Methane dropped from CEV

[tomnackid]

Weren't LH2 and LOX were stored throughout the Apollo missions for use in the fuel cells? Or was the H2 stored in gaseous form?

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p>Hypergolics lasted on Cassini for what, 12 years?<p><hr /></p></p></blockquote><br /><br />They've lasted even longer on the Voyagers. <img src="/images/icons/wink.gif" /> (Not being spin-stabilized, the Voyagers must continue to periodically expend propellant to maintain their accurate pointing at Earth.) <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[mikejz]

I think the issues are with Bi-propellent pressure fed hypergolics. Not too much knowedge of this issues. Of cource there is always good ol'e hydrogen peroxide for RCS too...........Not that that is likely.

 

[JonClarke]

Hydrogen slush was stored for at least 84 days on the Skylab 3 mission, as I recall . There were reserve LOX tanks on Mir as well, However, those tanks were comparitively small and thick walled compared to what would be used for propellants.<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>

 

[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." <br /><br /> />Not true, Hypergolic propulsion is a technology that is highly developed. No Lox/Methane propulsion system <br />has ever been developed to a space rated operational level. <br /><br />That was in response to a post suggesting a new hypergolic engine could be built using new fuels or geometry to significantly increase ISP. A legacy type hypergolic engine aught to be relatively cheap to put together, but a new hot-rod hypergolic engine would not.<br /><br />In removing a new methane engine from the requirements, it allows the contractors to choose whatever propulsion system can get the job done. They'll pick the cheapest option and go with an existing engine, or a new one that isn't very innovative.

 

[scottb50]

I still don't see the allure of methane. Lower performance, with basically the same operational difficulties as Hydrogen. <br /><br />You still have to take it as a liquid, because of the low performance, and you have to take LOX anyway either way. True, methane can be liquified at much lower temeratures, but Oxygen needs liquification and cryogenic storage and Hydrogen is just a little colder with the same basic requirements. The added structure to house Hydrogen is more than compensated for by the weight of Hydrogen compared to methane for equal performance.<br /><br /><br />The big problem I see is the weight of hypergolics. Water is much easier and safer to launch and does minimal environmental damage, both as a fuel and a health hazard. <div class="Discussion_UserSignature"> </div>

 

[scottb50]

And don't forget all that Carbon your hauling off the launch pad. <div class="Discussion_UserSignature"> </div>

 

[JonClarke]

What existing engines have the thrust or the throttle control neccessary, especially for the descent phase? Can the LM engines be rebuilt? Can they be improved thrust-wise, or clustered? They had an Isp of 311, not wonderful, but better than the 280 seconds that people have been quoting.<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>

 

[tap_sa]

<font color="yellow">"Hydrogen is just a little colder with the same basic requirements."</font><br /><br />Boiling points of hydrogen/oxygen/methane: 20K/90K/112K. The step from 20K to 90K isn't 'just a little', it's 4.5 times hotter. The difficulties of fooling at cryogenic temps is not linear. Cooling something from 300K to 230K is peanuts but cooling something from 90K to 20K is difficult and quite inefficient. LOX and methane stay liquid in space conditions if you put the tank in permanent shade.

 

[henryhallam]

<font color="yellow">the prop needs to be recirculated to the engines to prevent gas bubbles due to the Methane going to a gas state.</font><br /><br />Could you explain that in a bit more detail? is it an ullage issue?

 

[henryhallam]

Thanks!

 

[propforce]

<font color="yellow">If you do not then the Liquid Methane will change phase to a gas as it hits the non cryogenic temp lines and the valves. Thus the L. methane has to be circulated from the engine area to and back to the tank</font><br /><br />Most excellent and concise explanation! <br /><br />However; I was under the impression that RCS was suppose to be using <i>gaseous</i> oxygen and methane, e.g., GO2/GCH4?<br /> <div class="Discussion_UserSignature"> </div>

 

[tap_sa]

<font color="yellow">"I was under the impression that RCS was suppose to be using gaseous oxygen and methane, e.g., GO2/GCH4?"</font><br /><br />So was I, but if you read the ESAS report CEV part 5, page 242 bottom it states that RCS operates on liquid propellants. RCS thruster are film-cooled and were supposed to act as backup if the SM main engine fails. But who knows now if methane gets axed, perhaps SM will get the same GOX/ethanol system than CM?

