The Nineties in America Mars exploration 555
the Mars Observer on September 25, 1992. This
large observatory was intended to study the geology
and climate. On August 21, 1993, just three days be-
fore it was scheduled to enter orbit, radio contact
was lost. A review panel determined that a fuel-line
rupture in the propulsion system during prepara-
tion for orbital insertion probably caused its failure.
Mars Pathfinder Following the failure of the Mars
Observer, NASA shifted its Mars exploration efforts
to more frequent but smaller spacecraft. Mars Path-
finder, the second of NASA’s low-cost Discovery mis-
sions, was designed to test a new way to deliver pay-
loads to the Martian surface. Pathfinder was
launched by a Delta II rocket on December 4, 1996,
and landed on Mars on July 4, 1997, directly enter-
ing the Martian atmosphere using a small parachute
to slow its descent and a system of air bags to cushion
its impact. Pathfinder hit the surface at forty miles
per hour, bouncing five hundred feet into the air. It
bounced sixteen times before coming to rest after
2.5 minutes, about 0.6 mile from its initial impact.
The landing site, Ares Vallis, was selected because
photographs from the Viking spacecraft indicated it
was an ancient floodplain containing a variety of dif-
ferent types of rocks.
The six-hundred-pound Pathfinder carried the
twenty-two-pound Sojourner rover, named after the
civil rights crusader Sojourner Truth. The six-
wheeled rover rolled onto the surface of Mars on
July 6. It was controlled from Earth, but the ten-
minute time delay for communication required au-
tonomous control of some rover activities. Mars
Pathfinder took 16,500 images of the surface and
monitored weather. Sojourner took 550 images and
analyzed 15 rocks. The results suggest that Mars was
once warm and wet with a thick atmosphere. Com-
munications with Pathfinder and Sojourner were
lost, for unknown reasons, on September 27, 1997.
Mars Global Surveyor Launched on November 7,
1996, aboard a Delta II rocket, the Mars Global Sur-
veyor was a fast, low-cost spacecraft to perform most
of the science planned for Mars Observer. The
spacecraft entered a highly elliptical orbit around
Mars on September 12, 1997, and began sixteen
months of aerobraking, repeatedly passing through
the upper atmosphere to reduce the high point of
the orbit, putting it into a nearly circular, two-hour
polar orbit. This orbit allowed the Surveyor to ob-
serve each spot on Mars every seven days. Beginning
in March, 1999, Surveyor performed high-resolu-
tion mapping, studied the gravitational field, investi-
gated the role of water and dust on the atmosphere,
and mapped the Martian magnetic field. Some im-
ages showed bright, new deposits in two gullies, sug-
gesting that water may still flow, at least sporadically,
on the Martian surface. High-resolution images of
the Cydonia Region showed that the “face on Mars,”
a formation resembling a human face in lower-
resolution Viking images, was simply a natural rock
formation. After studying Mars for four times as long
as planned, the Mars Global Surveyor ceased trans-
mitting in November, 2006, probably resulting from
a computer error leading to battery failure. The Sur-
veyor was one of the first spacecraft in NASA’s
planned, decade-long exploration of Mars, with
launches every twenty-six months.Mars Global Surveyor prior to a second launch attempt on Novem-
ber 7, 1996.(NASA Kennedy Space Center)