Rotovator Speeds was Burt Rutans plans for a manned mission to Mars

Fred J. McCall :

Again, I don't see how that works. The tip is always moving and
always under acceleration relative to the surface.

Steve is making a classical mistake. Clearly he has not bother to read the
previous messages carefully.

He is assuming that the discussion is about a rotovator that is spinning so
fast (ie tip speed almost equal to orbital speed) that the tip appears near
stationary in relationship to the Earth's surface.

Such a rotvator is easy to dock with but since at the top of it's rotation it
imparts a speed twice that of the orbital speed of the rovator cargos get
released at far greater than escape velocity making it of limited use.

There is no fixed speed that a rotvator must operate at.

The slower it spins, the easier it is to insert a released cargo into a lower
orbit - but the faster the craft to carry the cargo that mates to the
rotvator must go.

The faster it spins, the higher the released velocity of the cargo will be
but the slower the carrier craft needs to go mate with the rotvator.

Steve is assuming a very fast rotvator.

Earl Colby Pottinger


--
Cruising, building a Catamaran, Rebuilding Cabin, New Peroxide Still Design,
Writting SF, Programming FOSS - What happened to the time?

Earl Colby Pottinger wrote:

:Fred J. McCall :
:
: Again, I don't see how that works. The tip is always moving and
: always under acceleration relative to the surface.
:
:Steve is making a classical mistake. Clearly he has not bother to read the
revious messages carefully.
:
:He is assuming that the discussion is about a rotovator that is spinning so
:fast (ie tip speed almost equal to orbital speed) that the tip appears near
:stationary in relationship to the Earth's surface.
:
:Such a rotvator is easy to dock with but since at the top of it's rotation it
:imparts a speed twice that of the orbital speed of the rovator cargos get
:released at far greater than escape velocity making it of limited use.
:
:There is no fixed speed that a rotvator must operate at.
:
:The slower it spins, the easier it is to insert a released cargo into a lower
rbit - but the faster the craft to carry the cargo that mates to the
:rotvator must go.
:
:The faster it spins, the higher the released velocity of the cargo will be
:but the slower the carrier craft needs to go mate with the rotvator.
:
:Steve is assuming a very fast rotvator.

Even then the tip would only be relatively stationary for a very short
time, after which it is going to show a huge relative 'up'
acceleration. So the thing comes screaming 'down' at you, you hope to
be in exactly the right place at the right time to get your cargo
attached, after which it goes screaming 'up' away from you.

I have to wonder what sort of g-loading the cargo gets during all
this.

Doesn't that rate of radial acceleration impose a huge centripetal
load on the structure, requiring MUCH strong materials than the "twice
as strong as Spectra" postulated in the Boeing paper?

--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw

Fred J. McCall :

Earl Colby Pottinger wrote:

:Steve is assuming a very fast rotvator.

Even then the tip would only be relatively stationary for a very short
time, after which it is going to show a huge relative 'up'
acceleration. So the thing comes screaming 'down' at you, you hope to
be in exactly the right place at the right time to get your cargo
attached, after which it goes screaming 'up' away from you.

I have to wonder what sort of g-loading the cargo gets during all
this.

Doesn't that rate of radial acceleration impose a huge centripetal
load on the structure, requiring MUCH strong materials than the "twice
as strong as Spectra" postulated in the Boeing paper?

Nope, taper is determined by the material strenght. Spectra and other high
tension materials can be use today to build a working rotvator. But the
larger taper needed would increase the starting weight of the base unit.
Since the more it masses the more expensive it is to setup, it makes more
sense to wait a few years for better materials and spend the extra time
raising money and checking over your design before deploying it.

I quote from the first page:
QUOTE
The tethers can be built today using presently available
commercial fibers. The tethers are long, typically 400 to 1600 km (1300 to
5300 kft) in length. The total mass of
the space tether plus the Tether Central Station typically will be 30-200
times the payloads being handled. Most of
that mass ratio requirement is driven by the fact that the tether system must
mass considerably more than the
payload it is handling, so that, upon pickup of the payload by the tether,
the payload will not pull the space tether
system down into the atmosphere. Thus, the advent in the future of better
tether materials with higher strength at
higher temperatures will not be used to lower the tether system mass
significantly, but instead will be used to
increase the tether safety margins, lifetime, and system performance, by
allowing payload pickup at lower altitudes
and lower speeds, thus decreasing the performance requirements on the
hypersonic airplane portion of the system.
/QUOTE

Second the speed/acceleration seen by the cargo is affected by the length of
the rotvator, make the rotvator longer and the acceleration. falls. Read the
the HASTOLAIAAPaper.pdf report again. The planned acceleration seen by the
cargo was 1.6 G. That I think is less than the worse roller coaster rides
out there.

