"John" wrote in
news:uzbbc.15$is5.3@newsfe1-win:

"Jorge R. Frank" wrote ...

The biggest development headache may well be automated rendezvous and
capture of HST. All the automated systems developed to date require
their targets to be cooperative to some degree (i.e. equipped with
navaids for the chaser vehicle). The Russian Kurs system requires a
rather elaborate set of RF antennas/avionics on the target vehicle.
The systems under development for ATV and HTV require the target
vehicle to have a GPS receiver and an array of laser retroreflectors.

It's as much of a problem as you make it. If you can park the hubble
within a few hundred meters from the ISS you can effectively attach a
line and real it in. Even if this is impractical,

It is. How do you plan to attach the line, for one? An EVA crewmember can't
go out that far from ISS; SAFER doesn't carry enough gas and is zero-fault-
tolerant. It's really just an emergency rescue device, not like the MMU.

get it close
enough in terms of deltaV and the shuttle could grab it and then
rondavouz with the ISS in 'perfect' safety.

The easiest way to dock the OTV to the ISS would be to give it a false
docking hatch. That way it can be attached to any number of
hard-points.

The ISS end isn't the hard one. It's the initial capture of HST in its
original orbit.

Trouble is, HST has *none* of those things - it's a completely
passive target, save the (visual) aids on its RMS grapple fixtures
and berthing mechanism. Attaching the navaids to HST becomes a
chicken-and-egg
problem -
any automated system that could attach the navaids to HST needs the
navaids
to be already there in order to get there in the first place.

Call me simplistic, but what's wrong with putting the OTV near the
hubble, pointing the two at each other manually and then pressing the
'go forward' button? Add a few dozen 100gram cameras to make sure
everything's perfectly lined up and hen press the 'dock' button.

The OTV won't keep going perfectly forward due to orbital mechanics, which
causes some decidedly non-intuitive effects in LEO. The OTV must have the
capability to constantly correct its lateral alignment as it approaches.

Besides, the base of the hubble is one big circle with the docking
mechanism in the middle. You can't really get a better bulls eye.

Careful with the terminology. It's a berthing target, not a docking target.
The distinction is important. In HST berthing, the telescope has already
been captured by the SRMS, and is moved very slowly over the FSS until it
lines up with the berthing camera. Then the capture latches are closed to
berth the telescope to the FSS. In other words, it was designed to work
with an already-captive target. The tolerances are very tight, tighter than
anything a docking system has achieved to date.

By
measuring the apparent size of the circle 'on screen' you can tell how
far away it is, it's closing speed, how far off axis it is and in what
direction that off axis is. Measuring the shape of the circle tells
you if the hubble is going off axis by measuring circle/eclipse

The Canadians have been working on such a system (SVS) for over a decade,
and they can tell you it's not nearly as simple as you make it out to be.
SVS requires dedicated visual targets on the target vehicle, but still gets
confused whenever lighting conditions change the picture on the camera. HST
would be a particularly difficult target due to its high reflectivity. It
is not an impossible problem to solve, but a lot of smart people have been
working on it for a long time and it still hasn't been solved.

Whatever docking systems required for hubble needs to be developed
anyway for the derbit module. Unless of course NASA wants to harpoon
it and 'tow' it out of orbit. Which would actually kind of work...

Right. For a deorbit system, you don't care about protecting the target.
Better than a harpoon would be a set of spikes on the nose of the OTV. It
is easier to ram than to shoot.


--
JRF

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