Polaris Program (Dragon and Starship crewed missions led by Isaacman)

[eeergo]

Easy answer: an off-the-shelf Cargo Dragon could do it equally well, adding significant upmass, mission timelime margins, stability, easing constraints... Doesn't hype Polaris though.

Technically totally agreed. But in this case it might be the mission is only (potentially) happening because of the crew, even if it would make infinitely more sense to do it without one (assuming it's 'just' reboost).

Sure, I can see that - but then this study is more about "we want to add value to this mission which we already decided will happen, at comparatively little cost" rather than "we're studying ways to boost Hubble in the next few years, and think the best way to go about it is with Polaris and its crew (who supposedly will be concentrated on their sizeable main goals: first private spacewalk, optical T/C, health experiments...)".

Polaris Dawn (first private spacewalk) is not related to any potential Hubble reboost mission, and will likely fly before this study is even completed.

True regarding the "first" qualifier, if indeed Polaris Dawn will not be considered for this task as can be expected as of today - but according to the program's own website, the second mission is the only other one currently expected to be carried out in Dragon before they move on to crewed Starship (if we're to believe their stated goals, of course). The objectives for that one also include "expanding the boundaries of future human spaceflight missions" and "in-space communications", alongside "scientific research", so they'd still be concentrated on many other stuff.

It's not lost on me how they could modify the aims for that one, or just include more Dragon missions under the Polaris designation, but I'm sticking to the plans they have publicized so far.

[AS_501]

My prediction is that they will end up doing 2 missions, first a cargo Dragon reboost, which might just need a docking adaptor for the docking system installed on the Hubble in the last servicing mission.  Presumably in the trunk, so the Dragon thrusters can point the right way to boost the Hubble.  NASA may or may not be able to scrape together some money to pay SpaceX to develop the docking adaptor and fly the mission, but it would be pocket change compared to what they would have spent to deorbit it.  This would be pretty low risk, NASA has gotten very comfortable with cargo Dragon. 

Then a Polaris manned mission with Jared and at least one NASA astronaut to do servicing, at a minimum a gyro swap out.  By then, EVA from the Dragon will have been tested by Jared and crew on Polaris Dawn.  NASA will presumably pay something to fly their astronaut, but most of the NASA money for that phase will probably go into building whatever parts are getting swapped out and training on what they want to do, support for the mission, etc. 

I'm guessing there will be a lot of support in NASA to do this, though, far more of the public has heard of Hubble and likes it than has heard of Artemis. 

If true about flying a NASA astronaut, it would be interesting to see if they choose one of the STS-125 crew that's still active.

[sevenperforce]

If they do it (which is a long pole), then I predict they dev an extensible docking adapter that is placed inside the trunk and pops out to dock with the Hubble adapter, perhaps with crew on EVA to troubleshoot.

Keep in mind that Crew Dragon's main propulsion is under the nose cone, so it would need to dock tail-first to reboost Hubble.

If they do develop an extensible docking adapter for the trunk of a Dragon would they be able to dock with and boost the ISS as well?

Yes, I would think so. Crew Dragon carries 1388 kg of propellant; if it spent half of this then it could add 4.15 m/s to the speed of the ISS which I believe is significantly larger than most reboosts that the station gets.

Of course, it would need to perform multiple transposition and docking maneuvers, which also require prop, and it still needs enough prop for the deorbit burn. So that's a consideration. And it would be unable to carry any other unpressed cargo during that flight. AND it would sacrifice the "back-in parking" docking adapter on each flight.

SpaceX hasn't been too shy about modifications to dragon though. Swapping out the cupola/docking adapter for example (and Polaris Dawn will have changes too I think). So it may be that changing out the standard docking adapter for an APAS adapter would be acceptable (not saying easy!)

The benefit is you can use all your proven docking sensors, in their proven flight configurations. Your guidance algorithms and control authority are the same (dragon isn't flying backwards...). And the crew can maintain visual contact in the event of emergencies. Bonus: you get to keep the system when the mission is over.

