Realistic, near-term, rotating Space Station

[JohnFornaro]

have tree cover which shades part of the corn

Sounds like a good opportunity for directed evolution / selective breeding, to select for good quality but more compact corn seed, etc.  That, too, will be a source of available feed stock, not just what we have on hand at the moment.

"Directed Evolution"?  You don't work for James O'Keefe, do ya?

But yeah. A selective breeding program will have to be implemented from the beginning, I'd say. I'd previously suggested that a load of Eastern Forest dirt be sent up, complete with soil, microbes, small animals and insects, and all.  The mighty oaks and other large flora would have to be planted as seeds, obviously.  I say Eastern Forest since that's my specialty, but I've also suggested a different biota in each of the four quadrants.  One problem with the latter would be cross pollination and invasive species, which is readily addressed by several more stations with different biota, and a strict quarantine protocol.  For the time being, I'd just stay with the Eastern Forest.

One of the guiding prinicples I espouse is that the station will already be in the strangest of environments; the first settlers, crew, occupants, citizens, or whatever they're called, will be familiar with  Earthly environments, and the early station at least should change that as little as can be.  This, and reproduction is the primary reason for one gee, for example.

[JohnFornaro]

Anyway, this means that if the solar gain for a design is indeed 1350 W/m2, 24 hours a day, then the cooling required will cover over 4 times that area, so about 4m2 or radiators for evert square meter of solar window.
If you get your power from solar panels, then the radiator area will be about equal to the solar cell area.

So food production means lots of radiators!

You did a spreadsheet about that.  Care to modify?

I haven't given enough time to considering the back of my station -- the shady side.  I'm suggesting attaching Stirling engines to heat tubes, to extract as much electricity as possible.

[Coastal Ron]

To be fair John, your attempts to address Ron’s point about the intermediate axis theorem were oblique at best, and at this point I’m still not 100% sure you actually understand what it is and why it could a problem that appears with certain docking arrangements.
That said Ron, John did mention spinning tennis rackets by the longitudinal axis (i.e. the axis running through the handle), which is the axis of minimum moment of inertia and is stable. Spinning Starship on it’s longitudinal axis should also be stable, propellant or not, because it’s so much longer than it is wide.

The problem is that Ron often uses the wrong terms.

None of us are writing graduate papers here worthy of intense scrutiny. So if you think something I wrote in a rush may not have been clear, then ask. I do it all the time on NSF and in real life, and I highly encourage it... 

Plus, like I'm sure it is with most everyone here, space is an avocation for me, not a vocation, and I spend my time here to discuss, debate, and learn. There are some that contribute to this thread that I think I learn less from, but I think I've probably given "Likes" to pretty much everyone at some point - usually when they provided usual information.

Also, if we turn the mirror around I think the same things you are saying about me apply to everyone at some point. Just sayin'... 

Going by his description, he seemed to be talking about momentum exchange between the primary and tertiary axes, but keeps using the term "intermediate axis", which is a completely unrelated instability. The latter is an immediate and ongoing instability, the former is a slow one-way drift from a semi-stable primary axis rotation to stable tertiary axis rotation. Starship won't have an issue with intermediate axis instability when rotating around it's primary (long) axis, but because of the liquid propellant, people moving around, etc, it will try to move towards minor axis rotation if there isn't a mechanism to counter the momentum exchange.

I'll put it this way. The most stable rotation for a 50m long Starship will be to tumble end over end. And no matter how much you try to spin like the ship in the 2001 movie, at some point as the RPM increases the lack of RCS control authority will not be able to stop the mass of the Starship from moving to an end over end rotation.

It's a solved problem in satellites, but it hasn't been done on the scale of Starship. (Indeed, nothing's been done on that scale.) It requires a movable mass (which can be a liquid in a specially shaped tube) that moves counter to the propellant's motion. I suspect the flaperons of Starship can be used as an active control system during docking, but an additional passive system might be desirable. (Belt'n'braces.)

Satellites don't experience the same conditions, so not sure what you are talking about. And the amount of sloshing propellant a Starship will be carrying is just a mitigating issue, not the primary issue. The primary issue is the length of the Starship, and the substantial mass at the far ends of that length that will overcome any attempt to rotate the Starship around its smaller diameter.

In the transportation world, inherent stability is what everyone tries to build. So if you need RCS to maintain stability, that won't be looked at as a preferred method - those with money at risk won't allow it.

[Twark_Main]

I ran my station thru Mike Le Page's calculator.  I used ( Raptor engines, the idea being that they would be paired on both sides of the ring at the spoke pieces.

