Artificial Gravity Testbeds

[Twark_Main]

I'm really starting to think that if we accept a paradigm of regular spin-up/spin-down operations - this might be key to moving forward for advocates of spin-G space stations. Everything becomes so much simpler, and uses higher TRL technologies.

In this scenario, the station designs can be expected to cluster around the shortest tolerable radius and the highest tolerable RPM. For the same gravity level, the spin-up and spin-down propellant mass scales in a linear fashion with the radius and with the (inverse) RPM.

I agree with your math, but not your conclusion, because optimising for propellant mass isn't a strong forcing factor for anything that is likely to be built in the near-term. If we're assuming we need starship to launch it, then surely we've also got access to starship-level quantities of propellant, right?

I have a saying I like to remind myself: SpaceX didn't make all the smart cost-optimizing decisions just so I can make a bunch of cost-maximizing decisions. 

The amount of propellant required to spin up /down a 1400 ton, 50m radius torus [or hammerhead    ] to Mars-level gravity is less than...

I would consider that roughly "minimum radius," so methinks we are finding ourselves in violent agreement here. 

[Paul451]

I have a saying I like to remind myself: SpaceX didn't make all the smart cost-optimizing decisions just so I can make a bunch of cost-maximizing decisions.

Trading some extra propellant for reduced engineering complexity isn't cost maximising, quite the opposite. [and explicitly Mike's point.]

[Twark_Main]

I have a saying I like to remind myself: SpaceX didn't make all the smart cost-optimizing decisions just so I can make a bunch of cost-maximizing decisions.

Trading some extra propellant for reduced engineering complexity

You have it backwards. A larger spinning station would have more engineering complexity, not less. Why would one think otherwise? 

The argument works great when you're replacing costly lightweight parts with cheaper heavier parts. This isn't one of those cases, however.

[mikelepage]

The amount of propellant required to spin up /down a 1400 ton, 50m radius torus [or hammerhead    ] to Mars-level gravity is less than...

I would consider that roughly "minimum radius," so methinks we are finding ourselves in violent agreement here. 

Oh, good to hear. Because I was responding to your “shortest tolerable radius and the highest tolerable RPM” statement - which depending who you talk to can be in the range 10-30 rpm with adaptation. Better to clarify that in future. You also linked to the Con Hathy video which is fairly explicitly in favour of short-arm centrifuges inside a single (9m diameter) starship.

It’s funny how he acknowledges the “amount of hate” such proposals get without mentioning the reason why - it’s still assuming a “medicinal” application of gravity - something you would do in addition to, or in place of the 2 hours of daily exercise in a zero-G space environment like ISS. It’s a very narrow solution (optimised for the incredibly mass-constrained pre-starship context) compared to the broad-ranging advantages that implementing a partial (or full) spin-gravity solution would achieve.

I have a saying I like to remind myself: SpaceX didn't make all the smart cost-optimizing decisions just so I can make a bunch of cost-maximizing decisions.

Trading some extra propellant for reduced engineering complexity isn't cost maximising, quite the opposite. [and explicitly Mike's point.]

You have it backwards. A larger spinning station would have more engineering complexity, not less. Why would one think otherwise? 

That argument works great when you're replacing costly lightweight parts with cheaper heavier parts. This isn't one of those cases, however.

You’re making a lot of assumptions in directly contradicting us, but without directly addressing the argument either Paul or I made, so it’s difficult to know whether you actually have a point.

This most recent argument of mine was about eliminating complex on-axis docking systems, in favour of rim-docking… and using the starship’s OMS to spin-up/spin-down in favour of high capacity flywheels/counter-rotating segments, or having to incorporate propellant/thruster systems on station. This essentially reduces the complexity of on-orbit assembly of a torus to that of a stick-station. And makes on-orbit operations arguably less complex than a stick station because all systems will always be at roughly similar acceleration levels, so we don’t have to worry as much interactions between components undergoing high acceleration and those low acceleration. Which part of that are you calling “cost maximisation”?

IMO the strongest argument for the torus is that the likely customer (government, military, commercial or tourism) is interested in a particular level of gravity (either Lunar or Martian), and maximising the available space at that level of gravity. My caveat is that this is for LEO. As I’ve said before, I think lower-mass stick stations have a much stronger case on interplanetary trajectories. Or any trajectory where you’d 1) need starship to be refuelled so mass constraints are an order of magnitude higher, and 2) boost the stick into that trajectory via high-acceleration Oberth maneuver - which definitely isn’t as friendly to the pre-assembled torus geometry. (This is why my on-asteroid station concept starts assembling with stick stations into an X, then erecting a low-mass torus structure around them onsite).