Earl Colby Pottinger

--
Cruising, building a Catamaran, Rebuilding Cabin, New Peroxide Still Design,
Writting SF, Programming FOSS - What happened to the time?

Earl Colby Pottinger wrote:

:Fred J. McCall :
:
: Earl Colby Pottinger wrote:
:
: :Steve is assuming a very fast rotvator.
:
: Even then the tip would only be relatively stationary for a very short
: time, after which it is going to show a huge relative 'up'
: acceleration. So the thing comes screaming 'down' at you, you hope to
: be in exactly the right place at the right time to get your cargo
: attached, after which it goes screaming 'up' away from you.
:
: I have to wonder what sort of g-loading the cargo gets during all
: this.
:
: Doesn't that rate of radial acceleration impose a huge centripetal
: load on the structure, requiring MUCH strong materials than the "twice
: as strong as Spectra" postulated in the Boeing paper?
:
:Nope, taper is determined by the material strenght. Spectra and other high
:tension materials can be use today to build a working rotvator. But the
:larger taper needed would increase the starting weight of the base unit.
:Since the more it masses the more expensive it is to setup, it makes more
:sense to wait a few years for better materials and spend the extra time
:raising money and checking over your design before deploying it.

But required material strength and amount of taper is presumably going
to go up when you increase the rotational speed so extremely that the
tip 'stands still' at the bottom.

:I quote from the first page:
:QUOTE
:The tethers can be built today using presently available
:commercial fibers. The tethers are long, typically 400 to 1600 km (1300 to
:5300 kft) in length. The total mass of
:the space tether plus the Tether Central Station typically will be 30-200
:times the payloads being handled. Most of
:that mass ratio requirement is driven by the fact that the tether system must
:mass considerably more than the
ayload it is handling, so that, upon pickup of the payload by the tether,
:the payload will not pull the space tether
:system down into the atmosphere. Thus, the advent in the future of better
:tether materials with higher strength at
:higher temperatures will not be used to lower the tether system mass
:significantly, but instead will be used to
:increase the tether safety margins, lifetime, and system performance, by
:allowing payload pickup at lower altitudes
:and lower speeds, thus decreasing the performance requirements on the
:hypersonic airplane portion of the system.
:/QUOTE
:
:Second the speed/acceleration seen by the cargo is affected by the length of
:the rotvator, make the rotvator longer and the acceleration. falls. Read the
:the HASTOLAIAAPaper.pdf report again. The planned acceleration seen by the
:cargo was 1.6 G. That I think is less than the worse roller coaster rides
ut there.

But that one required the Mach 13 rendezvous. Increase the rotational
speed enough to make it 'stand still' at the bottom and your gee loads
are presumably going to go up accordingly.

--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw

I realise the problem of the payload being released at a higher speed
than the orbital speed at that height, but with the additional weight
of the payload would not the whole system slow down so that the speed
could be controlled to that suitable for a higher orbit.

Earl Colby Pottinger wrote:

Second the speed/acceleration seen by the cargo is affected by the length of
the rotvator, make the rotvator longer and the acceleration. falls. Read the
the HASTOLAIAAPaper.pdf report again. The planned acceleration seen by the
cargo was 1.6 G. That I think is less than the worse roller coaster rides
out there.

