Space station artificial gravity - how to spin up to speed?

[jbriggs444]

The necessary technology to spin up a space station has been available for over a century. Make a big Crookes Radiometer by fitting paddles to the periphery of the station. Paint one side white and the other side black so solar radiation pressure can spin up the station. Then rotate half of the paddles to face backwards which will regulate the speed. Quick adjustments to rotation rate can be made by hanging stores from the hub inside the spokes. Changing the length of the winch wire will change the radius to the centre of mass of the stores and so will change rotational velocity.

But what to do with the gerbils already hired to keep the station turning?

 

[Baluncore]

But what to do with the gerbils already hired to keep the station turning?

Don't feed them, eat them.

 

[anorlunda]

It doesn't make sense to compare an electricity source to propellant. What are you going to do with electricity? Accelerate propellant. That's the ion thruster case I calculated.

Yes it does make sense. You could use solar to power an electric traction motor to accelerate rotation of a reaction wheel. No propellant needed. I think that was the thrust of the OP's question.

 

[mfb]

The necessary technology to spin up a space station has been available for over a century. Make a big Crookes Radiometer by fitting paddles to the periphery of the station. Paint one side white and the other side black so solar radiation pressure can spin up the station. Then rotate half of the paddles to face backwards which will regulate the speed. Quick adjustments to rotation rate can be made by hanging stores from the hub inside the spokes. Changing the length of the winch wire will change the radius to the centre of mass of the stores and so will change rotational velocity.

Radiation pressure is 3 μPa. For a very lightweight station of 100 kg/m², and assuming perfect heat conduction away from the black side, you get an acceleration of 3*10^-8 m/s² at the place of your paddles. Spinning the station up to 30 m/s with radiation pressure will take 30 years.
No way.

Yes it does make sense. You could use solar to power an electric traction motor to accelerate rotation of a reaction wheel. No propellant needed. I think that was the thrust of the OP's question.

That was an alternative discussed earlier, yes, but not in the post you quoted.

 

[Al_]

The necessary technology to spin up a space station has been available for over a century. Make a big Crookes Radiometer by fitting paddles to the periphery of the station. Paint one side white and the other side black so solar radiation pressure can spin up the station. Then rotate half of the paddles to face backwards which will regulate the speed. Quick adjustments to rotation rate can be made by hanging stores from the hub inside the spokes. Changing the length of the winch wire will change the radius to the centre of mass of the stores and so will change rotational velocity.

Radiation pressure will work very, very slowly, to start with.
Moving masses away from the CM can't slow the rotation to a halt completely. Space inside the station is at a premium so unlikely to be possible to move lots of mass to near the rim.
It might not even have spokes, it might have low-g upper floors.
The arrangement doesn't cancel gyroscopic forces.

 

[sophiecentaur]

. The window for contact is constrained very tightly by space as well as time.

