Jon Goff has an instructive post on NASA’s supposed risk aversion, and points out that had they taken the same attitude half a century ago, Apollo would likely have failed (as Constellation seems likely to fail today, ironically, because it’s too much like Apollo, but without either the requirements or the management talent of that project).
But this opens up a much broader discussion of risk. There are multiple kinds of risk for a space project (and technology projects in general). There is technical risk — the risk that what you are trying to do may not be achievable within the schedule or budget because the technologies haven’t been sufficiently demonstrated and there are too many unknowns (both “known” and “unknown”). There is program risk — the risk that you may not manage the various aspects (including risk) of the project adequately, also resulting in cost increases and/or schedule slips (it is clear that this has happened to Constellation, as many have been pointing out for years). There is market risk — the risk that the thing that you’re building won’t actually satisfy the need. And for government programs, there is political risk — the risk that your project will lose political support prior to completion (actually sort of the government version of market risk, except that you’ll often find out that the market has disappeared prior to project completion, which is, I suppose, a feature rather than a bug).
A key element of being a successful project manager is managing and mitigating these risks. A lot of it happens at the very beginning of the project, when it’s a lot cheaper to do risk mitigation, and decisions taken have long-term consequences.
In that context. Mike Griffin failed the day that he selected the current architecture, because it had so much risk (of all varieties described above) cooked in right from the get go.
Not having access to the probabilistic risk analysis (PRA) that is a standard management tool for such decisions (I’m being generous in the assumption that one was actually performed, and the decision based on it) it appears to an outsider that no risk was considered other than purely technical. NASA (in defiance of one of the roles stated in its charter) chose the path that was deemed to have the best chance of success because it broke no new technological soil. In its own parlance, it chose to develop launch systems built from components of high TRLs (Technology Readiness Level). That is, they had been demonstrated operationally in the operational environment, in previous programs. Of course, because they didn’t really understand the operational environments (it’s a lot more than just flying through the atmosphere and going into space), it bit them on the ass, and took out a lot of meat (almost doubling the initial estimates of development cost, and slipping the schedule one year per year since it started). “Demonstrated in the environment” includes the environment of an integrated launch system. For instance, the fact that the SRBs only killed one Shuttle crew didn’t make them safe or, in isolation, “human rated.” And the fact that the vibration environment when they were structurally buffered from the crew system by a tank full of a million and a half pounds of propellant was minimally acceptable didn’t mean that it was a good idea to put a much smaller stage directly on top of them.
They probably considered program risk, but assumed that it was non-existent, because they were running the program, and who was better at managing programs than them? They apparently completely ignored political risk, or misassessed it. They seemed to think that the way to maintain program support was to completely ignore the recommendations of the Aldridge Commission — to make it affordable, sustainable, support commercial activities and national security — and instead to cater to the parochial demands of a few Senators on the Hill, particularly Senator Shelby. That one hasn’t bitten them on the ass yet, but it probably will when the Augustine recommendations come out in the fall, removing whatever glutiginous meat remained.
The tragic thing, as Jon points out, is that in avoiding the narrow technical risk of delivering, storing, manipulating propellants on orbit, something that is absolutely essential for future space exploration and space development (because they’ll never be able to come up with a launch system that can do a Mars mission in a single launch), and focusing all their efforts on a perceived “low-risk” but unnecessary new launch system, and in ignoring the systems necessary to get beyond LEO (as opposed to simply getting to orbit, which the private sector has had down for years) they have wiped out more billions in taxpayer dollars, and allowed the day that we would once again go beyond earth orbit, to recede far into the future.
At least, that is, if the lunar-bound vehicle has the word “NASA” on its side.
Fortunately, some of us, more attuned to the real risks, have other ideas.
delivering, storing, manipulating propellants on orbit, something that is absolutely essential for future space exploration and space development (because they’ll never be able to come up with a launch system that can do a Mars mission in a single launch)
The following may be a nit, or might just be not realistic, but isn’t there also the “risk” that advanced propulsion techniques, that don’t require storing propellents in orbit will be made workable? I’m thinking of the many many varieties of beam-powered propulsion, for example…. They might require multiple launches to set up the relevant infrastructure, but would not require propellent depots (or at least, not the sort of propellent depots you are thinking of.) If so, might conventional propellent depots end up being a dead end and their development end up another waste?
