Replacing SLS/Orion using Starship HLS and Crew Dragon (AI data allowed)

[InterestedEngineer]

Re Number 5 above: I don't think you send 3 tankers to 1000*125 km for final fuelling. I think it is more like one depot filled by 2 tankers in 150*150 km orbit then send the depot to 1000*125 km to do one final fuelling. Maybe with 1000*125 km orbit we get away with a smaller tank and only need one tank filling the depot before going to 1000*125 for final fuelling?

Is fuelling and astronaut transfer in 1000*125 km orbit a lot more difficult than in circular orbits? Is 125km too low a perigee?

Yes, it is definitely better to add fuel to one ST to deliver fuel to the HEEO via multiple flights. Did this in my latest proposal. I can't answer the question about the viability of 125km perigee. I chose a more conservative 200km because I was concerned about leaving the HLS and Lifeboat Tanker in orbit for long periods of time, waiting for the next mission, which could be 6 to 12 months. How much would the orbit decay in that time? If 125km is acceptable, then better. I was originally concerned about matching elliptical orbits, but several people here have assured me that is not a problem.

you can leave them long term in 200km.  The deltaV to get from 200km to 125km is so little that you might as well do that just before the final burn to the moon.

[Roy_H]

you can leave them long term in 200km.  The deltaV to get from 200km to 125km is so little that you might as well do that just before the final burn to the moon.

If 125km circular is acceptable, then I would do all the low level fueling etc. at 125km, raise to a 3000km x 125km HEEO, top off fuel, and gain additional benefit. I wonder if this would be enough to have one less fueling flight? On return it could be to a 3000km x 200km to be left there until next mission and when preparing for next mission, drop the HLS and Lifeboat Tanker to 125km circular. Rinse and repeat.

[crandles57]

Re Number 5 above: I don't think you send 3 tankers to 1000*125 km for final fuelling. I think it is more like one depot filled by 2 tankers in 150*150 km orbit then send the depot to 1000*125 km to do one final fuelling. Maybe with 1000*125 km orbit we get away with a smaller tank and only need one tank filling the depot before going to 1000*125 for final fuelling?

Is fuelling and astronaut transfer in 1000*125 km orbit a lot more difficult than in circular orbits? Is 125km too low a perigee?

Yes, it is definitely better to add fuel to one ST to deliver fuel to the HEEO via multiple flights. Did this in my latest proposal. I can't answer the question about the viability of 125km perigee. I chose a more conservative 200km because I was concerned about leaving the HLS and Lifeboat Tanker in orbit for long periods of time, waiting for the next mission, which could be 6 to 12 months. How much would the orbit decay in that time? If 125km is acceptable, then better. I was originally concerned about matching elliptical orbits, but several people here have assured me that is not a problem.

Yes 125km perigee would be too low for a long period of time between missions. I was hopeful it would be ok for an orbit or two or three prior to TLI. After mission return to something more like 630km circular for astronaut transfer? (suggested just below lowest value of 640km I have seen for lower limit of Van Allen Belts)

Mission sequence would be more like:
1. Launch HLS, Lifeboat tanker, cargo Starship and crewed Dragon into 200km LEO.
2. Assembly astronauts perform EVA and assemble solar panels, radiator, and MLI shielding on HLS and NRHO Lifeboat Depot. Astronauts return on dragon after assembly work to avoid being around during refuelling.
3. Launch 2 LEO depots to 140km circular orbit.
4. Launch 19? tankers to same 140 km circular orbit to nearly fill depots. (150tons*21launches=3150 which is < 1585 tons * 2 depots. Nearly full as don't want a part full tanker hanging around or returning part full)
(3 and 4 can happen while 2 is completed.)
5. Boost depots to 200km circular orbit and fill 'NRHO lifeboat depot' retain just sufficient fuel in LEO depots to return to 140km circular orbit. The surplus fuel goes to cargo and HLS ship
6. NRHO lifeboat depot adjusts orbit to 1000*125 km orbit (possibly gets a refill?) and does TLI to NRHO (boil off is lower here)
7. One depot returns to 140km circular orbit.
8. Launch x? tankers to the 140 km circular orbit to refuel the LEO depot there.
9. Adjust orbits of cargo ship and HLS ship and LEO depot to 1000*125 km orbit
10. Add fuel to cargo ship and HLS ship from the LEO depot
11. Launch mission astronauts to transfer to HLS ship in 1000 * 125 km orbit
12. TLI of cargo ship and HLS ship to NRHO
13. Add fuel to cargo ship and HLS ship from NRHO lifeboat depot retaining sufficient for return to LEO.
14. Land cargo and then HLS ship on moon.
15. Unload cargo and complete mission objectives on moon.
16. Launch from moon to NRHO
17. Refuel returning ship.
18. Return to ~630km*630km orbit
19. Dragon launches to 630*630 km orbit to return astronauts to Earth

NRHO lifeboat depot stays there and is possibly of some use for future missions? Ion drive to maintain this orbit without using chemical fuels?

