Author Topic: Crew Dragon Mission Life Extension: Free-Flying, Uncrewed Duration  (Read 14084 times)

Offline TheRadicalModerate

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In innumerable Starship and HLS threads, we've discussed the possibility of a kludge, which would allow a Lunar Starship (aka LSS or HLS Starship) to act as an SLS/Orion replacement, when supplemented by an F9/D2.  The assertion for why this might be a good idea is that, by the time the LSS Option B work is complete, we have the makings of an Earth-NRHO-Earth system available off the shelf.  I don't think it's quite off the shelf, and I'd like to use this thread to discuss what's likely the long pole in the tent for implementing this:  D2 free-flying mission life.



There are plenty of variants on the conops for such an Artemis mission.  They're not the topic of this thread.  However, to get everybody on the same page for what the problem is, here's a reference conops:

1) LSS, which we'll call the "orbital transfer vehicle LSS" (OTV LSS) starts out in LEO, either freshly launched or returned from a previous Artemis mission.

2) OTV LSS uses a depot to take on enough propellant (it's <1000t) to perform an LEO-TLI-NRHO-RPOD-loiter-RPOD-TEI-LEOpropulsive mission.  (Note that it's the propulsive return to LEO, rather than using direct EDL or aerocapture, that makes the prop requirements considerably heftier--but not too hefty.)

3) Launch a crew of 4 on an F9/D2 to do rendezvous, prox ops, and docking (RPOD) with the OTV LSS.  Crew transfers to OTV LSS.

4) D2 undocks from the OTV, then goes into a low-consumption mode for a multi-week, uncrewed, free flight in LEO, waiting for the crew to return.  Note that this is different from what happens when D2 stays at ISS for a long duration, because ISS can provide power, ECLSS, and consumables while the D2 is docked.  In free flight, this support doesn't exist.  Free-flying crew Dragon mission life is currently about a week, but that's with the crew on board the whole time.  In this case, the crew would be on board for considerably less than a week (just long enough to do launch/RPOD with the OTV and then, after the OTV returned and did RPOD, long enough to take the crew to EDL).  But the free-flying time in LEO could be up to a couple of months while the D2 waited for the OTV's return.

5) OTV LSS now does LEO-NRHO (fast transit), then the crew transfers to the actual lunar lander HLS, does its potentially multi-week mission (per the Option B/SLD/SLT specs), then ascends back to NRHO.  Crew transfers back from the lander LSS to the OTV LSS.

6) OTV LSS does NRHO-TEI to return the crew.

7) D2 powers up back up and prepares itself to receive crew.

8 ) OTV does a propulsive insertion back into LEO, then does an RPOD with the D2.

9) Crew transfers to D2, which then returns crew through EDL.  OTV LSS waits in LEO for next mission.



The topics for this thread mostly revolve around steps #4 and #7 above:

a) Is such an uncrewed, low-consumption mode possible for a D2?
b) What modifications, if any, would need to be made to the current D2 to do this?
c) How much engineering and test work is needed to implement it?
d) What is the maximum duration of such a low consumption mode?
e) Are there any gotchas with RPOD with the LSS OTV, either post-launch or pre-EDL?
f) What contingency planning is needed for a failed post-return OTV-D2 RPOD?
g) If free-flying is impossible, is there a cheap widget that could support the D2 for the duration of the mission?  (ISS is obviously such a widget, but it's in a pretty high inclination for lunar departures and returns.



Topics that are not for discussion in this thread:

i) This is stupid, just get Starship crew-certified and you don't need to do this.  The premise is that Starship crew certification will be hard and take a long time.  That's a perfectly debatable premise; please don't debate it here.

ii) You can avoid the power-down if you use two D2s per mission, one for crew launch and one for crew EDL.  This is also a perfectly good discussion topic, but I'd like to focus on how to avoid doing this, since it'll be expensive to have two D2 launches per Artemis mission.

iii) Just use the D2 on a Falcon Heavy as the OTV instead of an LSS.  Again, a possibly viable idea, although it likely involves considerably more engineering.  Please, not here.

iv) This is all silly because NASA will never allow a competitor to SLS/Orion.  Possibly true, but it'll turn this thread into a food-fight.

v) Your reference D2+LSS conops is dumb.  It's much better to <insert your favorite variant here>.  Just stick to the essence of figuring out the D2 problems.

I've hopefully constrained this so that this is a relatively short thread.  The goal is to find out whether D2 mission life turns out to render this class of missions non-viable or really expensive to develop.  I don't know a lot about the relationship between mission life and consumables.  Hopefully people who do will chime in so we can figure out if this is viable.

