Subject: Israeli spysat coverage, resolution
From: [email protected] (Allen Thomson)
Date: 1995/04/11
Message-Id: <[email protected]>
Newsgroups: sci.space.policy
In order to see what kind of coverage is obtained by Ofeq-
3, Israel's alleged spysat, I ran recent orbital elements
through Rob Matson's Skymap 5.7 satellite tracking program. I
assumed that the satellite uses a direct downlink rather than
store-dump or a relay satellite, and thus its imaging is
constrained to times when it is in sight of the ground station,
most likely near Tel Aviv.
As the table at the bottom of this message shows, Ofeq does
quite well, getting a half-dozen daylight passes per day. The
first passes in the morning give coverage of Western India
(marginal), Pakistan, Central Asia, Iran, Iraq and the Arabian
Peninsula, and parts of Africa. As the day goes on, Middle East
targets are covered repeatedly -- Iraq, for example, is
accessible on virtually every pass -- and coverage extends to
most of Europe, all of North Africa, and substantial parts of
Central Africa. By way of comparison, a similar analysis
indicates that "KH-11/8," tracked by amateur satellite watchers
and believed to be an American reconnaissance satellite, makes
only one or two daylight passes over a target per day.
A longer run suggests that the Israelis will probably need
to perform periodic orbital adjustments: the current orbit will
have the satellite making mostly nighttime passes over the
Middle East in about a month, whereas it's now tuned to optimize
daytime coverage. Perigee is also currently in the northern
part of Ofeq's 36-degree orbit, maximizing resolution in the
Middle East.
In order to address the question of Ofeq's ground
resolution, I did a month-long run with Paul Traufler's Traksat
2.8 program and looked at the distribution of Ofeq-to-target
ranges which occurred over that span of time. Since only
geometry was of interest, I accepted all lighting conditions in
order to get better statistics (Traksat 2.8 has a bug that
causes it to miss an occasional pass, but it does compute
minimum range, which Skymap doesn't). Out of 229 passes, the
minimum range turned out to be 380 km for a near-zenith pass
(perigee is 365 km, apogee 730). The distribution of the 144
passes with ranges less than 1000 km was as follows:
365 to 400 km: 2
400 to 450 km: 2
450 to 500 km: 5
500 to 550 km: 8
550 to 600 km: 10
600 to 650 km: 13
650 to 700 km: 24
700 to 750 km: 23
750 to 800 km: 21
800 to 850 km: 13
850 to 900 km: 12
900 to 950 km: 6
950 to 1000 km: 5
So the closest to a target Ofeq gets is around 400 km, and
a typical figure is more like 700. For a one meter aperture
using 550 nm light, these ranges imply diffraction-limited
ground resolutions of 22 cm and 39 cm respectively: say 25 and
40 centimeters. Even if Ofeq has smaller optics (I suspect
they're probably 30 to 50 cm in diameter), it would still have
one-meter-class resolution. Certainly good enough for keeping an
eye on the neighbors.
If anyone else wants to go further with this, here are the
orbital elements I used:
Ofeq-3
1 23549U 95018 A 95096.85362148 .00113461 00000-0 33509-2 0 36
2 23549 143.3777 102.1910 0261160 83.0998 279.9378 15.06127287 200
KH 11-8
1 19625U 88099 A 95087.87099695 .00022500 00000-0 23689-3 0 02
2 19625 97.9268 151.7869 0505997 137.5151 222.4847 14.82016913 05
Daylight passes of Ofeq-3 over Tel Aviv 11-13 April 1995
Start of Track Peak Elevation End of Track
Local Times and Dates (UT + 2)
Date Time Azim Elev Time Azim Elev Time Azim Elev Sat.
4/11/95 8:03:21 112� 0� 8:05:59 147� 4� 8:08:41 182� 0� Ofeq-3
4/11/95 9:32:42 81� 0� 9:37:03 154� 25� 9:41:30 227� 0� Ofeq-3
4/11/95 11:03:20 70� 0� 11:07:59 345� 68� 11:12:31 259� 0� Ofeq-3
4/11/95 12:33:56 73� 0� 12:38:39 358� 34� 12:43:06 281� 0� Ofeq-3
4/11/95 14:04:10 89� 0� 14:09:16 10� 44� 14:13:54 290� 0� Ofeq-3
4/11/95 15:34:25 114� 0� 15:39:58 199� 67� 15:44:54 287� 0� Ofeq-3
4/11/95 17:05:31 145� 0� 17:10:46 208� 18� 17:15:31 273� 0� Ofeq-3
4/11/95 18:39:12 190� 0� 18:41:36 214� 2� 18:43:55 238� 0� Ofeq-3
4/12/95 9:25:18 87� 0� 9:29:22 151� 15� 9:33:29 215� 0� Ofeq-3
4/12/95 10:55:41 72� 0� 11:00:22 159� 79� 11:04:54 250� 0� Ofeq-3
4/12/95 12:26:18 71� 0� 12:31:06 353� 38� 12:35:34 275� 0� Ofeq-3
4/12/95 13:56:33 83� 0� 14:01:40 7� 38� 14:06:17 288� 0� Ofeq-3
4/12/95 15:26:40 106� 0� 15:32:18 19� 84� 15:37:16 289� 0� Ofeq-3
4/12/95 16:57:22 134� 0� 17:03:01 206� 28� 17:08:05 279� 0� Ofeq-3
4/12/95 18:29:43 171� 0� 18:33:49 213� 7� 18:37:40 256� 0� Ofeq-3
4/13/95 9:17:52 96� 0� 9:21:27 148� 9� 9:25:03 201� 0� Ofeq-3
4/13/95 10:47:52 75� 0� 10:52:31 157� 47� 10:57:00 240� 0� Ofeq-3
4/13/95 12:18:26 70� 0� 12:23:18 350� 47� 12:27:50 268� 0� Ofeq-3
4/13/95 13:48:44 79� 0� 13:53:52 3� 36� 13:58:29 285� 0� Ofeq-3
4/13/95 15:18:46 98� 0� 15:24:25 14� 62� 15:29:24 290� 0� Ofeq-3
4/13/95 16:49:09 124� 0� 16:55:05 203� 43� 17:00:20 284� 0� Ofeq-3
4/13/95 18:20:46 157� 0� 18:25:49 211� 12� 18:30:30 266� 0� Ofeq-3