SpaceX and Replacement of Russian module services on the ISS

[Jim]

Dragon XL would be the best candidate for this

Not really

[2megs]

Dragon XL would be the best candidate for this

Not really

So I said that because to my mind the ideal solution would have:

* IDA
* Thrusters 180° from the IDA
* Ample dV
* Long-term storable propellant
* Fine/gentle control of thrust
* Rated for up to a year on station

Dragon XL (if available on a useful timeline) is the only thing that would check all of those boxes. Am I thinking of the wrong requirements, or is there something else wrong about Dragon XL?

[nacnud]

Its probably defunct but some systems live on in the Orion service model but could a modified ATV be brought back.

[Jim]

Dragon XL would be the best candidate for this

Not really

So I said that because to my mind the ideal solution would have:

* IDA
* Thrusters 180° from the IDA
* Ample dV
* Long-term storable propellant
* Fine/gentle control of thrust
* Rated for up to a year on station

Dragon XL (if available on a useful timeline) is the only thing that would check all of those boxes. Am I thinking of the wrong requirements, or is there something else wrong about Dragon XL?

Cygnus already meets that and doesn't need an IDA

[daveglo]

Cygnus already meets that and doesn't need an IDA

True enough.  Capability being tested on orbit.

Now we just have to get more Cygnus to orbit. . .

Until Elon/NASA build a better system.

[Bananas_on_Mars]

Dragon XL would be the best candidate for this

Not really

So I said that because to my mind the ideal solution would have:

* IDA
* Thrusters 180° from the IDA
* Ample dV
* Long-term storable propellant
* Fine/gentle control of thrust
* Rated for up to a year on station

Dragon XL (if available on a useful timeline) is the only thing that would check all of those boxes. Am I thinking of the wrong requirements, or is there something else wrong about Dragon XL?

Dragon XL is a little bit like Cygnus on steroids…

If the need arises, there‘s a lot of possibilities. Even Rocketlab has quite capable thrusters with their Hypercurie engine… put a stripped down interplanetary photon in the trunk of a Cargo Dragon if you need to or whatever.

[Yggdrasill]

Too disruptive.   It isn't 2 million right now. Also, no low power thruster

It doesn't have it right now, but it will by the time they start doing orbital propellant transfer. They intend on settling the propellant with milli-G acceleration. If we assume Starship will be capable of 0.005G using methalox hot-gas thrusters, that would be around 0.001G when pushing the ISS around.

That means that for a 1 m/s reboost, Starship would have to burn for around 100 seconds.

I guess the question is really, when will Starship have low power thrusters? I would guess around 2024.

Edt: I guess *maybe* the propellant settling thrusters will still be too powerful. I guess they would actually need to be able to accelerate a fully loaded Starship at several milli-G. At 5 mG that would actually be up to around 70 kN. Which is substantial. I guess it would depend on the arrangement of thrusters and how low they could be throttled. But they should be able to throttle fairly low, to accomodate the full range between empty and full Starships without wasting propellant for propellant settling. So maybe my calculation is fine.

[zodiacchris]

Okay, let’s look at what is available: Cygnus is in production but has a pretty long lead time and if I remember correctly Antares is using Ukrainian components, which will be an issue. But medium term Cygnus could do the job if the launcher issue gets resolved.

Dragon is in production and available on fairly short notice if urgently required, it might need some reshuffling of upcoming missions but it’s eminently doable. Falcons are available off the shelf. So this might be the solution if the situation escalates and the Russian modules become unavailable.

Dragon XL and Starship are not available at this stage, even if Starship flies it will be a long time before that behemoth is allowed anywhere near the ISS. Dragon XL is likely still in design phase, if it ever gets built. Resurrection of discontinued spacecraft is not an option, the supply chains are gone, the facilities re-dedicated and even if possible would take forever.

Just my take on the situation…

[Kiwi53]

Do SpaceX still have some Dragon 1s available in storage? Would that do the job?

Dragon 1 berths with the CBM, as does Cygnus, so they couldn't go in this spot in this scheme. Dragon 2 (both crewed and cargo) use the IDA, as does Starliner.

For this, either you'd want to put additional fuel and thrusters in the Dragon 2 trunk, or you'd want to modify Cygnus to dock with an IDA. Neither is a simple ask.

I would expect that Elon already has a small team looking at "you'd want to put additional fuel and thrusters in the Dragon 2 trunk", with the objective of being able to put an unsolicited proposal to NASA before the end of March. The cost of doing that would be peanuts to SpaceX, so the downside is tiny but the upside is huge.
'SpaceX saves ISS in face of Russian intransigence' would go down very well everywhere except Moscow

[ThomasGadd]

A problem using Dragon 2's most of the Draco's face the wrong way. 
How many are in the clear to fire? 
They would have to be symmetric to minimize torque on the docking ring. 
At 90 lbf each it will be a long burn. 

I'm looking for a description or image of the location of the thrusters ...

[Lar]

A problem using Dragon 2's most of the Draco's face the wrong way. 
How many are in the clear to fire? 
They would have to be symmetric to minimize torque on the docking ring. 
At 90 lbf each it will be a long burn. 

This is an argument for a trunk insert. Proposal by end of March and unit by end of Sept is possible.