Earl Colby Pottinger


Rats. I'm not getting 1.6 gees.

w = angular velocity in radians/sec
r = (tether length) / 2
tip velocity = w * r
centrifugal acceleration = w^2 * r

Tether Orbital Orbital Plane Tip Ang Centrifugal
Length Radius Vel Vel Vel Vel Acceleration
(km) (km) (km/s) (km/s) (km/s) (rad/s) (km/s^2) (gees)
400 6878 7.611 4.65 2.491 0.0125 0.0310 3.1665
500 6978 7.557 4.34 2.747 0.0110 0.0302 3.0790
600 7078 7.503 4.03 3.003 0.0100 0.0301 3.0673
700 7178 7.451 3.72 3.261 0.0093 0.0304 3.0994
800 7278 7.399 3.41 3.519 0.0088 0.0310 3.1593
900 7378 7.349 3.1 3.779 0.0084 0.0317 3.2380
1000 7478 7.300 2.79 4.040 0.0081 0.0326 3.3302
1100 7578 7.251 2.48 4.301 0.0078 0.0336 3.4324
1200 7678 7.204 2.17 4.564 0.0076 0.0347 3.5423
1300 7778 7.157 1.86 4.827 0.0074 0.0359 3.6583
1400 7878 7.112 1.55 5.092 0.0073 0.0370 3.7794
1500 7978 7.067 1.24 5.357 0.0071 0.0383 3.9046
1600 8078 7.023 0.93 5.623 0.0070 0.0395 4.0332
1700 8178 6.980 0.62 5.890 0.0069 0.0408 4.1649
1800 8278 6.938 0.31 6.158 0.0068 0.0421 4.2992
1900 8378 6.896 0 6.426 0.0068 0.0435 4.4358

Hop

Hop David :

Earl Colby Pottinger wrote:

Second the speed/acceleration seen by the cargo is affected by the length
of
the rotvator, make the rotvator longer and the acceleration. falls. Read
the
the HASTOLAIAAPaper.pdf report again. The planned acceleration seen by
the
cargo was 1.6 G. That I think is less than the worse roller coaster
rides
out there.

Earl Colby Pottinger


Rats. I'm not getting 1.6 gees.

w = angular velocity in radians/sec
r = (tether length) / 2
tip velocity = w * r
centrifugal acceleration = w^2 * r

Tether Orbital Orbital Plane Tip Ang Centrifugal
Length Radius Vel Vel Vel Vel Acceleration
(km) (km) (km/s) (km/s) (km/s) (rad/s) (km/s^2) (gees)
400 6878 7.611 4.65 2.491 0.0125 0.0310 3.1665
500 6978 7.557 4.34 2.747 0.0110 0.0302 3.0790
600 7078 7.503 4.03 3.003 0.0100 0.0301 3.0673
700 7178 7.451 3.72 3.261 0.0093 0.0304 3.0994
800 7278 7.399 3.41 3.519 0.0088 0.0310 3.1593
900 7378 7.349 3.1 3.779 0.0084 0.0317 3.2380
1000 7478 7.300 2.79 4.040 0.0081 0.0326 3.3302
1100 7578 7.251 2.48 4.301 0.0078 0.0336 3.4324
1200 7678 7.204 2.17 4.564 0.0076 0.0347 3.5423
1300 7778 7.157 1.86 4.827 0.0074 0.0359 3.6583
1400 7878 7.112 1.55 5.092 0.0073 0.0370 3.7794
1500 7978 7.067 1.24 5.357 0.0071 0.0383 3.9046
1600 8078 7.023 0.93 5.623 0.0070 0.0395 4.0332
1700 8178 6.980 0.62 5.890 0.0069 0.0408 4.1649
1800 8278 6.938 0.31 6.158 0.0068 0.0421 4.2992
1900 8378 6.896 0 6.426 0.0068 0.0435 4.4358

Interesting, did I read the paper wrong? I will get to you.

Earl Colby Pottinger

--
Cruising, building a Catamaran, Rebuilding Cabin, New Peroxide Still Design,
Writting SF, Programming FOSS - What happened to the time?

Fred J. McCall :

But required material strength and amount of taper is presumably going
to go up when you increase the rotational speed so extremely that the
tip 'stands still' at the bottom.

Absolutly right. That is why the mistake is his. The reports were on
rotovator that you need to be travelling at mach 12 to meet.

:Second the speed/acceleration seen by the cargo is affected by the length
of
:the rotvator, make the rotvator longer and the acceleration. falls. Read
the
:the HASTOLAIAAPaper.pdf report again. The planned acceleration seen by
the
:cargo was 1.6 G. That I think is less than the worse roller coaster rides
ut there.

But that one required the Mach 13 rendezvous. Increase the rotational
speed enough to make it 'stand still' at the bottom and your gee loads
are presumably going to go up accordingly.

