FIPS at a glance
The Fast Imaging Plasma Spectrometer (FIPS) instrument is part of the Energetic Particle and Plasma Spectrometer (EPPS), one of seven instruments on board the MESSENGER spacecraft (http://messenger.jhuapl.edu/). FIPS is an imaging mass spectrometer combining a novel wide-angle electrostatic deflection system and a linear time-of-flight system. Once MESSENGER arrives at the planet Mercury, FIPS, with the rest of MESSENGER’s instrument suite, will work to provide a comprehensive view of the structure and composition of the planet. In particular, FIPS will work as a part of the EPPS instrument to investigate the nature of Mercury’s small, Earth-like magnetosphere and its interaction with the solar wind and Mercury’s thin atmosphere.
Launch
The MErcury, Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft was launched on August 3, 2004 aboard a Boeing Delta II rocket from Cape Canaveral Air Force Station.
Status
The FIPS instrument was activated for the first time on September 8, 2004. It has since made many successful measurements of the interplanetary medium. It has also made measurements during the Venus flyby in June 2007.
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Journey
In 2004 the MESSENGER spacecraft began its seven-year voyage to the planet Mercury. MESSENGER will be the first to orbit Mercury as well as the first spacecraft to visit Mercury in more than 30 years, following Mariner 10 in 1975. After completing two flybys of Venus and two of Mercury, MESSENGER will orbit Mercury for one Earth year, looking for similarities with Venus, Earth, and Mars.
Timeline:
Launch – August 3, 2004
Earth flyby – August 2, 2005
First Venus flyby – October 24, 2006
Second Venus flyby – June 5, 2007
First Mercury flyby – January 14, 2008
Second Mercury flyby – October 6, 2008
Third Mercury flyby – September 29, 2009
Mercury orbit insertion – March 18, 2011
Measurement Objectives
In order to better understand Mercury’s surface, MESSENGER must gather detailed information about the planet’s magnetic field. FIPS will contribute to this endeavor by analyzing pickup ions liberated from Mercury’s surface by the solar wind, as well as analyzing the solar winds themselves. The FIPS instrument is designed to measure particle count rates, energy distributions, velocity vector distributions, and mass spectra at a high time resolution and between 50 eV/e and 20 keV/e in energy.
Instrument
FIPS is composed of three major subsystems: an electrostatic analyzer (ESA) system, a time of flight (TOF) system, and the sensor electronics. Particles flow into the device from specific directions through an entrance mask. The particles then travel along separate channels into an electrostatic potential where they are deflected into a carbon foil. Detectors record information about time, the instrument’s position and the voltage in the entrance system.
ESA
The ESA serves both as a UV trap and an energy-per-charge filter, allowing only ions of a very specific energy-per-charge interval (determined by a stepped deflection voltage) to pass through the system. Ions are filtered as they pass through a deflection region and then through a collimator. The necessary UV suppression occurs as the ions travel through an hourglass-shaped deflection region between the first and second collimators.
TOF
The speed of every ion is determined by measuring its travel time between the carbon foil and the stop MCP, separated by a distance of approximately 7.4 cm. As an ion passes through the carbon foil, it is subjected to some directional scattering as a result of interactions with the foil. Low energy secondary electrons are also released from the foil due to these interactions. The secondary electrons are accelerated, and then reflected by a diagonal mirror harp onto the start MCP, which produces a start signal. After leaving the foil, the ion travels straight through the TOF system until it strikes the second MCP, which produces a stop signal. The electronics measure the time difference between the start and stop signals, providing the time-of-flight of the ion. The time-of flight, together with the previously measured energy per charge, allows the mass per charge for each ion to be determined. This in turn determines the identity of the ion or greatly narrows the list of possible identities, providing insight into the elements that make up the measured plasma and their change states.
In addition to E/q filtering and TOF measurement, FIPS measures the direction an ion came from. The position information recorded by the time-of-flight system is ultimately determined by the ion’s angle of entry into the ESA.
Electronics
The FIPS electronics consists of five board-level subsystems packaged with the sensor: 1) The ‘Digital’ board includes fast-pulse amplifiers, constant-fraction timing discriminators, and a time-to-digital converter in order to measure time-of-flight. 2) The ‘Analog’ board contains three channels of pulse shaping electronics to measure position from the WSZ anode. 3) The deflection system high voltage power supply provides the voltage for the ESA. 4) The post-acceleration power supply provides the voltage for the TOF system. 5) The MCP bias power supply supplies both MCP assemblies with several output voltage taps for each.
Team
Science team: Thomas Zurbuchen (Instrument Lead), George Gloeckler, Patrick Koehn
Engineering team: Jim Raines (Operations Engineer), Bob Lundgren (System Engineer), Ken Arnett, Curt Cooper, Charles Edmonson, Greg Ritter, Steve Rogacki
Technical Specifications
| Mass: | 1.41 kg |
| Volume: | 17.0 x 20.5 x 18.8 cm3 |
| Power (average/maximum): | 1.9/2.1 W |
| Bitrate (avg): | 80 bps |
| Field of View: | 1.4 |
| Energy Range: | 50 eV – 20 keV |
| M/Q Range: | 1 – 40 amu/e |
| Scan Speed (nominal/burst): | 65/2 sec |
Technical challenges
MESSENGER’s orbit brings it within 0.3 AU of the Sun. At this close range, the spacecraft will encounter plasma of a very high temperature and density. The MESSENGER mission required a sensor that would be able to withstand an extremely harsh environment, yet be efficient and reliable, provide fast resolution and a three-dimensional field-of-view, have very low weight and have the ability to suppress potential background signals from energetic particles and high-energy electromagnetic radiation. FIPS was developed to meet all these requirements.
Engineering Feats of Note
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The FIPS instrument maintains a nearly full-hemisphere field of view with a novel electrostatic analyzer system, which is combined with a position-sensitive time-of-flight system. Its low mass, low weight and power and its ability to suppress noise from a variety of sources make FIPS a unique tool for space exploration. Further applications include the exploration of other planetary environments, and the observations of heliospheric plasma near the Sun.
Additional Notes
During the recent Venus flyby 2, the EPPS team got an opportunity to try out their operations and analysis techniques for mapping Mercury’s magnetosphere prior to the first encounter with Mercury in January 2008. The FIPS instrument measured the ions present in Venus’ ionosphere to determine the composition of the planet’s atmosphere. The instrument also investigated the interaction of the solar wind with the ionosphere.
The figure shows E/Q spectra at three different points during the encounter. These spectra are used to calculate plasma distributions and compositional characteristics of the Venus environment.
