El satélite argentino de observación astronómica SAC-B se lanzó en 1996 (antes que el SAC-A). Tenía por objetivo de investigar las fuentes explosivas extragalácticas de alta energía. Su peso era de 191 kg, (50 kg de carga útil). Fue puesto en órbita montado en el cohete estadounidense Pegasus XL apodado Maggie. Debido a fallas en el vehículo lanzador no pudo ser desacoplado del mismo.

Launch and final state of the Mission

Launching operation details

The SAC-B mission was launched from the NASA base at the Wallops Islands on November 4, 1996.  An L-1011 airplane released the launcher Pegasus at 13,000 m height, the moment when Pegasus and the airplane became apart being considered the launching time.  SAC-B was deployed according to schedule, nearly meeting the nominal, i.e.05:09 p.m. GMT (02:09 p.m. Argentine local time).

A technical report by the team responsible for the SAC-B project stated that, after reaching the expected orbit (550 km height and 37.97° inclination),  Pegasus’ third stage should perform the following operations: to point the SAC-B major axis to the Sun; to have the satellite rotate up to the proper position; to fire at least one of the pyros to allow the SAC-B ejection; then to decrease rotation up to almost 0° and produce a 90° turn of the pointing axis. The next step was to fire the pyros to eject the HETE (SAC-B American launch partner), and to maneuver the launcher away from the satellite.

After 1 hour and 50 minutes from SAC-B expected ejection, the commander of the L-1011 reported that successful ejection of both satellites had shown on the radar screen.  Nevertheless, no confirmation could be obtained from the ground control teams.  82 minutes thereafter, during the primary pass of SAC-B over the ground control center at Wallops, USA (launch base), telemetry was downlinked indicating failing

Operations during the orbiting

Once radio-electrical contact with the satellite was established at Wallops, SAC-B was commanded to turn on the transmitter.  Excellent telemetry was transmitted on the spot, meaning that all systems on board were thoroughly working and command-reacting.  After confirming the lack of separation, commands were uplinked during the next pass over the tracking base at Goldstone, USA for the SAC-B to deploy the solar panels, and to turn on one of the transmitters.  A successful solar panels deployment took place.

Throughout the five contacts established with the SAC-B (two from the Wallops Islands (USA) and three from the San Miguel (Argentina) ground stations), all systems on board were nominal, and provided the expected response to commands uplinks and telemetry downlinks.

Both the Wallops Islands and the San Miguel control centers set immediately about analyzing the satellite’s attitude data in order to set up a strategy to optimize the use of power generated on board.  They first concluded that the launcher had wrongly oriented SAC-B to the sun, thus preventing replenishment in proportion to its consumption.  Furthermore, additional power was needed to reorient a whole assembly of 541 kg (SAC-B + Pegasus third stage + satellite HETE), almost three times heavier than the SAC-B itself (191 kg).

A report from Orbital Science Corporation (OSC) that provided the launcher stated that one out of the four electrical power distribution bus on the Pegasus third phase became disabled after approximately 8 minutes flight (upon separation from the second stage).  Consequently, both the pyros for the SAC-B ejection and the attitude control device of the Pegasus’ third stage remained unpowered, and could not fulfill their duties.

Since the last contact with SAC-B (12 hours from launch) until the launch of the SAC-A in December 1998, CONAE made considerable efforts intended to regain contact with the satellite via the San Miguel (Argentina), Córdoba (Argentina), and Malindi (Kenya) ground stations.  Unfortunately, with no results.  CONAE therefore declared the recovery phase closed as of the said SAC-A launching date.