I would say that Griffin thought he could reduce or eliminate the political risk by going with the architecture he did. If he came up with a low cost architecture, it would be seen as politically unimportant and easily canceled. But if he came up with an enormous and wildly expensive one, it would become “too big to fail” and the fact that so much has been spent on it is justification for demanding more money to see it through.
So to make a prediction for the future, just check Obama’s record on things that are “too big to fail”.
Rob- Part of the argument for depots is that the arbitrary size and launch rate of the payloads allows us to ‘get in the game’ of launching large numbers of payloads into orbit. That lesson would be useful in the end no matter how we eventually leave orbit. Besides, large amounts of hydrogen and oxygen in orbit can also be turned into water and/or the oxygen can be used to breathe on a hydrogen-cooled NERVA type engine as well.
On the risk thing, I’ve long held that NASA wouldn’t have been able to do the moon trip if it hadn’t been ‘inventing’ itself as it invented its methods to go to the moon. The rapid expansion of the agency at the time prevented bureaucratic inertia from bogging things down. I think that part of the argument over Saturn V’s “man rating” (acknowledging Rand hates the term) was the beginning of the bureaucratic vice tightening.
Actually, Saturn V was never “man rated” because, not being a munition, it didn’t have to be. It was simply designed to be safe.
Bob-1,
It’s possible. Most technologies only have a finite lifespan before being overtaken. But the reality is that most in-space systems use some sort of liquid propellant, and you’re eventually going to want to do maneuvers somewhere where beamed power systems aren’t close enough to help. Even if something else displaces depots in LEO at some point, they’ll still be useful elsewhere. There’s always risk.
But I think that depots still have a long future ahead of them yet.
~Jon
I guess what I never figured out is why at the very least doing engineering development on propellant caching and transfer was not a mission for ISS.
Or maybe these depots are best as unmanned stations, just as microgravity research is perhaps done from unmanned platforms rather than ones with people jostling around.
Besides practicing having people in microgravity for long times to preparation for long-duration missions, what do they actually do on ISS these days?
Paul,
The jury on whether those would be best manned or unmanned is still out I think. Dallas Bienhoff favors unmanned, because he is worried about what would happen to a LH2 tank if it was hit by a micrometeorite. I’m more of a fan of doing a manned station eventually. First generation something unmanned and automated might make sense, but for later depots, there’s something to be said for being able to colocate other services (like repair/maintenance/assembly facilities). Make it a real transportation node, not just a gas station.
But first gen can be something pretty small–I’ve actually seen some pretty darned compelling single-launch concepts.
~Jon
I’m not getting much enthusiasm for my preferred compromise, which is to use depots only for the lander and to use hypergolics for that. Hypergolic fluid transfer is a proven technology as are hypergolic landers so not only is that low risk, it’s lower risk than what’s currently on the table. It’s only a compromise and not an ideal solution, because compared to a cryogenic LEO depot for EDSs it would mean substantially less launch volume for RLVs or cheap expendables, but still a considerable amount, especially if you use a single stage reusable lander.
I think I know why SDLV proponents don’t like it. Depots are a threat to SDLVs (and vice versa) and they’d rather make vague promises about the much better cryo depots ten years or so from now than face the threat of even the less powerful hypergolics depots now.
But why am I not getting any enthusiasm from more enlightened people? Isn’t it a good idea to get a foot in the door as soon as possible? Or do you have hope cryogenic depots will emerge somewhere in the next few years?If NASA gets its way now it will ben ten to twenty years before the option is considered again.
Martijn, consider the possibility that hypergolics completely suck from an operational standpoint, due to their toxicity. We’d accordingly like to get away from them completely…
Yeah, I know they are toxic, carcinogenic, corrosive and their Isp is only meh. On the other hand, they are also hypergolic, dense and storable. Do they suck enough to make you want to forego an opportunity to establish a foothold for depots? Honest question, I don’t know precisely how much of a pain they are.
I’ve heard knowledgeable commentators say procedures for the Shuttle are now so routine it would actually be more costly, at least in the short run, to switch away from hypergolics. And others have said that they are mostly a problem for reusable systems that return to Earth, like the shuttle, and that they are fine for spacecraft. I’ve seen pictures of the safety equipment used at Kourou (I think), and it does look very cumbersome. Still, if this is what will give you a sufficiently high flightrate to develop RLVs, wouldn’t it be worth it?
