CEV is a capsule, period, full-stop, end quote. It is light enough that it can ride with its own Earth-return rocket, and so it should. The big SDV launcher can carry enough payload to launch a reasonably sized lander AND the TLI stage for both, and so it should.

The Lunar lander needs to be fully pressurized and enclosed because the ability to land far away from any Lunar base is a MUST, as well as the missions needed to set up a base will likly need a place to stay in the mean time. An inflatable structure doesn't save you much mass on such a small vehicle.

The whole point of the current mission plan is to be able to send bigger-than-Apollo crews, light payloads, and heavy payloads with the lowest practical complexity using exsisting launch hardware. The NASA plan in this respect is perfect things considerd. The big inline SDV will launch the lander and the TLI stage with either heavy cargo (>20MT!) or a Lunar crew lander/acent vehicle big enough for short stays with the light payload they need. No tankers, no seperate flights for light cargo, and maximum safety.

TwinBeam · 2005-08-25 20:28:54

There is no "fleet" of fuel tankers - one or two in use at any time, and they'd use the same launch vehicle as all other launches. There are no additional landers for the on-orbit tankers.

The objections to rendezvous make no sense, considering that the current plan calls for at least 2 rendezvous - one on the way to the moon, and another before returning to Earth. What I've proposed allows zero, one, or more rendezvous. (Zubrin's basic there-and-back mission is zero, refueling once lets you bring a lot more payload or more crew.)

At no point did I suggest developing many different vehicles, smaller or not (an ironic suggestion, considering I'm talking about one base launch vehicle vs the standard model's two). I guess one could completely replace the Crew-exploration-lander vehicle with a "tank and cryo" module, which should be quite a bit simpler and cheaper and carry more fuel.

Nor did I state or imply that using tankers somehow reduce fuel requirements. Tankers just give you a good deal of flexibility in how much of the last stages' mass has to go into fuel vs cargo or crew - because the rest of the fuel you'll need is already in space.

Flexibility to make changes in payload should NOT require an entirely different vehicle, just a modest degree of modularity. Do you put in more seats and life support, or more cargo, or just more fuel in the tanks? Without flexibility, you DO have to design a new vehicle for every different mission, or else limit your missions to what can be done with the (multiple) rigidly designed vehicles you have.

Cryogenic refueling in space is new - but that doesn't mean "impossibly difficult". A crude method would be to transfer filled tanks from a tanker to the CEV and connect them up. That's much less flexible than pumping fuel, but might be a reasonable way to get started, for manned missions - the crew could do a spacewalk to do the tank hook-up.

He seems to have actually read the idea of carrying a pressure tent for away-from-base landings, even though in the same paragraph he implies that away-from-base landings are the reason a pressurized lander is required. He argues with a strawman, saying "it doesn't save mass" - I never wrote that it would save mass, though it would if you're landing at an existing base and so don't need to bring along the tent or other long-term life support systems.

The actual point is that the pressurized cabin is unnecessary, and that a pressurized tent will give you much more room for about the same mass. It won't have seats and controls and other equipment filling it. Pressurized tents will probably be useful to develop for Mars, as well.

He finishes off with an implication that somehow separate flights would be required for "light cargo" - I have no idea where he got that from. The whole point of nearly everything I wrote was "right-sized cargo in one launch".

RobertDyck · 2005-08-25 22:07:23

Need I mention that the Moon has no hydrogen, carbon, or any other fuel except trace amounts of hydrogen at the bottom of craters at the poles? Hydrogen there will be a combination of ice and hydrated minerals such as clay from C-type carbonaceous chondrite asteroids that delivered the hydrogen. Those volatiles are so thin that is isn't worth mining for fuel. If you want material from a C-type asteroid you can get pure material on the asteroid itself. Near Earth Asteroids take less fuel to reach, land, and return to Earth than the Moon. This means you can get a lot more fuel from an asteroid than the Moon.

I made a presentation about asteroid mining at this year's Mars Society convention. As I pointed out there and various threads on this board, mining a C-type asteroid for fuel can be done as an unmanned drilling operation. The trick is to keep it simple, go for LOX/LH2 fuel from water. I also showed how to simply make dry ice to supply an M-type asteroid mine. That's the limit of what I would take from a C-type asteroid.

