DART nearly a bullseye

Glad to hear that NASA's DART mission was a near 100% success. Now on to a
full blown autonomous rendezvous and docking demo of two unmanned NASA
spacecraft. Hope NASA can pull this off soon.

The Soviets, of course, pioneered autonomous rendezvous (and docking)
procedures and have used them to support their Salyut and Mir space
stations. And Russian equipment (the Kurs system) was used to autonomously
dock the ISS Service Module to FGB/Unity assembly in July 2000.

The Russkies had to try several times before they worked out the bugs and
performed the world's first automated rendezvous and docking of two unmanned
spacecraft (Cosmos 186 and 188) in October 1967. Gee, that was nearly 40
years ago.

Later
Ray Schmitt

I think the problem part in this case though is that they want to do it to
demonstrate that the other vehicle needs no special equipment.

The cynics amongst us might suppose that in fact this is just what would be
needed to wage war in space of course.

Brian

--

Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"Ray S" wrote in message
m...
Glad to hear that NASA's DART mission was a near 100% success. Now on to a
full blown autonomous rendezvous and docking demo of two unmanned NASA
spacecraft. Hope NASA can pull this off soon.

The Soviets, of course, pioneered autonomous rendezvous (and docking)
procedures and have used them to support their Salyut and Mir space
stations. And Russian equipment (the Kurs system) was used to autonomously
dock the ISS Service Module to FGB/Unity assembly in July 2000.

The Russkies had to try several times before they worked out the bugs and
performed the world's first automated rendezvous and docking of two
unmanned spacecraft (Cosmos 186 and 188) in October 1967. Gee, that was
nearly 40 years ago.

Later
Ray Schmitt

On Sun, 17 Apr 2005 00:32:13 +0000, Ray S wrote:

Glad to hear that NASA's DART mission was a near 100% success. Now on to a
full blown autonomous rendezvous and docking demo of two unmanned NASA
spacecraft. Hope NASA can pull this off soon.

The Soviets, of course, pioneered autonomous rendezvous (and docking)
procedures and have used them to support their Salyut and Mir space
stations. And Russian equipment (the Kurs system) was used to autonomously
dock the ISS Service Module to FGB/Unity assembly in July 2000.

The Russkies had to try several times before they worked out the bugs and
performed the world's first automated rendezvous and docking of two unmanned
spacecraft (Cosmos 186 and 188) in October 1967. Gee, that was nearly 40
years ago.


http://www.msnbc.msn.com/id/7516571/

"When we started doing precise maneuvers, we started seeing excessive
propellant consumption. ... It went south pretty quickly," Snoddy said.
"The mission as designed, when it runs out of gas, completes itself."

lol, surely, the the DART community understood that they needed to
calibrate their flight control system?

Sounds like the DART had problems with their attitude control system. Dead
bands too tight and/or thruster to moment coefficients wrong. Sounds like
it hosed out it's remaining fuel when it got up close and tried to do
precision maneuvers.

To me it sounds like they were only a 50% success, and they missed most of
if not all the up close and personal rendezvous testing. The stuff that
comes just prior to docking. And if you judge success by the ability to
"actually" dock, it was a complete failure. Running out of fuel just prior
to docking is not a good thing.

This is not uncommon for a new vehicle. The simulations don't match
reality when the vehicle actually flies. The thrusters give too much or
too little moment, cross-coupling is different. People are overly
optimistic about how precise the vehicle can maneuver, dead band are too
tight. It doesn't take long for a vehicle that is bouncing back and forth
off both sides of a dead band band to hose out a lot of fuel.

Similar thing happened the first few times the Shuttle flew too. Too much
gimbaling of the OMS engines, RCS jet probably banging around in the dead
band. It takes a flight or two to get the control system calibrated.

It's easy to spot a control system that's working correctly or not. The
vehicle should always be bouncing off of just one side of it's dead bands,
with aerodynamic, gravity gradient, or whatever causes the moment slowly
bringing the vehicle back to the same side of the dead band every time.
Cross coupling being a little more difficult to sort out, but when it's
properly tuned, it should be bouncing off only one side of it's dead band,
coming close but never hitting the other side. Hit the other side of the
dead band just one time and now your just hosing out fuel bouncing back
and forth.

If DART had an auto calibration attitude control system onboard, it didn't
work.

