Starship On-orbit refueling - Options and Discussion

[oldAtlas_Eguy]

One obvious missing capability to turn the Option A LSS into Option B is the ability to refuel in cislunar, which is how the LSS becomes reusable. 

Don't they also need some way to inspect/test the vehicle before reuse? That seems to me to be the biggest missing piece--although it provides a great reason to have a crew at Gateway. :-)

There is no hard requirement in Option B for reuse of the HLS lander. The requirement is for "sustainable" access to the moon, meaning (more or less) one or more times a year for not too much money. The original NASA reference lander has three elements: transit, descent, and ascent, and only the ascent element was reusable in its Option B. The Starship HLS system has three elements: Depot, Tanker, and HLS. The tanker and Depot are reusable and the HLS is not very expensive, so even if it is expended  the system still meets the sustainability requirement. It is probably cheaper to expend it than to refuel it, but the big problems for reuse are reprovisioning and loading new large cargo. Provisioning and cargo are easy to load on a new HLS on Earth, much harder to transfer in space (cislunar, LEO, or other).

HLS is "not very expensive" because much of it is built from standard Starship parts in a high-production SpaceX factory.

Starship HLS also increases sustainability by eliminating most separate cargo missions. Cargo missions have generally been assumed to be one-way anyway.

It might make sense to reuse Starship HLS if SLS/Orion is retired and HLS conveys the crew from LEO to the Lunar surface and back.

The cost of the LSS is the crew habitat and other LSS crew related addons to the basic SS. A basic SS hardware may be easily as low as $50M. But an LSS hardware is likely to run at greater than $150M. NOTE here is that a depot and a BEO tanker would be at the close to a basic SS costs. Thus such to use an LSS at least 3 times will gain significant savings overall for surface missions of $50 to >$100M on each mission. Which can say a lot about a stripped down oneway cargo hardware to cost ~$75M for the cargo SS that delivers about 75 to 100t of cargo to the surface.

Even using a throw away tanker vs a Lunar Depot you would still save money by just reusing the LSS 3 to 5 times. You could even refuel the LSS for return to LEO so it could be loaded for next mission and still save money. Such that initially only Tankers are thrown away until its possible to return EDL the Tanker from Lunar orbit. Once that happens an additional ~$50M is saved per mission.

I question the $50m price tag on SS. An F9 full stack has been estimated at $30m and never hit the production numbers that SS is being designed for. Maybe something in the $10-25m range? A cost that low might skew the numbers against reuse although the landing engines would bump the costs.

A point to remember is the need for later landings to host a crew of four and stay alive through extended darkness. If folding this into the first build bumps the cost enough to justify reuse, so be it, but is does crimp redesign from 'lessons learned'.

In principal I am in favor of as much reuse as possible but I just can't make the case close in this instance. The build rate, the build cost, the expanding mission requirements, the inability to redesign for lessons learned, all seem to work against it.

OTOH, when it time for the 4 crew
overnight version, reuse might make sense.

My near term SS cost number for a Tanker equivalent is the ~$50M number. In the 2030 time-frame that number does decrease in my cost modeling to a little lower at the $30-40M level. The cost model is derived from some observed data about the superstructure manufacturing costs based on manpower during the initial SS suborbital builds and tests. I still use this data since it was easier to come to reasonable value for this cost since the manpower totals possible for this work was much more evident than now. Since then a significant amount of the build has been automated but so has the complexity due to swapping wall thickness for use of stringers to lower mass.

The bottom line here on the Depot and refueling is that having the depots do EDL may not be that important. Since the cost of a Depot that is likely to become obsolete in a couple of years for it to EDL so it can be scrapped is so low as in significantly less than $100M if even anywhere near that. And by not having the EDL equipment added it would save on cost for that while adding some additional equipment for long duration orbital operational stay. Such that a Depot that is used for 5 missions becomes ~$10M cost per mission that may have as many as 8 Tankers in one mission. As such that then would possibly make total prop cost for a mission to start at a value even less than $150M (good possibility that eventually a cost of $80-100M) to no higher than $400M when the Tankers have yet to be reused.

