Two Starships in "bolas" rotation

On Oct/3/2019 at 12:18, David Spain wrote :
On 2019-07-26 2:44 PM, Niklas Holsti wrote:
On 19-07-26 20:54 , David Spain wrote:

Or even
more simply, just put the spacecraft into a spin along the flight path
vector. Thus no 2nd ship required or fancy rendezvous and un-tether
maneuvers needed.

Spinning (rolling) around the long axis would give a rotational radius
of only 4.5 m, max, giving disorientating Coriolis and other effects.
The pseudogravity would be radial, 90 degrees offset from the real
longitudinal gravity when the ship stands on its rear fins. Not good,
IMO.

The centrifuge in Discovery was small in radius since it had to be
contained within the pressure sphere of the hull (12.2 meters). I wonder
if AC Clarke had done the math on that?

https://en.wikipedia.org/wiki/Discovery_One

This would also allow incremental build-up of
spacecraft by joining future Starships together in LEO to make a larger
spacecraft.

I don't understand how the spin/roll is related to incremental joining
of Starships. In a Starship, one end "kicks" (the aft end) and the
other "penetrates" (the front end); they are not easily connected
together to form a larger living space. At most, one could dock two
Starships front-to-front. Can you clarify what you mean?


Yes you can dock front-to-front. If fact, what if you dock to a
habitation module like a large inflatable Bigelow module? Once in orbit
the nose of a Starship docks to an already inflated an constructed
habitation module where the diameter expands to 20-30 meters and the
circular 'decks' run parallel to each other along the inner
circumference. Now you have an artificial gravity environment where the
rate of roll is much, much less to achieve a given gravity and you get
this without needing a 2nd Starship and all the complexity of trying to
counterbalance two Starships. Of course two Starships could share this
hab module if docked at each end. The habitation module would remain in
orbit and not land but could be reused from either destination. Also if
the roll rate is small enough it might be possible to work within the
original Starship cabins under micro-gravity where the role of walls vs
floors are inverted during transit, but because the Starship cabins are
much closer to the axis of rotation there is very little gravity here.
None along the center line of the Starship.

I think 20-30 meters diameter is still small for centrifugal artificial
gravity. It might be enough if people were inactive, but with people
moving around you would probably get dizzy from the Coriolis effect.

Of course nobody knows. Nobody knows what g force would be necessary.
Nobody knows if one would adapt to the Coriolis effect. Nobody knows...
It's really a shame that no serious artificial gravity tests have been
done in orbit.


Alain Fournier

In article , says...
I think 20-30 meters diameter is still small for centrifugal artificial
gravity. It might be enough if people were inactive, but with people
moving around you would probably get dizzy from the Coriolis effect.

Of course nobody knows. Nobody knows what g force would be necessary.

This is true, but I've read that researchers have been making progress
on ISS at combating the effects of microgravity. So, they're hopeful
that some fraction of 1g would be sufficient when traveling to/from
Mars. But as you say, we don't know for certain.

Nobody knows if one would adapt to the Coriolis effect. Nobody knows...
It's really a shame that no serious artificial gravity tests have been
done in orbit.

Actually, we do know this one. There were experiments done decades ago
which essentially had people living in a spinning habitat (on earth,
obviously). So, researchers have been able to characterize the size
needed to keep people from getting sick.

Cite:

J Neurosci Res. 2000 Oct 15;62(2):169-76.
Artificial gravity as a countermeasure in long-duration space flight.
https://www.ncbi.nlm.nih.gov/pubmed?...Med&list_uids=
11020210&dopt=AbstractPlus

From above:

Early studies suggested that 3 rpm might be the upper limit
because movement control and orientation were disrupted at
higher velocities and motion sickness and chronic fatigue
were persistent problems. Recent studies, however, are
showing that, if the terminal velocity is achieved over a
series of gradual steps and many body movements are made
at each dwell velocity, then full adaptation of head, arm,
and leg movements is possible. Rotation rates as high as
7.5-10 rpm are likely feasible. An important feature of
the new studies is that they provide compelling evidence
that equilibrium point theories of movement control are
inadequate. The central principles of equilibrium point
theories lead to the equifinality prediction, which is
violated by movements made in rotating reference frames.

So, if you want to be safe, keep the spin rate at 3 rpm max. If you
want to experiment with slowly increasing the rpm, you might be able to
get way with up to 10 rpm.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.

On 2019-10-04 8:45 AM, Jeff Findley wrote:
In article , says...
I think 20-30 meters diameter is still small for centrifugal artificial
gravity. It might be enough if people were inactive, but with people
moving around you would probably get dizzy from the Coriolis effect.

