Vast, a Startup for "human habitation, first in LEO, and then beyond"

[Paul451]

Bottom line, which Paul hasn't gotten to yet.  Non-rotating hub.

Because it's beyond the scope of this design, and therefore not relevant to the thread.

[It's also, IMO, a bad option. But that's a topic for the general rotating-stations thread.]

[JohnFornaro]

Bottom line, which Paul hasn't gotten to yet.  Non-rotating hub.

Because it's beyond the scope of this design, and therefore not relevant to the thread.

[It's also, IMO, a bad option. But that's a topic for the general rotating-stations thread.]

I don't understand this type of comment.  Continue discussing a faulty design, with the suggestion of corrective measures being considered off-topic.

[edzieba]

No need to despin the entire hub (which needs a bunch of bearings, rotating seals, and headaches). Despin a soft capture ring, and spin it (and the visiting vehicle) up before hard capture. But even easier is to spin up the visiting vehicle before soft capture, and implement the required RCS control for a rotating reference frame in software. As long as the visiting vehicle can handle spinning up on an axis about the centre of the docking adapter (may be an issue for Dream Chaser and HTV-X, depending on mass distribution) - something that is already a prerequisite for a vehicle to remain docked to the spinning station - then no additional hardware is then required above the standard IDA.

The easy solution to Starship's mass is not to dock Starship. Visit with any of the other existing (Dragon 2, Cygnus, CST-100) or proposed/in progress (Dream Chaser, HTV-X with proposed IDSS module) vehicles with an International Docking Adapter once the station is spun up, and use Starship for initial construction prior to spinup, or despin the station for any major module additions or changes.

---

Also, one last addition on the intermediate-axis problem, as already covered well by Paul451: It's the moment of inertia of the intermediate axis that is the issue, not the actual mass distribution ('balance'). That a visiting vehicle is 'off axis' is not a factor, only its contribution to that axis' moment of inertia. As long as the attached visiting vehicle is not sufficient to turn the initial rotation axis into the intermediate axis (in terms of moment of inertia) it is not an issue whether it is 'balanced' or not.

Bottom line, which Paul hasn't gotten to yet.  Non-rotating hub.

Because it's beyond the scope of this design, and therefore not relevant to the thread.

[It's also, IMO, a bad option. But that's a topic for the general rotating-stations thread.]

I don't understand this type of comment.  Continue discussing a faulty design, with the suggestion of corrective measures being considered off-topic.

Because a spinning hub is a solution in search of a problem, when the problem has yet to be demonstrated to exist.

[meekGee]

I'm going to re-order the conversation, for a reason:

They won't out-mass Starship, but they should have enough inertia (especially if they include radiators on the back) to have more rotational inertia than a small capsule/module docked close to the centre.

A Starship will never dock with this station. Never. Too dangerous.

Why? The Starship is not built to be stable when rotating, and besides the buttload of weight at one end of the ship (i.e. the engines), you have large tanks with lots of propellant that can slosh around and change momentum and center of gravity in ways that are likely unpredictable.

No captain of a Starship in their right mind would try to mate to a rotating space station.

What I think they will use, and what I'm assuming for my designs, is what you also suggested - some sort of small capsule/module to transfer cargo and crew. It could be a vehicle they keep at the station, which shuttles between the station and the visiting vehicle. Or it could park away from the station when not used. That is also what my plans call for.

Look, even the solar panels won't be perfectly balanced from a purely mechanical standpoint (i.e. imperfections, etc.), so the weight and weight distribution will be slightly different on each side (and this ignores how the inside of the station is balanced with cargo and crew).
But let's say that the solar panels are perfectly balanced.
[...]
From a physics standpoint they are just masses hanging off a larger mass, and if the amount of solar panels on each side, by mass, is the same, then their masses cancel out.

The solar panels don't been to be perfectly balanced, nor do their masses "cancel out".

They are in the plane of rotation...

They are in the plane or rotation no matter what orientation to the station they are in. Rotate the panels 90 degrees on the body of the station and they are still in the same exact plane of rotation for the body of the station. That is because there are an equal number of them on either side of the body of the station, so they don't affect the center of gravity for the cross section of the station, regardless what rotational position they are in.

...which adds momentum to the plane of rotation...

