Methane dropped from CEV

[nacnud]

More details over a nasaspaceflight.com<br /><br />It seems a shame but if it keeps the CEV on time and under budget then needs must...

 

[henryhallam]

Does seem a pity.. I would have liked to have seen a methane engine. I bet they go with hypergolics rather than LH2/LOX though. It's what I'd want if it were my butt sitting homesick on the moon...

 

[shuttle_rtf]

Hey all - sorry I've not been around, just too busy with the site, etc.<br /><br />Had this link posted over on our forum and thought it best to come here and address this head on.<br /><br />SG, how are you doing? Good I hope.<br /><br /> />The LSAM is to be Lox and Liquid Hydrogen, Lox Methane does not have the desired performance. The CEV spec from NASA was Lox Liquid Methane for the Lunar ascent stage and the Service Module, never the LSAM. <<br /><br />Might have been lost in the way I've worded it, but as you can see I said LSAM ascent stage, as in (and to quote the ESAS Final Report, Section 8, graph 8,8) "pressure-fed LSAM methane ascent and CEV SM engines."<br /><br /> />I think the report at NASAspaceflight is not correct. We have heard that there is a possibility of going to hypergolic prop for the SM and Ascent stages if the Lox Methane system does not mature in time for the Lunar missions.<<br /><br />The report I wrote simply states that it is being related, today, that SE&I have directed for all methane-related propulsion work to end.<br /><br />I will PM you some more.

 

[steve82]

It could also mean they are getting real serious about protecting the schedule and doing whatever they can to minimize risks to get this puppy up ASAP.

 

[mattblack]

Dropping Methane, especially for a CEV stored in Lunar orbit for 6-month missions, is a BIG mistake. Hypergolics aren't efficient enough and in Lunar orbit, let alone Mars orbit, LH2 can boiloff. This is a problem Methane (CH4) barely has. And deleting the methane requirement for the LSAM Ascent Stage means this vehicle wont be able to be upgraded for Mars ISRU use, unless you're near the poles and use water ice.<br /><br />'Manana, manana' is a mistake: they should be aiming for the future ISRU from the beginning, otherwise all they'll get for the first Mars mission will be a 20-day stay 'flags & footprints' landing. On the other hand, I strongly suspect that'll happen anyway. Could this be part of the Shuttle/ISS budget crunch: taking away advanced engineering studies and "related science"?<br /> <div class="Discussion_UserSignature"> <p> </p><p>One Percent of Federal Funding For Space: America <strong><em><u>CAN</u></em></strong> Afford it!!  LEO is a <strong><em>Prison</em></strong> -- It's time for a <em><strong>JAILBREAK</strong></em>!!</p> </div>

 

[josh_simonson]

Forcing the use of hydrogen engines could make CEV use as an ISS lifeboat impractical, and also sabotage the lunar program to preclude extended stays. - Or the use of hydrogen will force them to develop space-based re-liquification capability. This would do the heavy scientific lifting towards building a commercial LEO fuel depot. Mike Griffin has said he'd like to bootstrap such a thing, and it may be possible that they feel that the payoff of developing the technically risky reliquification capability is more useful in the immediate future than the moderate-risk methane engines.<br /><br />Re-liquification is more important for ISRU than Methane is. Methane can always be cracked for H2 in-situ.<br /><br />If NASA does neither it would be pretty sad.

 

[cuddlyrocket]

We must remember that the CEV has more purposes than lunar missions. It is also the means of LEO access, in particular to the ISS, both in crew rotation and cargo supply.<br /><br />Congress is unhappy at the current two-year gap between the end of STS and the bringing into service of the CEV. There is also a funding gap in the later years of the STS. Both these would probably be mitigated by not having to develop an entirely new engine, but to go with something known. The inferior performance of hypergolics is unlikely to be significant for LEO missions as the CEV's SM is over-specified for that purpose (it was sized on the basis of lunar mission requirements). <br /><br />As Dobbins said (at the other site), the CEV (and the LSAM) is modular. Once it's up and running, time can be taken to develop Methane engines, which I agree would be desirable for long-stay lunar missions (hypergolics having lower Isp and Hydrogen being bulkier and far more difficult to store aboard for long periods). We are a long way from lunar missions, let alone long-duration ones, and even further from Mars missions.

