Starship On-orbit refueling - Options and Discussion

[edzieba]

Designing payloads that can only be transported via Starship also means locking out Option P landers. And given that the Option P lander contract even exists in the first place, we can be that NASA suggesting such payloads would result in congress similarly pitching a fit (and a completely coincidental lack of budget being allocated to development of such payloads). That basically limits you to payloads that are of low enough mass to be transported by all prospective landers but are modular enough that you could cram more onto a Starship lander for a reasonable and useful benefit.

I'm not sure what the relationship is between Artemis, CLPS, and the HDL (the App. P-requested cargo version of whatever HLS gets picked).  But CLPS mission planners are free to pick whatever platform will get their job done.  And if Artemis planners can rely on a CLPS LSS, they can make a payload--especially a commodity payload--as big as they want.

Is there any reason that SX has to work through NASA to deliver a lunar science package? If SX were to announce intent to deliver science packages to the moon NASA would then be only one of many customers. IIUC NASA suggested that Artemus bidders have other uses for their hardware to make the program more sustainable.

No reason they have to, but developers and builders of science payloads are not set up to do things that way. Red Dragon had some tacit NASA backing to start with (as an EDL demonstrator) but very little takeup even at bargain basement prices for science payloads. Neither Dragon 1 nor Dragon 2 have flown a free-flying science mission, and none are on the books (despite takeup for the more expensive manned free-flyer missions). CLPS and VADR both involve NASA as the middleman soliciting payloads for commercial missions.
i.e. there's nothing to stop SpaceX from landing independent science missions, but there aren't any independent science missions looking for a ride.

[OTV Booster]

Designing payloads that can only be transported via Starship also means locking out Option P landers. And given that the Option P lander contract even exists in the first place, we can be that NASA suggesting such payloads would result in congress similarly pitching a fit (and a completely coincidental lack of budget being allocated to development of such payloads). That basically limits you to payloads that are of low enough mass to be transported by all prospective landers but are modular enough that you could cram more onto a Starship lander for a reasonable and useful benefit.

I'm not sure what the relationship is between Artemis, CLPS, and the HDL (the App. P-requested cargo version of whatever HLS gets picked).  But CLPS mission planners are free to pick whatever platform will get their job done.  And if Artemis planners can rely on a CLPS LSS, they can make a payload--especially a commodity payload--as big as they want.

Is there any reason that SX has to work through NASA to deliver a lunar science package? If SX were to announce intent to deliver science packages to the moon NASA would then be only one of many customers. IIUC NASA suggested that Artemus bidders have other uses for their hardware to make the program more sustainable.

No reason they have to, but developers and builders of science payloads are not set up to do things that way. Red Dragon had some tacit NASA backing to start with (as an EDL demonstrator) but very little takeup even at bargain basement prices for science payloads. Neither Dragon 1 nor Dragon 2 have flown a free-flying science mission, and none are on the books (despite takeup for the more expensive manned free-flyer missions). CLPS and VADR both involve NASA as the middleman soliciting payloads for commercial missions.
i.e. there's nothing to stop SpaceX from landing independent science missions, but there aren't any independent science missions looking for a ride.

There's a healthy market for cubesats. It's a big jump from cubesats to SS but not unimaginable.


First that sucker has to fly. Once it's demonstrated refueling and has done a demo lunar landing it will have demonstrated that it's the real thing.


Science packages are traditionally long lead time items so only he more adventurous that really understand the meaning of 'payload rich' will have shorter lead time packages ready for manifest within a couple of years of that first landing.


As "Quantity has a quality all its own" (J. Stalin, at Yalta) in reference to armies, so too does SS in deliverable mass. As a mind experiment, imagine the James Webb if designed to fly on SS. It could easily grow from 6.2t to 20t with simplified PV and sunshade and enough propellant to last until everybody looses interest in continued funding. It would have been less expensive to design and less expensive to build. How much is hard to say but IMO, significantly. Optical systems are inherently high dollar items. Other types of packages would show greater savings.


Between the private sector and universities looking for prestige programs it's not unthinkable that SX will run private science packages to the moon.


