Stephen E. Jaskulek

The MESSENGER mission to Mercury: scientific payload

Abstract The MErcury, Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission will send the first spacecraft to orbit the planet Mercury. A miniaturized set of seven instruments, along with the spacecraft telecommunications system, provide the means of achieving the scientific objectives that motivate the mission. The payload includes a combined wide- and narrow-angle imaging system; γ-ray, neutron, and X-ray spectrometers for remote geochemical sensing; a vector magnetometer; a laser altimeter; a combined ultraviolet-visible and visible-infrared spectrometer to detect atmospheric species and map mineralogical absorption features; and an energetic particle and plasma spectrometer to characterize ionized species in the magnetosphere.

INCA: the ion neutral camera for energetic neutral atom imaging of the Saturnian magnetosphere

Techniques developed for the detection and characterization of energetic (>20 keV) ions in space plasmas have been modified to include imaging so that energetic neutral atoms at Saturn may be used to form images of the Saturnian magnetosphere and its interaction with the atmosphere of the moon Titan. The basic elements of the ion-neutral camera head on the magnetospheric imaging instrument for the Cassini mission are described, with emphasis on developmental detection techniques and components. In particular, pulse-height analysis of the microchannel plate responses to different mass neutrals is used for rough composition determination, and deflection plates in the aperture as well as time-of-flight measurements allow imaging of neutral atoms from within regions of moderate intensity ambient ion and electron fluxes.

Energetic Particles at Venus: Galileo Results

At Venus the Energetic Particles Detector (EPD) on the Galileo spacecraft measured the differential energy spectra and angular distributions of ions >22 kiloelectron volts (keV) and electrons > 15 keV in energy. The only time particles were observed by EPD was in a series of episodic events [0546 to 0638 universal time (UT)] near closest approach (0559:03 UT). Angular distributions were highly anisotropic, ordered by the magnetic field, and showed ions arriving from the hemisphere containing Venus and its bow shock. The spectra showed a power law form with intensities observed into the 120- to 280-keV range. Comparisons with model bow shock calculations show that these energetic ions are associated with the venusian foreshock-bow shock region. Shock-drift acceleration in the venusian bow shock seems the most likely process responsible for the observed ions.

Return to Mercury: the MESSENGER spacecraft and mission

NASAs MESSENGER mission, part of its Discovery program, is the first mission to return to the planet Mercury since the Mariner 10 flybys in 1974 and 1975. The spacecraft incorporates many innovative features, including a sunshade made of ceramic cloth for protection from the Sun, a pair of electronically steerable phased-array antennas, and specially hardened solar panels. A suite of seven miniaturized science instruments, along with the antennas, will globally characterize the planets composition, structure, atmosphere, and charged particle environment. MESSENGER was launched on August 3, 2004, and performed its single Earth flyby on August 2, 2005. The spacecraft will make two flybys of Venus and three of Mercury prior to orbiting the planet for one Earth-year beginning in March 2011. Highlights of a busy first year of flight operations include initial testing of all spacecraft systems and instruments, execution of six trajectory control maneuvers, and instrument observations of the Earth and Moon surrounding the August flyby

Imaging-neutral camera (INCA) for the NASA Cassini mission to Saturn and Titan

The INCA sensor is the first energetic neutral atom (ENA) imager funded for flight by NASA. It is a part of the Magnetrospheric Imaging Instrument (MIMI) on the Cassini mission to Saturn, where it will be well suited to monitoring the global dynamics of the Saturn-Titan magnetospheric system throughout the orbital tour. INCA will perform remote sensing of the magnetospheric energetic ion plasmas by detecting and imaging charge exchange neutrals, created when magnetospheric ions capture electrons from ambient neutral gas. The escaping charge exchange neutrals were detected by the Voyager-1 spacecraft outside Saturns magnetosphere, and can be used like photons to form images of the emitting regions, as has been done at Earth. Since Cassini is 3-axis oriented, INCA is designed as a 2D imager with a field of view of 90 by 120 degrees. The technique involves sensing the position of the ENA as it penetrates an entrance foil and again ont he back-plane microchannel plate, thereby establishing the ENAs trajectory and time- of-flight. Along with rough composition determined by pulse- height analysis, the sensor produces images of the hot plasma interaction with the cold ambient neutral gas as a function of species and energy, from approximately 20 keV to several MeV. A large geometric factor allows sufficient sensitivity to obtain statistically significant images in approximately 1 to 30 minutes, depending on conditions and location. We will discuss several of the design details unique to this instrument, as well as recent calibration results.

Power remote input output ASIC (PRIO)

The ability to monitor a variety of voltages and currents is a basic need for spacecraft and other complex systems. Although this function can be performed with a handful of components (FPGA, ADC, op-amps, etc), it is at the expense of board area, mass and power. The power remote I/O (PRIO) ASIC is a single chip, multi-channel monitoring device. The PRIO has internal buffers with externally programmable attenuation to allow the PRIO to safely monitor voltages in the range of -40 V to +40 V DC. The current monitoring is accomplished with an external toroid pickup. The ASIC operates from a 5 V supply and communicates with the spacecraft via the I2C bus

Strofio: A novel neutral mass spectrograph for sampling Mercury's exosphere

Strofio is a scientific investigation to sample in-situ the neutral atoms in Mercurys exosphere. Strofio is based on a novel mass spectrograph that determines the particle mass-per-charge (m/q) by a time-of-flight (TOF) technique. This novel technique achieves a mass resolution (m/Δm) at mass 18 of >;100, with a high sensitivity of 0.14 (counts/s)/(particles/cm3) and a mass of only 4kg. Strofio employs a rotating electric field to “stamp” the start time of the incoming ionized particles and a micro-channel plate (MCP) detector to record the stop time and position. This eliminates the need for foils or shutters, resulting in nearly 100% duty cycle and a low mass design. Strofio is funded by NASA to fly on the European Space Agency mission BepiColombo to the planet Mercury. It is part of the four instrument SERENA suite situated on the Mercury Planetary Orbiter (MPO), which will enter in a 400 × 1500km polar orbit. This paper describes the theory of operation, the instrument components, and focuses on the front end electronics and processing required to read and accumulate the particle data.