--
Craig Fink
Courtesy E-Mail Welcome @

"Ray S" wrote in
m:

Glad to hear that NASA's DART mission was a near 100% success. Now on
to a full blown autonomous rendezvous and docking demo of two unmanned
NASA spacecraft. Hope NASA can pull this off soon.

The Soviets, of course, pioneered autonomous rendezvous (and docking)
procedures and have used them to support their Salyut and Mir space
stations.

Not quite. The Soviets/Russians use *automated* rendezvous and autonomous
prox ops, while DART is fully autonomous in both rendezvous and prox ops.

The distinction? With the Russian system, prior to Kurs acquisition the
maneuver plan is generated in mission control, and the Russian equivalent
of the FDO uplinks burn solutions to the spacecraft, which dutifully
executes them. The spacecraft has no "big picture" of the overall plan.
Once given a target vector, DART internally generates and executes its own
maneuver plan. The Soviets/Russians have never done anything like that.

--
JRF

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

On Mon, 18 Apr 2005 06:37:15 +0000, Jorge R. Frank wrote:

"Ray S" wrote in
m:

Glad to hear that NASA's DART mission was a near 100% success. Now on
to a full blown autonomous rendezvous and docking demo of two unmanned
NASA spacecraft. Hope NASA can pull this off soon.

The Soviets, of course, pioneered autonomous rendezvous (and docking)
procedures and have used them to support their Salyut and Mir space
stations.

Not quite. The Soviets/Russians use *automated* rendezvous and
autonomous prox ops, while DART is fully autonomous in both rendezvous
and prox ops.

The distinction? With the Russian system, prior to Kurs acquisition the
maneuver plan is generated in mission control, and the Russian
equivalent of the FDO uplinks burn solutions to the spacecraft, which
dutifully executes them. The spacecraft has no "big picture" of the
overall plan. Once given a target vector, DART internally generates and
executes its own maneuver plan. The Soviets/Russians have never done
anything like that.

Ahhh, so the Russians use "automated" rendezvous and "autonomous" prox
ops, while the DART uses "autonomous" rendezvous and "no" prox ops. Maybe
the next one will have prox ops.

Rendezvous: During rendezvous translational thruster firings are much more
important that rotational thruster firings and are orders of magnitude
larger. Any translation caused by a rotational burn to maintain attitude
is so small compared to the much larger translational burns that are
required, the cross coupling can essentially be ignored and it's effects
treated like other perturbations and taken out during the next
translational burn.

Proximity Operations: Both rotational thruster firings and translation
thruster firings are equally important, and of the same order of
magnitude. Any cross coupling can quickly lead to excessive thruster
firing and fuel usage. Need to translate, oops, now I'm rotating, oops,
now I'm translating, oops, ...

Prox Ops and Docking is one area were both the Russians and United States,
and soon the Europeans won't have learned the lessons of the past. The
first hand experience of the Russian, when the Progress slammed into Mir
has essentially been ignored by the Russian. The US being a bit arrogant,
thinking, "we would never do that". And, the Europeans, "well that's how
it's always been done by everybody else, it must be right."

At some point in the future it's going to take another accident for people
to realize there are better ways to dock with large space structures like
the Space Station. Tethered Capture seem to me to make more sense, and
would vastly reduce the maneuvering capability/requirements of a delivery
vehicle to the Space Station. The delivery vehicle could have fewer
thrusters, use less fuel, and improve overall safety. Tethered Capture,
then reel the delivery vehicle into a robotic arm capture, which moves it
to the proper docking port.

With such a system, the Shuttle could be captured then dock with the Space
Station using only the vernier jets for attitude control. RCS jets would
still be needed for translation, but only to get the Shuttle within a
couple of hundred feet (or is that yards). No RCS jet firings would be
required close to the Space Station. Do it along the Z-axis were orbital
mechanics will keep the tether taught and the vehicles separated.
Essentially, all proximity operations would be handled by the Space
Station, not by every other vehicle that wants to visit. Simplifying the
design and certification of those vehicles.

--
Craig Fink
Courtesy E-Mail Welcome @

On Sun, 17 Apr 2005 09:34:52 +0000, Brian Gaff wrote:


The cynics amongst us might suppose that in fact this is just what would
be needed to wage war in space of course.

Well, some people in the US are certainly talking about it lately. Only
the military would know if their satellite did something to the other
satellite.

Rendezvous in position, velocity and time is a harder problem than
rendezvous in position and time, which is waging war in space. While
the first might possibly be use to spy on someone else's satellite or remove
pieces of a dead satellite, it also has many more peaceful application
than that, in the future.

