SpaceDev presses on with Dream Chaser

[ragnorak]

<br />I guess they have to be hybrids because with a cryogenic system and the HL-20/Dream Chaser strapped to the side of the boosters they would have the Shuttle foam problem all over again. I like the HL-20 lifting body approach. It's about time more people started tapping NASA for the tech its developed over the years, look at Bigelow Aerospace, what a great job they did with their Genesis I spacecraft!<br />

 

[holmec]

docm, you should tape that and show us. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[docm]

The paraffin or the plexi? <br /><br />The paraffin should be ready this summer, but the plexi's NOX parts were cannibalized for it. Might be able to put together a demo using a GOX brazing torch tank though, hmmm....<br /> <div class="Discussion_UserSignature"> </div>

 

[josh_simonson]

>"Hybrids, since half the fuel is in the engine, cannot possibly be used in an 'engine out' manner. If the igniter or oxidizer valve fails you are stuck."<br /><br /> />You're grasping at straws here. A liquid propellant propulsion system also has an igniter and oxidizer valves that could fail...another commonality between liquid and hybrid propulsion systems. Liquids have the additional possibility of a fuel valve failure...something hybrids don't have. <br /><br />No I'm not. Hybrids require a valve and an igniter to fire while hypergolics only require 2 valves. That's a very comparable level of reliability. Add in the poor ISP and fuel fraction performance and it's clear that hybrids place is in booster stages, not space stages.<br /><br />Hybrids may also have handling issues that are half as bad as that of large solids (weighing about half as much un-oxidizered), spacedev hasn't built one big enough yet for this to be much of an issue, but the weight of the shuttle SRBs create a huge ripple effect of cost throughout the shuttle/aries programs. Dreamchaser would either have to be assembled on the pad with heavy machinery, or will need a shuttle-class crawler transporter to move around.<br /><br />Hybrids do have an area where they are showing promise, competing with solid boosters, but beyond that application space they aren't really suitable. SpaceDev, being a hybrid rocket manufacturer, of course tries to hype them as much as possible; this should be taken with a grain of salt. Supposedly their next generation hybrids will outperform solids, if that's the case then buisness should flock to them for both military and civil applications. I hope that's the case, we'll see.

 

[holmec]

>The paraffin or the plexi?<br /><br />The paraffin should be ready this summer, but the plexi's NOX parts were cannibalized for it. Might be able to put together a demo using a GOX brazing torch tank though, hmmm.... <<br /><br />Yeah man, pass on the coolness! <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[docm]

"No I'm not. Hybrids require a valve and an igniter to fire while hypergolics only require 2 valves."<br /><br />Wow ... 2 parts vs. 2 parts, and I bet a repeating igniter is really hard to design <img src="/images/icons/rolleyes.gif" /><br /><br />That igniter is likely to be <b><i>very</i></b> reliable and the hybrid more than a bit safer than hypergolics, where an incidental leak can go bada-BOOM and the fuel handling is dangerous <img src="/images/icons/tongue.gif" /> <div class="Discussion_UserSignature"> </div>

 

[Swampcat]

<font color="yellow">"No I'm not. Hybrids require a valve and an igniter to fire while hypergolics only require 2 valves. That's a very comparable level of reliability. Add in the poor ISP and fuel fraction performance and it's clear that hybrids place is in booster stages, not space stages."</font><br /><br />Well, it's true that you originally expressed concern for using hybrids as upper stages due to their lower I_SP compared to liquids, but I don't see where you're coming from concerning hypergolics or other liquid propellants with those arguments. As docm says, two valves to fail vs. one and an igniter is hardly a reliability trade-off. Throw in the risk of dealing with dangerous hypergolic chemicals and the only thing they gain you is some I_SP. I would assume SpaceDev has done their homework and understands those trade-offs.<br /><br /><font color="yellow">"Hybrids may also have handling issues that are half as bad as that of large solids (weighing about half as much un-oxidizered), spacedev hasn't built one big enough yet for this to be much of an issue, but the weight of the shuttle SRBs create a huge ripple effect of cost throughout the shuttle/aries programs. Dreamchaser would either have to be assembled on the pad with heavy machinery, or will need a shuttle-class crawler transporter to move around."</font><br /> <br />These issues are no different from those you would deal with in any large vehicle. The beauty of a hybrid fuel grain is that it is inert and takes a fair amount of effort to light. Solids, OTOH, are relatively dangerous to handle with their fuel and oxidixer already mixed.<br /><br /><font color="yellow">"Hybrids do have an area where they are showing promise, competing with solid boosters, but beyond that application space they aren't really suitable. SpaceDev, being a hybrid rocket manufacturer, of course tries to hype them as much as possible; this should be taken with a grain of salt. Supposedly their ne</font> <div class="Discussion_UserSignature"> <font size="3" color="#ff9900"><p><font size="1" color="#993300"><strong><em>------------------------------------------------------------------- </em></strong></font></p><p><font size="1" color="#993300"><strong><em>"I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."</em></strong></font></p><p><font size="1" color="#993300"><strong>Thomas Jefferson</strong></font></p></font> </div>