And of course when I say hypergolics, I’m thinking specifically of MMH/NTO and there are really more aspects to it than hypergolicity itself, there’s also storability and density. The second is what matters for depots of course, although the other two are useful for safety (your engine WILL start and will NOT tip over). You could also consider green propellants, but that will likely not help in the near term, because they are less mature.
And in the long term, would you expect to see all propellants other than cryogenic ones disappear? Or would there be a long term role for hypergolic, dense propellants (not necessarily MMH/NTO)?
A final thought to show where I’m coming from: I’m not thinking about giving up on campaigning for cryogenic depots soon, I’m thinking about insisting we get at least hypergolic depots soon because that might be an easier initial battle to win.
A hypergolics depot close to the ISS could have immediate payoff of the sort the public will understand: refueling an Orion that acts as a short range tug that makes ISS resupply more efficient. Later on, it could be used by commercial tugs as well. Implant the idea in people’s minds as soon as possible. Try to get a supply chain and its lobbying power behind it as soon as possible. There will be an Orion as a potential depot client long before there will be an EDS.
Getting back to the topic of risk management:
You are absolutely right it was a mistake to exclude low-TRL technologies entirely. In fact the whole program should have been based around maturing new technologies. On the other hand, it would have been a good idea to use high-TRL technologies exclusively for a very simple initial working system that could have been delivered very soon. DIRECT would have been much better in that respect. Ten years ago, Shuttle-C might have been an even better idea. No NASA launcher would of course have been even better. They could have started with a capsule that would fit on a Delta-IV Medium.
It was a mistake not to immediately start work on maturing key technologies in parallel. Instead, they chose to build a large number of new systems with an inexperienced team. Using high-TRL technology is fine, developing unnecessary new systems isn’t. They were maturing their development team, not maturing technology. They were playing catch-up, instead of breaking new ground.
Another mistake was that they set initial targets that were both too ambitious and too far in the future. This allowed them to live in fantasy land for far too long. Reality has now finally sunk in and it may be too late to fix things. They really should not have abandoned spiral development, which above all is a form of risk management.
Martijn,
I guess I’m not necessarily opposed to a storable propellant depot–there are actually some potential markets in certain orbits that might want just that. I just think a hypergolic depot doesn’t make as much sense for exploration missions. I think cryogenic is the way to go, and that the technology may be closer at hand than most people think.
~Jon
> For instance, the fact that the SRBs only killed one Shuttle crew didn’t
> make them safe or, in isolation, “human rated.”
Actually under the ESAS rules the SRBs didn’t destroy Challenger, i.e. the SRB failure was “benign,” an adverse aero environment destroyed Challenger. I wish I was kidding….
In the current Orion design environment some of the C&DH HW, e.g. the VMC (flight computer) and Display Unit, is not surviving the 1st stage vibration.
“You could also consider green propellants, but that will likely not help in the near term, because they are less mature.”
And irrelevant anyway, if burned only outside the atmosphere.
And to Bob-1, even beamed power systems require reaction mass (except laser-driven lightsails) that might be re-supplied on orbit. (Though it might not be a liquid, but an ablative solid, if heated by remote, more intense lasers)
If it is OK with Rand, I’d like to respond to Jon’s reply to my post about hypergolics depots. I’ll try to focus on how they relate to risk management and development of commercial space. Rand, just let me know if I stray too far or simply say too much and I’ll shut up. Sometimes my passion gets the better of me. You and the regular posters on this blog are the sort of people who might actually come up with a sensible strategy for commercial development of space and I’d like to have your feedback.
> I just think a hypergolic depot doesn’t make as much sense for exploration missions.
Are you thinking about the inefficiency of hypergolics? Based at L1, that’s really not a problem. Over a delta-v of 2.5 km/s to the Moon, you have only about 25% efficiency loss. And that’s only the final “mile and a half per second”, with the initial 12 km/s or so from the surface of the Earth being taken care of by cryogenic propellants, so the total percentage is much less. And you get back most of the inefficiency by taking slower but more efficient routes.
Now I’m mostly interested in the effect of depots on commercial space. L1 might be a bit ambitious as a first target for an RLV, but you could have LEO export depots to fix that. You could then contract transport services to L1 by players that have high energy upper stages that will do that efficiently. NASA could define a spacefaring equivalent of standard shipping containers, and ULA could develop an autonomous Centaur with docking capabilities that will take such a container to L1. There are some similar suggestion in papers on the ULA website.