--
Craig Fink
Courtesy E-Mail Welcome @

Craig Fink wrote in
news
On Mon, 18 Apr 2005 06:37:15 +0000, Jorge R. Frank wrote:

"Ray S" wrote in
m:

Glad to hear that NASA's DART mission was a near 100% success. Now
on to a full blown autonomous rendezvous and docking demo of two
unmanned NASA spacecraft. Hope NASA can pull this off soon.

The Soviets, of course, pioneered autonomous rendezvous (and
docking) procedures and have used them to support their Salyut and
Mir space stations.

Not quite. The Soviets/Russians use *automated* rendezvous and
autonomous prox ops, while DART is fully autonomous in both
rendezvous and prox ops.

The distinction? With the Russian system, prior to Kurs acquisition
the maneuver plan is generated in mission control, and the Russian
equivalent of the FDO uplinks burn solutions to the spacecraft, which
dutifully executes them. The spacecraft has no "big picture" of the
overall plan. Once given a target vector, DART internally generates
and executes its own maneuver plan. The Soviets/Russians have never
done anything like that.

Ahhh, so the Russians use "automated" rendezvous and "autonomous" prox
ops, while the DART uses "autonomous" rendezvous and "no" prox ops.
Maybe the next one will have prox ops.

That's how it turned out. You know that wasn't the intent.

Like Ray said, the Soviet system didn't work right the first time, either.

Prox Ops and Docking is one area were both the Russians and United
States, and soon the Europeans won't have learned the lessons of the
past. The first hand experience of the Russian, when the Progress
slammed into Mir has essentially been ignored by the Russian. The US
being a bit arrogant, thinking, "we would never do that".

I've read the accident reports. There are indeed a lot of stupid things the
Russians did that set up the Progress-Mir collision that we would never do,
period.

At some point in the future it's going to take another accident for
people to realize there are better ways to dock with large space
structures like the Space Station. Tethered Capture seem to me to make
more sense, and would vastly reduce the maneuvering
capability/requirements of a delivery vehicle to the Space Station.
The delivery vehicle could have fewer thrusters, use less fuel, and
improve overall safety.

Nope. It's just moving the problem. For docking you have a set of contact
condition limits to engage the docking mechanism, and for tethering you
have a set of capture conditions to catch the tether. You still need
translational thrusters and all the rest in order to achieve those
conditions. And as TSS taught us, tethers can be very dynamic, even when
you try your best to keep then taut along the gravity gradient. The
visiting vehicle can wind up hosing prop chasing the tether. All you really
buy with this scheme is reduced RCS plume impingement on the station, while
buying into a whole bunch of other headaches.

--
JRF

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

Thanks to the group for an interesting discussion of the various flavors of
rendezvous and docking technology. It's always good to get our thinking
clear on these things.

Certainly the Russian R&D systems have evolved and matured since the late
1960s. The first generation systems required lotsa help from the ground and
were more correctly termed "automated" rather than "autonomous" designs,
where "automated" refers to the absence of humans on either spacecraft.

BTW, and for the record, the infamous Progress-Mir collision was NOT due to
a problem with the Russian autonomous rendezvous and docking system. It
happened during a test of a manual docking method that the Russians wanted
to qualify as a backup to the Kurs system. The backup method relied on a TV
system and a Mir cosmonaut to complete the R&D maneuvers. The Kurs system
was not used in this test.

There were actually two tests. The first occurred on 4 March 1997 and was
unsuccessful as the Progress M-33 spacecraft (fortunately) flew past Mir, a
near miss. Moscow decided to repeat the test on 25 June 1997 with Progress
M-34. That's when the **** hit the fan and the collision occurred. On both
tests the TV system was less than adequate for the R^D task (noisy, poor
resolution) and the crew had great difficulty seeing the Progress vehicle
during the approach, visual acquisition being a backup to the backup,
apparently.

I guess you could say that progress (no pun intended) was made in this test
series since the M-34 vehicle got significantly closer to the docking port
than the M-33 spacecraft.

Reminds one of another half-assed test, Chernobyl.

Later
Ray Schmitt

"Jorge R. Frank" wrote in message
...
"Ray S" wrote in
m:

Glad to hear that NASA's DART mission was a near 100% success. Now on
to a full blown autonomous rendezvous and docking demo of two unmanned
NASA spacecraft. Hope NASA can pull this off soon.