Anybody know where I can get 25K tons of propellant?

[Edit:  Correction ... 21K tons of propellant!  Apparently the ISP of the Raptor is 360-ish, not 300.  Such a deal!]

Once you get started, Oooo, it's hard to stop.


[snip]

Has anyone noticed that the calculations in this spreadsheet appear to be wrong?

I can't reproduce the torus moment of inertia number. It's supposed to be I = m/4 (4 R² + 3 r²), but I notice that the spreadsheet uses not minor and major radii (r and R), but inside and outside radii (where r_inside = R - r, and r_outside = R + r).

[LarryCanuck]

"There's a lot of practical ag problems that hydroponics has that dirt farming doesn't have.  Fortunately, they seem to be engineering problems which can be solved."
 Sure, it's all a 3D packing problem. Some cubic grow spaces/cubes, if you will, could be tens of feet high, for fruit/nut trees - or corn. My point is that hydroponics gives the greatest density of nutrition per square foot of real estate, on earth or in space. And very effective atmosphere scrubbers. (quoting my alter-ego, Captain Obvious) 

[mikelepage]

I ran my station thru Mike Le Page's calculator.  I used ( Raptor engines, the idea being that they would be paired on both sides of the ring at the spoke pieces.

Anybody know where I can get 25K tons of propellant?

[Edit:  Correction ... 21K tons of propellant!  Apparently the ISP of the Raptor is 360-ish, not 300.  Such a deal!]

Once you get started, Oooo, it's hard to stop.


[snip]

Has anyone noticed that the calculations in this spreadsheet appear to be wrong?

I can't reproduce the torus moment of inertia number. It's supposed to be I = m/4 (4 R² + 3 r²), but I notice that the spreadsheet uses not minor and major radii (r and R), but inside and outside radii (where r_inside = R - r, and r_outside = R + r).

Technically true, but I used the more general equation for an annular disc of indeterminate width, since none (EDIT: few) of the designs we’re working on actually have a circular cross-section and I think it’s more useful this way anyway. Feel free to change it.

[Coastal Ron]

"There's a lot of practical ag problems that hydroponics has that dirt farming doesn't have.  Fortunately, they seem to be engineering problems which can be solved."
 Sure, it's all a 3D packing problem. Some cubic grow spaces/cubes, if you will, could be tens of feet high, for fruit/nut trees - or corn. My point is that hydroponics gives the greatest density of nutrition per square foot of real estate, on earth or in space. And very effective atmosphere scrubbers. (quoting my alter-ego, Captain Obvious) 

The Netherlands have focused on being more efficient with less land, and this article does a nice job of covering what they are doing:

Netherlands is the second-largest exporter of agricultural products - Washington Post

Relevant quote:

The country has nearly 24,000 acres — almost twice the size of Manhattan — of crops growing in greenhouses. These greenhouses, with less fertilizer and water, can grow in a single acre what would take 10 acres of traditional dirt farming to achieve. Dutch farms use only a half-gallon of water to grow about a pound of tomatoes, while the global average is more than 28 gallons.

They obviously leverage free air and free solar radiation, but I think it points to what the possibilities could be for human outposts and colonies off of Earth.

[lamontagne]

Anyway, this means that if the solar gain for a design is indeed 1350 W/m2, 24 hours a day, then the cooling required will cover over 4 times that area, so about 4m2 or radiators for evert square meter of solar window.
If you get your power from solar panels, then the radiator area will be about equal to the solar cell area.

So food production means lots of radiators!

You did a spreadsheet about that.  Care to modify?

I haven't given enough time to considering the back of my station -- the shady side.  I'm suggesting attaching Stirling engines to heat tubes, to extract as much electricity as possible.

If you do that, the radiator will bet even larger.... since they will be colder and radiation is to the fourth power of the temperature. You already have way too much power on a station, in particular a food producing one.  You want to reduce power usage, not add to it :-)

[lamontagne]

"There's a lot of practical ag problems that hydroponics has that dirt farming doesn't have.  Fortunately, they seem to be engineering problems which can be solved."
 Sure, it's all a 3D packing problem. Some cubic grow spaces/cubes, if you will, could be tens of feet high, for fruit/nut trees - or corn. My point is that hydroponics gives the greatest density of nutrition per square foot of real estate, on earth or in space. And very effective atmosphere scrubbers. (quoting my alter-ego, Captain Obvious) 

The Netherlands have focused on being more efficient with less land, and this article does a nice job of covering what they are doing:

Netherlands is the second-largest exporter of agricultural products - Washington Post

Relevant quote:

The country has nearly 24,000 acres — almost twice the size of Manhattan — of crops growing in greenhouses. These greenhouses, with less fertilizer and water, can grow in a single acre what would take 10 acres of traditional dirt farming to achieve. Dutch farms use only a half-gallon of water to grow about a pound of tomatoes, while the global average is more than 28 gallons.