One LEO depot is in 1000*125 and this is unstable for long period so slowly and efficiently change to something more like 500*200 km orbit if it will be a long time before reuse. If needed quickly it can go more directly to 140km circular orbit. Depot in 200*200 km orbit is probably fine there until needed.

Next missions would have first refuel in 630*630 km orbits before adjusting to 1000*125 for final refill astronaut transfer and TLI.

So how many things have I got wrong with that mission sequence?

What is x and/or number of fuel launches? Is one 'NRHO lifeboat depot' sufficient to provide fuel for two ships (in this case a lunar cargo ship and a HLS ship)? Alternately, could we aim to do better e.g. try to support 5 lunar landing ships with 2 NRHO depot ships?

[crandles57]

you can leave them long term in 200km.  The deltaV to get from 200km to 125km is so little that you might as well do that just before the final burn to the moon.

If 125km circular is acceptable, then I would do all the low level fueling etc. at 125km, raise to a 3000km x 125km HEEO, top off fuel, and gain additional benefit. I wonder if this would be enough to have one less fueling flight? On return it could be to a 3000km x 200km to be left there until next mission and when preparing for next mission, drop the HLS and Lifeboat Tanker to 125km circular. Rinse and repeat.

I am doubting 125km circular is high enough for a LEO depot to do ~10 proximity docking and fuel transfer operations particularly if there might be a delay to some of the refuelling launches. I suggested 140*140km for tanker fuelling depot operations, but others likely have a much better idea of what is sensible. I am thinking 10 refuelling operations might be over 5 days if all launches are from one pad. Perhaps you can reduce that to 2 or 3 days by using more pads perhaps in different locations? It is still a lot more orbits than 2 or 3 orbits in 1000*125 km for a refuel and an astronaut transfer prior to TLI at perigee.

[Roy_H]

6. NRHO lifeboat depot adjusts orbit to 1000*125 km orbit (possibly gets a refill?) and does TLI to NRHO (boil off is lower here)

If you don't top off fuel in the elliptical orbit, there is no advantage in going there at all. It would be more fuel efficient to simply do TLI from 125km circular.

[crandles57]

6. NRHO lifeboat depot adjusts orbit to 1000*125 km orbit (possibly gets a refill?) and does TLI to NRHO (boil off is lower here)

If you don't top off fuel in the elliptical orbit, there is no advantage in going there at all. It would be more fuel efficient to simply do TLI from 125km circular.

I had it in 200 * 200 km and wanted oberth effect of TLI at the higher speed of at perigee of 1000*125 km but yes if you don't need the refuel in 1000*125 then go directly in most efficient manner from 200*200 (or in later missions from 630*630km).

(Grok tells me better to go directly from 630 * 630 km to NRHO rather than via 1000*125 but I am not sure I totally trust it.

The direct path requires 3.85 km/s total (3.02 km/s Earth-side + 0.83 km/s insertion).
The indirect path requires 4.20 km/s total (3.37 km/s Earth-side + 0.83 km/s insertion)

https://x.com/i/grok/share/S9VqzcwP8VMV04PCsAcoYbnpO )

[Roy_H]

I tried to pick conservative values for perigee and apogee. I believe the values I chose produce a compelling mission with the Lifeboat Tanker being close to the same size as the HLS, the LT (Lifeboat Tanker) is basically an HLS with moon landing thrusters, legs, cargo area and half the crew quarters removed and replaced with larger fuel tanks. Entirely buildable and launchable.  Clearly higher apogee and lower perigee would yield additional benefits. Small changes like 150km vs 200 are negligible, I wondered how much I could lower the 3000km by going to 150km and the answer was 2915km.

I believe the only major issue that needs to be resolved is 3000km dangerously high into the Van Allan Belt?

It occurred to me that since I have specified that the HLS have a much higher radiation shielding than Dragon, that astronauts, and NASA, should be comfortable with 3000km altitude. If it is an issue for Dragon, then the astronauts could board the HLS in the 200km circular orbit before it is raised to the HEEO for fuel top off. Coming back would be trickier as the intention is to leave the HLS and LT in HEEO until next mission. Could Dragon dock in the HEEO orbit and astronauts board and undock while in the lower portion of the orbit, and immediately retro-thrust to lower orbit?