 

[JonClarke]

"Hypergolics aren't efficient enough" <br /><br />Care to expand on this Matt? I would not have thought the difference between 450 and 380 seconds was that critical<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[mattblack]

What I should have said is that hypergolics, though well-understood, cannot compare to Methane and cyrogenics such as hydrogen:<br /><br />CH4 (methane): isp 380+plus seconds.<br />Nitrogen Tet. & Hydrazine: isp 300+plus seconds.<br />LH2 (hydrogen): isp 450 seconds.<br /><br />http://www.asi.org/adb/04/02/04/fuel-options.html<br /> <div class="Discussion_UserSignature"> <p> </p><p>One Percent of Federal Funding For Space: America <strong><em><u>CAN</u></em></strong> Afford it!!  LEO is a <strong><em>Prison</em></strong> -- It's time for a <em><strong>JAILBREAK</strong></em>!!</p> </div>

 

[JonClarke]

that's about right for methane-LOX, but a bit pessimistic for hypergolics.<br /><br />N2O4/Aerozine-50 293-370 s http://astronautix.com/props/n2oine50.htm<br /><br />N2O4/UDMH 247-342 s http://astronautix.com/props/n2o4udmh.htm<br /><br />N2O4/MMH 238-347 http://astronautix.com/props/n2o4mmh.htm<br /><br />So 340 seconds would seem a not unreasonable figure for hypergolics.<br /><br />Jon<br /><br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[gunsandrockets]

"So 340 seconds would seem a not unreasonable figure for hypergolics."<br /><br />What American pressure-fed hypergolic-engine of the right size gets that high an ISP? If the problem with a CH4/LOX engine for NASA is cost of development (as seems most likely), then NASA will turn to existing design hypergolic engines. The old Apollo engines only got about 310 ISP performance.<br /><br />

 

[chriscdc]

Perhaps they are just dropping it for the immediate future and will get back to developing it before they get to the moon. Perhaps they just looked at the dates and don't want to rely on soyuz capsules getting to the ISS until they build the new engine. <br /><br />They want the CEV up in 2012 and will be going back to the moon in 2018. The first few moon missions don't sound like they will stay there long and so minimise the effect of boil off. Then they won't get to mars until 2025 at the earliest so they may just be delaying development.

 

[mikejz]

I remember one tech that Nasa wanted to develop was zero-boil off tanks, so I wonder if this has something to do with that. (That they feel confident enought in that tech to extend it's implementation).<br /><br />Also, what is the current state on size/weight/cost of active cooling?

 

[JonClarke]

Since we are talking the performance of both undesigned and unbuilt engines at this stage 340 sec. seems to be to be a reasonable figure for a conceptual advanced hypergolic engine, not too high and not too low. I would assume that the need for high performance would push the design towards the higher end of the performance range anyway, especially as it would be an alternative to LOX-methane. Unless somebody has information to the contrary.<br /><br />Jon<br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[josh_simonson]

If they can't afford to build an all-new pressure fed methane engine, they probably can't afford to build an all-new pressure fed hypergolic engine either. They'll likely go with something that's currently available, or reconstruct an apollo engine like they're doing with the J-2s.

 

[tap_sa]

<font color="yellow">"Since we are talking the performance of both undesigned and unbuilt engines at this stage 340 sec. seems to be to be a reasonable figure for a conceptual advanced hypergolic engine, not too high and not too low."</font><br /><br />I'd venture to say 340s is wishful thinking for a <i>pressure fed</i> hypergolics engine, a pump fed with XXL-nozzle might do it. But as you may have already read from NSF the latest word is that it's gonna be LH2 after all.

 

[JonClarke]

What are the practical implications of using LH2, other than the very low density (= very large tanks), the high leakage rate and the need for refrigeration to present boil off?<br /><br />If, as has been suggested, they might use an existing LH2 engine, or cluster of engines, has the thrust and fine throttle control needed for a lunar landing?<br /><br />How fixed in concrete is the decision - might we see a change back to methane, or on to hypergolics in the future? I get the impression that things are very fluid at the moment.<br /><br />Jon<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[trailrider]

Oscar SIERRA! (Sigh!)<br /><br />Here we go again! First we pull back from one of the things necessary to get to Mars. Then we pull back from LONG duration Lunar missions. And when the next blow comes, it will simply be, "We can't afford to go to the Moon! Just replace the Shuttle."<br /><br />These compromises are what turned the Shuttle from a true STS to what we wound up with. And we will repeat our mistakes of the past! Sooner, rather than later, the Moon missions will be killed altogether.<br /><br />I HOPE I'm wrong! But I'm sorely afraid that we are going to be nibbled to death by butterflies! Unless, of course, we can sign up for Berlitz lessons in conversational Chinese! <img src="/images/icons/frown.gif" /><br /><br />Ad Luna! (Ad Aries...?) (Ad Astra???)