[Coastal Ron]

And Mike might be right that below a certain size station, it's probably easier to design a fluid/pump system that can be turned off under zero-g for a couple of days during RPOD, than to design a system that has a counter-rotating docking port that allows pass-through to a rotating station. As you get bigger, the trades shift.

No counter-rotating dock is on the AG roadmap, e.g., at VAST.

The largest VAST space station on their roadmap is only for a crew of 8, and they are NOT showing all of engineering details yet for their station, so how they get resupplied is currently an unknown (and we know their notional artwork is only that, because they show a picture of someone looking out one of two portals, but their drawing showing the portals would not provide the gravity in the picture  ).

Not at any scale.

Everyone knows you like to close the door on any designs you don't like (and you provide links to your own posts to prove such reasons  ), so suffice it to say that a number of us have found ways to have rotating docks that are not very complicated, and we will be including them in future designs we are working on.

Why?

Why iare no well funded rotating space station teams proposing rotating docks yet? Because no well funded rotating space station teams exist for the size of stations that truly require rotating docks. As mikelepage has shown with his spreadsheet, small rotating space stations that could be testbeds could afford to use propellant to spin up and spin down the station as needed.

It is only when you get beyond the size of testbed rotating stations that rotating docks become a potential solution. And for rotating space stations that are true multi-generation colonies, they may be big enough to have docks like the kind used by the fictional Babylon 5.

We should notice what engineers include and omit in modern designs.

Yeah, if only you followed your own advice... 

However we are beyond the "cutting edge" here, because those of us that really care about what comes next are putting our energies into dreaming up potential solutions for rotating space stations that are not yet being pursued with money. So there are no "modern designs" for you to point to, not on the scale we are working at.

[Coastal Ron]

Just checking in.

A station as massive as the one I propose could not be spun up and down very easily.

I'm assuming the same.

As to the idea of a test bed, my station is intended to empirically prove that human life can reproduce in AG.  Is there something about an adjacent mass, like the Earth, which is necessary for humans and terrestrial life to thrive?

Besides being a source of supplies for the station? Individual cities on Earth are not self-sustaining, so I am assuming the same for "cities" in space, like multi-generational rotating space stations.

The benefits of living and working in AG versus micro or very low gee seem self evident.  If it is proven that we can't thrive and reproduce in AG, the utility of having a space station as a waypoint to Moon, Mars and Venus remains.

I don't know, but I sure hope that there is a way for humanity to reproduce and thrive away from Earth, and that is what inspires me to dream up artificial gravity habitats that could contribute to that goal.

[Twark_Main]

The amount of propellant required to spin up /down a 1400 ton, 50m radius torus [or hammerhead    ] to Mars-level gravity is less than...

I would consider that roughly "minimum radius," so methinks we are finding ourselves in violent agreement here. 

Oh, good to hear. Because I was responding to your “shortest tolerable radius and the highest tolerable RPM” statement - which depending who you talk to can be in the range 10-30 rpm with adaptation. Better to clarify that in future. You also linked to the Con Hathy video which is fairly explicitly in favour of short-arm centrifuges inside a single (9m diameter) starship.

Yes, good to hear that we're on the same page here.

It’s funny how he acknowledges the “amount of hate” such proposals get without mentioning the reason why - it’s still assuming a “medicinal” application of gravity - something you would do in addition to, or in place of the 2 hours of daily exercise in a zero-G space environment like ISS. It’s a very narrow solution (optimised for the incredibly mass-constrained pre-starship context) compared to the broad-ranging advantages that implementing a partial (or full) spin-gravity solution would achieve.

I would say it's optimized for Starship in transit to Mars, which isn't exactly "pre-Starship."

I have a saying I like to remind myself: SpaceX didn't make all the smart cost-optimizing decisions just so I can make a bunch of cost-maximizing decisions.

Trading some extra propellant for reduced engineering complexity isn't cost maximising, quite the opposite. [and explicitly Mike's point.]

You have it backwards. A larger spinning station would have more engineering complexity, not less. Why would one think otherwise? 

That argument works great when you're replacing costly lightweight parts with cheaper heavier parts. This isn't one of those cases, however.

You’re making a lot of assumptions in directly contradicting us, but without directly addressing the argument either Paul or I made, so it’s difficult to know whether you actually have a point.

