SpaceX to NASA quote : simplified mission architecture : Technical discussion

[Brigantine]

Very similar to the BLEO Dragon concept mentioned upthread, but with Orion:

I don't understand why two HLS is needed. Just one fully fueled HLS that docks Orion in LEO, performs TLI and LOI. Then descent and ascent, dock with Orion that does TEI and HLS is disposed.

This would be Constellation style, Ares V + Altair replaced with Starship.

Fair question.
Committing to two HLS is a way to buy extra margins to have up your sleeve.

How long do people think it will take, not just for HLS Starship to 'work', but to achieve its nominal performance with sufficient reliability?

With [EDIT: development~] risks not yet retired around refueling and boil-off in different thermal environments etc. - my thinking is you can move the goalposts closer for development, and just throw mass margins at any issues that come up for a quick fix.

Also, I don't think Orion's docking port is designed for it to be tugged inverted at high acceleration, so the flight profile will need to walk on eggshells around that. Just throw extra performance margins at it instead of developing a whole new docking port.

The mission is a one-off bodge using unfinished components ASAP. How can you work around the un-finished-ness without sacrificing safety? "just fly a skip reentry, the heat shield will be fine!"

[TheRadicalModerate]

Very similar to the BLEO Dragon concept mentioned upthread, but with Orion:

I don't understand why two HLS is needed. Just one fully fueled HLS that docks Orion in LEO, performs TLI and LOI. Then descent and ascent, dock with Orion that does TEI and HLS is disposed.

This would be Constellation style, Ares V + Altair replaced with Starship.

Fair question.
Committing to two HLS is a way to buy extra margins to have up your sleeve.

How long do people think it will take, not just for HLS Starship to 'work', but to achieve its nominal performance with sufficient reliability?

With risks not yet retired around refueling and boil-off in different thermal environments etc. - my thinking is you can move the goalposts closer for development, and just throw mass margins at any issues that come up for a quick fix.

Also, I don't think Orion's docking port is designed for it to be tugged inverted at high acceleration, so the flight profile will need to walk on eggshells around that. Just throw extra performance margins at it instead of developing a whole new docking port.

The mission is a one-off bodge using unfinished components ASAP. How can you work around the un-finished-ness without sacrificing safety? "just fly a skip reentry, the heat shield will be fine!"

The two-HLS version doesn't retire any operational risk (quite the contrary), because the actual HLS (as opposed to the "transit" HLS) still has to do launch - 200 x 800ish - refuel - TLI(BLT) - NRHO - loiter - RPOD(transitHLS) - LS - NRHO - RPOD(transitHLS) - loiter, which is exactly the same as if the Orion did the entire transit.  The advantage of two-HLS is that it kills SLS and Orion. 

It might shorten the development critical path a bit, because when the regular HLS is ready, so is the transit HLS.  They're basically identical.¹

The question is whether Orion on the nose significantly shortens the critical path or reduces operational risk.  It probably does both:

1) There's no need to make substantive mods to the D2.

2) The HLS has a lot more margin, since it only has to do LEO - refuel - RPOD(Orion) - TLI - LLO - Undock(Orion) - LS - LLO - RPOD(Orion) - dispose, and doesn't need to do the TEI burn.

3) The first crew RPOD point is VLEO (I use 200 x 200), so the depot doesn't have to maneuver at all, and the RPOD is a circular, low-MMOD orbit.

4) The VLEO orbit also avoids the radiation toastiness of the orbit needed to get the D2+HLS to LLO and back to TEI.

5) Because the Orion does the burn back to TEI, it saves about 1450t of prop to LEO, which is nothing to sneeze at.

However, you still have all of the development risk associated with refueling, and the in-space, landing, and ascent risks for the HLS are still the same.  Basically, the HLS development risk remains the same.

You also have to make the Orion handle about 1G of eyeballs-out acceleration, using its questionable implementation of IDSS. If I were handicapping which capsule would have more trouble with eyeballs-out (reverse) acceleration, I'd bet on Orion every time.  (Remember, this is the vehicle that had a failed power data unit, and had to fly it on Arty 1, because it was going to require a one year delay to de-mate the CM from the ESM, replace the PDU, and re-mate the ESM.  Given that things are that hinky with the design, what are the odds that there's something, somewhere, that fails when it spends any significant time effectively upside-down?

D2 has all the same eyeballs-out risks.  But I trust SpaceX a lot more not to have done something stupid with their design.  On the other hand, Orion theoretically has no modification to do it your way, while D2 requires a decent number of mods.

________
¹There's some risk, both developmentally and operationally, associated with doing an HLS-to-HLS prox ops and docking.