Is anybody working on cubesat mongo? Something based on maybe half meter cubes.

[TheRadicalModerate]

One other possible near- to medium-term market for third-party prop sales using a depot in LLO:  Point-to-point lunar missions with some fairly modest-sized hopper.  Hops on the Moon are expensive, because every mission has four big suborbital burns.  Rather than lowering prop for them onto the lunar surface, the difference between a long suborbital hop and going all the way to LLO on one of the hops isn't very much.  Stopping to refuel on the way back to base, the hopper would be ready to go for the next mission.

Making hydrolox out of lunar water would be great--eventually.  But the economics of doing lunar exploration this way will be far superior to capitalizing high-scale water mining and electrolysis.

[sdsds]

One other possible near- to medium-term market for third-party prop sales using a depot in LLO:  Point-to-point lunar missions with some fairly modest-sized hopper.  Hops on the Moon are expensive, because every mission has four big suborbital burns.  Rather than lowering prop for them onto the lunar surface, the difference between a long suborbital hop and going all the way to LLO on one of the hops isn't very much.  Stopping to refuel on the way back to base, the hopper would be ready to go for the next mission.

That's good out-of-the-box thinking. LLO is not generally a stable orbital regime. Maybe a depot in polar LLO could facilitate transfers between the north and south lunar poles?

[TheRadicalModerate]

One other possible near- to medium-term market for third-party prop sales using a depot in LLO:  Point-to-point lunar missions with some fairly modest-sized hopper.  Hops on the Moon are expensive, because every mission has four big suborbital burns.  Rather than lowering prop for them onto the lunar surface, the difference between a long suborbital hop and going all the way to LLO on one of the hops isn't very much.  Stopping to refuel on the way back to base, the hopper would be ready to go for the next mission.

That's good out-of-the-box thinking. LLO is not generally a stable orbital regime. Maybe a depot in polar LLO could facilitate transfers between the north and south lunar poles?

It can facilitate transfers to anywhere, as long as you're only going to touch LLO once.  There's a frozen LLO very near 90º, so you can have the following conops (which isn't prop-optimal, but has good abort properties):

1) Assume hopper is just full enough to return to the depot from a lunar base at the poles.  When the depot will cross the longitude of the target mission (which it will do every two weeks), launch to the depot and completely refuel.

2) De-orbit from the depot to land at the target.

3) Do the mission.

4) When the mission is over or at any time there's an abort, hop (suborbitally) back to the base.  Repeat.

Even if you only want a 5t crew module, this isn't a small amount of prop.  But it's a small amount of prop compared to a mission from Earth.  So if you got a serious exploration program going, this would be a pretty good market.

Again, Dynetics as it probably will be for SLD would be almost perfect for this role.  It's a lot smaller than Starship, but for expeditions of a few days, an ALPACA that can refuel at a Starship depot, using Starship prop logistics, might easily outperform the LSS itself.

It'd be nice if you could point to something that the other provider had that's actually superior to LSS for some purpose.

[OTV Booster]

One other possible near- to medium-term market for third-party prop sales using a depot in LLO:  Point-to-point lunar missions with some fairly modest-sized hopper.  Hops on the Moon are expensive, because every mission has four big suborbital burns.  Rather than lowering prop for them onto the lunar surface, the difference between a long suborbital hop and going all the way to LLO on one of the hops isn't very much.  Stopping to refuel on the way back to base, the hopper would be ready to go for the next mission.

That's good out-of-the-box thinking. LLO is not generally a stable orbital regime. Maybe a depot in polar LLO could facilitate transfers between the north and south lunar poles?

It can facilitate transfers to anywhere, as long as you're only going to touch LLO once.  There's a frozen LLO very near 90º, so you can have the following conops (which isn't prop-optimal, but has good abort properties):

1) Assume hopper is just full enough to return to the depot from a lunar base at the poles.  When the depot will cross the longitude of the target mission (which it will do every two weeks), launch to the depot and completely refuel.

2) De-orbit from the depot to land at the target.