Another issue is that I suggested a Dragon trip and astronauts would be required to equip HLS and LT with solar panels, radiator, and MLI (Multi Layer Insulation). I expect this will be done robotically. Has anyone designed 'space bots'? I envisage small bots equipped with Draco thrusters, cameras, and arms either teleoperated or more likely trained to assemble these parts. They could be included in the Starship cargo and there would be no need for the Dragon visit.

Edit:
Well, I probably screwed up big time trying to use https://oltaris.nasa.gov as I guessed at most of the parameters. However I submitted two almost identical projects one for a circular orbit of 500km and the other for 3000km circular. The 3000km had mGy and mSv values 2 to 3 orders of magnitude higher at 3k vs 500 so I take it that 3000km is a dangerous altitude.

I'm now wondering if leaving HLS in this HEEO for many months could be a bad thing as equipment gets higher radiation dose. So now I am thinking of adding a tanker flight to meet HLS and LT on return to add sufficient fuel to go to a lower parking orbit. This would also solve the issue of Dragon not having to go to high orbit for astronaut return. What would be a desirable long term parking orbit?

[Twark_Main]

The West took a very "maximalist" approach to assembly robots, utilizing significant industrial prowess. See Canadarm1/2/3, CanadaHand, etc. The Soviets took a more low-tech approach, see for example the Strela crane system that was used during the assembly of Mir and the Russian segment of the ISS.

https://en.wikipedia.org/wiki/Strela_(crane)

However usually in space it's simpler to design a specialized end effector and then simply bolt it to the ship. Now we call it a "deployment mechanism" and not a robot.    Even if this also requires adding protective doors or panels for launch, this is usually what's done.


Going from HEEO to a low circular orbit is free if your spacecraft can withstand a little heating. Aerobraking doesn't produce nearly as much peak heating as reentry, so even HLS or other Starships without heat shields can do it. On most satellites, it's the fragility of the solar panels that limits the amount of aerobraking achievable on each perigee pass.

[crandles57]

I submitted two almost identical projects one for a circular orbit of 500km and the other for 3000km circular. The 3000km had mGy and mSv values 2 to 3 orders of magnitude higher at 3k vs 500 so I take it that 3000km is a dangerous altitude.

I'm now wondering if leaving HLS in this HEEO for many months could be a bad thing as equipment gets higher radiation dose. So now I am thinking of adding a tanker flight to meet HLS and LT on return to add sufficient fuel to go to a lower parking orbit. This would also solve the issue of Dragon not having to go to high orbit for astronaut return. What would be a desirable long term parking orbit?

Yes I think 3000km is high enough you don't want crew spending too much time there. Polaris Dawn went to apogee of 1400km but didn't stay at that apogee for many orbits. While that was ok adding that radiation dose to a full trip through VAB to moon and back might be too much. So while going up to 1000 or even 1200 km may be ok above that seems likely to be an issue. At these 1000-3000 km altitudes, the higher the the radiation levels and also higher apogee means longer time each orbit at the higher altitudes. Your HLS ship might offer more protection and allow it to go higher before the TLI but the crew have to arrive on dragon. So you might have a choice between having radiation dose risk at higher altitude transfers or refuelling with crew present risk if you transfer crew earlier. Maybe after lots of successful refuellings, the fuel refuelling risk becomes preferable?

You might need a dragon boost trunk to reach 3000km apogee but that is ok as it has already been demonstrated on CRS-33 in August 2025 and maybe the extra performance offered allows you to add extra radiation protection to dragon?

How much would the cargo mass have to be reduced to keep final fuelling in a 1200 * 150km orbit? Or do we need to consider 3 landing ships supported by 2 NRHO ships (a NRHO depot and our NRHO lifeboat/depot?). Either makes it more expensive per Kg mass to surface, but which works out better?

I am calling it a lifeboat/depot rather than lifeboat/tanker because I assume it needs to have some boil off minimisation equipment and also ability to both receive and supply propellants. I assume NRHO to help reduce boiloff caused by being close to moon for a while time during mission.

.

I doubt we will see a 4 arm Optimus variant fitted with a jetpack soon ... but maybe one day

Dracos? Surely too powerful? Cold gas thrusters in a 'jetpack' seem more like it to me.

[Roy_H]

Maybe after lots of successful refuellings, the fuel refuelling risk becomes preferable?

How much would the cargo mass have to be reduced to keep final fuelling in a 1200 * 150km orbit? Or do we need to consider 3 landing ships supported by 2 NRHO ships (a NRHO depot and our NRHO lifeboat/depot?). Either makes it more expensive per Kg mass to surface, but which works out better?

