SpaceX to NASA quote : simplified mission architecture : Technical discussion

[dcporter]

SpaceX posted this update yesterday: https://www.spacex.com/updates#moon-and-beyond

It teases a "simplified mission architecture", with no details.

Since the contract was awarded, we have been consistently responsive to NASA as requirements for Artemis III have changed and have shared ideas on how to simplify the mission to align with national priorities. In response to the latest calls, we’ve shared and are formally assessing a simplified mission architecture and concept of operations that we believe will result in a faster return to the Moon while simultaneously improving crew safety.

There's a (partially L2?) policy thread over here, so this thread is for technical considerations. Please commence speculation or assembly of evidence

[leovinus]

I believe there is a thread for this at
SpaceX publicly commits to land crew on the Moon before any other nation
https://forum.nasaspaceflight.com/index.php?topic=63788.0

[envy887]

I believe there is a thread for this at
SpaceX publicly commits to land crew on the Moon before any other nation
https://forum.nasaspaceflight.com/index.php?topic=63788.0

That's in the Policy section and read-only for non-L2 members. The OP could link to it and clarify that this is for technical discussion only, not politics.

[InterestedEngineer]

Here's a potential simplified solution.

No NRHO.  Just straight from refueled Earth elliptical orbit to the moon surface with HLS.

HLS, a depot, and tankers.  Orion or Dragon for emergency return purposes only, which is a separate mission to park one in lunar orbit (e.g with falcon heavy or SLS)

A separate mission to put a few starlinks in orbit around the moon for 24/7/365 communications, so no worries about communication outages from the dark side of the moon.  Sell access to the Chinese.  Use the return to test high speed entry of a standard Pez starship.

[StraumliBlight]

Eric Berger discussed a simplified HLS mission architecture at 14:10 in yesterday's Off Nominal.

[Vultur]

Depends how aggressive they want to go on "simplified".

Musk tweeted about 'Starship will end up doing the whole mission', so that's one possible proposal. But I don't think NASA is ready for that one, for several reasons.

Short of that... Depends what delta-v they can get for a fully refueled HLS Starship.

[Oersted]

As for what SpaceX needs to show before credibly suggesting to "go it alone", I would say they have done most of the job. Starship is clearly capable of reaching orbit. It has done relights in space. It has even proved succesful reentry. The main outstanding tasks are in-space refuelling and lunar landing. Of those two I would say that only the second one is a major challenge. Compared to all else they have accomplished, in-space refuelling should not be a difficult task.

Crewed Earth landing and upper-stage reuse are not strictly necessary for a Moon shot, given that Dragon can ferry the astronauts to LEO and back. Starship would only need to aerobrake back into LEO and then transfer the astronauts to Dragon for landing, if a crewed Starship landing seems too scary.

I am guessing that by the time Starship lands a crew on the Moon we'll all feel less queasy about crewed Starship lift-off and landing ops on Earth.

So, we'll have a very simple architecture:
- Crewed Starship lift-off from Earth.
- Refuelling in LEO and then a TLI.
- Refuelling in LLO.
- Landing on the Moon and lunar surface ops.
- Lift-off from the Moon and refuelling in LLO.
- TEI and crewed Earth landing.

That will require one Starship HLS and as many Starship tanker/depot flights as it takes to position a full Starship depot in LEO and a full Starship depot in LLO.       

[Oersted]

I believe there is a thread for this at
SpaceX publicly commits to land crew on the Moon before any other nation
https://forum.nasaspaceflight.com/index.php?topic=63788.0

That's in the Policy section and read-only for non-L2 members. The OP could link to it and clarify that this is for technical discussion only, not politics.

Sorry, when I made that thread I didn't even realise that the Policy forum is read-only for non-L2-members. Indeed it is a good idea to have a thread like this here in the Starship Program forum. 

[TheRadicalModerate]

As for what SpaceX needs to show before credibly suggesting to "go it alone", I would say they have done most of the job. Starship is clearly capable of reaching orbit. It has done relights in space. It has even proved succesful reentry. The main outstanding tasks are in-space refuelling and lunar landing. Of those two I would say that only the second one is a major challenge. Compared to all else they have accomplished, in-space refuelling should not be a difficult task.