3) Do the mission.

4) When the mission is over or at any time there's an abort, hop (suborbitally) back to the base.  Repeat.

Even if you only want a 5t crew module, this isn't a small amount of prop.  But it's a small amount of prop compared to a mission from Earth.  So if you got a serious exploration program going, this would be a pretty good market.

Again, Dynetics as it probably will be for SLD would be almost perfect for this role.  It's a lot smaller than Starship, but for expeditions of a few days, an ALPACA that can refuel at a Starship depot, using Starship prop logistics, might easily outperform the LSS itself.

It'd be nice if you could point to something that the other provider had that's actually superior to LSS for some purpose.

Let's step back from purely a technical discussion and add in a bit of timing.


AIUI, Dynetics would have a mission ~2 years following the LSS crewed mission. Is it reasonable to expect a depot used for the LSS mission to have not boiled off? Neither we nor SX has a realistic boil off model based the hardware to be used. If the depot is dry, tankage of some sort needs a ride up there.


Integrating the Dynetics and depot operations, while theoretically routine, will not be simple. It's two different companies and different cultures. It can no doubt be done but at the cost of X hours of effort by both companies.


By SS standards it's not all that much propellant. If Dynetics is planning on buying a ride on SS with their own mini tanker/depot why bother with a dicy SS depot at all? The work would be less as would the revenue, but the risk would also be less.


If it were firmly known that the LLO depot would be alive and kicking it would be the basis for collaboration discussions. The only way I can see Dynetics going for it is if they hit a snag with their own plans.

[TheRadicalModerate]

AIUI, Dynetics would have a mission ~2 years following the LSS crewed mission. Is it reasonable to expect a depot used for the LSS mission to have not boiled off? Neither we nor SX has a realistic boil off model based the hardware to be used. If the depot is dry, tankage of some sort needs a ride up there.

Even if the depot is (mostly) dry, as long as it remains functional, it can be replenished with cheap propellant.  Just send the prop along in a Starship tanker, which returns from NRHO to EDL when it has transferred the prop.

The better question is whether a dry depot is still functional or not.  If it has solar panels and enough propellant for station keeping and attitude control, I suspect it's functional.  It may be able to store enough supercritical GCH4 and GOX in COPVs to accomplish those goals.

Another question is whether something like this would tip the balance between passive and active cooling.  If an Option B or SLT LSS only needs a non-integral number of tankers' worth of prop, it's possible that it wouldn't require any additional tanker launches at all.  But then you'd really need to have a ZBO depot.

Integrating the Dynetics and depot operations, while theoretically routine, will not be simple. It's two different companies and different cultures. It can no doubt be done but at the cost of X hours of effort by both companies...

I agree that this is a non-trivial amount of work.  From what we've seen recently, it's not happening right away.  But it also seems to be the case that Dynetics' tanks/tankers will fly on Starship as payloads, so they're getting quite a bit of cost reduction from that if things go well.

Note that handling cryogenic payloads in any payload bay is a new feature.  Two ways to do this:

1) Just-in-time filling of tanks on the launch pad, with the needed venting.

2) Launch the tanks dry (albeit pressurized for rigidity), then fill them on-orbit, before deploying them.

That second method may actually be the real answer here:  If you have a dry tank that's hooked up, via a PAF, to the Starship propellant system, then you've managed to forgo the docking requirements that you'd need to use the depot, and piggybacking off of most of the tanker's prop transfer plumbing makes the adaptation about as easy as possible.

This does bring up a question, though:  Assuming that Dynetics wants to second-source their tanks on Vulcan, how would this work then?  Centaur is hydrolox (as is New Glenn's second stage), so flowing through its GSE doesn't work, either on the pad or in orbit.  How does Dynetics expect this to work?

If it were firmly known that the LLO depot would be alive and kicking it would be the basis for collaboration discussions. The only way I can see Dynetics going for it is if they hit a snag with their own plans.

Don't confuse a hopper architecture with an HLS architecture.  SLD/SLT is going to have to refuel in NRHO.