I'm just talking about the radius, not any of the other things you go on to mention.

All other things being equal, it seems hard to imagine that a larger radius solution has simpler engineering than a smaller radius solution (again, neglecting extreme examples)

This most recent argument of mine was about eliminating complex on-axis docking systems, in favour of rim-docking… and using the starship’s OMS to spin-up/spin-down in favour of high capacity flywheels/counter-rotating segments, or having to incorporate propellant/thruster systems on station.

I expect the ultimate solution might be similar to ISS: incorporating thrusters on the station, but using thrusters on Soyuz (Starship) whenever possible to minimize wear-and-tear on the integrated thruster system.

And makes on-orbit operations arguably less complex than a stick station because all systems will always be at roughly similar acceleration levels, so we don’t have to worry as much interactions between components undergoing high acceleration and those low acceleration.

Given that everything needs to be able to handle microgravity conditions when despun, this seems like a small savings.

Which part of that are you calling “cost maximisation”?

Making it absurdly bigger than necessary. Fortunately, it seems (for a change!) nobody is proposing that in this thread. 

IMO the strongest argument for the torus is that the likely customer (government, military, commercial or tourism) is interested in a particular level of gravity (either Lunar or Martian), and maximising the available space at that level of gravity.

Again, a hammerhead configuration achieves the same advantage while still minimizing surface area to volume ratio for more geometrically efficient radiation shielding (less important in LEO) and reduced MMOD risk (especially important in LEO).

[Coastal Ron]

Thanks. I'm really starting to think that if we accept a paradigm of regular spin-up/spin-down operations - this might be key to moving forward for advocates of spin-G space stations. Everything becomes so much simpler, and uses higher TRL technologies.

On your spreadsheet, does it matter what the moment arm is for the engines?

I ask because on one of my station designs I was planning on putting some form of electric propulsion way out beyond the habitable part of the station, with the assumption that they could be more efficient on a longer moment arm. Not for spinning the station up or down on a regular basis, but it could be used in an emergency to reduce the RPM of the station (and I was going to use it for stabilizing any wobble, so twofer  ).

But I'd like some confirmation about that approach...

[Twark_Main]

Thanks. I'm really starting to think that if we accept a paradigm of regular spin-up/spin-down operations - this might be key to moving forward for advocates of spin-G space stations. Everything becomes so much simpler, and uses higher TRL technologies.

On your spreadsheet, does it matter what the moment arm is for the engines?

I ask because on one of my station designs I was planning on putting some form of electric propulsion way out beyond the habitable part of the station, with the assumption that they could be more efficient on a longer moment arm. Not for spinning the station up or down on a regular basis, but it could be used in an emergency to reduce the RPM of the station (and I was going to use it for stabilizing any wobble, so twofer  ).

But I'd like some confirmation about that approach...

Yes, a long moment arm should work. Double the lever arm, halve the spin-up / spin-down / axis precession propellant.   

One interesting calculation is how long a counterweight lever arm you can use before a suited astronaut (or a wrench) that accidentally falls off-station (from the shorter-radius hab section) will risk being hit by the long arm as it swings around. 

An astronaut might conceivably wear an automated jetpack to maneuver out of the way, but a piece of falling debris won't have that luxury. A spin-axis offset on the mast might be used to work around the problem, or again just limit the length.

Personally I don't expect EVAs while under spin for a long time (if ever), but debris shedding from the exterior still poses a self-collision risk.

[mikelepage]

I'm just talking about the radius, not any of the other things you go on to mention.

All other things being equal, it seems hard to imagine that a larger radius solution has simpler engineering than a smaller radius solution (again, neglecting extreme examples)

One thing that does push you above a certain minimum radii, is being able to dock 2+ starships to the station in a way that both 1) allows them to approach and dock without interfering with each other, and 2) also doesn't significantly upset the rotational balance of the station (we want 2+ visiting vehicles if there are to be crewed handovers, which is a priority for the CLD program).

For now, I'm supposing that the upcoming propellant transfer demos will get SpaceX comfortable with approaching and mating with another spacecraft using a port on the "dorsal" side of starship, so "nose-inwards" rim docking with a torus space station will be possible. If we're using the body of starship below the "garage" as a ~30m lever arm and the OMS at starship's tail as the torquing thrusters, then the ~20m of starship above the "garage" pretty much forces you to have a spin radius of 25m or more, unless the two starships are on opposite sides of a node to each other (e.g. on one arm of a baton). In which case I can't see a way to arrange them both with their heat shields pointed at the sun.

