Realistic, near-term, rotating Space Station

[LMT]

Autonomy

AG rendezvous should benefit greatly from robust autonomous GNC, first by removing complex mechanisms designed without autonomy in mind, such as rotating airlocks.  You can imagine other space benefits, e.g.:

- simplifying propellant transfer maneuvers among ships, satellites, depots, and stations

- automating stevedore cargo transfer in LEO, for maximized cargo delivery beyond LEO

- saving the costly labor presently required to drive planetary rovers, and in future, surface fleets

Notice the emphasis Elon places on autonomy.  Can we guess his actual ambition?

We're the only ones making cars that technically, we could sell for zero profit for now and then yield actually tremendous economics in the future through autonomy... I'm not sure many people will appreciate the profundity of what I've just said, but it is extremely significant.

https://www.youtube.com/shorts/6893yqtblP8

[Coastal Ron]

Autonomy

AG rendezvous should benefit greatly from robust autonomous GNC, first by removing complex mechanisms designed without autonomy in mind, such as rotating airlocks.

We already have computer systems that can do autonomous docking.

As to using such systems to dock with a rotating space station, rotating the visiting vehicle is the most complex solution, requires huge amounts of propellant, and has too much risk associated with failure. We've already identified better solutions. Move along...

Notice the emphasis Elon places on autonomy.  Can we see his actual ambition?

We're the only ones making cars that technically, we could sell for zero profit for now and then yield actually tremendous economics in the future through autonomy. I'm not sure many people will appreciate the profundity of what I've just said, but it is extremely significant.

I have a Tesla Model Y, and I bought it DESPITE Musk's "vision", not because. And nothing in the two years I've had that car has lead me to think I was wrong. Musk is a genius when it comes to hardware, but not so much when it comes to software... 

[LMT]

rotating the visiting vehicle... requires huge amounts of propellant

We saw the current req for challenging tumble-dock in thread already: two minutes of low-thrust RCS.

Leading with a falsehood is just FUD.

[Coastal Ron]

rotating the visiting vehicle... requires huge amounts of propellant

We saw the current req for challenging tumble-dock in thread already: two minutes of low-thrust RCS.

Leading with a falsehood is just FUD.

You THINK that is a solution, even though you have no idea what the center of mass, and center of rotation is for the visiting vehicles. Certainly Starship won't conform to your ideal, since it will be carrying far more propellant than cargo, making the cargo area NOT at the center of rotation.

[LMT]

rotating the visiting vehicle... requires huge amounts of propellant

We saw the current req for challenging tumble-dock in thread already: two minutes of low-thrust RCS.

Leading with a falsehood is just FUD.

You THINK that is a solution, even though you have no idea what the center of mass, and center of rotation is for the visiting vehicles. Certainly Starship won't conform to your ideal, since it will be carrying far more propellant than cargo, making the cargo area NOT at the center of rotation.

We should forget your "huge propellant" FUD now?

And of course neural net tumble-dock is designed to handle "disturbances, noise, uncertain dynamics, and faults".  We wouldn't want to overlook that, again and again.

[neoforce]

I haven't read this thread but I'm curious what those who have been discussing the ideas of a rotating Space Station here think about the Vast announcement this week?  Their plan seems to fit the category of a near term rotating space station.

Not a ton of detail, but on their roadmap, in the section that starts "2030s - 100-METER SPINNING STICK STATIONS" they show a "stick" of 7 modules to be delivered by Starship.

https://www.vastspace.com/roadmap

[LMT]

I haven't read this thread but I'm curious what those who have been discussing the ideas of a rotating Space Station here think about the Vast announcement this week?  Their plan seems to fit the category of a near term rotating space station.

Not a ton of detail, but on their roadmap, in the section that starts "2030s - 100-METER SPINNING STICK STATIONS" they show a "stick" of 7 modules to be delivered by Starship.

https://www.vastspace.com/roadmap

Wonderfully ambitious.  Can they compete if SpaceX chooses to enter that sector?  That is:

- offering a reusable Starship as low-cost microgravity station, or

- docking two reusable Starships as low-cost 100-m AG station

We see there's no counter-rotating airlock or grappling arm in VAST AG designs.  They're developing "systems and expertise for in-space maneuvers and approaches which are critical to space station assembly and re-supply."  Neural net GNC? 

