SpaceX Dragon XL

[Rocket Science]

Slightly out of left-field question: could a Dragon XL derivative be used as a transfer stage for a 3-stage lunar lander? (Artemis)

To be honest when I first heard of the XL for the gateway I though OK great... My next thought was how can this be used as a Lunar lander or Hab...

[MATTBLAK]

It might make an additional Hab space for the Gateway; though it doesn't have a life support system. I certainly was thinking about a derivative with increased propellant with just mainly its propulsion system to bring a Lander Descent and Ascent Stage down into low lunar orbit.

[su27k]

Slightly out of left-field question: could a Dragon XL derivative be used as a transfer stage for a 3-stage lunar lander? (Artemis)

I thought about this too, but if you read woods170's previous comments, it looks like Dragon XL would not have much delta-v, it would instead use a slow trajectory to reach Gateway, so doesn't look a good basis for transfer stage.

[Bob Shaw]

LRO, Chinese craft, other nations on the way mean that LLO should be kept clean (and the surface).

[Robotbeat]

Slightly out of left-field question: could a Dragon XL derivative be used as a transfer stage for a 3-stage lunar lander? (Artemis)

I thought about this too, but if you read woods170's previous comments, it looks like Dragon XL would not have much delta-v, it would instead use a slow trajectory to reach Gateway, so doesn't look a good basis for transfer stage.

It could have stretched tanks to serve in this capacity. Progress has had variants with stretched tanks.

[daedalus1]

LRO, Chinese craft, other nations on the way mean that LLO should be kept clean (and the surface).

There are already many crashed spacecraft on the surface, stretching back to 1960. Also when landers stop working they stay there.
I'm sure this material will be useful in the future, including museum sites.

[anof]

LRO, Chinese craft, other nations on the way mean that LLO should be kept clean (and the surface).

Anything in LLO without station-keeping will crash into the moon pretty quickly.

[baldusi]

I was just wondering from the various discussions on here if there was an answer as to how Falcon Heavy would get the Dragon XL to the Gateway?

As in fully expendable, center core expended with side boosters recovered, etc...my bet would be the second option with the side boosters potentially doing a sea landing on the drone ships. I know there is lots of talk about the Starship but I'm just wanting Falcon Heavy to be used as much as possible until more powerful rockets come online and are flight proven over time.

I'm about 99% sure that the FH will take the DXL to TLI, and then the DXL will be responsible for inserting itself into NRHO and later disposing of itself.  A DXL with 700 m/s of delta-v is more than adequate.

Whether you need an FH3R, an FH2R, or an FHE to go to TLI will likely be a function of the exact launch mass of the DXL.  I'd guess it will vary mission-by-mission.  I doubt that many of them will be light enough to use an FH3R.

Look up Low Energy Ballistic Transfers. You need a bit more C3, but can reduce total delta-v to a NRHO to below 200m/s.

[TheRadicalModerate]

Slightly out of left-field question: could a Dragon XL derivative be used as a transfer stage for a 3-stage lunar lander? (Artemis)

Yes, there has been speculation to that effect.  However, the 3-stage architectures appear to be falling out of favor.

I can think of four major uses for something like DXL:

1) Its intended purpose (Gateway logistics).
2) A refueling system for a reusable ascender (I'm assuming storable prop).
3) A NRHO-LLO-NRHO tug
4) A GTO-to-GEO tug for taking Starship payloads direct to GEO with no refueling in LEO.

DXL as currently configured can handle both the Gateway logistics and AE refueling roles (although I suspect that you'd put the refueling tanks with 5 t of MMH/NTO in the trunk).  Both of these require no more than 700 m/s of delta-v, which, if you assume a 3 t dry mass, requires about 1.7 t of MMH/NTO for DXL to get to NRHO and then dispose of itself empty.

Assuming that it's considered poor form to leave an empty DXL in LLO to eventually crash into the Moon, you'd need 750 m/s to go from NRHO to LLO with about 25 t payload (AE+DE), and then 900-ish m/s to dispose to a heliocentric graveyard.  At a 3 t dry mass, and assuming a 50 m/s BLT from TLI to NRHO, that comes out to 9.6 t of MMH/NTO.  So this seems like it would require stretching the main DXL tanks.

The final application, for taking Starship payloads direct to GEO from GTO, is probably a big deal for SpaceX, because it gives them a reasonable NSSL story for the military to get direct to GEO.  Space Force is unlikely to look kindly on Starship refueling for a while, because it takes longer and incurs considerably higher risk to the payload.  On the other hand, just mounting the payload on an MMH/NTO tug inside the fairing isn't nearly as scary.  No doubt commercial GEO satellite operators would find such a configuration equally compelling.