Take any point on the solar panel, then measure across the center of gravity for the cross section of the station, and you'll find the momentum change is likely negligible regardless how the panels are rotated.

And speaking of rotation, if this station is in orbit around the Earth, and the station itself is rotating, how the heck are the panels they show going to be effective? Are they going to be swiveling at the rpm of the stations, as well as the rpm of the orbit around the Earth?

Not sure I understand their solution yet... 

When the vehicle is attached to the side of the station, perpendicular to the solar panels, it won't be balanced by another vehicle (or mass) on the opposite side

"Balance" is irrelevant to the intermediate axis issue. If you had a balancing mass on the opposite side, it would increase the total potential rotational inertia in that axis, increasing the likelihood that is has more inertia than the axis with the solar arrays, thus increasing the likelihood that it will become the new secondary/intermediate axis, making the structure unstable.

I only mention balance to describe how the panels are not really a factor in regards to a vehicle docking at the station. The vehicle docking at the station will add weight/mass perpendicular to the direction of rotation, though because the station is a cylinder, the cylinder can easily rotate to bring the vehicle into the plane of the rotation.

If that happens, then undocking becomes far more difficult without using station thrusters to reorient the station so that the vehicle can leave to the side (just as it arrived). But relying on station thruster means that you have to have the propellant onboard in order to release the visiting vehicle - not really fail safe.

Starship does go from zero g to multiple g in various directions, with some propellant, when doing EDL.

I wouldn't rule it out.

[meekGee]

If the station is rotating at 4 revolutions per minute in order to create 1G at the ends, how do you spin a Starship up to 4 RPM and have a predictable center of rotation?

This is the part of their proposal which doesn't work at all.

Spinning the rotation up and down is not a good idea either. 

They need a central, non-spinning hub with electromagnetic bearings and enough play to balance the Starship when it docks.  An adjustable dead mass on the other side of the baton would also be helpful.

But what is the approach of the Starship?  Nose first, perpendicular to the axis of revolution? Or parallel, somehow at the center of mass of Starship?

De-spinning for visiting vehicles sounds awful to me.

If you need a non rotating docking hub, it can be added later - you just need an expansion port at the center of the center module.

Either way (rotating hub or rotating ship) , if you want to dock, you need the location center of rotation of the station to be controlled very precisely, to coincide with your rotating or non-rotating dock.

The best way I can think of doing that is shuffling waters between tanks.

EDIT:  I'm taking that back. You can design both a rotating and non-rotating docking hub to take out the offset.

[Paul451]

De-spinning for visiting vehicles sounds awful to me.

It's the cheap option. If you're trying to develop a low-cost, 1st-gen commercial station, it has to be on the table compared to complex options like separate logistics-shuttles, counter-rotating hubs, and the risks of docking under rotation.

And IMO, it's not unreasonable to expect an early station to be on a resupply and crew rotation schedule similar to ISS. Say once every three or six months.

While a 40 person 100m-long station seems to argue for more rapid ship visits and crew swaps, if you've got a resupply vessel the size of Starship, you don't need to resupply more often, so it's not unrealistic to think that ISS-like operation could still be common for early stations.

That doesn't even mean that experimental runs are limited to, say, three months. Many experiments (especially life-science) will be able to tolerate a few days of micro-g during de-spin. So even for multi-year, multi-generation animal/plant studies, I doubt having to regularly despin will be too complicating for useful research. Annoying. But you have to trade annoyance against simplified RPOD.

In the general rotation stations thread, Mike Lepage made an interesting point that his group thinks that there's going to be demand in the micro-g manufacturing market for a spin-g facility that despins during manufacturing runs, but provides gravity during set-up, harvesting, maintenance, etc. They think micro-g manufacturing will only want short bursts of zero-g. [edit: reading is hard] If so, then regularly despinning will be SoP for commercial stations.

[Coastal Ron]

De-spinning for visiting vehicles sounds awful to me.

It's the cheap option. If you're trying to develop a low-cost, 1st-gen commercial station, it has to be on the table compared to complex options like separate logistics-shuttles, counter-rotating hubs, and the risks of docking under rotation.

And IMO, it's not unreasonable to expect an early station to be on a resupply and crew rotation schedule similar to ISS. Say once every three or six months.

