Alternative Capabilities to send Cargo to ISS while Baikonur Site 31/6 is down

[Vettedrmr]

With Soyuz grounded for the foreseeable future, how much slack can SpaceX pick up with cargo Dragon?

[spacenut]

There is still Northrop Grumman who can deliver cargo.  There is also Boeing Starliner that can be stripped out to deliver cargo.  If necessary Space X can launch another's cargo with a F9.  Dragon can probably take up the slack by reuse of a Dragon capsule multiple times. 

[DanClemmensen]

With Soyuz grounded for the foreseeable future, how much slack can SpaceX pick up with cargo Dragon?

I don't know. There are 3 cargo dragons, and they have flown 13 times in the last 72 months. We know NASA intends to stretch the CCP missions, so the SpaceX Dragon refurbishment crews may have some slack. However, if they must continue to provide reboost, they will need longer time in orbit, which in theory reduces the time available for refurbishment.

Starliner is a complication. If it flies crew, the Dragon refurbishment team will have even more slack.

You might want to also ask about Cygnus, especially since they now have the new bigger XL version. Also the JAXA HTV.

[Comga]

It’s not a question of “surging” cargo missions
It is a question of ISS orbit maintenance.
If the Russians can’t reestablish Soyuz launch before their fuel on orbit runs out (How long will that be?) then Dragon (or Cygnus) would have to step in.

At what pace can SpaceX launch Dragons, crew and cargo?
If it’s, say, 4 per year, can the Boost Kit cover, or be expanded to cover, 3 months of reboosting?

At the current density altitude that’s very close to 10 km per quarter or ~3.3 m/sec delta-V.
For a 4,200 ton ISS, that’s ~3400 seconds of 400 N Draco firing time.
With an Isp of 234 sec, where it burns ~0.78 kg/sec/Draco, that’s ~2,650 kg.
Can the Boost Kit carry, or be expanded to carry, that much propellent?
Will that kill the cargo capacity?
Would that be allowed with astronauts?

[zubenelgenubi]

Cross-post; discuss here:

I'm really glad that Dragon has demonstrated the ability to reboost ISS.

Cygnus too.

We know a Dragon at Harmony forward can apply axial force for reboost. I'm less certain about CMG desaturation, which requires applying the right kind of angular acceleration. Does anyone here know? My crude mental model says that a Dragon at harmony zenith can do it if ISS is oriented properly, but I do not trust my mental model.

I suspect NASA will be doing some mathematical modeling very quickly to see what is possible.

I suspect such contingency plans already exist.

[Vettedrmr]

Starliner is a complication. If it flies crew, the Dragon refurbishment team will have even more slack.

I didn't consider Starliner because, IMO, it's still in development, and we don't know when it'll fly next.  And then you'd only want non-essential cargo on that first flight, in case it's not cleared for docking.

You might want to also ask about Cygnus, especially since they now have the new bigger XL version. Also the JAXA HTV.

I didn't consider those because, due to their expendable nature, I assumed that their production would be geared towards their defined schedules.  AFAIK, SpaceX is the only supplier with "surplus" vehicles that could replace Progress in the resupply schedule.  Cygnus can launch on an F9, but HTV can only launch on a JAXA launch vehicle (I think), and again, IDK where those vehicles are in their production cycle.

[Vettedrmr]

It’s not a question of “surging” cargo missions
It is a question of ISS orbit maintenance.
If the Russians can’t reestablish Soyuz launch before their fuel on orbit runs out (How long will that be?) then Dragon (or Cygnus) would have to step in.

At what pace can SpaceX launch Dragons, crew and cargo?
If it’s, say, 4 per year, can the Boost Kit cover, or be expanded to cover, 3 months of reboosting?

At the current density altitude that’s very close to 10 km per quarter or ~3.3 m/sec delta-V.
For a 4,200 ton ISS, that’s ~3400 seconds of 400 N Draco firing time.
With an Isp of 234 sec, where it burns ~0.78 kg/sec/Draco, that’s ~2,650 kg.
Can the Boost Kit carry, or be expanded to carry, that much propellent?
Will that kill the cargo capacity?
Would that be allowed with astronauts?

I think there's a Progress mission that is scheduled for December; to meet that schedule by a cargo Dragon I'd call it a surge.  And I absolutely agree that, probably the key part, is ISS orbit maintenance.  With Progress out of the loop, it's going to fall to SpaceX and Cygnus to do that job for the foreseeable future.

[DanClemmensen]

In addition to Cargo Dragon, we also have spare upmass capacity on Crew Dragon that might be usable. We know this because Crew Dragon usually flies with a booster RTLS. The problem here is that CRS missions must also take out the trash and dispose of it. I don't know what the logistics would look like to put the trash in some sort of container or net, put it out an airlock, and secure it inside the Dragon's trunk for disposal.

[Comga]

Not Dragon but….

This is where Boeing and Starliner could shine as a cargo vehicle beyond the next flight.  Probably not, but it's good PR potential for them.