I am calling it a lifeboat/depot rather than lifeboat/tanker because I assume it needs to have some boil off minimisation equipment and also ability to both receive and supply propellants. I assume NRHO to help reduce boiloff caused by being close to moon for a while time during mission.

Dracos? Surely too powerful? Cold gas thrusters in a 'jetpack' seem more like it to me.

Since I am suggesting 27 fuelings per moon mission, and it will be several missions before astronauts are aboard, I think the risk of a fueling mishap will be very low. There will be lots of experience with it.

Well, I suppose a Depot might be a better description, I just have this earth bound mind set that Depots don't move around like tanker trucks do. All variants will have to transfer fuel either way, and I think it would be a good idea to include HLS in that. There might be an emergency situation where crew needs to transfer to Lifeboat and moving some fuel back to the Lifeboat could be desirable.

From what I understand SpaceX is already planning on MLI and solar panel active cooling for both HLS and NHRO tanker, so yes, boil off mitigation is already addressed.

Yeah, you are right, Dracos would be too powerful.

Twark_Main, No I do not think Aerobraking is an option as the ships will have solar panels and MLI wrapping.

I'm still trying to think of what would be the most desirable parking orbit, high enough not to worry about decay for a year, and in order to not waste energy, it should still be elliptical with perigee of 200km, so maybe 600km x 200km? This would keep it out of drag area most of the time and make it easy for Dragon to dock. Do you agree?

[Twark_Main]

Twark_Main, No I do not think Aerobraking is an option as the ships will have solar panels and MLI wrapping.

These are both "bog standard" features on regular satellites, and regular satellites were the first vehicles to demonstrate aerobraking.

I'm still trying to think of what would be the most desirable parking orbit, high enough not to worry about decay for a year, and in order to not waste energy, it should still be elliptical with perigee of 200km, so maybe 600km x 200km? This would keep it out of drag area most of the time and make it easy for Dragon to dock. Do you agree?

To reduce the orbits decay from drag, the best way is to increase the perigee altitude. So you might go to a perigee of 300 or 350 km instead of 200 km.

[crandles57]

Twark_Main, No I do not think Aerobraking is an option as the ships will have solar panels and MLI wrapping.

I'm still trying to think of what would be the most desirable parking orbit, high enough not to worry about decay for a year, and in order to not waste energy, it should still be elliptical with perigee of 200km, so maybe 600km x 200km? This would keep it out of drag area most of the time and make it easy for Dragon to dock. Do you agree?

600*200 does sound sensible to me but that might not mean much. Might even get away with 700*200 or 800*200. What concerns me is how you get there. You want one rapid transit through VA belts.

Perhaps solar panels can be rolled up or folded and the MLI made robust enough that you could do some light aerobraking without much heating by doing several passes through high atmosphere slowly lowering apogee on each pass but this means several passes through VA belts which is not at all what we want for crew.

Do you do TEI burn to put you in a 200,000*75km earth orbit. Then do retro burn at latest time possible to complete before reaching 100km to put you in something like 50,000*70 km orbit? Use positive lift to adjust perigee up to 90km+ then use negative lift to keep you at 90km altitude for longer in order to scrub off more speed than just a quick trip down to 90km? Leave atmosphere in something like 2000*90km orbit and on way up to apogee propulsively adjust to 600*200 km orbit.

I really have no idea if that is the sort of profile you want or if it is possible. How should it be done?

[Roy_H]

What concerns me is how you get there. You want one rapid transit through VA belts.

No, I do not think that is doable. To keep fuel requirements low, has to go to the 3k x 200 orbit first. Then a tanker visits and supplies enough fuel to go to a lower orbit like my proposed 600 x 200. Hopefully just 2 or 3 orbits to refuel and burn to a lower orbit.

Can't wait for multiple passes for aerobraking as the astronauts must be in radiated area for shortest possible time and the plan is to get to 600 x 200   500km circular for Dragon to visit.

Turns out we can be sloppy. Upon arriving back at 3k x 200 orbit, a single Starship Tanker can deliver more than enough fuel for both HLS and Lifeboat Tanker to go to a 500km circular orbit unload astronauts, loiter for 1 year and still have excess fuel to lower themselves to a 200km x 200km orbit for the next mission.

[InterestedEngineer]

Twark_Main, No I do not think Aerobraking is an option as the ships will have solar panels and MLI wrapping.

https://www.universetoday.com/articles/foldable-solar-sails-could-help-with-aerobraking-and-atmospheric-reentry

[Roy_H]

Twark_Main, No I do not think Aerobraking is an option as the ships will have solar panels and MLI wrapping.

https://www.universetoday.com/articles/foldable-solar-sails-could-help-with-aerobraking-and-atmospheric-reentry

Interesting application. But this example shows designed for high strength aerobraking and release as stresses get too high.