Yes, but where are you going to get thrust from?

The aft thrusters would have prohibitively high cosine losses. If you flew with an auxiliary propulsion pallet in the trunk then it would need a separate propellant supply which raises questions for abort.

I have to think that simply adapting the software to allow back-in parking is the shortest pole here.

My favorite way to do this : two Dragons

1) Dragon airlock (with a bigger side hatch which allows to do EVA with a back pack) and a docking interface with Hubble in the trunk ; it is derived from Cargo Dragon (no Super Dracos)
2) Crew Dragon : carry the crew and the ORUs in the trunk.

Dragon A/L docks with the Hubble at Dragon A/L trunk level. Crew Dragon docks with the front docking of the Dragon A/L.

EVA is through side hatch of Dragon A/L, first installing hand rails and so forth to create a path between both trunks. Then the ORUs are manually transferred along the created paths by the EVA crew

Airlock is built in a Dragon to make it recoverable, reusable and recover the suits. All what is lost is the Hubble interface in the trunk and the spent ORUs in the other trunk (also some spent ORUs could be put in the Airlock Dragon for return and expertise)

Reboost is performed with the thrusters around the front hatch of the Dragon A/L once the crew Dragon has separated so it is the cleanest possible wrt Hubble

The reboost is performed with the non human rated Dragon so the propellant quantity devoted to reboost can be higher (no need for propellant for ejection at launch for instance).

Non EVA crew can remain in a pressurized environment in the Crew Dragon during the EVAs.

Oh, I do like this.

SpaceX could use an unmodified Crew Dragon for the crew since they'd be docking nose-to-nose just as they would with the ISS.

Or, hear me out: what about using Dragon XL? Put the APAS docking adapter on the tail and add a hatch to turn it into a de facto airlock. It goes up on a Falcon 9, docks with Hubble, and performs an initial/test reboost. Polaris II then launches, performs a rendezvous, and docks with Dragon XL just like it would with ISS. Crew can then EVA without the need for depressing Crew Dragon and they can do some basic tests of Hubble servicing. If all goes to plan, more servicing missions can be subsequently conducted, and the XL can remain attached to Hubble and perform additional reboosts until its propellant is expended.

[jarmumd]

Hubble was left with the wide ring LIDS design for soft capture, not APAS.  It has "towel bars" that can be used for hard capture.

Not saying it couldn't possibly be adapted, but they are different connections.  For instance, technically APAS and IDSS could soft capture, but not hard capture (maybe they could, but I think umbilicals are in the wrong place).  IDSS and LIDS wide ring cannot soft capture without a lot of modifications to either/both.

[etudiant]

If they do it (which is a long pole), then I predict they dev an extensible docking adapter that is placed inside the trunk and pops out to dock with the Hubble adapter, perhaps with crew on EVA to troubleshoot.

Keep in mind that Crew Dragon's main propulsion is under the nose cone, so it would need to dock tail-first to reboost Hubble.

If they do develop an extensible docking adapter for the trunk of a Dragon would they be able to dock with and boost the ISS as well?

Yes, I would think so. Crew Dragon carries 1388 kg of propellant; if it spent half of this then it could add 4.15 m/s to the speed of the ISS which I believe is significantly larger than most reboosts that the station gets.

Of course, it would need to perform multiple transposition and docking maneuvers, which also require prop, and it still needs enough prop for the deorbit burn. So that's a consideration. And it would be unable to carry any other unpressed cargo during that flight. AND it would sacrifice the "back-in parking" docking adapter on each flight.

SpaceX hasn't been too shy about modifications to dragon though. Swapping out the cupola/docking adapter for example (and Polaris Dawn will have changes too I think). So it may be that changing out the standard docking adapter for an APAS adapter would be acceptable (not saying easy!)