I posted above some calculation results for reboosting the ISS with Boost Kits in Dragon Trunks

While Starliner has many sub-optimal characteristics for the ISS cargo role, and we don’t need to rehash the Boeing development fiasco (Please don’t!), it may be adaptable and advantageous for the reboost role.
Its disposable OMAC LES engines are pointed axially.
There are six Atlas V rockets reserved for it.
There are six Service Modules waiting.
As originally planned, it would be “Dissimilar Redundancy” for Dragon reboosting, and could be used in addition to them.

Can someone please post the total impulse of Starliner’s LES (in Newton-Seconds)?
Edit 2 with frame counting of the pad abort: 4.24E+6 N-sec over 5.30 seconds

Can someone compare the thrust of an OMAC engine to the Progress or Zvezda engine groups?
Zvezda’s 2 S5.79 engines generate 3.09 kN each
Starliner’s 4 OMAC engines generate 1.5 kN each
So 3% less in total theoretically, essentially equal

We could then calculate how long each Starliner flight could cover the reboosting role.
Edit calculated with above value for 420 ton ISS:
49 days of reboosting, not very much

[Jim]

roll control is the issue and not reboost

[russianhalo117]

Soyuz and Progress's KD engine is an S5.92 model.

Zvezda
The Zvezda service module's KD engines (equivalent to TKS modules DKS engines) are two orbit-correction engines (designated S5.79) used for orbital maneuvering and attitude control, along with 32 smaller thrusters (DMT, designated 11D428A-10). The KD engines provide a thrust of 300 kilograms each and are part of the module's integrated propulsion system.

KD engines: These are the primary engines for orbital corrections and maneuvering. There are two KD engines, also designated S5.79. They have a thrust of 300 kilograms each.

DMT thrusters: In addition to the KD engines, the Zvezda module uses 32 smaller reaction control thrusters (DMT) for attitude control, yaw, and roll movements. These thrusters are designated 11D428A-10. Each has a thrust of 12.5 kilograms.
The TKS module family's DU propulsion system has a pair of KRD-442 (11D442) main orbit-correction engines, DKS, developed at the Isaev KBKhM design bureau in Korolev. They are also known as DKS-1 and DKS-2. Each engine produces 417 kilograms of thrust. In addition there are 32 smaller thrusters, (DPS (11D458) and DTS (17D58E)) and, specific to Nauka, 12 MDDK thrusters (S5.144 originating from the Ikar upper stage) with a thrust of 300 kilograms. Note that the DKS, DPS, and DTS and inhibited on Nauka and Zarya.

Manufacturer:
https://en.wikipedia.org/wiki/A.M._Isayev_Chemical_Engineering_Design_Bureau

[sdsds]

Is the prop load on a crew dragon sized for an ascent abort? If so, is there "excess" propulsion for ISS reboost available once the crew dragon is at e.g. Harmony FWD?

[DanClemmensen]

Is the prop load on a crew dragon sized for an ascent abort? If so, is there "excess" propulsion for ISS reboost available once the crew dragon is at e.g. Harmony FWD?

I don't know. but here's a related question. I think the Crew Dragon trunk is usually empty. Would NASA certify the boost kit to be used on a Crew Dragon? It is already having its "uncrewed demo" on CRS-33.

One big problem with Progress replacement it that Progress apparently carries propellant for the Russian RCS thrusters on the station that were supposed to handle attitude control and CMG desaturation, for normal operation and eventually for de-orbit.  But I cannot find the references for this so maybe I'm wrong.

[russianhalo117]

Is the prop load on a crew dragon sized for an ascent abort? If so, is there "excess" propulsion for ISS reboost available once the crew dragon is at e.g. Harmony FWD?

Yes the entire onboard prop load is depleted for a pad/ascent abort/emergency deorbit (when primary thrusters are unavailable or fail/timer deorbit for abandoned vehicle reentry)/and non parachute contingency mode splashdown. The same prop load is used for mission flight operations when there is a nominal launch.

[russianhalo117]

Is the prop load on a crew dragon sized for an ascent abort? If so, is there "excess" propulsion for ISS reboost available once the crew dragon is at e.g. Harmony FWD?

I don't know. but here's a related question. I think the Crew Dragon trunk is usually empty. Would NASA certify the boost kit to be used on a Crew Dragon? It is already having its "uncrewed demo" on CRS-33.

One big problem with Progress replacement it that Progress apparently carries propellant for the Russian RCS thrusters on the station that were supposed to handle attitude control and CMG desaturation, for normal operation and eventually for de-orbit.  But I cannot find the references for this so maybe I'm wrong.

It would require certification and would change the flight profile to account for the additional mass plus changed abort mode escape conditions from the additional mass.

[sdsds]

[...] I think the Crew Dragon trunk is usually empty. Would NASA certify the boost kit to be used on a Crew Dragon?

I think during an ascent abort Crew Dragon takes the trunk along for the ride, maybe for aerodynamic reasons. So the added mass of boost kit propellant counts against the total allowable mass of Dragon in the abort scenario. (Unless somehow the boost kit were tied into the abort mode logic so its thrusters could help Dragon get away from the launch vehicle. I'm sure they could introduce that change without inadvertently adding any other new behavior, but....)

[Comga]

[...] I think the Crew Dragon trunk is usually empty. Would NASA certify the boost kit to be used on a Crew Dragon?