Of course nobody knows. Nobody knows what g force would be necessary.

This is true, but I've read that researchers have been making progress
on ISS at combating the effects of microgravity. So, they're hopeful
that some fraction of 1g would be sufficient when traveling to/from
Mars. But as you say, we don't know for certain.


I completely agree with this argument. I'd love to be able to spin a
Bigelow module in LEO at different RPMs as a gravity lab. Several
colleagues agree that until this is done we aren't really being serious
about expansion much beyond the moon.

Nobody knows if one would adapt to the Coriolis effect. Nobody knows...
It's really a shame that no serious artificial gravity tests have been
done in orbit.

Actually, we do know this one. There were experiments done decades ago
which essentially had people living in a spinning habitat (on earth,
obviously). So, researchers have been able to characterize the size
needed to keep people from getting sick.

Cite:

J Neurosci Res. 2000 Oct 15;62(2):169-76.
Artificial gravity as a countermeasure in long-duration space flight.
https://www.ncbi.nlm.nih.gov/pubmed?...Med&list_uids=
11020210&dopt=AbstractPlus

From above:

Early studies suggested that 3 rpm might be the upper limit
because movement control and orientation were disrupted at
higher velocities and motion sickness and chronic fatigue
were persistent problems. Recent studies, however, are
showing that, if the terminal velocity is achieved over a
series of gradual steps and many body movements are made
at each dwell velocity, then full adaptation of head, arm,
and leg movements is possible. Rotation rates as high as
7.5-10 rpm are likely feasible. An important feature of
the new studies is that they provide compelling evidence
that equilibrium point theories of movement control are
inadequate. The central principles of equilibrium point
theories lead to the equifinality prediction, which is
violated by movements made in rotating reference frames.

So, if you want to be safe, keep the spin rate at 3 rpm max. If you
want to experiment with slowly increasing the rpm, you might be able to
get way with up to 10 rpm.

Jeff


3 RPM is a very interesting figure. Plugging that into a centrifugal
force calculator such as:

http://www.calctool.org/CALC/phys/newtonian/centrifugal

at exactly 3 RPM yields g forces that are almost exactly 1/100th the
radius of rotation. Thus a shell of 100m radius rotating at 3rpm yields
a centrifugal force of 1.00642g. 80m ~.8g 30m ~.3g (slightly Mars) 10m
yields ~.1g (Moon). Why did I not notice this before?

So a 30m radius (60m diameter) Bigelow cylinder would yield near Mars
gravity on its inner surface at 3 rpm. Fine for the outbound leg. More
dicey if you want to up it for the return leg to Earth. Here the
calculator yields a figure of about 5.5rpm for 1.01g or 5rpm for .83g.

If we HAD a gravity lab we could experiment with various rates of
rotation given a fixed radius hab. And increments/decrements and notice
their effects.

As an aside (love the Internet) here is the shot taken from the 0g
connecting passageway into the hub of the centrifuge on Discovery from
2001 A Space Odyssey.

https://www.youtube.com/watch?v=-RGGK2uyJOw

Since this is a motion stabilized shot, I can get a reliable time
estimate only for about 1/2 a rotation which is 12 seconds. Thus
assuming 1 rotation every 24 seconds yields an RPM figure of 2.5 Ha!
Under the 3 by half! Given that, using the calc tool, here are the rim g
forces for various radii that fit within a 12.2m radius sphere at its
midsection. I'm assuming the centrifuge rotates AROUND the center line
axis of the ship to avoid sideways induced reactions required constant
RCS correction, (even though the sequel movie 2010 might indicate it was
otherwise).

Thus we have:
8m = 0.055g
9m = 0.062g
10m = 0.069g
11m = 0.076g
12m = 0.083g

Thus AC Clarke may have believed that folks can live indefinitely at
near lunar gravity aboard Discovery. (Running spin-ward in the
centrifuge would increase the g load you experience while exercising as
well, but the pacing and stride would certainly NOT match that of
someone running at the bottom of a squirrel cage on Earth. But a pretty
good try for 1966).

Given the movie already has established the existence a long term lunar
colony and lunar habitation, this makes complete sense. I wonder if this
was that carefully thought out? I used to have a book called: "The
Making of 2001" written by Clarke, but alas long lost after a couple of
moves. It might talk about this. Seems unlikely to have been just a
co-incidence.

Dave

On Oct/4/2019 at 08:45, Jeff Findley wrote :
In article , says...
I think 20-30 meters diameter is still small for centrifugal artificial
gravity. It might be enough if people were inactive, but with people
moving around you would probably get dizzy from the Coriolis effect.

