Reusable 1st stage question

[jimfromnsf]

"f we had an engine that imparted twice as much energy to the propellant as current engines,"<br /><br />It is the other way around. Propellants impart the energy

 

[gunsandrockets]

<It is the other way around. Propellants impart the energy><br /><br />Oh really? Is that how an NSTAR ion engine works? Or a NERVA nuclear thermal rocket engine?<br /><br />Propellants impart the energy only in conventional chemical rocket engines or in cold-gas thrusters and not in every type of rocket engine. When describing the entire universe of possible rocket engines it is incorret to claim that "propellants impart the energy". You are 'correcting' something which is not a mistake!

 

[jimfromnsf]

"Is that how an NSTAR ion engine works? Or a NERVA nuclear thermal rocket engine? "<br /><br />Now I have to correct your mistake<br /><br />We are talking launch not in space uses. Neither of those two are practical for launch<br /><br />Read first, then post.

 

[gunsandrockets]

<Read first, then post. ><br /><br />Ah, if only you would follow your own advice. <br /><br />Even in the limited context of only launch vehicle applications, that universe still includes more than just chemical rockets.

 

[Boris_Badenov]

<font color="yellow"> Even in the limited context of only launch vehicle applications, that universe still includes more than just chemical rockets. </font><br /><br />So true.<br /><br /> PARAMETRIC ANALYSIS OF PERFORMANCE AND DESIGN CHARACTERISTICS FOR ADVANCED EARTH-TO-ORBIT SHUTTLES <br /><br />Here are the plans for an SSTO Nuclear Powered Shuttle courtesy of NASA 1972. <div class="Discussion_UserSignature"> <font color="#993300"><span class="body"><font size="2" color="#3366ff"><div align="center">. </div><div align="center">Never roll in the mud with a pig. You'll both get dirty & the pig likes it.</div></font></span></font> </div>

 

[kelvinzero]

Beamed power thermal propulsion is another way of putting more energy into the propellent than chemical rockets. Also has the advantage that it would not require carrying such an explosive mix. However that deserves a thread of its own.<br />http://en.wikipedia.org/wiki/Beam-powered_propulsion#Thermal_propulsion <br /><br />I suspect 3-stage rockets are given a bum rap, and reusable rockets would become practical without dramatic new technology if we had a motivation to fly them as often as 747s etc. Comments?

 

[jimfromnsf]

I said practical. Nuclear is not practical for launch applications

 

[gunsandrockets]

Buh-bye!

 

[drwayne]

One *minor* qualification on the "only thing stronger"<br /><br />There are in fact chemical combinations that have better Isp and Isp - density factors than LH2/LOX - but they involve nasty stuff like Flourine and are very difficult to deal with and of course you probably do not wish to use them in the atmosphere...<br /><br />I said it was a *minor* qualification.<br /><br /><img src="/images/icons/smile.gif" /><br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[vulture2]

I remember talking to an engineer at Bell Aerospace many years ago. They had been experimenting with a thruster using liquid fluorine as an oxydizer. A drop of fluorine leaked from a valve and hit the concrete floor. it detonated with a sound like a firecracker. They decided fluorine was a little too reactive. <br /><br />For a liquid-fueled first stage, thrust is the limiting factor; hydrocarbon propellant is much denser than LH2 and allows the fuel tank to be much smaller and uninsulated, and the engine to be smaller and lighter than a hydrogen-fueled engine of the same thrust. Hence the Saturn, Atlas, etc used hydrocarbon fuel for the first stage and hydrogen for upper stages where weight and Isp are more important and less thrust is required. I would assume the same considerations apply for a reusable system.<br /><br />Re: PARAMETRIC ANALYSIS OF PERFORMANCE AND DESIGN CHARACTERISTICS FOR ADVANCED EARTH-TO-ORBIT SHUTTLES mentioned above, the report talks about how useful a higher Isp would be, then concludes that the only credible way to achieve it is nuclear-thermal which isn't likey to be acceptable for launch. Consequently it seems a futile exercise. <br /><br />To me we should not focus solely on Isp as the solution; the problem is launch cost, not mass fraction, and fuel costs are an insignificant part of launch costs.

