SpaceX Dragon XL

[TheRadicalModerate]

Would it have to be expendable? Fuel is cheap and customers don't need 20 tonnes to GEO, so recovering the tug would make launch cheaper, which customers do like. Customers who do want to go big or launch BEO can still pay more to expend the tug.

Not if it wants to deliver a very small payload, but the delta-v to get back to GTO is also about 1850 m/s.

A single SuperDraco with its mount inside the tunnel where the docking collar currently is, fully-expanded bell nozzle hanging out the back. The theoretical maximum Isp for NTO/MMH is around 330s.

How does that change your payload numbers?

That'll take you to 8.8 t to GEO, expendably, and 6.5 t reusably.

Note that you're dealing with about 9.1 t of prop here, so even if you have a fully-expended SuperDraco with Isp=330 s and thrust of 70 kN, that's a mass flow of 21.6 kg/s, and therefore a burn time of 420 seconds.

When you factor in the different packaging, the full expansion, and the engine life, that's starting to sound a bit like a new engine.  That would be a problem for this scheme.

[TheRadicalModerate]

Where does the PAF attach to the DXL?

Ring around the docking collar.

Just checked the Falcon PAF and NDSB1 specs.  The standard PAF fitting is 1.58 m and the NDSB1 static envelope is 1.73 m.  This isn't the end of the world, but it does mean that they'll have to do a custom PAF.

Just to make sure I have this right, the order of modules/gizmos, sitting on the pad, from the bottom up, is:

1) The (somewhat wider than standard) PAF.
2) The DXL PAF connector, which is coaxially outside the docking port.
3) The docking port/tunnel, which is inserted through the doughnut of...
4) The DXL "bus" (tankage, avionics, thrusters, plumbing, what have you).
5) The DXL pressure vessel (hooked up to the docking tunnel).
6) The trunk.

Do I have this right?  Launched trunk-first into the unknown?

Update: I understand that the NDS block 1 isn't what SpaceX uses, but it's probably a pretty good proxy for what they use, since its static envelope has to be compatible with the IDA static envelopes.

[Paul451]

6) The trunk.

6) The exposed attachment points for forward payloads and solar panels.

There's no "trunk" in the Dragon sense.

[Asteroza]

6) The trunk.

6) The exposed attachment points for forward payloads and solar panels.

There's no "trunk" in the Dragon sense.

Just a "Frunk" in the Tesla sense...

[Paul451]

6) The trunk.

6) The exposed attachment points for forward payloads and solar panels.
There's no "trunk" in the Dragon sense.

Just a "Frunk" in the Tesla sense...

No. There's no enclosure. It's more like a roof-rack.

[woods170]

6) The trunk.

6) The exposed attachment points for forward payloads and solar panels.
There's no "trunk" in the Dragon sense.

Just a "Frunk" in the Tesla sense...

No. There's no enclosure. It's more like a roof-rack.

Yes. This.

No trunk on DragonXL. A trunk is not needed. The external payloads only require protection during the launch phase. The FH fairing takes care of that. Beyond that point the external payloads are fully exposed to space. Which is fully OK because that is how they will sit on Gateway as well: fully exposed to space.
So, beyond the launch phase there is no need for a protective enclosure around the external payloads. So, naturally, there isn't one. Which translates into: no trunk.

[Asteroza]

6) The trunk.

6) The exposed attachment points for forward payloads and solar panels.
There's no "trunk" in the Dragon sense.

Just a "Frunk" in the Tesla sense...

No. There's no enclosure. It's more like a roof-rack.

Yes. This.

No trunk on DragonXL. A trunk is not needed. The external payloads only require protection during the launch phase. The FH fairing takes care of that. Beyond that point the external payloads are fully exposed to space. Which is fully OK because that is how they will sit on Gateway as well: fully exposed to space.
So, beyond the launch phase there is no need for a protective enclosure around the external payloads. So, naturally, there isn't one. Which translates into: no trunk.