Starship is now rated at 21 t to GTO, so if you use all of that capacity and have a 3 t tug, you can take an 8.3 t payload to GEO with 9.5 t of MMH/NTO.  (Note: some rounding errors here.)

But note that the NRHO-LLO tug and the GTO-GEO tug both require almost identical amounts of prop.  That might militate toward a DXL variant that's just a bus with a 10 t prop tank, and a pair of connectors on each end.  In the case of the LLO-NRHO tug, it'd be a PAF female connector on the bottom and a IDA-like passive docking port on the top.  In the case of the GTO-GEO tug, it'd be a PAF female on the bottom and something like a PAF male on the top.  But there'd be no pressurized space, and no trunk.

[TheRadicalModerate]

Look up Low Energy Ballistic Transfers. You need a bit more C3, but can reduce total delta-v to a NRHO to below 200m/s.

You can find BLTs that are only about 50 m/s to NRHO insertion, but the Gateway logistics system has a fast transfer requirement.  That's about 430 m/s from an Apollo-like (3190 m/s) TLI.

And don't forget disposal.  I'm budgeting 270 m/s for that, although that might be too small.

[Robotbeat]

Look up Low Energy Ballistic Transfers. You need a bit more C3, but can reduce total delta-v to a NRHO to below 200m/s.

You can find BLTs that are only about 50 m/s to NRHO insertion, but the Gateway logistics system has a fast transfer requirement.  That's about 430 m/s from an Apollo-like (3190 m/s) TLI.

And don't forget disposal.  I'm budgeting 270 m/s for that, although that might be too small.

It doesn’t have a fast transfer requirement. It has a fast transfer OPTION. Also, disposal should be less than insertion.

[Rocket Science]

It might make an additional Hab space for the Gateway; though it doesn't have a life support system. I certainly was thinking about a derivative with increased propellant with just mainly its propulsion system to bring a Lander Descent and Ascent Stage down into low lunar orbit.

I meant lunar surface Hab Matt, sorry I wasn't clear... I'm only looking at it as a starting point with extra tanks and engines similarly like we did when we looked at the CST-100 and Dragon as a lander over the years here on NSF...

Started a new topic so as to not derail this discussion:
https://forum.nasaspaceflight.com/index.php?topic=50563.0

[woods170]

Look up Low Energy Ballistic Transfers. You need a bit more C3, but can reduce total delta-v to a NRHO to below 200m/s.

You can find BLTs that are only about 50 m/s to NRHO insertion, but the Gateway logistics system has a fast transfer requirement.
That's about 430 m/s from an Apollo-like (3190 m/s) TLI.

And don't forget disposal.  I'm budgeting 270 m/s for that, although that might be too small.

Emphasis mine.

That fast transfer requirement is a mission unique optional requirement, and unlikely to be used in early missions. The additional delta V required will come from addtional FH performance, not from Dragon XL.

Remember, this vehicle is allowed to mass just 14 metric tons at first docking with Gateway, inclusive both pressurized AND unpressurized cargo. The additional delta V you're adding translates into a lot of additional propellant, for which there really isn't available room in the mass break-down of Dragon XL.

[Robotbeat]

If you can find a BLT trajectory very near C3=0 that only needs a 50m/s insertion delta-v, that implies that you just need about 50m/s to do a disposal burn (as there's no reason that disposal needs to be particularly fast) plus maybe a bit more to send it into the Moon, into the Earth's atmosphere, or to Earth escape.

[TheRadicalModerate]

That fast transfer requirement is a mission unique optional requirement, and unlikely to be used in early missions. The additional delta V required will come from addtional FH performance, not from Dragon XL.

Remember, this vehicle is allowed to mass just 14 metric tons at first docking with Gateway, inclusive both pressurized AND unpressurized cargo. The additional delta V you're adding translates into a lot of additional propellant, for which there really isn't available space in the mass break-down of Dragon XL.

Thanks for the correction on the fact that fast transfer is optional, not a requirement.

But you can't do it with additional FH performance, because the impulse required occurs long after the S2's mission life.  You need about 180 m/s to do the lunar-flyby plane change to the NRHO transfer orbit about 3 days into the mission, and then about 250 m/s to do the actual NRHO insertion 2 days later.

I'm willing believe that I've been too generous with my disposal budget.  If we can get away with 50 m/s for disposal, then fast transfer takes a total of 480 m/s, and BLT insertion would take 100 m/s.

