SSME does not make a good 2nd/ 3rd stage engine because of too much thrust like S_G said. I don't know the new CEV 2nd stage thrust requirement, but if they're talking about J-2 then it should be around 200K lbf range. Frankly the J-2 is not a good choice because it is a GG cycle, hence a lower Isp than the existing upper stage (vacuum-start) engine. The RS-68 engine cycle is a 'big brother' variant of the J-2. <br /><br />The RL10 on centaur upper stage is too small, with 15K lbf thrust. But its engine cycle is very efficient. Pratt & Whitney has proposed to develop a 200K lbf version of RL-10, so has Rocketdyne, to meet the new CEV requirements. <br /><br />Frankly I like some of existing Russian upper stage engines, it has the right thrust range and they have the same engine cycle like the SSME, e.g., very efficient, and they are already developed --- hence inexpensive. <div class="Discussion_UserSignature"> </div>
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As mentioned in the Space Review article, the concept and picture initially came from the Planetary Society's report<br /><br /><font color="yellow"><b>Extending Human Presence into the Solar System</b><br />An Independent Study for the Planetary Society on Strategy for the Proposed U.S. Space Exploration Policy</font><br /><br />http://planetary.org/aimformars/study-report.pdf<br /><br />The report is interesting, and I encourage people to read it.
I would think the reliability of an SSME would be much better at reduced power. If it could be returned as cargo it would be even more efficient, the extra thrust could be used to carry a return container. It does seem a waste to throw it away every time. Also, a different nozzle would probably have to be used, with an air-start it could be better optimzed for the lower air density. <div class="Discussion_UserSignature"> </div>
><i>Also, a different nozzle would probably have to be used, with an air-start it could be better optimzed for the lower air density.</i><p>The SSME nozzle <i>is</i> optimized for high altitude operation, the plume is seriously over-expanded at launch from sea level.</p>
The SSME has a nozzle area ratio of 69:1, the space engines have area ratio as high as 300:1 to get that high Isp. <br /><br />SSME can not throttle below 60% power level. At 200K thrust that would require a ~40% throttling. These deep throttling may not be realistic as it goes way out of engine operating range. <div class="Discussion_UserSignature"> </div>
That seems like an invitation for more payload then a problem. <div class="Discussion_UserSignature"> </div>
shuttle_guy,<br /><br />I am curious how the Solid Rocxet Boosters generate the power to move the nozzles. Or are the nozzles fixed at a pre-set value? <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>
Yeah, good question. Something has to power those gimbal servos. <div class="Discussion_UserSignature"> </div>
http://www.amsat-dl.org/launch/l_image062.jpg<br /><br />This is a picture of people loading hydrazine into a satellite---you tell me!<br /><br /><img src="/images/icons/laugh.gif" />
In the battle for wickedness, which is worse: LOX or hydrazine? <div class="Discussion_UserSignature"> </div>
shuttle_guy,<br /><br />Those of us who consider drain cleaner (lye) or battery acid to be nasty stuff probably never even think about what happens when a few ounces of gasoline vaporizes and then is ignited somehow. Driving around with a nearly empty fuel tank is like driving around with several sticks of dynamite, fused and ready to go. But because we don't see huge fireballs where an automobile was a moment ago very often, (if at all,) we tend to forget about how dangerous our lives are.<br /><br />People who work with hazardous materials understand them, and know what will happen if they screw up. It is the average Joe, or Jane, who mixes ammonia and bleach, throws gasoline on a smoldering fire to 'get it going', or tries to jump-start a jet ski while standing in the water that we all have to watch out for.<br /><br />Personally, the idea of hydrogen powered automobiles scares the willies out of me, because the people who will be operating them will not have had the kind of training that the folks at the Cape who work with hydrogen get. And having a hydrogen filling station on the corner? Not if the corner is in MY county, thank you.<br /><br />But thank you for the info. I was wondering if the Solid Rocket Boosters would have to be modified to have steering ability if they were to be used as a stand-alone launcher. Apparently not. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>
I guess that's what the steering fins you can almost make out in the image posted earlier in the thread are for.
Hmm...interesting. Perhaps then they would have to use bigger fins, somewhat like the Saturn 1-B. I've always loved the look of that booster with the extra-large fins - which, I guess, were needed to provide stability since it would be top-heavy with the CSM on top.
