SRB-derived CEV

[najab]

><i> The G'loads would be formidable...</i><p>The propellant grain could be shaped to reduce G-loads to acceptable levels (3-4Gs).<p>><i>It's simplicity underlies a complex and difficult manufacturing process--quality control is absolutely critical to the safe operation of these things.</i><p>Quality control is essential for <b>any</b> component of a manned launch vehicle. I agree that the 'one-shot' nature of solid rockets does reduce the scope for testing.<p>><i> 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.</i><p>Man-rating isn't determined by lottery, it is determined by design. The SRB has redundant computers, hydralic systems and actuators. It can perform its mission sucessfully in the event of a single system failure, and the probabilty of a systems failure has been calculated to be less than 1%.<p>><i>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!) </i><p>The joint has been completely redesigned to eliminate the cold-weather susceptibility in the original design. There is very little chance of the new design leaking as long as the motor is operated within specifications. BTW The motor isn't too big to be monolithic, the 'problem' is that (Morton-)Thiokol is located in Utah and there was no way to get monolithic boosters back there for refurbishment. There were at least two efforts to switch from segmented to monolithic boosters, however Thiokol's home state has significant pull in Congress and the efforts were shot down each time.</p></p></p></p></p></p></p>

 

[steve82]

"It is safe - in 224 launches there has been one failure, and that was with an obsolete design"<br /><br />And the one failure we had (Challenger) would most likely have given way to an intact abort mode in this scenario. That Challenger SRB kept on trucking all the way through the breakup even though it was spilling its guts out the side. The crew would be able to escape from this vehicle, having gotten ample warning that something was off-nominal below. The main thing is, we've never seen an STS SRB explode.

 

[googlenaut]

The main advantage to solid rocket motors is not only their simplicity, but also their bulk density is much higher than an equivalent system using say LOX/LH2. The resultant reduction in cross sectional area due to a slimmer booster design greatly reduces aerodynamic drag.<br /><br />The SRB's are a robust design--but once they're lit, the ride is on! Thrust termination may be a real problem. Whereas in a liquid propellant booster, the lox valves can be commanded to shut, followed a second later by the fuel valves. The engines will shut down almost immediately. Solid boosters usually thrust terminate by blowing the whole nozzle+throat assembly off with a special shaped charge of high explosives. The engine will continue to burn--it just won't generate nearly as much thrust.<br /><br />Space shuttle SRBs contain a linear shaped charge to slice through one side of the motor casing. Internal chamber pressure will then blow the whole thing wide open. This procedure was done only once (thankfully) during the Challenger disaster when the RSO (Range Safety Officer) sent the Destruct Command to the two loose SRBs so they could not leave the immediate area in an uncontrolled manner.<br /><br />As for keeping an emergency rescue vehicle in a Silo--it was just a thought. I like the idea of having a vehicle always on Standby that can be used with short notice. Putting an unmanned CEV on top, loaded with emergency supplies could provide a needed redundant rescue capability for the Space Program. In this way it could quickly rendezvous with either a disabled orbiter or the space station. Putting something at the station will improve safety at the station--and there should be an extra vehicle there just in case--but the delta-V required to reach another orbit (for another vehicle) is prohibitively high. This requires a larger vehicle, carrying more reaction mass which must stored without maintenance for a longer time. Furthermore, things like changing orbital inclinations and altitudes

 

[scottb50]

The only conceivable alternative I can find is a hydrid solid, like Space Ship 1, whether the bulk tradeoff would work is another story. 70% of the SRB propellant is oxydizer, but storage and containment would add a lot of weight. One, probably cheaper and safer means, would be ejectable motor cores and manned vehicles with ground to orbit escape capability. <div class="Discussion_UserSignature"> </div>

 

[drwayne]

"Of course however if you want the vehicle to be aerodynamically stable you need fins."<br /><br />Note though that the fins on the Saturn 5 did very little for stability in normal flight, their primary function was to maintain stability in certain failure modes. If the Saturn 5 had been further developed, plans were in the works to remove them.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[jsbsim]

"That is without a LEM and a reduced Sm prop. load."<br /><br />Yes, that's the point - that's why I wrote that the CM/SM combo weighed about 31,000 lbs. This is a pretty fair guess at what an ISS taxi CEV might weigh. Given that the bottom limit is probably Soyuz at ~18K for three people, 31K for four doesn't sound unreasonable.

 

[jsbsim]

Jon: "Fins wouldn't be of any use higher up due to low qbar." <br /><br />Shuttle_guy: Of course however if you want the vehicle to be aerodynamically stable you need fins. <br /><br />Jon replies: Not true. The CG can be placed ahead of the CP without fins. If you watch the SRB flyout after the disintegration of 51L you can see that the left SRB (the undamaged one) actually rights itself fairly quickly and flies a fairly stable path. In that case the CP and CG were quite close to each other. If a heavy payload is placed at the top, the CG moves much further forward than the CP and the moment arm that the SRB nozzle can provide is also increased. Pitch and yaw ought not to be a problem. Roll can be controlled via jets of some kind.<br /><br />Jon wrote: "Note also that your argument about cg being ahead of CP is true for model rockets, but not required for guided space vehicles." <br /><br />shuttle_guy: Not required IF the Thrust Vector Control system can keep the vehicle stable, however the SRB TVC system does not have the capability with out a modification which is not desirable due to cost.<br /><br />Jon replies: See my comment above. This is a moot point.<br /><br /><br />Jon<br />