Tiny CEV SM module?

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willpittenger

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In the article http://www.nasaspaceflight.com/content/?cid=4659, they show a really short service module for CEV. It appears no bigger than the command capsule. Since there is no scale drawing to compare with the Apollo equivilent modules, how much of the visual size difference is due to the following:<br />* Lack of scale drawing hiding the different diameters<br />* Improved technology<br />* Solar power<br /><br />I should note that the engine bell is nearly as long as the rest of the service module. If that bell is the same size as the Apollo service module bell, that suggests the module is smaller than the Apollo version.<br /><br />The image shown is the same image that I was talking about. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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nacnud

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There is a difference in the amount of delta-v the CEV SM and Apollo SM have. IIRC the Apollo SE provided 2.8 km/s while the CEV SM only has to provide1.6 km/s.<br /><br />That is going to make a large difference in SM size.
 
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edkyle98

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"There is a difference in the amount of delta-v the CEV SM and Apollo SM have. IIRC the Apollo SE provided 2.8 km/s while the CEV SM only has to provide1.6 km/s.<br /><br />That is going to make a large difference in SM size."<br /><br /><br />Right. This is a clever design. Not having CEV do the lunar orbit insertion burn means that the SM is smaller relatively speaking) than for Apollo (which was probably bigger than *it* needed to be). As a result, NASA can design only one spacecraft to do both lunar missions and ISS missions.<br /><br /> - Ed Kyle
 
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darkenfast

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Besides the fact that the LOI burn is performed by the LSAM, the other factor in "shrinking" the CEV's Service Module is the use of solar cells for electrical power instead of fuel cells. These choices make the CEV a bit more versatile for two reasons. One, it can be "parked" for a longer time, such as at the ISS or in Lunar orbit. Two, when used for ISS or (eventually) Mars-bound crew ferrying duties, it's not hauling around larger propellant tankage than needed (the result of moving some of that to the LSAM's Descent Stage, with it's LH/LOX engines). <br />Edited to change TLI to LOI (oopsie!).
 
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subzero788

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"...the TLI burn is performed by the LSAM.."<br /><br />Correct me if I'm wrong, but I believe Trans Lunar Injection (TLI) will be preformed by the big earth depature stage (EDS). The LSAM engines will handle Lunar Orbit Insertion. <img src="/images/icons/wink.gif" />
 
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mattblack

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I think you mean 'LOI' burn. <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>
 
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geminivi

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Big change like this must mean loss of capabilities too. Anyone know what mission capabilities were lost on lunar missions? SM was overly large for ISS missions so impact there will be minimal.<br />Finally, is the CM+SM light enough to be launched by a 4 seg SRB?
 
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josh_simonson

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The CEV SM was always going to have about 1600m/s d-V. That drawing has the SM about the same length as appeared in the ESAS report (relative to CEV), just bottlenecked down at the back. Perhaps the denser hypergolic fuels require less SM volume?
 
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nacnud

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There is no change in the capablities for Luna missions, if anything it is the ISS missions that are impacted with it no longer being able to carry astronauts over 6'4" in two of the six seats. There is also some question over the unmanned mass to the ISS capablity.<br /><br />For this version of the CEV to be launched on a 4 seg SRB you would need a more energetic upper stage, which would then need more thrust to overcome gravity losses, so you would need more engines ie 2 J-2X or greater than 6 RL-10s. That would be costly.
 
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willpittenger

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<blockquote><font class="small">In reply to:</font><hr /><p>LSAM's Descent Stage, with it's LH/LOX engines<p><hr /></p></p></blockquote><br />I should note that Grumman went with hypergolic fuels for the Apollo lander for reliablity. Each engine had only one moving part: the valve releasing helium into the fuel tanks. LH/LOX need an ignition system. Personally, I doubt cryogenic fuels could be used if the lander must wait a couple of weeks before leaving the surface. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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gunsandrockets

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"I doubt cryogenic fuels could be used if the lander must wait a couple of weeks before leaving the surface."<br /><br />So far as I know, the current NASA moon plan has never included a LOX/LH2 propellant engine for the LSAM ascent stage. The ESAS plan was for LOX/CH4, which although cryogenic propellants are much more tractable than liquid hydrogen.
 
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gunsandrockets

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"Perhaps the denser hypergolic fuels require less SM volume?"<br /><br />Exactly right.
 
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gunsandrockets

Guest
"The current plan for the assent [ascent] engine is storeables."<br /><br />Link please.
 
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docm

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http://www.nasaspaceflight.com/content/?cid=4659<br /><blockquote><font class="small">In reply to:</font><hr /><p>The study, called the Design Analysis Cycle Review (DAC-2), reveals that the current CEV is overweight- as per DAC-1 study - by about 5,200 lbs. The changes being made by NASA address this problem by <b><i>including a significant shrink of the SM, decreasing its mass by almost 3,000 lbs.</i></b> The SM's length is to be reduced by about half, such that it only accommodates the volume of the spacecraft propellant tanks.<p><hr /></p></p></blockquote><br /><br /> <div class="Discussion_UserSignature"> </div>
 
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subzero788

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Try this:<br />http://www.nasaspaceflight.com/content/?id=4191<br /><br />"Engineers and designers involved with the Crew Exploration Vehicle (CEV) project are in the process of being told to cancel all work relating to methane propulsion for the LSAM (Lunar Surface Access Module) ascent stage and CEV Service Module. It is understood that NASA is moving to the use of either Hypergolic or Liquid Oxygen (LOX)/Liquid Hydrogen (LH2) as the form of propulsion for both elements of the CEV."<br /><br />Hope it helps <img src="/images/icons/wink.gif" /><br />
 
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vulture2

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Any word on the total launch weight of the CEV/SM as configured ofr ISS missions?
 
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nacnud

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Launch weight is about 27T, orbited weight is about 22T. There may be a need to reduce that, probably by reducing the amount of OMS/RCS propellant for the high inclination ISS orbit.
 
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nacnud

Guest
I don't think so, well not according to the info on NSF. The exact amount of pressureised cargo is still to be worked out I belive. and I don't think there is any capacitly for unpressurised cargo in place of propellant/tankage.<br /><br />The exposed section on the SM below is the bay you refer to, right?
 
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john_316

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Well lets start cutting metal and get this lil puppy in the air!<br /><br /><br /><img src="/images/icons/smile.gif" /><br />
 
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willpittenger

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Which modules are they bidding on? I assume it will be like Apollo where there were competitions for the LM, CM, and SM with each primary contractor picking system contractors. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
 
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