Wanted:

- Experience in orbital mechanics as well as attitude dynamics and control.
- Experience using linear control principles and tools to design feedback control systems.
- Experience analyzing non-linear simulations of closed-loop dynamics.
- Working knowledge of outer loop control law performance requirements.

Perhaps their SpaceX veterans are applying SpaceX's "The best part is no part" principle.
 

[Coastal Ron]

You THINK that is a solution, even though you have no idea what the center of mass, and center of rotation is for the visiting vehicles. Certainly Starship won't conform to your ideal, since it will be carrying far more propellant than cargo, making the cargo area NOT at the center of rotation.

We should forget your "huge propellant" FUD now?

Propellant is a large, uncontrolled mass that can move around unexpectedly, and for the Starship it is housed in the bottom half of the vehicle. The cargo area of the Starship is in the top half of the vehicle, so right away you end up with challenges in matching the docking port of a rotating Starship with a rotating space station.

But sure, way away all concerns because you saw a paper you thought solved everything... 

And of course neural net tumble-dock is designed to handle "disturbances, noise, uncertain dynamics, and faults".  We wouldn't want to overlook that, again and again.

No one uses the term "neural net" these days - you are so 2010. 

And look, everything everyone is proposing is a "theory" until it is proven useful, and you are in love with your theory. Fine. Don't demand others to have the same fondness.

[Coastal Ron]

I haven't read this thread but I'm curious what those who have been discussing the ideas of a rotating Space Station here think about the Vast announcement this week?  Their plan seems to fit the category of a near term rotating space station.

Not a ton of detail, but on their roadmap, in the section that starts "2030s - 100-METER SPINNING STICK STATIONS" they show a "stick" of 7 modules to be delivered by Starship.

https://www.vastspace.com/roadmap

The design has been debated, and there is a lot of disagreement as to whether the design as shown would be workable. For now it is just a concept, and kudos for them for committing their own money to start the journey of getting to a rotating space station. But my bet is that their rotating space station design will change substantially before it becomes reality.

[LMT]

rotating the visiting vehicle... requires huge amounts of propellant

Strangely, you're still pushing that falsehood.

Propellant is a large, uncontrolled mass that can move around unexpectedly, and for the Starship it is housed in the bottom half of the vehicle.

Starships would typically AG-dock with header tanks, not full loads.

you are in love with your theory. Fine. Don't demand others to have the same fondness.

Who thinks casual info is a "demand", to be rejected over and over, emotionally?

--

ARPOD

A sophisticated neural net GNC system with potential AG station application is given in Ikeya et al. 2023.

Spacecraft automated rendezvous, proximity maneuvering, and docking (ARPOD) plays
a significant role in many space missions including on-orbit servicing, and active debris
removal. Precise modeling and prediction of spacecraft dynamics can be challenging due
to the uncertainties and perturbation forces in the spacecraft operating environment and
due to the multi-layered structure of its nominal control system. Despite this complication,
spacecraft maneuvers need to satisfy required constraints (thrust limits, line of sight cone
constraints, relative velocity of approach constraints, etc.) to ensure safety and achieve ARPOD
objectives. This paper considers an application of a Learning-based Reference Governor (LRG)
to spacecraft ARPOD operations to enforce constraints without relying on a dynamic model
of the spacecraft during the mission. Similar to the conventional Reference Governor (RG),
the LRG is an add-on supervisor to a closed-loop control system, serving as a pre-filter on
the command generated by the ARPOD planner. The LRG modifies, if it becomes necessary,
the reference command to a constraint-admissible value to enforce specified constraints. The
LRG is distinguished, however, by the ability to rely on learning instead of an explicit model
of the system, and guarantees constraints satisfaction during and after the learning. In this
paper, the LRG is applied to the control of combined translational and rotational motion of a
chaser spacecraft, and three case studies with different sets of safety constraints and thruster
assumptions are used to demonstrate the benefits of the LRG in ARPOD missions.

The significance of the LRG is that we can reduce the risk of hazardous accidents by employing learning without the need for developing, identifying, and simplifying detailed models of system dynamics that can be difficult in certain situations...

Additionally, extensions of our approach to more complex spacecraft configurations and constraints, such as... docking to a rotating chief spacecraft, and formation flight between two or more deputy spacecraft with respect to one chief spacecraft could be tractable...

The controller is hierarchical, with outer-loop control law and nonlinear closed-loop dynamics -- something like the outer-loop / closed-loop GNC programming underway at VAST?

