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.

Detailed technical information

Scientific Instruments

The Argentine instrument provided by CONAE and developed by the Institute of Astronomy and Space Physics, was the Hard X Radiation Spectrometer (Hard X-Ray Spectrometer - HXRS) that was intended to study gamma-ray flares and emissions X-ray emitted in solar flares.

Two of the instruments were provided by the NASA Radiation Experiment X Goddard (Goddard X-Ray Experiment - GXRE) for the detection of gamma rays from the sun and other sources and X Radiation Detector Fuzzy Fund (Unresolved Cosmic X-Ray Background instrument - CUBIC) instrument provided by Penn State University, which used a CCD for the study of X-rays from certain regions of the sky. NASA also provided dual launch services aboard a Pegasus XL vehicle.

The Italian Space Agency (ASI) provided a scientific instrument for the study of high energy neutral atoms that are at the height of the satellite orbit, the Particle Imaging Spectrometer for Energetic Neutral Atoms (Isena) and solar panels. Environmental testing and qualification of the SAC-B were carried out in the Laboratory of Integration and Test that has the National Institute for Space Research of Brazil (INPE) in Sao Jose Dos Campos.

1-The Hard X-ray Spectrometer (Hard X-Ray Spectrometer - HXRS), provided by the Institute of Astronomy and Space Physics (IAFE), Argentina. HXRS observes the hard X-ray range between 20 and 320 keV rapidly changing events in scales of tens of milliseconds. The instrument had the capability to provide information on the temporal evolution of the X-ray emission in solar flares both as non-solar flares of gamma radiation.

2-The X-ray experiment Goddard (Goddard X - Ray Experiment - GXRE), provided by NASA / Goddard Space Flight Center, consisted of two sets of detectors:

  • The Soft X-Ray Spectrometer (soxS), acting in coordination with the HXRS for solar observation.
  • Eruptores Spectrometer Gamma Radiation (Grabs).

3-X Radiation Detector Fuzzy Fund (Unresolved Cosmic X-Ray Background Instrument-CUBIC), provided by Pennsylvania State University. United States, with high spectral sensitivity between 0.1 and 10 keV of selected areas of the sky.

4-The Imaging Spectrometer High Energy Neutral Atom (Particle Imaging for Energetic Neutral Atoms Spectromenter-Isena), provided by the Italian Institute of Interplanetary Space Physics.

Satellite Platform

The SAC-B satellite was 191.5 kg. The satellite body was a rectangular parallelepiped of 62 cm x 62 cm by 80 cm high with four solar panels 62 cm wide by 76 cm long.

The satellite platform is composed of the following subsystems:

  • Structure
  • Power
  • Thermal Control
  • Attitude control
  • Command and data handling
  • RF communications


The solar instruments (the HXRS and soxS) were mounted on the platform facing the Sun, along with the Solar Sensor Thin, with angles of view pointing to the Sun solar platform (lower deck) contained the whole of the interface the Pegasus launch vehicle and Marman clamp band. The grabs also was mounted solar platform, but with fields of view of the satellite opposite sides perpendicular to the axis pointing to the Sun The CUBIC field of view is normal to the axis pointing to the Sun, while the Isena not impose pointing any specified address.

The structure contained two panels "pseudo-honeycomb". Inside an aluminum sandwich structure was machined solid material, with two circular protrusions to grip.

The lower platform interface makes the Pegasus launch vehicle and is connected to a second sandwich panel (equipment platform) by eight columns 6061-T6 aluminum, and also with an angle frame 6081-T6 aluminum in the higher structure called PSU. Side panels of 6081-T6 aluminum are subject to the two sandwich panels, to the upper structure and the support columns, forming a structure "semi-monocoque".

Shock isolation was used to mitigate the effects of violent impact, caused by the separation system to release Marman clamp band on instruments mounted solar platform.


The power system consisted of solar panels to collect power, batteries, power distribution bus, the battery charging system circuits and power dissipation. The four panels were coated GaAs cells and feeding power loads directly to the satellite through a primary bus 28 V regulated.

The table shows the power consumption available for airborne equipment.


The two batteries of 10 Ah NiCd supplied power storage. Solar panels were within 10° of boresight of the Sun producing 256 watts and 235 watts BOL EOL.

