The Cluster mission, consisting of four identical spacecraft flying in formation between 25,000 and 125,000 km above the Earth, will study the planet's magnetic and electric fields and the behavior of plasmas and energetic charged particles in those fields. In particular, Cluster will be looking at the effects of the solar wind, the radially expanding atmosphere of the Sun, as it buffets the Earth's protective magnetosphere. The large variations in this solar wind set up processes within the Earth's magnetosphere that are responsible for producing the spectacular aurora or "northern lights". Cluster will study these processes and will investigate many of cause and effect relationships of the Sun on the near Earth space environment.
Each of the Cluster spacecraft carries an identical set of 11 instruments. These are designed to detect electric and magnetic fields, various electric and magnetic waves, as well as electrons and charged atoms over an extensive range of particle energies. The satellites will fly in a tetrahedral (triangular pyramid) formation, and the data they collect will allow scientists to build a three-dimensional model of all the processes at work in the Earth's immediate space environment. This should provide insights into the influence of the Sun on the Earth environment.
The Cluster mission was conceived by the European Space Agency [ESA] as one of their cornerstone missions and involvement by NASA funded investigations were welcomed. The RAPID experiment team was formed from an international group of scientists in the mid 1980s to propose an investigation involving the measurement of energetic charged particles on the four satellite mission. The principal investigator and team leader was Dr. Berend Wilken of the Max Planck Institute for Aeronomy in Katlenburg-Lindau, Germany. The scientific and technical proposal developed by this team was successful and a two-sensor system integrated into a single hardware package was developed in the early 1990s.
On June 4, 1996 the four CLUSTER satellites were destroyed when the Ariane 501 rocket exploded shortly after lift off from the launch complex at Kourou, French Guiana. Efforts to prepare the flight spare spacecraft and instruments for a launch in the Spring/Summer of 1997 were then developed and called the Phoenix mission but ESA made the decision that Cluster would be rebuilt as a full four-satellite mission. This effort culminated in the successful launch of the Cluster II satellites in pairs on two Russian Soyuz launch vehicles from the Baikonur launch complex in Kazakhstan with the first launch occurring on July 16, 2000 and the second on August 9, 2000. The commissioning of the four satellites required five months. The two-year mission operational phase began in January 2001.
Research into Adaptive Particle Imaging Detectors (RAPID)
The RAPID spectrometer for the Cluster mission is an advanced particle detector for the analysis of suprathermal plasma distributions in the energy range from 20-400 keV for electrons, 40-1500 keV (4000 keV) for hydrogen, and 10 keV/nuc - 1500 keV (4000 keV) for heavier ions. Novel detector concepts in combination with pin-hole acceptance allow the measurement of angular distributions over a range of 180° in polar angle for either species. The detection principle for the ionic component is based on a two-dimensional analysis of the particle's velocity and energy. Electrons are identified by the well known energy-range relationship.
Ion Spectrometer (IIMS) - The Nuclei Detector SCENIC
The centerpiece of the IIMS sensor system is the so-called SCENIC detector head. The acronym stands for "Spectroscopic Camera for Electrons, Neutral and Ion Composition". In essence SCENIC is a miniature telescope composed of a time-of-flight (TOF) and energy (E) detection system. The novel aspect is the imaging of flux distributions and the capability to identify energetic neutral atoms (ENA) in a certain energy band. For more information, click here.
Electron Spectrometer (IES)
Electrons with energies from 20 keV to 400 keV are measured with the Imaging Electron Spectrometer (IES). Advanced microstrip solid state detectors having a 0.5 cm × 1.5 cm planar format with three individual elements form the image plane for three acceptance "pin-hole" systems. Each system divides a 60° segment into 3 angular intervals. A schematic cross-section of an IES pin-hole camera is presented the figure. Three of these detectors arranged in the configuration shown provide electron measurements over a 180° fan. For more information, click here.
The Role of Boston University and the Center for Space Physics
Professor Theodore Fritz was designated the responsible scientist in the RAPID team for the design and fabrication of the IES sensor. Dr. Fritz prior to coming to Boston University was a staff scientist at the Los Alamos National Laboratory in Los Alamos, New Mexico. At LANL he was involved in two other NASA experiments for the ISTP GGS Polar satellite and was responsible for the design of energetic particle sensors for the CAMMICE and CEPPAD investigations on that satellite. Using the synergism of these three projects, scientist and engineers at LANL under the direction of Dr. Fritz were able to develop a novel, compact sensor system to detect energetic electrons described above as the Imaging Electron Sensor or IES.
Dr. Fritz moved to Boston University in 1992-1993 with plans to involve students in the data reduction and analysis of the scientific data returned from these three energetic particle measuring experiments following their launch. Many students were involved in the integration and testing of these instruments on the respective satellites and trips to the spacecraft contractors and/or launch complexes by students were common in the 1992-1996 period.
Following the destruction of the four Cluster satellites on the Ariane 501, an effort to replace the four Cluster IES sensors was undertaken with Boston University as the lead organization with effort within the USA required from LANL and the Aerospace Corporation, El Segundo, CA. LANL had responsibility under the direction of Mr. Richard Belian and Mr. Roy Cope for the fabrication of the IES electronic assemblies and integration of all components into a final deliverable system. The Aerospace Corporation under the direction of Dr. Joseph Fennell had the responsibility for the fabrication of the IES data processing unit. The involvement of Boston University was as outlined:
- The many components of IES mechanical hardware were fabricated at the BU Scientific Instrument Facility.
- The IES solid state detectors were procured commercially and then tested by the CSP — mostly by students.
- The assembled IES units were calibrated using a particle beam accelerator facility at the NASA/Goddard Space Flight Center in Greenbelt, MD. Student Josh Glasel has provided the documentation of these calibration tests that were performed under the direction of Dr. David Matthews. The reduction of these data into the meaningful calibration parameters were done by a number of students and are documented on a web site at the Rutherford Appleton Laboratory in the UK.
- The interface to NASA, to the European satellite contractor, Dornier Systems and to the RAPID team principal investigator and project manager was provided by a project manager at BU, Mr. Peter Anderson, working with Dr. Fritz.