Solar panels (was: RADARSAT/SURFSAT)
Walter Nissen (dk058@cleveland.Freenet.Edu)
Fri, 10 Nov 1995 18:45:57 -0500
> From: jim.varney@24stex.com
> Subject: RADARSAT/SURFSAT
> about mag 3.5. A candidate for the "Visual 100," especially once the antennae
> and solar panels get fully unfurled?
I don't pretend to know much about the early days of payload operations,
but I'm pretty dubious that the typical solar-panel deploy is likely to
greatly increase the visual magnitude from the ground. In a slightly
different context, Bart and I have a long-running discussion about how
likely it is that an operating, functioning, active satellite would glint
our eyes with a specular reflection, and our ability to distinguish
solar-panel glints from other brightenings.
Bart thinks a solar-panel glint from an active satellite is somewhat
likely. I think not. He argues that power generation from a panel will
vary with the cosine of the incident ray to the normal. As far as I know,
that is quite true. But he goes on to argue that operators don't
accurately point at the Sun, for various reasons, including that the
cosine penalty is initially small, and that consequently, visual observers
on the ground have a substantial possibility of observing a solar-panel
glint. I claim they mostly glint right back into the Sun, right over
observers' heads. I point to the fact that observers (or at least, this
observer) have very seldom observed very bright glints from active
satellites. The glints we do see seem consistent with the presence of
booms or other such structures. As an example, HST frequently glints at
observers for a few seconds, once per pass, by a few magnitudes,
presumably off the very long tube. I would freely admit that these could
be solar-panel glints, but I see no strong evidence for that and no
necessity.
Conversely, in looking at the C* 1933 family of payloads, I and others
have observed very bright glints (of 3, 4, or 5 magnitudes or more), but
only under inoperative conditions, or more precisely, apparently
inoperative conditions. Particularly, in satellites like C* 1933 a year
or two back, or C* 1953 last fall and winter, or SROSS-C2 or DMSP F3 in a
similar time-frame, observers report seeing very brief but spectacular
flashes. I have advanced the hypothesis that these result from
solar-panel glints on a rapidly rotating satellite which has very recently
lost attitude control. This hypothesis is further supported by observed
monotonic, exponential increases in the period of the flashes, consistent
with the loss of angular momentum of a metallic body to the
electromagnetic field of the Earth because of the development of internal
Eddy currents. (I have to mention that C* 2242 would be an apparent
exception, but is it perhaps inoperative)??
Older C* 1933 family objects have glinted at me only by extended (many
second) glints which occur merely once per pass. This is consistent with
a structure which over time has lost nearly all its angular momentum.
SeaSat, long inactive, is known for very bright glints, presumably off its
long boom, but, like HST, not for very rapid, repeated glints in a single
pass.
There are a few active, or presumably active, satellites which do flash
rapidly, such as COBE, USA 32, USA 81, and some others. I don't pretend
to any theory about them, but I don't think I'm seeing solar-panel glints.
EGP glints wildly for obvious reasons (hundreds of planar mirrors cover
its exterior and it never had any attitude control). I used to think of
UME 1 as a fainter version of EGP, but haven't seen wild flashing behavior
from it in a long time. Is that consistent with others obervations of
UME 1?
Mir varies greatly from pass to pass and seems to have so many solar
panels that not all can be deployed normal to solar rays simultaneously.
I would readily believe that some of its brightest passes achieve that
status because of solar-panel glints.
Cheers.
Walter I. Nissen, Jr., CDP 216-243-4980 dk058@cleveland.freenet.edu
---
If it isn't win-win, then it's lose-lose.
---
UME 1 0.8 0.9 0.0 8.5
1 08709U 76019A 95307.24702224 -.00000012 +00000-0 +44567-4 0 07570
2 08709 069.6681 021.8982 0013599 300.3723 059.6018 13.70490295984254
DMSP B5D1-3 6.4 1.7 0.0 6.1
1 10820U 78042 A 95307.06410933 .00000093 00000-0 36898-4 0 6360
2 10820 98.6419 138.3377 0009312 339.5057 20.5747 14.28953655910811
Seasat 21.0 1.5 0.0 5.1
1 10967U 78064A 95307.24932298 -.00000015 +00000-0 +39654-4 0 04411
2 10967 107.9965 065.2073 0002092 226.6672 133.4295 14.38065893908820
Mir big, and getting bigger
1 16609U 86017A 95307.25471847 +.00009350 +00000-0 +12914-3 0 03661
2 16609 051.6464 181.2045 0003301 279.1865 080.8772 15.57927130554631
EGP 2.2 0.0 0.0 6.7
1 16908U 86061A 95307.20672372 -.00000083 +00000-0 +10000-3 0 00681
2 16908 050.0105 334.8402 0011494 155.2694 204.8693 12.44412913088146
C* 1933 6.0 2.0 0.0 5.9
1 18958U 88020A 95307.24076538 +.00000323 +00000-0 +36623-4 0 01622
2 18958 082.5365 052.6169 0018462 124.5355 235.7608 14.83122271412376
C* 1953 6.0 2.0 0.0 5.9
1 19210U 88050A 95307.19452128 +.00000216 +00000-0 +24058-4 0 09521
2 19210 082.5269 351.7493 0024354 089.3041 271.0961 14.81928494398828
USA 32 6.0 3.0 0.0 5.4
1 19460U 88078 A 95301.22418046 .00000106 00000-0 40193-4 0 07
2 19460 84.9900 121.8637 0000010 225.9332 134.0666 14.31115481 02
COBE 4.9 8.5 0.0 3.9
1 20322U 89089A 95307.45568062 .00000279 00000-0 20594-3 0 1637
2 20322 98.9557 321.3904 0008888 310.9116 49.1283 14.03458389305122
HST 13.3 4.3 0.0 4.3
1 20580U 90037 B 95305.39294525 .00000214 00000-0 21080-4 0 7322
2 20580 28.4696 249.1483 0006218 302.6869 57.3113 14.90961600104409
USA 81 6.0 3.0 0.0 5.4
1 21949U 92023 A 95269.19026858 .00000026 00000-0 10223-4 0 04
2 21949 85.0050 53.0646 0003000 43.1610 316.8389 14.29356558 03
C* 2242 6.0 2.0 0.0 5.9
1 22626U 93024 A 95304.13942045 .00000146 00000-0 22343-4 0 5956
2 22626 82.5258 213.6624 0024764 159.7524 200.4675 14.73673414136622
SROSS-C2 1.0 0.0 0.0 8.4
1 23099U 94027 A 95307.02560962 .00001517 00000-0 64282-4 0 2464
2 23099 46.0422 163.8353 0133709 182.5227 177.5007 15.14563838 82733