Of course, you could do all that with cryogenic depots too and I would be thrilled if that were to happen. It’s just that hypergolics seem much lower risk. No need not to work on cryogenics in parallel, but let’s not put cryogenics on the critical path to depots.
Hypergolics depots in support of ISS resupply tugs or Orions on short excursions can deliver benefits sooner than cryogenic depots, which are mostly useful for travel beyond LEO, which is not likely to happen before 2020. I think this is still true even if a crazy billionaire decided to develop cryo depots tomorrow and had one up and runing two years from now. A depot needs clients and Orion is an obvious first client.
Well, maybe not if you use depots in support of the unmanned landers of a robotic precursor program or for launching interplanetary probes, which might not be a bad idea. Based at L1, you could do something similar with hypergolics. But for landers, hypergolics are probably still easier.
I think it boils down to three things: earlier markets, lower development cost and lower risk. This is important for the success of a space program, but the earlier markets are also crucial for commercial development of space. Time is money. Substantial launch volume for RLV prototypes three years from now would be an enormous boost. If it doesn’t happen until 2020, a number of current initiatives may wither on the vine.
Thanks Jon. As an aside, I like to imagine various ways to get from Florida to the surface of Mars without using any liquid propellent, but precluding a dramatic change in direction, I know these aren’t near-term solutions. The train of thought started with this article, which pointed out that chemical rockets probably aren’t sufficient for landing on mars:
http://www.universetoday.com/2007/07/17/the-mars-landing-approach-getting-large-payloads-to-the-surface-of-the-red-planet/
(I’m curious whether the folks at Masten think this article is off-base…)
Frank, I was thinking of Benford’s ablative sail approach, but, if I understand correctly, some versions of Jordin Kare’s Sailbeam approach also don’t require onboard reaction mass – only power is needed to vaporize the micro-sails. Finally, even if something like M2P2 was used, along with propellent for maneuvering, the needed reaction mass would be orders of magnitude less than conventional propulsion requirements (right?)
For use in space only – at least for the foreseeable future – would it not be useful to spend a tiny fraction of the NASA budget on really blue-sky stuff such as Polywell? This holds the promise (according to Professor Bussard, who is worth listening to) of being directly turned into a reaction engine if the reactor field geometry is altered – and without much radiation either, if 1H/B11 fusion is used. Even if that isn’t practical, it allows the possibility of a compact, high-power power source for such things as mass-driver based engines or ion drives.
And the total development budget being asked for is less than a third the cost of one Shuttle launch.
I’ve heard knowledgeable commentators say procedures for the Shuttle are now so routine it would actually be more costly, at least in the short run, to switch away from hypergolics.
A few years ago, it was estimated that the Shuttle orbiter refurbishment costs could be reduced by something like 30 (?) percent, just by replacing the hypergolics with LOX/alcohol.
As another datapoint, it’s estimated that it will cost $60 million to decontaminate and safe each Shuttle orbiter when it is retired and sent to a museum.
@Edward Wright:
These costs are related to a vehicle that returns to Earth, not to one that remains in space. If you had an RLV with an expendable, hermetically sealed propellant container, you wouldn’t have to deal with this issue.
@Frank Glover:
I think the concern with green propellants is not so much about pollution as about safety and cost of ground operations.
Another point to bear in mind: various flight segments (Earth to LEO, LEO to L1, L1 to the Moon, L1 to SML-1, SML-1 to LMO) could require different propellants. Most of the interplanetary segments have delta-v L1, whereas storables combined with SEP are preferable for in-space propulsion. And if lunar ISRU works out, as I hope it will, silane + H2O2 is a noncryogenic, dense and hypergolic propellant combination that could be more interesting than LOX/LH2, especially if used in metallised gel form.
Sorry, that last post got messed up.
Another point to bear in mind: various flight segments (Earth to LEO, LEO to L1, L1 to the Moon, L1 to SML-1, SML-1 to LMO) could require different propellants. Most of the interplanetary segments have delta-v <= 2.5 km/s, meaning that storables are quite competitive, especially if prepositioned by SEP and perhaps sourced from ISRU. In fact, such a scheme could be more efficient than LOX/LH2 without prepositioning. LOX/LH2 with prepositioning would of course be even more efficient, but by no more than 25%.