Not really. The actual time that your path takes you to coincide with the (continuous) periphery rail hardly matters at all if the ship can make contact with any point on the perimeter rail. A boat arriving at an uncluttered mooring pontoon only needs to get its course and speed right and can arrange to touch on at any time.
In the sort of system I am thinking of, the capture mechanism could extend over several metres of intercept area. I wouldn't call that a tight constraint, considering the last very successful landing system that was used on Mars, in which timing was highly relevant. (Who would have thought of sky crane without knowing a lot about space landings?)
The consequence of a flyby due to 'failure to connect' would be, say, 60m/s worth of fuel and not any sort of disaster; just an expensive one-off. An actual collision with an inner part of the wheel would not be good news but that would be predicted with loads of time to spare and the abort procedure would be very similar to that for any medium speed collision.
I am no longer touting my system for business but I want to make sure that the objections are not just intuitive. People seem to be ignoring the fact that, in space manoeuvres, there are no surprises due to wind and waves. Also, we are not talking in terms of a man with a joystick and a thrust control for this sort of system.
Any capture mechanism could be expected to cope with a (radial) distance offset of a metre or so and I can't see that the navigation would have a problem with flying the ship to an accuracy of course of a fraction of a metre. The actual time of the contact is not very significant; what counts is the distance between the rail and ship's course.
Aiming to kiss the rail but ending up 1m closer will result in a radial ('vertical')speed of around 4m/s. 0.1 m gets a vertical speed of around 1m/s. How does that compare with aircraft undercarriage performance? Reading various flying forums, I get the impression that a commercial jet makes a 'good' landing at around 1m/s and an undercarriage can cope with several times that. There is no direct comparison between the two structures and an aircraft undercarriage has other things to deal with but the cost of a bad aircraft landing can be the deaths of hundreds of passengers, which is comparable with the disaster of taking our a whole space station. In either case, it needs to be 'right'. But the 'landing would be arranged to be appreciably outside the surface with a very low possibility of 'ploughing in'. I would envisage the ship, once captured, would be (in their view) hanging from the rail by an appropriate length of suspension. Once settled, it would move along the rail and branch off to an entry port,. Another ship could arrive or depart very soon after - just like at an ariport..
Those figures are not sufficient to reject the idea - even if there are lots of other valid objections to the system. My scenario is based around a busy and pretty massive space station. That could well make it a totally unreasonable suggestion - but that's not the purpose of this post.

 

[mfb]

The actual time that your path takes you to coincide with the (continuous) periphery rail hardly matters at all if the ship can make contact with any point on the perimeter rail.

10 seconds before docking, you know you'll either dock in 10 seconds (+- a very small window for steering) or not at all in this attempt. If something needs more time, you have to scrub the attempt, waste 60 m/s of delta_v and try again.

That's an issue you don't have if you dock to the non-rotating part.

 

[sophiecentaur]

10 seconds before docking, you know you'll either dock in 10 seconds (+- a very small window for steering) or not at all in this attempt. If something needs more time, you have to scrub the attempt, waste 60 m/s of delta_v and try again.
That's an issue you don't have if you dock to the non-rotating part.

I should hope that you would know if your course was good along a tangent a lot more than 10s before contact. I'd reckon in terms of many minutes, with plenty of time to correct course. Speed difference could be +/- 0.1m/s which would be well within the capabilities of a coupling mechanism. You could do that by hand and eye, even.
If you got it a bit wrong and you kiss at 9.5 seconds, because of a small difference in velocity, what is the difference? You latch on to a different part of the rail. The count down will be useful for the system to know when to deploy its grab / net / hook but why do you say you need to plan your rendezvous at a particular time? You draw a line on your nav chart (virtual) and, if that line is a tangent, that's all you need. Yes, you could miss but what could cause that miss? Is there a wind or a tide or waves, or pockets of warm air / turbulence? You must be subconsciously basing a lot of your objection on those things. There are none. Just consider the accuracy with which slingshot orbits involve and they are not something you can do much correction for. Fine tuning yes but you have only one shot at them and they have far more imponderables. Ship and station are comparatively so near to each other, when the docking course is set that the calculations have to be relatively straightforward.
What "something" are you suggesting could need more time? The tolerance to errors is way higher than you imply. Time doesn't matter. Speed difference is nothing like as important compared with a head-on docking. Course is important but you still have a up to a metre. according to my sums. (I do wish more people would commit themselves to some calculations in situations like this one. I am always grateful when someone shows me an error on my sums.)
I have already yielded to the point that docking with a non-rotating part has fewer obvious problems. I am just setting out some hard figures relating to the peripheral docking because the instinctive reactions do not agree with the simple sums.

 

[mfb]

Let me rephrase it:

300 meters before docking, you know you'll either dock in 10 seconds (+- a very small window for steering) or not at all in this attempt. If something needs more time, you have to scrub the attempt, waste 60 m/s of delta_v and try again.

300 meters. The time where currently a docking process still takes more than one hour. Why? To make sure the position and velocity are correct and can be controlled in every step, with multiple course corrections within this hour.

If you got it a bit wrong and you kiss at 9.5 seconds, because of a small difference in velocity, what is the difference?