<i><font color="yellow">"In the battle for wickedness, which is worse: LOX or hydrazine? " <br /><br />Hydrazine </font>/i><br /><br />Well put it this way, 10 yrs ago I have had hydrazine soaked into my bare skin during an engine test checkouts and I am still alive today.<br /><br />I would not soak my bare hand into LOX though !!</i> <div class="Discussion_UserSignature"> </div>
I just had a physical earlier this year. I have a high chlorestrol count, blood sugar is a little high, and my liver is only 70% functional (too much grease), but I don't think I can attribute these to hydrazine exposure. <img src="/images/icons/smile.gif" /><br /><br />Now cutting out steaks, shrimp and lobster, and cheese is going to hurt!! <img src="/images/icons/crazy.gif" /> <div class="Discussion_UserSignature"> </div>
What if a cluster of RL-10s were used. 3 maybe or even 4? Originally, 5 RL-10s were clustered for an early Saturn launch.<br /><br />Forget the mass ratio, what is the total cost? $40M for a 5 segment RSRM and $15M for 5 RL-10s? <br /><br />Edit: I thought I was quoting shuttle guy's mass estimates for a RSRM plus SSME. Sorry
Shuttle_guy wrote:<br /><br /> /> The Apollo CM and SM weight in at a bit less that <br /> /> 100,000 pounds so that is not a consideration for a <br /> /> SRB launch vehicle ! Most concepts carry 5-6 people in <br /> /> the CEV. <br /><br />According to the Skylab Saturn 1B flight manual the CM/SM combination weighed 31,000 lb at liftoff.<br /><br />Jon Berndt<br />
Shuttle_guy wrote:<br /><br /> /> It does look like they may have small fins in that <br /> /> drawing however remember that the aft skirt <br /> /> of the SRB flares out also. In any event fins would be <br /> /> needed because the C.G. (Center of Gravity) of the <br /> /> vehicle must be in front of the C.P. (Center of <br /> /> Pressure) by about 0ne SRB diameter. The Aft skirt <br /> /> flare helps move the C.P. aft however the large upper <br /> /> stage and payload diameter move the C.P. fwd. <br /> /> Therefore fins are required. They probably <br /> /> would also be used for roll control. <br /><br />Fins wouldn't be of any use higher up due to low qbar. Note also that your argument about cg being ahead of CP is true for model rockets, but not required for guided space vehicles. For instance, the S-IVB stage carrying the CM/SM to orbit had (at ignition) the CG far back and the CP about 550 inches forward of that around the SM engine bell. You can notice the S-IVB ullage rockets aimed through the CG.<br /><br />Jon Berndt<br />
SRB's, or advanced SRB's, would work, combined with a liquid upper stage. I would think a vehicle with two SRB's, a few turbo-jets and wings, would be a very nice first stage, takeoff, release the orbital stage and return for re-fueling and re-use. <br /><br />The second stage would operate for lift off then throttle back approaching max-q. Prior to SRB burnout second stage engines throttle up, the vehicle separates from the first stage and establishs orbit, performing subsequent burns to get you where you want to go, to begin with. <br /><br />Once enough upper stages are in orbit payloads would be put into a minimal orbit, Tugs would retrieve them and take them to higher orbits, further increasing available payload as techiques became better refined would be expected.<br /><br /> Manned flights would be similar, but with better safeguards. Zero/Zero to orbit abort capabilities.<br /><br />It also follows that these suddenly abundant upper stages, sitting in orbit, will need something to do. Powering transit vehicles to the Moon and Mars would be a good first step, though building manned, or at least man accessable, communications platforms in GEO would probably be the first objective. With access to just three platforms, and proprietary equipment, you could have continuous, reliable service everywhere on the globe at any time. For whatever you want to put out there. <br /><br />Build this system with Lego type modules and it's easy and quick.<br /><br /> <br /> <div class="Discussion_UserSignature"> </div>
I think an SRB derived CEV is dangerous. The G'loads would be formidable--and then there is the vibration and controllability. Once you light that thing--your in for a hell of a ride! One engineer described the SRB years ago as the "...world's largest flying pipe bomb..." There is an uncomfortable amount of truth to this statement.<br /><br />It's simplicity underlies a complex and difficult manufacturing process--quality control is absolutely critical to the safe operation of these things. And I would hesitate to call them "man rated." Just because one burned all the way through, it cannot really be said that there has been only one failure in 228. Before Challenger, there were several other leaks--I don't know of any since then, but those joints are complex and are by definition a weak point in the design (because the motors are too big to be manufactured as one piece!)<br /><br />An SRB-CEV is a bad idea--maybe a good, quick and cheap way to get a rescue vehicle up with spare parts or emergency supplies (something that could be packed into a Silo--which I think is a good idea
but I wouldn't use the thing the routinely put crews into space.
but I wouldn't use the thing the routinely put crews into space.Solid rockets are proven every day by the military and have been used in submarine launchers for years. There have been problems with the Shuttle SRB's true, but they have proven very reliable and the one fault has been defined and seems to have been fixed very well. <br /><br />I would rather see a spimpler configuration, maybe a solid single piece canister as part of the fly-back first stage and a slide in propellant stack, either one piece or multiple pieces, whichever proves easier to handle. <br /><br />I also would rather have crew rescue available at a station, not in a silo on the ground. I think using the same vehicle would be the only way to do it. Orbit either a cargo module or a 5-6 person crew module with the same launch system. If nothing else the cost per unit would drop. dramatically. <div class="Discussion_UserSignature"> </div>
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