Refs

Ikeya, K., Liu, K., Girard, A. and Kolmanovsky, I., 2023. Learning Reference Governor for Constrained Spacecraft Rendezvous and Proximity Maneuvering. Journal of Spacecraft and Rockets, pp.1-15.
 

[Coastal Ron]

rotating the visiting vehicle... requires huge amounts of propellant

Strangely, you're still pushing that falsehood.

Happy to be proved wrong, but you don't have the ability to prove me wrong.

Propellant is a large, uncontrolled mass that can move around unexpectedly, and for the Starship it is housed in the bottom half of the vehicle.

Starships would typically AG-dock with header tanks, not full loads.

Actually you don't know that. And if a Starship only had the propellant in its header tanks, and no propellant in the main tanks, then how is it maneuvering to and from the space station? Or are you assuming the Starship will undock from the space station and just drift away...

Ships visiting space stations will have the propellant they need to leave the station and make it to their next refueling location, or to their landing location - with plenty of reserve. You assuming they will arrive at a space station with dry propellant tanks is just plain silly.

ARPOD

A sophisticated neural net GNC algorithm with potential AG station application is given in Ikeya et al. 2023.

Look, computers can simulate a lot of things, and 3-body motion prediction using camera input is not a stretch. But solid bodies rotating in space are one thing, and vehicles rotating with moving mass within them are something else.

I've said my peace, and if you want to actually BUILD something and prove me wrong, great. But otherwise I think you are extrapolating too much from those studies. And we have already proposed solutions that DON'T require visiting vehicles to rotate when docking with rotating space stations.

[LMT]

rotating the visiting vehicle... requires huge amounts of propellant

Strangely, you're still pushing that falsehood.

Happy to be proved wrong, but you don't have the ability to prove me wrong.

No, two minutes of sporadic RCS hardly taps header tanks, obviously.

solid bodies rotating in space are one thing, and vehicles rotating with moving mass within them are something else.

...if you want to actually BUILD something and prove me wrong, great.

That pose ignores info in the post and paper, despite relevance.  They developed NN LRG specifically to handle the hardest dynamics, even where the "moving mass" can't be readily modeled, in order to "enforce constraints without relying on a dynamic model of the spacecraft".

The significance of the LRG is that we can reduce the risk of hazardous accidents by employing learning without the need for developing, identifying, and simplifying detailed models of system dynamics that can be difficult in certain situations...

And we see that VAST is coding just such tricks today, notably without the old counterrotating airlock business.

Simplest explanation?

[Paul451]

I haven't read this thread but I'm curious what those who have been discussing the ideas of a rotating Space Station here think about the Vast announcement this week?  Their plan seems to fit the category of a near term rotating space station.

There's a specific thread for it: https://forum.nasaspaceflight.com/index.php?topic=55810.0

The Vast proposal was the reason this thread was resurrected for general AG discussion, we didn't want to clog up the Vast thread with non-specific discussion and people's own personal takes on spin stations.

It's neat that someone actually putting real resources into an AG station. I hope that JAXA and ESA (which both have shown more interest in AG than NASA/US-govt) are willing to support them with research payloads and don't suffer the usual "not-invented-here" syndrome.

[JohnFornaro]

I haven't read this thread but I'm curious what those who have been discussing the ideas of a rotating Space Station here think about the Vast announcement this week?  Their plan seems to fit the category of a near term rotating space station.

Not a ton of detail, but on their roadmap, in the section that starts "2030s - 100-METER SPINNING STICK STATIONS" they show a "stick" of 7 modules to be delivered by Starship.

https://www.vastspace.com/roadmap

I'm taking a wait and see attitude.  From the time of their initial announcement of the project, to now seems to me to have been too short to manufacture a ready made station.  Has SpaceX announced Vast being on SpaceX's launch cadence? 

Remember, there's a Vast thread.

[JohnFornaro]

The Vast proposal was the reason this thread was resurrected for general AG discussion, we didn't want to clog up the Vast thread with non-specific discussion and people's own personal takes on spin stations.

That's not quite my take.  This thread pre-dates Vast by several years, and it just got resurrected during the natural course of events.

Edit, a few minutes later:

Huh.  Maybe the "resurrection" was timed as you say.  This, i think, is the first mention here, of the Vast baton:

https://forum.nasaspaceflight.com/index.php?topic=34036.msg2400142#msg2400142

[lamontagne]

My guess is that if the incoming craft is symetrical and can rotate around a docking port without too much torque being induced and the centers of rotation are within the 10 cm or so allocation of the existing port designs, then you just rotate the craft as LMT mentions and no need for a rotating port.