Thermal Control

The instruments and electrical components are thermally controlled between -10° and +40° using a semi-passive thermal system of heaters and radiators. The batteries were thermally isolated from the rest of the satellite and were controlled by heaters and radiators.

The outer surface of SAC-B was covered except the openings MLI instruments and radiators. There were two radiators and two batteries for the main thermal compartment, while the CUBIC instrument had a heater itself, the TEC (Thermal Electric Cooler).

The surfaces of the radiators were covered with white paint GSFC MS-74.

Requerimientos Térmicos

Temperature Limits - ° C




Attitude Control (ACS)

3-axis stabilization SAC- B was obtained with two inertia wheels in a configuration in "V" for the z-axis control ( rolido ) and the x-axis (yaw ) . The pitch axis control (pitch ) was done with magnetic coils air center . These coils also unloaded inertia wheels .

The sun sensor thick, fine sun sensor 2-axis (FSS ) and 3-axis magnetometer ( TAM ) allowed the determination of the attitude with an accuracy of 3 in real-time, 2 in the subsequent analysis. The attitude was obtained using the standard Triad method . This method requires knowledge of vectors and inertial two bodies : the sun vector (measured by the FSS ) and the magnetic field vector (as measured by TAM ) in the satellite system , solar vector magnetic field in the system onboard inertial calculated . The magnetic field is obtained from a table stored on board, from the Earth's Magnetic Field Model IGRF 10 terms . The Solar Sensor Thickness (8 cells mounted in the corners of the solar panels ) provided complete coverage during maneuvers Sun acquisition.

The SAC -B should be oriented to the sun for several roll offset angles to accommodate the requirements of CUBIC . The ACS operated in various modes. It was expected that during launch the ACS was in " stand by" , the system would continue with the actuators disabled while performing a self test to determine the decision to "go - no / go " for the separation of aircraft L1011 . Before the separation of the third stage of Pegasus , SAC- B and Pegasus should be brought to a rotation of 4 rpm .

Separation, it was planned that the ACS raise the wheel speed and reduce the inertia of the satellite spin zero. Nutation control was performed with a controller Bdot using 3-axis magnetometer and the magnetic coils . At that time it should deploy the solar panels , and solar sensor thickness and 3-axis magnetometer lead to precede z axis around the axis pointing to the SunIt is anticipated that the engineering phase comienzara with a command from the ground to check and calibrate responses to commands ACS solar sensor derived automatic coarse and fine sun sensor 3-axis magnetometer (as well as director of land commands ) and the behavior of the inertia wheels and torque coils . Once the engineering phase , the satellite should have come into normal operation in which
the satellite maintains the Z axis pointing to the Sun and the field of view of CUBIC (X axis ) pointing to any part of the ring around the sun with a width of + / - 180° + / _ 5° for two days.

During normal operation , the inertia wheels automatically be discharged by the three magnetic coils of torque. In case of a failure of attitude, ACS enter in a " safe hold" where the Z-axis is kept within the line 10 to the Sun.

The acquisition and processing of data in attitude , and control actuators were to be performed by two 80C86 microprocessor-based systems redundant (one on standby ) and associated logic circuits .

Command and Data Management

Commando tasks and data management SAC-B was provided by two fully redundant systems based on microprocessors. Each system comprising a microprocessor 80D86, 64 Kbytes of EEPROM, 64 Kbytes of RAM and 16 Kbytes of data RAM.

The command system should provide:

  • Relays commands (in real time and deferred) for circuit breakers
  • Command pulse (in real time and deferred) for functions on / off and reset
  • Serial Commands for data loading platform and tools

The telemetry system must collect, format and store data engineering and attitude in core 2 Mbits. The scientific data were stored in the memories of each of the instruments, and be transmitted to ground 50, 100 or 200 Kbits / s (nominal speed 100 Kbits / s). Ground was expected to transmit up to 100 Mbits per day of scientific data.

RF communications

For cost transmitters and receivers were used instead of transponders redundant.
Receptors were connected by electrical hardware of the satellite bus for continuous operation.
5 watt transmitters were lit with commands from the ground they passed over the ground station. Two quadrifilar helix antennas were mounted one on each side of the circularly polarized satellite, one right and one left, with a quasi-omnidirectional RF broadcast.