The only released image doesn't clearly show that area yet, just a cylinder band that looks to have foil lining it, and what appears to be a demonstrative external payload on some struts sticking out front a bit. The cylinder band area itself doesn't look that deep so I will concede the odds are low for a frunk-ish area, but here is also the weird bracket where the solar array attaches that doesn't make obvious sense why it's shaped the way it is and how it interacts with that area generally.

[CrazyHorse80]

Updated the vehicle with solar panels, same size as original Dragon.

Maybe they'll have to be slightly bigger to meet the power requirements from RFP:
https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=48353.0;attach=1622448;sess=58318

3.08 POWER
L3-GLS-0005 Power To Payloads
The Logistics Module shall provide no less than 1.8kW continuous power to cargo &
payloads from the time of handover on the ground, until the time of offloading from the LM to
the Gateway.
Rationale: Pressurized and unpressurized Logistics Module cargo and payloads may require
power during transit and while docked at the Gateway. These powered payloads may be within
the pressurized area, such as a cold stowage system, or in the unpressurized area, such as the
Robotic Arm system. 1.8 kW is consistent with an Orion Co-Manifested Payload available power
budget.
A mission Interface Control Document will specify additional detail such as peak power
requirements and interfaces required for each powered payload on each Logistics mission.
Derived From/Parent Requirement:
L2-GW-0012 Utilization Resources

According to Wikipedia they're capable of only 1.5kW continuous power output (4.0kW peak).

EDIT: Typo.

[DistantTemple]

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.

I'll speculate:  Because then they can remove the dock and the pressure vessel, stretch the tanks, and turn DXL into a tug for taking Starship payloads direct to GEO.

Starship can get 21 t to GTO and still de-orbit and land.  But it can get zero tonnes to GEO, even if it were expendable, and it takes 700 tonnes of tanker prop (7 launches, more or less) to get both to and from GEO reusably.

An expendable tug version of DXL would almost certainly be cheaper than the tanker launches needed to go all the way to GEO with Starship.  If you arm-wave the early flights of Starship at $20M (which I think is optimistic, until we get to a mature version of Starship), then a direct GEO launch costs $160M and likely takes three days to get on station from when they start launching prop for the mission.  I'm guessing that an expendable DXL tug (essentially a third stage for Starship) costs less than $50M, so the mission costs $70M, and it'll get you on station within a couple of days.

Weasel words:  Dracos are significantly underpowered to do this job quickly, and I'm not sure that they have the design life to do it.  You might need a pair of SuperDracos attached to the back of the trunk for this tug.

Opening a previous idea....
Connecting more than one!  If the fundamental design has access through the centre of the "service" section, then without a major redesign a docking port could be added at the other (roof-rack) end, making a complete pass through possible, and thus daisy-chaining.
OK this is not in current plans, but despite the name Dragon, this is a completely new vehicle, just using the SX lego box. SX must think "What would we like to be able to do with this?", and "What purposes could variations on this serve?
Since they are getting a contract to build it, "How can we make this meet our own needs and vision?" is the obvious question, as well as "How can we anticipate other contracts and have something ready to meet/adapt to their requirements?
Despite the coming SS, if done in volume, manufacturing a DXL derivative will be a smaller task than manufacturing an SS, (one that is rated for human access in space).
Once they can "production line" its parts, it could be knocked out just like Falcon s2's (I understand it is much more complicated)
So even my Idea of an airlock in the docking tube isn't daft in the future.
Maybe in 6 yeas there will be a dozen of these in use, and a 100 within the decade!

[Kaputnik]

The ATV was designed with an second (aft) docking port in mind, although this was never actually developed and built. So the idea has a precedent.

[Paul451]

No trunk on DragonXL. A trunk is not needed. The external payloads only require protection during the launch phase. The FH fairing takes care of that.

