Thinking Clearly About Space

[gunsandrockets]

"AFAIK, only hydrogen gives you Isp = 900sec, all other propellants are much less efficient and usually not worth the expense." -- Syndroma<br /><br />You are correct.<br /><br />If water was used, as Dobbins suggested, for a nuclear rocket launch vehicle then it would be inferior to chemical rockets. Compared to a LH2/LOX rocket a nuclear thermal rocket using water would have not only inferior ISP, it would have inferior thrust to weight plus the other headaches of nuclear rocket operation.<br /><br />Most concepts of nuclear thermal rockets as launch vehicles use ammonia for propellent. But even in this case the gain in performance over a chemical rocket is considered not high enough to be worth dealing with the difficulties of nuclear rocket operation. However a nuclear rocket does have much promise as an upper stage for a launch vehicle, and in this case it would use Hydrogen propellent for maximum ISP.

 

[gunsandrockets]

"There weren't any 0.5 kiloton bombs at the time Orion came into existence, there were only the designs used at Hiroshima and Nagasaki, and the Hiroshima design had the lower yield of the two."<br /><br />Wrong as usual. The sizing of the Orion pulse units were made after 1958 when project Orion became a serious study project. This is the same period of time when very small tactical nuclear warheads were being developed, some with yields much less than 0.5 kilotons. <br />

 

[dobbins]

Your make-believe spaceship dates back to 1947, and international treaties and political reality will ensure that it will never be anything other than a make-believe design. The tree huggers are already up in arms over the RTG in the New Horizons mission.<br /><br />http://www.news-journalonline.com/NewsJournalOnline/Opinion/Editorials/03OpOPN45120405.htm<br /><br />Do you really think there's a snowball's chance in Hell of a design that actually emits fallout from hundreds of detonations of any size device after reading that? If you do I have a bridge in Brooklyn that I'd like to sell to you.<br /><br />Now are you finished splitting hairs over a pointless unrealistic daydream?<br /><br />

 

[danwoodard]

The cost of operation of an RLV is of course dependent on its design. A small, unmanned, suborbital design like the X-34 (partly the work of Burt Rutan, our foremost aeronautical engineer) had a total budget (including propulsion) of less than $100 million. The X-33 was hobbled by artificial misson goals that precipitated the ridiculous descison to switch to metal tanks rather than develop the new technology that was obviously needed for composite LH2 tanks of acceptable weight. A technolgy development agency should develop new technology. (Dedicated engineers actually tested a successful composite LH2 tank with close-out funds after the program was cancelled).<br /><br />In either case, small, unmanned reusable vehicles could gradually evolve to orbital capability while developing real flight experience with each design alternative. The best concepts for a manned vehicle can be tested and selected, and operating cost and safety can be verified in actual flight before selecting design elements for a manned vehicle. <br /><br />The vast majority of the errors in estimates of operating cost and safety of the Shuttle resulted from the absence of any flight experience with many of the critical systems at the time design decisions that were made.<br /><br />Expendables generally cost less than the shuttle but there is little chance the CEV/CLV will cost significantly less than the shuttle since it will require essentially the same infrastructure that still has to be maintained, and the plan is to retain essentially the same workforce.<br /><br />Finally, if RLVs are so expensive, why is DOD taking over the X-37 and starting a new program for a fully reusable first stage booster? I regret that NASA has not been able to retain leadership of these programs.

 

[gunsandrockets]

"Now are you finished splitting hairs over a pointless unrealistic daydream?"<br /><br />I never claimed Orion was politically viable. I only was pointing out your factual errors about Orion. In the interest of accurate debate.

 

[cuddlyrocket]

"Expendables generally cost less than the shuttle but there is little chance the CEV/CLV will cost significantly less than the shuttle since it will require essentially the same infrastructure that still has to be maintained, and the plan is to retain essentially the same workforce."<br /><br />Space Shuttle: 16,500kg /36,400lb to LEO for a launch cost of $800 million at $48,485/kg / $21,978/lb. Magnum SDLV: 125,000kg/275,750lb, $350 million, $2,800/kg / $1,269/lb. "The Stick" CLV: 25,900kg / 57,135lb, $100 million, $3,861/kg / $1,750/lb.<br /><br />(Figures from kraisee on this thread at NASASpaceflight.com.)<br /><br />Griffin has stated that he wants far fewer people involved in the launching of the CEV/SDLV as opposed to those involved in launching the Shuttle. He expects the total same workforce in NASA as <i>they will be doing other things</i>.<br /><br />"Finally, if RLVs are so expensive, why is DOD taking over the X-37 and starting a new program for a fully reusable first stage booster? I regret that NASA has not been able to retain leadership of these programs."<br /><br />What mission do the DoD have in mind? And in any event, if the DoD is already doing it why should NASA fund an equivalent programme out of its much smaller budget?

 

[josh_simonson]

I doubt the SDHLV will fly for $350M. Rocketdyne charges $60M for a SSME and says they might be able to get it down to $40M by cutting corners on the re-use area - but that's still $240M for only the 6 engines on the SDHLV.<br /><br />Interestingly the 3 segment Falcon 9 could orbit payloads for the same $/lb as just the engine costs for the SDHLV.<br /><br />Big, dumb, boosters have considerable merit, but using the most complex and expensive engine ever created is not in line with a proper BDB design philosophy.