The benefit is you can use all your proven docking sensors, in their proven flight configurations. Your guidance algorithms and control authority are the same (dragon isn't flying backwards...). And the crew can maintain visual contact in the event of emergencies. Bonus: you get to keep the system when the mission is over.

Yes, but where are you going to get thrust from?

The aft thrusters would have prohibitively high cosine losses. If you flew with an auxiliary propulsion pallet in the trunk then it would need a separate propellant supply which raises questions for abort.

I have to think that simply adapting the software to allow back-in parking is the shortest pole here.

My favorite way to do this : two Dragons

1) Dragon airlock (with a bigger side hatch which allows to do EVA with a back pack) and a docking interface with Hubble in the trunk ; it is derived from Cargo Dragon (no Super Dracos)
2) Crew Dragon : carry the crew and the ORUs in the trunk.

Dragon A/L docks with the Hubble at Dragon A/L trunk level. Crew Dragon docks with the front docking of the Dragon A/L.

EVA is through side hatch of Dragon A/L, first installing hand rails and so forth to create a path between both trunks. Then the ORUs are manually transferred along the created paths by the EVA crew

Airlock is built in a Dragon to make it recoverable, reusable and recover the suits. All what is lost is the Hubble interface in the trunk and the spent ORUs in the other trunk (also some spent ORUs could be put in the Airlock Dragon for return and expertise)

Reboost is performed with the thrusters around the front hatch of the Dragon A/L once the crew Dragon has separated so it is the cleanest possible wrt Hubble

The reboost is performed with the non human rated Dragon so the propellant quantity devoted to reboost can be higher (no need for propellant for ejection at launch for instance).

Non EVA crew can remain in a pressurized environment in the Crew Dragon during the EVAs.

Oh, I do like this.

SpaceX could use an unmodified Crew Dragon for the crew since they'd be docking nose-to-nose just as they would with the ISS.

Or, hear me out: what about using Dragon XL? Put the APAS docking adapter on the tail and add a hatch to turn it into a de facto airlock. It goes up on a Falcon 9, docks with Hubble, and performs an initial/test reboost. Polaris II then launches, performs a rendezvous, and docks with Dragon XL just like it would with ISS. Crew can then EVA without the need for depressing Crew Dragon and they can do some basic tests of Hubble servicing. If all goes to plan, more servicing missions can be subsequently conducted, and the XL can remain attached to Hubble and perform additional reboosts until its propellant is expended.

Sounds attractive, but afaik, the key operating function for Hubble is super precise pointing.
Not sure how that would remain possible after attaching a large mass to the telescope.

[Blackstar]

There is no mission!

Lots of people seem to have missed that. Eric Berger enthusiastically tweeted out that this was a mission, and lots of people seem to have seen that (and then followed up with a bit of rah-rah SpaceX/bash NASA).

I don't think that many people yet understand that somebody would have to pay for any mission.

[FutureSpaceTourist]

https://twitter.com/the_stargazer/status/1575894246552489984

If it is going to Hubble there will likely be professional NASA astronauts on board, not just an assortment of part-time trained spaceflight participants.

twitter.com/rookisaacman/status/1575924786915573765

Maybe..maybe not.

IMHO the focus should be on the objective itself. Can commercial space affordably upgrade & extend the life of Hubble to support science for decades in to the future? More important than debating human competency & limitations by the color of a flight suit.

https://twitter.com/rookisaacman/status/1575934396833861632

Kids are growing in a world where commercial space is turning science fiction in to reality --opening up so many exciting possibilities. I don't think we need to crush their dreams by perpetuating the belief you need to be hand picked by NASA to become a 'real' astronaut.

[gemmy0I]

Hubble was left with the wide ring LIDS design for soft capture, not APAS.  It has "towel bars" that can be used for hard capture.

Not saying it couldn't possibly be adapted, but they are different connections.  For instance, technically APAS and IDSS could soft capture, but not hard capture (maybe they could, but I think umbilicals are in the wrong place).  IDSS and LIDS wide ring cannot soft capture without a lot of modifications to either/both.