 

[drwayne]

Chlorine compounds, such as ClF5, are indeed nasty, satisfying that criteria by the fact they are hypergolic with just about anything, including asbestas and things you tend to try to put fires out with.<br /><br />I have seen a fair amount of work done with a Flourine/LOX mixture (FLOX) as an oxidizer. It still has a kick, and is not as hard on seals and such.<br /><br />I have a throughly fascinating book on my nightstand called "Ignition" - it covers with a certain sense of humor a long history of fuel/oxidizer experimentation, and the errr....more interesting results.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[vulture2]

>>Thats why you build a high strength housing and cast the motor segments in throwaway inserts.<br /><br />This is certainly a reasonable approach for smaller solids. I am uncertain it would be practical for something the size of the SRB. Even with the full-thickness steel case, the fuel segments are so heavy they sag into an egg shape during the trip from Utah an often have to be forced back into a circle by huge presses at KSC. I am dubious a thinner case could support the weight, and the pressure and temperature during launch are so high, it's hard to see how welding of the inset to the rocket casing could e avoided.

 

[scottb50]

I'm thinking more on the lines of a multiple layer tube with Carbon/Carbon inner windings and high strength kevlar or similar material outer windings held inside an outer cage.<br /><br />The propellant segments could be kept small enough that they could be shipped in containers to maintain their shape and integrity. If the propellant casing is Carbon/Carbon with an ablative inner coating it would absorb the burn forces protecting the tube. After use it would be removed and refurbished for reuse.<br /><br />I'm thinking an SRB structurally at least 50% lighter than the Shuttle with the same performance. <div class="Discussion_UserSignature"> </div>

 

[gunsandrockets]

<For a liquid-fueled first stage, thrust is the limiting factor; hydrocarbon propellant is much denser than LH2 and allows the fuel tank to be much smaller and uninsulated, and the engine to be smaller and lighter than a hydrogen-fueled engine of the same thrust. Hence the Saturn, Atlas, etc used hydrocarbon fuel for the first stage and hydrogen for upper stages where weight and Isp are more important and less thrust is required. I would assume the same considerations apply for a reusable system.><br /><br />A hydrogen engine capable of changing the O/F mixture ratio during flight might obviate the need for a hydrocarbon engine. By not running at a typical high-ISP fuel rich mixture, a hydrogen engine might mimic a lot of the performance of a hydrocarbon engine. Since propellant density is the combined density of the fuel and the oxydizer and LOX is pretty dense. <br /><br /><br />During a little googling, I discovered that J-2 engines had a slight programmed adjusment in mixture ratios that improved vehicle performance, and all that just from careful loading of the propellant tanks to control feed as they ran out (and not from any kind of throttling). I also wonder about the potential of the RS-68 engine. From what I found the RS-68 can throttle but I wasn't able to find if it could also adjust the mixture ratio. Maybe this is a path for future enhancement?<br /><br />

 

[vulture2]

Just keep in mind that an oxygen-rich exhaust is quite corrosive to the nozell.

 

[drwayne]

Another resource that might be of interest:<br /><br />http://yarchive.net/space/rocket/fuels/fuel_table.html <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[gunsandrockets]

<Just keep in mind that an oxygen-rich exhaust is quite corrosive to the nozell.><br /><br />I think running oxygen-rich would degrade a hydrogen engine ISP too much anyway; one number I saw for a GOX + hydrogen rocket that did not run rich was an ISP of 360 seconds, quite a drop from the customary hydrogen-rich ISP of 450 seconds.