 

[nacnud]

The thing is switching from LOX/CH4 to hypergolics might actually make long duration Luna missions more achievable as the long term storage of these fuels is much easier. I think you would have to actively refrigerate LOX if not CH4 as well.<br /><br />Also I don't think that it is going to affect the payload of a cargo only LSAM.<br /><br />Perhaps once a base is up and running with a power supply to help long term storage of LOX/CH4/LH2 these options will be looked at again. <br /><br />I just hope that dropping this now shows that Griffin and NASA are on top of things, cancelling it now an building what they can with the available money is much better than spending the money on a theoretically better design that won't get built because there is no money left.<br />

 

[scottb50]

The thing is switching from LOX/CH4 to hypergolics might actually make long duration Luna missions more achievable as the long term storage of these fuels is much easier.....<br /><br />I seem to remember storage of hypergolics being the reason Soyus can only stay at ISS for a limited time. <br /><br />The simplest solution all around is water and solar power. Generate Hydrogen and Oxygen gasses from water with solar power and store it under pressure to power fuel cells. For propulsion cryo-coolers would keep enough LH2 and LOX cold for the planned engine firings. <div class="Discussion_UserSignature"> </div>

 

[mikejz]

If I remember correctly, there were issues with leaking hypergolics with Apollo during its long stays at Skylab.

 

[spacester]

Terrific posts here; my first reaction was a bit of disappointment but as has been said the main thing is to get lunar capability. Yet we indeed must be vigilant that this is not a slippery slope to a compromised vehicle. I think Dr. Griffin will not allow his new spaceship to be anything less than kick-ass, so I'm at peace with this decision.<br /><br />My reading of the relevant documents indicates that methane has not been "dropped" per se. They dropped the <i>requirement</i> for that particular fuel but they are not <i>excluding</i> it from the list of possiblities. The contractors can still propose methane engines from what I can tell.<br /><br />Speaking of which, why does kerosene not get any attention in this discussion?<br /><br />I have a hard time imagining that we'll end up with hypergolics, it's just too expensive to handle.<br /><br />Can the same tanks and plumbing be used for multiple fuels? This would enable the change-out of only the engine system to create a methane-fueled vessel for Mars. The lower dV capability compared to LH2 might still be enough for its mission.<br /><br />This might represent the first steps down the path towards in-space storage and transfer of LOX/LH2 to true spaceships, and that is very alluring.<br /> <div class="Discussion_UserSignature"> </div>

 

[najab]

The limiting factor on Soyuz duration is the propellants they use are corrosive to the seals in the propulsion system. I'm confident this isn't an insurmmountable engineering problem - and even as is, 6+ months is plenty of endurance for a Lunar mission.

 

[JonClarke]

Hypergolics lasted on Cassini for what, 12 years? How long between fuelings for hypergolic ICMBS, like all the Soviet ones and the Titan series?<br /><br />Hypergolics despite their toxicity, have a good operational record. There was a leak on Soyuz T9 mission to Salyut 7 during a progress refueling, and of course the ASTP leak, which was due to operator error. I don't recall any problems on actual missions, although there have been some nasty ground accidents, of course.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[cuddlyrocket]

"They dropped the requirement for that particular fuel but they are not excluding it from the list of possiblities. The contractors can still propose methane engines from what I can tell."<br /><br />Perhaps the contractors - who are going to be LM, according to people on the inside posting on the boards - approached NASA and said: Look, we can perform the missions much more cheaply, or get the thing built much quicker, if you let us use something other than LOX/Methane? Given that Mars is decades away, that might be difficult to resist in this climate of limited budgets and development time.<br /><br />"Speaking of which, why does kerosene not get any attention in this discussion?"<br />Or ethanol. Or even ethane, propane etc. However, those same 'inside sources' say it will be LH2.