Of course nobody knows. Nobody knows what g force would be necessary.

This is true, but I've read that researchers have been making progress
on ISS at combating the effects of microgravity. So, they're hopeful
that some fraction of 1g would be sufficient when traveling to/from
Mars. But as you say, we don't know for certain.

Nobody knows if one would adapt to the Coriolis effect. Nobody knows...
It's really a shame that no serious artificial gravity tests have been
done in orbit.

Actually, we do know this one. There were experiments done decades ago
which essentially had people living in a spinning habitat (on earth,
obviously). So, researchers have been able to characterize the size
needed to keep people from getting sick.

Cite:

J Neurosci Res. 2000 Oct 15;62(2):169-76.
Artificial gravity as a countermeasure in long-duration space flight.
https://www.ncbi.nlm.nih.gov/pubmed?...Med&list_uids=
11020210&dopt=AbstractPlus

From above:

Early studies suggested that 3 rpm might be the upper limit
because movement control and orientation were disrupted at
higher velocities and motion sickness and chronic fatigue
were persistent problems. Recent studies, however, are
showing that, if the terminal velocity is achieved over a
series of gradual steps and many body movements are made
at each dwell velocity, then full adaptation of head, arm,
and leg movements is possible. Rotation rates as high as
7.5-10 rpm are likely feasible. An important feature of
the new studies is that they provide compelling evidence
that equilibrium point theories of movement control are
inadequate. The central principles of equilibrium point
theories lead to the equifinality prediction, which is
violated by movements made in rotating reference frames.

So, if you want to be safe, keep the spin rate at 3 rpm max. If you
want to experiment with slowly increasing the rpm, you might be able to
get way with up to 10 rpm.

Thanks for the link to the article. But those experiments were done on
people sitting and moving their limbs and head. That's different from
people walking around in a spinning spacecraft. They do address that
(the paragraph that ends page 174 and starts page 175) but it isn't a
settled issue.

Personally, I don't think that it would be a problem. But I would like
to know, not just think, before using artificial gravity on a trip to Mars.

They also note in that article, that if you have a spinning spacecraft
and you have some kind of emergency where you need to stop the spinning,
the people on board will need an adaptation period because when you
adapt to the Coriolis force of spinning you lose your "adaptation" to
the zero Coriolis force environment. Needing an adaptation period during
an emergency isn't good. They do provide a solution to that. I doubt
anyone would implement their solution without first doing a serious
testing programme in an on orbit artificial gravity experiment.


Alain Fournier

On 19-10-03 17:23 , David Spain wrote:
I have an update for you Niklas.

Thanks!

Here's a fellow (smallstars) who has proposed an artificial gravity
system based on the same physical principles you rely on but uses a
third Starship as a cargo and axis vehicle that holds an bi-directional
extruding truss system to attach the remaining two crewed Starships. The
rigid structure allows each Starship to pivot on its own pitch axis to
align them for a short Raptor burn to initiate and terminate rotation.
Then they can pivot so that the pitch axis aligns with the rotational
hub to provide the artificial gravity within the Starship for the months
long journey outbound and inbound. At either destination the crewed
Starships detach from the hub for landing. The hub ship also lands
robotically for refueling and reuse.

See:

https://www.youtube.com/watch?v=3CRiJTJikjk

I had a look, and of course the basic idea is the same -- rotation of
two Starships linked nose-to-nose, but sufficiently far apart to avoid
Coriolis problems. After my initial posting I have also found other
presentations of the same idea, some even with wires -- but those are
usually connected to the Starship's nose, not its legs, so they assume
that a Starship can stand the resulting longitudinal tension.

I am totally unconvinced by the video's arguments for a rigid truss
connection, instead of a cable or wire, and many commenters seem to
agree with me (but I didn't read all 1798 comments :-) ).

If the RCS is not powerful enough to spin up the system, even with a
cable one can certainly use the main engines to spin it up, either with
the cable initially loose and then (smoothly!) tightened, or by making
the wire fork near the Starship into two tails, with one tail connected
amidships or at the aft end of the Starship, and the other tail
connected to the nose. By adjusting the lengths of the two tails one can
switch the StarShip from the tangential pose, where the main engines can
be used to speed up or slow down, to the radial pose.

However, it seems to me simpler and more efficient in terms of delta-v
to have an extra-long wire and to use the RCS to give the two Starships
just a little rotational velocity with the wire fully extended, and then
reel in the wire until the desired centripetal acceleration is reached.
Such a wire could even be tapered to reduce its weight, because the
tension on the wire is low when the Starships are far apart and
increases as they come closer.