I didn't explicitly state this before, but by ditching the central element, I am aiming for a process where no matter how many modules are in the torus (12, 24, 60 etc), they all have pretty much the exactly same shape / outer mould line, and are mated to each other using the exact same procedure. Taking a production-line mentality, I want simplify as much as possible the process from the moment the payload arrives at Starbase/KSC or wherever, and is mounted within starship for launch. It's the internals that are modified for whatever purpose.

IMO the strongest argument for the torus is that the likely customer (government, military, commercial or tourism) is interested in a particular level of gravity (either Lunar or Martian), and maximising the available space at that level of gravity.

Again, a hammerhead configuration achieves the same advantage while still minimizing surface area to volume ratio for more geometrically efficient radiation shielding (less important in LEO) and reduced MMOD risk (especially important in LEO).

Note that a hammerhead configuration also decreases the ratio of the station's moments of inertia (short axis vs long axis) for a given contained volume, so it may need to be proportionally bigger in order to be stable with n number of starship-sized vehicles docked. Not to minimise the radiation and MMOD concerns at all, but I have yet to see a hammerhead design I thought would be simpler to assemble, visit and operate than an equivalent volume torus. Perhaps you have one you'd point to in this context?

PS. what's going on with your quoted "quote" symbols? (I get these characters = ” )

[rsdavis9]

So how "matched" do the weights of the starship's need to be?

If you had 2 starships. One 1400t with full fuel load and one empty 200t. They would spin around a common center very off axis.

[Twark_Main]

I'm just talking about the radius, not any of the other things you go on to mention.

All other things being equal, it seems hard to imagine that a larger radius solution has simpler engineering than a smaller radius solution (again, neglecting extreme examples)

One thing that does push you above a certain minimum radii, is being able to dock 2+ starships to the station in a way that both 1) allows them to approach and dock without interfering with each other, and 2) also doesn't significantly upset the rotational balance of the station (we want 2+ visiting vehicles if there are to be crewed handovers, which is a priority for the CLD program).

Heck, you need 2 docking ports just to resupply with a crew onboard! This is what makes a "third generation space station."

IMO the strongest argument for the torus is that the likely customer (government, military, commercial or tourism) is interested in a particular level of gravity (either Lunar or Martian), and maximising the available space at that level of gravity.

Again, a hammerhead configuration achieves the same advantage while still minimizing surface area to volume ratio for more geometrically efficient radiation shielding (less important in LEO) and reduced MMOD risk (especially important in LEO).

Note that a hammerhead configuration also decreases the ratio of the station's moments of inertia (short axis vs long axis) for a given contained volume, so it may need to be proportionally bigger in order to be stable with n number of starship-sized vehicles docked.

I doubt the rotational stability is the bottleneck here?

Not to minimise the radiation and MMOD concerns at all, but I have yet to see a hammerhead design I thought would be simpler to assemble, visit and operate than an equivalent volume torus. Perhaps you have one you'd point to in this context?

Why do you think a torus is simpler to assemble/visit/operate than an equivalent volume hammerhead?

And again, you're ignoring the zeroth-order scaling. Even if it's not "simpler" etc (I see no reason why there should be significant differences IMO), it simply has less mass and lower risk, which still matters even in Starship Land.   

PS. what's going on with your quoted "quote" symbols? (I get these characters = Ă˘â‚¬Â )

Forum software bug, by the looks of it. You're using "smart quotes" and the forum software is very dumb.

So how "matched" do the weights of the starship's need to be?

If you had 2 starships. One 1400t with full fuel load and one empty 200t. They would spin around a common center very off axis.

They don't need to be "matched" at all. They'll simply spin around a common axis very off center   

[LMT]

No counter-rotating dock is on the AG roadmap, e.g., at VAST.

...they are NOT showing all of engineering details yet for their station, so how they get resupplied is currently an unknown

The dock is shown plainly; there's no counter-rotating hw, even at 100-m scale.  With modern GNC -- which VAST applies -- that makes sense.

we are beyond the "cutting edge" here...

docks like the kind used by the fictional Babylon 5...

Well, if "Babylon 5" didn't care about modern GNC... 

[Coastal Ron]

No counter-rotating dock is on the AG roadmap, e.g., at VAST.