The only released image doesn't clearly show that area yet, just a cylinder band that looks to have foil lining it

It's not a "cylinder", the silver-foil insulated parts are the visible portions of the round or conical dome-ends of the pressure vessel.

but here is also the weird bracket where the solar array attaches that doesn't make obvious sense why it's shaped the way it is and how it interacts with that area generally.

I suspect it doesn't make sense because you're picturing the front of the pressure vessel wrong. I noticed a lot of the early renders treated everything as a flat-ended cylinder sections, with mystery silver rings just... attached... because? Only more recently have people got their heads around the structure. Once you properly grok that it's a pressure vessel [slaps forehead], then the other oddities make sense.

[Paul451]

[...] daisy-chaining. OK this is not in current plans, but despite the name Dragon, this is a completely new vehicle, just using the SX lego box. SX must think "What would we like to be able to do with this?", and "What purposes could variations on this serve? Since they are getting a contract to build it, "How can we make this meet our own needs and vision?" is the obvious question, as well as "How can we anticipate other contracts and have something ready to meet/adapt to their requirements?

IMO, anything else SpaceX wanted to do would also be a "completely new vehicles, just using the SX lego box".

DXL is narrowly specialised to its task, to delivery pressurised cargo to a space-station. That's it. It isn't a baby space-station in disguise. If SpaceX wanted to offer a baby space-station to customers, they'd design something fit-for-purpose, not jury-rigged from a logistics module. It will share elements, because it would be built from the same lego box by the same people, but it wouldn't be derived from DXL.

Same with a GEO tug. Same with a lunar lander. Same with a lunar surface habitat. Or any other proposed uses of this thing. If you have the guys who designed the rockets and capsules still working there, just point them to the job and say "what you did before, do it for this".

[Robotbeat]

Call it derived or not, suit yourself. They're calling this thing "Dragon XL" even though it's very much not Dragon, they argue it's Dragon-derived.

[TheRadicalModerate]

No. There's no enclosure. It's more like a roof-rack.

The temptation to photoshop Mitt Romney's dog onto that picture is almost overwhelming.

[TheRadicalModerate]

IMO, anything else SpaceX wanted to do would also be a "completely new vehicles, just using the SX lego box".

DXL is narrowly specialised to its task, to delivery pressurised cargo to a space-station. That's it. It isn't a baby space-station in disguise. If SpaceX wanted to offer a baby space-station to customers, they'd design something fit-for-purpose, not jury-rigged from a logistics module. It will share elements, because it would be built from the same lego box by the same people, but it wouldn't be derived from DXL.

Same with a GEO tug. Same with a lunar lander. Same with a lunar surface habitat. Or any other proposed uses of this thing. If you have the guys who designed the rockets and capsules still working there, just point them to the job and say "what you did before, do it for this".

The reason I disagree with you is that I don't think there's enough money in a Gateway contract to pay back the R&D opportunity cost, and the resources would be better spent on habitable modules for Starship.  On the other hand, if this just turns out to be the first application of a heavy-payload bus made out of Dragon guts, then the investment is well worth it.  It's especially worth it if it allows SpaceX to bid Starship for direct-to-GEO NSSL flights.

I largely agree with your "SX lego box" comment.  It's just that I think one of the lego pieces will be a lot better defined than the other ones.

[kkattula]

IMO, anything else SpaceX wanted to do would also be a "completely new vehicles, just using the SX lego box".

DXL is narrowly specialised to its task, to delivery pressurised cargo to a space-station. That's it. It isn't a baby space-station in disguise. If SpaceX wanted to offer a baby space-station to customers, they'd design something fit-for-purpose, not jury-rigged from a logistics module. It will share elements, because it would be built from the same lego box by the same people, but it wouldn't be derived from DXL.

Same with a GEO tug. Same with a lunar lander. Same with a lunar surface habitat. Or any other proposed uses of this thing. If you have the guys who designed the rockets and capsules still working there, just point them to the job and say "what you did before, do it for this".