Putting my supply chain hat on, I find the assumption that a Starship has to be the only option for resupply and crew rotation to be odd. Also, assuming that the station will have to take on 3-6 months of supply at a time (and disgorge 3-6 months of trash) just doesn't make sense to me.

Here we have an organization creating the most complex space station ever built, but the solution for logistics is to also build a very low-tech zero-G logistics warehouse that floats close to the station. Then just use a space-only cargo/crew vehicle to make runs between the warehouse, the visiting vehicle, and the rotating space station. That allows the station to carry the least amount of unneeded material, and maximizes the micro-gravity experiment space.

As to docking with a rotating space station, once intermediate axis issues are resolved, then you just have a rotating capture mechanism that can capture, then rotate and dock the cargo/crew vehicle.

This would eliminate the need to de-spin the station for logistics reasons, and even for crew transfer reasons - though there may still be other reasons for occasionally de-spinning the station.

In the general rotation stations thread, Mike Lepage made an interesting point that his group thinks that there's going to be demand in the micro-g manufacturing market for a spin-g facility that despins during manufacturing runs, but provides gravity during set-up, harvesting, maintenance, etc. They think micro-g manufacturing will only want short bursts of zero-g. If so, then regularly despinning will be SoP for commercial stations.

Manufacturing usually needs long periods of consistent conditions to solve production problems, and the same with science in general. I would imagine that if given the choice between full time artificial gravity or short periods, that most everyone would choose full time. Assuming they can access their work and resupply while the artificial gravity is in effect.

We need revenue sources to support space stations of every kind in space, so likely whatever the first customers want is what they will get - whichever version of rotating space station that may be.

[Paul451]

Here we have an organization creating the most complex space station ever built

If they do, then they've failed, IMO.

Then just use [...]
[... ]then you just have [...]

If you find yourself describing your solution/proposal as "then just", then you're... just... wrong.

In the general rotation stations thread, Mike Lepage made an interesting point that his group thinks that there's going to be demand in the micro-g manufacturing market for a spin-g facility that despins during manufacturing runs, but provides gravity during set-up, harvesting, maintenance, etc. They think micro-g manufacturing will only want short bursts of zero-g. If so, then regularly despinning will be SoP for commercial stations.

Manufacturing usually needs long periods of consistent conditions to solve production problems, and the same with science in general. I would imagine that if given the choice between full time artificial gravity or short periods, that most everyone would choose full time.

You got the situation backwards. Mike is talking about micro-g manufacturing. The actual production is in free-fall. He believes such processes will operate on a 90/10 system, where the manufacturer spends 90% [Edit: 10% - reading is hard] of their time setting up the next production run and harvesting/post-processing the results of the prior run, during which time AG can drastically lower their cost of ops. The station despins during the actual production run.

[JohnFornaro]

The problem has yet to be demonstrated to exist.

Then what are all your proposed solutions addressing?

[Twark_Main]

The problem has yet to be demonstrated to exist.

Then what are all your proposed solutions addressing?

The only detectable problem is you chanting "non-rotating hub" over and over, and believing that this somehow constitutes a valid technical argument. 

[Twark_Main]

Can't see any sign of such a vehicle on their site.

Unsurprising, since the station render itself was only posted a few days ago.

I meant it isn't mentioned on the site, anywhere in the description of the station.

What, the tiny two sentence paragraph? Again, color me unsurprised.

It's clear they're not sharing all their cards yet. So saying "they didn't show us that card!" isn't terribly informative.

No radiators either.

As mentioned, I suspect the radiators are on the backside of the PV. If you look closely, you'll note that the "PV" is actually made up of two slightly different size panels, one in front of the other.

I think you are reading way more into a hand-drawn sketch than is there.

And I think you're silly to believe a bunch of ex-SpaceXers somehow "forgot" something as basic as radiator panels.

You're welcome to bow out if you'd prefer not to discuss the image at all.

It looks like the panels might not pivot.

I'm not trying to read anything into the "look" of the sketch, [proceeds to read into the sketch, which is a visual medium so is nothing other than its "look"]

So it's okay when you do it.

"You're reading too far into the sketch" and "Paul451 happens to disagree with you" are now officially indistinguishable. 

my speculation about them being fixed is because they can be, so why wouldn't you. The rotational axis can be pointed at the sun, so the arrays will permanently face the sun.