[Greg Hullender]

It's at least theoretically possible to fabricate a tank that will hold liquid oxygen or methane indefinitely. Not in LEO, but certainly at NRHO.

If a coating can be fabricated with about a 0.01 α/ϵ ratio and if this is placed on a sphere at uniform temperature, far from other heat sources, then the sphere will come to a steady state temperature of about 88 K, sufficient to passively store liquid oxygen.
Development of a thermal control coating optimized for cryogenic space applications (A Krenn et al 2022 IOP Conf. Ser.: Mater. Sci. Eng. 1240 012001)

[Robotbeat]

And, of course, we can do much better than a sphere. JWST is one such example. Or even just a long cylinder pointed toward the Sun.

[Greg Hullender]

The biggest issue seems to be that the coating that can actually achieve that is a bit thick--5 mm or so. However, if the tanks are meant to be used over and over, perhaps it wouldn't be a big deal to send them up empty to start with.

[TheRadicalModerate]

It's at least theoretically possible to fabricate a tank that will hold liquid oxygen or methane indefinitely. Not in LEO, but certainly at NRHO.

If a coating can be fabricated with about a 0.01 α/ϵ ratio and if this is placed on a sphere at uniform temperature, far from other heat sources, then the sphere will come to a steady state temperature of about 88 K, sufficient to passively store liquid oxygen.
Development of a thermal control coating optimized for cryogenic space applications (A Krenn et al 2022 IOP Conf. Ser.: Mater. Sci. Eng. 1240 012001)

The issue here is TRL.  They know what they need, but I'm not sure that's what they have yet.

[Robotbeat]

It's at least theoretically possible to fabricate a tank that will hold liquid oxygen or methane indefinitely. Not in LEO, but certainly at NRHO.

If a coating can be fabricated with about a 0.01 α/ϵ ratio and if this is placed on a sphere at uniform temperature, far from other heat sources, then the sphere will come to a steady state temperature of about 88 K, sufficient to passively store liquid oxygen.
Development of a thermal control coating optimized for cryogenic space applications (A Krenn et al 2022 IOP Conf. Ser.: Mater. Sci. Eng. 1240 012001)

The issue here is TRL.  They know what they need, but I'm not sure that's what they have yet.

JWST shows high TRL even for passive cooling to like LH2 temperatures far from Earth…

But SpaceX probably wants to keep far away from deployable MLI if they can. (But they shouldn’t be so afraid of it.)

[TheRadicalModerate]

The issue here is TRL.  They know what they need, but I'm not sure that's what they have yet.

JWST shows high TRL even for passive cooling to like LH2 temperatures far from Earth…

But SpaceX probably wants to keep far away from deployable MLI if they can. (But they shouldn’t be so afraid of it.)

Webb only has to shade against one source in ES-L2.  There are two (at least) in NRHO.

[Twark_Main]

It's at least theoretically possible to fabricate a tank that will hold liquid oxygen or methane indefinitely. Not in LEO, but certainly at NRHO.

If a coating can be fabricated with about a 0.01 α/ϵ ratio and if this is placed on a sphere at uniform temperature, far from other heat sources, then the sphere will come to a steady state temperature of about 88 K, sufficient to passively store liquid oxygen.
Development of a thermal control coating optimized for cryogenic space applications (A Krenn et al 2022 IOP Conf. Ser.: Mater. Sci. Eng. 1240 012001)

The issue here is TRL.  They know what they need, but I'm not sure that's what they have yet.

JWST shows high TRL even for passive cooling to like LH2 temperatures far from Earth…

But SpaceX probably wants to keep far away from deployable MLI if they can. (But they shouldn’t be so afraid of it.)

Not passive, or not "like" LH2 (<30 K, or <20 K at 1 bar). The only part of JWST that drops below the critical point of hydrogen requires active cooling.


https://old.reddit.com/r/jameswebb/comments/s4yfs8/jwst_temperature_v_time_cooldown_profile_from/

[OTV Booster]

AIUI, Dynetics would have a mission ~2 years following the LSS crewed mission. Is it reasonable to expect a depot used for the LSS mission to have not boiled off? Neither we nor SX has a realistic boil off model based the hardware to be used. If the depot is dry, tankage of some sort needs a ride up there.

