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Date: Wed, 09 Jul 2008 16:13:49 -0700
From: Nigel Angold
Subject: Ulysses Status
Dear Ulysses friends and colleagues,
As you are aware, the proposed July 1st Ulysses operations end date
has come and gone. And as a result of our fuel bleeding and other
operations strategies, we have managed to avoid freezing the
hydrazine so far!
Now we are continuing operations on a day-to-day basis until the
fuel freezes. That includes fuel bleeding every 2 hours to keep the
hydrazine moving through the pipes and Earth-pointing manoeuvres
interleaved, when required.
When we see the fuel freezing, we will switch off the S-band and
some instruments for a couple of days in an effort to thaw the
hydrazine. After that, we'll try to switch on the X-band once again
using some more radical (and hence more risky) procedures.
If the fuel has not frozen by the end of July, we'll try some benign
X-band switching in early August and plan for radical switching in
late August.
What will happen in the unlikely event that we re-establish our
X-band downlink? Well, obviously we'll leave it on!!! And at the end
of August we should have enough fuel remaining to continue for a
number of months (assuming that we stop the fuel bleeding). The
short portion of pipe that is currently close to freezing will warm
up but other areas of pipework will cool down and they will get
close to freezing during the last quarter of 2008. As for funding
for operations beyond August, that's another question.
This coming weekend, we will be testing the redundant on-board
receiver which is connected to the front low gain antenna (LGA-F).
This is to validate our ability to command the spacecraft when the
HGA is not pointing towards Earth e.g. if no manoeuvres have been
performed for several days due to frozen fuel.
I know some of the instrument teams have held wakes to celebrate the
fantastic journey that we have been on all these years. However, I
make no apology for the fact that Ulysses is not dead yet. I hope
that in the coming weeks we get to see the transition from fast to
slow solar wind.
Very best regards,
Nigel
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