NASA Relies on Thrusters to Steer Station

Craig Fink wrote:

Your right there are a lot of ways to get
attitude without the traditional gyroscopes. As you said fiber optic gyros,
or couple of star trackers. When the Hubble is pointed at a
star, pitch and yaw can come from the target image. All that is needed are
a couple of cameras perpendicular to get roll. I wouldn't think there is
anything more accurate than using the stars.

The problem isn't getting a measurement of the attitude, stars work
just fine for that. The problem is maintaining that reference as the
craft changes attitude, and measuring the rates of change and motion,
which is pretty hard to do with star sensors. Two different
functions, which only a gyroscope or similar technology can provide in
a single system.

D.
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Bjørn Ove Isaksen wrote:

Rusty B wrote:
NASA Relies on Thrusters to Steer Station

Last time I saw the numbers for required upmass it was pretty tight
conserning especialy water. Without gyros and back to RCS the station
would spend a lot more fuel (IIRC it was a new feature of Mir). Is there
someone here that has an idea of the problems this might lead to?

Sincerely
Bjørn Ove

If they only have two CMGs, then they can use only two and still maintain
attitude control without using any fuel. They might have to slightly modify
the software, but it should be doable.

Treat the sum of the torques on the Station as a controller in place of the
broken CMG. Leave the remaining two CMGs perpendicular to each other, but
not perpendicular (45 degrees might be best) to the sum of the torques.
Allow the two remaining CMGs to fight the sum of the torques. When a CMG
become saturated, flip over changing the sign on the sum of the torques to
desaturate the CMG. The two remaining CMGs and sum of the torques would be
able to perform the flip maneuver. I would think that it would give an
almost full range (only slightly degraded) of attitude control away from
the stable attitude. Essentially, allow the sum of the torques to act as a
controller in place of the third CMG and pick an attitude where the sum of
the torques is never close to being perpendicular to the other two CMGs.

Of course, maybe they already have this downmode capability built into the
software and have downmoded to thrusters because they aren't concerned
about fuel usage.

Things get a little tougher with only one CMG, but it could still be used
to minimize fuel usage.

Craig Fink

Do the Russians have any plans to include gyrodines in any of the future modules?




(Derek Lyons) wrote in message ...
Craig Fink wrote:

Your right there are a lot of ways to get
attitude without the traditional gyroscopes. As you said fiber optic gyros,
or couple of star trackers. When the Hubble is pointed at a
star, pitch and yaw can come from the target image. All that is needed are
a couple of cameras perpendicular to get roll. I wouldn't think there is
anything more accurate than using the stars.

The problem isn't getting a measurement of the attitude, stars work
just fine for that. The problem is maintaining that reference as the
craft changes attitude, and measuring the rates of change and motion,
which is pretty hard to do with star sensors. Two different
functions, which only a gyroscope or similar technology can provide in
a single system.

D.
--
The STS-107 Columbia Loss FAQ can be found
at the following URLs:

Text-Only Version:
http://www.io.com/~o_m/columbia_loss_faq.html

Enhanced HTML Version:
http://www.io.com/~o_m/columbia_loss_faq_x.html

Corrections, comments, and additions should be
e-mailed to , as well as posted to
sci.space.history and sci.space.shuttle for
discussion.

On 7 Dec 2003 08:04:21 -0800, (Explorer8939)
wrote:

Do the Russians have any plans to include gyrodines in any of the future modules?


There are half a dozen RS gyrodynes sitting in a building outside
Moscow waiting for a home. Originally the gyrodynes were to be housed
in the SPP (Science Power Platform) but it got downsized. Then they
were to be in the UDM (Universal Docking Module). Ditto.

Craig Fink wrote in
ink.net:

If they only have two CMGs, then they can use only two and still
maintain attitude control without using any fuel. They might have to
slightly modify the software, but it should be doable.

Correct. ISS uses two-axis CMGs, so two CMGs gives you three-axis control
with one redundant axis. No software changes needed. And in fact, that is
what they are doing right now.

Several of the stories in the media appear to be incomplete (surprise!) ISS
is currently using CMGs for attitude hold, thrusters only for maneuvering
from one attitude to another. Or at least that was the case last I checked.

--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.

Jorge R. Frank wrote:

Several of the stories in the media appear to be incomplete (surprise!)
ISS is currently using CMGs for attitude hold, thrusters only for
maneuvering from one attitude to another. Or at least that was the case
last I checked.