You'll be off by 15 meter in some random direction if your velocity vector is wrong in arbitray directions.

 

[A.T.]

If you got it a bit wrong and you kiss at 9.5 seconds, because of a small difference in velocity, what is the difference? You latch on to a different part of the rail.

It's not about arriving late for dinner, but about having enough time correct the course. Velocity is a vector that can be wrong in magnitude and direction.

 

[sophiecentaur]

Let me rephrase it, too.
As long as your path is tangential and your speed is within fairly lax limits, the actual time of your arrival doesn't matter. I still get the feeling that you have not understood what I am describing. So many of your questions are based on colliding with the centre of the wheel. The centre of the wheel ( and the docking bay of the ISS) is a 'solid' object with little resilience. What I am discussing is nothing like that; it doesn't need to be because contact is 'outside' the station body. It can be flexible and allow for much more variation in position and speed. If you still have a problem, try drawing out the situation and do the same sums I have done, to work out the relative velocities and positions. The mechanical requirements are very much on the same lines as for aircraft landing gear. You do not seem to take that into account.
If you can tell me of a mechanism that can stop the ship from traveling in a straight line whilst drifting towards the station and how that line cannot be set up at a significant distance away then I could take on board what you are claiming.
I understand that the tolerances (lateral, alignment and speed) are very stringent for a normal docking. But the situation is really not the same for what I am describing. Why do you keep insisting that it is?

You'll be off by 15 meter in some random direction if your velocity vector is wrong in arbitray directions.

Why should it be, if all you are doing is aiming to keep to a line that's a tangent to the wheel? Do you not see how your time of arrival is of minor importance?

 

[A.T.]

all you are doing is aiming to keep to a line that's a tangent to the wheel

Which requires corrections for which you have limited time, because you have to approach the point of tangency at a fixed speed. At the hub you can approach as slowly as you wish.

 

[Baluncore]

Radiation pressure will work very, very slowly, to start with.

Yes. But I wanted to reapply riverboat paddle-wheel technology to the future.

I was also considering delivery of construction material by attachment while passing on the fly to a spinning loop, a polygon, or a star of carbon fibre cable with a great radius. Then using solar power to operate winches that symmetrically pull the construction modules towards the centre with the radius reduction and inherent angular acceleration.

It might not even have spokes, it might have low-g upper floors.

I think a docking hub with two spokes would be essential for access and construction. Note that transport of stores from the hub to the periphery would decelerate the 'station'.

The access hub of a rotating station is another possible application for the anti-twister mechanism.
https://en.wikipedia.org/wiki/Anti-twister_mechanism

 

[sophiecentaur]

Which requires corrections for which you have limited time, because you have to approach the point of tangency at a fixed speed. At the hub you can approach as slowly as you wish.

I have asked, in vain for some numbers here. How is it that the best artillery can achieve such high accuracy in placing shots under all the perturbations you get on Earth but you guys are claiming that course corrections are constantly necessary in the space docking scenario? What is it that can disturb the relative velocity of the ship so that a tangent to the wheel will be waving about? I realize that, over a longish period, there will be gravitational effects but will there really affect the motion, once the ship is a few km from the station? The objections I read have been a bit too arm waving and not quoting calculations or results of experiment. I am totally prepared to be convinced but the least you guys can do is to give me some numbers. PF threads don't work well on 'assurances' alone.
You can tell me as often as you like that a near zero velocity approach to the hub has its advantages. I accept that.

 

[Baluncore]

I don't think it is necessary to dock a delivery vessel to the rotating station to unload materials.

Delivery of most of the stores, material and crew to the rotating station should be by attachment of a modular delivery capsule to a long station tether while on a synchronous tangential flyby. The delivery capsule is pulled in, unloaded, then dismantled for reuse. The capsule would be assembled from a regular set of parts that are reused to fabricate more station modules.

Passengers in transit or crew on exchange could arrive and depart from the hub so as to save materials and conserve rotational energy. Exports should depart from the central hub. With time the station can grow in size while maintaining the same virtual gravity.