[spacenut]

SpaceX can launch Cygnus.  NG could begin to work on new Cygnus craft ASAP.  In the meantime, Space X can put Draco, or Super Draco thrusters in the Trunk of Dragon 2, probably in about the same length of time a new Cygnus can be made.  Gives Two options. 

[Jorge]

SpaceX can launch Cygnus.  NG could begin to work on new Cygnus craft ASAP.  In the meantime, Space X can put Draco, or Super Draco thrusters in the Trunk of Dragon 2, probably in about the same length of time a new Cygnus can be made.  Gives Two options. 

Every time one of you armchair designers suggests using Super Draco for ISS reboost, an ISS structural engineer feels a great disturbance in the Force, as if all the solar array longerons cried out in terror and were suddenly ripped off.

Stop it. Just. Stop. It.

[Jorge]

A problem using Dragon 2's most of the Draco's face the wrong way. 
How many are in the clear to fire? 
They would have to be symmetric to minimize torque on the docking ring. 
At 90 lbf each it will be a long burn. 

Ok, it'll be a long burn.

So?

The space shuttle used vernier RCS thrusters to reboost ISS. Those were 24 lbf each. Required an even longer burn.

Don't optimize your solution on the wrong variable.

[DanClemmensen]

If we are considering spacecraft that do not exist yet, why not look at the Gateway PPE module? It is currently under development and is intended for precisely the function of re-boosting a big space structure. The Artemis programs needs the PPE before it needs Dragon XL, so surely it will be available sooner?

[ThomasGadd]

A problem using Dragon 2's most of the Draco's face the wrong way. 
How many are in the clear to fire? 
They would have to be symmetric to minimize torque on the docking ring. 
At 90 lbf each it will be a long burn. 

Ok, it'll be a long burn.

So?

The space shuttle used vernier RCS thrusters to reboost ISS. Those were 24 lbf each. Required an even longer burn.

Don't optimize your solution on the wrong variable.

I was going look them up and got sidetracked thanks. 
So the existing Dragon 2's should work as long the Draco's are fired symmetrically. 

[russianhalo117]

If we are considering spacecraft that do not exist yet, why not look at the Gateway PPE module? It is currently under development and is intended for precisely the function of re-boosting a big space structure. The Artemis programs needs the PPE before it needs Dragon XL, so surely it will be available sooner?

The current design version of the PPE is undersized for the ISS. An earlier version with the add on European-built Hall Effect Auxiliary Thruster (eHEAT) and the four US Advanced Electric Propulsion System (AEPS) thrusters was more capable. As for the chemical propulsion system I haven't finished my research.

https://rocket.com/space/space-power-propulsion

AR in space propulsion catalog:
https://rocket.com/sites/default/files/documents/In-Space%20Data%20Sheets_7.19.21.pdf

[nacnud]

A problem using Dragon 2's most of the Draco's face the wrong way. 
How many are in the clear to fire? 
They would have to be symmetric to minimize torque on the docking ring. 
At 90 lbf each it will be a long burn. 

This is an argument for a trunk insert. Proposal by end of March and unit by end of Sept is possible.

Thinking about the trunk insert idea it seems it could superficially like the Space Station Freedom Primary Propulsion System. Where a self contained unit is taken up in the trunk mounted to some fixture for use then disposed of on a subsequent flight.

This could give two independent systems for for station reboost, attitude control, and contingency manoeuvres. Namely Cygnus and this trunk insert. It would also give the station control independent of visiting vehicles.

[Lee Jay]

A problem using Dragon 2's most of the Draco's face the wrong way. 
How many are in the clear to fire? 
They would have to be symmetric to minimize torque on the docking ring. 
At 90 lbf each it will be a long burn. 

Ok, it'll be a long burn.

So?

The space shuttle used vernier RCS thrusters to reboost ISS. Those were 24 lbf each. Required an even longer burn.

Don't optimize your solution on the wrong variable.

If a Hohmann transfer uses impulses, is a transfer that uses a substantial fraction of an orbit also named something? Or just spiral?

[FunBobby]

I like the idea of a combination of the near-ish term solutions working for 2-3 years while contracting Axiom or maybe Blue to build one big integrated module that effectively replaces the Russian module with a like amount of Delta V, attitude control, living space etc. 

I still don't like the idea of de-orbiting ISS in 2030, I know how it has soaked up the vast majority of human spaceflight spending for two decades, however perhaps now with better crew delivery and logistics vehicles it can continue to exist and slowly grow without eating everyone's budget.  Yes I know in the long run it is more efficient to just start over even to just not have a permanent LEO station.  However, I think the world loses a valuable cultural symbol about co-operation and persistence.  I would rather just have NASA boost in to 1000KM and seal the hatches to leave it as a museum for another generation to appreciate.  Okay back to the topic - the Cygnus and/or modified Dragon are probably an option by the end of 2022 with a few hundred million thrown at the problem.  Perhaps either HALO/PPE or Dragon XL is a solution for another couple of years.  After that one big (20-30MT) module from Axiom or Blue is the semi-permanent replacement.  Of course I am also hopeful that the ongoing deterioration in International Relations doesn't permanently end the West's co-operation with Russia, so maybe a solution that doesn't involve jettisoning a whole 1/3 of the station is better!