You will need a rotating port for vehicles with side entry, I expect.  If Starships happens to be designed that way, then a rotating port is useful.  If they can have a port in the nose of a Starship capable of Earth re-entry, then rotating Starship lengthwise might work.  If it's a question of redesigning the header and fuel system vs designing a rotating port, I expect the rotating port is simpler.

Also depends if you just dock and transfer, or dock and remain attached for a long time.
For larger stations such as John's and my Mars one, docking will be achieved by other means.  It'll be more like landing, then attaching some kind of port, like an aircraft.

So the rotating docking port may have a limited operational life 

[Coastal Ron]

Happy to be proved wrong, but you don't have the ability to prove me wrong.

No, two minutes of sporadic RCS hardly taps header tanks, obviously.

OK, but you previously said that a Starship had to have empty propellant tanks, and you're sticking with that, right? Because you are now just claiming that there needs to be some propellant, just not much.

So what happens if the Starship comes in with full propellant tanks? Remember rotating space stations can be anywhere, in LEO, MEO, and beyond, so are you mandating that they can only dock if they have very little propellant?

I'm trying to understand all of your previous statements to see how consistent you are being.

Plus, Starship is not being built to rotate, so the docking port (or whatever they will eventually use) is unlikely to be at the center of rotation - which you seem to overlook.

As I've stated before, autonomous docking software is not new, but it requires HARDWARE that is built to take advantage of it, and Starship is not being built for docking to rotating space stations. Elon Musk doesn't even care about rotating space stations, so it is unlikely that they will try to redesign Starship to rotate in a way that your favorite software could us.

[LMT]

Happy to be proved wrong, but you don't have the ability to prove me wrong.

No, two minutes of sporadic RCS hardly taps header tanks, obviously.

OK, but you previously said that a Starship had to have empty propellant tanks, and you're sticking with that, right? Because you are now just claiming that there needs to be some propellant, just not much.

"OK, but [straw man text]".  Ref.

--

Orbiter

VAST intends to use the recently-acquired Launcher Orbiter for station development.  The first Orbiter failed, but more are on the way.

Looking at the large propellant volume, it's clear Orbiter is truly a "high delta-v capable space tug" -- up to 500 m/s delta-v (Ethane / N2O).  And now VAST intends to augment Orbiter to "develop systems and expertise for in-space maneuvers and approaches which are critical to space station assembly and re-supply".

Orbiter is a versatile tug.  How might VAST modify Orbiter, to accomplish these challenging station tasks?

https://assets-global.website-files.com/6175ee2ca86f1b8d99c3c52d/639a05a8f26ed434c25a3c27_Website_Turntable01_White-transcode.mp4

[Coastal Ron]

Happy to be proved wrong, but you don't have the ability to prove me wrong.

No, two minutes of sporadic RCS hardly taps header tanks, obviously.

OK, but you previously said that a Starship had to have empty propellant tanks, and you're sticking with that, right? Because you are now just claiming that there needs to be some propellant, just not much.

"OK, but [straw man text]".  Ref.

Just repeating what you implied here:

Starships would typically AG-dock with header tanks, not full loads.

And you are avoiding the fact that Starship is not being designed to rotate for docking, nor to rotate for artificial gravity at all. And you are ignoring that the cargo area would not be in the center of rotation if the Starship did rotate.

So it doesn't matter that software exists that could dock two rotating objects, because Starship will not be one of them.

And that is not a problem, because a number of solutions have been proposed where a Starship does NOT have to rotate end over end in order to transfer cargo and passengers to a rotating space station. For purposes of this topic thread this is a solved problem.

As to how Vast intends to transfer cargo and passengers to their stations, they have yet to make that public, so we'll have to wait and see what they propose.

[LarryCanuck]

May have been discussed somewhere in here, but I've been away for awhile, so please bear with me ... 
Regarding the rotating port discussion, could there not be a Mechazilla-like extension at the centre of Station rotation that is an extensible cylinder, and including a spin-up / spin-down action as well?
The Starship has a loading dock in its nose, like the Falcon but much bigger. The Ship approaches the station as normal, and the Mech "spins down" to zero rotation, docks with the Ship, and then "spins up" the Ship to match the Station. The cylinder has a freight elevator built in. When loading/unloading is complete, the Zilla reverses the process and the Ship departs.
Best regards!