[sdsds]

Dragon 2 from Earth to LEO
One instance of Starship HLS acting as an OTV (Orbital transfer vehicle) takes crew to NRHO
another Starship HLS  (HLS) takes crew to lunar surface and back to NRHO   (just like the Artemis III PoR)
OTV takes crew to LEO
Dragon 2 returns crew to Earth.

First, kudos to @DanClemmensen for the prescience of starting that discussion topic two years ago! My contribution here is just to reiterate that LEO is not a single place; instead it is a large set of trajectories and getting from one to another within that set requires huge amounts of propulsion (delta-v). The simplest way to make the architecture described above work is to launch a second Dragon 2 into the specific LEO trajectory that matches the one the returning orbital transfer vehicle will be entering.

[Vultur]

What modifications would be required for D2 to handle deep space? Supposedly the heat shield is already designed for higher energy reentry. Is it communications that's the issue?

[thespacecow]

Interesting how space x all of a sudden released video of simplified starship lander and saying achieved milestones in design and starting to build hardware.

...

In short ain`t going to happen.

The majority of this post seems like AI slop to me. (Note this account has a history of posting AI slop without labeling it as such)

[sdsds]

What modifications would be required for D2 to handle deep space? Supposedly the heat shield is already designed for higher energy reentry. Is it communications that's the issue?

Yes, there are a number of possible issues that might require minor (or major) modifications to D2 if it were to be used for the trans-lunar and trans-Earth segments of the mission. Those include as you mention its ability to function in deep space and its ability to re-enter safely after a return from the Moon. The comms issue you mention is just one of several related to D2 electronics. The other would be radiation hardening. Finally, the mission architectures discussed require D2 to ride "on the nose" of the Starship-based transport vehicle, which in turn requires D2 to handle "eyeballs-out" acceleration.

None of these capabilities are proven. Even an aggressive program to test them would push the crewed mission outside the timeframe being discussed here.

[DanClemmensen]

Dragon 2 from Earth to LEO
One instance of Starship HLS acting as an OTV (Orbital transfer vehicle) takes crew to NRHO
another Starship HLS  (HLS) takes crew to lunar surface and back to NRHO   (just like the Artemis III PoR)
OTV takes crew to LEO
Dragon 2 returns crew to Earth.

First, kudos to @DanClemmensen for the prescience of starting that discussion topic two years ago! My contribution here is just to reiterate that LEO is not a single place; instead it is a large set of trajectories and getting from one to another within that set requires huge amounts of propulsion (delta-v). The simplest way to make the architecture described above work is to launch a second Dragon 2 into the specific LEO trajectory that matches the one the returning orbital transfer vehicle will be entering.

The discussion started even earlier, by other forum denizens. My contribution was to consolidate it and to provide an initial focus. The heavy lifting was then done by others as I watched in awe.

As you know, we discovered the LEO orbit problem you mention and christened it "the RAAN problem", and as you say the best short-term brute-force solution is to simply use two separate Dragon flights. It's still a lot cheaper than SLS/Orion.

[dondar]

Reading comprehension is the key real problem for the z generation.

let take boiling off.
Boiling off  during fuel transfer is not a problem per se. There is no thermal equilibrium anyway in big cryogenic hydraulic system. EVER. "Industrial level" zero boil-off is achieved  obviously by continuous/periodic refrigeration. (there is no other practical way lol because entropy is a bitch).

 Practical restrictions lie elsewhere.
There is problem of "clinging to the walls" coupled with "trying to escape" during fuel transfer, i.e. specific instances of boil off in very specific places in specific conditions. These very specific "boil-off"(i.e. liquid/gas bubbles) instances lead to local  negative pressure gradients, which can and do (if not mitigated) stall fuel flow.
There are mechanical and hydraulic solutions for that. Heck banal venting during fuel transfer "solves" that.
The whole story of HLS is "easy" in a sense that every solution is "visible" and HLS is very hard project because the real problem lies in "rocket science", i.e. choosing and implementing these 100s (literally) rather sketchy (i.e. untested industrially) solutions and to clue in reasonable time some working kludge that works. Preferably  not with Apollo budget.

[TheRadicalModerate]

What modifications would be required for D2 to handle deep space? Supposedly the heat shield is already designed for higher energy reentry. Is it communications that's the issue?

1) Heat shield tested for 11km/s entry.

2) Avionics rated for deep space radiation, including GCR.

3) Everything has to work with 1G backward acceleration.

4) Hard docking system has to endure compressive loads induced by 1G (approximately 125kN). There will also be bending forces as the Raptors gimbal.