Crewed Earth landing and upper-stage reuse are not strictly necessary for a Moon shot, given that Dragon can ferry the astronauts to LEO and back. Starship would only need to aerobrake back into LEO and then transfer the astronauts to Dragon for landing, if a crewed Starship landing seems too scary.

I am guessing that by the time Starship lands a crew on the Moon we'll all feel less queasy about crewed Starship lift-off and landing ops on Earth.

So, we'll have a very simple architecture:
- Crewed Starship lift-off from Earth.
- Refuelling in LEO and then a TLI.
- Refuelling in LLO.
- Landing on the Moon and lunar surface ops.
- Lift-off from the Moon and refuelling in LLO.
- TEI and crewed Earth landing.

That will require one Starship HLS and as many Starship tanker/depot flights as it takes to position a full Starship depot in LEO and a full Starship depot in LLO.     

If you think an EDL-capable HLS is ready in the time allotted (I don't), there's a much simpler route via HEEO:

1) Launch the crew.
2) Fully refuel in VLEO.
3) Boost to VLEO+2500m/s  (this is 200 x 38,600)
4) Refuel again, at a second depot.
5) Go to the lunar surface, do you mission.
6) Ascend, TEI, and go straight to EDL.

Even this is arguably more complicated, because it takes 2800t of prop brought to LEO, which is somewhere between 19 and 28 tankers.  By comparison--and you have to use my assumptions, but they're apples-to-apples, at least--Option A takes half that amount of prop, and it only requires one refueling, in a just-barely-eccentric Earth orbit.  (I get 200 x 370, which is only ~50m/s above VLEO.)

If the goal is to kill SLS/Orion, or even just throw a brush-back pitch at LockMart, Boeing, and NorGrumm, then the two-HLS strategy we've discussed ad nauseam here is the way to go.  That costs 2250t of prop to LEO.  (The reason that this is cheaper than the direct launch/HEEO case is because an EDL-capable HLS has a much higher dry mass than the non-EDL HLS.

The cheapest single-HLS case I can come up with is the "D2 on the nose" variant, which only requires about 1600t of prop and a single, uncrewed refueling.  However, there's a catch, as you'll see:

1) HLS launches, uses its residual prop to boost to VLEO+400m/s (about 200 x 1740).
2) Crew launches on F9/D2, into the 200 x 1740 orbit, where it docks with the HLS.
3) HLS does TLI, with the D2 still docked to the nose.
4) HLS goes to LLO, where the D2 undocks.
5) HLS does lunar surface mission.
6) HLS re-docks with D2 after surface mission.
7) HLS+D2 does TEI.
8 ) Before entry interface, crew climbs into the D2 and does direct EDL.
9) HLS either disposes of itself or aerocaptures into LEO.

As we've discussed, ad nauseam, on the thread I linked above, this requires non-trivial but still fairly modest mods to the D2, because it has to work in a deep space environment (different radiation and thermal requirements), the heat shield has to be qualified for ~11km/s entry speed, and the D2 and docking system have to withstand about 1G eyeballs-out acceleration from the Raptors during TLI, LOI, and TEI.  But the prop to LEO load is small, there are no crewed refuelings, and the HLS doesn't have to return propulsively to LEO to do RPOD with the D2, where it may be subject to "the RAAN problem".²

___________
¹This isn't a lot farther than Polaris Dawn did, and that was before the advent of the D2's "boost kit", which should allow an even higher apogee.  Note, however, that this is a pretty toasty apogee in terms of Van Allen Belt #1 radiation.

²If you leave the D2 in LEO to wait for the HLS to return, the Moon moves in its orbit, so that the right ascension of ascending node changes, making the HLS and the D2 wind up in different orbital planes, which is extremely expensive to fix.  If you've planned your mission properly, the HLS returns with the same RAAN that it left, and everything's fine.  But if you have to abort, things are messed-up.

There are two solutions to this:

1) D2 on the nose (see above, and the ad nauseam thread).
2) Keep a second D2 on warm standby on the ground, so it can launch into the proper RAAN if there's an abort.