The recent Starship design change that replaces the combined
fins-and-legs with separate fins and legs means, of course, that my
original suggestion of connecting wires to the bottom of the aft fins is
no longer valid. I believe SpaceX still plans to stack the Starship on
top of the Superheavy booster by crane with a wire to the nose of the
Starship. However, probably the nose lifting-point is currently designed
only to stand the dry weight of the Starship, plus crew and cargo, and
would then have to be strengthened to stand also the weight of the
propellants left on board for the Mars-Earth-Mars transits.

--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
. @ .

On 19-10-03 17:59 , David Spain wrote:
On 2019-05-21 2:15 PM, Niklas Holsti wrote:

So that's the suggestion. Comments are welcome...


The other popular scheme is attaching two Starships end-to-end rather
than nose-to-nose.

That seems to have so many draw-backs that I'm surprised that anyone
would suggest it -- I haven't happened to see those suggestions, however.

With nose-to-nose it might be possible to use the sea-level Raptors to
gimbal enough to provide the side thrust needed to induce and remove
rotation, even if less efficient in vacuum. Not that much thrust is needed.

I think one could use the main engines for inducing rotation with a
nose-to-nose wire between two Starships, and without engine gimballing,
as I described in my preceding post.

The end the rotation, one simply disconnects the wire. This turns the
rotational velocity into linear velocity, which might even be useful to
define the final orbital path before entry into the atmosphere of Mars
or Earth.

--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
. @ .

On 19-10-03 19:18 , David Spain wrote:
On 2019-07-26 2:44 PM, Niklas Holsti wrote:
On 19-07-26 20:54 , David Spain wrote:

[snip]

This would also allow incremental build-up of
spacecraft by joining future Starships together in LEO to make a larger
spacecraft.

I don't understand how the spin/roll is related to incremental joining
of Starships. In a Starship, one end "kicks" (the aft end) and the
other "penetrates" (the front end); they are not easily connected
together to form a larger living space. At most, one could dock two
Starships front-to-front. Can you clarify what you mean?


Yes you can dock front-to-front.

The present Starship design does not have a docking port in the nose.
Moreover, Musk recently said that the nose will contain integral
propellant header tanks, which could make it difficult to have a docking
port there, seems to me -- there would have to be a tunnel between or
through the tanks, to the port.

If fact, what if you dock to a
habitation module like a large inflatable Bigelow module? Once in orbit
the nose of a Starship docks to an already inflated an constructed
habitation module where the diameter expands to 20-30 meters and the
circular 'decks' run parallel to each other along the inner
circumference. Now you have an artificial gravity environment where the
rate of roll is much, much less to achieve a given gravity

It seems to me that this would require very accurate alignment of the
Starship's rotation axis with the rotation axis of the habitat. Any
misalignment, perhaps caused by people moving around in the Starship or
shifting cargo around, would quickly create large off-axis forces on the
docking hardware, as the off-center Starship starts to feel centrifugal
forces. Possibly propellant slosh could also cause this.

and you get
this without needing a 2nd Starship

In SpaceX's plans, there is already a 2nd Starshipt to hand.

and all the complexity of trying to
counterbalance two Starships.

Hm, a nose-to-nose wire does not seem very complex to me. But of course
there must be some wire-reeling mechanisms, so a bit of complexity, yes.

Counterbalancing is automatic, but there could be some oscillations
which I think could be suppressed with the RCS.

Of course two Starships could share this hab module if docked at each end.

A good point.

[snip]

The main reason I like this scheme is that it places far less burden on
changes and potential stresses to Starship itself and fancy in-space
maneuvers and configurations, over more straightforward docking and roll.

I don't see much "fanciness" in connecting a nose-to-nose wire, reeeling
it in or out, and using the RCS to start rotation (using the main
engines would be fancier, though). A docking mechanism is much more
complex, but of course that design is already done, and proven in flight.

There are a TON of issues remaining to get crewed Starships to Mars.

Nah, I would say two tons :-)

No matter how you slice it, there is complexity to artificial gravity. I
have the sneaking suspicion that EM thinks this can be short circuited
by routine exercise inside a Starship. If I can compensate for the
deleterious effects using exercise, drugs, or alcohol (lol) well...
'tight is right'. :-)

I agree that this seems to be the SpaceX plan. And it will probably
work, too, at least for the fast and quick transits that SpaceX will
probably start with.