RobertDyck · 2005-08-25 23:11:19

On orbit fuel transfer: I actually presented this at the conference too. The polymer PolyChloroTriFluoroEthylene (PCTFE) has many applications in space. One is a membrane for cryogenic fuel transfer. Today the Russians transfer UDMH and N2O4 fuel from the Progress cargo ship to ISS using a membrane to separate liquid fuel from helium gas. In zero gravity if you don't use a membrane the gas and liquid will mix. With the membrane, helium gas pushes fuel out of the tank into the fuel transfer line. The service temperature of PCTFE is -240...+132°C, it's non-reactive and impermeable to oxygen, nitrogen and hydrocarbons. Oxygen is liquid at -182.96°C, methane at -161.6°C. That means you can use PCTFE as the membrane for fuel transfer of liquid oxygen and liquid methane.

Liquid hydrogen is different, it permeates just about everything and is liquid at -252°C. PCTFE or any other polymer I know is brittle when that cold, it would break when bent. To make a polymer membrane impermeable to hydrogen gas on Earth we use metallized layer. Aluminized Mylar is impermeable because of the aluminum, but of course Mylar's service temperature is -70...+150°C. One manufacturer who bid to make the propellant tank for the MRV bus of the Minuteman missile offered a titanium tank. He lost the bid but had an interesting idea of a titanium spring tank designed to roll up as propellant is drained. That maintains pressure so you can use pressure fed thrusters, no turbo pumps. A titanium alloy (Ti-5Al-2.5Sn) has been tested at 4.2°K (-268.95°C). Contrary to the name, the paper says it consists of 5.60% Al, 2.61% Sn, 0.011% C, 0.05% Fe, 0.072% O, 0.035% N, 0.0012% H. It says this alloy sustained some plastic deformation under elastic load. Does that mean it will form a self rolling spring tank at liquid hydrogen temperature? Pressurized fuel transfer without helium or pumps.

Yang Liwei Rocket · 2005-10-01 17:34:55

If all that is needed is a quick crew rotation vehicle, then it would fit this bill. But definitly not for long duration,

some quick links on the current ideas

Nasa reaches for the Moon - as a launch pad to Mars
http://news.independent.co.uk/world/sci … 313792.ece
New Spaceship Designed for Travel to Moon and Mars
http://www.voanews.com/english/2005-09-20-voa43.cfm
Can NASA repeat lunar trip?
link
NASA to Unveil Plans to Send 4 Astronauts to Moon in 2018
http://www.space.com/news/050914_nasa_cev_update.html

redhorizons · 2005-10-13 13:02:13

This argument makes a lot of sense to me.

http://www.space.com/adastra/adastra_me … 51013.html

GCNRevenger · 2005-10-13 13:55:07

The argument in the link is stupid, and avoids the one great monolithic elephant-in-room problem with piecemeal missions: you have split your payloads up. Splitting a Lunar mission into small ton-scale pieces is stupid because you couldn't possibly split your payload up into pieces that small. Even the CEV service module will weigh ~20MT. Thats to say nothing of a crushing, idea-smashing costs associated with breaking up your mission into so many (critical!) pieces.

The costs associated with building 20-50MT class rockets are high enough that you wouldn't see a huge savings over one big HLLV, and a large RLV capable of 20MT class payloads would easily cost some tens of billions of dollars. Even a 10MT class vehicle could easily top $20Bn to develop.

"SpaceShipOne provides another example"

He's right, it does provide an example, that Mr. Wright is an idiot. Anyone who invokes the holy SpaceShipOne for comparison in ANY real venture is automatically a moron.

"Small reusable vehicles can revolution access to space the way microcomputers revolutionized access to computing"

No, they can't. The smaller your payload capacity is, the less things that you can reasonably do with it.

NASA should encourage private business to get into the game, but NASA neither can nor should give up pints of its own blood to private firms who aren't first willing to stick their necks out. NASA has been burned once over Lockheed's betrayal over the X-33, and no matter how much T/Space and the like whine about "if only we had some (no strings) NASA money, we could do XYZ!," they have to step up to the plate and make a commitment to space flight. Being that these are private companies, who naturally want to minimize risk and maximize their ability to bail if things go wrong, the only way that they can make such a commitment is by coming up with their own cash to get started.

And I'm talking real money, not pretend SpaceShipOne money, the kind with nine or more digits... THEN they can petition NASA for help.

publiusr · 2005-10-21 15:20:19

Well said, well said!

CEV
http://forum.nasaspaceflight.com/forums … 3&start=61
http://forum.nasaspaceflight.com/forums … 3&start=71

SpaceNut · 2006-02-10 22:06:25

If we are to go forward with a small CEV design would on orbit refueling to aid for extended mission a need?
Ball Aerospace Completes Payload-to-Bus Integration for Orbital Express NextSat/CSC Spacecraft

The NextSat/CSC bus is part of a dual-satellite mission to demonstrate the capability of robotic refueling, reconfiguring and repairs of a spacecraft on orbit. The program is expected to be the first-of-its-kind autonomous servicing demonstration.