I originally took Twark_Main's proposal to be high stress to  aerobrake in one or two orbits. The alternative given the fragility of solar panes and MLI would be a large number of passes with gentle braking. But this would have astronauts being subjected to Van Alan Belt radiation much longer than necessary.

Fuel is cheap. SpaceX has applied to drill 5 gas wells on their own property at Starbase. They are building a factory to remove Oxygen and Nitrogen from the air. They are planning on a large solar field to power all this. High capital expense, yes, but after all this is accomplished fuel will be very low cost. Starship Tankers will be re-used, so only launch costs and hopefully minimal refurbishment.

[Roy_H]

Latest plan now revised to eliminate time astronauts in Dragon have to spend in Van Alan Belt.

As before initial flight preparation takes place at 200km circular orbit.
No Dragon flight required to outfit HLS and LT (Lifeboat Tanker) with solar panels, radiators, and MLI as this can be done robotically.
Change is that astronauts board HLS at this orbit so Dragon doesn't have to spend time in Van Allan Belt. The HLS is equipped with much higher radiation shielding than Dragon.
HLS and Lifeboat Tanker fly to 3000km x 200km HEEO. There they get topped off via additional Starship Tanker flight.
HLS and Lifeboat Tanker fly to Moon as before and return to HEEO.
One more Starship Tanker flies to HEEO and adds as much fuel as it can carry. This turns our to be comfortably more than required to descend to 500km circular orbit, remain there for a year or more and still have fuel to descend to 200km circular orbit for next mission.
In both cases launching to the Moon and returning, it is desirable to spend as little time in the HEEO orbit as possible even though high shielding makes it safe. So hopefully fuel top-off can be accomplished in 2 or 3 orbits.
Astronauts transfer to Dragon in 500km circular orbit and perform EDL.
New updated mission profile diagram attached.

[Roy_H]

Asked Grok to produce a graph showing radiation levels at various altitudes. Should have done this long ago. So 3,000km turns out to be beyond the middle of the inner Van Allan Belt. Note scale distortion on upper end as I was only concerned with up to 3,000km.

[crandles57]

Can MLI be applied before launch? Why is depot white as opposed to grey steel of lander and tanker?

https://ntrs.nasa.gov/api/citations/20250008727/downloads/IAC%2025%20B3%201%20v3.pdf

[Twark_Main]

Asked Grok to produce a graph showing radiation levels

How can we be sure this isn't wholly hallucinated?

Can Grok produce a source?

[crandles57]

Asked Grok to produce a graph showing radiation levels at various altitudes. Should have done this long ago. So 3,000km turns out to be beyond the middle of the inner Van Allan Belt. Note scale distortion on upper end as I was only concerned with up to 3,000km.

Some Grok comments

Inner Belt (1,000-6,000 km): Sharp peak around 3,000-4,000 km, where dose rates can reach 10-20 rad/hour or higher. This is the most hazardous for prolonged exposure due to penetrating protons.
Slot Region (6,000-13,000 km): Lower radiation (~0.1-1 rad/hour), acting as a "gap" between belts.
Outer Belt (13,000-20,000+ km): Broader peak around 15,000-17,000 km, with dose rates ~5-10 rad/hour at max. Levels taper off more gradually.
Beyond 30,000 km: Negligible belt radiation; reverts to background GCR levels.
Variability: During solar storms, levels can increase by factors of 10-100. Shielding (e.g., 25 g/cm²) can reduce inner belt peaks to ~5 rad/hour.
Human Relevance: Quick transits (e.g., Apollo missions) result in low total doses (~0.1-1 rad total), but satellites or long stays require heavy shielding.

refs used include
https://pubmed.ncbi.nlm.nih.gov/12056428/

The flux of energetic protons in the maximum intensity zone of the inner Van Allen belt is by about four orders of magnitude higher, their energy and penetration power, of course, lower. A shield of 25 g/cm2 would reduce the dose rate from 20 rad/hour under 2 g/cm2 to 5 rad/hour.

also
https://spacemedicineassociation.org/download/history/ (1959 PDF)
image attached

.

Anyway:
3,000*200km means passing through the inner belt peak twice each orbit. For long RPOD operations it looks like it might be better to go to something like 7,000*4,000km orbit. The extra delta-v cost of doing this might not be worth it if RPOD operations don't take long and you have sufficient shielding.