...they are NOT showing all of engineering details yet for their station, so how they get resupplied is currently an unknown

The dock is shown plainly; there's no counter-rotating hw, even at 100-m scale.

Apparently you missed what I said what I pointed out that the VAST drawings are not realistic when compared to the image showing someone looking out a window with another window next to it. Either they are two different stations that VAST is working on, and they are not showing the second one, or they are just making pictures that look interesting but are not related to any real engineering.

I think it is the later, unless you can prove that the image matches the drawing.

Meaning that assuming that VAST is showing us everything they are doing is foolhardy at best. Don't be foolhardy... 

With modern GNC -- which VAST applies -- that makes sense.

You are making a statement that insinuates a fact. Provide a citation from VAST to support the claim, or admit you were wrong to make such a claim.

we are beyond the "cutting edge" here...

docks like the kind used by the fictional Babylon 5...

Well, if "Babylon 5" didn't care about modern GNC...

Apparently you are not familiar with how the Babylon 5 space station works, and I only mentioned it as a design that is well into the future, not a testbed nor even "near-term".

[LMT]

With modern GNC -- which VAST applies -- that makes sense.

You are making a statement that insinuates a fact. Provide a citation from VAST to support the claim, or admit you were wrong to make such a claim.

You ignored the info.  Don't pester.

"Babylon 5"...

[edzieba]

With modern GNC -- which VAST applies -- that makes sense.

You are making a statement that insinuates a fact. Provide a citation from VAST to support the claim, or admit you were wrong to make such a claim.

You ignored the info.  Don't pester.

"Babylon 5"...

Quoting your own claims to back up your own claims is not exactly of any utility.

Vast's notional renders are just that: notional. The 'spinning station' video does not even have any docking adapters on it at all, just CBM ports on the end of the modules. These are not engineering drawings, but marketing visualisations, and trying to diving CONOPS from them is about as useful as tea-leaf reading.

[LMT]

With modern GNC -- which VAST applies -- that makes sense.

You are making a statement that insinuates a fact. Provide a citation from VAST to support the claim, or admit you were wrong to make such a claim.

You ignored the info.  Don't pester.

"Babylon 5"...

The 'spinning station' video does not even have any docking adapters on it at all, just CBM ports on the end of the modules.

Not true, and you also ignored the GNC info.  Another Babylon 5 fan?

[Coastal Ron]

You ignored the info.  Don't pester.

"Babylon 5"...

The 'spinning station' video does not even have any docking adapters on it at all, just CBM ports on the end of the modules.

Not true, and you also ignored the GNC info.  Another Babylon 5 fan?

Yes, stop quoting yourself as the only source of information. All that does is prove you don't have any proof.

The VAST concept is, so far, just that. A concept. It is NOT the only concept out there, and this thread is SPECIFICALLY for generating ideas for artificial gravity testbeds, not just what VAST has come up with (that would be on a VAST thread, if there is one).

And, as usual, you are confusing the Babylon 5 reference, probably because you have never seen the show, where massive rotating space stations in the future will not need a rotating dock on the side of the station, they will have a dockyard where entire ships can berth. And I already stated that is something that is well beyond what this thread covers, and well beyond what the "Near Term" thread covers too. So stop looking silly by mentioning it... 

Now, lets get back to talking about artificial gravity testbeds that can be built "soon-ish" to test out the things that need to be validated before we build artificial gravity rotating space stations for work and living needs.

[LMT]

You ignored the info.

The 'spinning station' video does not even have any docking adapters on it at all, just CBM ports on the end of the modules.

Not true, and you also ignored the GNC info. 

Yes, stop quoting yourself as the only source of information. All that does is prove you don't have any proof.

Doubling down on nonsense there.  No, we saw the VAST info, including their GNC job opening.  And we saw the job matches SOTA GNC docking methods, i.e., without counter-rotating hw.  We don't see "counter"-examples in the industry.

You might start a new thread for "counter-rotating docks", specifically, where you can dismiss engineering that doesn't fit.

[edzieba]

Doubling down on nonsense there.  No, we saw the VAST info, including their GNC job opening. 

Said job posting does not mention docking or berthing at all. So by your logic nobody, will be visiting the Vast station ever because no vehicles will ever dock or berth there.

To be explicitly clear: a job posting will not detail mission architecture, and it will not detail vehicle design. Trying to diving CONOPS from one is beyond tea-leaf reading and into examination of goat entrails.

where you can dismiss engineering that doesn't fit.

Some supreme irony there.