SpaceX to NASA quote : simplified mission architecture : Technical discussion

[Legios]

I disagree, the timeframe being discussed here is 3 to 4 years, which is a long time for SpaceX development program. Remember it took only 2.5 years from the announcement of Polaris Dawn to its flight, and most of the development time in that case was spent on spacesuits.

3 to 4 years should be more than enough to modify Crew Dragon for lunar operations. BTW, current D2 can already handle "eyeballs-out" acceleration since that's how it does high delta-v maneuvers: by firing the thrusters around the docking port.

The main obstacle for using Crew Dragon in lunar operation is Elon Musk's desire to retire it asap and replace it with Starship. But I think old space p*ssed him off enough that he would be willing to accept a less than perfect solution in this case.

There's no reason to do this.  Orion and SLS already work and are proven.  There's no reason to modify a Dragon for deep space.  That part of the mission is solved.  It's the lander that needs work.

The main reason to do this is to kill off SLS/Orion.

But it just so happens using Dragon for deep space also simplify the architecture/conops (slightly) and improves crew safety (by a lot), and may be able to speed things up (slightly).

1.  It doesn't really simplify anything.  There is no difference between HLS (or Gateway?) docking with Orion or with Dragon.

2.  Orion is already deep space rated and test-flown.  It absolutely would not increase crew safety trying to crash convert a Dragon for deep space and extended endurance.

3.  It will not be faster to redesign a capsule vs using one that already exists, is built, and is flight tested.
2. 

[Roy_H]

I couldn't find any mention of re-fueling HLS however from
https://www.nasa.gov/general/nasas-artemis-iv-building-first-lunar-space-station

"Prior to launching the crew and I-Hab with the SLS rocket, NASA and its partners will pre-position two additional spacecraft for the mission: SpaceX’s Starship Human Landing System that will carry the next-generation spacesuits for moonwalks, and the SpaceX Dragon XL logistics module carrying science experiments and other supplies for the mission. An upgraded Starship will support Artemis IV with expanded capabilities for long-term exploration and future missions, including docking with Gateway."

The bolded section implies re-use of HLS and that means it has to be refueled.

[CoolScience]

The main reason to do this is to kill off SLS/Orion.

But it just so happens using Dragon for deep space also simplify the architecture/conops (slightly) and improves crew safety (by a lot), and may be able to speed things up (slightly).

1.  It doesn't really simplify anything.  There is no difference between HLS (or Gateway?) docking with Orion or with Dragon.

2.  Orion is already deep space rated and test-flown.  It absolutely would not increase crew safety trying to crash convert a Dragon for deep space and extended endurance.

3.  It will not be faster to redesign a capsule vs using one that already exists, is built, and is flight tested.
2.

1. It at a minimum removes the use of NRHO which only became part of any architecture due to underperformance of SLS/Orion. Removing unnecessary constraints is a simplification.
2.Your statements here are false and these false assertions may result in the deaths of astronauts. Orion's systems are not fully tested. The heat shield does not work good enough as proven by its flight test. Putting humas on the 2nd launch of any vehicle is simply not good enough for modern spaceflight. Nevermind that this is a rocket built by the same company that has numerous safety culture problems in its airline division, and put astronauts in a capsule that once in space was determined to not be safe enough to return those astronauts outside of an emergency. Converting Dragon to work around the moon may or may not be the best alternative (I think LEO transfer to Starship is preferable), but reasonably would be safer and cheaper than the SLS/Orion system.
3. Besides the fact that you are repeating the same dangerous and untrue claims, can you state what you think the flight rate of SLS is and what the turnaround time is if there are even minor problems that need to be resolved?

[DanClemmensen]

I couldn't find any mention of re-fueling HLS however from
https://www.nasa.gov/general/nasas-artemis-iv-building-first-lunar-space-station

"Prior to launching the crew and I-Hab with the SLS rocket, NASA and its partners will pre-position two additional spacecraft for the mission: SpaceX’s Starship Human Landing System that will carry the next-generation spacesuits for moonwalks, and the SpaceX Dragon XL logistics module carrying science experiments and other supplies for the mission. An upgraded Starship will support Artemis IV with expanded capabilities for long-term exploration and future missions, including docking with Gateway."