5) I’m a little worried about thermal issues, especially if the HLS needs to put its nose to the Sun. That would expose the trunk and heat shield to continuous insolation. Probably better it’s the heat shield than some other part, but it’s still something to be simulated and tested.

6) RPOD at 200 x 1700ish has nav and crew health issues. Probably will need the boost kit to be qualified for deep space.

7) Nav, comms, thermal, and idle endurance issues staying in LLO uncrewed for a week or so.

None of these are showstoppers, but there’s real work to be done.

[Roy_H]

I really don't understand the focus of taking Dragon all the way to the Moon, when it is so easy to just bring HLS back to LEO. The Artemis IV mission already includes the proposal to have a Depot come to NHRO to re-fuel HLS for subsequent Moon landings. A similar amount of fuel is all that is required to return HLS to LEO.

I know, many are hung up on the safety of having crew onboard HLS during re-fueling. So if Gateway is a thing then the astronauts could wait there while refueling takes place. Or maybe Orion could be left in NHRO as a cheap replacement for Gateway.

But I remind you that astronauts already sit in Dragon while it is being fueled for a mission to ISS, and that many in-orbit refuelings are required just to get HLS to the Moon. How many in orbit refuelings are required before they are considered safe enough to have astronauts aboard?

[Vultur]

What modifications would be required for D2 to handle deep space? Supposedly the heat shield is already designed for higher energy reentry. Is it communications that's the issue?

1) Heat shield tested for 11km/s entry.

2) Avionics rated for deep space radiation, including GCR.

3) Everything has to work with 1G backward acceleration.

4) Hard docking system has to endure compressive loads induced by 1G (approximately 125kN). There will also be bending forces as the Raptors gimbal.

5) I’m a little worried about thermal issues, especially if the HLS needs to put its nose to the Sun. That would expose the trunk and heat shield to continuous insolation. Probably better it’s the heat shield than some other part, but it’s still something to be simulated and tested.

6) RPOD at 200 x 1700ish has nav and crew health issues. Probably will need the boost kit to be qualified for deep space.

7) Nav, comms, thermal, and idle endurance issues staying in LLO uncrewed for a week or so.

None of these are showstoppers, but there’s real work to be done.

Granted. What I was trying to ask is ... How many of these are capabilities Dragon actually already has but just haven't been demonstrated?

It would probably be quite quick to do a test flight to demonstrate things like 11 km/s heat shield entry and surviving deep space radiation and thermal (launch Dragon on a FH to a high energy trajectory?) if the existing hardware can do it .

[DanClemmensen]

I really don't understand the focus of taking Dragon all the way to the Moon, when it is so easy to just bring HLS back to LEO. The Artemis IV mission already includes the proposal to have a Depot come to NHRO to re-fuel HLS for subsequent Moon landings. A similar amount of fuel is all that is required to return HLS to LEO.

I do not recall seeing this as part of any formal contract or as part of any any statement form SpaceX or NASA. do you have a reference?

I know, many are hung up on the safety of having crew onboard HLS during re-fueling. So if Gateway is a thing then the astronauts could wait there while refueling takes place. Or maybe Orion could be left in NHRO as a cheap replacement for Gateway.

But I remind you that astronauts already sit in Dragon while it is being fueled for a mission to ISS, and that many in-orbit refuelings are required just to get HLS to the Moon. How many in orbit refuelings are required before they are considered safe enough to have astronauts aboard?

I keep this as a requirement for an Artemis III alternative mission because I want to pull in the schedule as much as possible. This means reducing the time it takes to make the decision, and that in turn means removing stuff like crewed in-orbit refilling.

Yes, as a practical matter crewed in-orbit refill almost certainly has a very low pLOC, much lower than a lot of stuff NASA tolerates in SLS/Orion, and the formal pLOC will drop rapidly as experience accumulates with uncrewed refill.  Let's wait and fight that battle later.

[Roy_H]

I really don't understand the focus of taking Dragon all the way to the Moon, when it is so easy to just bring HLS back to LEO. The Artemis IV mission already includes the proposal to have a Depot come to NHRO to re-fuel HLS for subsequent Moon landings. A similar amount of fuel is all that is required to return HLS to LEO.

I do not recall seeing this as part of any formal contract or as part of any any statement form SpaceX or NASA. do you have a reference?

