High Energy Transient Explorer 2 (HETE-2; also known as Explorer 79) was a NASA astronomical satellite with international participation (mainly Japan and France). The satellite bus for the first HETE-1 was designed and built by AeroAstro, Inc. of Herndon, Virginia and was lost during launch on 4 November 1996; the replacement satellite, HETE-2 was built by Massachusetts Institute of Technology (MIT) based on the original HETE design.
International participation The PI Institution at MIT is the headquarters for the HETE-2 Team; however, team members in science, instrument, and engineering are global. Participating institutions with HETE-2 team members include the following:
MIT, Center for Space Research (MIT/CSR) in Cambridge, Massachusetts — main investigator for HETE-2; George Ricker. MIT built and tested the spacecraft bus, the satellite control software, the primary ground station at Kwajalein Atoll, and the burst alert stations in the Galápagos, Ascension, Gabon, Kwajalein Atoll, and Kiribati. MIT/CSR designed and built the optical camera and soft X-ray camera systems for the HETE-2 project; these instruments used MIT Lincoln Lab CCD sensors. Los Alamos National Laboratory (LANL), Los Alamos, New Mexico – designed and built the WXM coded aperture and WXM flight and ground support software. University of California, Berkeley Space Sciences Laboratory (SSL), Berkeley, California – responsible for Fregate instrument data analysis and instrument health software, as well as SXC software effort. University of California, Santa Cruz (UCSC), Santa Cruz, California – aided in the design and construction of the spacecraft and ground control systems. University of Chicago, Illinois – responsible for gamma-ray burst localization methods and sophisticated spectrum analysis tools. Centre d'Étude Spatiale des Rayonnements (CESR), Toulouse, France – responsible for Fregate flight software, operations, and on-orbit commands. The Hiva Oa and Cayenne burst alert stations are also theirs. Centre Nationale d'Études Spatiales (CNES), Toulouse – built and tested the GPS required to provide precise timing and orbital elements for HETE-2. École Nationale Supérieure de l'Aéronautique et de l'Espace (Sup'Aero), Toulouse – constructed Cayenne's primary ground station. Instituto Nacional de Pesquisas Espaciais (INPE), São José dos Campos, Brazil – Joao Braga of INPE, a scientific collaborator on the HETE-2 team, oversees the Burst Alert Station located in Natal, Rio Grande do Norte, Brazil. Tata Institute of Fundamental Research (TIFR), Mumbai, India – TIFR's Ravi Manchanda is in charge of the Burst Alert Station in Bangalore. Consiglio Nazionale delle Ricerche (CNR), Bologna, Italy – Graziella Pizzichini of TESRE in Bologna guided the HETE-2 team and manages the Burst Alert Station in Malindi, Kenya. Institute for Chemistry and Physics (RIKEN), Wakō, Saitama, Japan – built and tested the WXM hardware, built the principal ground station at NUS, and are responsible for the burst alert stations in Palau and Singapore. They also work with Miyazaki University to command and maintain the WXM instrument in orbit.
History After the launch mishap of HETE-1, NASA agreed to rebuild the satellite using flight spares. The funding for HETE-2 was approved in July 1997, and construction began at MIT in mid-1997. Prior experiences including observations of GRBs in early 1997 by BeppoSAX and ground-based telescopes indicated that "the effect of background electrons and protons would have a profound effect on the observing efficiency and lifetime of HETE-2's X-ray instruments". As a result, the UV cameras were removed, two of which were replaced with a CCD-based coded-aperture imager (Soft X-ray Camera or SXC). The other two were replaced with optical CCD cameras, which serve as star trackers on HETE-2. NASA agreed in 1998 that HETE-2 would fly in an equatorial orbit. The HETE-2 satellite was completed in January 2000, and was fully tested and in ready state at Vandenberg Air Force Base in California. The plan was to ferry the satellite to Kwajalein Atoll for a 28 January 2000 launch; however, on 14 January 2000, NASA postponed the launch over concerns of not having everything comfortably in place prior to launch time. Among the contributing factors was NASA's concern that neither of the HETE-2's backup stations (Cayenne, French Guiana; Singapore) were fully operational. The Cayenne station needed approval for export from the International Traffic in Arms Regulations (ITAR) (U.S. State Department) which meant it would not come online until a week prior to the scheduled launch, whereas the Singapore station may not be available until after the scheduled launch date. The need for ample telemetry contact with HETE-2 during the critical early phases of the mission served to heighten concern over ground station availability. Without it, they could not properly respond to, avoid or minimize, any unforeseen satellite activation difficulties, such as those encountered by a number of prior NASA-launched missions. Another determining factor in the postponement was the reservation date of 28 January – 8 February for HETE-2's launch at Kwajalein Missile Range (KMR). NASA rescheduled the first launch at KMR in favor of a mid-May time frame. They also determined that the extra time would allow for the HETE-2 satellite to be returned to the East Coast for additional simulations and further testing to enhance the likelihood of a successful mission. A limited budget and "single string" designs for HETE-2's major systems placed practical limits on the level of performance testing that could be performed to increase reliability. A 1000-hour thermal vacuum cycle (1.5 times longer than HETE-2's pre-shipment thermal vacuum testing, and 1/4 of the required mission life) were among the additional shock and vibration tests. HETE-2 was successfully launched on 9 October 2000.
Mission
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