Plasma Experiment for Planetary Exploration (PEPE)

The Plasma Experiment for Planetary Exploration (PEPE) flown on Deep Space 1 combines an ion mass spectrometer and an electron spectrometer in a single, low-resource instrument. Among its novel features PEPE incorporates an electrostatically swept field-of-view and a linear electric field time-of-flight mass spectrometer. A significant amount of effort went into developing six novel technologies that helped reduce instrument mass to 5.5 kg and average power to 9.6 W. PEPE’s performance was demonstrated successfully by extensive measurements made in the solar wind and during the DS1 encounter with Comet 19P/Borrelly in September 2001. P. Barker is deceased.     

The Plasma Ion and Electron Instruments for the Genesis Mission

The Genesis Ion Monitor (GIM) and the Genesis Electron Monitor (GEM) provide 3-dimensional plasma measurements of the solar wind for the Genesis mission. These measurements are used onboard to determine the type of plasma that is flowing past the spacecraft and to configure the solar wind sample collection subsystems in real-time. Both GIM and GEM employ spherical-section electrostatic analyzers followed by channel electron multiplier (CEM) arrays for detection and angle and energy/charge analysis of incident ions and electrons. GIM is of a new design specific to Genesis mission requirements whereas the GEM sensor is an almost exact copy of the plasma electron sensors currently flying on the ACE and Ulysses spacecraft, albeit with new electronics and programming. Ions are detected at forty log-spaced energy levels between ∼ 1 eV and 14 keV by eight CEM detectors, while electrons with energies between ∼ 1 eV and 1.4 keV are measured at twenty log-spaced energy levels using seven CEMs. The spin of the spacecraft is used to sweep the fan-shaped fields-of-view of both instruments across all areas of the sky of interest, with ion measurements being taken forty times per spin and samples of the electron population being taken twenty four times per spin. Complete ion and electron energy spectra are measured every ∼ 2.5 min (four spins of the spacecraft) with adequate energy and angular resolution to determine fully 3-dimensional ion and electron distribution functions. The GIM and GEM plasma measurements are principally used to enable the operational solar wind sample collection goals of the Genesis mission but they also provide a potentially very useful data set for studies of solar wind phenomena, especially if combined with other solar wind data sets from ACE, WIND, SOHO and Ulysses for multi-spacecraft investigations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Drilling systems for extraterrestrial subsurface exploration

Drilling consists of 2 processes: breaking the formation with a bit and removing the drilled cuttings. In rotary drilling, rotational speed and weight on bit are used to control drilling, and the optimization of these parameters can markedly improve drilling performance. Although fluids are used for cuttings removal in terrestrial drilling, most planetary drilling systems conduct dry drilling with an auger. Chip removal via water-ice sublimation (when excavating water-ice-bound formations at pressure below the triple point of water) and pneumatic systems are also possible. Pneumatic systems use the gas or vaporization products of a high-density liquid brought from Earth, gas provided by an in situ compressor, or combustion products of a monopropellant. Drill bits can be divided into coring bits, which excavate an annular shaped hole, and full-faced bits. While cylindrical cores are generally superior as scientific samples, and coring drills have better performance characteristics, full-faced bits are simpler systems because the handling of a core requires a very complex robotic mechanism. The greatest constraints to extraterrestrial drilling are (1) the extreme environmental conditions, such as temperature, dust, and pressure; (2) the light-time communications delay, which necessitates highly autonomous systems; and (3) the mission and science constraints, such as mass and power budgets and the types of drilled samples needed for scientific analysis. A classification scheme based on drilling depth is proposed. Each of the 4 depth categories (surface drills, 1-meter class drills, 10-meter class drills, and deep drills) has distinct technological profiles and scientific ramifications.