I think during an ascent abort Crew Dragon takes the trunk along for the ride, maybe for aerodynamic reasons. So the added mass of boost kit propellant counts against the total allowable mass of Dragon in the abort scenario. (Unless somehow the boost kit were tied into the abort mode logic so its thrusters could help Dragon get away from the launch vehicle. I'm sure they could introduce that change without inadvertently adding any other new behavior, but....)

The Trunk carries the conformal solar arrays and Dragon’s thermal radiator.

Burning the abort propellents with the Boost Kit would require plumbing them through the actuated “Claw” that reaches around Dragon’s heat shield to carry the coolant and electrical power to and from the Trunk.  This would be difficult, to say the least, as it was sized for its current role.

Edit: I misread the quoted post
sdsds wants to use the Boost Pack to aid the LES to compensate for its added mass, not burn the abort propellants on orbit. “Never mind!”
But the first part stands.

[DanClemmensen]

[...] I think the Crew Dragon trunk is usually empty. Would NASA certify the boost kit to be used on a Crew Dragon?

I think during an ascent abort Crew Dragon takes the trunk along for the ride, maybe for aerodynamic reasons. So the added mass of boost kit propellant counts against the total allowable mass of Dragon in the abort scenario. (Unless somehow the boost kit were tied into the abort mode logic so its thrusters could help Dragon get away from the launch vehicle. I'm sure they could introduce that change without inadvertently adding any other new behavior, but....)

The Trunk carries the conformal solar arrays and Dragon’s thermal radiator.

Burning the abort propellants with the Boost Kit would require plumbing them through the actuated “Claw” that reaches around Dragon’s heat shield to carry the coolant and electrical power to and from the Trunk.  This would be difficult, to say the least, as it was sized for its current role.

Don't burn the abort props. Just use the boost kit. The boost kit on CRS-33 is apparently modular and there is room for additional propellant tanks.

[Comga]

roll control is the issue and not reboost

The OP discussed cargo in the absence of Progress
My concern was boosting for maintaining the orbit.
Jim argues that the main issue is roll


AFAIK the only “cargo” on Progress of concern to the USOS is propellant.
Without Soyuz, no cosmonauts are going to the ISS. 
Russia isn’t going to buy seats on Dragon, and probably can’t because of sanctions, and have nothing to trade for them. 
Without cosmonauts there is no need for cargo on their side.

Both Dragon and Starliner have engines pointed sideways for wheel desaturation.
Also the USOS has demonstrated “Zero Net Momentum” attitude control, so desaturation shouldn’t be needed (very much)
So I don’t know why Jim says that.

I still believe reboosting is the biggest challenge without Progress.
And neither Dragon with the demonstrated Boost Kit or Starliner with its Service Module LES has enough impulse.

[Helodriver]

Absence of Progress and its fuel seems to be a more pressing issue than crew rotation. F9 could easily fit a fully loaded Progress in its fairing. The problems to adapt it for US launch would seem to be more political than technical. More likely though if the service platform cannot be fixed easily, Progress flies from the Soyuz carrier rocket pads at Plesetsk or Vostochny with GSE modifications. Crew Soyuz waits until the 31/6 pad is repaired.

[catdlr]

Absence of Progress and its fuel seems to be a more pressing issue than crew rotation. F9 could easily fit a fully loaded Progress in its fairing. The problems to adapt it for US launch would seem to be more political than technical. More likely though if the service platform cannot be fixed easily, Progress flies from the Soyuz carrier rocket pads at Plesetsk or Vostochny with GSE modifications. Crew Soyuz waits until the 31/6 pad is repaired.

Plesetsk is too far north in latitude to match the ISS's orbit, Vostochny is just 30 km too high to do the same, and Progress doesn't have cross-range capability. 

Plesetsk was designed to launch military spy satellites in polar orbits; Vostok was intended primarily for communication satellites.

[Lee Jay]

Absence of Progress and its fuel seems to be a more pressing issue than crew rotation. F9 could easily fit a fully loaded Progress in its fairing. The problems to adapt it for US launch would seem to be more political than technical. More likely though if the service platform cannot be fixed easily, Progress flies from the Soyuz carrier rocket pads at Plesetsk or Vostochny with GSE modifications. Crew Soyuz waits until the 31/6 pad is repaired.

Yes...I was going to ask if we really, for sure know that Progress cannot be launched by Russia.  They have seemed pretty adaptable in the past in such situations.  I would expect a delay of the December Progress, but I'm not convinced yet that they cannot launch it at all until the pad that was damaged is repaired.  Can someone convince me?

[russianhalo117]

Absence of Progress and its fuel seems to be a more pressing issue than crew rotation. F9 could easily fit a fully loaded Progress in its fairing. The problems to adapt it for US launch would seem to be more political than technical. More likely though if the service platform cannot be fixed easily, Progress flies from the Soyuz carrier rocket pads at Plesetsk or Vostochny with GSE modifications. Crew Soyuz waits until the 31/6 pad is repaired.

Plesetsk is too far north in latitude to match the ISS's orbit, Vostochny is just 30 km too high to do the same, and Progress doesn't have cross-range capability. 

