Propellant Depot Dreams

Jon Goff weighs in too:

Very few people (IMHO) actually argue that propellant depots are a bad idea. On the other hand, should we be spending tax dollars on building them, right now? If yes, why?

I think propellant depots are a great idea, in theory.

However I see little reason to spend more than a tiny fraction of NASA's 2009 or 2010 budget on them.

Why? Because there isn't yet a market for them.

Well, yeah. There's no existing market for them because there're no space architectures that assume their exisence. And there're no space architectures that assume their existence because there are no propellant depots. (Actually, we should be talking about consumables depots -- non-propellant consumables will eventually be important, although their current usage is miniscule compared to propellants). One argument for government action in space is that it should capitalize up-front solutions that break out of the chicken-and-egg dilemma such as is faced here. It has the further benefit that if successful, it would greatly expand options for things like Luanr return and Martian settlement, and lower the overall, long-term price tag. We should at least be working seriously on the precursor issues, both technical and institutional.

Who is best positioned to break this ice?

There's no existing market for them because there're no space architectures that assume their exisence. And there're no space architectures that assume their existence because there are no propellant depots.

If one wishes to look to the American taxpayer to accomplish this,

One argument for government action in space is that it should capitalize up-front solutions that break out of the chicken-and-egg dilemma such as is faced here.

Propellant depot advocates now need to prepare concrete proposals that can be carried door to door in the House and Senate office buildings on Capitol Hill.

If other funding sources are envisioned, modify the approach as appropriate. Otherwise, propellant depots will remain an alluring fantasy or perhaps a useful cudgel to support gripes against NASA.

Well deserved gripes, perhaps, but how useful is that?

Bill, I agree. If this is to get beyond the bull-session phase, we need concrete, implementable proposals drafted and circulating. Maybe a Deep Space Initiative Organization would even put out a call for white papers on it. Hey, maybe even NASA, depending on who the leadership is.

By the way, if we want to go even more radical, instead of NASA contracting for delivery, have an open-purchase committment -- the propellant depot entity will buy all the propellants meeting the spec that are delivered in orbit, up to some large final number. The really fun part -- have a series of quantity targets, and every time the amount of propellants delivered get above a certain step, the price per pound delivered drops by a stated amount.

In my opinion, Rob and Jon are simply talking past one another.

Jon Goff offers an attractive vision of what could (and should) be developed. Jon is 100% correct in saying that a true spacefaring species will be able to do on-orbit propellant transfer and depots are a very sensible idea.

Rob is also 100% correct that there is no current market and that no arguments have yet been presented that will be persuasive to potential funding sources such as NASA (US taxpayers) or ESA (EU taxpayers) or JAXA (Japanese taxpayers) or Roskosmos (Russian taxpayers).

Point A and Point B. Both Goff and Coppinger are correct, on their own terms.

Now, the challenge becomes how do we bridge that gap.

How can anybody claim there's no market? Keep in mind that 'orbit is halfway to anywhere' Is that Heinlein or Pournelle? Can't remember.

Anyway; A fuel depot turns every orbital rocket into a potential transorbital... that's a market.

Second, arguments about the cost of putting fuel into orbit miss the fact that once you have a depot in orbit that will buy from the lowest cost provider... somebody is going to seriously think about getting those resources cheaper from places other than the Earth. The depot(s) become a market for them.

No Market??? Sheesh!

Bill,
Notice I *didn't* say that I think there are no current markets. I think there are a few existing markets that could be tapped in the near-term, they just have very challenging barriers to entry. If someone can figure out how to pull it off though, those barriers to entry are actually a good thing for them. :-)

I'm actually working this concept on the side, and not just as a theoretical one.

~Jon

Jon, I have no quarrel with your propellant depot proposals. As I wrote above, I agree 100% that a spacefaring species will be doing such things.

But we also need to be less harsh with Rob Coppinger because he also is correct in saying there are NO current markets and few prospects (at the moment) for persuading the powers that be to gut current NASA, ESA, Roscosmos agendas in favor of a massive shift to a depot approach.

Fuel depots simply are a fantasy UNTIL someone presents a well vetted proposal in a format that the check writers (primarily the U.S. Congress) will find persuasive.

And if you write up that proposal, I will cheer as loudly as anyone. So get to work, young man! ;-)

= = =

As an aside, LEO fuel depots are leading a current Daily Kos poll which asks what NASA's next objective should be.

http://www.dailykos.com/storyonly/2008/11/20/141651/04/305/663790

Bill,
I still disagree with you about there being "NO current markets" for propellant depots. There are customers, right now, that have systems that could benefit from a tug/depot system. Existing customers, with existing needs, and existing money. Now, they're not likely to be using cryogenic depots, and they'd likely be a lot smaller than what I'd be interested in for manned projects. But just repeating that you think there aren't markets doesn't prove there isn't demand. I freely admit that it's a market demand that while existing and provable is going to be very hard to break into, but it isn't a "chicken and egg" problem per se.