The bolded section implies re-use of HLS and that means it has to be refueled.

Sorry, but no. This statement does not require HLS reuse. You and a lot of other folks are reading something that is not there, and that is why you must use the word "implies". A stream of expended HLSs can support long-term exploration a lot easier than a system that depends on Dragon XL logistics.

Note: I would really like to see reusable HLSs because I think it's cool. However, until you solve the reprovisioning problem you are crippled. You can load 100 tonnes of lunar downmass if you load it on HLS on Earth. Dragon XL can carry at most 5 tons and those provisions must be hand-carried by the crew through the Gateway from Dragon XL into the HLS, through the two IDSS ports, before the crew gets into the HLS to descend to the lunar surface.

[dabomb6608]

1.  It doesn't really simplify anything.  There is no difference between HLS (or Gateway?) docking with Orion or with Dragon.

2.  Orion is already deep space rated and test-flown.  It absolutely would not increase crew safety trying to crash convert a Dragon for deep space and extended endurance.

3.  It will not be faster to redesign a capsule vs using one that already exists, is built, and is flight tested.

Did you read any this?

Fair enough.  Although I suggest you read Casey Handmer's Orion post and still see if you feel the same way.  (Lots of ranting in this, but I also learned a few additional scary things.)

You are unknowingly, or maybe knowingly, ignoring some major issues coming from Orion. Then asserting that a incomplete test article making one flight around the moon somehow makes the Artemis II version is flight proven. Even though subsystems as critical as the Environmental Control and Life Support System were not even fully tested on Artemis I. Not to mention the heat shield redesign post Artemis I.

[xvel]

And also it is very common for LLMs to not recognize bad quality quality sources, outdated sources (the fact that something was published yesterday doesn't necesarily mean the content is up to date) and misinterpreting the sources.

[Robotbeat]

LLMs are like Wikipedia. Always follow the sources.

[Roy_H]

Sorry, but no. This statement does not require HLS reuse...

I agree, and you are right about my use of "implies".

Note: I would really like to see reusable HLSs because I think it's cool. However, until you solve the reprovisioning problem you are crippled. You can load 100 tonnes of lunar downmass if you load it on HLS on Earth. Dragon XL can carry at most 5 tons and those provisions must be hand-carried by the crew through the Gateway from Dragon XL into the HLS, through the two IDSS ports, before the crew gets into the HLS to descend to the lunar surface.

Again I agree. However I think the " until you solve the reprovisioning problem you are crippled." part is solvable, and can be done in LEO.

[DanClemmensen]

Sorry, but no. This statement does not require HLS reuse...

I agree, and you are right about my use of "implies".

Note: I would really like to see reusable HLSs because I think it's cool. However, until you solve the reprovisioning problem you are crippled. You can load 100 tonnes of lunar downmass if you load it on HLS on Earth. Dragon XL can carry at most 5 tons and those provisions must be hand-carried by the crew through the Gateway from Dragon XL into the HLS, through the two IDSS ports, before the crew gets into the HLS to descend to the lunar surface.

Again I agree. However I think the " until you solve the reprovisioning problem you are crippled." part is solvable, and can be done in LEO.

OK, but I don't want to waste my precious and scarce brain cells worrying about bringing HLS back to LEO until that solution is being designed, or an EDL-capable HLS is being designed, or some other solution is proposed. Two expended HLS per year are still a lot cheaper than one SLS/Orion mission, and I expect to see a solution before the tenth expended HLS mission. Crew-rated EDL Starship is a lot more important than reusable HLS, because a crew-rated EDL Starship could carry a crew of 20 to meet with an expendable HLS that can carry 20. That's five times as effective in crew-hours on the Moon. SpaceX needs to create that crewed EDL Starship as a critical part of their core mission.

[meekGee]

LLMs are like Wikipedia. Always follow the sources.

Just like when a friend tells you something.
AI's "hallucinations" is usually confusing some data due to context, which is how a lot of wrong human opinions happen.

