Heliocentric TDRS?

"Hyper" wrote in message
ups.com...

IIRC Galileo was to be boosted by a Centaur - which got banned from
shuttle flights after Challanger - and the antenna problems stemmed
from spending too much time in storage and being moved from location
to location until flights were resumed. However, because there was no
alternative to Centaur it had to use Venus aand Earth for grav
slingshots.


Yeah. Since it was closer to the sun because of that, they kept the antenna
closed.

But had they been able to launch it via the original trajectory, the antenna
would have been opened at the shuttle (actually I think they still had the
option to open and close it, but later used that relay for something else
since there didn't seem to be much point in closing it once it was beyond
LEO).


snip

BTW, to illustrate the silliness of the *establishment*:
...
The COMPLEX team ruled out the option of using gravity to eject
Galileo from orbit around Jupiter, sending the craft into a
heliocentric orbit because of uncertainty where the nuclear-laden
satellite might ultimately go.

Such an option, the panel said, might require a launch-safety review
similar to the one ordered before Galileo was sent aloft by a space
shuttle 11 years ago.

"The reason for this is the very small, but nonzero, chance of
eventual impact with Earth. The anticipated cost of such a review is
so great -- in excess of Galileo's current annual operations budget of
some $7 million -- that NASA has no option but to dispose of the
spacecraft within the jovian system."
...

Wouldn't a close look at Jupiter's Trojans or at Ceres warrant the
"non-zero" risk?

Eh.. probably not.

But still stupid. I hadn't head that.






--
Greg Moore
SQL Server DBA Consulting
Email: sql (at) greenms.com http://www.greenms.com

In article . net,
Greg D. Moore \(Strider\) wrote:
And in any case, if you're doing simple assembly, you could simply do that
from the shuttle anyway.
Launch the probe on one rocket (shuttle or other), launch a upperstage or
two on another, and join them in orbit. Also been done with the Shuttle.

Indeed, Goldin was interested in the idea of doing that for Cassini, the
price of buying a Titan IV launch from the USAF being non-trivial. Didn't
work out well enough to be worth pursuing, alas.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

In article et,
Greg D. Moore \(Strider\) wrote:
They're not radiating detectable signals, and that's a fairly strong
statement, given the things that DSN *can* pick up. They didn't just go
out of range; they actually stopped sending.

How can you tell the difference? (Seriously not my area of expertise).

Signal strength plotted against time, after many years of following a nice
smooth predictable curve due to growing distance, suddenly starts dropping
faster. Either the probe has drastically speeded up, which would call for
some explanation :-), or its transmitter is dying.
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spsystems.net is temporarily off the air; | Henry Spencer
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In article . com,
Hyper wrote:
And was to be done on Galileo, except the delay required a different
trajectory that took it closer to the Sun, so the antenna had to say closed
longer.

IIRC Galileo was to be boosted by a Centaur - which got banned from
shuttle flights after Challanger - and the antenna problems stemmed
from spending too much time in storage and being moved from location
to location until flights were resumed.

That's the leading theory, but nobody will ever be sure. In any case,
though, even after all that, had the antenna been opened before release
from the shuttle, the problem would have been discovered. It certainly
could have been diagnosed much more easily, and it might well have been
curable, given eyes and hands on the spot.

(For that matter, if the pins really were stuck due to loss of lubricant,
it might have been possible to cure it just by running the antenna
deployment drive back and forth, to slowly walk them out. For opening
before release, the deployment drive had to be reversible, so the antenna
could be folded again if they pushed the RELEASE button and it didn't
release. But when the antenna was no longer to be opened before release,
the requirement for reversible drive went away. And when a relay was
needed to control some small modifications needed for the new trajectory,
it was attractive to reuse the reversing relay rather than finding a place
to add a new one... Galileo being, by this time, on a rather tight budget.
So as actually launched, the deployment drive was not reversible and
couldn't be backed up.)

"The reason for this is the very small, but nonzero, chance of
eventual impact with Earth. The anticipated cost of such a review is
so great -- in excess of Galileo's current annual operations budget of
some $7 million -- that NASA has no option but to dispose of the
spacecraft within the jovian system."
Wouldn't a close look at Jupiter's Trojans or at Ceres warrant the
"non-zero" risk?

The risk was not the problem. The problem was that the added risk would
(by rules imposed on NASA from above) require that a new review be done,
no matter how small the added risk seemed. An expensive new review. At a
time when Galileo was on its fourth or fifth mission extension and money
was *very* tight. The risk would have been trivial, but the project
simply didn't have the money to *prove* that with a full-scale review.
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spsystems.net is temporarily off the air; | Henry Spencer
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Greg D. Moore (Strider) wrote:
"Henry Spencer" wrote in message
...
In article
nk.net,

They're not radiating detectable signals, and that's a fairly
strong statement, given the things that DSN *can* pick up. They
didn't just go out of range; they actually stopped sending.

How can you tell the difference? (Seriously not my area of
expertise).

As SNR degrades, BER increases. Even when the BER approaches 0.5, one
can still detect the signal. One simply can't tell what symbols are
being sent.

One way of detecting weak signals (while giving up the ability to decode
symbols) is to integrate and dump over an interval much longer than a
symbol. In this manner, a weak signal will be detectable, but not decodable.

--
Dave Michelson

In article 9oPKh.27419$zU1.6632@pd7urf1no,
Dave Michelson wrote:
One way of detecting weak signals (while giving up the ability to decode
symbols) is to integrate and dump over an interval much longer than a
symbol. In this manner, a weak signal will be detectable, but not decodable.

A notable recent example of this was Earth radio telescopes listening to
the channel A signal from Huygens's little transmitter. They heard it,
and they got good solid Doppler measurements on it -- which is good, since
Cassini didn't -- but it was, alas, much too faint to decode any data.
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spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |