Well, on topic if something goes wrong...
I'm posting this for a friend at the MESSENGER operations and control
center at JHU who informs me of an upcomming critical event. In the event
of something going wrong there could possibly be something visible to
observers on Earth within a limited geographical area. She has set up an
email contact for questions or reports (should that come to pass) and I
will also forward any discussion from the list.
------
On 21 November, day of year 325, shortly after 14:30 UT, MESSENGER is
going to pressurize the oxygen tank in the delta-V thruster system.
If all goes well, there'll be nothing to see. However, this is a critical
event and there have been cases of spacecraft being lost during these
activities. Some of the failure modes could be observable to well equiped
properly situated observers on Earth.
This is a 'real time' activity (1-way light time is 3.5 minutes)-- there
are pauses to wait for confirmation of successful completion at a couple
of steps leading up to and during the pressurization so we can't be too
certain about the timing. The current timeline calls for:
14:30 begin preparatory commanding from ground
15:06 poll system engineers for readiness to execute pressurization macro
15:13 begin ox tank pressurization
15:25 verify pressurization macro completed
Actual events could be delayed, but should not occur earlier than this.
Visibility:
A serious failure of the O2 tank or pressurization system could also
result in rupture of an adjacent hydrazine tank. We have very crudely
estimated that such a failure could be as bright as mag 21. Quite
challenging, though there should be a number of groundbased observers who
can reach that deep.
Also quite limiting is the geographical window for visibility, given the
spacecraft proximity to the sun for Earthbound observers.
MESSENGER is near the ecliptic at 30 deg western elongation from the sun,
.42 au from Earth and .66 from the sun. Extreme western Canada, Alaska,
and the eastern Pacific will have the best chance for visibility.
Hawaii is ideally placed, based on the nominal timeline. Using Honolulu as
a proxy for both the Big Island and Maui...
Honolulu:
Date__(UT)__HR:MN R.A.__(a-apparent)__DEC Azi_(a-appr)_Elev
****************************************************************
2005-Nov-21 14:30 m 13 43 42.80 -14 03 07.6 104.6721 -1.0834
2005-Nov-21 14:45 r 13 43 43.99 -14 03 07.3 106.0467 2.2903
2005-Nov-21 15:00 m 13 43 45.18 -14 03 07.0 107.4816 5.6403
2005-Nov-21 15:15 m 13 43 46.36 -14 03 06.7 108.9867 8.9633
2005-Nov-21 15:30 Am 13 43 47.54 -14 03 06.4 110.5734 12.2557
2005-Nov-21 15:45 Am 13 43 48.71 -14 03 06.1 112.2542 15.5130
2005-Nov-21 16:00 Nm 13 43 49.88 -14 03 05.8 114.0428 18.7302
****************************************************************
('m' is moon up, 'r' is target rise, 'A' is astronomical twilight)
Here are the geocentric coordinates from Horizons:
Geocentric RA/DEC
Date__(UT)__HR:MN R.A.__(a-apparent)__DEC r delta
**************************************************************************
2005-Nov-20 12:00 13 41 37.85 -14 04 34.3 0.6627197982 0.4121169908
2005-Nov-21 00:00 13 42 32.94 -14 03 44.3 0.6606331586 0.4174553376
2005-Nov-21 12:00 13 43 29.50 -14 03 06.4 0.6585710703 0.4228467929
2005-Nov-22 00:00 13 44 27.54 -14 02 40.6 0.6565342985 0.4282909228
2005-Nov-22 12:00 13 45 27.05 -14 02 26.6 0.6545236118 0.4337872680
The JPL Horizons site (http://ssd.jpl.nasa.gov) recognizes 'MESSENGER' as
the spacecraft name and can provide detailed topocentric ephemerides for
specific locations.
Of course the goal here is to see nothing since the operation will go
smoothly and MESSENGER will continue on to Mercury and return a wealth of
new science! But in the event of loss of contact with the spacecraft this
next monday...
If anyone out in the eastern Pacific feels up to an observing challenge,
questions or reports can be sent to msgr_helen@yahoo.com.
Helen Hart, Mission Analyst
Space Science Mission Operations
Johns Hopkins University, Applied Physics Laboratory
msgr_helen@yahoo.com
--
Richard Clark
rclark@lpl.arizona.edu
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