LOX/LH2 and kero/LOX could be ideal for Earth to LEO, LOX/LH2 for LEO to L1, whereas storables combined with SEP are preferable for in-space propulsion. And if lunar ISRU works out, as I hope it will, silane + H2O2 is a noncryogenic, dense and hypergolic propellant combination that could be more interesting than LOX/LH2, especially if used in metallised gel form.
Are there any proposed interesting variant launchers designed specifically for getting just fuel to a depot?
Because ground-based rail launchers would seem to be a lot more useful when you can exceed 4g by an extreme margin.
See http://en.wikipedia.org/wiki/Aquarius_Launch_Vehicle for one concept. I used to be enthusiastic about this, but I’m not so sure anymore. In the long run, we will hopefully get export of lunar oxygen to LEO, much reducing the need to launch propellant from Earth. So from that perspective Aquarius may be a dead end and the high flight rate that could be generated by the first phases of a lunar program might be better used to develop RLVs, since those would remain useful for launching people.
For use in space only – at least for the foreseeable future – would it not be useful to spend a tiny fraction of the NASA budget on really blue-sky stuff such as Polywell?
Maybe if the Polywell people published a well-founded theoretical argument why they should be taken seriously. As it stands, a lot of it is just handwaving, or “Bussard said…”.
Go to talk-polywell.org and read Art Carlson’s critical posts. There are lots of reasons the idea makes no sense, and they don’t seem to get any serious rebuttal. Why ANYONE takes Polywell seriously, I have no idea.
I was looking from it more from the “What are the benefits of a depot?” perspective.
Being able to say “We’ll get the fuel there for $1000/kilo – or less,” is a strong statement in favor. It doesn’t ultimately matter if the fuel is coming from the moon. Just that you aren’t flying it up to depot range in 1-in-1000 LOC vehicles.
might conventional propellent depots end up being a dead end and their development end up another waste?
This has already been responded to above but… did tv kill radio?
It takes so much fuel to get to orbit that it just makes sense to refuel and go farther. It’s a no brainer. NASA isn’t the only game in town. Other customers for orbital fueling would use it regardless of other technological developments.
Risk in isolation is almost meaningless; rewards must also be considered. What normally happens is all sorts of things are tried and a shakeout determines the winners. The expense of space activities makes this all happen in slow motion, but it will still take place (excuse me, it is already taking place.)
An orbital refueling station will happen the moment after someone puts a spaceship in orbit. A spaceship being a craft that just requires provisions and never lands. There is already a market for such a ship and it can be a very modest design (Dragonlab might be 90% there.)
Once you have an orbital refueling station in operation most of the risk associated with choosing it as an optional component of any mission disappears.
Bob-1,
Regarding the Mars landing problem. I’ll admit I haven’t spent a lot of time looking at the issue. I’m not too worried about having to use some brute-force propulsion for braking. The only part that’s worrying is his point about firing engines forward into the relative wind causing weird aerodynamics issues. I could see that taking some work to figure out. But I also don’t think it’s an unsolveable problem.
~Jon
I’ve read that hypersonic firing into the wind is a fiendishly difficult problem. Brute force should still be possible however. In the extreme case you would kill all tangential velocity and then descend gently. This should be possible provided you have enough propellant. Enter propellant depots in LMO and SEP tugs or the Interplanetary Transport Network. Or Martian ISRU and propellant depots in LMO.
“The tragic thing, as Jon points out, is that in avoiding the narrow technical risk of delivering, storing, manipulating propellants on orbit, something that is absolutely essential for future space exploration and space development…”
This is the crux of the matter. Propellant depot advocates *assume* that there is going to be a great deal of “space exploration and space development” in the immediate future. Since such assumptions have been made for the last 50 years or more the ones with the cash tend to be skeptical.
This forces a retreat to the next assumption that if a propellant depot is built costs will fall to the point where a great deal of “space exploration and space development” becomes desirable. This, of course, is the “build it and they will come” argument which has an equally spotty track record in the space arena.
Propellant depots, although they have much less technical risk, are similar to space elevators in this regard. They assume a level of traffic far above the current levels.
Propellant depots, although they have much less technical risk, are similar to space elevators in this regard. They assume a level of traffic far above the current levels.