When posters here complain about the AI trying to cover its tracks, they even recognize emotions in it... 

If you want an infallible computer, I have an old LED HP calculator.  RPN FTW!

[TheRadicalModerate]

Sorry, but no. This statement does not require HLS reuse...

I agree, and you are right about my use of "implies".

Note: I would really like to see reusable HLSs because I think it's cool. However, until you solve the reprovisioning problem you are crippled. You can load 100 tonnes of lunar downmass if you load it on HLS on Earth. Dragon XL can carry at most 5 tons and those provisions must be hand-carried by the crew through the Gateway from Dragon XL into the HLS, through the two IDSS ports, before the crew gets into the HLS to descend to the lunar surface.

Again I agree. However I think the " until you solve the reprovisioning problem you are crippled." part is solvable, and can be done in LEO.

There are four basic requirements for reuse:

1) Replenishment of consumables.  This can be handled via any of Orion, a transit HLS, or a DXL, as long as the consumables fit through an IDSS port.

2) Attachment of new non-pressurized cargo.  There's no mechanism for this.  Even if the Gateway arm were added, it still wouldn't be sufficient to move cargo from one vehicle to another.

3) Maintenance of interior systems:  new ECLSS parts, swapping out bad boards or displays, cleaning or replacement of filters, and general housekeeping.  Doable in theory, hard in practice.  Requires identification of a whole bunch of requirements we don't currently know.

4) Maintenance of exterior systems, especially engines.  Flat-out impossible right now.  Equally impossible to swap out engines in microgravity.

I can see limited reuse via consumables replenishment (maybe 2-3 missions) after performance has been validated.  But the lunar dust problem makes that validation very, very difficult to do for an HLS without extensive microgravity EVAs.

Meanwhile, I question the economics of sending expendable HDL missions to land unpressurized, deployable cargo, instead of just expending an HLS and having a crew to oversee the deployment of new cargo that was integrated before launch.  There's certainly a place for HDL to handle really big cargoes, but there will be a zillion payloads that people want to deploy using humans to provide some of the muscle and otherwise supervise as they're activated.

Note that the Option B (Arty 4), SLD (Arty 5), and SLT (Arty 6+) requirements say a lot about "sustainability", but never explicitly call for "reusability".

[thespacecow]

I disagree, the timeframe being discussed here is 3 to 4 years, which is a long time for SpaceX development program. Remember it took only 2.5 years from the announcement of Polaris Dawn to its flight, and most of the development time in that case was spent on spacesuits.

3 to 4 years should be more than enough to modify Crew Dragon for lunar operations. BTW, current D2 can already handle "eyeballs-out" acceleration since that's how it does high delta-v maneuvers: by firing the thrusters around the docking port.

The main obstacle for using Crew Dragon in lunar operation is Elon Musk's desire to retire it asap and replace it with Starship. But I think old space p*ssed him off enough that he would be willing to accept a less than perfect solution in this case.

There's no reason to do this.  Orion and SLS already work and are proven.  There's no reason to modify a Dragon for deep space.  That part of the mission is solved.  It's the lander that needs work.

The main reason to do this is to kill off SLS/Orion.

But it just so happens using Dragon for deep space also simplify the architecture/conops (slightly) and improves crew safety (by a lot), and may be able to speed things up (slightly).

1.  It doesn't really simplify anything.  There is no difference between HLS (or Gateway?) docking with Orion or with Dragon.

2.  Orion is already deep space rated and test-flown.  It absolutely would not increase crew safety trying to crash convert a Dragon for deep space and extended endurance.

3.  It will not be faster to redesign a capsule vs using one that already exists, is built, and is flight tested.

1. It simplifies architecture/conops by removing the need for HLS to wait at NRHO, and replace a docking in NRHO with a docking in LEO.

