USA-40

 1989-061B

---

The USA 40 satellite was deployed on mission STS-28R in Aug 1989 into a 300 km, 57 degree orbit. Amateur observers recorded it raise its orbit to 432 x 487 km a week later, and noted that it was spin stabilized based on optical flashing - the mystery satellite was nicknamed the `Flasher'. Further small burns were made in early November, and then in mid November it was lost by observers. At the same time Space Command cataloged a rocket stage, `USA 40 R/B', implying that this rocket had just separated from USA 40. The obvious implication is that a major burn had placed USA 40 in a higher orbit, with the rocket stage separating after completion of its task. It is now believed that the orbit was a Molniya-type 12 hour, 63 degree elliptical path like those used by the SDS satellites.

The three month wait between deployment and orbit raising might just have been to let the orbital plane precess to a desired longitude, but this seems rather unlikely. It is possible that the three month delay may have involved a separate mission; this recalls the original plan for the CRRES science satellite, which in its Shuttle launched incarnation was to have carried out a several-month low orbit radiation study mission followed by a high orbit chemical release mission. Another explanation would be a partial failure of control of some kind. Perhaps the attitude control system failed and the motor firing was postponed until appropriate new software and/or control techniques were developed. However, the fact that the second flight (USA 89, below) may also have had a several month low orbit phase argues against a failure.

Another open issue is the nature of the upper stage. It seems likely that the small maneuvers made early in the mission may be a liquid propulsion system associated with the payload itself, while the separately cataloged rocket stage was used for a single burn and may be a solid motor. Cargo bay drawings of the USA 89 flight suggest a configuration similar to the Hughes Leasat; Hughes was also contractor for the first generation SDS, so design commonality with Leasat would be plausible although for a dedicated Shuttle mission the mass must be significantly higher. Nevertheless a Minuteman-3-third-stage-class solid perigee motor, either the CSD Orbus 7S or more likely the similar Thiokol TU-844, must be one of the prime candidates for the USA 40 upper stage. A Star 48 or Star 63 (PAM D) would have used the sunshade ASE and there is no evidence of this. The Leasat used a Thiokol motor, while the more powerful Orbus 21S was used in TOS. The latter required an IUS type tilt table, also incompatible with the payload bay arrangement for STS 53 (if that diagram can be trusted). I conclude that an TU-844/Leasat class vehicle is the most probable configuration for the USA 40 type payloads, but the 7t mass of such a vehicle is lower than one would expect. Dwayne Day has concluded that the satellite is actually derived from the Intelsat 6 bus, the HS-389.

Another factor is that it appears that Orbus 6 motors have been used in some classified application, and this is the most likely option for that application; and the R4D-11 engine was used on some classified Hughes satellite around that time. I conclude that a plausible configuration for the SDS Mark II is an Intelsat-6 or Leasat-type bus with a TU-844 or Orbus 6 solid PKM and an R4D-11 liquid apogee engine for orbit trim burns.

For the sake of experiment, let us assume a further burn a couple of days later at perigee, 1956 UTC on Dec 2, to a Molniya orbit of 507 x 39400 x 63. We estimate that the pre and post burn mass are of order 5277 kg and 3000 kg; this would give a dV of around 1.7 km/s. The burn to Molniya orbit needs about 1.4 km/s for the apogee increase, but around 4.9 km/s if the inclination change is included - this seems large. The inc change is less than 1 km/s if it is done at equator crossing: a total of 1.82 km/s is needed for a burn at 1926 UTC at southbound equator crossing at an altitude of 3200 km; this is much cheaper and fits the Orbus 7S capability pretty well for an SDS-like final orbit of 1040 x 39400 x 63 deg. The higher perigee is a natural consquence of doing the burn away from transfer orbit perigee. Apogee is at high northern latitudes as required.

USA 40
Date	Time	Event	Orbit
1989 Aug 8		Launch by Shuttle
1989 Aug 8	1835?	Deployed from OV-102	300 x 300 x 57
1989 Aug 10		Fiducial burn 37m/s	295 x 432 x 57
1989 Aug 11		Fiducial burn 49m/s	431 x 469 x 57
1989 Aug 16		Raised orbit, spinning	432 x 487 x 57
1989 Oct		Reduced flashing noted
1989 Nov 8		Raise orbit	409 x 510 x 57.0
1989 Nov 13	0400		93.63 401 x 502 x 57.0 (CSS)
1989 Nov 30?		Upper stage burn - about 1284 m/s	504 x 8161 x 57.0
1989 Nov 30		Upper stage sep	532 x 8135 x 57.0
1989 Dec?			500? x 39400? x 63? (Speculation)
1989 Dec 2	1953	Notional LAM burn 4.94km/s?