Planetary Exploration Missions 877
FIGURE 6 Magellanwas launched in 1989 into a
series of orbits enabling it to map the entire planet
using synthetic-aperture radar.Magellan
The ubiquitous clouds of Venus forever hide the planet’s
surface from outside visual examination.Veneralanders in
1975–1981 gave close-up surface panoramas and in 1983
radars on theVenera 15and 16 orbiters mapped most of
the northern hemisphere. Long delayed through years of
attempts to gain government approval,Magellan(Fig. 6)
was finally launched in 1989 into a series of orbits enabling
it to map the entire planet using synthetic-aperture radar.
Once the radar mission was complete, the spacecraft was
moved into a lower orbit to map the Venusian gravity field
and to test aerobraking techniques. (See http://www.jpl.nasa.gov/
magellan/.)
Galileo Venus Flyby
En route to Jupiter, theGalileospacecraft performed a
gravity assist flyby at Venus in February 1990. Space-
craft observations included infrared imaging of the planet’s
cloud layers and even surface features, through infrared
“windows” in the atmosphere and clouds. (See galileo.jpl
.nasa.gov/facts.cfm.)
Venus Express
By modifying the design to cater for the hot environment
near Venus, but otherwise using many proven components
and operational techniques, ESA was able to mount a low-
cost mission to place in Venus orbit a spacecraft based on
the successfulMars Expressto be described later below.
Launched by a RussianSoyuz-Fregatin 2005, the mission
has delivered unique images of Venus’s north polar cloud
vortex. (See sci.esa.int/venusexpress/.)6. Earth
Among the thousands of spacecraft launched to date, at
least hundreds have made some contributions to the study
of our Earth as a planet. Here we make no attempt at a
catalog of all those ventures. Instead we highlight a few
recent and representative missions that illustrate the state of
humans’ ongoing endeavor to understand Earth’s interior,
its oceans and lands, its atmosphere, its evolution and its
fate, including that of its biosphere.Resurs
Soviet and Russian film-return photo-reconnaissance satel-
lites have operated over many years for Earth observation.
Civil uses have been publicized since 1979, with increas-
ingly capable camera systems used for both applications
and science.
Corresponding US imagery was mostly kept classified
until 1995, when much previously secret overhead recon-
naissance information was released for public use in his-
torical and scientific studies. (See http://www.fas.org/spp/guide/
russia/earth/resurs-f.)