2. It massively improve crew safety by:
a. Change staging orbit from NRHO to LLO, this allows immediate abort from surface at anytime, instead of having to wait 6.5 days for Orion to come back at NRHO. This is a key point even old space supporters like Mike Griffin talked about.
b. As I said before, when going to/from Moon, the crew always have two active spacecraft they can rely on, so if one has issues they can use the other as lifeboat, similar to Apollo 13. You wouldn't have this if you send HLS and Orion separately to NRHO.

3. Redesigning a capsule can be done in parallel to HLS development, as long as it can be done quicker than HLS it doesn't hurt the timeline. It could reduce timeline by lessen the performance requirement on HLS, via no NRHO wait period and possible less surface time as well.

[mikelepage]

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.

Tried the simple mission I had in mind in Excel and my numbers seem to close (see spreadsheet)... This involves sending an HLS + tanker to the moon. HLS descends to lunar surface. HLS ascent from lunar surface to LLO is followed by single prop transfer in LLO (~400ton), followed by both performing TEI. HLS brakes propulsively into LEO, while tanker aerocaptures. D2 shuttles back and forth from LEO. What am I missing?

NASA has always talked about lunar exploration being a stepping-stone to Mars, and although that's not true in many ways, the one way it is true and relevant to SpaceX is that it's an opportunity to do *many* re-entry tests of Starship's heat shield at interplanetary velocities. Not with anyone onboard of course.

It seems to me that SpaceX would say using D2 as a lifeboat has about as much merit as designing a launch escape system for starship. Better to put more effort into making the main ship reliable.

That said, Earth EDL is the most intense challenge for starship's heat shield, so keep D2 as a proven Earth to LEO shuttle until crewed/P2P starship proves itself.

Since this CONOPS works, a CONOPS that uses two HLSs will also work without the need for a crewed refill. Just do your mission, but also send a second HLS as an OTV to that same LLO and refill it so it is waiting for the actual HLS when it ascends. crew transfers to the OTV and goes back to LEO. HLS and Depot make their way back to LEO more or less as you describe for Depot.

Disadvantage: needs more tanker flights and a second HLS.
Advantages:
   1) Removes crewed refill from the argument. This is more political than  technical.
   2) Provides for rescue in lots of failure scenarios.
   3) A variant can replace the SLS/Orion functionality even when the lander is Blue Moon Mk II (Artemis V).

Most of the disadvantages go away if you assume pairs of (HLS and tanker) with overlapping missions to the moon base.

Then:
1) HLS mission 1 doesn’t commence lunar ascent until HLS mission 2 successfully captures in lunar orbit.
2) HLS mission 2 doesn’t commit to lunar descent until HLS mission 1 successfully performs prop transfer in prep for return.

[TheRadicalModerate]

1. It simplifies architecture/conops by removing the need for HLS to wait at NRHO, and replace a docking in NRHO with a docking in LEO.

But it still requires a docking in lunar orbit, either by a tanker, for refueling (one-HLS, no D2 case) or by the D2 (one-HLS, D2-on-nose case, where the D2 has to wait in LLO while the HLS goes to the surface and back).

2. It massively improves crew safety by:
a. Change staging orbit from NRHO to LLO, this allows immediate abort from surface at anytime, instead of having to wait 6.5 days for Orion to come back at NRHO. This is a key point even old space supporters like Mike Griffin talked about.

Good point, but it's not a simplification; it's a bonus feature.

b. As I said before, when going to/from Moon, the crew always have two active spacecraft they can rely on, so if one has issues they can use the other as lifeboat, similar to Apollo 13. You wouldn't have this if you send HLS and Orion separately to NRHO.

D2 is supposed to be able to support 40 crew-days (10 days for a crew of 4), which is probably adequate for an outbound abort, as long as the RPOD in the eccentric LEO (200 x ~1600) doesn't take more than a day or two.  (And if it does, there are probably radiation limits.)

That said, the D2 has a tiny amount of thrust, if it needs to fiddle with the return trajectory.  Going into a polar LLO is not the same as what Apollo did, so I'm not sure a free return is possible.  And of course, if the D2 had to separate from the HLS in translunar, all of the deficiencies we've enumerated would either need to be fixed or endured.