Plesetsk was designed to launch military spy satellites in polar orbits; Vostok was intended primarily for communication satellites.

Soyuz-2.1b can because it can carry more

[Twark_Main]

Yes, I expect they'll try to fly the ISS in TEA to minimize CMG desaturation burns.




Zero-Propellant Maneuvers are a closely related technique, using the same natural external forces to reorient the station without using propellant.

https://en.wikipedia.org/wiki/Zero-propellant_maneuver

[Twark_Main]

Vostochny is just 30 km too high to [match the ISS's orbit], and Progress doesn't have cross-range capability. 

It's only a 37 m/s plane change, by my math, but the problem is more a lack of suitable ground infrastructure.

[StraumliBlight]

I still believe reboosting is the biggest challenge without Progress.
And neither Dragon with the demonstrated Boost Kit or Starliner with its Service Module LES has enough impulse.

Progress's Refuelling Module likely fits inside Dragon's trunk. If a docking probe with fuel lines and a grapple fixture were installed, then Canadarm could retrieve it and refuel Zarya.

EDIT: Progress is currently critical to the ISS deorbit plans.

The Joint Commission wants a secondary deorbit capability in case something goes awry with the USDV. The contingency plan is using two Russian Progress cargo vehicles and the Russian segment itself to dispose of the ISS. That requires ensuring the propellant tanks on the Russian segment are full. Cabana said they reviewed a plan to have the tanks on the Zvezda Service Module and Zarya Functional Cargo Block (FGB) “sufficiently filled by 2028,”

If there was long delay between launches or Roscosmos don't have the resources to repair the pad, this idea would be to cannibalise existing Progress spacecraft in production into a smaller form factor (transportable by SpaceX) that could be manipulated by either the arm or a spacewalk to simulate a normal docking and fuel transfer.

[Jim]

I still believe reboosting is the biggest challenge without Progress.
And neither Dragon with the demonstrated Boost Kit or Starliner with its Service Module LES has enough impulse.

Progress's Refuelling Module likely fits inside Dragon's trunk. If a docking probe with fuel lines and a grapple fixture were installed, then Canadarm could retrieve it and refuel Zarya.

no,  it requires docking on the Russian segment. 

[Comga]

I still believe reboosting is the biggest challenge without Progress.
And neither Dragon with the demonstrated Boost Kit or Starliner with its Service Module LES has enough impulse.

Progress's Refuelling Module likely fits inside Dragon's trunk. If a docking probe with fuel lines and a grapple fixture were installed, then Canadarm could retrieve it and refuel Zarya.

no,  it requires docking on the Russian segment. 

Jim, you make me chuckle
That the Canadarm can't reach the Russian end of the ISS assembly is not the first fatal flaw in this idea.
How is NASA going to get a stand-alone "Progress Refueling Module", never mind one ready to launch, ready to hang in the Dragon trunk or one commandable through a Dragon?
This is "rocket Legos(tm)" at its finest.
It would be sufficiently difficult, maybe impossible, to add enough impulse to either the Dragon Boost Kit or Starliner's Service Module, but at least these are NASA suppliers.

[Space Pete]

How about Progress on Falcon 9?

I'll get my coat. 

[laszlo]

A kluge for use on the ground is a lot safer and easier to develop, test and certify than one for orbit.

By the time the suggested orbiting kluges could be worked up, the damaged launch pad will have been made usable somehow.

[TrevorMonty]

A kluge for use on the ground is a lot safer and easier to develop, test and certify than one for orbit.

By the time the suggested orbiting kluges could be worked up, the damaged launch pad will have been made usable somehow.

I can see some Russian driving new diamond coated car by time repair is complete.
Good thing they aren't using SLS launch pad contractors as repair will cost 1000 diamond coated cars.

[catdlr]

After key Russian launch site is damaged, NASA accelerates Dragon supply missions
It is by no means specific that Russia will be able to fix Site 31 soon.

Eric Berger – Dec 10, 2025 10:13 AM

[Comga]

It’s not a question of “surging” cargo missions
It is a question of ISS orbit maintenance.
If the Russians can’t reestablish Soyuz launch before their fuel on orbit runs out (How long will that be?) then Dragon (or Cygnus) would have to step in.

At what pace can SpaceX launch Dragons, crew and cargo?
If it’s, say, 4 per year, can the Boost Kit cover, or be expanded to cover, 3 months of reboosting?

At the current density altitude that’s very close to 10 km per quarter or ~3.3 m/sec delta-V.
For a 4,200 ton ISS, that’s ~3400 seconds of 400 N Draco firing time.
With an Isp of 234 sec, where it burns ~0.78 kg/sec/Draco, that’s ~2,650 kg.
Can the Boost Kit carry, or be expanded to carry, that much propellent?
Will that kill the cargo capacity?
Would that be allowed with astronauts?

Pardon the self-quote but I found an answer to the question above in Arstechnia.

The proven Dragon Boost Kit can provide 9 m/s to the ISS.
That’s equivalent to ~3 months of reboosting.
It’s almost the “calendar quarter” discussed above
It’s also equivalent to ~1.5 Progress loads, so each Progress covers ~2 months.