My thoughts exactly.

"Perfection is achieved not when there is nothing left to add, but when there is nothing left to take away." -- Some Smart Guy

[JohnFornaro]

The problem has yet to be demonstrated to exist.

Then what are all your proposed solutions addressing?

The only detectable problem is you chanting "non-rotating hub" over and over, and believing that this somehow constitutes a valid technical argument. 

That's not really an argument.

Anyhow, the baton design has a number of problems as pointed out above.  I certainly approve of the Vast team proposing a rotating station of some sort in principle.

[Twark_Main]

The only detectable problem is you chanting "non-rotating hub" over and over, and believing that this somehow constitutes a valid technical argument. 

That's not really an argument.

That's what I said. Finally some agreement in this thread! 

As a reminder, your latest "argument" was:

  • a logistic vehicle also adds complexity. This is obvious. But this doesn't kill the idea of a logistic carrier. At best this rhetoric would merely get you to "six of one and half-dozen of the other"

  • a logistics carrier would require astros move cargo twice. This is just bad planning. Simply load cargo on the ground and launch the entire module, like MPLM/HTV/Cygnus.


Your tactic has been to consistently over-inflate the impact of relatively trivial objections, then claim that your preference is the only option left "by default." Don't do that.

[Twark_Main]

A logistics carrier would greatly reduce the cost of ground processing. Rather than tie up a Starship for days-to-weeks while cargo is loaded by hand ($$$ due to large opportunity costs), Vast can load cargo and inspect the work at their leisure.

Lower cost, and less risk of "go fever" too.

This reason alone is probably enough to choose a logistics carrier design.

[Twark_Main]

Regarding 1G at 4.25 RPM, I don't understand why they would want to test for that, because we know that humans are already adapted to 1G, so I'm not sure why that should be a high priority.

Control group.

Lets you separate the side-effects of spin (if any) from the effects of partial-g, and controls for effects of the station itself: ECLSS, air-quality/VOCs, vibration, noise, people/carers, that annoying high-pitched buzzing from the lights they won't fix I keep putting in maint.reqs but noone ever does anything this wouldn't happen at NASA I hate my job if I wasn't under contract I'd...

It's not highly necessary (IMO) for early work looking for big-obvious effects. But if there is an unknown quirk on the station equivalent to the CO2 issue on ISS, you'll end up needing to do a 1g run to figure it out.

This.

For biomedical research, the other big one is radiation in LEO.

[JohnFornaro]

Your tactic has been to consistently over-inflate the impact of relatively trivial objections, then claim that your preference is the only option left "by default." Don't do that.

I'm not sure which "trivial objections" you're referring to.  Anyhow, it's not about "tactics", it's about one's argument and whether it makes sense.

[Twark_Main]

I'm not sure which "trivial objections" you're referring to.

Read my post.

[edzieba]

The problem has yet to be demonstrated to exist.

Then what are all your proposed solutions addressing?

My 'proposed solution' is to not despin anything, and instead rotate the visiting vehicle.

ISS RPOD already requires the visiting vehicle to match relative rotation rates (in all 3 axes) with the ISS, those rates are just sufficiently low that you do not notice unless in extreme time lapse. If both were left to their own devices you'd see them 'tumble' relative to each other once per orbit (neither are gravity gradient stabilised). Thus 3-axis rotation matching for docking a visiting vehicle with a rotating object is current state of the art, and the major change is to increase the maximum rotation rate that can be tolerated. Don't try and solve a problem by adding hardware if that problem does not exist in the first place.

[bad_astra]

There's no such thing as a non-rotating anything in orbit. Such a hub is just going to be rotating contrary to the motion of the larger station in such a way that makes it appear so to the observer, whose position is also relative to some other body. That stability achieved via the vehicles RCS. So why not just use the RCS and match the rotation of the larger item and be done with it?

So a "non-rotating hub" becomes something equivalent to a tourbillon in modern watchmaking, an extreme complication with very little use beyond showing off the degree of difficulty to which it was designed and implemented.

[Robotbeat]

Because if your docking port’s center is even slightly misaligned with your axis of rotation, it will wobble around and make docking impractical. Better to offload that to the station side.