Hopefully the automated docking problem has been resolved.

SpaceNut · 2006-03-13 21:30:28

Another source indicating that the CEV capsule will be smaller.

NASA set to reduce CEV size as Ames starts tunnel tests

Agency says that making crew module design smaller will give performance benefits
NASA is on the verge of selecting a baseline crew exploration vehicle (CEV) design with a 5m (16.5ft)-diameter crew module, 0.5m smaller than originally considered.

Something seems not all on the up and up. It would seem that Nasa is leaning towards a Boeing build and that would make the already existing infrastructure of the Delta IV medium a good match since it is based on that value for a payload flairing.

GCNRevenger · 2006-03-14 20:03:13

No, its that with the switch from SSME to J-2 on the TheStick and using storables instead of Methane on the CEV, NASA has less mass for the capsule and needs less volume for the service module, so it only makes sense to make it a little bit smaller. We're only talking by two feet here. The fact that it would be the right diameter to fit on Delta-IV or Atlas-V is incidental most likly, TheStick is really the only option NASA has for timely launch ability required to mate with the EDS stage.

SpaceNut · 2006-03-15 09:28:02

What it does do by being able to be coupled to either the Atlas or Delta is give Nasa a means to test out the capsules design without building up the rest of the rocket or waiting for the SSME air restartable version or the restart of production of the J2-s.

Yang Liwei Rocket · 2006-03-17 01:57:29

Another source indicating that the CEV capsule will be smaller.
NASA set to reduce CEV size as Ames starts tunnel tests
Agency says that making crew module design smaller will give performance benefits
NASA is on the verge of selecting a baseline crew exploration vehicle (CEV) design with a 5m (16.5ft)-diameter crew module, 0.5m smaller than originally considered.
Something seems not all on the up and up. It would seem that Nasa is leaning towards a Boeing build and that would make the already existing infrastructure of the Delta IV medium a good match since it is based on that value for a payload flairing.

I'm not so sure about it all, Saturn-V and Energia looked like great launchers. So are Deltas and Atlas designed for manned missions or man rated ? So they want the Stick and the Ares/CaLV, the Ares or CaLV looks like one of those great Saturn-V rockets. That Delta II sometimes looked like a kind of sounding rocket, I'm amazed they got those payloads into orbit some of them looked like an Elephant payloads trying to sit on a little mouse rocket. TitanCentaur and the Shuttle launched much bigger payloads such as the Vikings, Galileo spacecraft, Cassini-Huygens. The little MERs Spirit and Opportunity are great rovers but the Delta-2 just lifted the the little Rovers out and let the Red Planet run into them, they had to come up with some risky aerobraking moves and slowed down by the bouncing payload across the Mars. Other missions like Raman, MSR, the Mars Science Laboratory can't be sent on a Delta-II because bouncing these future craft and science labs off the planet is not the best way to do this. Today NASA has no big launcher it needs foreign help from ESA and Russia's rockets that's why NASA has been asking Europe or Ariane for a lift with the future missions like JWST. Atlas has a good record the early Atlas had few failures over 70% success, then came Atlas-2 types 1991-93 it was a great launcher and now they have plans for a heavy. The new Atlas is a start and the Delta III which uses the Mitsubishi-Tank from Japanese H2 launcher was also a start for bigger payloads, but Delta-3 is expensive and has failed a number of times and I've yet to see the Delta 4 Heavy.

GCNRevenger · 2006-03-17 07:04:34

"Today NASA has no big launcher it needs foreign help from ESA and Russia's rockets that's why NASA has been asking Europe or Ariane for a lift with the future missions like JWST. Atlas has a good record the early Atlas had few failures over 70% success, then came Atlas-2 types 1991-93 it was a great launcher and now they have plans for a heavy. The new Atlas is a start and the Delta III which uses the Mitsubishi-Tank from Japanese H2 launcher was also a start for bigger payloads, but Delta-3 is expensive and has failed a number of times and I've yet to see the Delta 4 Heavy."

Um, what?

The Delta-IV Heavy and the Atlas-V 551 work just fine, and are quite powerful rockets. The Atlas II/III and V series doesn't have a 70% sucess rate, they have a 100% sucess rate. The 551 model is a "heavy," able to haul >20MT to orbit with its present stock configuration.