Have at it.

Offline TheRadicalModerate

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IMO, most of the problems are going to be thermal:

1) What freezes without ISS ECLSS blowing around in the crew area?

2) What boils away without ISS consumables available while docked?

3) Are water or refrigerants actively consumed keeping things within operational limits during free flight?  Is water lost?  Is there an ammonia loop that needs a bigger reservoir?

4) Is there some limit to the radiators in the trunk that gets exceeded for long free flights?

5) Do the helium COPVs for the propulsion system exceed some critical temperature without some kind of expendable cooling?

6) What happens to ECLSS and cabin instrumentation if it doesn't stay within environmental limits that are satisfied by the ISS but not satisfied in free flight?

7) Are there mechanical components in the thermal management system (valves, pumps, etc.) whose cycle life is exceeded in a long mission?

If we can identify the gotchas, then we can figure out what needs beefing up.

Offline joek

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a) Is such an uncrewed, low-consumption mode possible for a D2?
Certainly.
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b) What modifications, if any, would need to be made to the current D2 to do this?
A service module, likely stuck in, or replacing, the trunk.
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c) How much engineering and test work is needed to implement it?
Unknown. However, DragonLab was advertised as a free flyer with a duration of "up to 2 years" and which would host pressurized and unpressurized cargo. Presumably SpaceX did the analysis for such a claim. Whether two years with full pressurized and associated ECLSS is anyone's guess. However have to expect that, given the 2-year claim, all systems would still be nominal-operational.
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d) What is the maximum duration of such a low consumption mode?
Unknown. But if we take DragonLab's claims at face value, nominally 1-2 years.

There are undoubtledly additional clues in the various NASA requirements related to lifeboat and crew return vehicle requirements; unfortunately can't find them at the moment. Another clue would be ISS interface requirements--which might tell us what Dragon needs to stay alive as a free flyer, or what an attachment needs to provide. (Unfortunately the ISS interface requirements are not public AFAICT.)

edit: Are we talking about a free flyer in LEO or NHRO or ... ? Will make a difference in terms of thermal-nav-comm-etc. but doubt significant enough to materially change the equation.
« Last Edit: 10/07/2023 09:00 pm by joek »

Offline joek

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6) What happens to ECLSS and cabin instrumentation if it doesn't stay within environmental limits that are satisfied by the ISS but not satisfied in free flight?
As long as equipment stays within operational limits, should not matter. ISS limits are intended to satisfy humans; free flight or "stasis" does not need to satisfy the same. Just need to ensure that when crew boards (or is about to board), the spacecraft is capable of bringing the environment to within limits for crew. Orion works the same way.

Offline TheRadicalModerate

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b) What modifications, if any, would need to be made to the current D2 to do this?
A service module, likely stuck in, or replacing, the trunk.

If that's necessary, then the whole conops starts to look kinda unattractive, because that's a lot of work.

However, a D2 used for this conops doesn't have any payload in the trunk.  That means that, if all you need is a few tanks to super-size the consumables stores, you can build a specialized trunk payload that contains all that stuff.  You then still need some plumbing between the crew module and the trunk.  I don't know if that currently exists, although I suspect there's plumbing already there for radiators.

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c) How much engineering and test work is needed to implement it?
Unknown. However, DragonLab was advertised as a free flyer with a duration of "up to 2 years" and which would host pressurized and unpressurized cargo. Presumably SpaceX did the analysis for such a claim. Whether two years with full pressurized and associated ECLSS is anyone's guess. However have to expect that, given the 2-year claim, all systems would still be nominal-operational.

Since DragonLab never had any customers, we don't really know if everything was already built in, or if it was an Elon fever-dream.  We also don't know if stuff to enable DragonLab was removed from D2.

I'm confident that D2 can be modified for long-duration uncrewed free flight, followed by a brief stint of crewed operation at the end of the mission.  The real question is whether the mods to do so are near-trivial, or a significant cost.  If they're trivial, then you have an SLS/Orion replacement that can be spun up very quickly, and the total mission cost is:

LSSmanufacturingCost/numberOfLSSmissions + LSSlaunchAndOpsCost + tankerLaunchCost*4or5 + D2launchCost

If they're non-trivial, then SpaceX has to bet considerably bigger on modifying the D2, which will annoy NASA, and the total mission cost is:

(LSSmanufacturingCost + D2reengineeringCost)/numberOfLSSmissions + LSSlaunchAndOpsCost + tankerLaunchCost*4or5 + D2launchCost

Or, alternatively, they could go the "use 2 D2's" route, which I'd rather not discuss here.


