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Plasma Experiment for Planetary Exploration (PEPE)

NSSDCA ID: 1998-061A-02

Mission Name: Deep Space 1
Principal Investigator:Dr. David T. Young


The Plasma Experiment for Planetary Exploration (PEPE) is a multiple instrument package designed to measure the three dimensional mass-resolved plasma distribution. PEPE will be used to collect scientific data during cruise and asteroid encounter, measure the effects induced by the ion propulsion system on the space environment, including interactions with the solar wind, and on spacecraft surfaces and instruments, and to validate new plasma sensor technologies for use on future space flights. PEPE is mounted on the edge of the octagonal top of DS1.

The experiment will be operated in two principal modes. At the time the ion propulsion is operating, the instrument will be used to characterize the xenon and molybdenum ions, the two major products of the ion engine, to study the effects of the engine on the spacecraft and its surroundings. Science data will be collected when the propulsion is turned off. During cruise PEPE will characterize the solar wind ion and electron velocity distributions, ion composition, suprathermal distributions, high speed streams, shocks, and coronal mass ejections. During the asteroid flyby, the instrument will be used to search for material outgassed from, or produced by photo-ionization of. the asteroids surface. During the possible future comet flyby, PEPE will study pick-up ions, coma plasmas, solar wind/comet interactions, and water-group ions.

PEPE will measure ions and electrons simultaneously. The ions and electrons enter through an aperature grid and are electrostatically deflected to the appropriate energy analyzer. The particles are collimated and deflected into a toroidal tophat electrostatic analyzer. The ions are accelerated by a -15 kV field into carbon foils which emit electrons starting the timing circuitry. Incoming electrons are directed onto a conversion dynode stimulating secondary electron emission which is detected by an electron microchannel plate. The experiment is also equipped with a microcalorimeter to study plasma/surface interactions.

PEPE has a total field of view of 2.8 pi steradians which it sweeps over electrostatically, using no moving parts. A single sample has a range of 5 degrees in elevation and 45 degrees in azimuth, with one 45 degree sector subdivided into 5 degree fine resolution sectors. A complete scan requires 2048 steps of the angle and energy deflection optics, each energy step takes approximately 30 ms, so a full 3-D scan requires 64 s. PEPE is capable of measuring the energy spectrum of electrons over the range 10 eV to 10 keV and ions from 3 eV to 30 keV per unit charge with a resolution of 0.05. It also measures ion mass from 1 to 135 amu/charge at a resolution M/(delta M) of 50 (FWHM). Most data is compressed at roughly 150:1 prior to transmission. The nominal data telemetry rate is 50 bps, high time resolution observations near the asteroid will require periods of 1000 bps.

Alternate Names

  • DeepSpace1/PEPE
  • PEPE

Facts in Brief

Mass: 6 kg

Funding Agency

  • NASA-Office of Space Science United States


  • Planetary Science: Fields and Particles
  • Engineering: None assigned

Additional Information

Questions and comments about this experiment can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail
Dr. David T. YoungLead InvestigatorSouthwest Research
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