I was poking around at some of the other articles on that Lockheed page ,that I got sent a link to, and found some more interesting stuff. Once again, big caveat about hyperbole being used, but I still think that they make some really solid points. Particularly the section at the very bottom about Cryogenic Propellant Transfer. If you have the time, I’d seriously recommend poking through all these papers, particularly this one, and this one (which I’ll comment on later).
Here’s some thoughts, comments, and things I noticed on the technical side:
- This paper supports my point I’ve made here several times that once you have a good way to settle propellants, all of the other issues related to Zero-G propellant transfer go from being unknown tech-development projects, to straightforward engineering projects directly based on existing hardware and processes.
- I was wrong about the amount of settling force needed to make things manageable. I’d always used 0.001-0.01g as a conservative estimate. According to LM, they’ve flight proven that .0001g works, and they’ve flight demonstrated settling at as low as .00001g accelerations. That’s only about 10 micro-gees!
- Even without Zero-Boiloff techniques, it’s possible to keep the boiloff rate well below 1% per month with existing technology.
As I said, I’d seriously recommend reading the whole thing. The thing to remember, is that this is LOX/LH2 we’re talking about–pretty much the toughest commonly used rocket propellant combination to work with. I had never realized that while the Centaur was in orbit, that they have ducted vents being used to settle the propellants continuously, and that they have over 100 flights worth of experience with this stuff. As they point out, every Centaur flight demonstrates on-orbit propellant transfer–to the RL-10 engines. Including chill-down, propellant acquisition, propellant mass guaging, etc.
Now, the architecture they suggest is a “Vehicle to Vehicle” fueling architecture–basically it doesn’t include a propellant depot. Adding a depot would possibly require finding a non-propulsive settling route for the propellants, but would possibly simplify the remaining problems substantially. If the depot is manned, you could use remote piloting instead of fully Autonomous Rendezvou and Docking, you could add a small arm like the Canadarm Mini I suggested to allow you to berth modules instead of docking, which makes that even easier. And you could manually attach propellant transfer lines in a shirt-sleeve environment, which gets rid of the last complication.
There still is some work left to be done, but if anyone can honestly read these papers and not get the feeling that “this is a technology that is most of the way there, and not a long-shot bet at all”, I’d be surprised. In fact, I’m going to make a prediction. I’ll be so bold as to say that before a full CLV stack flies for the first time, there will have already been an on-orbit demonstration of cryogenic propellant transfer by a commercial company.
What do you guys think?
Jonathan Goff
Latest posts by Jonathan Goff (see all)
- NASA’s Selection of the Blue Moon Lander for Artemis V - May 25, 2023
- Fill ‘er Up: New AIAA Aerospace America Article on Propellant Depots - September 2, 2022
- Independent Perspectives on Cislunar Depotization - August 26, 2022
I need to actually read the papers but ‘in-vehicle’ is one thing, while ‘vehicle-to-vehicle’ is another… Maybe :o)
Demonstration will be ‘the’ thing :o)
On another note though, if you only need ‘micro-Gs’ for settling manuvers that is right in the ball park for ED tethers.
With an automated docking set up and ED tether ‘propulsion and orbital’ correction you’d definitly be on your way.
Randy
Randy,
If you read the papers, you can see that once you settle the propellants, pretty much all of the zero-g fluid-dagnabits weirdlichkeit goes away, and it really does reduce to a very similar process to standard propellant transfer on the ground. The only difference between in-vehicle and vehicle-to-vehicle propellant transfer is the docking/berthing process (which we’ve been doing since my dad was in High School), and the actual fluid coupling system, which while it could be complicated could also be very simple.
But yeah, if you really only need dozens of micro-G’s, there are all sorts of ways that might work. It’s just a question of which is the lowest hassle, highest reliability.
~Jon
Jon wrote:
“The only difference between in-vehicle and vehicle-to-vehicle propellant transfer is the docking/berthing process (which we’ve been doing since my dad was in High School), and the actual fluid coupling system, which while it could be complicated could also be very simple.”
That last is what worries me :o)
For the most part, people I’ve run into assume its simple. Really the only way we’ll KNOW is to test it.
(Which all in all shouldn’t be THAT damn tough to actually do :o)
Randy
How much would a minimum honest vehicle to vehicle test cost ?
To keep it honest, it would require two launches from ground. This means at least one of the vehicles has to have active last mile guidance and propulsion.
Docking/berthing/fluig coupling ? Could this be ripped from Progress/Zvezda ?
How small vehicles could you fit all this on ? Falcon 1 or Dnepr is probably out of the question, which would push this to multiple tens of millions in launch costs already.
A fuel depot could acquire the needed acceleration for propellant tranfer while doing the orbital corrective manouvering, i.e. the periodical boosting of the orbit if the depot is stationed on LEO…
The low accelerations required could probably be achieved with some highly efficient thrusters, an ionmotor perhaps?
The low accelerations required could probably be achieved with some highly efficient thrusters, an ionmotor perhaps?
Use the boil-off as fuel for cold gas thrusters?
Kert,
How much would a minimum honest vehicle to vehicle test cost?
Possibly very cheap. A lot depends on what you’re trying to demonstrate. If you split the propellant transfer part of the research off from the docking/rendezvous part, you could probably demonstrate a lot of the basics on a Zero-G flight. If you insist on at least docking in addition to propellant transfer, you might be able to do a subscale demo on a suborbital RLV flight. Your timeframe would be short, but you can try a bunch of times until you get it right (if you setup the experiment right).
If you do a full-up orbital demo, I would suggest using a spent upper stage, and a “free-rider” like LM was suggesting, hooked to their Centaur stage. If done right, you could keep the costs in the low single-digit millions possibly.
Basically, it all depends on how fast you need it, and how much money you have to spend on the research. If you are on a shoestring budget, you can still do it, you just have to take a different path.
~Jon
Olaf wrote:
“Use the boil-off as fuels for
cold gas thrusters?”
This seems to be what they have in
mind… from the paper: the “…
settling propellant could easily
consist of warm vented GH2 and GO2
extracted […] for pressure
control…”
I believe the Saturn V 3rd stage
also did the same thing, using
boiloff venting during the coast
period to keep the propellant
correctly settled for the lunar
departure relight.
-dw