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There are undoubtedly additional clues in the various NASA requirements related to lifeboat and crew return vehicle requirements; unfortunately can't find them at the moment.

Doesn't necessarily help, because any lifeboat never free-flies except during ascent and EDL, both of which take very little time.

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Another clue would be ISS interface requirements--which might tell us what Dragon needs to stay alive as a free flyer, or what an attachment needs to provide. (Unfortunately the ISS interface requirements are not public AFAICT.)

I'm pretty sure that all that's implemented in NDS are power and data umbilicals.  IIRC, IDSS had room for some fluid transfer umbilicals, but I don't think anybody ever implemented them.

You can accomplish an awful lot with a blower duct and a human transferring the occasional bag of water back and forth.  Neither of those would be available during free flight.

6) What happens to ECLSS and cabin instrumentation if it doesn't stay within environmental limits that are satisfied by the ISS but not satisfied in free flight?
As long as equipment stays within operational limits, should not matter. ISS limits are intended to satisfy humans; free flight or "stasis" does not need to satisfy the same. Just need to ensure that when crew boards (or is about to board), the spacecraft is capable of bringing the environment to within limits for crew. Orion works the same way.

That all gets back to temperature.  If some consumable's rate of consumption is temperature-dependent (e.g. water), then a low temperature can cause condensation and a variety of yucky stuff.

Offline Jorge

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Another clue would be ISS interface requirements--which might tell us what Dragon needs to stay alive as a free flyer, or what an attachment needs to provide. (Unfortunately the ISS interface requirements are not public AFAICT.)

I'm pretty sure that all that's implemented in NDS are power and data umbilicals.  IIRC, IDSS had room for some fluid transfer umbilicals, but I don't think anybody ever implemented them.

The NDS IDD is public:
https://ntrs.nasa.gov/api/citations/20150014481/downloads/20150014481.pdf

joek may be referring to the ISS/COTS IRD (SSP-50808) which is controlled under EAR.
JRF

Offline DanClemmensen

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Another clue would be ISS interface requirements--which might tell us what Dragon needs to stay alive as a free flyer, or what an attachment needs to provide. (Unfortunately the ISS interface requirements are not public AFAICT.)

I'm pretty sure that all that's implemented in NDS are power and data umbilicals.  IIRC, IDSS had room for some fluid transfer umbilicals, but I don't think anybody ever implemented them.

The NDS IDD is public:
https://ntrs.nasa.gov/api/citations/20150014481/downloads/20150014481.pdf

joek may be referring to the ISS/COTS IRD (SSP-50808) which is controlled under EAR.
NDS is an implementation of IDSS. Crew Dragon uses an independent SpaceX active-only implementation of IDSS that is compatible with NDS. I don't think IDSS is controlled under ITAR.

The ISS has IDA ports, which implement passive-only NDS.

Offline Zed_Noir

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Not free flying, but a simple solution. Outfit the widget (depot tanker Starship) with a deck module that have a few radial docking ports above the propellant tanks. So the docked Crew Dragon capsule draws power and consumables from the depot waiting for the return of the OTV. Advantage of little modifications to the Dragon capsule.

Offline DanClemmensen

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Not free flying, but a simple solution. Outfit the widget (depot tanker Starship) with a deck module that have a few radial docking ports above the propellant tanks. So the docked Crew Dragon capsule draws power and consumables from the depot waiting for the return of the OTV. Advantage of little modifications to the Dragon capsule.
There are several ways to sustain the Crew Dragon in LEO.
   1) dock it to ISS
   2) Fly another unmodified Starship HLS that will sit in LEO and act as a minimal CLD to sustain the Crew Dragon. No new engineering needed.
   3) Add a second IDSS port to all the Starship HLSs. I think this qualifies as a minimal change, and it adds operational flexibility. One of these HLSs acts as a slightly less minimal CLD and sustains the Crew Dragon.
   4) Go ahead and build a real Starship CLD with multple IDSS ports.

The advantage of a CLD with two or more ports is that the Dragon and the Starship OTV can both dock to it for the crew transfers. The Dragon stays docked until the crew returns to LEO for the homeward transfer. No need for three separate Dragon dockings.