[Oersted]

Oops, I forgot that Starship HLS cannot land or even (I guess) aerocapture coming back to Earth. So, they'll have to transfer to a normal Starship somewhere enroute, probably in LLO. 

[TheRadicalModerate]

I believe there is a thread for this at
SpaceX publicly commits to land crew on the Moon before any other nation
https://forum.nasaspaceflight.com/index.php?topic=63788.0

That's in the Policy section and read-only for non-L2 members. The OP could link to it and clarify that this is for technical discussion only, not politics.

Sorry, when I made that thread I didn't even realise that the Policy forum is read-only for non-L2-members. Indeed it is a good idea to have a thread like this here in the Starship Program forum.

dcporter, would you mind if we widened this out to cover all the implications of the Wall of Text and the updated "moon" section that SpaceX provided?

catdlr, the other alternative is to re-home Oersted's thread from policy to Starship.  We should really have someplace rational (and non-L2) for the artwork pixel-counters and engineering thread folks to pore over this.

[Roy_H]

As for what SpaceX needs to show before credibly suggesting to "go it alone", I would say they have done most of the job. Starship is clearly capable of reaching orbit. It has done relights in space. It has even proved succesful reentry. The main outstanding tasks are in-space refuelling and lunar landing. Of those two I would say that only the second one is a major challenge. Compared to all else they have accomplished, in-space refuelling should not be a difficult task.

Crewed Earth landing and upper-stage reuse are not strictly necessary for a Moon shot, given that Dragon can ferry the astronauts to LEO and back. Starship would only need to aerobrake back into LEO and then transfer the astronauts to Dragon for landing, if a crewed Starship landing seems too scary.

I am guessing that by the time Starship lands a crew on the Moon we'll all feel less queasy about crewed Starship lift-off and landing ops on Earth.

So, we'll have a very simple architecture:
- Crewed Starship lift-off from Earth.
- Refuelling in LEO and then a TLI.
- Refuelling in LLO.
- Landing on the Moon and lunar surface ops.
- Lift-off from the Moon and refuelling in LLO.
- TEI and crewed Earth landing.

That will require one Starship HLS and as many Starship tanker/depot flights as it takes to position a full Starship depot in LEO and a full Starship depot in LLO.     

This has been discussed in other threads https://forum.nasaspaceflight.com/index.php?topic=63305.60

Latest version goes like this:
LD is Lifeboat Depot, ST is Starship Tanker

LD has to be only 705 ton fuel capacity.
LD gets filled at 200km orbit, 5 ST flights.
LD burns to 10,000km x 200km orbit and gets topped off with 4 more ST flights (one gets partially filled from 3 more at 200km orbit then it flies to 10,000km x 200 km orbit to top off LD).
LD performs TLI to LLO
HLS is filled at 200km orbit, 8 ST flights.
Dragon meets HLS and astronauts transfer. Dragon performs EDL.
HLS flies to 800km circular orbit (below Van Allan Belt)
One more ST flight to top off HLS.
HLS performs TLI to LLO and gets fuel from LD to perform lunar landing payload drop off and return to LLO.
HLS gets more fuel from LD.
HLS returns to 500km circular Earth orbit.
LD returns to 5,000km x 200km HEEO
one more ST flight to LD adds fuel to return to 500km circular and later to 200km circular.
Dragon flies to HLS to return astronauts to Earth.

[TheRadicalModerate]

Oops, I forgot that Starship HLS cannot land or even (I guess) aerocapture coming back to Earth. So, they'll have to transfer to a normal Starship somewhere enroute, probably in LLO.

Hey, if an HLS crew-certified to lift off, it's almost certainly crew-certified to land.  Otherwise, it can't do a boatload of ascent aborts.  I don't think you can launch a plain-vanilla HLS with no EDL capability--or at least not one with a NASA crew.

The real trick with an EDL-capable HLS is getting the landing legs and landing thrusters to make nice with the TPS.  Legs should be easy.  Thrusters, not so easy.