So evaluate design speculations by looking at cost of the various options. Since SpaceX will go for the ultimate mission lowest cost while still being able to have high number of missions usability rate/year.

[TheRadicalModerate]

I'd like to ask how effective are current TPS tiles as long time insulation for supply depot? Most proposals suggest stripping the depot bare, but wouldn't it be more effective to do the opposite a cover it all around with tiles? They could be dual used as simple omnidirectional insulation (so Earth radiation would be blocked too) instead of some deployable sunshield and the depot can also be used for Lunar missions and return to LEO by aerobraking, saving a lot of propellant.
Adding 20+tons to ship dry mass is not that big problem, if they can be used this way...

TL;DR version: the TPS will help a little bit, but not enough.

The longer version is complicated.  TPS really does three things:

1) It's an insulator:  it has a very low heat conductivity.  If you put a big heat pulse on one side of it, it takes a long time for the pulse to reach the other side.  But eventually, all things being in equilibrium, it will transfer just as much heat, at the same rate, once it reaches equilibrium.  Not great for long-term storage.  However:

2) It also has high radiant emittance.  The amount of heat re-radiated into space is εσT⁴, where ε is the emissivity (loosely, how much the material behaves like a black body), σ is a constant, 5.76E-8 W/m²/K⁴, and T is the temperature difference between the surface and the environment.

3) It's a reflector.  TPS does this very poorly, but any radiation that just bounces off obviously doesn't heat up anything.

During reentry, the high emissivity property dominates, because as the temperature rises, the emittance increases as the fourth power.  The reflectivity is relatively unimportant.  But the insulation is very important because reentry is short, so not much heat can soak through the insulation.  (Note that there's a non-trivial problem after a spacecraft lands, because there can be a big enough heat pulse making its way through the insulation to damage the spacecraft, and there's no way to remove it--because it's a good insulator.)

For a coating to keep cryogens cold, TPS isn't great.  Once the system reaches equilibrium, the insulation doesn't really help you.  And high emissivity doesn't help a lot, because space isn't very hot compared to reentry, so that T⁴ term doesn't help very much.  But reflectivity is quite important.

What you really want is a coating with extremely high reflectivity and emissivity.  There's an experimental coating that's called Solar White, which has very good emissivity in infrared wavelengths and very good reflectivity in optical wavelengths.  As passive coatings go, this is probably the best you can do.  You can also obviously put up sun shades and active cryocooling, but indications are that the LSS will likely go with some version of white, at least as the minimum viable product.

[TheRadicalModerate]

My near term SS cost number for a Tanker equivalent is the ~$50M number. In the 2030 time-frame that number does decrease in my cost modeling to a little lower at the $30-40M level. The cost model is derived from some observed data about the superstructure manufacturing costs based on manpower during the initial SS suborbital builds and tests. I still use this data since it was easier to come to reasonable value for this cost since the manpower totals possible for this work was much more evident than now. Since then a significant amount of the build has been automated but so has the complexity due to swapping wall thickness for use of stringers to lower mass.

This jibes pretty well with how I do this, which is that a naked Starship's costs (no crew) is somewhere between 25%-50% engines.  If you conservatively estimate the cost of Raptors at $2M/engine, that comes out to $24M-$48M.  I'd guess that SuperHeavy is closer to 75% engine cost, which would be $88M.

The bottom line here on the Depot and refueling is that having the depots do EDL may not be that important. Since the cost of a Depot that is likely to become obsolete in a couple of years for it to EDL so it can be scrapped is so low as in significantly less than $100M if even anywhere near that. And by not having the EDL equipment added it would save on cost for that while adding some additional equipment for long duration orbital operational stay. Such that a Depot that is used for 5 missions becomes ~$10M cost per mission that may have as many as 8 Tankers in one mission. As such that then would possibly make total prop cost for a mission to start at a value even less than $150M (good possibility that eventually a cost of $80-100M) to no higher than $400M when the Tankers have yet to be reused.