Offline TheRadicalModerate

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Not free flying, but a simple solution. Outfit the widget (depot tanker Starship) with a deck module that have a few radial docking ports above the propellant tanks. So the docked Crew Dragon capsule draws power and consumables from the depot waiting for the return of the OTV. Advantage of little modifications to the Dragon capsule.
There are several ways to sustain the Crew Dragon in LEO.
   1) dock it to ISS
   2) Fly another unmodified Starship HLS that will sit in LEO and act as a minimal CLD to sustain the Crew Dragon. No new engineering needed.
   3) Add a second IDSS port to all the Starship HLSs. I think this qualifies as a minimal change, and it adds operational flexibility. One of these HLSs acts as a slightly less minimal CLD and sustains the Crew Dragon.
   4) Go ahead and build a real Starship CLD with multple IDSS ports.

The advantage of a CLD with two or more ports is that the Dragon and the Starship OTV can both dock to it for the crew transfers. The Dragon stays docked until the crew returns to LEO for the homeward transfer. No need for three separate Dragon dockings.

1) ISS is too high an inclination.
2) Another LSS is a possibility, albeit an expensive one.
3) A second docking port violates the "almost off the shelf" rule.
4) As does a real-live CLD.

Here's one I haven't though through:  What if you take the D2 with you on the nose of the OTV-LSS?  You probably couldn't use more than one RVac and one low-throttle RSL if you want to stay within the torque and load envelope of IDSS, but that doesn't seem particularly difficult.

You'd likely have to undock the D2 for the OTV-to-lander RPOD, redock it after the lander left, and then repeat the process when the lander came back.  If you're really, really confident in your RPOD reliability, that might be acceptable.

Offline TheRadicalModerate

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Not free flying, but a simple solution. Outfit the widget (depot tanker Starship) with a deck module that have a few radial docking ports above the propellant tanks. So the docked Crew Dragon capsule draws power and consumables from the depot waiting for the return of the OTV. Advantage of little modifications to the Dragon capsule.

If you can build all the consumables and ECLSS support you need into the depot, you can build it into the D2 trunk in the first place.  The D2 mods are easier, faster to make, and cheaper.

Offline pochimax

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1) ISS is too high an inclination.

Maybe other CLD proposals will not have the ISS inclination (for example, Starlab? I don't know)

Just contract a private port to extend the Dragon life on orbit. Or at least, compare the cost of doing it to modifying Dragon.

Offline joek

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The NDS IDD is public:
https://ntrs.nasa.gov/api/citations/20150014481/downloads/20150014481.pdf

joek may be referring to the ISS/COTS IRD (SSP-50808) which is controlled under EAR.

Thanks (long time no see!). Yes, it's the IRD don't have access to.

Thought was that information about what the ISS provides to visiting vehicles (and vv.) might provide some insight into what is needed to keep the vehicle nominal as a free flyer beyond a few days.

Offline joek

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... I don't know if that currently exists, although I suspect there's plumbing already there for radiators.

Yes, for radiators and power; For Dragon 2, see Development of the Crew Dragon ECLSS, SpaceX, 2020. Would note that much of the ECLSS requirements are driven by crew occupancy--as you would expect (crew of 4 for 5 days as a free flyer).

Offline DanClemmensen

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3) A second docking port [on HLS-as-CLD] violates the "almost off the shelf" rule.
I am not a spacecraft engineer. However, the HLS is still in its design phase and I think it's likely that a second IDSS port is a simple design change.  This is especially true if the IDSS ports are on the airlock deck. It's also a useful addition to HLS in general in several scenarios. I think SpaceX may choose to design the very first HLS (uncrewed demo) as full-up Option B, skipping Option A altogether. A single HLS-as-CLD can be reused, first for Polaris 3, then as a CLD for any other demo missions, and then for the SLS/Priion replacement scenarios starting as early as Atemis III in the most aggressive case.  This allow for as many incremental test missions as desired, instead of the Artemis III "big bang" test.

This drifts very far from the topic of this thread, except in one sense: Why will a long-duration D2 ever be needed? IF (big IF) one or more crewed Starship types become available, what missions are left for D2 except to handle the Earth-LEO-Earth segment until Starship itself can handle it?

Offline joek

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This drifts very far from the topic of this thread, except in one sense: Why will a long-duration D2 ever be needed? IF (big IF) one or more crewed Starship types become available, what missions are left for D2 except to handle the Earth-LEO-Earth segment until Starship itself can handle it?

Think that violates OP rule #i (?) ...
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i) This is stupid, just get Starship crew-certified and you don't need to do this.  The premise is that Starship crew certification will be hard and take a long time.  That's a perfectly debatable premise; please don't debate it here.

Thus the question: What would it take to provide a "long-duration D2" as an interim solution? Where "long-duration" means: (a) 2-3 months uncrewed in LEO; and (b) crewed for last few days of that time (LEO to Earth surface). Am I getting that right?