Again right. I was commenting more that the mistake of assuming the
discussion was about rotovators with low mating speeds.

Earl Colby Pottinger

--
Cruising, building a Catamaran, Rebuilding Cabin, New Peroxide Still Design,
Writting SF, Programming FOSS - What happened to the time?

on Mon, 15 May 2006 14:03:04 GMT, Earl Colby Pottinger sez:
` Fred J. McCall :

` Again, I don't see how that works. The tip is always moving and
` always under acceleration relative to the surface.

` Steve is making a classical mistake. Clearly he has not bother to read the
` previous messages carefully.

` He is assuming that the discussion is about a rotovator that is spinning so
` fast (ie tip speed almost equal to orbital speed) that the tip appears near
` stationary in relationship to the Earth's surface.

No, I think it's your error there. Steve started by asking why not
build such a tether as you describe. And the answer is that this
requires much more heroic quantities of mass for the tether, beyond
what is feasible to contemplate in the near term.

` Such a rotvator is easy to dock with but since at the top of it's rotation it
` imparts a speed twice that of the orbital speed of the rovator cargos get
` released at far greater than escape velocity making it of limited use.

Note that for a certain angle of arc of the tether as the payload is
swung up, a little past horizontal, if it is released at that point, it
will acquire an orbit that will carry it past the centre of the tether
rotation at relatively small velocity. You don't have to run the load
all the way to the top. By including a small thruster with the payload
module, you can arrange it to dock at the tether c.o.m. as it goes by.

` There is no fixed speed that a rotvator must operate at.

` The slower it spins, the easier it is to insert a released cargo into a lower
` orbit - but the faster the craft to carry the cargo that mates to the
` rotvator must go.

` The faster it spins, the higher the released velocity of the cargo will be
` but the slower the carrier craft needs to go mate with the rotvator.

` Steve is assuming a very fast rotvator.


--
================================================== ========================
Pete Vincent
Disclaimer: all I know I learned from reading Usenet.

on 17 May 2006 01:43:14 GMT, pete sez:
` on Mon, 15 May 2006 14:03:04 GMT, Earl Colby Pottinger sez:
` ` Fred J. McCall :

` ` Again, I don't see how that works. The tip is always moving and
` ` always under acceleration relative to the surface.

` ` Steve is making a classical mistake. Clearly he has not bother to read the
` ` previous messages carefully.

` ` He is assuming that the discussion is about a rotovator that is spinning so
` ` fast (ie tip speed almost equal to orbital speed) that the tip appears near
` ` stationary in relationship to the Earth's surface.

` No, I think it's your error there. Steve started by asking why not
` build such a tether as you describe. And the answer is that this
` requires much more heroic quantities of mass for the tether, beyond
` what is feasible to contemplate in the near term.

` ` Such a rotvator is easy to dock with but since at the top of it's rotation it
` ` imparts a speed twice that of the orbital speed of the rovator cargos get
` ` released at far greater than escape velocity making it of limited use.

` Note that for a certain angle of arc of the tether as the payload is
` swung up, a little past horizontal, if it is released at that point, it
` will acquire an orbit that will carry it past the centre of the tether
` rotation at relatively small velocity. You don't have to run the load
` all the way to the top. By including a small thruster with the payload
` module, you can arrange it to dock at the tether c.o.m. as it goes by.

addendum: in fact, if you are willing to wait longer, there are several
release points where the payload will catch up to the c.o.m. at lower and
lower relative velocity over several orbits. It would probably be well
worth waiting 8 or 10 hours for rendezvous for the saving in docking
adjustemnt propellant...

` ` There is no fixed speed that a rotvator must operate at.

` ` The slower it spins, the easier it is to insert a released cargo into a lower
` ` orbit - but the faster the craft to carry the cargo that mates to the
` ` rotvator must go.

` ` The faster it spins, the higher the released velocity of the cargo will be
` ` but the slower the carrier craft needs to go mate with the rotvator.

` ` Steve is assuming a very fast rotvator.


` --
` ================================================== ========================
` Pete Vincent
` Disclaimer: all I know I learned from reading Usenet.

--
================================================== ========================
Pete Vincent
Disclaimer: all I know I learned from reading Usenet.