So evaluate design speculations by looking at cost of the various options. Since SpaceX will go for the ultimate mission lowest cost while still being able to have high number of missions usability rate/year.

Depots in LEO that can't do EDL are a no-brainer.  The question is whether to have a depot in cislunar and, if so, whether it's expendable.

Ideally, a plain ordinary lift tanker can top off at the LEO depot, go to NRHO, use an included "depot kit" to do RPOD with the LSS, refuel it, and go straight back to EDL.  Since the LSS itself has good prop storage properties, this is probably cheapest.

If the lift tanker can't carry a depot kit for whatever reason, or if it's not capable of carrying enough prop in one trip, then a depot in cislunar may make sense.  That way the depot kit is on the depot, so it can be an intermediary between the lift tanker and the LSS.

The only case where you'd have an expendable depot in cislunar is if there's some really compelling reason to carry the prop from LEO to cislunar in the depot itself (something you'd probably do on the first trip anyway, but then it'll need to be refilled), or if there's something particularly complex about the lift tanker-depot-LSS intermediation.  That seems unlikely to me.

Another big plus for having a reusable depot in cislunar:  The other App P winner can use it, as long as they don't do something stupid like use hydrolox.  This would seem to militate very strongly toward making the depot docking and transfer interfaces an open system, so SpaceX can sell (or even buy!) methalox to/from third parties.  Even if the Starship transport system were to go down for an extended period (due to an accident, for example), the depot would still be there, able to be refueled by third parties, until there was enough prop in it for an App P mission.  That's obviously more expensive than hauling the prop in a Starship lift tanker, but there are ways to jigger the price to defray third parties' risk if Starship isn't available.¹

______________
¹BTW, if Starship flights cost $50M/launch, the cost of prop delivered to a depot in NRHO is roughly $1M/t.  The cost of prop delivered by an FHE would be roughly $10M/t.  The cost of prop delivered on a VC-6 Heavy would be $17M/t.  SpaceX can assign risks to the possibility that Starship might not be available, forcing it to use an FHE, and set a price that defrays that risk while still providing a high likelihood of making a tidy profit.

[InterestedEngineer]

______________
¹BTW, if Starship flights cost $50M/launch, the cost of prop delivered to a depot in NRHO is roughly $1M/t.  The cost of prop delivered by an FHE would be roughly $10M/t.  The cost of prop delivered on a VC-6 Heavy would be $17M/t.  SpaceX can assign risks to the possibility that Starship might not be available, forcing it to use an FHE, and set a price that defrays that risk while still providing a high likelihood of making a tidy profit.

TFW throwing away Starships is still 10x cheaper than the competition.

[Anguy]

The cost of the LSS is the crew habitat and other LSS crew related addons to the basic SS. A basic SS hardware may be easily as low as $50M. But an LSS hardware is likely to run at greater than $150M. NOTE here is that a depot and a BEO tanker would be at the close to a basic SS costs. Thus such to use an LSS at least 3 times will gain significant savings overall for surface missions of $50 to >$100M on each mission. Which can say a lot about a stripped down oneway cargo hardware to cost ~$75M for the cargo SS that delivers about 75 to 100t of cargo to the surface.

So what if just crew section is reusable and prop section is expendable? After each mission CS can detach on orbit and wait for brand new PS from Earth that will dock to it...

[Greg Hullender]

I'm still wondering what sort of testing/refurbishing will be done either at Gateway or on the lunar surface. Or is that just not interesting if you aren't planning very frequent trips to the moon?

[DanClemmensen]

I'm still wondering what sort of testing/refurbishing will be done either at Gateway or on the lunar surface. Or is that just not interesting if you aren't planning very frequent trips to the moon?

And I still wonder how to reprovision and load new cargo. I don't think the single IDSS port suffices.

[oldAtlas_Eguy]

I'm still wondering what sort of testing/refurbishing will be done either at Gateway or on the lunar surface. Or is that just not interesting if you aren't planning very frequent trips to the moon?