[TheRadicalModerate]

This has been discussed in other threads https://forum.nasaspaceflight.com/index.php?topic=63305.60

Just for everybody's information, Roy's thread points at a version of the Replacing SLS/Orion using Starship HLS and Crew Dragon thread that allows AI-generated computations.  The one I just linked discourages grok vomit.

[Roy_H]

  The one I just linked discourages grok vomit.

I am not a rocket engineer, but I have checked some of Grok's calculations, and all have been accurate. You should try Grok yourself before deciding it is vomit.

[Oersted]

This has been discussed in other threads https://forum.nasaspaceflight.com/index.php?topic=63305.60

Latest version goes like this:
LD is Lifeboat Depot, ST is Starship Tanker

LD has to be only 705 ton fuel capacity.
LD gets filled at 200km orbit, 5 ST flights.
LD burns to 10,000km x 200km orbit and gets topped off with 4 more ST flights (one gets partially filled from 3 more at 200km orbit then it flies to 10,000km x 200 km orbit to top off LD).
LD performs TLI to LLO
HLS is filled at 200km orbit, 8 ST flights.
Dragon meets HLS and astronauts transfer. Dragon performs EDL.
HLS flies to 800km circular orbit (below Van Allan Belt)
One more ST flight to top off HLS.
HLS performs TLI to LLO and gets fuel from LD to perform lunar landing payload drop off and return to LLO.
HLS gets more fuel from LD.
HLS returns to 500km circular Earth orbit.
LD returns to 5,000km x 200km HEEO
one more ST flight to LD adds fuel to return to 500km circular and later to 200km circular.
Dragon flies to HLS to return astronauts to Earth.

That's a more serious analysis than mine for sure. I didn't realise so many flights were needed. Is that scenario sure?

In any case, with that many Starship flights and landings under the belt I think it is more probable that vanilla Starships will replace the Dragons in your scheme. By then they should be considered trustworthy enough for crewed lift-offs and landings on Earth.

[Roy_H]

That's a more serious analysis than mine for sure. I didn't realize so many flights were needed. Is that scenario sure?

In any case, with that many Starship flights and landings under the belt I think it is more probable that vanilla Starships will replace the Dragons in your scheme. By then they should be considered trustworthy enough for crewed lift-offs and landings on Earth.

If you go and read the thread, I have tried to be conservative. This includes 50 tons of PE radiation shielding added to the HLS for crew protection and a 100 ton payload to Moon surface.

[crandles57]

The cheapest single-HLS case I can come up with is the "D2 on the nose" variant, which only requires about 1600t of prop and a single, uncrewed refueling.  However, there's a catch, as you'll see:

1) HLS launches, uses its residual prop to boost to VLEO+400m/s (about 200 x 1740).
2) Crew launches on F9/D2, into the 200 x 1740 orbit, where it docks with the HLS.
3) HLS does TLI, with the D2 still docked to the nose.
4) HLS goes to LLO, where the D2 undocks.
5) HLS does lunar surface mission.
6) HLS re-docks with D2 after surface mission.
7) HLS+D2 does TEI.
8 ) Before entry interface, crew climbs into the D2 and does direct EDL.
9) HLS either disposes of itself or aerocaptures into LEO.

As we've discussed, ad nauseam, on the thread I linked above, this requires non-trivial but still fairly modest mods to the D2, because it has to work in a deep space environment (different radiation and thermal requirements), the heat shield has to be qualified for ~11km/s entry speed, and the D2 and docking system have to withstand about 1G eyeballs-out acceleration from the Raptors during TLI, LOI, and TEI.  But the prop to LEO load is small, there are no crewed refuelings, and the HLS doesn't have to return propulsively to LEO to do RPOD with the D2, where it may be subject to "the RAAN problem".²

200*1740 km seems like it is a little toasty inner VAB radiation wise.

Could the streamlining partly be in the timings?
By this, I mean do the HLS demo immediately before HLS launches returning HLS Demo to NRHO with a little fuel rather than doing second landing attempt after lunar launch. Could that fuel be transferred to HLS starship after lunar mission or will it all be boiled off by then even with HLS mission immediately after HLS demo?