Alas, both links provided by Grok are either dead or not accessible by me. HLS Operations Concept Document (OCD) https://ntrs.nasa.gov/api/citations/20250004567/downloads/Artemis-HLS-OCD-Q3-2025-Redacted.pdf
and https://www.nasa.gov/artemis/library
and https://www.nasa.gov/artemis-iv

On re-reading, I made a bad interpretation. There are only discussions about post Artemis IV refueling of HLS, not actual demonstration.

I guess I get too wrapped up in SpaceX mantra of re-usability and cannot imagine a new HLS being built and discarded for each follow on moon mission beyond Artemis IV. But I suppose NASA thinks that way.

[TheRadicalModerate]

What modifications would be required for D2 to handle deep space? Supposedly the heat shield is already designed for higher energy reentry. Is it communications that's the issue?

1) Heat shield tested for 11km/s entry.

2) Avionics rated for deep space radiation, including GCR.

3) Everything has to work with 1G backward acceleration.

4) Hard docking system has to endure compressive loads induced by 1G (approximately 125kN). There will also be bending forces as the Raptors gimbal.

5) I’m a little worried about thermal issues, especially if the HLS needs to put its nose to the Sun. That would expose the trunk and heat shield to continuous insolation. Probably better it’s the heat shield than some other part, but it’s still something to be simulated and tested.

6) RPOD at 200 x 1700ish has nav and crew health issues. Probably will need the boost kit to be qualified for deep space.

7) Nav, comms, thermal, and idle endurance issues staying in LLO uncrewed for a week or so.

None of these are showstoppers, but there’s real work to be done.

Granted. What I was trying to ask is ... How many of these are capabilities Dragon actually already has but just haven't been demonstrated?

It would probably be quite quick to do a test flight to demonstrate things like 11 km/s heat shield entry and surviving deep space radiation and thermal (launch Dragon on a FH to a high energy trajectory?) if the existing hardware can do it .

I'd guess that none of them have been demonstrated/tested.

If I were SpaceX, I'd turn the Option A demo into a full-up test and cart the D2 to LLO and back, then release it and let it do the EDL.  I can't remember if the demo requires a visit to NRHO or not.  If it does, this wouldn't work.  This would also require committing to the work to get D2 ready by the time the demo flies.

I'm still not sure I'd describe this as a "simplified mission architecture."  It's more of a way to make LockMart, Boeing, and NorGrumm wish they'd never decided to take a run at SpaceX like this.

If there's a genuine simplification, I can't think of what it would be.  Everything requires refueling.  Everything requires landing a tall (maybe not quite as tall) Starship on the Moon.


This is contrast to Blue, which could eliminate refueling by providing expendable CTs, with exactly 45t launch mass, to NRHO and LLO, then re-kludging the BM1 to handle a small crew module.  The CT in NRHO takes the BM1 down to crasher level, and the other CT takes it back to NRHO when the BM1 comes back to LLO.

There has been recent (in the last couple of days) talk that Blue's actual proposal involves a BM2 for the crew and BM1's as adjuncts.  I haven't tried to figure that one out.  I guess by "BM2", they could mean, "a thing roughly sized as a BM1, but with the crew module between the thrust structure and the LOX tank," and the BM1's could be 45t wet-mass vehicles that are launched in the fairing, rather than stacked like the CT.  Then they'd take the place of the CTs in what I proposed in the previous paragraph.

[TheRadicalModerate]

I really don't understand the focus of taking Dragon all the way to the Moon, when it is so easy to just bring HLS back to LEO. The Artemis IV mission already includes the proposal to have a Depot come to NHRO to re-fuel HLS for subsequent Moon landings. A similar amount of fuel is all that is required to return HLS to LEO.

I've seen no mention of a reuse of the HLS for Arty 4, so there's no need for a depot in NRHO.  Even if there were an attempt at reuse, the refueling would occur before the crew arrived.

I know, many are hung up on the safety of having crew onboard HLS during re-fueling. So if Gateway is a thing then the astronauts could wait there while refueling takes place. Or maybe Orion could be left in NHRO as a cheap replacement for Gateway.

But I remind you that astronauts already sit in Dragon while it is being fueled for a mission to ISS, and that many in-orbit refuelings are required just to get HLS to the Moon.

It's not a question of "many" being hung up on safety; it's a question of NASA being hung up on safety.  NASA doesn't like extra RPODs, and they're certainly not going to like a crewed refueling in a place where a failure condemns the crew to death.¹

And the Gateway isn't available as a bolt-hole for Arty 3.  That's the mission NASA's looking to accelerate.

How many in orbit refuelings are required before they are considered safe enough to have astronauts aboard?

For NASA, the answer to this is likely that they want enough data to be confident that a probabilistic risk assessment yields accurate results.  RPOD and refueling are a lot simpler than launch and EDL, so I would guess they'll get comfy with the PRA much sooner, but I doubt it'll be a number of refuelings less than 50.