And I still wonder how to reprovision and load new cargo. I don't think the single IDSS port suffices.

Use of 2 berthing ports inside the cargo bay of the LSS where each airlock has 1. To then berth a container to one of them or even 2 of them. Each container would be 2.5mX2.5mX3m in size ~18m^3 in volume. Sized so that they fit not only through the cargo hatch but also on the elevator. Such that a permanently landed LSS could be reprovisioned. Can also be done in orbit. And would travel with vehicle down and can be offloaded on the surface with the trash. Or loaded with the items to be returned to Earth and returned to orbit and then transferred as needed to eventually get it back to Earth.

Is that a solution you could work with?

[DanClemmensen]

I'm still wondering what sort of testing/refurbishing will be done either at Gateway or on the lunar surface. Or is that just not interesting if you aren't planning very frequent trips to the moon?

And I still wonder how to reprovision and load new cargo. I don't think the single IDSS port suffices.

Use of 2 berthing ports inside the cargo bay of the LSS where each airlock has 1. To then berth a container to one of them or even 2 of them. Each container would be 2.5mX2.5mX3m in size ~18m^3 in volume. Sized so that they fit not only through the cargo hatch but also on the elevator. Such that a permanently landed LSS could be reprovisioned. Can also be done in orbit. And would travel with vehicle down and can be offloaded on the surface with the trash. Or loaded with the items to be returned to Earth and returned to orbit and then transferred as needed to eventually get it back to Earth.

Is that a solution you could work with?

I think you are headed in the right direction. That probably suffices for provisioning and pressurized cargo, but not for large unpressurized cargo like rovers. It also requires SpaceX to implement functionality on the Option B lander that is not an Option B (or appendix P) requirement, Which means NASA would need a different mission plan for Appendix P, Unless you think the Appendix P bidders will implement the same interface?

[sebk]

1) It's an insulator:  it has a very low heat conductivity.  If you put a big heat pulse on one side of it, it takes a long time for the pulse to reach the other side.  But eventually, all things being in equilibrium, it will transfer just as much heat, at the same rate, once it reaches equilibrium.  Not great for long-term storage. 

This is incorrect. It wont transfer heat at the same rate. If you use higher thermal resistivity material, you'd get slower heat transfer.

Of course you'd still have boiloff unless you used active cooling. But you'd get much slower boiloff and you could use lower power active cooling to stop the boiloff.

[oldAtlas_Eguy]

I'm still wondering what sort of testing/refurbishing will be done either at Gateway or on the lunar surface. Or is that just not interesting if you aren't planning very frequent trips to the moon?

And I still wonder how to reprovision and load new cargo. I don't think the single IDSS port suffices.

Use of 2 berthing ports inside the cargo bay of the LSS where each airlock has 1. To then berth a container to one of them or even 2 of them. Each container would be 2.5mX2.5mX3m in size ~18m^3 in volume. Sized so that they fit not only through the cargo hatch but also on the elevator. Such that a permanently landed LSS could be reprovisioned. Can also be done in orbit. And would travel with vehicle down and can be offloaded on the surface with the trash. Or loaded with the items to be returned to Earth and returned to orbit and then transferred as needed to eventually get it back to Earth.

Is that a solution you could work with?

I think you are headed in the right direction. That probably suffices for provisioning and pressurized cargo, but not for large unpressurized cargo like rovers. It also requires SpaceX to implement functionality on the Option B lander that is not an Option B (or appendix P) requirement, Which means NASA would need a different mission plan for Appendix P, Unless you think the Appendix P bidders will implement the same interface?

For unpressurized cargo as long as it fits in a 2.5m W by 3m L by 2.5m T form factor that will fit on the elevator it would be transferred into the cargo bay by the Gateway CANDARM or other like arm in LEO. That size is about the max size that will fit on the current design size for the elevator.

For a rover that would be a large rover at ~4X the size of the Apollo rovers. Is that big enough? Various framing and pallets to be able to hold and move enmasse as a large group of smaller items in a very lightweight frame. Also strong enough to be handled and moved around and secured against acceleration.

