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HETE 2
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.
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:
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.
The prime objective of HETE-2 was to carry out the first multi-wavelength study of gamma-ray bursts (GRB) with ultraviolet (UV), X-ray, and gamma-ray instruments mounted on a single, compact spacecraft. A unique feature of the HETE mission was its capability to localize GRBs with ~10 arcseconds accuracy in near real time aboard the spacecraft, and to transmit these positions directly to a network of receivers at existing ground-based observatories enabling rapid, sensitive follow-up studies in the radio, infrared (IR), and visible light bands. The High Energy Transient Explorer 2 (HETE-2) is designed to help determine their origin and nature.
The spacecraft is basically a rectangular cube, roughly 100 × 50 × 50 cm (39 × 20 × 20 in), with four solar panel petals protruding from the bottom. The bottom section of the spacecraft holds the power, communications, and attitude control and the upper section the science instruments. Power is supplied by the solar panels, which are made of honeycomb aluminum with a silicon substrate, each supplying 42 W. There are 6 battery packs, each containing 24 1.5 V NiCd cells, each with 1.2 A-hr capacity. Communication is via S-band uplink (2.092 GHz) and downlink (2.272 GHz) using 5 dual-patch antennas. A very high frequency (VHF) downlink (137.9622 MHz) was used for the real-time burst alerts via a whip antenna mounted on one of the solar panels. Attitude control is achieved by a momentum wheel and three orthogonal magnetic torque coils, controlled by inputs from two magnetometers, twelve Sun sensors, and an optical camera.
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HETE 2
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.
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:
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.
The prime objective of HETE-2 was to carry out the first multi-wavelength study of gamma-ray bursts (GRB) with ultraviolet (UV), X-ray, and gamma-ray instruments mounted on a single, compact spacecraft. A unique feature of the HETE mission was its capability to localize GRBs with ~10 arcseconds accuracy in near real time aboard the spacecraft, and to transmit these positions directly to a network of receivers at existing ground-based observatories enabling rapid, sensitive follow-up studies in the radio, infrared (IR), and visible light bands. The High Energy Transient Explorer 2 (HETE-2) is designed to help determine their origin and nature.
The spacecraft is basically a rectangular cube, roughly 100 × 50 × 50 cm (39 × 20 × 20 in), with four solar panel petals protruding from the bottom. The bottom section of the spacecraft holds the power, communications, and attitude control and the upper section the science instruments. Power is supplied by the solar panels, which are made of honeycomb aluminum with a silicon substrate, each supplying 42 W. There are 6 battery packs, each containing 24 1.5 V NiCd cells, each with 1.2 A-hr capacity. Communication is via S-band uplink (2.092 GHz) and downlink (2.272 GHz) using 5 dual-patch antennas. A very high frequency (VHF) downlink (137.9622 MHz) was used for the real-time burst alerts via a whip antenna mounted on one of the solar panels. Attitude control is achieved by a momentum wheel and three orthogonal magnetic torque coils, controlled by inputs from two magnetometers, twelve Sun sensors, and an optical camera.
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