Offline joek

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That all gets back to temperature.  If some consumable's rate of consumption is temperature-dependent (e.g. water), then a low temperature can cause condensation and a variety of yucky stuff.

For a free flyer with no crew, what consumables? D2 has thermal (radiator) and power (solar cells) needed to maintain an uncrewed environment nominally indefinitely[1]. That "yucky stuff" is largely an artifact of crew presence; remove crew and you remove the problem during the free-flyer "stasis" period.

During "stasis" (uncrewed) ... Humidity control? Nothing going in-out; should not a problem[2]. N2-O2-CO balance-scrubbing? Nothing going in-out; should not a problem.

So maybe turn the question around: What is it that you see as a problem with extending uncrewed D2 LEO life to weeks-months as an uncrewed free flyer that may require substantive changes?

[1] Conjecture. Feel free to challenge if you have information to the contrary, but Orion and DragonLab suggest that, without crew, they can free fly for extended periods.
[2] Except maybe venting for some undefined purpose? Why would that be needed if existing thermal controls work?

Offline Zed_Noir

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This drifts very far from the topic of this thread, except in one sense: Why will a long-duration D2 ever be needed? IF (big IF) one or more crewed Starship types become available, what missions are left for D2 except to handle the Earth-LEO-Earth segment until Starship itself can handle it?

Think that violates OP rule #i (?) ...
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i) This is stupid, just get Starship crew-certified and you don't need to do this.  The premise is that Starship crew certification will be hard and take a long time.  That's a perfectly debatable premise; please don't debate it here.

Thus the question: What would it take to provide a "long-duration D2" as an interim solution? Where "long-duration" means: (a) 2-3 months uncrewed in LEO; and (b) crewed for last few days of that time (LEO to Earth surface). Am I getting that right?
Also if SpaceX is willing to further developed the Crew Dragon.

Instead of using up resource on modifying the Crew Dragon. Think they will be more likely to mod some flavor of Starship for the purpose of the thread subject. Not necessary something crew rated.

Offline DanClemmensen

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In a desperate attempt to keep from dragging this thread off topic any further I started a new topic for
   Replacing SLS/Orion using Starship HLS and Crew Dragon
at
   https://forum.nasaspaceflight.com/index.php?topic=59662.0


Offline TheRadicalModerate

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...
This drifts very far from the topic of this thread, except in one sense: Why will a long-duration D2 ever be needed? IF (big IF) one or more crewed Starship types become available, what missions are left for D2 except to handle the Earth-LEO-Earth segment until Starship itself can handle it?

Think that violates OP rule #i (?) ...
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i) This is stupid, just get Starship crew-certified and you don't need to do this.  The premise is that Starship crew certification will be hard and take a long time.  That's a perfectly debatable premise; please don't debate it here.

Thus the question: What would it take to provide a "long-duration D2" as an interim solution? Where "long-duration" means: (a) 2-3 months uncrewed in LEO; and (b) crewed for last few days of that time (LEO to Earth surface). Am I getting that right?

Yes, but with one additional constraint, which I should have made explicit in the initial premise:  The LSS / tanker / depot work needed to get to at least Option A, and probably Option B / SLT, can't be slowed down by whatever the D2/LSS kludge solution is.

Remember when Bridenstine yanked on Elon's chain in 2019 because he spent time on the Starship roll-out event while the CCtCap schedule appeared to be slipping?  Now imagine how NASA would react if the HLS schedule were on the critical path for a while, but SpaceX was making modifications to the LSS, or diverting resources to D2 mods, which caused a further slip in the schedule, solely for the purpose of being able to sabotage SLS/Orion in the not-too-distant future. 

I suppose if a SpaceX CLD solution were to magically appear before Option B was complete, that might be OK.  But I suspect NASA's reaction to that would be roughly the same:  "Why are you pouring so many resources into CLD, which we only care about a little, at the expense of Artemis, which we care about a lot?"

I think that rules out depot nannies, itty-bitty CLD precursors, second docking ports on LSS, and a whole host of other possible solutions.

However, using a second LSS as a nanny might be a solution, albeit a kinda expensive one.  Putting the D2 on the OTV-LSS's nose during the LEO-NRHO-LEO transit might be a solution.  And certainly some modest consumable extension that took the form of a trunk payload with a bit of plumbing could be solution, as would a pressurized extension package that didn't eat up too much pressurized cargo volume.

Best solution of all, of course, is that the uncrewed loiter just works as-is.  I don't rule that out, but it's always something, isn't it?

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