Introduction - Introduction to Planetary Geomorphology - page 12

NASA missions can be categorized as (1) strategic
missions, (2) Principal Investigator (PI)-led missions,
and (3) supporting missions. Strategic missions include
the Mars Science Laboratory and the Cassini spacecraft in
orbit around Saturn. Such missions cost multiple billions
of dollars and might be flown once or twice per decade.
PI-led missions are proposed, designed, and executed by a
planetary scientist, who assembles the science team,
industry partners, and a planetary research center, such
as the JPL or APL. PI-led missions of interest for geo-
science are found in the Discovery Program (such as the
MESSENGER mission to Mercury) and the New Frontiers
Program (such as the New Horizons Pluto mission).
Speci c missions within these programs are “ cost-
capped, ” with New Frontiers being at the upper level of
$1 billion.
Supporting missions are designed to collect data to
enable follow-on missions. While science is not usually
the primary motivation, such data are often used for sci-
enti c research, and the missions typically have a cadre of
scientists involved. For example, the Lunar Reconnais-
sance Orbiter has the primary goal of obtaining data
necessary for the eventual return of humans to the
Moon, but these data are of high value for science as well.
For strategic and supporting missions, scientists can
propose to be the PI for an instrument or suite of instru-
ments as part of the payload. The selected PI forms the
science team, designs the instrument, has it built, and
implements the experiments through operation of the
instrument and collection of the data. In some cases,
facility instruments are provided directly by NASA and
scientists can propose to be a member or team leader of
that instrument science team; the team is then responsible
for carrying out the investigation.
The European Space Agency (ESA) also flys planetary
missions, but operates differently from NASA. The ESA
is composed of 17 member nations and is headquartered in
Paris, with its primary operations center in the
Netherlands. Once a mission has been selected for flight,
the ESA develops and builds the spacecraft and is respon-
sible for its operation. The scienti c payload, however, is
competed for among the member nations through their
science communities; if selected, that nation is responsible
for funding and delivering the instrument or suite of
instruments to the ESA.
Operation of an active flight project is exciting and
complicated! After launch, the mission goes through
cruise (the journey from Earth to its destination), nominal
operations (at the target for the duration approved in the

budget), and, if all goes well, an extended mission (a
speci c period of time following the nominal mission
and budgeted separately). During cruise, the instruments
are typically turned on brie y for calibration and check-
out before arrival at the target; otherwise they are either in
a dormant state or turned off. During planetary operations,
the data needed to meet the objectives of the mission are
obtained and returned to Earth through the Deep Space
Network (DSN), which consists of large antennas located
at Goldstone (southern California), Madrid (Spain), and
Canberra (Australia). This distribution enables complete
coverage of spacecraft, regardless of the time of day or the
position of the spacecraft in the Solar System.
Science operation of a spacecraft involves fundamen-
tally two aspects: sending commands to the spacecraft
(called uplink) and receiving the data from the spacecraft
(called downlink), both through the DSN. Putting the
plan together for the uplink involves integrating the
desires of all the instrument teams to t the power, on-
board computer processing, and other resources of the
spacecraft. As one might imagine, there are often compet-
ing wishes for these resources among the scientists, and
compromises almost always are required for the final plan.
After each instrument has sent its commands, data are
downlinked and, again, there is often competition for
downlink resources. Modern instruments generally can
take far more data than can be returned, and decisions
must be made to satisfy the overall mission objectives.

1.5 Planetary data

As soon as a successful mission goes into operation, the
science flight team plans the acquisition of data (such as
targeting areas to be imaged), collects the data, and ini-
tiates their analysis. Some of these data are posted on the
website for that particular mission (go to the general
NASAwebsite http://www.nasa.gov/ , or the ESAwebsite
http://www.esa.int/, and look for the speci c mission by
name). These data are for general public interest and often
have not been calibrated or veri ed for accuracy. It is
considered

for the science community to pub-
lish results from such data before they are officially
released for scienti c analysis. Such release is done on a
project schedule after validation by the science team,
posted in the Planetary Data System (PDS, http://pds.jpl.
nasa.gov/) , and publicly announced. Because of the pace
of mission operations, the volume of data from modern
missions, the complexity of the data, and the possibility of

“ bad form ”