I've reflected on these issues before, which given what SpaceX is doing
vs some of the still to be resolved issues for Mars & Mars transit,
makes me think the Moon is still much less of a harsh mistress and the
hidden agenda here.

If someone pays for Starships to the Moon, no doubt SpaceX will be happy
to do that.

--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
. @ .

On Oct/5/2019 at 11:01, Niklas Holsti wrote :
On 19-10-03 17:59 , David Spain wrote:
On 2019-05-21 2:15 PM, Niklas Holsti wrote:

So that's the suggestion. Comments are welcome...


The other popular scheme is attaching two Starships end-to-end rather
than nose-to-nose.

That seems to have so many draw-backs that I'm surprised that anyone
would suggest it -- I haven't happened to see those suggestions, however.

With nose-to-nose it might be possible to use the sea-level Raptors to
gimbal enough to provide the side thrust needed to induce and remove
rotation, even if less efficient in vacuum. Not that much thrust is
needed.

I think one could use the main engines for inducing rotation with a
nose-to-nose wire between two Starships, and without engine gimballing,
as I described in my preceding post.

The end the rotation, one simply disconnects the wire. This turns the
rotational velocity into linear velocity, which might even be useful to
define the final orbital path before entry into the atmosphere of Mars
or Earth.

Presumably, both ships are going to the same place on Mars. If it helps
for the final trajectory of one ship then it's a nuisance for the other
ship. So I don't see this as helping. The velocities involved are small
enough that it wouldn't be a big nuisance, but it would be a nuisance. I
think you would first stop the rotation, then disconnect the wire.


Alain Fournier

On Oct/5/2019 at 11:44, Niklas Holsti wrote :
On 19-10-03 19:18 , David Spain wrote:

There are a TON of issues remaining to get crewed Starships to Mars.

Nah, I would say two tons :-)

No matter how you slice it, there is complexity to artificial gravity. I
have the sneaking suspicion that EM thinks this can be short circuited
by routine exercise inside a Starship. If I can compensate for the
deleterious effects using exercise, drugs, or alcohol (lol) well...
'tight is right'. :-)

I agree that this seems to be the SpaceX plan. And it will probably
work, too, at least for the fast and quick transits that SpaceX will
probably start with.

I think that the SpaceX plan is a bit of a if you build it they will
come plan. They want to build a rocket that can bring humans to Mars
cheaply. They figure that if they send a few people to Mars, even if
these few people can't do much on Mars because their spacesuit isn't
optimised for Mars and they are unfit to do work because of bone and
muscle loss, SpaceX still showed that Mars missions can be done. Others
will work on the N tons of details [ choose your value of N, but I agree
with you that one is a small value for N :-) ] that will make Mars
missions interesting and Mars colonisation possible.

Anyway that's my impression. Maybe they are working on all the details
and have solutions. But until now they haven't shown so.

I would have hoped that some people would have started to be vocal about
the needs of Mars travellers by now. I mean there should be some company
somewhere telling SpaceX, we can make great Mars spacesuits, or we have
a great solution for disembarkation and embarkation from a cabin on a
rocket on Mars, or artificial gravity or ... Even NASA and other space
agencies should be calling SpaceX. Maybe there is some of that going on,
but they sure are quiet about it.


Alain Fournier

On 19-10-05 23:05 , Alain Fournier wrote:
On Oct/5/2019 at 11:01, Niklas Holsti wrote :

[snip]

I think one could use the main engines for inducing rotation with a
nose-to-nose wire between two Starships, and without engine
gimballing, as I described in my preceding post.

The end the rotation, one simply disconnects the wire. This turns the
rotational velocity into linear velocity, which might even be useful
to define the final orbital path before entry into the atmosphere of
Mars or Earth.

Presumably, both ships are going to the same place on Mars.

Indeed, but probably it would be better for them not to re-enter and
land at the same time, but perhaps one or two sols apart. For example,
say that the first ship to arrive has a problem and lands on Mars some
kilometers off the intended spot; then the second ship may have time to
shift its landing place, too, to land near the first ship. For another
example, perhaps the crew of the first ship should have time to prepare
a landing place for the second ship that is surrounded by soil banks or
other means to contain landing ejecta that could damage the first ship.

I think you would first stop the rotation, then disconnect the wire.

I agree that is the cleaner way, if there is enough propellant to do it.
It would make mid-course orbit-corrections easier and also easier to
spool in the wire without any whip-lash problems.

Note that one can save on delta-v by having an extra-long wire and first
unspooling the wire to its full length, reducing the rotational velocity
by angular-momentum conservation, and then using thrusters to stop it
fully (before or after disconnecting the wire).

--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
. @ .