Return To The Equator

December 10, 1997

A satellite named EQUATOR-S was launched from the Guiana Space Center on 2 December 1997 on an Ariane 4. The spacecraft was built at the Max-Planck-Institut fuer extraterrestrische Physik, Garching (Germany). Its goal is to support the Inter-Agency Solar-Terrestrial Physics Program by measurements near the equator.

In 1980, NASA began to plan a comprehensive program for the study of the Earth's magnetosphere, the space that is dominated by the Earth's magnetic field. The name of the program was OPEN for "Origin of Plasmas in the Earth's Neighborhood". Four spacecraft were foreseen, one in front of the magnetosphere, one in the magnetotail, one above the north-polar region and the fourth one in the equatorial plane. A few years later, the objectives were widened and the program renamed to "Global Geospace Science" program (GGS). The four spacecraft received the names WIND, GEOTAIL, POLAR, EQUATOR. Among a great many institutes, also from outside USA, the Max-Planck-Institut fuer extraterrestrische Physik (MPE) at Garching had proposed instruments to measure the electric field and the ionic energy and mass distribution, in particular for the EQUATOR spacecraft. Unfortunately, this very spacecraft was cancelled in 1986 in an effort of NASA to limit the total costs of the GGS program.

In 1980, the same group of MPE had delivered to the European launch facility in Kourou, French Guayana (located 7 degrees north of the equator), the Firewheel spacecraft for launch on the second test flight (L02) of the new European satellite carrier Ariane. The launch opportunity, to which the European Space Agency (ESA) had invited MPE, was cheap, and the five battery powered spacecraft, built by MPE and three other laboratories in the USA, Canada and United Kingdom, were relatively cheap as well. They were designed to perform a number of plasma cloud releases in the outer magnetosphere under comprehensive in-situ diagnostics by more than twenty instruments on the mother and four daughter satellites. Unfortunately, the launch on 23 May 1980 was a failure. The equator had not brought luck to MPE.

Scientists tend to adhere to their goals tenaciously. Another program called AMPTE, which was carried out jointly with USA and the United Kingdom, brought MPE in 1984 - 1985 the opportunity of performing six plasma cloud experiments in the solar wind and magnetotail, among them two artificial comets. This made up for the loss of Firewheel. But also EQUATOR was not forgotten. After several unsuccessful attempts of other space agencies to revive this mission, Professor Gerhard Haerendel, director at MPE and head of the group of MPE that had built the Firewheel and AMPTE IRM spacecraft, conceived the idea to build with this group a small version of the EQUATOR, the EQUATOR-S spacecraft. The idea was triggered by the news that the University of Rome was in the process of modernizing the San Marco launch platform, which Italy had built in 1966 off the coast of Kenya close to the equator, and to launch from there an Advanced Scout rocket for which a passenger had yet to be found. Contacts with the University of Rome developed very positively. Unfortunately, after about three years also this attempt had to be buried, because the expected funding of the University of Rome had not materialized.

However, EQUATOR-S was not allowed to die. Other launch opportunities were investigated and seven different versions of the spacecraft designed. Finally, in December 1994 the German Space Agency, DARA, accepted MPE's proposal to build the spacecraft in-house and launch it as in "Auxiliary Passenger" on an Ariane 4 at very moderate costs.

MPE went to work and produced the spacecraft of 230 kg mass housing six particles-and-fields and three technology instruments in less than three years with a team of only ten persons and an extremely low budget. Only few subsystems, the solar panels, the kick motor, and the RF components as well as the structural and thermal analysis were procured by external contractors, everything else was developed, built, tested and integrated at the institute.

Finally, the MPE team returned to the equator, to Kourou, where Firewheel had been lost seventeen years ago. In spite of this history, the feelings of the team were not dominated by anxiety. Confidence in the Ariane 4 rocket, confidence in its own work prevailed. However, when on 2 December at 22:52:32 UT the rocket roared into the tropical sky, the tension was great, only to burst into a wave of relief and joy, when 25 minutes later EQUATOR-S was injected into the predicted orbit.

At the time of writing, EQUATOR-S is still in this orbit, a geostationary transfer orbit with an apogee of 36 000 km. All systems operate as expected. In a few days, the onboard kick-motor is to be fired, and the apogee will be raised to 66 000 km height. This way the satellite will be able to reach and penetrate through the dayside magnetopause and explore the source region of the aurora borealis on the night-side. Thus it will become a valuable member of the fleet of 12 or more already orbiting satellites combined in the Inter-Agency Solar-Terrestrial Physics program of NASA, ESA, IKI (Moscow) and ISAS (Japan), among them WIND, GEOTAIL and POLAR. If the injection into the final orbit and the commissioning of the experiments proceeds as smoothly as the launch, the science phase will begin, and the return to the equator after this long waiting and preparation period will have paid.


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