Assuming that this will not be a launch of a new type of payload, then the available clues point to a Lacrosse payload. The payload fairing is 66 ft (20.1 m) in length, which in the past has always been used for Lacrosse and KeyHole payloads. The launch periods announced to-date would not permit a direct launch into either of the standard KeyHole orbital planes, leaving Lacrosse as the most likely payload. Since Lacrosse 2 is by far the older of the orbiting Lacrosses, it is reasonable to speculate that it is the one to be replaced, but will it orbit at the same inclination? Lacrosse 1 orbited at a 57 deg inclination; Lacrosse 2 orbits at 68 deg, and Lacrosse 3 orbits at 57 deg. The launch azimuth will be 160 deg, requiring only a modest dog-leg manoeuvre to enter a 57 deg or 68 deg inclination. Lacrosse 3 was launched on a Titan IV-A into a 153 deg azimuth, and entered a 57 deg orbit. The slightly greater azimuth of the upcoming launch may be due to the use of the more powerful Titan IV-B, which may enable/require a larger dog-leg. I have been given a rough verbal description of the groundtrack with respect to geographical locations near the launch site, which indicates to me a 57 deg inclination. Additional clues may be found in the latest delay in the launch date, which resulted in the advancement of the launch period by 4 hours, consistent with the rate of precession of the Lacrosse 2 and 3 orbital planes, and suggesting that there is some optimal spacing relative to one of the those planes. But which plane? If it is deemed necessary to continue to operate one Lacrosse in a 68 deg inclination orbit like that of Lacrosse 2, and if Lacrosse 2 is expected to remain in orbit for some time to come, then it might make sense to establish some optimal separation of their orbital planes. It may be argued that the relationship with Russia has improved sufficiently since the 1991 launch of Lacrosse 2, that imaging radar surveillance of the high Arctic is no longer required, in which case its 68 deg orbit would not be required. It may also be argued that greater surveillance emphasis is now required of nations closer to the equator, such as India, Iraq, N. Korea, and Pakistan, in which case, the 57 deg inclination would provide somewhat better coverage than a 68 deg orbit. Lacrosse 2 has been in orbit for more than 9 years. Lacrosse 1 was de-orbited after 8.3 years in orbit. This suggests that Lacrosse 2 may well be nearing the end of its useful life, in which case it would seem unnecessary to maintain an optimal plane spacing with a new Lacrosse, even if it enters a 68 deg orbit like Lacrosse 2's. Analysis of the orbital plane spacing opportunities afforded by the announced launch periods may assist in guessing the intended inclination. The launch period On 01 Aug 2000, of 02:00 UTC to 06:00 UTC, would have enabled a new Lacrosse to be placed between 41 deg and 101 deg east of Lacrosse 2; or, between 186 deg and 126 deg west of Lacrosse 3. If the optimal spacing is that which provides the most even coverage during a 24 hour period, then the Lacrosse 3 spacings seem to have been better than those of Lacrosse 2. The launch period On 11 Aug 2000, of 02:00 UTC to 06:00 UTC, would have enabled a new Lacrosse to be placed between 80 deg and 141 deg east of Lacrosse 2; or, between 138 deg and 78 deg east of Lacrosse 3. If the optimal spacing is that which provides the most even coverage during a 24 hour period, then the Lacrosse 3 spacings seem to have been better than those of Lacrosse 2. Had the launch period on 16/17 August not been advanced by 4 hours, then the spacing would have been between 99 deg and 159 deg east of Lacrosse 2; and between 110 deg and 49 deg west of Lacrosse 3, in which case the Lacrosse 2 spacings would have been better than those of Lacrosse 3. The present launch period of 16 Aug 2000 22:00 UTC to 17 Aug 2000 02:00 UTC nearly restores the plane spacings of 01 August, which seemed to favour an orbit like that of Lacrosse 3. My interpretation of the evidence leads me to believe that a 57 deg inclination is most likely, separated by somewhere between 130 to 170 deg from Lacrosse 3. Superimposing the initial 432 km x 678 km orbit of Lacrosse 3's Titan 2nd stage onto this launch, and assuming lift-off at the start of the launch period: 22:00 UTC on 16 August, the initial orbit would be: 1 70000U 00230.09372315 .00000000 00000-0 00000-0 0 05 2 70000 57.0090 20.7000 0177212 165.0881 195.5654 15.06051010 02 The greater dog-leg of this launch (compared with Lacrosse 3) could shift the RAAN by a few degrees. The Lacrosse can be expected to remain in a parking orbit near the 2nd stage for a day or two, before circularizing its orbit at the apogee of 678 km. The above orbit would be visible immediately at latitudes south of about 35 N, in the morning, and would rapidly enter morning visibility at more northerly latitudes. A launch later in the period would delay the start of morning visibility. I will update this analysis if new information warrants, and I will post updated elements once the launch occurs, including 68 deg elements, in case my 57 deg speculation is incorrect. Ted Molczan ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Wed Aug 02 2000 - 12:12:43 PDT