3. Redesigning a capsule can be done in parallel to HLS development, as long as it can be done quicker than HLS it doesn't hurt the timeline. It could reduce timeline by lessen the performance requirement on HLS, via no NRHO wait period and possible less surface time as well.

If you're using a D2 on the nose, there's not a huge addition to the mass margin budget, because D2 can't do TEI from LLO.  On the other hand, if you put an Orion on the nose, the margin addition is huge.¹  (Of course, then you have to deal with whatever horrible stuff emerges if you breathe on Orion for anything other than its exact planned conops.)

Not sure about the D2 mods.  SpaceX has allowed the D2 line to go inactive.  Resurrecting it is possible, and apparently it's a contingency plan if D2's were lost or Starship crew-certification took too long, so it's doable.  But my guess is that it would take resources away from Starship, so it's not completely independent.

____________
¹The "boost kit" is supposed to provide 9m/s of delta-v for the ISS, which should be about 1290kg of prop.  Add that to the 2560kg in the bus, less, say, 800kg for LEO maneuvers, and you've got about 640m/s of delta-v available.  You need ~1050m/s for TEI.  (Anybody know the higher orbit an expendable F9 can insert a D2 into?  Any idea what it would do to the abort profiles?)

Of course, the USDV has much larger tanks.  If those could be adapted to a translunar D2, it might be possible have it do its own TEI. 

There's also the possibility of a two-orbit departure, where the HLS boosts itself + D2 into an eccentric lunar orbit, then the D2 finishes off the maneuver around the next pericynthion.  That would provide quite a bit more margin for the HLS.  At the very least, it's a contingency in case the HLS underperformed getting into LLO.

[TheRadicalModerate]

Since this CONOPS works, a CONOPS that uses two HLSs will also work without the need for a crewed refill. Just do your mission, but also send a second HLS as an OTV to that same LLO and refill it so it is waiting for the actual HLS when it ascends. crew transfers to the OTV and goes back to LEO. HLS and Depot make their way back to LEO more or less as you describe for Depot.

Disadvantage: needs more tanker flights and a second HLS.
Advantages:
   1) Removes crewed refill from the argument. This is more political than  technical.
   2) Provides for rescue in lots of failure scenarios.
   3) A variant can replace the SLS/Orion functionality even when the lander is Blue Moon Mk II (Artemis V).

I'm still a bit nervous about two Starships docking nose-to-nose.  That's an awful lot of torque on the docking mechanism if things are even slightly weird.  I consider this to be yet another argument for D2-on-the-nose:  we have ample evidence that D2's can dock to big things with no problem.

[dchenevert]

are you sure you need to refill the 2nd HLS?

since HLS2 is saving the amount of fuel intended for descend+ascend..

what are the numbers? how much delta-v,  from NRHO to "LEO" (any orbit Dragon can reach)

[Brigantine]

the USDV has much larger tanks.  If those could be adapted to a translunar D2, it might be possible have it do its own TEI.

The ISS de-orbit vehicle?

I looked into that. (though not as a thing on HLS' nose - I was looking if it could give Orion a leg down)
Wet mass "over 30 tons" incl "16 tons of propellant" implying dry mass over 14 tons - and ISP of 2,300 m/s (or 300s per a different source??)

That's beyond what F9 can put in orbit. FH is not crew-rated. So we're looking at a dual-Dragon architecture:
(this is comparable to a "launch Orion uncrewed on FH" architecture)

- Dragon 1 launches uncrewed on a (partly re-usable?) FH with deep space mods and USDV trunk, direct to final tanking orbit. Most of the hypergol prop reserved for TEI from LLO
- Dragon 2 launches crewed on re-usable (ASDS landing) F9 and use dracos to get to final tanking orbit
- Crew transfers from Dragon 2 to Dragon 1, then docks to HLS


It's really much better if you can get just a slight stretch of the boost trunk, and launch crewed on F9.

_______________________

Highest orbit will depend on the extra mass of any boost kit... I look at MVac ISP = 3,350m/s and make naive assumptions (1:1 trade payload to residual kerolox), taking F9S2 dry mass as 4.5 ton. (based largely on ignorance).

