Planetary Exploration Missions 881
FIGURE 9 TheLuna 16spacecraft.
in 1959 and continued with increasing capabilities until
- The second was the Proton-launched circumlunar
ZOND(a name meaning sounder) human-precursor tests.
The third was the human lunar landing effort based on the
giant N-1 vehicle that failed in four launch attempts.
Lunas 16through 24 were emissaries of the first pro-
gram. The Proton-launchedLuna 16, 20 , and 24 (Fig. 9)
drilled into the regolith, encapsulated small soil samples
and returned them to Earth.Luna 17and 21 delivered
Lunokhod rovers to the Moon’s surface. (See nssdc.gsfc
.nasa.gov/database/MasterCatalog?sc=1976-081A.)
Clementine
The mission that revived lunar exploration in 1994 after its
decades of stasis,Clementine, had an innovative manage-
ment and technical plan. Proposed as a test of instrument
technologies for the American Strategic Defense Initiative,
it was sponsored by the Ballistic Missile Defense Organi-
zation and NASA, managed by the Naval Research Labo-
ratory, and launched from the Pacific Missile Range on a
Titan II-G.
During two months in lunar orbit, it mapped the en-
tire Moon at many wavelengths and hinted at the presence
of theoretically predicted excess volatiles, possibly a signa-
ture of cold-trapped water ice near the lunar poles. (See
http://www.cmf.nrl.navy.mil/clementine/.))
Lunar Prospector
Launched in 1998 by an Athena solid-fueled vehicle, the
NASALunar Prospectorcontinued the trend toward small,
highly capable lunar spacecraft and relatively low mission
costs. With neutron, gamma-ray, and alpha-particle spec-
trometers plus measurements of lunar magnetic and gravity
fields, the mission yielded data on the Moon’s surface com-
position and its geochemical and geophysical properties. It
added confidence to theClementinefindings of possible
polar ices. (See lunar.arc.nasa.gov/project/index.htm.)Smart-1
ESA’s first lunar mission,Smart-1, was launched in 2003
with a small, highly advanced spacecraft demonstrating
solar-electric propulsion, onboard autonomy, and several
new instrument technologies. Spiraling slowly outward
from Earth and then inward toward the Moon, the craft
was captured by the Moon’s gravity late in 2004 and began
science operations in lunar orbit in 2005, whence it deliv-
ered a fine harvest of imaging and other remote-sensing
data until its planned crash into the Moon on 3 SeptemberNew Lunar Missions
Continuing the worldwide revival of interest in the Moon,
several robotic lunar orbiting missions are being prepared
for launch: Japan’sLunar-Afor seismic penetrators and
SELENE for a broad set of remote-sensing objectives;
China’sChang’E-1for remote sensing and surveying for
later landing missions, and India’sChandrayaan-1for re-
mote sensing.SELENEis an acronym.
In addition, NASA will execute lunar orbital missions
both for science and in preparation for a new American
space program employing the Moon as a stepping stone
toward eventual human exploration of Mars. The first such
mission is that of theLunar Reconnaissance Orbiter, a large,
multipurpose remote-sensing spacecraft to be launched in
2008 or 2009. Because its launch vehicle has excess payload
capacity, the mission will also carry an experiment called
LCROSS for observing a planned lunar crash of the ve-
hicle’s translunar injection stage. The program is intended
to continue with robotic landers and rovers exploring the
prospects for use of lunar resources, including the polar ice
deposits if they do exist.8. Mars
With 19th-century telescopic observation showing polar
caps and other indications of an atmosphere and chang-
ing surface features, Mars became the planet of choice for
speculation about other life in the cosmos and about human
travel to other worlds.
These pervasive ideas have since driven planetary pro-
gram priorities with the result that huge resources have
been devoted to Martian robotic exploration and to studies
of the prospect of human ventures to Mars. But Mars has
proved to be a difficult destination: Failure has been an ever
present hazard—not only in flight missions but also in the
councils where budget decisions are made.