[DanClemmensen]

I'm still wondering what sort of testing/refurbishing will be done either at Gateway or on the lunar surface. Or is that just not interesting if you aren't planning very frequent trips to the moon?

And I still wonder how to reprovision and load new cargo. I don't think the single IDSS port suffices.

Use of 2 berthing ports inside the cargo bay of the LSS where each airlock has 1. To then berth a container to one of them or even 2 of them. Each container would be 2.5mX2.5mX3m in size ~18m^3 in volume. Sized so that they fit not only through the cargo hatch but also on the elevator. Such that a permanently landed LSS could be reprovisioned. Can also be done in orbit. And would travel with vehicle down and can be offloaded on the surface with the trash. Or loaded with the items to be returned to Earth and returned to orbit and then transferred as needed to eventually get it back to Earth.

Is that a solution you could work with?

I think you are headed in the right direction. That probably suffices for provisioning and pressurized cargo, but not for large unpressurized cargo like rovers. It also requires SpaceX to implement functionality on the Option B lander that is not an Option B (or appendix P) requirement, Which means NASA would need a different mission plan for Appendix P, Unless you think the Appendix P bidders will implement the same interface?

For unpressurized cargo as long as it fits in a 2.5m W by 3m L by 2.5m T form factor that will fit on the elevator it would be transferred into the cargo bay by the Gateway CANDARM or other like arm in LEO. That size is about the max size that will fit on the current design size for the elevator.

For a rover that would be a large rover at ~4X the size of the Apollo rovers. Is that big enough? Various framing and pallets to be able to hold and move enmasse as a large group of smaller items in a very lightweight frame. Also strong enough to be handled and moved around and secured against acceleration.

But my basic problem is at the system level. Someone must deliver this stuff from Earth to NRHO. It may very well be cheaper to just send a new HLS and discard the old one.

[tbellman]

But my basic problem is at the system level. Someone must deliver this stuff from Earth to NRHO. It may very well be cheaper to just send a new HLS and discard the old one.

The real basic problem is that there is no heavy cargo that NASA wants to send on the HLS lander, and thus there is no problem with cargo transfer to be solved.

The Lunar Terrain Vehicle is to be delivered to the lunar surface by the LTV provider, and probably months in advance of the first crew to use it.  The LTV provider might contract SpaceX to do the delivery on a Starship, but that ain't gonna be the HLS lander.

The foundation surface habitat is currently just a vague hope in NASA's eyes, and if and when that gets built, it's not going to be delivered on the HLS lander, but on dedicated cargo landers.

The pressurised rover that is tentatively assumed to be built by JAXA is something that NASA could potentially want to be delivered together with the crew that's going to use it, but I believe it is much more likely that it will be sent on a dedicated cargo lander (and it may be that JAXA will be responsible for delivering it to the Moon as well, but that is very uncertain).

The nuclear reactor that NASA wants to test on the Moon—no way that's going to be sent on the same lander as the crew!  Dedicated cargo lander for certain.

Any other cargo NASA wants on the HLS lander can easily be transfered through the IDSS docking tunnel: tools, sample containers, food, clothes, spacesuits (with at least backpack detached, possibly arms and legs as well), water, air.  The IDSS port is what they use for reprovisioning ISS, after all.  (OK, they use the larger CBM as well, but the Cygnus implementation is not that much larger than the IDSS.)

Maybe NASA will come up with some large cargo that they want on the HLS lander, but that's going to be 2035 at the earliest.

Stop worrying about problems that no-one have!

[Twark_Main]

I'd like to ask how effective are current TPS tiles as long time insulation for supply depot? Most proposals suggest stripping the depot bare, but wouldn't it be more effective to do the opposite a cover it all around with tiles? They could be dual used as simple omnidirectional insulation (so Earth radiation would be blocked too) instead of some deployable sunshield and the depot can also be used for Lunar missions and return to LEO by aerobraking, saving a lot of propellant.
Adding 20+tons to ship dry mass is not that big problem, if they can be used this way...

