I’m sorry I haven’t had much opportunity to blog lately. The move’s going behind schedule due to me getting so sick last weekend that I could barely get out of bed for three days straight, which of course happened while Tiff was in Oregon for a week so I could pack. And of course, the day she came home, she and little Jon got sick, just as I was getting better. Add on top of that the fact that I was trying to get another iteration out on the sheetmetal and other hardware for our latest engine, trying to design and build an alignment jig, trying to help pack up the shop, etc, etc, etc.
So, apparently now that I’m no longer having sucky birthdays like I used to [long story], my bad luck has hopped over to my blogiversaries. Could be worse I suppose.
Anyhow, enough self-pity, I really did have a point I wanted to make with this post!
In a lot of the commentary to my post below about propellant depots, many people seemed to take the Henry Ford “You can have any color you want so long as it’s black” sort of attitude. Basically, there are some propellants that are harder to handle than others–the poster boy being hydrogen. Having dealt a little with hydrogen, I can understand others’ dislike for the stuff.
That said, we’re not Henry Ford. If someone wants to buy hydrogen from me on-orbit, I’m not about to tell him “Sorry pal, come back when you want a Real Man’s propellant!” The fact is that for all the extra hassles, there are plenty of benefits for using hydrogen in some systems, and having the ability to sell it to those who want it is going to be important.
I guess this all boils back down to the whole monoculture idea that I hit on in one of my very first posts. The fact is that there are likely going to be many different things done in space that demand different vehicles, made and operated by different companies, not all using the same fuels, engines, etc. There will likely be stations in equatorial orbits as well as higher inclination orbits. VTVL vehicles and HTHL vehicles will likely have niches. You’re going to see hydrogen powered vehicles as well as hydrocarbon powered ones. I think that even ELVs and RLVs will coexist for a while.
So, while some propellants can be stored using simple rubber bladders with Murphy Straps, there’s going to be someone (likely quite a few) who want to buy hydrogen from you. There are ways of solving the problems of cryogenic propellant storage for hydrogen, so we may as well investigate those technologies anyway. The good news is that once we know how to store and transfer liquid hydrogen, pretty much everything else is going to be easy.
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 have one question regarding orbital fuel depots – Do you think it’d be feasible to ‘collect’ propellant from the atmosphere in areobraking-like maneuver?
Thanks for the plug, Jon, though I prefer to think of this concept as Murphy Bags. Murphy Straps are for a different kind of docking maneuver market I’m aiming for, more along the lines of Bigelow hotels than fuel depots.
That said, I don’t see a need to use exactly the same storage method for everything.
If you can use Murphy bags for everything except LH, and it’s the cheapest and most reliable solution, then do it. Then for the LH, come up with something else, whether it’s a modified Murphy bag or a giant slurpee machine filled with hydrides that are outgassed, with the LH flowing under pressure to a fridge unit that liquifies it and pumps it on the spot. Whatever works best, works best. Just don’t knock other solutions just because they don’t inherently support LH.
I expect it will be desirable to develop a pumping system that can work with almost any tank, and that it is probably better to keep the complexity on the side of the pumping system, leaving the tanks as simple and cheap as possible.
A very small rotovator, (200-300m/s delta v), using the propellant depot as the counter weight sounds like one fairly nice solution. The tether would weigh less than many of the other pumping systems being proposed, and could do useful work besides.
Jv,
Do you think it’d be feasible to ‘collect’ propellant from the atmosphere in areobraking-like maneuver?
Not really. Aerodynamic drag becomes bad enough to start requiring a lot of thrust to make up for it long before you’re plowing through enough air to actually be able to “mine” anything from the atmosphere.
Just seems like a losing proposition to me.
~Jon
Big D,
That said, I don’t see a need to use exactly the same storage method for everything.
Fair enough. I could see a mix of options being used for propellant settling dependent on what the propellant is. I was just saying that assuming that you didn’t have to solve the LH2 problem ever was being naive.
~Jon
Pete,
I’m assuming that the actual pumps themselves may just be COTS electric pumps–nothing particularly fancy. Now if for some reason a higher feed rate is needed, there are other options. But realistically, taking a couple of hours or days to tank up a big ship isn’t neccessarily bad.
I’m not sure I agree with you about keeping all the complexity with the pumps. Complexity doesn’t have to be mind bogglingly expensive or high maintenance. I think that the correct balance of complexity will be whatever can be designed with the best combination of low development costs, low maintenance, and low operational costs.
And yeah, while a rotovator is one possible solution, it has drawbacks like most others. In the end, the decision for which method among the many will be used for settling is likely going to be based on the personal preferences of the first company that gets enough money to try putting something like this together.
~Jon
I’m assuming that the actual pumps themselves may just be COTS electric pumps–nothing particularly fancy. Now if for some reason a higher feed rate is needed, there are other options.
Like, say, several electric pumps.
But realistically, taking a couple of hours or days to tank up a big ship isn’t neccessarily bad.
Unless you’re equatorial, you’re going to have to wait for your launch window anyway. What’s a few extra hours of pumping?
Chris,
>> Now if for some reason a higher
>> feed rate is needed, there are
>> other options.
>
> Like, say, several electric pumps.
To a point. I could see a situation
where you wanted to pump stuff fast
enough that solar powered electric
pumps might not be feasible. The
good news though is that most of the
more realistic solutions for the
propellant settling problem probably
incorporate most of the hardware
you’d need to pump stuff faster
anyway.
> Unless you’re equatorial, you’re
> going to have to wait for your
> launch window anyway. What’s a few
> extra hours of pumping?
I could see situations where the
ability to pump stuff fast could
be beneficial to some customers.
But that situation should be filed
under “problems we wish we had”. 🙂
~Jon
If you collect mass from the atmosphere, and you compensate for the drag with a rocket, you need a rocket with an exhaust velocity at least as great as your orbital velocity.
It might be better to use an electrodynamic tether. Collecting 1 kg/s would require a power of at least 30 MW, in low earth orbit.
Paul, what about counteracting the pressure with a solar sail?