The Delta-III was going to be a bridge between Delta-II and Delta-IV, but since the -IV is relativly easy to build and can be fitted with a light upper stage, there is no reason to have the -III anymore. So, it was scraped after the third flight.

And, if you haven't been paying attention, Boeing did manage to launch the big Delta-IV Heavy last year which was basically a sucess. They have learned that the things take a while to build however.

The reason why NASA is looking to use the ESA's Ariane-V rocket isn't because of lifting power, the Delta-IV Heavy is every bit its equal, its because of cost. See, NASA wants to trade a free launch with the ESA for time on the telescope (saving a ~$300M Delta-IV HLV launch), since the JWST price is starting to spiral out of control just like Hubble did.

EuroLauncher · 2006-03-17 11:51:15

The reason why NASA is looking to use the ESA's Ariane-V rocket isn't because of lifting power, the Delta-IV Heavy is every bit its equal, its because of cost. See, NASA wants to trade a free launch with the ESA for time on the telescope (saving a ~$300M Delta-IV HLV launch), since the JWST price is starting to spiral out of control just like Hubble did.

The Delta rockets look very good but Delta-4H didn't do the best performances in December. The launch entered orbit at a height of about 100 km and the orbit started to decay raipdly.

GCNRevenger · 2006-03-17 11:54:53

None the less, all the major systems of the rocket performed flawlessly. The only thing that went wrong was the fuel sensor in the center core tank read a little low, which caused the main engine to shut down prematurely. Thus, the Centaur upper stage did not have the fuel required to put the payload in the proper orbit. I think that this is a minor problem that won't happen again, as the Delta-IV HLV core stage is just like its two brethern and just like the rest of the Delta-IV Medium first stages, which have thus far flown perfectly. For intents and purposes, I think this rocket can be reguarded as operational, albeit takes some time to build and prepare.

publiusr · 2006-03-23 15:26:55

Boeing is stretching it calling the one Delta IV heavy flight three successful launches due to the three CBCs. Sensor or no--it has still not demonstrated its ability to place as much as the late Titan IV in orbit. That will have to come first.

GCNRevenger · 2006-03-23 15:50:01

Boeing is stretching it calling the one Delta IV heavy flight three successful launches due to the three CBCs. Sensor or no--it has still not demonstrated its ability to place as much as the late Titan IV in orbit. That will have to come first.

What? Where did you get this idea of Boeing "tripple billing" its reliability?

And it doesn't have to "demonstrate" its maximum lift capacity, only prove that a rocket with X amount of fuel launches Y payload. The actual maximum payload can then be accurately calculated. Its simple Newtonian physics.

publiusr · 2006-03-23 16:06:10

That was from AV week--a couple issues back--with the Delta IV heavy photo.
We still need a few more Delta IV heavy flights to really prove it.

I am really impressed with Atlas V, however. They have managed to get a lot more flights of their EELV under their belt.

Mars_B4_Moon · 2006-03-24 04:44:33

Those Boeing guys should not be trying to inflate their numbers, we have enough trouble with pretenders in the private sector as it is without Boeing trying to get in on the act by inflating its figures. I like the Delta rockets but the Atlas boys are doing better and more honest work.

GCNRevenger · 2006-03-24 07:52:16

That was from AV week--a couple issues back--with the Delta IV heavy photo.
We still need a few more Delta IV heavy flights to really prove it.
I am really impressed with Atlas V, however. They have managed to get a lot more flights of their EELV under their belt.

Aviation Week? They tend to say lots of things that aren't entirely true.

publiusr · 2006-03-29 15:17:38

With respect to 'secret aircraft' yes. I have the issue at home--and I do believe the part about Boeing calling each core a seperate flight for test purposes.

Mars_B4_Moon · 2006-04-06 13:19:54

CLV Cost Escalation
http://www.nasawatch.com/archives/2006/ … scala.html
Editor's note: According to reliable sources NASA's initial internal estimate of what it would cost to modify the current SRB used for Shuttle missions to serve as the first stage of the new Crew Launch Vehicle had been around $1 billion. That estimate has been revised up to around $3 billion.

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#51 2005-08-24 12:00:10

Re: The Case for a Small CEV

#52 2005-08-24 18:16:09

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#53 2005-08-25 17:03:32

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#54 2005-08-25 20:28:54

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#55 2005-08-25 22:07:23

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#56 2005-08-25 23:11:19

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#57 2005-10-01 17:34:55

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#58 2005-10-13 13:02:13

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#59 2005-10-13 13:55:07

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