 

[vulture2]

Assembling the segments is one of the more costly and dangerous parts of the operation, and the cost of a composite shell wouldn't be significantly more if it were thick enough to tolerate flight pressure.<br /><br />So it might be considerably more practical to use a single expendable composite shell to cast the fuel grain, and bolt on a recoverable aft skirt containing the nozzle, thrust vector control, and all the electronics. At burnout the case could be severed by a circumferential linear shaped charge just forward of the aft skirt attach bolts and the aft section recovered with a small parachute and bolted onto a new composite shell while the empty shell, now uaseless, hits the ocean at full speed. This would be much cheaper than recovering the whole booster, and hey, you'd have a free built-in zero-thrust abort mode. What a concept! <br /><br />Don't look for it any time soon, though. The monolithic fuel grain would be to big to ship by rail, and would have to be cast at a plant with water access, better yet at the launch site. Utah would not be feasible.

 

[scottb50]

I was thinking more along the lines of a fixed outer frame and a fairly thin inner tube. The propellant segments would slide into the tube and the aft end of the frame with the attached nozzle would be bolted in place.<br /><br />Once the first stage lands the aft section is unbolted, the spent segment tubes removed and replaced with new ones. No parachutes or separation needed. Nozzles would have an ablative coating that could be renewed after flight, or possibly the nozzle could simply be replaced, hydraulics and the rest of the nozzle assembly would be reused. <br /><br />propellant segments would basically be like those used on the Shuttle, except they would be a much lighter tube that fits into a single piece tube that is encased in an outer cage that is an integral part of the airframe. <div class="Discussion_UserSignature"> </div>

 

[gunsandrockets]

Yeah, whatever happened to FLOX? According to "Ignition!" FLOX was the wave of the future and HTHP was a dead end. Yet look at what's going on in the the world of rockets today.

 

[drwayne]

The toxic element is still there in FLOX - so its pretty well restricted to upper stage/space applications. I know of a program or two that have planned for using it in that role, but it has not happened.<br /><br />(Isn't "Ignition" a "blast" to read - the subtle sense of humor about the process makes me roll in the floor sometimes - I had to go through a special service to get it some years ago - boy - it was worth it)<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[vulture2]

"No parachutes or separation needed."<br />I am curious to know how the stage would actually land, without parachutes. Actually, I'd like to hear what everyone else thinks is the best way to actually land a recoverable stage. Of course the Shuttle uses a fixed delta wing, but this imposes weight, drag, and a pretty high touchdown speed, particularly since a reusable first stage could easily be larger than the orbiter. At least a liquid-fuel pump-fed stage would be lighter than the SRBs. What about landing? piloted or autonomous? Land or water?<br /><br />

 

[vulture2]

"The toxic element is still there in FLOX"<br /><br />The constant focus on performance to the neglect of overall cost has been a continuing problem in our space program. Every time we've accepted a toxic fuel, (i.e. hypergols) thinking that it would get easier to handle with experience, in reality it has become even more expensive to deal with as the years go by and more hazards and hidden costs of ownership are discovered. <br /><br />The performance boost with fluorine is fairly small, and it is "really" hard to handle. I remember a fellow who just got a trace of HF on his hand; it gets absorbed into the tissue and was still burning days later. IMHO it would be much cheaper to use LOX and make the rocket a little bigger.

 

[webtaz99]

What about 2 parafoils, one on each end. This would give control of both attitude and course. The stage (or strapons) will travel downrange (probably over water for safety), and it would save $$ and saltwater exposure to get it (them) back to land. Which of course means bringing them it (them) down slower. <br /> <div class="Discussion_UserSignature"> </div>

 

[scottb50]

"No parachutes or separation needed." <br /><br />I'm thinking pretty much along the lines of White Knight. Wings attached to the outer SRB housings and simple fairings over the main propellant tanks. A lower lower landing gear structure would attach to all the Modules, to spread the load.<br /><br />Two or four turbojet engines would allow a normal approach and landing and carry their own weight, and that of their fuel during launch.<br /><br />As far as piloted or autonomous I am planning both. A crew Modules would be attached for manned payloads and removed for cargo only payloads. The Module would be like the F-111 allowing escape for the crew in all phases of launch and flight. <br /><br />Land or water...<br /><br />Definitely land with the capability of taxiing directly to the refurbish facility after landing for turnaround. <div class="Discussion_UserSignature"> </div>