Could the HLS Starship with dragon on nose be boosted by HLS towards Earth until fuel depletion (or maybe retain sufficient fuel for HLS to return to NRHO) After astronauts get in Dragon, undock and use some fuel to continue TEI, head for Earth, do a propulsive retro burn before atmospheric entry then some aerobraking, maybe including some skips? If the heatshield isn't rated for such high speed EDL then after aerobraking perhaps could dock to the next HLS already launched for next lunar mission. This in order to then be able to transfer to another dragon?

If we want to test Dragon on HLS nose before using it with humans on the HLS perhaps it is tried out on the HLS demo which is now close to HLS launch time. A couple of dragons to use to store some mass needed for return journey but a waste to carry to lunar surface? Adapting dragon to store methalox propellants seems likely to be too difficult?

Could these tricks be enough to reduce the fuel needed sufficiently that you can fully fuel in something like 200*1200 km orbit (or maybe 500*1200 km?) before TLI?

[crandles57]

This has been discussed in other threads https://forum.nasaspaceflight.com/index.php?topic=63305.60

Latest version goes like this:
LD is Lifeboat Depot, ST is Starship Tanker

LD has to be only 705 ton fuel capacity.
LD gets filled at 200km orbit, 5 ST flights.
LD burns to 10,000km x 200km orbit and gets topped off with 4 more ST flights (one gets partially filled from 3 more at 200km orbit then it flies to 10,000km x 200 km orbit to top off LD).
LD performs TLI to LLO
HLS is filled at 200km orbit, 8 ST flights.
Dragon meets HLS and astronauts transfer. Dragon performs EDL.
HLS flies to 800km circular orbit (below Van Allan Belt)
One more ST flight to top off HLS.
HLS performs TLI to LLO and gets fuel from LD to perform lunar landing payload drop off and return to LLO.
HLS gets more fuel from LD.
HLS returns to 500km circular Earth orbit.
LD returns to 5,000km x 200km HEEO
one more ST flight to LD adds fuel to return to 500km circular and later to 200km circular.
Dragon flies to HLS to return astronauts to Earth.

That's a more serious analysis than mine for sure. I didn't realise so many flights were needed. Is that scenario sure?

In any case, with that many Starship flights and landings under the belt I think it is more probable that vanilla Starships will replace the Dragons in your scheme. By then they should be considered trustworthy enough for crewed lift-offs and landings on Earth.

Roy's proposal includes 100t payload mass. That is way more than is going to happen on Artemis III.

[TheRadicalModerate]

Could the streamlining partly be in the timings?
By this, I mean do the HLS demo immediately before HLS launches returning HLS Demo to NRHO with a little fuel rather than doing second landing attempt after lunar launch. Could that fuel be transferred to HLS starship after lunar mission or will it all be boiled off by then even with HLS mission immediately after HLS demo?

SpaceX doesn't have to return the demo to NRHO; it just has to get off the ground and into stable flight.  Allocating 100-200m/s of delta-v instead of ~2000m/s saves a huge amount of prop.  Beside that, the idea is not to have to do a refueling in NRHO at all.

Could the HLS Starship with dragon on nose be boosted by HLS towards Earth until fuel depletion (or maybe retain sufficient fuel for HLS to return to NRHO) After astronauts get in Dragon, undock and use some fuel to continue TEI, head for Earth, do a propulsive retro burn before atmospheric entry then some aerobraking, maybe including some skips? If the heatshield isn't rated for such high speed EDL then after aerobraking perhaps could dock to the next HLS already launched for next lunar mission. This in order to then be able to transfer to another dragon?

This is an interesting idea.  By my model, If you limit the D2 to an apogee of about 1100km (less than Polaris Dawn), you're about 160m/s short on delta-v for the TEI.  That might easily be in the range where the boost kit could make up the difference.

The only problem with this is you're providing delta-v to get out of lunar orbit, not slowing to Earth apogee.  As a result, the delta-v would have to be provided contiguous with the TEI, which means that the crew is cooped up in the D2 for several days.  That's a bigger mod to the D2 than just using the D2 for the last hour or two before entry.