As I said up-thread, single-HLS is not a "simplification".  It's a way of spanking NASA and all the aerospace contractors that depend on SLS/Orion.  I really can't think of a genuine simplification for Starship HLS.

If it turned out that putting Orion on the Starship HLS's nose was simple and risk-free, what Brigantine proposed up-thread might be a genuine simplification--and something that the SLS/Orion patrons might support, since it involves launching an Orion on an SLS--even though it's only going to LEO.  It still requires refueling, but only once, with no crew onboard, and only in VLEO.  And it provides hundreds of tonnes of extra prop margin, which could be used to implement any number of short-cuts where extra mass could simplify otherwise-complex systems.

The problem, of course, is that nothing on Orion is ever simple or risk-free.  If you even breathe on the mission plan, it takes LockMart months to wring its hands and adjust.  And this is far from just breathing on it; this is throwing the plan into a hurricane.

______________
¹Single-HLS missions always require refueling in lunar orbit, but there are two flavors:

1) Pre-descent refuelings.  If a pre-descent refueling fails, the HLS has enough prop to get back to a propulsive insertion into LEO.  The problem is that you're hauling all the prop to get from lunar orbit to TEI to LEO with you down to the Moon and back up again, so the amount of prop that needs to be provided to (multiple) depots in LEO is huge.

2) Post-ascent refuelings.  The amount of prop for these is quite modest, but if the refueling doesn't work, the crew is stranded in lunar orbit with few options for rescue.

[Roy_H]

2) Post-ascent refuelings.  The amount of prop for these is quite modest, but if the refueling doesn't work, the crew is stranded in lunar orbit with few options for rescue.

That is why I proposed a Lifeboat version of the Depot. With an Orion or even Dragon sized crew compartment in the nose of the Depot, a failed fuel transfer could be followed by the astronauts transferring to the Lifeboat Depot and returning to LEO. Picture the nose of the Depot being replaced with an actual Dragon, plus extra radiation shielding.

[TheRadicalModerate]

2) Post-ascent refuelings.  The amount of prop for these is quite modest, but if the refueling doesn't work, the crew is stranded in lunar orbit with few options for rescue.

That is why I proposed a Lifeboat version of the Depot. With an Orion or even Dragon sized crew compartment in the nose of the Depot, a failed fuel transfer could be followed by the astronauts transferring to the Lifeboat Depot and returning to LEO. Picture the nose of the Depot being replaced with an actual Dragon, plus extra radiation shielding.

But that's hardly a simplification.

[Roy_H]

2) Post-ascent refuelings.  The amount of prop for these is quite modest, but if the refueling doesn't work, the crew is stranded in lunar orbit with few options for rescue.

That is why I proposed a Lifeboat version of the Depot. With an Orion or even Dragon sized crew compartment in the nose of the Depot, a failed fuel transfer could be followed by the astronauts transferring to the Lifeboat Depot and returning to LEO. Picture the nose of the Depot being replaced with an actual Dragon, plus extra radiation shielding.

But that's hardly a simplification.

Compared to what? SLS/Orion, Blue Origin's proposal? It is more complicated than a Depot without a lifeboat, but given that almost all the lifeboat components are already included in the Dragon, it shouldn't be too hard to incorporate.

[DanClemmensen]

2) Post-ascent refuelings.  The amount of prop for these is quite modest, but if the refueling doesn't work, the crew is stranded in lunar orbit with few options for rescue.

That is why I proposed a Lifeboat version of the Depot. With an Orion or even Dragon sized crew compartment in the nose of the Depot, a failed fuel transfer could be followed by the astronauts transferring to the Lifeboat Depot and returning to LEO. Picture the nose of the Depot being replaced with an actual Dragon, plus extra radiation shielding.

SpaceX is already developing a Ship very similar to Depot but with crew accomodations. It's called Starship HLS. If you want your mission to include a lifeboat, use another HLS.

[Roy_H]

SpaceX is already developing a Ship very similar to Depot but with crew accomodations. It's called Starship HLS. If you want your mission to include a lifeboat, use another HLS.

HLS crew quarters are much larger, and reduce potential fuel tank size. Would the HLS have enough fuel capacity to refuel the landing HLS and retain enough fuel for both to return to LEO? Also HLS has landing thrusters, cargo space, not desired on a Depot. My argument is that the Dragon is already designed, and in production, building a whole other HLS would be more costly. The Dragon would be stripped of Draco and Super Draco thrusters.