Thanx for clearing that up. The only diffrence is as I understand it that
only attitude manuvering is now done by thrusters, instead of CMG's.
Attitude hold is still done by CMG's. This should'nt have a big impact on
fuel usage as it is'nt preformed all the time.

Sincerely
Bjørn Ove

Craig Fink wrote in message link.net...

If they only have two CMGs, then they can use only two and still maintain
attitude control without using any fuel. They might have to slightly modify
the software, but it should be doable.

It's already in the software. Two can be used (and have been used).

Of course, maybe they already have this downmode capability built into the
software and have downmoded to thrusters because they aren't concerned
about fuel usage.

There were some inaccuracies in the reports that came out. The use of
thrusters only was for attitude *maneuvers*, not attitude control
during normal bore-hole-in-the-sky operations. Maneuvers are
relatively uncommon events, maybe once every few weeks. During
steady-state ops, control is still going to be maintained on CMGs and
that's where all the propellant savings comes from. The reason there
isn't much concern on prop usage for maneuvers on thrusters is
because, frankly, they really aren't much less efficient than using
CMGs with thruster assist. Maneuvers were utilized with CMGs in
control more for operational convenience than anything else (no
control handover to the Russian Segment required).

Things get a little tougher with only one CMG, but it could still be used
to minimize fuel usage.

Interesting point. Someone who worked on Skylab told me IBM was
developing one-CMG control software when they started to have problems
with a second CMG after the first one failed (Skylab only had three).
I've not seen any evidence of how far that got.

On 06 Dec 2003 11:24:54 -0500, Jim Kingdon wrote:

Apparently somewhere in between the size that will pass through a
Progress docking port and that which will pass through a Shuttle
docking port.

I don't actually know whether it is size or mass which prevents use of
Progress (possibly both). The CMG itself is over 220 kg and the
following article also refers "to the weight and volume of equipment
needed to carry the CMG into orbit":

http://www.space.com/missionlaunches...te_020608.html

That's because a CMG package - the gyro and necessary
sub-assemblies - weighs some 1,100 pounds [500 kg] at launch and
must be mounted on a special carrier beam in the shuttle's cargo
bay. http://spaceflightnow.com/station/sts111/020608cmg/

Thank you. I must confess that I didn't realize just how massive they
are (and obviously need to be).

Dale

I would imagine that the Hubble Space Telescope staff is working the
same issue right now.


(cyclone96) wrote in message . com...
Craig Fink wrote in message link.net...

If they only have two CMGs, then they can use only two and still maintain
attitude control without using any fuel. They might have to slightly modify
the software, but it should be doable.

It's already in the software. Two can be used (and have been used).

Of course, maybe they already have this downmode capability built into the
software and have downmoded to thrusters because they aren't concerned
about fuel usage.

There were some inaccuracies in the reports that came out. The use of
thrusters only was for attitude *maneuvers*, not attitude control
during normal bore-hole-in-the-sky operations. Maneuvers are
relatively uncommon events, maybe once every few weeks. During
steady-state ops, control is still going to be maintained on CMGs and
that's where all the propellant savings comes from. The reason there
isn't much concern on prop usage for maneuvers on thrusters is
because, frankly, they really aren't much less efficient than using
CMGs with thruster assist. Maneuvers were utilized with CMGs in
control more for operational convenience than anything else (no
control handover to the Russian Segment required).

Things get a little tougher with only one CMG, but it could still be used
to minimize fuel usage.

Interesting point. Someone who worked on Skylab told me IBM was
developing one-CMG control software when they started to have problems
with a second CMG after the first one failed (Skylab only had three).
I've not seen any evidence of how far that got.

Assuming that the girodines can be placed in any reasonably sized
module, I would assume that sooner or later they will be sent to ISS
aboard some sort of module. Can the girodines operate successfully
with the CMGs?



capbrit wrote in message . ..
On 7 Dec 2003 08:04:21 -0800, (Explorer8939)
wrote:

Do the Russians have any plans to include gyrodines in any of the future modules?


There are half a dozen RS gyrodynes sitting in a building outside
Moscow waiting for a home. Originally the gyrodynes were to be housed
in the SPP (Science Power Platform) but it got downsized. Then they
were to be in the UDM (Universal Docking Module). Ditto.