David E. Steitz
Headquarters, Washington, DC                 October 21, 1996
(Phone: 202/358-1730)

Jim Sahli
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-0697)


RELEASE: 96-213

TWO SPACE SCIENCE SPACECRAFT SET FOR LAUNCH FROM WALLOPS 

     NASA is scheduled to place two new space science 
spacecraft into orbit aboard a expendable launch vehicle this 
month from NASA's Wallops Flight Facility, Wallops Island, 
VA.

     SAC-B (Scientific Applications Satellite-B) is an 
international cooperative project between NASA and 
Argentina's National Commission of Space Activities (CONAE). 
The spacecraft is designed to advance the study of solar 
physics and astrophysics through the examination of solar 
flares, gamma-ray bursts, diffuse X-ray cosmic background, 
and energetic neutral atoms. Goddard's International Projects 
Office is managing SAC-B. 

     The SAC-B spacecraft will be launched with a companion 
payload named High Energy Transient Experiment (HETE). The 
HETE mission is led by the Massachusetts Institute of 
Technology under a contract with the Goddard International 
Projects Office.

     "A primary goal of the SAC-B program is to develop and 
test scientific technology on a new, light, capable 
spacecraft designed and developed in Argentina. Follow-on 
spacecraft will form a series of light spacecraft for space 
applications, scientific investigations, and technology 
development," said Dr. Mario Acuna, project scientist for 
SAC-B in Goddard's International Projects Office. 

     SAC-B and HETE will be launched from Wallops Flight 
Facility using a winged Pegasus-XL launch vehicle. The 
Pegasus-XL, built by Orbital Sciences Corp., Dulles, VA, is a 
three-stage, solid-propellant booster system carried aloft L-
1011 jet aircraft and released from the aircraft at an 
altitude of about 40,000 feet and an airspeed of Mach 0.8, 
100 miles east of Walllops.

     For the SAC-B mission, NASA is providing two scientific 
instruments, launch services on the Pegasus launch vehicle, 
and support for initial orbit operations and emergency backup 
throughout the mission life. CONAE is responsible for the 
design and construction of the SAC-B spacecraft, the Hard X-
ray Spectrometer (HXRS) instrument, the ground station and 
the scientific data distribution. 

     Under a separate agreement between Argentina and Italy, 
the Italian Space Agency (ASI) provided the solar arrays plus 
a scientific instrument named ISENA that will measure 
energetic neutral atoms.  Under an additional agreement 
between Argentina and Brazil, the Brazilian National Space 
Research Institute is providing the facilities required to 
perform environmental testing of the spacecraft.

     SAC-B, weighing 400 pounds (181 kilograms), will be 
operated by CONAE from their San Miguel Mission Operation 
Control Center located just outside of Buenos Aires, 
Argentina. An Argentine flight operations team will be 
responsible for the spacecraft and instruments, as well as 
tracking, data acquisition and science data management.  
Wallops and NASA's Bermuda Island tracking station will 
provide complete powered flight ascent coverage. 

     NASA's Wallops Tracking Station will provide launch 
support command and engineering telemetry support augmented 
by the NASA Deep Space Network which will provide one contact 
per orbit for up to 30 days after launch. With a 342-mile 
circular, 38-degree inclination orbit, the planned lifetime 
for the SAC-B mission is three years.

     SAC-B will carry three astrophysical instruments. The 
Argentine-built HXRS instrument which was developed by the 
Institute of Astronomy and Space Physics, will study changes 
in the spectra of gamma-ray bursts and solar X-ray flares. 

     Goddard will provide one instrument called the Goddard 
X-Ray Experiment (GXRE) that has twenty-two detectors of soft 
X-rays and gamma ray bursts emitted by solar flares and gamma 
ray bursts.  A diffuse X-ray background detector, the Cosmic 
Unresolved X-ray Background Instrument (CUBIC), is being 
provided by Penn State University.  It will map the X-ray sky 
in order to study the background radiation emanating from the 
galaxy and the universe. 

     HETE, a 275 pound spacecraft, will carry three 
instruments; a gamma-ray burst detector; an X-ray camera 
viewing the sky through a coded aperture; and ultraviolet 
(UV) cameras, which together allow investigators to detect a 
gamma-ray burst, use the associated X-ray emission to obtain 
a general location in the sky, and examine the output of the 
UV cameras to search for faint, associated UV emissions that 
can be located with great precision (within a few arc-
seconds). Some of this information will be continuously 
transmitted in real time for numerous ground observatories to 
participate in rapid co-investigations of observed targets.

     The HETE spacecraft also will be placed in a 342-mile 
(550 kilometer), 38-degree inclination orbit. The planned 
lifetime for the mission is six months. HETE has its own 
ground data collection system consisting of three primary and 
secondary receiving stations, and therefore does not require 
NASA communications, tracking or ground systems support. 

     Information on the SAC-B and HETE instruments can be 
obtained via the Internet World Wide Web at the following 
URLs: 

      CUBIC (SAC-B):
      http://www.astro.psu.edu/xray/cubic
      HETE (MIT):
      http://space.mit.edu/HETE/
      SAC-B (CONAE-Argentina):     http://www.conae.gov.ar/

                         -end-

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