To clarify what seems to be a recurring point of confusion in this thread:

People keep talking about "APAS" in relation to Hubble, but APAS has nothing to do with Hubble or Dragon. APAS is the legacy "high-impact" docking system that was used by Shuttle at Mir and ISS. Both Hubble and present-day ISS (via the IDA adapters) use completely redesigned "low-impact" docking systems.

APAS (Androgynous Peripheral Attachment System) was originally the standard co-designed by the United States and Soviet Union for the Apollo/Soyuz Test Project. This "APAS-75" standard was implemented in substantially different ways by the two parties, which were nonetheless compatible with each other. The U.S. made no further developments on APAS in the subsequent years. The Soviet Union, meanwhile, made substantial improvements to APAS as they intended to use it as a successor to Soyuz's (non-androgynous) probe-and-drogue SSVP system for docking the Buran shuttle to Mir. This became the "APAS-89" standard and was installed at Mir. Buran never ended up flying to Mir, but for Shuttle-Mir the Soviets/Russians provided a docking adapter to NASA which was installed in the Shuttle's payload bay. This docking adapter was retained (and IIRC multiple of them were built) and evolved into the slightly improved "APAS-95" standard which was used at ISS (again, with Russian-built docking hardware on both ends).

The major limitation of APAS is that it is a "high-impact" standard meaning a fair amount of momentum is needed at docking to get the mechanisms to engage. This was not a problem for Shuttle since it was so massive, but for smaller capsule-type vehicles it could be challenging as it would require dockings at speeds too fast for the onboard thrusters to be able to abort at the last second. (My understanding is that neither Apollo nor Soyuz had this problem because they had fairly powerful thrusters, but it was seen as a potential constraint on more modern designs. This may or may not actually be an issue for Dragon since it has beefy forward-firing thrusters.) A high-impact system also precludes berthing of visiting vehicles with a robotic arm as an alternative to self-propelled docking.

Hence, in the mid-'90s, NASA began work on low-impact docking systems, originally for the X-38 and subsequently for Orion and commercial vehicles. This initially produced a unilateral NASA implementation known as LIDS (Low-Impact Docking System). This (or at least the soft-capture part of it) was what got installed on Hubble during STS-125 in 2009.

In 2010, NASA got on board with an internationally standardized version of LIDS, called the International Docking System Standard (IDSS). IDSS made some minor improvements to LIDS which made the two not intercompatible, but the changes are minor enough that it would not be difficult to adapt a vehicle designed for one to use the other for a particular mission.

In other words: the LIDS port on Hubble is essentially a "beta version" of the IDSS ports used on the ISS today.

The ISS presently has Boeing-built International Docking Adapters (IDAs) to convert the two externally-facing docking ports on the American side from the legacy APAS-95 standard to IDSS. Dragon and Starliner both comply with IDSS using their own independent yet compatible implementations.

Adding to the confusion, you will sometimes hear NASA refer to the "NASA Docking System" or NDS. This is NASA/Boeing's reference implementation of a docking system that is compatible with the IDSS standard. NDS was initially referred to as "iLIDS" or "International Low Impact Docking System" since it was a direct evolution of the LIDS prototype design. The Boeing NDS implementation is commercially available and is what's used in the IDAs as well as on Starliner and Orion. SpaceX chose to develop and manufacture their own independent implementation for Dragon which is compatible with the same standard.