The Soviets, of course, pioneered autonomous rendezvous (and docking)
procedures and have used them to support their Salyut and Mir space
stations.

Not quite. The Soviets/Russians use *automated* rendezvous and autonomous
prox ops, while DART is fully autonomous in both rendezvous and prox ops.

The distinction? With the Russian system, prior to Kurs acquisition the
maneuver plan is generated in mission control, and the Russian equivalent
of the FDO uplinks burn solutions to the spacecraft, which dutifully
executes them. The spacecraft has no "big picture" of the overall plan.
Once given a target vector, DART internally generates and executes its own
maneuver plan. The Soviets/Russians have never done anything like that.

--
JRF

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

On Mon, 18 Apr 2005 14:42:20 +0000, Jorge R. Frank wrote:

Craig Fink wrote in
news
On Mon, 18 Apr 2005 06:37:15 +0000, Jorge R. Frank wrote:

"Ray S" wrote in
m:

Glad to hear that NASA's DART mission was a near 100% success. Now on
to a full blown autonomous rendezvous and docking demo of two
unmanned NASA spacecraft. Hope NASA can pull this off soon.

The Soviets, of course, pioneered autonomous rendezvous (and
docking) procedures and have used them to support their Salyut and
Mir space stations.

Not quite. The Soviets/Russians use *automated* rendezvous and
autonomous prox ops, while DART is fully autonomous in both rendezvous
and prox ops.

The distinction? With the Russian system, prior to Kurs acquisition
the maneuver plan is generated in mission control, and the Russian
equivalent of the FDO uplinks burn solutions to the spacecraft, which
dutifully executes them. The spacecraft has no "big picture" of the
overall plan. Once given a target vector, DART internally generates
and executes its own maneuver plan. The Soviets/Russians have never
done anything like that.

Ahhh, so the Russians use "automated" rendezvous and "autonomous" prox
ops, while the DART uses "autonomous" rendezvous and "no" prox ops.
Maybe the next one will have prox ops.

That's how it turned out. You know that wasn't the intent.

Like Ray said, the Soviet system didn't work right the first time,
either.

Prox Ops and Docking is one area were both the Russians and United
States, and soon the Europeans won't have learned the lessons of the
past. The first hand experience of the Russian, when the Progress
slammed into Mir has essentially been ignored by the Russian. The US
being a bit arrogant, thinking, "we would never do that".

I've read the accident reports. There are indeed a lot of stupid things
the Russians did that set up the Progress-Mir collision that we would
never do, period.

lol, so we'll do something different to cause a collision, or complain a
lot when someone else does it. Having a large spacecraft maneuvering up to
and dock with a huge spacecraft may be glamorous, but it's inherently
risky and dangerous.


At some point in the future it's going to take another accident for
people to realize there are better ways to dock with large space
structures like the Space Station. Tethered Capture seem to me to make
more sense, and would vastly reduce the maneuvering
capability/requirements of a delivery vehicle to the Space Station. The
delivery vehicle could have fewer thrusters, use less fuel, and improve
overall safety.

Nope. It's just moving the problem. For docking you have a set of
contact condition limits to engage the docking mechanism, and for
tethering you have a set of capture conditions to catch the tether. You
still need translational thrusters and all the rest in order to achieve
those conditions. And as TSS taught us, tethers can be very dynamic,
even when you try your best to keep then taut along the gravity
gradient. The visiting vehicle can wind up hosing prop chasing the
tether. All you really buy with this scheme is reduced RCS plume
impingement on the station, while buying into a whole bunch of other
headaches.

I'll provide more detail.

The early portion of the rendezvous is the same. Approach along the Vbar
with a bunch of loops to get closer. On the last loop, the one that loops
under the Space Station, when the Shuttle approaches the Rbar the Hook on
the end of the line flys down the RBar, maneuvering in the x-y plane and
attaching to the Shuttle. The Shuttle could be in a very loose attitude
hold, or even a short period of free drift so as not to disturb the Hooks
approach and Capture. At the Rbar or close to it, the Hook attachers, then
the Shuttle does a small Translation burn to match the Space Station
velocity, and a small attitude adjustment to align the Shuttle's cg thru
the tether. Stable long term Capture has just been achieved.

Rendezvous and Capture are now complete and everyone can sit back and
monitor the reel in, Arm Capture, and mating. As you pointed out, with the
current docking mechanism the Shuttle may have to apply a little bump to
get the latches to catch. Future docking mechanisms wouldn't require this.