Well, since current levels of traffic to the moon are almost non-existent, that’s not much of an assumption. I think that the comparison of depots to elevators is off by orders of magnitude, in both technical risk and cost, and need for high levels of traffic to justify them.
Depots trade favorably against heavy lift for going to the moon, even at the paltry traffic level planned by NASA, and they scale much, much better, with low marginal costs (at least for utilizing the depot itself — the marginal mission costs depend on the cost of getting propellant into them).
Since such assumptions have been made for the last 50 years or more the ones with the cash tend to be skeptical.
Thankfully the next 50 years are not the last fifty and different people will have cash.
This is the crux of the matter. Propellant depot advocates *assume* that there is going to be a great deal of “space exploration and space development” in the immediate future.
It’s more a matter of: if manned spaceflight is worth doing now at all, it is worth doing on a large scale. Perhaps there will not be a great deal of space exploration and development soon. If so, let’s just shut down the manned space program for a generation or two and stop pretending it’s actually getting us anywhere.
Three dry launch questions:
(1) A technical one:
Suppose LH2 and LOX have been stockpiled on orbit and a lunar mission launches from Earth. Do you re-fill whatever tanks contained the fuel that propelled the payload to LEO (meaning the upper stage Centaur in the case of Atlas V and Delta IV or the Merlin 1C for SpaceX) or do you fill otherwise empty tanks incorporated into an Earth departure stage payload included as payload on top of the 2nd stage?
How much work has been done on this aspect of propellant depot operations?
Where would you place the TRL status and how long do you believe it would take to develop and deploy an operational dry launched Centaur that can re-fuel in LEO and depart for the Moon?
(2) Politics & bureaucracy question
Assume a top down order (from POTUS?) to use dry launched EELVs for the VSE while everything STS is ordered scrapped.
How long would it take (and how many people would need to be fired and/or re-assigned) to re-structure NASA management sufficiently to allow NASA to execute this assignment.
Speculation encouraged. 😉
(3) Choice of fuel question:
Should RP-1 depots be part of the critical path to allow SpaceX to participate?
i think that the Direct Team has hit the nail right on its head. They want space depots. It may not make getting the moon cheaper, but it allows you to land alot more cargo and supplies to the moon.
As to what it should store? Let industry decide. NASA needs LOX and hydrogren–so for a first generation station –make one. If it is sucessful, the commerical sector will want another one…and another one. People will start to design spacecraft that have the protential to be refueled. If you know you can fuel in orbit, then the satalitles life be longer. When you drive to from LA to NYC, you do want to take all that fuel with you. You would rather take little car and fill it up on the way. If there is no fuel depot, and you want to go to NYC or the stars, guess what–you are going to need all that fuel. NASA can even do a prize for a gas fuel depot to help lessen some of the technical risks. Reading papers from Dallas (BOEING), there is not that much technical risk to migrate. What do you do with excess fuel-sell it, use it for shielding. How much does it cost to deliver now 1kg to space on the shuttle –over $20,000. A space depot would also up the market for a RLV and further space expansion.
The problem–you have got to start somewhere. NASA had its own ideas and we are seeing how well they are panning out. Now is the time for some bold leadership and enable depots along.
> Propellant depots, although they have much less technical risk, are similar to space elevators in this regard. They assume a level of traffic far above the current levels.
Depots are also useful for refueling tugs that support ISS resupply. Much smaller market of course.
> i think that the Direct Team has hit the nail right on its head. They want space depots. It may not make getting the moon cheaper, but it allows you to land alot more cargo and supplies to the moon.
That’s what they say. Their actions suggest their motives are more complicated than that. They absolutely resist any suggestion of early depots – even if they are not on the critical path. And yet they are willing to put other unproven technologies on the critical path. DIRECT is not an ally.
Jim,
I actually don’t assume there will be a huge demand for manned spaceflight soon. My real plans with propellant depots has always assumed a lot of painful bootstrapping with NASA at best providing benign neglect (and maybe some occasional SBIR money for semi-related technologies). Without NASA as an anchor tenant, there isn’t an existing market for cryogenic propellant depots. I do see some hints of a path that could lead there without NASA help, but it’s going to be a slog.
However, that doesn’t stop me from trying to convince NASA to throw propellant depots a bone. Even a program about the size of COTS could likely end with a first-generation bare-bones depot capability in orbit. And quite frankly, that’s only a drop in the bucket of the overall exploration budget. For a small depot, it doesn’t actually require massive manned/unmanned exploration demand to make a positive difference, and to make quite a bit of money if it’s allowed to be commercially operated.