The reason I disagree with you is that I don't think there's enough money in a Gateway contract to pay back the R&D opportunity cost, and the resources would be better spent on habitable modules for Starship.  On the other hand, if this just turns out to be the first application of a heavy-payload bus made out of Dragon guts, then the investment is well worth it.  It's especially worth it if it allows SpaceX to bid Starship for direct-to-GEO NSSL flights.

I largely agree with your "SX lego box" comment.  It's just that I think one of the lego pieces will be a lot better defined than the other ones.

$7 Billion ought to pay back a lot of R&D!

However, I also suspect that a deep space, long endurance, logistics module could find other applications with minor changes.  E.g. extra axial or even radial docking ports, airlock, full ECLSS.

The two things it doesn't appear to have, and would need to be a tug, is a high thrust, high Isp engine, and large propellant tanks.  IMO, that would be a very different vehicle.  More likely based on Falcon 2nd stage.

[TheRadicalModerate]

$7 Billion ought to pay back a lot of R&D!

However, I also suspect that a deep space, long endurance, logistics module could find other applications with minor changes.  E.g. extra axial or even radial docking ports, airlock, full ECLSS.

The two things it doesn't appear to have, and would need to be a tug, is a high thrust, high Isp engine, and large propellant tanks.  IMO, that would be a very different vehicle.  More likely based on Falcon 2nd stage.

The $7B is for the entire program, for all vendors, over 15 years.  And it's still IDIQ, which means that they're not paying that money out up front, and aren't obligated to spend the whole budget.  No doubt SpaceX is getting something up front, but I'd be surprised if it was more than a couple hundred million.  SpaceX is guaranteed two missions, IIRC.  That might be worth $1B, although I think it's more likely to be in the $700M range.

I'd strongly suspect that cryogenics inside the Starship payload bay, unless engineered to be part of the Starship fuel system and vented accordingly, is a big pain.  So an F9S2-derived stage seems unlikely.  Storables, on the other hand, have been managed for years.

I do think that a handful of Dracos is unlikely to do for a tug that needs 1800-ish m/s of delta-v.  They have to burn for a really long time, which makes the actual delta-v requirements even higher.  But even a single SuperDraco, mounted in the space where the docking ring is right now, would be more than adequate--especially if fully expanded.

Here's what I'm thinking:

There's a Dragon Guts bus.  It's roughly toroidal (or at least it's a cylindrical ring), and has enough prop for its Dracos to manage enough delta-v for a fast NRHO transfer and disposal.  That's about a tonne and a half of MMH/NTO with a 5 tonne payload and 1 tonne of trash on disposal.

On top of that, SpaceX can build out one of two modules:

1) The pressurized cargo system shown in the current DXL drawings.  If you did an exploded drawing of this, it would be a cylindrical pressure vessel with a tunnel and docking ring sticking out of the bottom.  The tunnel and docking ring fit into the hole in the bus.

2) Or they can build a module with an extra 7.5 tonnes of prop and a single SuperDraco sticking out the bottom, which fits into the hole in the bus.  This module also needs a PAF on the top, to which a standard payload up to about 8.8 tonnes can be attached.

Whether the "roof rack" with the solar wings is the same between the two different module options is an open question, but if so, it can't interfere with the payload attached for the GTO-to-GEO tug.

[pochimax]

We don' t know the prices offered.
Price of the first mission is different (higher) from the next missions. So I expect a lot of investment return for SpaceX in that first mission.

[guckyfan]

I see a service tug that can fly people and supplies between Starships on the way to Mars. Maybe replace the Draco with tiny methalox thrusters. With a robot arm it can do minor repairs too. That's assuming that a small fleet flies parallel.

[Paul451]

How many Draco Thrusters on Dragon XL?  20?

Judging by the image: Four triplets and 4 tail thrusters around the hatch. So 16.