While the six tank Boost Kit is seen in another Arstechnia article to occupy only a fraction of the trunk of CRS-33 Dragon, the mass is a large fraction of the 3,300 kg cargo capacity.

So a Cargo Dragon every 3 months and the ISS reboost needs will be fully met until the Russians resume Progress launches.

(Somebody please check my arithmetic)

Edit: If the above is correct, and if reports are also correct that the Russian launch site can be repaired in 4 months, the on-orbit boost kit may have the deficit covered.  If it’s 6 months, one more Boost Kit.

[AmigaClone]

SpaceX has shown that the forward hatch of their Crew Dragon 2 can be replaced with a dome (Inspiration 4, Fran2) or a 'porch' (Polaris Dawn). Would it be possible to replace the docking interface of one of the Crew and one of the Cargo Dragons to dock to the Russian side?

[Comga]

SpaceX has shown that the forward hatch of their Crew Dragon 2 can be replaced with a dome (Inspiration 4, Fran2) or a 'porch' (Polaris Dawn). Would it be possible to replace the docking interface of one of the Crew and one of the Cargo Dragons to dock to the Russian side?

Probably not, but why would that be needed?
Dock to Node 2 Forward and turn the ISS around.
That's how the Boost Kit is being used, IIUIC.

Edit: Even if they did manage to dock to the Russian docking interface, they couldn't transfer propellant to the Russian side.

[DanClemmensen]

SpaceX has shown that the forward hatch of their Crew Dragon 2 can be replaced with a dome (Inspiration 4, Fran2) or a 'porch' (Polaris Dawn). Would it be possible to replace the docking interface of one of the Crew and one of the Cargo Dragons to dock to the Russian side?

Technically possible, but by the time you got the paperwork done, followed by the design, test, and implementation, it would take at least a year until the first uncrewed test flight. This still does not allow transfer of propellant for the Russian RCS on ISS. It does increase flexibility, by freeing up an IDSS port, especially after the USDV is connected.

[Brigantine]

How about Progress on Falcon 9?

How about Progress on ZhuQue-3? JiuQuan is not much further from Russia than Baikonur

[russianhalo117]

How about Progress on Falcon 9?

How about Progress on ZhuQue-3? JiuQuan is not much further from Russia than Baikonur

Requires custom processing hardware that is only at RKK Energia and Baikonur.

[AmigaClone]

SpaceX has shown that the forward hatch of their Crew Dragon 2 can be replaced with a dome (Inspiration 4, Fran2) or a 'porch' (Polaris Dawn). Would it be possible to replace the docking interface of one of the Crew and one of the Cargo Dragons to dock to the Russian side?

Probably not, but why would that be needed?
Dock to Node 2 Forward and turn the ISS around.
That's how the Boost Kit is being used, IIUIC.

Edit: Even if they did manage to dock to the Russian docking interface, they couldn't transfer propellant to the Russian side.

The reason would be flexibility in docking locations. Those modified Dragons would be capable of docking in four locations as opposed to only two on the US side.

[Comga]

@Brigantine, @AmigaClone :Why?
There is no need, and probably no money, to develop anything new, especially Franken-systems.

Some here object when others suggest SpaceX solving every problem, but for the ISS it’s close to correct.

Dragon brought back cargo runs to the ISS, with both pressurized and external cargo.
(Yes Cygnus is needed for larger cargo and bulk transport.)
Dragon brought back significant downmass.
Dragon does crew transport and lifeboat support.
Dragon’s Boost Kit can handle as much reboosting and Collision Avoidance Maneuvers as is needed.

It’s all paid for, developed, and proven.
Lego(tm) Launches not needed

A Dragon variant will deorbit the ISS when the time comes.
For speculation, Dragon capsules firing their lateral Dracos could provide angular momentum to desaturate the CMGs.
If the Boost Kit was to incorporate a 0.2 N thruster and run it continuously, it could even improve (but not perfect) the microgravity environment, countering the exoatmospheric drag and maintaining nearly constant altitude.

[Jim]

Still have the roll control problem.

[woods170]

Still have the roll control problem.

You refer to desaturation of the CMGs, which is usually done by firing the thrusters on Progress?

[DaveS]

Still have the roll control problem.

You refer to desaturation of the CMGs, which is usually done by firing the thrusters on Progress?

No, roll control of the station itself. The CMGs can only provide pitch and yaw control not roll control hence the need of the roll control thrusters on the MLM.

[Brigantine]

Why?

I heard progress was launcher-agnostic, so was thinking about it as 'just a payload'. JiuQuan is the home of the Soyuz-derived Shenzhou capsule, so I wrongly presumed it would be fine.

My point in picking the knock-off-F9 over CZ-2F was just that American launchers are not the 1st place Russia would go looking for a commercial launch, so F9 seems unlikely. It seems we can now narrow it down to launchers present at Baikonur

[Yellowstone10]

No, roll control of the station itself. The CMGs can only provide pitch and yaw control not roll control hence the need of the roll control thrusters on the MLM.

Is there a reference for that, by any chance? I had assumed CMGs give you 3-axis control (until they're saturated, of course), and my Google-fu is not turning up anything about roll control being different from pitch/yaw.