I've been using 3.0 t as a guess at dry mass, but let's up that to 4.0 t just to be conservative.  I'm also going to assume 1 t of trash onboard at disposal time.  As usual, Isp=300 s.

To stay under the 14 t wet mass delivery limit and a 15 t limit to TLI, I get:

480 m/s version: 4.0 t dry mass + 8.8 t payload + 2.1 t prop
100 m/s version: 4.0 t dry mass + 9.9 t payload + 0.3 t prop

So it's pretty easy to meet the fast transfer conditions without blowing out any of the other constraints.

Note that 15 t to TLI is FHE performance.  I don't have good numbers for FH2R or FH3R, but you have an awful lot of bonus payload above NASA requirements to play with, and no doubt some if not most missions can be done with an FH2R.  ISTM that they'd be crazy not to size the MMH/NTO tanks for fast transfer.

Update:  I found much more than you ever want to know about NRHO disposal orbits here.  Looks like 15 m/s will usually get you to heliocentric in most cases, so 50 m/s is generous.

[pochimax]

Only remember that "fast" transit in the NASA optional requirement actually means <30 days transit.

[Robotbeat]

Is there any hint of propellant transfer capability?

I sincerely doubt it, but it’d be interesting (and the IDSS standard supports it as an option).

[woods170]

Is there any hint of propellant transfer capability?

I sincerely doubt it, but it’d be interesting (and the IDSS standard supports it as an option).

No propellant transfer capability thru the docking system for Dragon XL.

But, there is this from the RFP Requirements:

L3-GLS-1079 Mission-Specific, Permanently Mounted, Unpressurized Cargo and Payload Services & Interfaces

The Logistics Module shall provide structural support and electrical anddata services via interfaces with mission-specific cargo and payloads that are permanently mounted to the exterior of the Logistics Module.

Rationale: Externally-mounted payloads that are not intended for EVR transfer from the Logistics Module or other manipulation/handling by the Gateway EVR System, may be permanently mounted to an exterior site on the unpressurized volume of the Logistics Module, or to an external adapter interface that may include mission-specific physical interfaces for electrical or data connections. This requirement is intended to allow the Logistics Module to transport permanently-mounted external cargo, such as pressurized tanks of gases or fuel, which commodities may be transferred to the Gateway through hoses or by other means that do not involve interaction with the Gateway EVR (Extra Vehicular Robotics) system.

[TheRadicalModerate]

Is there any hint of propellant transfer capability?

I sincerely doubt it, but it’d be interesting (and the IDSS standard supports it as an option).

No propellant transfer capability thru the docking system for Dragon XL.

But, there is this from the RFP Requirements:

L3-GLS-1079 Mission-Specific, Permanently Mounted, Unpressurized Cargo and Payload Services & Interfaces

The Logistics Module shall provide structural support and electrical anddata services via interfaces with mission-specific cargo and payloads that are permanently mounted to the exterior of the Logistics Module.

Rationale: Externally-mounted payloads that are not intended for EVR transfer from the Logistics Module or other manipulation/handling by the Gateway EVR System, may be permanently mounted to an exterior site on the unpressurized volume of the Logistics Module, or to an external adapter interface that may include mission-specific physical interfaces for electrical or data connections. This requirement is intended to allow the Logistics Module to transport permanently-mounted external cargo, such as pressurized tanks of gases or fuel, which commodities may be transferred to the Gateway through hoses or by other means that do not involve interaction with the Gateway EVR (Extra Vehicular Robotics) system.

I don't think you can look at just Gateway logistics when analyzing this thing.  You also have to look at the logistics of the HLS system, and then there's a clear need for a refueling capability.

Since Loverro seems hellbent on using this Boeing two-stage HLS proposal as his first-choice architecture, there's simply no way that every single lunar sortie can require two SLS launches.  The first one, sure, where you send a mated AE/DE on a Block 1B and the Orion on a Block 1.  But after that, the cost of flying two SLS launches for every lunar sortie is just ridiculous.

I think that means they have to be planning on a reusable AE and refueling it in NRHO from the git-go.  That then allows subsequent expendable DEs to be co-manifested along with Orion on a single Block 1B launch.  So, instead of two SLS launches per sortie, you have an SLS launch and an FH2R/DXL launch per sortie.  Quite a bit cheaper.

[DreamyPickle]

From source selection statement:

Its design approach would locate the service section of the Dragon XL between
the pressurized volume and the Gateway, meaning crew would have to translate through the
service section, which is mechanically active.

Any speculation regarding why SpaceX would dock through the service section? This seems to be unique among cargo spacecraft.