Likewise (and even more confusing), you will sometimes hear modern Russian sources referring to their own IDSS-compatible systems as "APAS". This is because the Russian implementation of IDSS is directly derived from their historical APAS implementations. Yet it is nonetheless a low-impact system comporting with the modern IDSS standard, just like the Boeing and SpaceX implementations. (I've heard that Russia's modern APAS systems are supposed to be easily convertible with a stand-up EVA between high-impact APAS-95 compatibility and low-impact IDSS compatibility...as well as the "hybrid" standard used by Russia for connecting large modules, which combines APAS's hard-capture ring with the soft-capture mechanism from their SSVP probe-and-drogue standard.) Most likely, the IDSS-compatible ports on China's Tiangong station follow a similar design heritage (as they used the old high-impact APAS on the earlier Tiangong-1 and -2 stations).

So, what does this mean for a Dragon mission to Hubble?

1. Dragon is normally outfitted with an IDSS-compatible active port, but this shouldn't be too difficult to adapt to Hubble's LIDS standard. The soft-capture ring on Dragon would need to be switched out with a slightly wider one. (SpaceX's machine shop could probably cook this up in their sleep.) There may also be some tweaks needed to Dragon's active docking components as IDSS was supposed to simplify this somewhat compared to LIDS.

2. Since Hubble's LIDS installation lacks a hard-capture ring and instead uses a bespoke "towel bar" mechanism (as jarmumd pointed out), SpaceX would need to develop a similarly bespoke mechanism to allow Dragon to hard-latch to those "towel bars". I'm guessing this isn't too difficult either and they have a rough idea already of how they could do this.

Long story short: Dragon's existing docking system should be already 90-95% of the way there. The differences are minor and should be an easy project for SpaceX's engineers and machinists.

[matthewkantar]

It seems that Isaacman is going in any case. If he can find something weighty and respectable to do while whizzing around the planet, so much the better. NASA gets a free boost for Hubble, Isaacman get bragging rights.

[Comga]

Easy answer: an off-the-shelf Cargo Dragon could do it equally well, adding significant upmass, mission timelime margins, stability, easing constraints... Doesn't hype Polaris though.

Technically totally agreed. But in this case it might be the mission is only (potentially) happening because of the crew, even if it would make infinitely more sense to do it without one (assuming it's 'just' reboost).

gemmyol and jarmumd have discussed the docking mechanisms in great detail.
Neither an "off-the-shelf" Crew Dragon or Cargo Dragon could dock to Hubble, particularly grabbing the "towell bars".
It has been speculated in the general Polaris thread that a compatible mechanism would be mounted in the trunk of the Dragon.
Of course, this could be added to the trunk of a Cargo Dragon as well as Crew Dragon.

But the goal is not to "hype Polaris". 
It's to use an otherwise free flying LEO mission to do something practical.
I don't even thnk it's "bragging rights" Issacman wants, Mathew.  I think he wants to participate.
(If bragging was important to him, he already could make a full time job out of it.)

From the NASA Hubble program standpoint, they most likely wouldn't address the decaying orbit until it was a crisis, at which point they might be able to build or buy a system to control its deorbit. 
The mission under study could add years to Hubble's operations, as said in the press conference.
This is beyond good.
Snark is way out of line.

[jarmumd]

1. Dragon is normally outfitted with an IDSS-compatible active port, but this shouldn't be too difficult to adapt to Hubble's LIDS standard. The soft-capture ring on Dragon would need to be switched out with a slightly wider one. (SpaceX's machine shop could probably cook this up in their sleep.) There may also be some tweaks needed to Dragon's active docking components as IDSS was supposed to simplify this somewhat compared to LIDS.

2. Since Hubble's LIDS installation lacks a hard-capture ring and instead uses a bespoke "towel bar" mechanism (as jarmumd pointed out), SpaceX would need to develop a similarly bespoke mechanism to allow Dragon to hard-latch to those "towel bars". I'm guessing this isn't too difficult either and they have a rough idea already of how they could do this.

Long story short: Dragon's existing docking system should be already 90-95% of the way there. The differences are minor and should be an easy project for SpaceX's engineers and machinists.