They obviously leverage free air and free solar radiation, but I think it points to what the possibilities could be for human outposts and colonies off of Earth.

Yes, and that is why I am suggesting 50-60 tonnes per hectare, while the average production in farms is about 10% that. Bananas are surprisingly productive.

http://marspedia.org/Food
 

[lamontagne]

Coastal Ron has hired me to illustrate a rotating airlock.  I'm really cheap, it just cost the time to explain!

First iteration, basic idea his, all errors mine.

There are two rotating seals, shown in green.  The flexible tube allows for many types of movement, the illustrated arms are a first attempt at showing some kind of restraining system, that maintains contact while limiting some movements but allowing others.

If a rotating seal fails to rotate, for some reason, there is always the second one.  So nicely redundant.

This is not a permanent connection.  It's a form of gangway, to be tucked away as soon as possible.

[Coastal Ron]

Coastal Ron has hired me to illustrate a rotating airlock.  I'm really cheap, it just cost the time to explain!

First iteration, basic idea his, all errors mine.

As usual lamontagne (Michel) is being modest, and the version he is showing is actually a simplified version of what I proposed to him, and it is actually a much better version for small station applications, so he gets a lot of credit. 

There are two rotating seals, shown in green.  The flexible tube allows for many types of movement, the illustrated arms are a first attempt at showing some kind of restraining system, that maintains contact while limiting some movements but allowing others.

If a rotating seal fails to rotate, for some reason, there is always the second one.  So nicely redundant.

As you know, I like to think of what happens when the unplanned happens, so this layout seems to provide some level of redundancy.

This is not a permanent connection.  It's a form of gangway, to be tucked away as soon as possible.

There is a larger version that may or may not be needed for larger stations - the version shown could probably be scaled up and not need to be retracted or otherwise stowed while not in use since it doesn't mass much.

The advantage of this approach is that the visiting vehicle does not need to rotate when transferring cargo and passengers to a rotating space station.

Lots of prior discussion about imprecise words, so I asked for visual help... 

Thoughts?

[mikelepage]

Let's exclude John's 3rd or 4th generation station for now, since his is so far out into the future that it is hard to imagine what reality will look like.

Most rotating space station designs being proposed are not really that big from a volume standpoint, and I have yet to see any that take into account all of the infrastructure that will be required for a full time community. Water systems, sewage systems, air storage and processing, warehousing, trash, etc. There is a constant amount of material going into a community and coming out.

My background is in manufacturing operations, which includes production and inventory control, so I think in terms of supply chains and flows of material. And I also think in terms of logistics.

Here on Earth the models we use are to separate out warehousing from the point of use. We even see that in the U.S. Navy with their use of supply ships.

Indeed. It's a knotty problem, but even so, are we really talking first generation space stations when the word "warehouse" comes into play?

I'm hoping I can put my proposed solution up for comment in the near future, but life keeps getting in the way. You may have noticed the figures I left filled into my calculator specified a toroidal station around 24-28m radius, Mars-G, massing somewhat more than 2x bigger than ISS, and perhaps 24-36 people on board at any one time. Modular construction architecture where the design of the modules/assembler system can be done out of Starship with minimum astronaut intervention.

That modular architecture includes (for example), the assumption that there's a cartridge system for astronaut waste solids and liquids. Each cartridge would plug into a standard interface in the toilet facilities located in all of the habitation modules. When each crew member's cartridge is ready to empty out, that crew member takes their cartridge down to a module dedicated to processing waste, which I've notionally named the Septics, Compost, Worms and Maggots (SCWorM) Module.  That's where they empty it out and put it in some kind of cleaning setup for sterilisation, then take a fresh cartridge and the cycle repeats. This module turns that waste into the feedstock used in the Algae Bioreactor and Aquaponics units, located all around the torus, that are intended produce some portion of the food and air required by the station.

All of these systems will benefit from partial spin gravity. It really is the research and recreation components will have priority on any space available at zero-G.

You can have multiple specialised habitats maintaining relative position as is done with satellites in a constellation, but for safety’s sake these will need to be hundreds if not thousands of km apart.