 

[vt_hokie]

<i>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."</i><br /><br />I predicted a long time ago that we will end up getting the LEO version of the CEV capsule, and not much else. The rest of the ESAS fluff may just have been a way to sell the public on the downgrade to a cheap capsule for transport to/from ISS.

 

[JonClarke]

Ah, so it is ONLY the ascent stage that is going to change to hypergolics?. I missed that.<br /><br />Thanks<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>

 

[nacnud]

Yeah sorry, I should have mentioned that at the start.

 

[JonClarke]

OK, that makes much more sense. I will still miss the methane because of its longer term applications, but LOX-H2 descent and hypergolic ascent seems workable.<br /><br />Thanks<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>

 

[josh_simonson]

The earth return stage will also be 'x' propellant instead of LOX/Methane. The mass may be small, but the propellant to get it there is not... <br /><br />Another intersting thought, is if the lunar ascent stage is underpowered, they might go with leaving more infrastructure on the moon. As it is now the entire lunar hab is launched back to LLO. That's hardly expandable.

 

[JonClarke]

I assume the whole spacecraft is fairly conceptual at this stage. It should be possible to have a surface hab in the descent stage that remains behind and can be used again later. The crew only have to spend a few hours in the ascent stage so it can be really cramped (maybe 10 m3). Something like this was a feature of the Rockwell Mars Excursion Module design in 1967. You would have to have exhaust baffles to avoid damage, but it should be possible.<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]

1): For the LSAM Ascent Stage -- If the most efficient hypergolic propellant combination is used in concert with the most modern engine designs -- N2O4/Aerozine-50: 293-370s isp.<br /><br />2): Plus not taking quite so much rocks and regolith back.<br /><br />3): AND modern composite materials are used, which didn't exist in Apollo: then they just MIGHT be able to pull this thing off. And perhaps using LOX/Ethanol (or Kerosene) for the CEV's SM is not out of the bounds of possibility?<br /><br />http://www.astronautix.com/props/loxcohol.htm<br /><br /><br /><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>

 

[chriscdc]

The ideal solution would be to somehow use the descent stage fuel tanks as a wet lab, but that would need one large tank, or the mass of the airlocks would be prohibitive.

 

[trailrider]

The PERMISSION to use something other than LCH4/LO2 gives the green light for L-M to go to hypergolics. Although there will be gravity on the Moon to settle the propellants against the feed lines, I suspect there may be conditions once the ascent stage is in lunar orbit when one might want to re-ignite the engine. If so, Lock-Mart would have an edge as they have experience with the Shuttle orbiter RCS tanks and thruster system, PLUS all the Titan II/34-D/IV LV's using N2O4/Aerozine 50. So far as long-term storage of these propellants, there is plenty of experience with loaded tanks sitting for YEARS, and I know of only one incident with Titans where there was a problem, and that started with a dropped wrench, and subsequent explosion due to flooding the silo with water, that caused a reaction with the N2O4 (acid and water...chem class fans???). <br /><br />Ad Luna! Ad Aries! Ad Astra!<br /><br />(Sigh!) Still, perhaps L-M or even N-G might go ahead with research on the LCH4 engine (though that would seem to be more in the province of Boeing (Rocketdyne) or Aerojet.

 

[JonClarke]

Well Matt, if they got away with it in Apollo they will get away with it here, I am sure. I can't see them getting an Isp out of the hypergolics less than with the LM, which was 311. <br /><br />Same with the service module.<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]

True enough. With the "J-Series" LM they'd managed to squeeze another 1.5 seconds isp out of the descent engine. And with modern lightweight materials the LSAM Ascent Stage with hypergolics could probably do the job. The important thing is it's ESSENTIAL to have LOX/LH2 in the Descent Stage so as to have good LOI capability for the CEV/LSAM 'stack' and especially wide-ranging landing ability anywhere on the lunar surface. <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]

Agreed.<br /><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>