Dragon XL (or equivalent Starship) as space tug for module delivery to Gateway?

[Robotbeat]

This is a thread for discussion DragonXL (or an equivalent capability Starship variant) as a reusable space tug for orbital modules.

With SLS block 1B, the plan is to use Orion. A comanifested payload is extracted from the stage by Orion, which does the staging, turnaround, redock, and extraction maneuver that the Apollo CM did with the LM.

All the upper stage has to do is maintain basic 3axis attitude control. Pretty basic for most upper stages for regular payload deployment.

The difficulty is WHERE this would occur. If done immediately after module burnout, the DragonXL would have to be in a near exact orbit with it, maybe waiting in HEO. If done later on, this could be after a pure ballistic transfer to the Moon, the upper stage would need to last for a few days (not necessarily a huge problem as just the 3axis system needs to live that long, not the whole stage with boiling off propellants). Also possible to use a very small dedicated propulsion unit, like those MEVs that NG developed for GSO bird life extension. (Heck, the MEV could actually do the whole docking thing). Another possibility is berthing, if Gateway has an appropriate robotic arm. (I think LIDS docking ports support berthing, too?)

The module being carried by DragonXL would need two docking ports, but I think that’s required for Orion, too.

Going dedicated launch vastly opens up the available launch vehicles, and even larger modules than SLS 1B can co-manifest. And it should be much cheaper than an EUS stage. PLUS, it can go slower, taking advantage of low energy transfers or even electric propulsion.

[Robotbeat]

The tug, if efficient enough, could, in principle, do multiple tugs. You could even use a refueled Orion at Gateway to do the tugging.

[Zed_Noir]

The tug, if efficient enough, could, in principle, do multiple tugs. You could even use a refueled Orion at Gateway to do the tugging.

The Orion got a terrible vehicle mass fraction. Never mind the requirement to stored and be able to transfer large quantities of hypergolics at the Gateway.

[DanClemmensen]

I vote for a dedicated custom single-use kicker/maneuvering unit for each gateway module. This unit is similar to a cut-down Dragon XL with no cargo holds. It is mated to the module, not with a docking port but with a simplified one-time custom attachment. it is mated prior to launch and the unit+module are launched together as a single pre-mated payload, very similar to PPE+HALO. When it reaches Gateway, it connects the module to Gateway in a manner similar to the autonomous docking of a Dragon XL. After hard dock and checkout, the unit initiates the one-time disconnect, backs off, and disposes of itself.

Reuse is nice, but this is not the place for it. Each of those modules is unique, and the mass savings from a custom maneuvering unit are worth throwing the thing away. As an example, an ordinary Dragon XL is discarded at the end of a supply mission.

[Robotbeat]

The tug, if efficient enough, could, in principle, do multiple tugs. You could even use a refueled Orion at Gateway to do the tugging.

The Orion got a terrible vehicle mass fraction. Never mind the requirement to stored and be able to transfer large quantities of hypergolics at the Gateway.

So what, you don’t need much delta-v to capture & dock something hanging out just outside the Gateway keep-out zone.

Prop transfer is part of the NDS standard and it’s an obvious candidate for upgrading Orion.

[Robotbeat]

The real reason I’m thinking to do reuse is because Starship could deliver like 100 tons of hypergols to Gateway so the mass penalty is small.

[Robotbeat]

Something like a big version of the Vigoride tug would be an interesting option as it uses water as propellant.

[DanClemmensen]

I don't think Gateway is needed at all, but If we need a station in NRHO, then I cannot get interested in any scheme that uses a Starship to support it. If you need a Starship, then the Starship should replace the Gateway, not just support it. Take all the interesting bits from each module design and design them all into one Starship.

[TheRadicalModerate]

This is a thread for discussion DragonXL (or an equivalent capability Starship variant) as a reusable space tug for orbital modules.

With SLS block 1B, the plan is to use Orion. A comanifested payload is extracted from the stage by Orion, which does the staging, turnaround, redock, and extraction maneuver that the Apollo CM did with the LM.

All the upper stage has to do is maintain basic 3axis attitude control. Pretty basic for most upper stages for regular payload deployment.

Remember that there are two (or maybe three) different SLS co-manifesting profiles.  There's the one you mention, where the EUS maintains attitude control for co-manifest deployment, then the Orion provides the small delta-v and attitude control to wrangle the co-manifest on its nose, once it's extracted from the EUS.

But there's also a "free-flyer" profile, where the Orion separates from the EUS, and the co-manifest itself is responsible for its own propulsion and attitude control. 

