CONTOUR's Orbit Correction Maneuver #6 on July 27
New: 2002 July 29
CONTOUR's OCM6 maneuver took place as planned at 12:02 UT
on Saturday, July 27. Doppler residuals of the spacecraft's radio
signals during the burn, analyzed at JPL's Multi-Mission Navigation
Center and shown here, showed that either the burn delivered 1.8%
more delta-V than expected, or if its size were perfect, then there
was a 0.3 deg. pointing error, both quite reasonable and good
performance for such a burn. We'll learn what the errors were once
a good post-burn orbit is determined from the tracking data, and
compared with the pre-burn orbit.
However, nobody on the ground saw the burn. Since CONTOUR was
about magnitude 14.5 before, during, and after OCM6, a few
observers in California who tried to videorecord the maneuver with
8-inch telescopes and Supercircuits PC164C cameras were unable to
see it, even when multiple frames were averaged to reach to about
mag. 12.5. But Gordon Garradd, using his 45cm telescope and an
integrating CCD camera at Loomerah, N.S.W., Australia, was able to
record stars to 16th mag. and made the animated .gif files given
below from his images. He wrote:
__________________________________________________
From: Gordon Garradd
To: 'Joan and David Dunham'
Subject: RE: OCM6, nothing to see
Date: Sun, 28 Jul 2002 23:53:38 -0000
Hi David, here is the animation during the burn time. I measured
the satellite images to be about 14.5 unfiltered.
As you can see the intensity is not constant along the short trails
during each 6 second time span. Also note the stars are elongated. I
had to cover the telescope tube framework and add a large cardboard
shield at the top end to stop moonlight creating a huge brightness
gradient across the images, but since the wind was blowing this
turned the scope into a giant sail, which was buffetted by the
breeze, and I suspect this is the main cause of the variations over
the 6 sec exposure durations.
The exposures were 6 sec, in hindsight 2 sec like I used in later
images would have been better, but I was hoping the longer exp. may
have more chance of showing a plume.
exposure times (UTC)
h m s
1 12 01 47 Before burn
2 12 02 10 During burn
3 12 02 26 During burn
4 12 02 42 During burn
5 12 02 57 During burn, including its end
6 12 03 13 After burn
7 12 03 29 After burn
8 12 03 44 After burn
9 12 04 00 After burn
10 12 04 16 After burn
11 12 04 31 After burn
cheers, Gordon
NOTE that the animated .gif files shown here are copyrighted by
Gordon Garradd. On his Web site, with many other interesting
astronomical images at
http://members.ozemail.com.au/~loomberah/index.html
he writes about his copyright: "Specifically NO use by millennium/
conspiracy theory/UFO websites is allowed. Private and educational
use IS allowed, however anyone who wishes to reproduce them,
including on the internet, should contact me first
at: loomberah@ozemail.com.au
__________________________________________________
The fuel is designed to burn cleanly, leaving few byproducts
that would ionize in sunlight, so the relatively small (two 5-pound)
thrusters apparantly just were not bright relative to sunlight
reflected from the spacecraft. In another animated .gif file from
Gordon Garradd here taken after OCM6, he
also briefly caught (by chance) a Russian upper-stage rocket from a
2000 February launch that was lower and brighter than CONTOUR.
__________________________________________________
OCM7 on July 31 will be even farther from the Earth than OCM6,
so it should be even harder to observe, with the spacecraft probably
about 16th mag. But OCM8 will be lower so that CONTOUR will be
brighter, maybe 12th or even 11th mag., and might then be captured
with video, at least with image-intensified systems working with
Watec 902H or Supercircuits PC164C (or other Sony HAD Exview CCD)
cameras. Maybe the small brightening that might occur during the
burn will be detectable.
David Dunham, IOTA and CONTOUR Mission Design Team
e-mail dunham@erols.com, 2002 July 29
office e-mail david.dunham@jhuapl.edu
Phone home 301-474-4722; office 240-228-5609