The other option is to cover it with white blankets ala Shuttle. Might not survive intense aerobraking (moderate aerobraking should be fine), but it should mass a lot less than tiles.

I presume R&D could share commonality with HLS. Blanket performance should be substantially superior to paint, which buys down thermal risks in contingency planning.



Edit: Shuttle FRSI blankets massed 1.6 kg/m², so roughly 1/8th to 1/6th the mass of Starship tiles.

[DanClemmensen]

But my basic problem is at the system level. Someone must deliver this stuff from Earth to NRHO. It may very well be cheaper to just send a new HLS and discard the old one.

The real basic problem is that there is no heavy cargo that NASA wants to send on the HLS lander, and thus there is no problem with cargo transfer to be solved.

Maybe NASA will come up with some large cargo that they want on the HLS lander, but that's going to be 2035 at the earliest.

Stop worrying about problems that no-one have!

I know that the current mission concepts depend on one-way cargo landers to deliver large cargo to the Moon. But those concepts predate the selection of Starship as the HLS. Option B is supposed to be about "sustainability": i.e., allowing for an increased cadence by reducing costs. Starship HLS has many tons of downmass capability, not the tiny amount in the Option B and Appendix P requirements. This capability could be used to reduce or eliminate the costs of one-way cargo missions. This total cost of delivery of the cargo on a single-mission HLS may very well be lower than the cost of reuse of HLS plus the cargo missions. Or not. It should be analyzed.

[tbellman]

I know that the current mission concepts depend on one-way cargo landers to deliver large cargo to the Moon. But those concepts predate the selection of Starship as the HLS. Option B is supposed to be about "sustainability": i.e., allowing for an increased cadence by reducing costs. Starship HLS has many tons of downmass capability, not the tiny amount in the Option B and Appendix P requirements. This capability could be used to reduce or eliminate the costs of one-way cargo missions. This total cost of delivery of the cargo on a single-mission HLS may very well be lower than the cost of reuse of HLS plus the cargo missions. Or not. It should be analyzed.

It Does. Not. Matter. that the HLS Starship has tonnes of more cargo capability than required, because NASA does not have the ability to make use of it.  They do not have any such payloads now, they do not have any such payloads on their (vague) roadmaps, and they don't even have any such payloads in their wildest dreams.  Before NASA can make use of the cargo capabilities of the HLS Starship, they need to:

• Figure out what they want.  And despite the Artemis program being five years in, they haven't really figured out what kind of science they would want to do with even minimal cargo capacity, so how long do you think it will take them to figure out how to do even more (while still being limited to four crew once a year at best)?

• Secure financing for new payloads.  If not hard promises, at least reasonable indications that the US president, the OMB and the US congress won't just laugh when NASA tells them what they want.

• Procure such payloads.

• Wait for those payloads to actually be designed, manufactured and tested.

Before worrying about transferring large cargo to the HLS Starship, you need to pass at least the first point above: figuring out the relevant cargo.  And then you only need to worry about cargo transfer if those payloads actually benefit from being delivered on the HLS lander together with the crew, as opposed to being delivered on dedicated cargo flights directly from Earth (without passing NRHO and LOP-G).



I also think you are naïve in your interpretation of "sustainability".  For example, the  requirements document in the HLS RFP says this about HLS Sustainability:

Beyond the initial HLS missions, the HLS will support sustainable presence on the Moon by providing a regular cadence of reliable transportation services for humans and cargo.

(My bolding.)  Note the words "regular" and "reliable"; nothing about increased cadence, just regular.  Once every 12 months is regular.

[OTV Booster]

My near term SS cost number for a Tanker equivalent is the ~$50M number. In the 2030 time-frame that number does decrease in my cost modeling to a little lower at the $30-40M level. The cost model is derived from some observed data about the superstructure manufacturing costs based on manpower during the initial SS suborbital builds and tests. I still use this data since it was easier to come to reasonable value for this cost since the manpower totals possible for this work was much more evident than now. Since then a significant amount of the build has been automated but so has the complexity due to swapping wall thickness for use of stringers to lower mass.