[Jim]

No, roll control of the station itself. The CMGs can only provide pitch and yaw control not roll control hence the need of the roll control thrusters on the MLM.

Is there a reference for that, by any chance? I had assumed CMGs give you 3-axis control (until they're saturated, of course), and my Google-fu is not turning up anything about roll control being different from pitch/yaw.

Desaturation is required on all axis.  Due to the length of the truss and the short lever arms of thrusters on the SM or Progress docked axially to the SM, it takes a lot of propellant to desaturate roll.  Progress and other modules with thrusters that are docked orthogonally to the SM can provide more effective roll desaturation.

[DanClemmensen]

No, roll control of the station itself. The CMGs can only provide pitch and yaw control not roll control hence the need of the roll control thrusters on the MLM.

Is there a reference for that, by any chance? I had assumed CMGs give you 3-axis control (until they're saturated, of course), and my Google-fu is not turning up anything about roll control being different from pitch/yaw.

Desaturation is required on all axis.  Due to the length of the truss and the short lever arms of thrusters on the SM or Progress docked axially to the SM, it takes a lot of propellant to desaturate roll.  Progress and other modules with thrusters that are docked orthogonally to the SM can provide more effective roll desaturation.

From a pure physics standpoint, you would have tiny little thrusters at the extreme ends of the truss for roll control? Another set out there would work well for yaw, but handling yaw while doing boost works well so yaw control from the truss is not needed.

[Jim]

From a pure physics standpoint, you would have tiny little thrusters at the extreme ends of the truss for roll control? Another set out there would work well for yaw, but handling yaw while doing boost works well so yaw control from the truss is not needed.

And who is going to design, build and qualify them?

[DanClemmensen]

From a pure physics standpoint, you would have tiny little thrusters at the extreme ends of the truss for roll control? Another set out there would work well for yaw, but handling yaw while doing boost works well so yaw control from the truss is not needed.

And who is going to design, build and qualify them?

Yep, that's why I said "from a pure physics standpoint". It's almost certainly not practical to add them at this point. I only posted this to see if I understood the physics correctly. It's easy to say that they could just strap a Starlink Ion thruster and a COPV full of Argon onto the truss ends . It's a heck of a lot harder to actually do the design/build/qualify/install, not to mention the massive contract, program, and project management.

[Comga]

No, roll control of the station itself. The CMGs can only provide pitch and yaw control not roll control hence the need of the roll control thrusters on the MLM.

Is there a reference for that, by any chance? I had assumed CMGs give you 3-axis control (until they're saturated, of course), and my Google-fu is not turning up anything about roll control being different from pitch/yaw.

Desaturation is required on all axis.  Due to the length of the truss and the short lever arms of thrusters on the SM or Progress docked axially to the SM, it takes a lot of propellant to desaturate roll.  Progress and other modules with thrusters that are docked orthogonally to the SM can provide more effective roll desaturation.

Jim!
That’s an excellent and clear explanation.

Of course, Crew Dragons are sometimes docked radially, and not having used their LES, have “a lot of propellant”.  Are they plumbed to also feed it to the ACS Dracos?

PS: Dan, “from a pure physics standpoint” such hardware does not exist.

[Nicolas PILLET]

A Dragon variant will deorbit the ISS when the time comes.

The Dragon-derived vehicle will give about one half of the dV needed to deorbit the ISS. The other half should be given by Russian Segment (Progress engines and Zvezda engines burning Progress-delivered propellant).

[Nicolas PILLET]

From a pure physics standpoint, you would have tiny little thrusters at the extreme ends of the truss for roll control? Another set out there would work well for yaw, but handling yaw while doing boost works well so yaw control from the truss is not needed.

And who is going to design, build and qualify them?

This is, of course, a dream. But since 2021 there are small roll control engines at the end of Nauka, using its length to increase moment.

[Jim]

Yep, that's why I said "from a pure physics standpoint". It's almost certainly not practical to add them at this point. I only posted this to see if I understood the physics correctly. It's easy to say that they could just strap a Starlink Ion thruster and a COPV full of Argon onto the truss ends

Need more thrust than that

[Jim]

Of course, Crew Dragons are sometimes docked radially, and not having used their LES, have “a lot of propellant”.  Are they plumbed to also feed it to the ACS Dracos?

Their thruster alignments are not proper for that role

[DanClemmensen]

Yep, that's why I said "from a pure physics standpoint". It's almost certainly not practical to add them at this point. I only posted this to see if I understood the physics correctly. It's easy to say that they could just strap a Starlink Ion thruster and a COPV full of Argon onto the truss ends

Need more thrust than that

Sure. If NASA decided to add roll control thrusters, they would would use real engineers to do a real study and design a real system, and I agree with your point that this is not cost-effective given the remaining lifetime of ISS.

[robertross]

Here's a question: Is there any way to refuel the current Progress on orbit via external methods?
I doubt Dextre can reach with Canadarm 2, but perhaps there are alternative methods that can be considered?

[Comga]

A Dragon variant will deorbit the ISS when the time comes.