 

[A.T.]

I have asked, in vain for some numbers here.

https://en.wikipedia.org/wiki/Space_rendezvous#Rendezvous_phases

They currently have 45-90min for corrections over the last 100m. With your method they would have only a few seconds.

 

[sophiecentaur]

https://en.wikipedia.org/wiki/Space_rendezvous#Rendezvous_phases

They currently have 45-90min for corrections over the last 100m. With your method they would have only a few seconds.

Can you explain that reasoning? That argument would suggest that landing an aircraft would be too risky to undertake.
The fact that present docking uses a long period of time is no reason to suggest that the same limits apply to the alternative method. Position, velocity and time are all less critical. You do not need to have zero relative speed and the lateral tolerance could be a matter of metres. Please tell me what perturbations can be present to cause a problem. Does the 30m/s speed difference produce an incalculable uncertainty in the rendezvous point?

 

[A.T.]

That argument would suggest that landing an aircraft would be too risky to undertake.

An aircraft cannot hover / land slowly without using lots of fuel and be specially build for it. A spaceship can do this naturally.

 

[sophiecentaur]

An aircraft cannot hover / land slowly without using lots of fuel and be specially build for it. A spaceship can do this naturally.

What is the relevance to that remark? Aircraft land perfectly well and, but for the vagaries of weather and the military, they would have an even better record of making contact with Earth at high speed. If an aircraft could hover for free, are you sure it would wait for 45-90 minutes to land, as a spacecraft takes to dock? You are not putting logical arguments together here. I asked for some (quantitative) reason to suggest that the accuracy of manoeuvring would be as bad as you claim. If it works for aircraft the why not for spacecraft ? (Same potential cost of human life.)

 

[mfb]

Aircraft don't land on ceilings where they have to get attached within a fraction of a second. They are also quite sturdy - their mass is not as important as it is for spacecraft , so they can handle larger relative velocities and accelerations. Compare to spacecraft s hey have a very large region to land, even on aircraft carriers.

Aircraft that can land vertically do that slowly as well. They don't take an hour for that, but they also don't do a hoverslam where you reach zero velocity exactly on contact.

 

[sophiecentaur]

We may as well finish this conversation if you can't give me a serious reason that the errors would be as high as your intuitions tells you.

 

[Baluncore]

With today's navigation technology the docking process would be automatic and use minimum fuel.

But I doubt a visiting ship would ever dock physically to the periphery of a rotating station without causing huge stresses within the station structure as the centre of the rotating mass was relocated. The angular momentum of the station would immediately fall as the visiting ship attached and changed from linear to circular motion. With the arrival of the visiting ship's linear momentum, the rotating station would move onto a new trajectory.

Departure would have a similar set of disadvantageous changes to angular and linear momentum.

 

[sophiecentaur]

With today's navigation technology the docking process would be automatic and use minimum fuel.

But I doubt a visiting ship would ever dock physically to the periphery of a rotating station without causing huge stresses within the station structure as the centre of the rotating mass was relocated. The angular momentum of the station would immediately fall as the visiting ship attached and changed from linear to circular motion. With the arrival of the visiting ship's linear momentum, the rotating station would move onto a new trajectory.

Departure would have a similar set of disadvantageous changes to angular and linear momentum.

I agree in principle. I must say, I have been thinking in terms of a massive space station and a modest sized ship. But the impulses could be spread over time by suitable use of resilient mountings for the rail and capture 'arm'. It would not be practicable to have to warn the crew "Incoming!"

 

[A.T.]

If an aircraft could hover for free, are you sure it would wait for 45-90 minutes to land, as a spacecraft takes to dock?

If an aircraft could hover for free, then it would use this ability to land. And no sane person would suggest it should instead land by approaching a rotating platform tangentially.

 

[sophiecentaur]

If an aircraft could hover for free, then it would use this ability to land. And no sane person would suggest it should instead land by approaching a rotating platform tangentially.