This jibes pretty well with how I do this, which is that a naked Starship's costs (no crew) is somewhere between 25%-50% engines.  If you conservatively estimate the cost of Raptors at $2M/engine, that comes out to $24M-$48M.  I'd guess that SuperHeavy is closer to 75% engine cost, which would be $88M.

The bottom line here on the Depot and refueling is that having the depots do EDL may not be that important. Since the cost of a Depot that is likely to become obsolete in a couple of years for it to EDL so it can be scrapped is so low as in significantly less than $100M if even anywhere near that. And by not having the EDL equipment added it would save on cost for that while adding some additional equipment for long duration orbital operational stay. Such that a Depot that is used for 5 missions becomes ~$10M cost per mission that may have as many as 8 Tankers in one mission. As such that then would possibly make total prop cost for a mission to start at a value even less than $150M (good possibility that eventually a cost of $80-100M) to no higher than $400M when the Tankers have yet to be reused.

So evaluate design speculations by looking at cost of the various options. Since SpaceX will go for the ultimate mission lowest cost while still being able to have high number of missions usability rate/year.

Depots in LEO that can't do EDL are a no-brainer.  The question is whether to have a depot in cislunar and, if so, whether it's expendable.

Ideally, a plain ordinary lift tanker can top off at the LEO depot, go to NRHO, use an included "depot kit" to do RPOD with the LSS, refuel it, and go straight back to EDL.  Since the LSS itself has good prop storage properties, this is probably cheapest.

If the lift tanker can't carry a depot kit for whatever reason, or if it's not capable of carrying enough prop in one trip, then a depot in cislunar may make sense.  That way the depot kit is on the depot, so it can be an intermediary between the lift tanker and the LSS.

The only case where you'd have an expendable depot in cislunar is if there's some really compelling reason to carry the prop from LEO to cislunar in the depot itself (something you'd probably do on the first trip anyway, but then it'll need to be refilled), or if there's something particularly complex about the lift tanker-depot-LSS intermediation.  That seems unlikely to me.

Another big plus for having a reusable depot in cislunar:  The other App P winner can use it, as long as they don't do something stupid like use hydrolox.  This would seem to militate very strongly toward making the depot docking and transfer interfaces an open system, so SpaceX can sell (or even buy!) methalox to/from third parties.  Even if the Starship transport system were to go down for an extended period (due to an accident, for example), the depot would still be there, able to be refueled by third parties, until there was enough prop in it for an App P mission.  That's obviously more expensive than hauling the prop in a Starship lift tanker, but there are ways to jigger the price to defray third parties' risk if Starship isn't available.¹

______________
¹BTW, if Starship flights cost $50M/launch, the cost of prop delivered to a depot in NRHO is roughly $1M/t.  The cost of prop delivered by an FHE would be roughly $10M/t.  The cost of prop delivered on a VC-6 Heavy would be $17M/t.  SpaceX can assign risks to the possibility that Starship might not be available, forcing it to use an FHE, and set a price that defrays that risk while still providing a high likelihood of making a tidy profit.

A depot kit would be handy but tough (not impossible) to self deploy. Does it make dV sense to spot one at the gateway for visiting tankers? It would only launch once, the gateway arm could help in assembly and deployment, and it gives gateway a reason to exist.


BTW, I like your cost comparisons. Keep a lid on it or you might find multiple space programs fighting for a chance to wack you.

[OTV Booster]

I'm still wondering what sort of testing/refurbishing will be done either at Gateway or on the lunar surface. Or is that just not interesting if you aren't planning very frequent trips to the moon?

And I still wonder how to reprovision and load new cargo. I don't think the single IDSS port suffices.

Use of 2 berthing ports inside the cargo bay of the LSS where each airlock has 1. To then berth a container to one of them or even 2 of them. Each container would be 2.5mX2.5mX3m in size ~18m^3 in volume. Sized so that they fit not only through the cargo hatch but also on the elevator. Such that a permanently landed LSS could be reprovisioned. Can also be done in orbit. And would travel with vehicle down and can be offloaded on the surface with the trash. Or loaded with the items to be returned to Earth and returned to orbit and then transferred as needed to eventually get it back to Earth.