Depots can scale up quite a bit, but the nice thing is that they can also scale down pretty well too. If NASA can’t be convinced, it’ll get there, it’ll just take another 5-10+ years longer than it ought to.
~Jon
If the DIRECT guys flew their highest thrust variant with the minimum extra weight, how close does the main tank get to any kind of orbit?
“For a small depot, it doesn’t actually require massive manned/unmanned exploration demand to make a positive difference, and to make quite a bit of money if it’s allowed to be commercially operated.”
Jon, you must realize that the propellant depot idea is a very old one and that most previous investigators came to the conclusion that, like infrastructure in general, there has to be a level of use sufficient to amortize the depot’s costs and that current traffic levels beyond LEO are far below that.
If you feel you have something original to add to the depot concept to make it viable at lower levels than hitherto thought why not publish the results of your studies? The feedback would be valuable.
Your use of the phrase “if it’s allowed to be commercially operated” suggests a certain degree of special treatment is necessary for the propellant depot. What exactly do you mean by that?
Jim, can you explain your reasoning for thinking that a propellant depot requires a higher level of activity than does a heavy-lift launcher?
“Jim, can you explain your reasoning for thinking that a propellant depot requires a higher level of activity than does a heavy-lift launcher?”
I don’t recall making such a claim, Rand. Can you refresh my memory?
I don’t recall making such a claim, Rand. Can you refresh my memory?
You are implicitly making such a claim in a discussion about how NASA should be spending its exploration money, since a heavy-lift vehicle is currently the baseline.
Our claim is that a depot would be a much better use of the resources than a heavy-lift vehicle. That is true, regardless of whether or not you think that NASA’s ambitions for traffic are too small, or that NASA shouldn’t be spending money on VSE. The option of having NASA not spend VSE money is not on the table currently, thus we are discussing how it might be best spent.
I would also note that you did compare a depot to a space elevator, in terms of traffic level needed to justify it, and technical risk. Such an equivalence is nonsensical, and we still await the justification for that as well.
“You are implicitly making such a claim in a discussion about how NASA should be spending its exploration money, since a heavy-lift vehicle is currently the baseline.”
Utter nonsense, Rand. That would be like me claiming that since someone doesn’t like Obama he must like McCain. There are many possible positions to take on the issue of how NASA spends its allocation. My own, in case you’re interested, is that manned missions to the moon cannot currently be justified and that the money is far better spent on its long neglected aeronautical responsibilities.
“Our claim is that a depot would be a much better use of the resources than a heavy-lift vehicle. That is true, regardless of whether or not you think that NASA’s ambitions for traffic are too small, or that NASA shouldn’t be spending money on VSE.”
That may be true or it may not be. I claim that Jon really hasn’t made his case with any degree of rigor. Hence my suggestion for publication to garner professional feedback.
“The option of having NASA not spend VSE money is not on the table currently, thus we are discussing how it might be best spent.”
I think that option is *very* much on the table, certainly as much on the table as a propellant depot.
“I would also note that you did compare a depot to a space elevator, in terms of traffic level needed to justify it,”
Yes. I said both assume higher levels of traffic than currently exist.
“and technical risk.”
Yes. I said propellant depots had much less technical risk.
“Such an equivalence is nonsensical, and we still await the justification for that as well.”
I am not going to bother justifying my claim that propellant depots have much less technical risk. I am astonished that you or anyone else would think otherwise.
As for higher traffic levels I’ll repeat myself since you can’t seem to read my posts in their entirety: ” …the propellant depot idea is a very old one and that most previous investigators came to the conclusion that, like infrastructure in general, there has to be a level of use sufficient to amortize the depot’s costs and that current traffic levels beyond LEO are far below that.” I could dig up specific references but I’ll pull a Simberg and say I can’t be expected to do your research for you. 🙂
Jim, to be brief, the context of this discussion was how NASA should best implement the VSE, which, agree or not, calls for humans to the moon by 2020. Our claim is that propellant depots make more sense for that goal (and those beyond) than developing a heavy lifter. If you want to complain that VSE is an utter waste of federal funds, I wouldn’t necessarily disagree, but that is a separate discussion.