The Dragon-derived vehicle will give about one half of the dV needed to deorbit the ISS. The other half should be given by Russian Segment (Progress engines and Zvezda engines burning Progress-delivered propellant).

“should”
If needed, the ISS can drift down.
But the point was what Dragon could do in the absence of Progress launches.

Of course, Crew Dragons are sometimes docked radially, and not having used their LES, have “a lot of propellant”.  Are they plumbed to also feed it to the ACS Dracos?

Their thruster alignments are not proper for that role

“proper”?
Ah
Not properly aligned
That’s visible in images of Dragon docked to the zenith port. 
But the question was if the plumbing accommodates sub-optimal roll torque thrust
Even with the lousy lever arm for Dragon on the axial Node 2 Forward, it’s a lot of propellant.

But again, you and Nicolas and others have poked at nits in front of the big main issue.
(You should refrain, you Nattering Nabobs of Negativity.)

While there is a hiatus in Progress and Soyuz launches, be it 4 months, a year, or the remaining life of the ISS, NASA and its “western” partners can maintain the ISS themselves, using what they have, which is mostly from SpaceX.

No NASA logoed Progress on Chinese launchers 
No Rube Goldberg
No Lego Rockets
No fantasy hardware needed

[russianhalo117]

Here's a question: Is there any way to refuel the current Progress on orbit via external methods?
I doubt Dextre can reach with Canadarm 2, but perhaps there are alternative methods that can be considered?

I don't know if their tanks and their pressure fed backfill system allows that but the rest of the ships plumbing allows Soyuz and Progress to receive propellant system transfer from the entire RS and its VV's.

[AmigaClone]

While there is a hiatus in Progress and Soyuz launches, be it 4 months, a year, or the remaining life of the ISS, NASA and its “western” partners can maintain the ISS themselves, using what they have, which is mostly from SpaceX.

No NASA logoed Progress on Chinese launchers 
No Rube Goldberg
No Lego Rockets
No fantasy hardware needed

Using purely existing or equipment in development before 1 November 2025 the long-term crew for the ISS would be reduced to 4 when the newest Soyuz has to return.

Avoiding that situation was the primary reason I suggested perhaps investigating what it would take to modify a Dragon to dock on the Russian side.

Using certain docking ports on the Russian side would also make the idea of trying to use a Dragon to control the roll slightly less difficult.

[DanClemmensen]

While there is a hiatus in Progress and Soyuz launches, be it 4 months, a year, or the remaining life of the ISS, NASA and its “western” partners can maintain the ISS themselves, using what they have, which is mostly from SpaceX.

No NASA logoed Progress on Chinese launchers 
No Rube Goldberg
No Lego Rockets
No fantasy hardware needed

Using purely existing or equipment in development before 1 November 2025 the long-term crew for the ISS would be reduced to 4 when the newest Soyuz has to return.

Avoiding that situation was the primary reason I suggested perhaps investigating what it would take to modify a Dragon to dock on the Russian side.

Using certain docking ports on the Russian side would also make the idea of trying to use a Dragon to control the roll slightly less difficult.

Are the Russian ports APAS-95?  If so, NASA has an existing design for the IDA, which can be attached to an APAS-95 port to turn it into an IDS port. The two US IDSS docks use IDAs. There are a number of major issues to resolve to actually use this approach, so it is probably infeasible.

[russianhalo117]

While there is a hiatus in Progress and Soyuz launches, be it 4 months, a year, or the remaining life of the ISS, NASA and its “western” partners can maintain the ISS themselves, using what they have, which is mostly from SpaceX.

No NASA logoed Progress on Chinese launchers 
No Rube Goldberg
No Lego Rockets
No fantasy hardware needed

Using purely existing or equipment in development before 1 November 2025 the long-term crew for the ISS would be reduced to 4 when the newest Soyuz has to return.

Avoiding that situation was the primary reason I suggested perhaps investigating what it would take to modify a Dragon to dock on the Russian side.

Using certain docking ports on the Russian side would also make the idea of trying to use a Dragon to control the roll slightly less difficult.

Are the Russian ports APAS-95?  If so, NASA has an existing design for the IDA, which can be attached to an APAS-95 port to turn it into an IDS port. The two US IDSS docks use IDAs. There are a number of major issues to resolve to actually use this approach, so it is probably infeasible.

https://www.russianspaceweb.com/docking.html

[DanClemmensen]

Are the Russian ports APAS-95?  If so, NASA has an existing design for the IDA, which can be attached to an APAS-95 port to turn it into an IDS port. The two US IDSS docks use IDAs. There are a number of major issues to resolve to actually use this approach, so it is probably infeasible.

https://www.russianspaceweb.com/docking.html

Thanks for that excellent link. However, that page is quite dense, and I cannot figure out from it exactly how the four current VV docks on the Russian segment are configured. It appears that they are NOT APAS-95, but what are they? If you understand this stuff as I do not, and if you have time, please provide a simplified explanation. Thanks!

The page also mentions that some ports are or were reconfigurable, so if that can be done using resources that are already available aboard ISS, then we have even more confusing options. My guess: the work needed to dock a Dragon to a Russian port cannot be done in time to make a difference, no matter what approach is taken.