Is that a solution you could work with?

I think you are headed in the right direction. That probably suffices for provisioning and pressurized cargo, but not for large unpressurized cargo like rovers. It also requires SpaceX to implement functionality on the Option B lander that is not an Option B (or appendix P) requirement, Which means NASA would need a different mission plan for Appendix P, Unless you think the Appendix P bidders will implement the same interface?

For unpressurized cargo as long as it fits in a 2.5m W by 3m L by 2.5m T form factor that will fit on the elevator it would be transferred into the cargo bay by the Gateway CANDARM or other like arm in LEO. That size is about the max size that will fit on the current design size for the elevator.

For a rover that would be a large rover at ~4X the size of the Apollo rovers. Is that big enough? Various framing and pallets to be able to hold and move enmasse as a large group of smaller items in a very lightweight frame. Also strong enough to be handled and moved around and secured against acceleration.

Um, uh, am I missing something? Doesn't the big stuff get delivered direct to the lunar surface? When there's big bulky unpressurized cargo to deliver, a berthing hatch would be an unnecessary self imposed limit. Same for a 'standard' elevator. If another company needs access give them the keys and a set of instructions.


If the ship is a one way it's no big thing. If it comes back, aero brake and store it on orbit (probably near a depot) until another overdimentional load shows up on the manifest.

[OTV Booster]

But my basic problem is at the system level. Someone must deliver this stuff from Earth to NRHO. It may very well be cheaper to just send a new HLS and discard the old one.

The real basic problem is that there is no heavy cargo that NASA wants to send on the HLS lander, and thus there is no problem with cargo transfer to be solved.

Maybe NASA will come up with some large cargo that they want on the HLS lander, but that's going to be 2035 at the earliest.

Stop worrying about problems that no-one have!

I know that the current mission concepts depend on one-way cargo landers to deliver large cargo to the Moon. But those concepts predate the selection of Starship as the HLS. Option B is supposed to be about "sustainability": i.e., allowing for an increased cadence by reducing costs. Starship HLS has many tons of downmass capability, not the tiny amount in the Option B and Appendix P requirements. This capability could be used to reduce or eliminate the costs of one-way cargo missions. This total cost of delivery of the cargo on a single-mission HLS may very well be lower than the cost of reuse of HLS plus the cargo missions. Or not. It should be analyzed.

To use a trucking analogy, wind turbine blades are well within the weight limits of a standard flatbed but will not fit. They use a specialized trailer that will never find a backhaul. These trailers are deadheaded back for another blade, and that's part of the cost of doing business.


Like all analogies, it can only go so far. It may be more economical to just run one way with big items. One way or return, if it's too big to fit on an unmodified crewed ship, it needs an adequate cargo carrier.


If the bulk of cargo can be carried on crewed ships (an untested assumption) a specialized cargo ship will absolutely add costs. But, it adds value that the crewed ship can't. They can explore only so far on foot.

[TheRadicalModerate]

It Does. Not. Matter. that the HLS Starship has tonnes of more cargo capability than required, because NASA does not have the ability to make use of it.  They do not have any such payloads now, they do not have any such payloads on their (vague) roadmaps, and they don't even have any such payloads in their wildest dreams.

I agree, with one caveat:  There's a class of "commodity" payloads that could be planned and slotted into any surface architecture very quickly.  Examples:

1) 150t of solar panels.
2) 150t of batteries, fuel cells, or APUs.
3) A big tank of LOX.
4) A big tank of LCH4.
5) A big tank of water.
6) 150t of the equivalent of portland cement for regolith.

But these are all payloads where their most important property is scale, and HLS can't scale its payloads large enough to matter.

The HLS LSS, at least with its current conops, is a lot more marginal than most people think.  An expendable CLPS or HDL LSS, on the other hand, is not.