Neither your comments nor mine on that particular topic are relevant to the question I have been asking about the quantitative practicalities involved. Sanity is not a parameter that affects the risks (apart from a maniac behind the wheel, I suppose) The fact is that aircraft land in thousands, every day, with pretty basic automation and their approach speeds are very much higher than I am suggesting and conditions are orders of magnitude more variable. So there is no basic principle that says it can't be done. There is no point in more comments against the idea unless they involve actual numbers or new insights - such as . . . .

With today's navigation technology the docking process would be automatic and use minimum fuel.

This has been my opinion about the idea. I looked at a Wiki page about docking in space and it actually showed a picture of some guy using a rangefinder, through the spacecraft window, whilst docking with the ISS. I would agree that, if that's the sort of navigation you have available then creeping up to the docking bay as slowly as possible would have to be the way. We would have to assume next generation (or the one after that) systems would be involved.

With the arrival of the visiting ship's linear momentum, the rotating station would move onto a new trajectory.

Now that's a new and relevant idea, not based on intuition. The only question there would be 'by how much?' and that would depend on relative sizes. A change of orbit would not have to be a disaster if the station were in its own band of operation and there would be momentum changes in the other direction when the ship leaves.
Something that struck me is that the station could be used as a construction platform for building big ships for big voyages. They would certainly need to be non-rotating and, I guess, so would the materials, throughout their passage through the station.

 

[A.T.]

So there is no basic principle that says it can't be done.

Nobody argued otherwise. But the mere physical possibly doesn't make it a good idea for a standard operating procedure, if there are safer methods.

 

[sophiecentaur]

Nobody argued otherwise. But the mere physical possibly doesn't make it a good idea for a standard operating procedure, if there are safer methods.

Hmm. That's not how I have been interpreting your posts.
Safety in such matters is based on numbers and actual risk and that's what I'm after at the moment. Your comments have been along the same lines as what people say who have a phobia of flying. Percieved risk etc.
Apart from telling me that it's hard to aim at the periphery of a spinning wheel in space, you have actually added very little. I assume that most of your objection is based on what wiki can tell us and, from what I have read there, the majority of the stuff on Wiki describes historical or present systems. Not relevant.
The word "safer" is an advertiser's term. You are safer standing ten metres from the edge of a cliff than standing five metres away but how relevant and what is the actual risk involved? The risk of some medical conditions according to lifestyle are often discussed without talking of absolute risk. That's no use if you want to know the relevance to your life. How does the risk of a bad tangential docking compare to the risk of failed takeoff or re entry? Anyone who wants to be an astronaut will be putting themselves at more risk of dying at work than your average office clerk I reckon they all must be batty.

 

[A.T.]

Safety in such matters is based on numbers and actual risk and that's what I'm after at the moment.

Fixed time for last X meters versus as long you need, just in case something takes longer. It's obvious which is more fail save.

 

[sophiecentaur]

Fixed time for last X meters versus as long you need, just in case something takes longer. It's obvious which is more fail save.

So I take it, you have no answer and that you did not read my last post.

 

[mfb]

A faster approach is so much more risky that no one ever did it to save an hour.
Going to the ISS currently takes several hours. Which is a huge improvement over the previous standard procedure which needed 2 days.

No one has specific numbers for impact and other failure probabilities for such a system. That would need development of such a system. I'm not aware of anyone even considering that at the moment. Which means the experts think it is so risky that they don't even bother evaluating the risk in more detail.

 

[sophiecentaur]

Non risky space travel is an oxymoron.

 

[mfb]

Everything has a risk. 100 years of R&D brought the risk to die in an airplane flight down to 1 accident in several million flights - so low that you can safely neglect it as customer. Let's see what decades of commercial manned spaceflight can do, once they start.

