A MORE IN-DEPTH STUDY OF THE FORCES AT WORK IN THE MAGNETOSPHERE THANKS TO ISEE-3
ISEE-3 is a satellite from the ISEE program “International Sun-Earth Explorer”. The purpose of this program was to study the relations between the solar wind and the terrestrial magnetosphere.
AN AMBITIOUS COOPERATION BETWEEN EUROPEAN AND AMERICAN AGENCIES
This project was born thanks to the cooperation between the European space agency (ESA) and the National Aeronautics and Space administration (NASA). After the discovery of the magnetosphere by the satellite Explorer 12, scientists had a common will to study the variations and the strengths involved in the magnetosphere in the late sixties.
THE THIRD SATELLITE OF THE ISEE PROGRAM
Historically, ISEE-3 is the third satellite of the ISEE program. It was preceded by two other satellites: ISEE-1 and ISEE-2, respectively built by NASA and ESA. The 22nd of October 1977 a Delta 2914 rocket launched from the Cape Canaveral launching base and proceeded to the orbit insertion of the ISEE 1 and 2 satellites. Their mission was to take measurements of the Magnetosphere from a close range (for accuracy purposes). ISEE-1 (or “ISEE-A” or “Explorer 56”), was developed by NASA, it was the parent satellite, which explains why it was nearly twice the mass of ISEE-2, which was developed by ESA. With that said, ISEE-2 was of crucial importance because it was endowed with a propulsion mechanism that allowed scientists and engineers on the ground to reduce the distance between them in order to execute the planned measurements. They were between 50 and 5000 km away from each other and had the same measuring instruments at their disposal for comparative measurements. Ten years later and almost 1600 orbits around the Earth, the first two satellites of the ISEE program were destroyed the 26th of September 1987, during their re-entry into the Earth’s atmosphere.
THE FIRST MACHINE TO REACH LAGRANGE POINT (L1)
The thrilling story of the ISEE-3 satellite begins a little less than a year after the successful launch of its predecessors on 12th of August 1978. It was built by NASA, and is very similar in design to the ISEE-1 satellite. Its fame results from the fact that it is the first spacecraft to be placed in orbit in the Earth-Sun frame reference on a “Lagrange point” (also known as “libration points“): a position in space wherein the gravitational field of two bodies “nullify” each other (to be more precise, “compensate” each other), thus creating a point of stability for a third body of negligible mass. It was Joseph-Louis de Lagrange (1736-1813), an Italian-French mathematician, who spoke about this as a privileged point in a relationship between two massive objects.
WHAT ARE THE LAGRANGE POINTS ?
There are five Lagrange points. The first one (L1) is located on the Earth-Sun axis about one hundredth of its distance, roughly about 1,500,000 kilometers from our planet. The second (L2) is located, once again on the Earth-Sun axis, but in the opposite direction. This point is located behind the Earth and faces outwards the Solar System. The third point (L3) is “approximately” opposite of the Earth compared with the Sun. The fourth and fifth points (L4 and L5), also called “Trojan points”, are located in the orbit of the smallest mass (the Earth). All of these points are very useful for anyone wishing to gather information about our Solar System or beyond. For example, L1 is ideal for observing the Sun. Finally, there is a distinction between these different points, the so-called “stable” point and the so called “unstable” point. L1, L2, and L3 are not in the same orbit as the Earth (around the Sun), so they would have to be faster or slower than the Earth to orbit the Sun. However, the gravitational forces of the Earth and of the Sun influence the speed of these satellites. Ultimately, it is the gravity generated by these two masses that will stabilise the trajectory and speed of these points. However, if the object on these same points deviates at a given moment, it can leave its orbit and move away from the Earth and the Sun indefinitely. This is why the Lagrange points L1, L2, and L3 are said to be “unstable”, they need propulsion instruments to compensate this instability and not leave their orbit. On the other hand, points L4 and L5 are “stable”, so natural bodies such as asteroids, for example, can be found there. In the Sun-Earth frame of reference, for example, an asteroid (name: 2010 TK7) was discovered at point L4 in October 2010.
ISEE-3 has reached the Lagrange point L1 the 20th of November 1978. It managed to collect datas both on the solar wind, the cosmic rays and gamma rash. The 10th of June 1982, ISEE -3 left the Lagrange point L1, another mission has been assigned to it, return close at hand of the Earth to study the magnetoqueue and collect datas about the Giacobini-Zinner comets and Halley in 1985- 1986. It will be renamed as ICE (“International Cometary Explorer“). In the Earth-Sun frame reference, the spacecraft which have reach that same point, are the ISEE3, Wind, Genesis and Lisa Pathfinder satellite. Today, new space probes are there like the Soho spacecraft (“Solar and Heliospheric Observatory“) launched in December 1995 and it’s still in activity or the DSCOVR satellite (discover or GoreSat) it contributes to the regular publication on internet about the Earth pictures and the hidden side of the Moon.
ISEE-3 SATELLITE’S LAST MISSION
This project is being carried out by the Space College Foundation. The members of the ISEE-3 Reboot project had obtained NASA’s approval to take control of the spacecraft, they wanted to bring it back to the Lagrange point L1. Even though NASA had been persuaded by this ambitious project, NASA didn’t want to get financially involved. The first step for the members of the ISEE-3 Reboot Project was a fundraising via crowdfunding to deal with the extreme urgency of the deadline of the 10th of August 2014 at the end of which it was impossible to contact the satellite again. This fundraising would allow them to raise $160,000, which is enough money to help them set up a space control center and obtain the basic equipment necessary for their project. The ISEE-3 Reboot Project engineers were assisted by NASA engineers, they were developing a communication device compatible with the satellite. In May 2014, the Space College Foundation team finally re-established contact with the satellite and activated its control system. The satellite returned to the Earth’s vicinity in August 2014, but unfortunately after all the efforts made by the members of the Space College Foundation, the contact had been lost in mid-August 2014 after the probe flew over the Moon and since then there was no more news of ISEE-3.
This article was written by Yacine BENARAB, Aurélien CORNE, Julie DODIN, Rémy JIN, Kévin MAYELE, Hawawou Modjissola SADISSOU and Flavien SALGADO (Paris-Saclay).