For standard 12.5 ton Dragon, that's 4.2 ton too high to reach GTO, so 3,350*ln(1-4.2/(12.5+4.5))~=950 m/s less than GTO.
9,245 m/s at 200km pe implies 200 x 9,882 km (+/- thousands of km)

Add a 3 ton boost kit, and now it's LEO+1,197 m/s or 200 x 6,715 km (+/- thousands of km)

These 2 results are separated by 308 m/s, when it naively should be a difference of 544 m/s. Grain of salt, until someone else comes up with better

[EDIT] It occurred to me I didn't consider the LES and acceleration limits for crewed launches. So "highest orbit expendable F9 can launch Dragon into" and "highest orbit F9 can launch a Dragon into with crew aboard" are two materially different questions

[mikelepage]

Since this CONOPS works, a CONOPS that uses two HLSs will also work without the need for a crewed refill. Just do your mission, but also send a second HLS as an OTV to that same LLO and refill it so it is waiting for the actual HLS when it ascends. crew transfers to the OTV and goes back to LEO. HLS and Depot make their way back to LEO more or less as you describe for Depot.

Disadvantage: needs more tanker flights and a second HLS.
Advantages:
   1) Removes crewed refill from the argument. This is more political than  technical.
   2) Provides for rescue in lots of failure scenarios.
   3) A variant can replace the SLS/Orion functionality even when the lander is Blue Moon Mk II (Artemis V).

I'm still a bit nervous about two Starships docking nose-to-nose.  That's an awful lot of torque on the docking mechanism if things are even slightly weird.  I consider this to be yet another argument for D2-on-the-nose:  we have ample evidence that D2's can dock to big things with no problem.

Here’s a thought: what if HLS has two docking ports? One on the nose for D2, and another on the “rear” side of HLS not shown in the  current renders, on the same side as the prop transfer ports, 180° opposite the hatch/crane assembly but on the same level as the other airlocks.

If they did that, then they could potentially use the same probe/drogue capture system as used for prop transfer, but instead to pull two docking ports together when starships need to dock to each other. Not all starship variants are going to be able to have docking ports on the nose.

[DanClemmensen]

Since this CONOPS works, a CONOPS that uses two HLSs will also work without the need for a crewed refill. Just do your mission, but also send a second HLS as an OTV to that same LLO and refill it so it is waiting for the actual HLS when it ascends. crew transfers to the OTV and goes back to LEO. HLS and Depot make their way back to LEO more or less as you describe for Depot.

Disadvantage: needs more tanker flights and a second HLS.
Advantages:
   1) Removes crewed refill from the argument. This is more political than  technical.
   2) Provides for rescue in lots of failure scenarios.
   3) A variant can replace the SLS/Orion functionality even when the lander is Blue Moon Mk II (Artemis V).

I'm still a bit nervous about two Starships docking nose-to-nose.  That's an awful lot of torque on the docking mechanism if things are even slightly weird.  I consider this to be yet another argument for D2-on-the-nose:  we have ample evidence that D2's can dock to big things with no problem.

I also worry about HLS nose docking with a heavy delicate target, but it is a NASA requirement to dock HLS to the Gateway. I also ended up doing (and then re-doing) the calculations about docking forces and ended up with a force in the range of only 10 N. yes, I know linear force is not torque. Conceptually, the ogive shape will do a good job of distributing that torque. I do not have enough experience or training to have a good feel for this issue, so I will wait and see what the professionals come up with.

[Roy_H]

I also worry about HLS nose docking with a heavy delicate target, but it is a NASA requirement to dock HLS to the Gateway. I also ended up doing (and then re-doing) the calculations about docking forces and ended up with a force in the range of only 10 N. yes, I know linear force is not torque. Conceptually, the ogive shape will do a good job of distributing that torque. I do not have enough experience or training to have a good feel for this issue, so I will wait and see what the professionals come up with.

I am curious about what would cause these forces. Fuel sloshing in the tanks? Torque is a twisting force, I cannot imagine what would induce that, to me more likely side force producing yaw.