 

[sophiecentaur]

I agree that time will tell. Incidentally, the R&D times for space flight and terrestrial flight are really not that different. (60 yrs vs 100yrs). I think it's more a matter of money spent than time taken.
But are you suggesting that commercial space flight will always involve docking between craft which uses the same techniques that they use these days?
Perhaps we are talking at cross purposes and our timescales are just very different.
At the moment, though, space travel is very risky and I can understand that you look upon every manoeuvre as a potential disaster. The survival statistics are really pretty dodgy, up till now but the whole business is so attractive that people choose to forget that. A climate in which there are people lining up to take a one way trip to Mars is perhaps one in which the actual sums should be made more public.

 

[mfb]

I don't make predictions about "always". They would be as pointless as people in 1800 discussing how advanced mechanical calculators might be in 2000.
Who knows how spaceflight will look like in the distant future. Maybe we don't dock at all because the concept of spacecraft flying around is as outdated as mechanical calculators are today.

The only timescale where we can hope to get predictions right is the not so distant future. Rotating space stations are possible with today's technology (and dedicated R&D of course). Within the foreseeable future, docking will look similar to today. The details change, but the main concept does not: Spacecraft approach each other, connect to each other, establish a solid mechanical contact, and make it airtight and combine their pressurized volumes if docking is done for manned spacecraft .

 

[sophiecentaur]

Who knows how spaceflight will look like in the distant future. Maybe we don't dock at all because the concept of spacecraft flying around is as outdated as mechanical calculators are today.
The only timescale where we can hope to get predictions right is the not so distant future. Rotating space stations are possible with today's technology (and dedicated R&D of course). Within the foreseeable future, docking will look similar to today. The details change, but the main concept does not: Spacecraft approach each other, connect to each other, establish a solid mechanical contact, and make it airtight and combine their pressurized volumes if docking is done for manned spacecraft .

Did we ever disagree about that?

as pointless as people in 1800 discussing how advanced mechanical calculators might be in 2000.

In my experience, the majority of threads about space flight on PF are doing the equivalent of just that. You are being very pessimistic if you think that landing on the periphery of a rotating wheel couldn't be considered in the conceivable future. We wouldn't get far if we only did things 'the way we've always done them'. Your objections have been very backward looking from the beginning of this thread.

 

[mfb]

I'm sure someone studied that. No follow-up studies happened, at least none I would be aware of. Which usually means the approach was discarded as impractical.

It might become more realistic in the distant future. But then you still have disadvantages without advantages. I don't see the point.

 

[sophiecentaur]

I'm sure someone studied that.

Very likely but a citation would be useful - as for most PF topics. Their studies would, no doubt, have involved more calculations than intuitions. And that's all I am after.

without advantages.

Not so sure about that. Unless the central docking uses a lot of retro thrust at the last moment, there is a not inconsiderable delay for all arrivals. (In which case, your 'take as long as you like' argument doesn't apply and a failure would produce a serious crash*) In a tangential approach, you do not need to 'slow down' your linear approach speed and can more or less step off the ship onto the 'platform'. The deceleration is over in a couple of seconds. Mass transit type of process.
Of course, most of these ideas take us further and further into the future.
* The hub could be open and the ship could fly into the 'hole' and into an arrestor net; there's a possibly solution for every problem.

 

[A.T.]

In a tangential approach, you do not need to 'slow down' your linear approach speed

Why would this final delta v matter, given orbital speeds are several orders of magnitude higher? And all that linear impulse the tangential docking transfers to the station has to be corrected by the stations thrusters, so you don't save any fuel in total.

 

[sophiecentaur]

The effect on station orbital speed would depend on relative masses. It could be negligible. Also, when the ship leaves, the linear momentum would be back to what it was.

 

[sophiecentaur]

I read this again and I think I get the message this time. My point is that a constant approach velocity actually gets you there and at the right speed. The conventional method involves a gradual change in speed towards the final docking. (Zeno' Paradox at work ;-). This takes more time than what happens when you latch on to the rotating wheel. The approach involves no changes, once the right velocity is achieved. It's actually 'more' fail safe, involving, at worst, a miss or a glancing blow at low speed. Retro failure in the present system involves a major impact.

 

[mfb]

Retro failure in the present system involves a major impact.

