Subject: Israeli spysat coverage, resolution
From: thomsona@netcom.com (Allen Thomson)
Date: 1995/04/11
Message-Id: <thomsonaD6w4ow.IA5@netcom.com>
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 112ø 0ø 8:05:59 147ø 4ø 8:08:41 182ø 0ø Ofeq-3
4/11/95 9:32:42 81ø 0ø 9:37:03 154ø 25ø 9:41:30 227ø 0ø Ofeq-3
4/11/95 11:03:20 70ø 0ø 11:07:59 345ø 68ø 11:12:31 259ø 0ø Ofeq-3
4/11/95 12:33:56 73ø 0ø 12:38:39 358ø 34ø 12:43:06 281ø 0ø Ofeq-3
4/11/95 14:04:10 89ø 0ø 14:09:16 10ø 44ø 14:13:54 290ø 0ø Ofeq-3
4/11/95 15:34:25 114ø 0ø 15:39:58 199ø 67ø 15:44:54 287ø 0ø Ofeq-3
4/11/95 17:05:31 145ø 0ø 17:10:46 208ø 18ø 17:15:31 273ø 0ø Ofeq-3
4/11/95 18:39:12 190ø 0ø 18:41:36 214ø 2ø 18:43:55 238ø 0ø Ofeq-3
4/12/95 9:25:18 87ø 0ø 9:29:22 151ø 15ø 9:33:29 215ø 0ø Ofeq-3
4/12/95 10:55:41 72ø 0ø 11:00:22 159ø 79ø 11:04:54 250ø 0ø Ofeq-3
4/12/95 12:26:18 71ø 0ø 12:31:06 353ø 38ø 12:35:34 275ø 0ø Ofeq-3
4/12/95 13:56:33 83ø 0ø 14:01:40 7ø 38ø 14:06:17 288ø 0ø Ofeq-3
4/12/95 15:26:40 106ø 0ø 15:32:18 19ø 84ø 15:37:16 289ø 0ø Ofeq-3
4/12/95 16:57:22 134ø 0ø 17:03:01 206ø 28ø 17:08:05 279ø 0ø Ofeq-3
4/12/95 18:29:43 171ø 0ø 18:33:49 213ø 7ø 18:37:40 256ø 0ø Ofeq-3
4/13/95 9:17:52 96ø 0ø 9:21:27 148ø 9ø 9:25:03 201ø 0ø Ofeq-3
4/13/95 10:47:52 75ø 0ø 10:52:31 157ø 47ø 10:57:00 240ø 0ø Ofeq-3
4/13/95 12:18:26 70ø 0ø 12:23:18 350ø 47ø 12:27:50 268ø 0ø Ofeq-3
4/13/95 13:48:44 79ø 0ø 13:53:52 3ø 36ø 13:58:29 285ø 0ø Ofeq-3
4/13/95 15:18:46 98ø 0ø 15:24:25 14ø 62ø 15:29:24 290ø 0ø Ofeq-3
4/13/95 16:49:09 124ø 0ø 16:55:05 203ø 43ø 17:00:20 284ø 0ø Ofeq-3
4/13/95 18:20:46 157ø 0ø 18:25:49 211ø 12ø 18:30:30 266ø 0ø Ofeq-3