I am not going to bother justifying my claim that propellant depots have much less technical risk. I am astonished that you or anyone else would think otherwise.
I’m sorry, I misread your post on that point. I of course agree that there is much less technical risk to a depot than an elevator. I thought you were stating that (like the traffic necessary) they were equivalent.
But do you really believe that the level of traffic required to justify a fuel depot relative to a space elevator is equivalent? Really?
“Our claim is that propellant depots make more sense for that goal (and those beyond) than developing a heavy lifter.”
All well and good. Now make the case for the depot, something on the level that the DIRECT advocates make their case, or Zubrin makes his, or Wingo, or whomever. Hence my suggestion for publication. Elevate the discussion to something above a Web watercooler bull session, if indeed either of you take the notion that seriously.
“But do you really believe that the level of traffic required to justify a fuel depot relative to a space elevator is equivalent? Really?”
“Equivalent” is your word, Rand. This is what I said: “Propellant depots, although they have much less technical risk, are similar to space elevators in this regard. They assume a level of traffic far above the current levels.”
Note that there is no suggestion that the levels in each case would be equivalent, merely that both are far above current levels.
Note that there is no suggestion that the levels in each case would be equivalent, merely that both are far above current levels.
But one of them is not at all, let alone “far” above projected traffic levels for the VSE. So you remain disingenuous on that point.
“But one of them is not at all, let alone “far” above projected traffic levels for the VSE.”
Really? This is precisely the type of point Jon should make in a paper or conference presentation describing the virtues vis-a-vis heavy lift. It would lift the argument from the hand waving stage we seem to be stuck at presently to something more quantitative.
“So you remain disingenuous on that point.”
I think I’ve been very clear. “They assume a level of traffic far above the current levels.” “Current levels”, Rand, not “projected traffic levels for the VSE”. If there has been disingenuity, it has not been from me.
If the DIRECT guys flew their highest thrust variant with the minimum extra weight, how close does the main tank get to any kind of orbit?
They can get the tank into orbit whout problems. In fact, I’m told the tank itself is the problem. The insulating foam would “popcorn” off. If you’re looking for a large habitable volume, they say you’d be better off launching it separately. Or you could use an inflatable of course. There doesn’t appear to be a away to salvage anything of use from the tank in orbit.
Hmm. Is the popcorning just from the entrained gases in the foamlike insulation? Or is there a phase-shift in one of the solids?
Because this -isn’t- just like getting an external tank up. There’s the full instrumentation ring and overpowered thrusters as well as the insulated tank. The ‘useless bit’ is well on its way to being the depot -or- the tug. If there was something to be done about the popcorning.
I mean, the brute force fix would be to wrap the whole thing in fancy aluminum foil in orbit. Something that doesn’t seem overly heavy from a payload standpoint, and could probably be mechanized satisfactorily.
And, hell, if it fails, you push it into the atmosphere and try again next time. The DIRECT plan calls for an astronomical number of precisely this piece to make it into a stable orbit. And be discarded.
Hmm. Is the popcorning just from the entrained gases in the foamlike insulation? Or is there a phase-shift in one of the solids?
I’m not sure, I think I’ve heard it’s the entrained gases.
Because this -isn’t- just like getting an external tank up. There’s the full instrumentation ring and overpowered thrusters as well as the insulated tank. The ‘useless bit’ is well on its way to being the depot -or- the tug. If there was something to be done about the popcorning.
A lot of problems with that. The tank would need some kind of power system. That could probably be fixed. The thrusters are overpowered to be point of being useless. The SSME cannot be air-restarted. And the isogrid panels are perfect for transferring heat into the tanks – precisely what you don’t want.
It seems like such a waste to throw away a perfectly good tank, but there doesn’t seem to be a good way to reuse it. All the obvious applications seem to have major problems. I wonder if it wouldn’t be better to split up the core into two stages instead, in which case you could perhaps recover the first stage. Of course that would still be an unneeded NASA launcher.
Note that the DIRECT plan is to turn the Jupiter Upper Stage into a depot later – once a man has landed on the moon. If I believed this was really going to happen I wouldn’t be so opposed to DIRECT. It would still be putting the cart before the horse, but better than what is planned today.
Note that the DIRECT plan is to turn the Jupiter Upper Stage into a depot later – once a man has landed on the moon.
“I will gladly pay you Tuesday for a hamburger today.” — J. Wellington Wimpy.