Even if the depot is (mostly) dry, as long as it remains functional, it can be replenished with cheap propellant.  Just send the prop along in a Starship tanker, which returns from NRHO to EDL when it has transferred the prop.

The better question is whether a dry depot is still functional or not.  If it has solar panels and enough propellant for station keeping and attitude control, I suspect it's functional.  It may be able to store enough supercritical GCH4 and GOX in COPVs to accomplish those goals.

Another question is whether something like this would tip the balance between passive and active cooling.  If an Option B or SLT LSS only needs a non-integral number of tankers' worth of prop, it's possible that it wouldn't require any additional tanker launches at all.  But then you'd really need to have a ZBO depot.

Integrating the Dynetics and depot operations, while theoretically routine, will not be simple. It's two different companies and different cultures. It can no doubt be done but at the cost of X hours of effort by both companies...

I agree that this is a non-trivial amount of work.  From what we've seen recently, it's not happening right away.  But it also seems to be the case that Dynetics' tanks/tankers will fly on Starship as payloads, so they're getting quite a bit of cost reduction from that if things go well.

Note that handling cryogenic payloads in any payload bay is a new feature.  Two ways to do this:

1) Just-in-time filling of tanks on the launch pad, with the needed venting.

2) Launch the tanks dry (albeit pressurized for rigidity), then fill them on-orbit, before deploying them.

That second method may actually be the real answer here:  If you have a dry tank that's hooked up, via a PAF, to the Starship propellant system, then you've managed to forgo the docking requirements that you'd need to use the depot, and piggybacking off of most of the tanker's prop transfer plumbing makes the adaptation about as easy as possible.

This does bring up a question, though:  Assuming that Dynetics wants to second-source their tanks on Vulcan, how would this work then?  Centaur is hydrolox (as is New Glenn's second stage), so flowing through its GSE doesn't work, either on the pad or in orbit.  How does Dynetics expect this to work?

If it were firmly known that the LLO depot would be alive and kicking it would be the basis for collaboration discussions. The only way I can see Dynetics going for it is if they hit a snag with their own plans.

Don't confuse a hopper architecture with an HLS architecture.  SLD/SLT is going to have to refuel in NRHO.

I'm not sure I understand that last paragraph. I was alluding to a snag in Dynetics refueling plans.


The idea of the Dynetics tanker up in the cargo bay being loaded from the SS main tanks would be easily done using existing plumbing IF the SS depot has the QD up top. We have a difference of opinion on this.


Most all payloads need some custom TLC while mounted and waiting to launch. Keeping propellants topped off would be just another one of those things. A cryo cooler on board or a few holes in a fairing half for feeds and vents. Just have to be careful not to vent methane and O2 at the same time.


The Dynetics ship needs a ride to LEO. Is it a done deal that SS also takes it to LLO? The 1600/1550t tanks would make it a tight fit. Does anybody make an OTV that would physically fit in a standard cargo SS and make it from LEO to LLO?


Wouldn't that be a hoot? A Dynetics tanker launched on a SpaceX ship with a Neutron kicker from Rocket Labs. All done on a commercial basis.


Maybe we should wait and see how much propellant we're talking about.

[TheRadicalModerate]

I'm not sure I understand that last paragraph. I was alluding to a snag in Dynetics refueling plans.

A Dynetics HLS will have to fuel in NRHO, not LLO.  LLO only makes sense if they're going to use it has a point-to-point hopper as well as a descent-ascent element.

The idea of the Dynetics tanker up in the cargo bay being loaded from the SS main tanks would be easily done using existing plumbing IF the SS depot has the QD up top. We have a difference of opinion on this.

Even without the QD, it should be easy to flow prop up through the PAF into the Dynetics tank(er)s--on a Starship.  But if they do that, how do they get a second source via Vulcan or New Glenn?  Neither of those second stages have methane on board--nor will their GSE on the pad above the first stage.