You are mostly correct, but I am going to nit pick, just because little errors have a way of becoming fact on the internet.  LIDS the Light Impact Docking System was the precursor to IDSS, but none of the current IDSS compatible systems are "light impact".  Possibly IBDM is, I'm not familiar with that system.  LIDS used active force feedback control to dock with almost no force.  NDS-B1/B2 and SxDS both require significant closing velocity to effect capture.

As far as how easy it would be do to.  It's harder than you think.  The latching system is completely different (magnets vs latches), and the soft capture ring geometry is different (different parts contact).  So SpX would need to completely replace the ring.  It does appear from my notes to be a very similar Outer Diameter, so that's a plus!

As far as Hard Capture goes, the towel bars look to be a larger radius than the Spacex Nosecone.  That would mean if you needed hard capture, you would have to put a whole mechanism in the trunk and dock backwards.  Which could solve other problems even though it makes new ones.

I'm not convinced you actually need to have hard capture to do a reboost, but you might have to do it slowly.

It's a little less about the hardware in some ways.  All the designs are out there, and they are all NASA so they aren't really proprietary.  But it's the integration of the hardware, operations, hazards that represent the bulk of the work.  This has always been true when we lego rockets together.

well that's my 0.02

[AnalogMan]

The following comments from a report on Hubble Disposal Study (Nov 2012) concur with the above comments:

"The SCM, which was added to HST during Servicing Mission 4 (SM4) in 2009, was intended
to enable reuse of human spaceflight items, such as the Low Impact Docking System (LIDS),
to lower the development cost of a disposal mission. This study also found that use of a
LIDS variant would be effective. The standard version used on the International Space Station
(ISS), the International Low Impact Docking System (iLIDS) (also known as the NASA Docking
System, or NDS) is not mechanically compatible with HST’s SCM. Due to differences in diameter
and hard-dock mechanisms, developing an HST-compatible LIDs version requires a customized
design. Just prior to the completion of this report, NASA retired and terminated development of
the standard iLIDS. In response to this announcement, the COR Program Office is documenting
the location of both the Soft Capture Mechanism (SCM) and LID-related diagrams, drawings,
and GFE for future availability and development. A decision to design and manufacture the
HST-compatible version of LIDS should be reevaluated prior to a Phase A mission start."

[AstroWare]

To clarify what seems to be a recurring point of confusion in this thread: (...)

This is excellent thank you!

[gemmy0I]

You are mostly correct, but I am going to nit pick, just because little errors have a way of becoming fact on the internet.  LIDS the Light Impact Docking System was the precursor to IDSS, but none of the current IDSS compatible systems are "light impact".  Possibly IBDM is, I'm not familiar with that system.  LIDS used active force feedback control to dock with almost no force.  NDS-B1/B2 and SxDS both require significant closing velocity to effect capture.

As far as how easy it would be do to.  It's harder than you think.  The latching system is completely different (magnets vs latches), and the soft capture ring geometry is different (different parts contact).  So SpX would need to completely replace the ring.  It does appear from my notes to be a very similar Outer Diameter, so that's a plus!

As far as Hard Capture goes, the towel bars look to be a larger radius than the Spacex Nosecone.  That would mean if you needed hard capture, you would have to put a whole mechanism in the trunk and dock backwards.  Which could solve other problems even though it makes new ones.

I'm not convinced you actually need to have hard capture to do a reboost, but you might have to do it slowly.

It's a little less about the hardware in some ways.  All the designs are out there, and they are all NASA so they aren't really proprietary.  But it's the integration of the hardware, operations, hazards that represent the bulk of the work.  This has always been true when we lego rockets together.

well that's my 0.02

Fascinating - thanks for the details! Glad to have these "nitpicks" as I certainly don't want to tell fish-tales. (I learned most of what I know on the subject from a combination of Wikipedia and various NSF posts where people in the know have commented on specific details as you've done here.) I've bookmarked your post for future reference...