I guess that there's some small possibility of getting a burn out of the EUS after translunar coast as well, although that's not part of the mission planner's guide at this point.

The difficulty is WHERE this would occur. If done immediately after module burnout, the DragonXL would have to be in a near exact orbit with it, maybe waiting in HEO. If done later on, this could be after a pure ballistic transfer to the Moon, the upper stage would need to last for a few days (not necessarily a huge problem as just the 3axis system needs to live that long, not the whole stage with boiling off propellants). Also possible to use a very small dedicated propulsion unit, like those MEVs that NG developed for GSO bird life extension. (Heck, the MEV could actually do the whole docking thing). Another possibility is berthing, if Gateway has an appropriate robotic arm. (I think LIDS docking ports support berthing, too?)

The module being carried by DragonXL would need two docking ports, but I think that’s required for Orion, too.

Going dedicated launch vastly opens up the available launch vehicles, and even larger modules than SLS 1B can co-manifest. And it should be much cheaper than an EUS stage. PLUS, it can go slower, taking advantage of low energy transfers or even electric propulsion.

I think it's a mistake to think of DXL as what you'd want for this.  DXL has a pressure vessel, even though it doesn't have a heat shield.  That's suboptimal for carrying big modules.

However, DXL, like all Dragon variants, is really two separate components:

1) There's a toroidal bus-like component, with most of the RCS, most of the MMH/NTO tanks, the avionics, F9S2 attachments, etc.  This, I suspect (but don't know) is common to both the D2 Cargo, D2 Crew, and DXL.

2) Then there's a "payload".  In the DXL's case, the docking port of a pressurized cylinder fits into the "doughnut hole" in the bus toroid, with the other end of the pressure vessel holding the solar panels and spots for co-manifested payloads.  For D2, the doughnut hole is a pressurized storage area, with the rest of the pressure vessel being the familiar frustum-shaped system.  D2 also obviously has a heat shield attached to the bottom of the bus.

I've been on this soapbox before, but you can build a version of the Dragon with no pressure vessel at all.  There are then three possible configurations:

a) Just the naked bus, with a PAF attached to the top of the doughnut.  The bus does all the maneuvering, then docks the payload to whatever you're building.  Presumably the Dragon would then jettison itself and head off to disposal.

b) Build your payload so it fits its docking system through the doughnut hole, similar to the DXL.  The bus then becomes part of the structure, and is available for maneuvering.

c) You can also build a Starship-hosted version of this that's good for deploying about 9t directly to GEO (assuming that the 21t direct to GTO number still holds from the Starship User Guide).  You'd put a pretty big extra MMH/NTO tank in the doughnut hole, and mount a couple of PAFs on the top of the tank.  9t is about right to carry a couple of VHTS birds to GEO, allowing them to be on station in hours instead of weeks-to-months.

[Jim]

Cygnus Service module or PPE equivalent could do it too.

[Jim]

I don't think Gateway is needed at all, but If we need a station in NRHO, then I cannot get interested in any scheme that uses a Starship to support it. If you need a Starship, then the Starship should replace the Gateway, not just support it. Take all the interesting bits from each module design and design them all into one Starship.

Again, SpaceX is not the Taco Bell of the space industry

[DanClemmensen]

I don't think Gateway is needed at all, but If we need a station in NRHO, then I cannot get interested in any scheme that uses a Starship to support it. If you need a Starship, then the Starship should replace the Gateway, not just support it. Take all the interesting bits from each module design and design them all into one Starship.

Again, SpaceX is not the Taco Bell of the space industry

Agreed. A custom Starship is not the answer to life, the universe, and everything. But If your concept depends on a custom Starship to service Gateway, then you may as well depend on a different custom Starship to replace Gateway. As I said, my vote is for no Gateway at all.

[niwax]

I don't think Gateway is needed at all, but If we need a station in NRHO, then I cannot get interested in any scheme that uses a Starship to support it. If you need a Starship, then the Starship should replace the Gateway, not just support it. Take all the interesting bits from each module design and design them all into one Starship.

Again, SpaceX is not the Taco Bell of the space industry

Agreed. A custom Starship is not the answer to life, the universe, and everything. But If your concept depends on a custom Starship to service Gateway, then you may as well depend on a different custom Starship to replace Gateway. As I said, my vote is for no Gateway at all.

In theory, they could even deliver modules with HLS in the first place. It needs to go to gateway and hang out there waiting for the astronauts to arrive anyway.