If the Capture is missed, the Shuttle can do a small translational burn to
enter a circular orbit around the Space Station for additional Capture
attempts. The Shuttle essentially in a stable circular orbit around the
Space Station were capture can be attempted every 90 minutes. Or, 45
minutes if they are willing to capture up along the Rbar.

This sounds like a much simpler way to approach and dock many different
spacecraft to the Space Station than putting all the requirements on the
individual and different spacecraft. It has a lot of good attributes.

1) All Captures and Dockings are operationally the same, no matter what
vehicle is coming to visit. The same for the US, Russian, European,
Chinese, Private Enterprise, robotic, or manned. The requirements and all
that they entail for the visiting vehicle are vastly reduced. Training,
Maneuverability, Redundancy, Software, Fuel (actual and reserve)
requirements are all reduced.

2) Safety, no large vehicles freely maneuvering close to each other. Since
it's always best to have the lightest vehicle doing the maneuvering, with
the larger vehicle station keeping or in free drift. The Hook on the
tether does the maneuvering. It's much much lighter and therefore would do
much less damage in a mishap.

3) I'm sure there are some more attributes to be added.

The maneuvering Hook at the end of the tether is a much simpler rendezvous
vehicle (if you could call it that) than any other vehicle built. A
relatively simple concept. Since the Hook is at the end of the tether, the
reel on the Space Station controls the radial (Rbar) direction. Since
tension in the tether is important, the Hook needs to be thrusting all
the time, once it leaves the reel. A very small amount of thrust would be
necessary, and throttling would be nice but not necessary. The tether
cable attaching to a rod the goes right up aft end of the nozzle.
Attaching to the inside of the small cold (or hot?) gas engine that will
be running during the Capture maneuver. This aligns the engine thrust to
the tether cable. X-Y maneuvering is just as simple with the Hook's single
engine design. Since the tether bar is coming out the nozzle of the
engine, simply pitching and yawing the bar would maneuver the Hook in X
and Y. That with the reel Z axis give the Hook 5 axis control with one
tether and one small continuously thrusting engine. The last axis being
the roll axis about the tether. This would probably require some roll
control fins in the nozzle.

So the Hook has 6 axis control with a reel, tether, one engine and roll
control fins. It requires no throttling (but would be nice), just a
continuous small amount of thrust to keep a small amount of tension in the
line. Since, the critical z direction (R-bar) is under positive control of the tether
and reel, much faster closing rates would be acceptable during much of the
cast of the Hook.

As the maneuvering Hook approaches it's coasting target, the reel slows
the closing rate. The Hook's only engine is thrusting towards the target,
but the exhaust is away from the target and towards the Space Station, no
plume impingement problems with the coasting target. Soft capture could be
achieved with a magnet on the Hook and a corresponding magnet on the
target vehicle. The magnets automatically align the Hook to the targets
capture plate and the reel lets out a little more line until they come
into contact. Capture complete.

Other considerations:

A plug on the reel matches the shape of the inside of the nozzle. The reel
could be attached to the fishing pole, in this case the robotic arm. When
the Hook is reeled in, and the reel's plug inserted into the Hook's
nozzle, Arm capture is complete.

Video cameras, range finders, radio control, add a computer with all the
nice bells and whistles. Hook propellant recharging, battery recharging.
Redundancy, a couple of extra fishing rods (Reel, Line and Hook).
Emergency cable cutters. Now it's finally beginning to sound like a
project NASA could love.

I'm sure there's more, but I would think all the positive aspects would
make it worth it when compared to all the current requirements to do a
rendezvous.

I think it will happen at some point, maybe not with this Space Station,
maybe when it becomes a space town, or a space city.

Need some pictures to go with this long winded description?

--
Craig Fink
Courtesy E-Mail Welcome @

Ray S wrote:
There were actually two tests. The first occurred on 4 March 1997 and was
unsuccessful as the Progress M-33 spacecraft (fortunately) flew past Mir, a
near miss. Moscow decided to repeat the test on 25 June 1997 with Progress
M-34. That's when the **** hit the fan and the collision occurred. On both
tests the TV system was less than adequate for the R^D task

Wasn't the second attempt done with the Radar off because they suspect
that radar screwed up the first attempt ? And lack of radar helped
bring in a situation where crew lacked situation awareness and reacted
too late to the information that the thing was coming in real fast and
real close.