Why so far? Even if they are only a couple of km apart, that is a huge volume of space. You should calculate what percentage of the "sky" another station would occupy if you were looking at it from the station you are one - it would be very tiny. What is it that would cause a collision danger?

Plus everyone will know the relative distance and position on a constant basis, and there is no way for any of these stations to move quickly in any direction. And if the zero-G transit/warehouses also store propellant, then they will have station keeping ability that will likely exceed the station keeping ability of the rotating stations.

I can't give you a super precise answer. I just remember playing with some orbit propagation software and being surprised at how quickly you could see perturbations due to non-Keplerian effects (like mass cons and solar wind puffing up the atmosphere). IIRC, we're talking single digit km in the space of days. Also, they weren't necessarily things that would affect the whole formation equally - for instance you can have a big solar event and the whole formation's perigees drop by 10-20km in the space of a day (like what happened to that whole Starlink batch). If different parts of the formation have different mass-area profiles, you've got quite the traffic management problem - all of which is a non-issue if you just space them further from each other. In any case, it's unlikely you'll have spacing much less than 10s of km for a while yet, so I think any near term station has to be a single connected object to be considered realistic. 

So you’d be talking many hours if not days to transfer across, which would mean the transfer vehicle would have to be nearly as capable as Starship. Much more efficient if your design can accomodate direct Starship docking..

It depends on the use case (where the station is at, what is it being used for, etc.), and also on the design of the station. Does the station need daily, weekly, or monthly provisioning? How often are crew exchanges needed, and what is the flow of visitors? Will food be grown on the station, locally (like LMT's proposal), or is every shipped from Earth?

My assessment of all of that is that circumstances, including safety considerations (i.e. where do you abandon the station to?) will require that no rotating space station will be alone in space.

Oh, and I just thought of a solution for having a large non-rotating visiting vehicle dock with a rotating space station - not sure why no one else thought of it till now, but we'll find out when I detail it later (busy day, gotta go!). 

Curious to see your solution (is that what you asked Lamontagne to depict?). I much prefer this to having a cluster of stations.

I think you're right that you'll want space stations co located in orbits such that you can move from one to the next relatively easily so they can share provisioning and such, or safety in case of station evacuation, but even if its only a 3-6 hour transit, the transfer vessel still needs to be capable of supporting the passengers for days at a time. Better that you can handle a direct docking with a Starship.

[Twark_Main]

I ran my station thru Mike Le Page's calculator.  I used ( Raptor engines, the idea being that they would be paired on both sides of the ring at the spoke pieces.

Anybody know where I can get 25K tons of propellant?

[Edit:  Correction ... 21K tons of propellant!  Apparently the ISP of the Raptor is 360-ish, not 300.  Such a deal!]

Once you get started, Oooo, it's hard to stop.


[snip]

Has anyone noticed that the calculations in this spreadsheet appear to be wrong?

I can't reproduce the torus moment of inertia number. It's supposed to be I = m/4 (4 R² + 3 r²), but I notice that the spreadsheet uses not minor and major radii (r and R), but inside and outside radii (where r_inside = R - r, and r_outside = R + r).

Technically true, but I used the more general equation for an annular disc of indeterminate width

I'm not sure how using a different equation could be considered "more general"; it just doesn't match the describing text. 

Okay, so the documentation is the problem. But can you clarify, what is the shape exactly?

Do you mean a hoop with infinitesimal width? If so, is all the mass assumed to lie at the location of the major radius, the inner radius, or the outer radius?

Or are you assuming a toroid with a rectangular cross-section? That would at least make sense with the specification of both inner and outer radius.

I don't care what shape is used, but it should be no surprise if people are misled by misleading documentation.



Edit: I can't get either of these shapes to match the spreadsheet. It seems to be off by a factor of ~3x, which is too large an error to be explained by simply the difference between a torus vs. a rectangular toroid.

For instance, the example sheet linked has m = 1e6 kg, r_inner = 24 m, and r_outer = 28 m. If we assume a uniform rectangular toroid (or equivalently, an infinitesimally thin 2D annulus), then the moment of inertia should be I = m/2 (r_inner² + r_outer²) = 1e6 kg / 2 ((24 m)² + (28 m)²) = 6.8e8 kg m². However the spreadsheet gives the answer as 2.08e8 kg m².

[LarryCanuck]

[snip]
There are two rotating seals, shown in green.  The flexible tube allows for many types of movement, the illustrated arms are a first attempt at showing some kind of restraining system, that maintains contact while limiting some movements but allowing others.

