The Complete Book of Spaceflight: From Apollo 1 to Zero Gravity

324 Planet Imager (PI)
Planet Imager (PI)
A possible future NASA mission, part of the Origins
Program, that would follow on from the Terrestrial Planet
Finder (TPF) and produce images of Earth-like planets.
To obtain a 25 × 25 pixel image of an extrasolar
planet would call for an array of five TPF-class optical
interferometers flying in formation. Each interferometer
would consist of four 8-m telescopes to collect light and
to null it before passing it to a single 8-m telescope,
which would relay the light to a combining spacecraft.
The five interferometers would be arranged in a parabola,
creating a very long baseline of 6,000 km with the combining
spacecraft at the focal point of the array. The
Planet Imager is identified in NASA’s Office of Space Science
Strategic Plan as a potential mission beyond 2007
but remains in the very early concept definition phase.
planetary protection test
A test performed to assess that the potential for contamination
of (1) Earth by returned spacecraft hardware, or
(2) spacecraft destinations by spacecraft hardware is
within acceptable limits. It typically consists of bacterial
spore counts from swabs taken from hardware surfaces.
Planetary Society, The
A nonprofit, public organization, founded in 1980 by
Carl Sagan, Bruce Murray, and Louis Friedman, and
based in Pasadena, California, to encourage and support,
through education, public information events, and special
events, the exploration of the Solar System and the
search for extraterrestrial life. With a membership of more
than 100,000, from over 100 countries, the Planetary Society
is the largest space advocacy group in the world. It
publishes the bimonthly Planetary Report and provides
financial support for SETI hardware development. It is
also developing the Cosmos 1 solar sail project.
plasma
A low-density gas in which the individual atoms are ionized
(and therefore charged), even though the total number
of positive and negative charges is equal, thus
maintaining overall electrical neutrality. Plasma is sometimes
referred to as the fourth state of matter. A partially
ionized plasma, such as Earth’s ionosphere, is one that
also contains neutral atoms.
plasma detector
A device for measuring the density, composition, temperature,
velocity, and three-dimensional distribution of
plasmas that exist in interplanetary regions and within
planetary magnetospheres.
plasma sheath
An envelope of ionized gas that surrounds a body moving
through an atmosphere of hypersonic velocity.
plasma sheet
Low energy plasma, largely concentrated within a few
planetary radii of the equatorial plane, distributed
throughout the magnetosphere, throughout which concentrated
electric currents flow.
plasma wave detector
A device for measuring the electrostatic and electromagnetic
components of local plasma waves in three dimensions.
platform
A spacecraft, usually unmanned, that serves as a base for
scientific experiments.
Plesetsk Cosmodrome
A Russian launch complex and missile test range, located
at 62.8° N, 40.4° E, which has launched the most satellites
since the beginning of the Space Age. Built in 1960,
south of Archangel in northern Russia, its existence was
not officially acknowledged by the Soviet Union until
1987, but it became publicly known in the West after the
tracking of Cosmos 112 by a team of schoolboys at Kettering
Grammar School in England. Prior to this, it had
been the source of many UFO reports from people living
below the site’s launch trajectories. Western journalists
allowed onto the site in 1989 were told of two fatal accidents
that had happened there: on June 26, 1973, nine
technicians were killed in a launch pad accident, and on
March 18, 1980, 50 technicians were killed by an explosion
while fueling a Soyuz booster.
Plesetsk’s location makes it ideal for launching into
polar or high-inclination orbits (63° to 83° inclination)—
those typically favored by military reconnaissance and
weather satellites. Between 1969 and 1993, it was the
busiest spaceport in the world, accounting for more than
a third of all orbital or planetary missions. It continues to
be highly active today, especially for military launches
and all Molniya-class communications satellites.
Plesetsk has traditionally supported four launch vehicle
types: Cosmos-3M, Soyuz/Molniya, Tskylon-3, and
Start. The Russian government is keen to shift more
activity, especially unmanned launches, away from
Baikonur (which first surpassed Plesetsk in number of
launches in 1993), since its current agreement with Kazakhstan
to use that facility expires in 2014. To this end,
a program has been put in place to build the launch support
infrastructure for the new Angara vehicle at the
northernmost spaceport. The first launch of this new gen-