I was somewhat surprised that my earlier Dual-Fluid Depot post generated as much interest as it did.Â I didn’t think there were many people who cared about depots who hadn’t read any of the papers by Frank Zegler, Bernard Kutter, or myself on the topic.Â But I wanted to include an intro just for sake of thoroughness before tossing out this variation on the theme.Â Now, I’m glad I did that.
With that introductory post out of the way I wanted to share a variant on the theme that I looked into about a week ago–using the 5m diameter DCSS instead of the Centaur as a baseline for single-launch depots.
I ran the numbers for this concept, and if you:
- Did the “depot LH2” tank as just a stretched version of the 5m diameter LH2 tank on the DCSS, using existing tooling
- Used both the LOX and LH2 tanks from the DCSS as the “depot LOX” tanks
You could store somewhere between 100-103mT of LOX/LH2 (at a MR of ~5.8-6:1) using a depot based on existing stages and existing tooling.Â This would give you ~90% of the capacity of an ACES derived depot, even if ACES never gets funded.
A couple of quick notes:
- The existing DCSS 5m LH2 tank is load-bearing.Â It actually connects at the bottom of the tank to the interstage, and at the top of the tank to the PLF.Â This means that a depot LH2 tank built using the same structure, and with no payload on top, could actually replace a good chunk of the cylindrical part of the PLF for a depot flight.
- One of the challenges that will need to be addressed is that with the tank built into the PLF diameter, you can’t put normal MLI on the outside of the tank, since normal MLI can’t take aerodynamic loads.Â A deployable sunshield is one solution, but might only work at La Grange points.Â Another interesting one being developed by Quest Product Development Corp (in conjunction with Ball Aerospace) is LV-IMLI, an advanced version of MLI that might be able to be up to the task. A third option would be qualifying a larger diameter, “hammerhead” style fairing with say 6-7m diameter.
- You don’t necessarily need to use both the DCSS tanks as “Depot LOX Tanks”.Â It is also possible to say use just the DCSS LH2 tank, and leave the DCSS LOX tank for use in storing Argon, Xenon, or some other SEP propellant.Â This would make more sense for L1/L2 based depots.Â You’d still be at somewhere around 74-75mT of LOX/LH2, but you’d also have about 28mT of liquid argon storage capacity.Â And you could store up to 60mT if you used Xenon instead of Argon.
- The 100mT number was assuming a target depot O/F ratio of 6.0, which is actually probably on the lean side.Â The actual PLF volume is big enough to support a much bigger LH2 tank, so you could account for boiloff, etc.
- You’d still use a CRYOTE-like module between the DCSS and depot LH2 tank to handle all of the actual depot operations functions such as power, control, rendezvous and docking, propellant transfer, etc.
- DCSS LH2 tanks are less nice from a heat transfer standpoint because they have isogrid ribs on the inside that serve to lower the thermal resistance between the LH2 and the tank wall (more wetted surface area to conduct heat through–think of the ribs as “heating fins”), but the surface are to volume ratio of a squatter larger tank might make up for this somewhat.
Anyhow, this isn’t a thoroughly modeled idea, but it’s one way to get a 100mT capacity depot in a single launch using existing stages and existing tooling.Â Whether you actually need a depot this big or not is open for debate, but I wanted to point out that it was possible, even if ACES is never funded.
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its good to see mention of fuel depot as a transient and storage point for Liquid Argon and Xenon 🙂
not being an engineer handicaps me when it comes to liquid or gas on a ion powered tug or interplanetary transfer vehicle,do you save mass on the tanks if you are using liquid and not gas?
On the other hand can liquid Noble’s weigh to much?
and the question above is also a engine question 🙂
over on Lori Garver’s face book page I have suggested CRYOTE with liquid Xenon and a NEXT ion engine to test the concept………….
test Liquid Xenon cooled by the Centaur (LH)
Test LAr fluid transfer from Centaur to CRYOTE
test Ion powered CRYOTE
suggest to NASA combining the Ion and solar FTD missions using Centaur and CRYOTE, involve Air force/DOD moneys for this.
That’s a heck of a lot of xenon, more than the current annual production of the pure element, I think. I’m not sure you’d want to put it all in one tank.
Also, liquid Xenon is exceptionally heavy, would this cause a problem in a solely ion powered vehicle?
I think this is why the Vasimer folks want to use liquid Argon, their weight penalty is in the power source for their engine.I wonder if the Vasimer engine can use the DCSS for its tank 🙂
To be honest, I’m not a super big fan of SEP, except maybe for travel outside of cislunar space. The manufacturing nerd in me still thinks that if you do a fair apples-to-apples comparision of cislunar transportation with chemical and SEP systems, that the chemical will end up coming out on top due to lower development and unit costs, higher reusability, more “inventory turns” per year, etc. But doing that analysis fairly is a serious research project I haven’t had time to really do yet.
Also, I agree wrt: Xenon Paul. I think Argon is a better match. Not as good as Xenon, but a lot more plentiful (I think).
Argon is 0.93% of the Earth’s atmosphere and 1.6% of Mars’ atmosphere .
Xenon is 0.0000087% of the Earth’s atmosphere and 0.000008% of Mars’ atmosphere.
The price reflects this.
if its Liquid argon it masses a lot less,
The idea for the hybrid RL-10 with ion engine was that the chemical engine would fire for a L2 to earth flyby with a interplanetary payload.
the alternative is the Centaur/DCSS uses RL-10 only, but LH cools the liquid Argon, after L2 to earth flyby(gravity assist) the Centaur or DCSS transfers liquid Argon to a CRYOTE with a NEXT ion engine.So CRYOTE is our outer planet in space transfer stage
Another configuration idea:
Stretch both the LOX and LH2 tanks on the stage. Insulate the LH2 tank for long term storage. Feed engines from the same tanks used for storage. Fill tanks only part way for launch, enough to power the engine for the launch plus margin. Once in orbit any propellant not used in launch is already in the tank where it will be stored.
You could in principle do something like that…but then you’d be modifying the whole stage…Not sure if that would actually be easier or not. Also, right now the DIV-H upper stage I was basing this on has a smaller diameter LOX tank. In order to get the same volume, it would end up needing to be pretty long. It’s an option, but it’s unclear if it’s the best way of doing things.
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