[Robotbeat]

I don't think Gateway is needed at all, but If we need a station in NRHO, then I cannot get interested in any scheme that uses a Starship to support it. If you need a Starship, then the Starship should replace the Gateway, not just support it. Take all the interesting bits from each module design and design them all into one Starship.

Again, SpaceX is not the Taco Bell of the space industry

You keep saying this, and I have agreed in the past, but… are you sure?

Crew is getting to ISS solely on Dragon. Cargo is going up and down on dragon, even Cygnus is riding Falcon 9. OneWeb is launching On Falcon. *ESA* now looking at launching on Falcon! Starlink dominates the global launch mass and is eating the market share of players like ViaSat. Viasat is also launching on Falcon.

Gateway is launching on… Falcon. DragonXL is the closest thing we have to a selected service provider for Gateway.

Look at an actual Artemis surface mission, and sure you have one SLS/Orion launch, but you’ll have like *10* Starship launches, with Starship launchers, Starship tankers, Starship depot, Starship lander.

The spaceflight industry at the moment IS like the Demolition Man future with Taco Bell for everything, plus the addition of like ONE tiny Quiznos restaurant.

I hope it’s temporary because it’d be very good to have redundancy and competition. (And it will be temporary.) But it’s actually kind of insane the degree to which the annoying SpaceX fanboi wet dream has come literally true.

[DanClemmensen]

I don't think Gateway is needed at all, but If we need a station in NRHO, then I cannot get interested in any scheme that uses a Starship to support it. If you need a Starship, then the Starship should replace the Gateway, not just support it. Take all the interesting bits from each module design and design them all into one Starship.

Again, SpaceX is not the Taco Bell of the space industry

You keep saying this, and I have agreed in the past, but… are you sure?

It really cannot be Taco Bell. They do use methane, but raptor is not a gas generator. On second thought, maybe "full-flow" also counts.

[Hog]

I don't think Gateway is needed at all, but If we need a station in NRHO, then I cannot get interested in any scheme that uses a Starship to support it. If you need a Starship, then the Starship should replace the Gateway, not just support it. Take all the interesting bits from each module design and design them all into one Starship.

Again, SpaceX is not the Taco Bell of the space industry

You keep saying this, and I have agreed in the past, but… are you sure?

It really cannot be Taco Bell. They do use methane, but raptor is not a gas generator. On second thought, maybe "full-flow" also counts.

Raptor is a "Full-flow, Staged (in)Digestion" and "Gas/Gas" rocket engine.  After TB consumption I suggest a "reduction of ullage space", in private.

[whitelancer64]

I don't think Gateway is needed at all, but If we need a station in NRHO, then I cannot get interested in any scheme that uses a Starship to support it. If you need a Starship, then the Starship should replace the Gateway, not just support it. Take all the interesting bits from each module design and design them all into one Starship.

Again, SpaceX is not the Taco Bell of the space industry

You keep saying this, and I have agreed in the past, but… are you sure?

Crew is getting to ISS solely on Dragon. Cargo is going up and down on dragon, even Cygnus is riding Falcon 9. OneWeb is launching On Falcon. *ESA* now looking at launching on Falcon! Starlink dominates the global launch mass and is eating the market share of players like ViaSat. Viasat is also launching on Falcon.

Gateway is launching on… Falcon. DragonXL is the closest thing we have to a selected service provider for Gateway.

Look at an actual Artemis surface mission, and sure you have one SLS/Orion launch, but you’ll have like *10* Starship launches, with Starship launchers, Starship tankers, Starship depot, Starship lander.

The spaceflight industry at the moment IS like the Demolition Man future with Taco Bell for everything, plus the addition of like ONE tiny Quiznos restaurant.

I hope it’s temporary because it’d be very good to have redundancy and competition. (And it will be temporary.) But it’s actually kind of insane the degree to which the annoying SpaceX fanboi wet dream has come literally true.

SpaceX is in full steamroller mode, indeed they are snapping up launches from other providers left and right.

However, that does not mean they are the only game in town. SpaceX is not a panacea, and there are a lot of applications SpaceX is not the best choice for.

[Robotbeat]

If you think that’s what I’m suggesting, then I suggest you re-read. Due to historical events (Russia removing themselves from the global commercial launch market, etc), and having perfected a few groundbreaking technologies and operational practices, SpaceX is running the board.

[Asteroza]

Cygnus Service module or PPE equivalent could do it too.

Does that suggest gateway could end up having multiple PPE more or less, and thus be power rich?

[Asteroza]

For that matter, I wonder if the winner of the NASA ISS deborbit RFI might also be a candidate tug?