[Jim]

Are the Russian ports APAS-95?  If so, NASA has an existing design for the IDA, which can be attached to an APAS-95 port to turn it into an IDS port. The two US IDSS docks use IDAs. There are a number of major issues to resolve to actually use this approach, so it is probably infeasible.

https://www.russianspaceweb.com/docking.html

Thanks for that excellent link. However, that page is quite dense, and I cannot figure out from it exactly how the four current VV docks on the Russian segment are configured. It appears that they are NOT APAS-95, but what are they?

Probe and drogue.

[Nicolas PILLET]

but what are they?

Standard SSVP system. I have a description here (in French) : https://www.kosmonavtika.com/vaisseaux/ssvp/tech/2/2.html

[Nicolas PILLET]

“should”

We are speaking of ISS deorbit. The plan is to make (approximately) half of the deorbit burn with RS, and the other half with the SpaceX deorbit vehicle.

[Comga]

“should”

We are speaking of ISS deorbit. The plan is to make (approximately) half of the deorbit burn with RS, and the other half with the SpaceX deorbit vehicle.

That is actually off topic
The thread title includes “while Baikonur site 31/6 is down”
Until the site gets repaired, in the absence of an alternative launch site for Progress, the Russians are not able to do “half the deorbit burn”.
If that persists, which is unlikely but possible, NASA can either send extra Dragon Boost Packs, or just let the orbit decay before the Deorbit Vehicle brings it down.


What has been generally agreed upon is that aside from roll CMG desaturation, Dragon and Cygnus and HTV-X, docked and berthed to the USOS side, can provide all the support the ISS needs through its deorbit.

[daedalus1]

It looks like it will be repaired in February, so only one progress less and no difference for Soyuz plan. July 2026.

[AndrewM]

There are only 2 more CRS2 cargo Dragons on contract (CRS-34 & -35) which have reportedly been accelerated to May and August. Ahead of CRS-33, it was stated that CRS-33 was the only planned boost trunk. In addition, 1 of the 2 missions is supposed to carry the final set of iROSA arrays which I believe is on CRS-34. Given that, I don't think there will be another boost trunk in the near term. I'd say its more likely that Cygnus fulfills this need in the near-term and I think Starliner-1 would likely demo it as well since it was a planned capability.

[DanClemmensen]

There are only 2 more CRS2 cargo Dragons on contract (CRS-34 & -35) which have reportedly been accelerated to May and August. Ahead of CRS-33, it was stated that CRS-33 was the only planned boost trunk. In addition, 1 of the 2 missions is supposed to carry the final set of iROSA arrays which I believe is on CRS-34. Given that, I don't think there will be another boost trunk in the near term. I'd say its more likely that Cygnus fulfills this need in the near-term and I think Starliner-1 would likely demo it as well since it was a planned capability.

How much boost can Starliner provide? While docked to Harmony Forward it's in the right place, and its thrusters are pointing in the right direction. Total available fuel is a question. The other question is sustained thruster endurance. CRS-33 just completed a 19-minute boost. Can Starliner thruster sustain a long boost? we know there were thermal issues on CFT and we know NASA and Boeing have made modifications, so this may be a really good way to test the results.

[Comga]

There are only 2 more CRS2 cargo Dragons on contract (CRS-34 & -35) which have reportedly been accelerated to May and August. Ahead of CRS-33, it was stated that CRS-33 was the only planned boost trunk. In addition, 1 of the 2 missions is supposed to carry the final set of iROSA arrays which I believe is on CRS-34. Given that, I don't think there will be another boost trunk in the near term. I'd say its more likely that Cygnus fulfills this need in the near-term and I think Starliner-1 would likely demo it as well since it was a planned capability.

How much boost can Starliner provide? While docked to Harmony Forward it's in the right place, and its thrusters are pointing in the right direction. Total available fuel is a question. The other question is sustained thruster endurance. CRS-33 just completed a 19-minute boost. Can Starliner thruster sustain a long boost? we know there were thermal issues on CFT and we know NASA and Boeing have made modifications, so this may be a really good way to test the results.

I can’t find my own post but if a Starliner could and did use its abort motors with the ISS turned around (USOS trailing) it could provide ~2 months of reboosting.
The Dragon Boost Kit can provide ~3 months.
This post may have those calculations.

PS The “thermal issues” were with the ACS thrusters in the “doghouses” external to the body of the Service Module.  The OMAC abort engines are not there.  They are in the body of the Service Module.

[AmigaClone]

There are only 2 more CRS2 cargo Dragons on contract (CRS-34 & -35) which have reportedly been accelerated to May and August. Ahead of CRS-33, it was stated that CRS-33 was the only planned boost trunk. In addition, 1 of the 2 missions is supposed to carry the final set of iROSA arrays which I believe is on CRS-34. Given that, I don't think there will be another boost trunk in the near term. I'd say its more likely that Cygnus fulfills this need in the near-term and I think Starliner-1 would likely demo it as well since it was a planned capability.

I would not be surprised if, before CRS-34, NASA announces some more Cygnus and Cargo Dragon CRS-2 missions, with potentially one or more of the new Dragon missions including Thrust Trunks.