Since I have your $0.02, may I follow this up with a few more questions so I can be more knowledgeable about this going forward:

1. Would it be correct to say that, although IDSS isn't quite as low-impact as LIDS (due to not having the "active force feedback control"), it is still much lower-impact than the legacy APAS-95 used by the Shuttle? Basically, that IDSS is a compromise on the more "ideal" design of LIDS that gets most of its benefits (compared to legacy APAS) without quite as much implementation complexity (and without diverging as much in mechanical compatibility from legacy APAS; I'm guessing Russia was the "international partner" who requested these design changes since they wanted the use a unified implementation)?

2. Wikipedia's article on IDSS states that IDSS utilizes "6 servo-actuated legs" to "remove any relative motion [prior to retraction]". How does this differ from the more advanced "active force feedback control" used by LIDS? Is it a question of IDSS waiting until after initial capture to damp out relative motion versus LIDS actively compensating for it from the first moment of contact? Or is this where the distinction of magnets vs. latches/servos comes into play?

3. For berthing scenarios where a robotic arm is used to precisely maneuver a vehicle/module to the port, does the soft-capture mechanism matter at all, or is only the hard-capture mechanism needed since the robotic arm already has (enough) control of the vehicle's positioning on all relevant axes? The ability to support both docking and berthing is often cited as a key feature of both IDSS and LIDS; was this ever prohibitive with legacy APAS or is selling this up for IDSS/LIDS just "marketing speak"?

4. [if you (or anyone else) know the answer...] Is the reason why Russia went to the trouble of creating its "hybrid" APAS/SSVP ports for the attachment of large modules (which, IIRC, use an APAS hard-capture ring in conjunction with the SSVP system's probe-and-drogue soft-capture mechanism) because this allowed them to use the wider tunnel and superior structural connection of the APAS hard-capture ring in conjunction with a lower-impact (and/or less-complicated) soft-capture system?

[Robotbeat]

I think much may depend on if it's a boost only or a boost and service mission... If no eva is planned, I think they go nose-first docking. If they plan an EVA, then Aft-first. And either way - spaceX has the expertise to find the best technical option.

If they decide to do a boost-only mission, I suspect they will decide to not do it as a crewed Polaris mission, but as a robotic mission - probably pitched to NASA as a commercial offering to be paid for by the agency. ( ... )

There is a good chance that a Polaris 2 mission could cost >>>NASA<<< less than purchasing a traditionally procured robotic mission.

I bet Dragon reboosting would likely be cheaper than a robotic mission. Dragon is reusable.

[tappa]

How useful will am orbit boost be without changing the gyroscopes?

How feasible is replacing the gyroscopes?

[AmigaClone]

How useful will am orbit boost be without changing the gyroscopes?

How feasible is replacing the gyroscopes?

That might be part of what the study will determine.

[Barley]

The aft thrusters would have prohibitively high cosine losses.

Not sure what the angle of the aft thrusters is but cos(45) = .707, which may be annoying, but it is hardly ruinous.  You could certainly design one or more missions around that if the alternative is hundreds of millions of custom hardware.

Also you are making unstated assumptions about the alignment of the docked Dragon.  The only reason the axis of the Dragon would point through the center of mass of the combined spacecraft is because a docking adaptor is designed that way.  The docking adaptor could be designed with an offset angle so that one of the aft thrusters points through the center of mass so cosine = 1.

In short this is an economic trade off, not a can't do.

[Star One]

I suppose this mission could open the door to a more comprehensive servicing mission at a later date using Starship especially in light of the orbital boost to a higher orbit.

[Bob Shaw]

Either de-rating the Dragon SuperDracos or replacing them outright with baseline Dracos would solve the RCS physical placement issues. There’d still be some cosine losses, but no need for a new-build thruster module in the Trunk. Cheap and cheerful!

The showstopper, as I see it, is the capsule’s apex cap and the way it would fit - or not - up against the base of Hubble (handrails etc). The old Cargo Dragons had no nose covering during re-entry so maybe that’ll be the way forward.