Quote from: jongoff on 04/24/2013 12:12 amQuote from: yg1968 on 04/24/2013 12:09 amWhat about a methane upper stage as SpaceX is contemplating?I think that while Methane isn't as bad as storables or solids, I'm not convinced it's actually better than LH2 except in some limited situations (like when you can easily make Methane via ISRU such as on Mars). Especially with XCOR's comments that LH2 doesn't seem to be the Cryogenic Satan Juice that some people make it out to be, my take is that LH2 still makes a lot of sense for in-space large-deltaV-propulsion.That said, while I think LH2 makes more sense, CH4 isn't as bad as most of the other alternatives, and might even win out in some corner cases.~JonDoesn't methane have less boiloff?
Quote from: yg1968 on 04/24/2013 12:09 amWhat about a methane upper stage as SpaceX is contemplating?I think that while Methane isn't as bad as storables or solids, I'm not convinced it's actually better than LH2 except in some limited situations (like when you can easily make Methane via ISRU such as on Mars). Especially with XCOR's comments that LH2 doesn't seem to be the Cryogenic Satan Juice that some people make it out to be, my take is that LH2 still makes a lot of sense for in-space large-deltaV-propulsion.That said, while I think LH2 makes more sense, CH4 isn't as bad as most of the other alternatives, and might even win out in some corner cases.~Jon
What about a methane upper stage as SpaceX is contemplating?
Sure. But boiloff isn't everything. I don't think it's worth contorting a design just because some people are too afraid of the right answer.
Quote from: jongoff on 04/24/2013 01:35 amSure. But boiloff isn't everything. I don't think it's worth contorting a design just because some people are too afraid of the right answer.Now that's getting personal.
Storable propellant depots could be done right now with existing technology. The engines that use storable propellants are available from more suppliers and cost a lot less too.
Boiloff isn't everything, but neither is ISP.
The fact is, NASA's not planning on using either because the goal isn't to actually get into space, go anywhere or do anything.
I made the mistake of reading about a Senate Commerce "hearing" held today [April 23, 2013] regarding NASA’s human spaceflight plans. While some of the points made I actually agree with, one of the witnesses (Steve Cook of Dynetics) made an argument that I think merits some skepticism. The argument, which you’ve likely seen a lot recently, goes like this "If only NASA had a stable long-term exploration program, with established destinations and dates, the private sector would be jumping all over itself to create business plans supporting NASA’s exploration efforts"” At its core, this argument and others like it seem to imply that if only we hadn’t cancelled the Constellation Program, everything would’ve been better.
If Congress really wants commercial industry to more actively engage themselves in NASA’s exploration efforts, and to invest private money in ways that are synergistic with their exploration goals, they could try establishing a realistic long-term plan for NASA that fits within realistic budgets, they could try to seriously work with industry to understand what markets industry sees as viable that are also synergistic with NASA’s exploration desires, and work with them to retire the technological risks that are impeding the commercial development of those markets.
Stafford mentions that SLS is essential because it is not possible to use many small rockets because of the boiloff of LH2.
Ugh. As soon as anybody mentions Helium-3 it's time to change the channel.
Quote from: Blackstar on 04/23/2013 07:35 pmUgh. As soon as anybody mentions Helium-3 it's time to change the channel.As has been noted long ago, the appropriate substitution is s/Helium 3/snake oil/g .
And it's really odd for an SLS supporter to make this argument. Mars is supposedly SLS's ultimate destination. Multiple SLS launches would be needed for this. If a multi-launch lunar mission isn't possible, how can a multi-launch Mars mission be possible?
Quote from: ChileVerde on 04/25/2013 12:33 pmQuote from: Blackstar on 04/23/2013 07:35 pmUgh. As soon as anybody mentions Helium-3 it's time to change the channel.As has been noted long ago, the appropriate substitution is s/Helium 3/snake oil/g .Nahhh... just change the channel.
The idea that it is "depot" vs "SLS" and an "either/or" situation has to be changed. Any ideas on how to get that through "peoples" heads?
Quote from: RanulfC on 04/25/2013 03:30 pmThe idea that it is "depot" vs "SLS" and an "either/or" situation has to be changed. Any ideas on how to get that through "peoples" heads?From an engineering standpoint SLS could presumably use depots, but from a budgetary standpoint they seem incompatible. Where are we going to find the budget to develop SLS, depots, and payloads?
Quote from: deltaV on 04/25/2013 04:04 pmQuote from: RanulfC on 04/25/2013 03:30 pmThe idea that it is "depot" vs "SLS" and an "either/or" situation has to be changed. Any ideas on how to get that through "peoples" heads?From an engineering standpoint SLS could presumably use depots, but from a budgetary standpoint they seem incompatible. Where are we going to find the budget to develop SLS, depots, and payloads?The "political" incompatibilty seems to be the basis for the conflict, rather than any serious "budget" conflicts but given an "assumption" of conflict in the first place they DO "seem" to be mutually exclusive systems However it is like Jon noted, SLS is going to need technologies like "boil-off" control itself among others that would be useful to either system. So there is a synergy on working both systems at the same time since there is no direct need to "add" items to the budget. As long as the research isn't too "focused" on one specific system more than neccessary it can be applied to others.About the ONLY "specific" technolgy that isn't something directly related is propellant transfer technologies, and I would argue that this is something with long term benifits we WANT to develop anyway.The tricky part comes in getting the people who are currently lined up on either side of the "debate" to stop making it a "political" issue and get them to understand there is lots of "value-added" to both sides in developing the technology. The budget can handle a lot of technological research and development as long as it keeps an "open" approach rather than being forced to focus on a single "system" approach as has been the habit in the past.The problem is short of going to Washington and visiting a lot of people with liberal applications of a "clue-bat" I'm not sure how to convince the necessary parties involved to get out of their ruts and start thinking longer-term instead of short-term Randy
Quote from: deltaV on 04/25/2013 04:04 pmQuote from: RanulfC on 04/25/2013 03:30 pmThe idea that it is "depot" vs "SLS" and an "either/or" situation has to be changed. Any ideas on how to get that through "peoples" heads?From an engineering standpoint SLS could presumably use depots, but from a budgetary standpoint they seem incompatible. Where are we going to find the budget to develop SLS, depots, and payloads?And, given that depots are effectively a launch-vehicle multiplier, what foreseeable affordable mission is there that will require a multiplied SLS?
While they strained to connect all the dots and make the case for each of these various and sundry activities and programs, it struck me how the witnesses and Senators were feeling around (but not touching) the biggest issue of all: Why human spaceflight? ...Now that we sit amongst the smoldering ruins of a once-great space program, perhaps we should take time once again to re-examine this issue from a different perspective. Just as the barbarian hordes lived in squalor after the fall of Rome because they could not repair the aqueducts built by their predecessors, we gaze at reposing Saturn Vs as strange artifacts of a former golden age, now reduced to tourist attractions ...This is the elephant in the room: Why should there be a national human spaceflight program? While this beast is clearly seen by many of us, it appears to be largely invisible to some elected and appointed officials and space experts whose concerns seem to be near-term, and focused solely on how much things cost.Our space budget will continue to shrink because there is no compelling rationale to fly stunt missions (no matter how skillfully logic is twisted). To regain our lost footing we must begin with the understanding that becoming a space faring people is the long-term goal, not “Mars” nor the “Quest for Life Elsewhere.”