This is a series of status reports on the final phase of the Ulysses
mission which is characterised by the following operational constraints:
These reports were sent by e-mail from the Ulysses Mission Operations
Manager to the Ulysses community. They are reproduced verbatim below in
reverse chronological order with the exception of the e-mail headers.
Date: Mon, 22 Jun 2009 08:59:44 -0700
From: Nigel Angold
Subject: Ulysses Status Update 7 - The Time Has Come
Dear Ulysses colleagues,
Well, another couple of months have rolled by and still Ulysses
continues to function. But I'm sure that you've all noticed the
dramatic reduction in the data return figures now that the link
margin precludes playback of data recorded on the spacecraft. We've
tried to bolster our dwindling tracking allocation with some success
by grabbing antenna time released on short notice (mostly by the
Spitzer Project). However, weekly data return figures are now
typically 10% or less. And soon, even 512 bps from 70m antennas will
be a thing of the past.
So both Agencies have decided that it's time for the Ulysses Mission
to end and we are planning to perform our final track on 30 June
2009. Unfortunately, due to the heavy demand on the DSN, that will
not give us time to switch on the GRB, DUST and URAP instruments or
to try to switch the X-band transmitter on one last time.
At our End of Mission press conference last year, we talked about the
1 July 2008 as the mission end date. So although I'm sad that the
mission is finally coming to an end, I'm delighted that we've
successfully navigated our way through another complete year.
Earlier this month, the Ulysses Mission Team received a NASA Group
Achievement Award so I congratulate all the PI teams for their
excellent work. And we reached another milestone on 10 June when
Ulysses became the longest-running ESA-operated spacecraft,
overtaking IUE's 18 years and 246 days. It's nice to be going out in style!
Our final pass on Tuesday 30 June will run from 15:25 until 20:20 UTC or
until we send the last command to switch the telemetry off. We will have
many of the original team members present to celebrate the culmination of
this amazing mission.
It's been such a pleasure working with you all and I hope our paths
continue to cross from time to time.
Best regards,
On behalf of all the Ulysses Team at JPL,
Nigel
Date: Thu, 23 Apr 2009 16:53:04 -0700
From: Nigel Angold
Subject: Ulysses Status Update 6
Dear Ulysses colleagues,
It's been a couple of months since my last status update and I'm
happy to report that we have witnessed impressive science data
returns because we have been able to play back data from the on-board
tape recorder. But those of you who have been looking at the science
from Ulysses in near-real time will have noted a significant drop in
the last few weeks. At the end of March, the spacecraft-Earth range
had increased again to a point where playback was no longer possible
via the 70m antenna in Madrid. However, we continued to play back
data at 1024 bps whenever we had a DSS-14 track because the 70m
antenna at Goldstone has a slightly better performance.
Unfortunately, DSS-14 suffered a severe failure on 9 April which left
a large gouge in the metal surface of its bearing runner and this
impacted Ulysses significantly. We attempted to replace lost tracking
time with support from the 34m DSN antennas by dropping the telemetry
bit rate to 128 bps (our lowest science data rate) but, although we
could lock onto the carrier, there was insufficient downlink signal
strength to acquire lock on the telemetry. So telemetry reception was
only possible from the few DSS-63 tracks that were scheduled for
Ulysses support.
Ulysses is currently at 30 deg North in ecliptic latitude so it rises
above the horizon for just a couple of hours at Canberra. Yesterday,
we had our first DSS-43 pass for quite a while - it was short and
sweet with good telemetry reception at 128 bps. In addition, DSS-14
is expected to return to service on 30 April. So we expect one more
week of low data return and then hopefully the numbers will improve.
In the meantime, the spacecraft continues to function without drama
and decommissioning activities will be started when the tracking time
increases to the expected levels. The PIs of several instruments that
are currently switched off would like to have their experiments
powered on one last time before the data stops flowing to determine
their end of mission status. We are currently finalizing these
switch-on sequences.
That's all for now. I hope the Sun continues to fascinate!
Best regards from the (dwindling) Ulysses Mission Operations Team at JPL.
Nigel
Date: Thu, 20 Feb 2009 11:45:38 -0800
From: Nigel Angold
Subject: Ulysses Status Update 5
Dear Ulysses colleagues,
Yesterday was mission day 6712 and we surpassed 400 days of S-band
mission operations. Given that we thought the spacecraft would only
survive a few months after the X-band transmitter failure on 15
January 2008, that's pretty good going!
The last month or so has seen a dramatic increase in data return.
This is due in part to a request by NASA HQ for additional DSN
coverage and also due to the fact that we can record and play back
data again on board the spacecraft. That's possible because the
spacecraft-Earth distance is low enough to support a 1024 bps
telemetry data rate at the moment (this situation will last until
sometime in mid-March). I've attached a plot of our weekly data
return percentages which clearly shows the recent improvements.
As far as the hydrazine is concerned, it's obviously not frozen yet,
but there can't be very much left. Our estimate is that we have
almost no fuel left even using our best-case estimates. However, it's
very difficult to get an exact figure of fuel usage over the mission
given that we have had about 3 years of closed-loop conscan
operations to control nutation when the spacecraft fired the thruster
autonomously. During those periods, we had to estimate the number of
pulses fired by monitoring the increase in catalyst bed temperature
after each period of thruster activity which is not the easiest thing
to do. So the bad news is that we don't have an exact estimate of how
much fuel is left but the good news is that it's still above zero!
We hope that the data returned is continuing to excite you as the
solar activity slowly begins to increase.
Best regards,
Nigel