If a rotating seal fails to rotate, for some reason, there is always the second one.  So nicely redundant.
[snip]

An elegant solution. An arriving astronaut, though, and cargo that they are carrying, would exit the Starship (or whatever) into a cylindrical room that is rotating around him/her at one revolution every 20 seconds, if I have that correctly. And they will have to "spin" themselves up, to match the station proper, by grabbing onto the interior wall or a handle or other structure. Will be disorienting, perhaps?
Or there could be some sort of spin-up mechanism that they could strap themselves into ...

[lamontagne]

[snip]
There are two rotating seals, shown in green.  The flexible tube allows for many types of movement, the illustrated arms are a first attempt at showing some kind of restraining system, that maintains contact while limiting some movements but allowing others.

If a rotating seal fails to rotate, for some reason, there is always the second one.  So nicely redundant.
[snip]

An elegant solution. An arriving astronaut, though, and cargo that they are carrying, would exit the Starship (or whatever) into a cylindrical room that is rotating around him/her at one revolution every 20 seconds, if I have that correctly. And they will have to "spin" themselves up, to match the station proper, by grabbing onto the interior wall or a handle or other structure. Will be disorienting, perhaps?

Time for another little movie? 
BTW I think Coastal Ron's station is turning at about 1 rpm, so perhaps not quite so bad.

[Coastal Ron]

[snip]
There are two rotating seals, shown in green.  The flexible tube allows for many types of movement, the illustrated arms are a first attempt at showing some kind of restraining system, that maintains contact while limiting some movements but allowing others.

If a rotating seal fails to rotate, for some reason, there is always the second one.  So nicely redundant.
[snip]

An elegant solution. An arriving astronaut, though, and cargo that they are carrying, would exit the Starship (or whatever) into a cylindrical room that is rotating around him/her at one revolution every 20 seconds, if I have that correctly. And they will have to "spin" themselves up, to match the station proper, by grabbing onto the interior wall or a handle or other structure. Will be disorienting, perhaps?

Keep in mind that the gangway is not rotating, so the cargo and passengers coming out of the visiting vehicle can safely exit without any orientation concerns. It is when the cargo and passengers want to exit into the station that the orientation issues come into play, and they are not trivial when cargo of substantial mass is concerned. But I think simple techniques can be worked out.

And of course cargo and passengers leaving the station need to handle the RPM change too, but you could have equipment on the station that would pre-spin up the large cargo to match the gangway RPM. People I don't think will have an issue as long as someone in the gangway are assisting.

Plus, keep in mind that this is a solution for applications where the whole visiting vehicle cannot be captured by the station.

[Coastal Ron]

[snip]
There are two rotating seals, shown in green.  The flexible tube allows for many types of movement, the illustrated arms are a first attempt at showing some kind of restraining system, that maintains contact while limiting some movements but allowing others.

If a rotating seal fails to rotate, for some reason, there is always the second one.  So nicely redundant.
[snip]

An elegant solution. An arriving astronaut, though, and cargo that they are carrying, would exit the Starship (or whatever) into a cylindrical room that is rotating around him/her at one revolution every 20 seconds, if I have that correctly. And they will have to "spin" themselves up, to match the station proper, by grabbing onto the interior wall or a handle or other structure. Will be disorienting, perhaps?

Time for another little movie? 
BTW I think Coastal Ron's station is turning at about 1 rpm, so perhaps not quite so bad.

My Mars-gravity station rotates at 3 RPM in order to keep the diameter as small as possible, so this will be both a solution that I can use (probably mounted on one side of the station hub), and an operating condition that we will have to live with.

[LarryCanuck]

Lamontagne "suggesting a movie" reminds me of a short video I saw a while back, where an astronaut was positioned, stationary, in the middle of a segment of the ISS, a couple of feet away from the closest wall. He was completely unable to move, flailing his arms and legs, until another astronaut "rescued" him by grabbing onto him. 

[LMT]

NN GNC in the field

[Coastal Ron]

NN GNC in the field

2D navigation in crowded conditions is not relevant to realistic, near-term, rotating space station.

And if you look at the chart of how much human intervention Tesla FSD needs (starting at 2:20), you'll see that it is still nowhere close to be reliable.

But again, Tesla 2D driving software is not relevant to this topic, because EVERYONE knows that computer systems can do navigation tasks in the right conditions - commercial airliners can take off, fly a route, and land on their own with no human intervention. So this is not new, or news.