You can pre-load the LCH4, but it's a freakin' nightmare keeping it cold from the time it leaves payload processing to launch time.  Unless you're willing to travel with a big cryocooler and proper venting, you can't do it.

[cAsE-sEnSlTivE]

what if they make the entire fuel depot rotate and transfer the fuel to a docking vehicle through a rotating seal? That way the vehicle that docks doesn't have to rotate

[SkyRate]

what if they make the entire fuel depot rotate and transfer the fuel to a docking vehicle through a rotating seal? That way the vehicle that docks doesn't have to rotate

A long-term storage depot will want to reflect in the ecliptic plane and radiate out of it, and to be easy to dock to, so some kind of stabilization is clearly needed.
But I think that thrusters/momentum wheels have to be the lower-risk option compared to an entirely new (and mission-critical) solution.

[Jim]

And yet if you think about it, the Shuttle orbiter was 'refueling' from the external tank on every launch.

Shuttle was rigidly mounted to the ET. The connector and structural mating was done on the ground. For the tank, it was a one night stand. Spending a hundred tech hours (a total WAG) on shuttle side inspection and refurb would not even have been a rounding error on shuttle turnaround. Other than that...

Yeah, and that was, if not insane, at least kinda dumb, as it turned out.  More importantly for this discussion:  It required a large team of humans in a shirtsleeve environment to align the bipods, connect them, tension them, and--last but hardly least--arm their pryrotechnic frangible bolts.  That's a silly--and likely impossible--design for in-space automated operations.

How the vehicles were mated doesn't negate the analogy.   It was the fact that the shuttle was sucking out the propellant with pumps.  In any refueling scenario, it is the tanker pushing fluid to the receiver.  The receiver is not taking low pressure fluid and pumping it up into high pressure tanks.

[edzieba]

And yet if you think about it, the Shuttle orbiter was 'refueling' from the external tank on every launch.

Shuttle was rigidly mounted to the ET. The connector and structural mating was done on the ground. For the tank, it was a one night stand. Spending a hundred tech hours (a total WAG) on shuttle side inspection and refurb would not even have been a rounding error on shuttle turnaround. Other than that...

Yeah, and that was, if not insane, at least kinda dumb, as it turned out.  More importantly for this discussion:  It required a large team of humans in a shirtsleeve environment to align the bipods, connect them, tension them, and--last but hardly least--arm their pryrotechnic frangible bolts.  That's a silly--and likely impossible--design for in-space automated operations.

How the vehicles were mated doesn't negate the analogy.   It was the fact that the shuttle was sucking out the propellant with pumps.  In any refueling scenario, it is the tanker pushing fluid to the receiver.  The receiver is not taking low pressure fluid and pumping it up into high pressure tanks.

As risky as it is to argue against Jim:
The Shuttle did not have any in-tank boost pumps. Liquid propellants were pushed out of the tanks and over the tank-to-vehicle connections and into the engine pumpheads by pressure from the ullage gas, not suction from the pump heads. Being autogenously pressurised that gas was supplied by the SSMEs, but could just as well have come from gas bottles inside the tanks (terrible idea though, no mass margins). Disconnect the tank-to-vehicle lines, and that ullage pressure would have equally well pushed propellants out the end of the lines into free space. Plumb those lines into a tank with a hole in the top, and they would have been pumped into that second tan (until it overflowed and propellants leaked out, or the first tank emptied and your ullage gas started bubbling across the link and making a mess, or you forgot to do all this under acceleration and just had a messy mixed flow shooting everywhere).

STS demonstrated that you can move cryogens over a pipe then disconnect the pipe and leave it permanently disconnected until remoted by hand on the ground. But Atlas also demonstrated that decades earlier with the LOX feeds to the booster engines. The hard part will be a cryogenic fluid coupler that can mate in orbit, demate, and remate again, multiple times, in orbit, whilst still allowing the receiving end of that connector to seal against flight pressures. That's been done for storable propellants, but not for cryogens, and cryogenic sealing and connectors are a notorious pain.