It does not, because the approach speed is slow. The spacecraft never approach each other head on at significant speeds. At points where the relative velocity is larger (still small compared to 30m/s), they don't have to fly directly in the direction of the station.

 

[sophiecentaur]

So they have to fly a course that will not collide, until they fire the retros and then they have to do all manoeuvring at safe, low speed (= a long time). You can't have it both ways.
I have already acknowledged that the time factor is not that important these days.

 

[Al_]

Would it be better to have the pressure skin of the station remain static, and just spin the internal structure?
I'm imagining a station that does not have spokes - it's shape is just a wide disc or even a sphere.
This would mean windage losses between the hull and the spinning structure, but it would have one big advantage -
crossing between parts rotating at different speeds or in different directions would be much easier. You would cross at the hub.
There could even be a zero-g section there for experiments, processes, manufacturing etc.

 

[Al_]

Non risky space travel is an oxymoron.

Oooh, I don't know about that. The ISS has done maybe 2.7 billion miles already without a fatality on board.

 

[mfb]

This would mean windage losses between the hull and the spinning structure

Orders of magnitude higher than the overall power consumption of the space station, probably.

crossing between parts rotating at different speeds or in different directions would be much easier.

A vacuum-tight connector for different rotation speeds is certainly not the easiest component, but I would expect it to be possible.

Putting a zero-g section into a separate rotating part within the space station would be easier than the other option: much lower wind speeds.

You can't have it both ways.

Right, you cannot have the same safety as in a slow approach if you approach the station quickly, no matter where you dock. No one ever questioned that. No one suggested a hoverslam approach to dock at the hub.

Oooh, I don't know about that. The ISS has done maybe 2.7 billion miles already without a fatality on board.

~3% fatality rate for astronauts, not from in-orbit operation but from launches and landings.

 

[Al_]

~3% fatality rate for astronauts, not from in-orbit operation but from launches and landings.

What is the rate so far for docking maneovers? I can't think of one fatality.

 

[mfb]

0%.

1967: Parachute failure during landing: One Soyuz cosmonaut dies.
1971: Decompression while preparing for landing (but still in space): All 3 in a Soyuz capsule die, still the only deaths in space so far.
1986: Challenger explodes shortly after launch: 7 die
2003: Columbia disintegrates on re-entry: 7 die

Some more people died in atmospheric test flights or during ground operations

 

[A.T.]

I have already acknowledged that the time factor is not that important these days.

When will it ever be? When space travel becomes like air travel today? Here approach, landing, parking and docking to gate also takes tens of minutes. You are obsessing about a non-issue.

 

[csmyth3025]

AL: You mention a disc shaped space station. This concept has been described in detail by Al Globus, et al ( http://space.alglobus.net/papers/Easy.pdf )

I'm not sure why your concerned with a reaction wheel. A spinning space station will continue it's initial spin with very little need for adjustments to its angular velocity. The movement of supplies, people air and water within the structure presents a negligible change in the distribution of mass compared to the overall mass of the station. Moreover, cabled counterweights (similar to those used for elevators) can easily be reeled in and out to compensate for any minor wobble caused by changes in mass distribution.

The notion that a spinning space station will be spinning while it's under construction is no more sensible than expecting that a passenger airliner will be flown while it's under construction.

Docking at a central docking port is much safer because the closing velocities can be kept much lower. All that needs to be done is to impart a spin to the docking spacecraft that matches the spin of the station. This assumes, of course, that docking spacecraft are purpose designed with a docking port aligned with one of its axes of rotation.

A docking craft that matches a tangential velocity of 30 m/sec necessarily approaches the station at a closing velocity of 30 m/sec (67 miles/hr). Any navigational error or malfunction that results in an impact will potentially result in the same catastrophic damage as driving a truck into a brick wall at 67 mph. .

 

[jbriggs444]

Any navigational error or malfunction that results in an impact will potentially result in the same catastrophic damage as driving a truck into a brick wall at 67 mph. .

On the other hand, a navigational error or malfunction risks the same impact on a two lane highway every day of the week.