But I do agree that if NASA (or the DoD) started taking depots more seriously, that it would make all of this a lot easier. That or finding a billionaire interested in space who can be talked into not funding yet another rocket company.

~Jon

Very few people (IMHO) actually argue that propellant depots are a bad idea. On the other hand, should we be spending tax dollars on building them, right now? If yes, why?

Since when have you been opposed to spending tax dollars, Bill?

Orbital propellant depots would allow NASA to accomplish the goal you want -- sending NASA astronauts back to the Moon -- in a more efficient manner.

They would also help open the space frontier for things *other* than flag and footprint missions.

Why is that a bad thing?

Do you think NASA is only worth funding when they aren't doing anything useful?

Edward, I never said federal taxpayer funding of propellant depots was a bad idea.

However, I am saying that no one is framing the arguments in favor of propellant depots in a manner likely to persuade Congress.

Jon, I agree with you that a non-cryogenic market may exist today (or at least after the first Bigelow crewed hab goes up).

An RP-1 / LOX depot might well support a rudimentary tug built around the Russian RD-58 engine (Block D) or a SpaceX kerosene upper stage engine and the up front R&D costs needed storing kerosene on orbit shall be vastly lower than the R&D needed to deploy a liquid hydrogen depot.

= = =

Google Lunar contestants might be a customer.

Pre-deploy an RD-58 based Earth escape propulsion module and collect Google Lunar contestants in LEO and send them on to the Moon. Pre-deployed (depot) RP-1 could be used to extend the engine burn for that Block D increasing its ability to transit payload to lunar orbit.

That permits more massive Google XPrize lunar landers.

Er...Rand, a minor quibble: there certainly was a market for launch vehicles in 1956. The military was very interested in ballistic missiles. That's why von Braun had a good steady job with them.

There's no real market for fuel depots, but there's no real _market_ for the space station, or the shuttle whose main "market" is the space station, or for manned lunar exploration or Ares 1 and IV. And there are much cheaper ways of getting pretty screen savers than the Hubble Space Telescope.

Don't forget this piece by an up-and-coming, humble rising star (;))in the premiere issue of the AIAA Space Operations Communicator:

http://www.aiaa.org/tc/sos/communicator/jan_mar_2004/supply_depots.html

PS: Since this writing, I've re-thought the idea of shipping up water and electrolyzing it, for anyone who actually clicks on the link.

Bill,
If you're trying to sell propellant depots to Congress, there are several arguments you could use:

1) Typical parochial interests: higher flight rate for LM, Boeing (and eventually SpaceX and Orbital) means more jobs in certain congressional districts. Now that most of the Shuttle-district congresspeople/senators are either recently retired or now in the minority (Nelson being the exception), this should be easier. After all, LM is HQ'd in Mikulski's area, Boeing in Obama's backyard, and ULA and SpaceX in important blue states.

2) Military benefits. Tugs and depots (of the right sort in the right place) have very important benefits for both operationally responsive space (ORS isn't just about getting new satellites up there quicker, but milking more out of existing satellites and making them more useful and more survivable).

There are probably others. But those are two. Remember that while some areas would lose jobs with such a situation, they're areas that no longer have anywhere near as much legislative clout.

But I'm still not planning on NASA or DoD intentionally doing the right thing, so I'm working on other options at the same time.

~Jon

Tom,
Yeah electrolizing water is a pain in the backside. You'd likely spend less energy just keeping LOX/LH2 from boiling off (with a good passive thermal design) than you would trying to split it out of water.

~Jon

Edward, I never said federal taxpayer funding of propellant depots was a bad idea.

You've repeatedly said that anything other than ESAS would be a bad idea.

However, I am saying that no one is framing the arguments in favor of propellant depots in a manner likely to persuade Congress.

I'm not sure you speak for the entire Congress, Bill.

Again, you're the one who made the argument that NASA should spend huge amounts of money to send almost no one to the Moon. Orbital propellant depots would allow NASA to send *lots* of people to the Moon for the same huge sums of money, or an equal number of people to the Moon for smaller sums of money.

I'm waiting for you to frame your argument as to why it's better to send fewer people to the Moon, for the same amount of money, rather than more people.

Now, if you've decided you don't want NASA to return to the Moon after all (or go Mars, or an asteroid, or carry out more ambitious missions in LEO), then perhaps NASA doesn't need a propellant depot. Have you decided that, Bill?

This entire "no market" argument .. DARPA did Orbital Express for a reason. A scaled-up ASTRO _is_ your propellant depot already, and minimum cost-optimized NextSat would be your tanker. Yes, non-cryo system, but a step forward.
Btw i wonder if anyone has ever looked at refuelling Xenon tanks for XIPS ? It could create some interesting scenarios for long-duration deep space probes.

Jon-

Stuck on design, like most of us (probably part of the problem), but what I've come down to is delivering the LH2 and LOX separately. If a greater-than-necessary proportion of LH2 is delivered, it can be used to passively cool the LOX, and the boiloff can be used to make water. I think that's the simplest solution.