12 AUSTRALIAN SKY & TELESCOPE July 2017
Mars Pathfinder and its rover, Sojourner, were interplanetary trailblazers.
First wheels on Mars
ALTHOUGH THE SPACE PROGRAMS
of the major nations have been always
largely been engineering and logistic
endeavours to ‘prove it could be done’
and to gather scientific information
upon the way, these enterprises have also
long carried geopolitical baggage. The
1960s ‘race to the Moon’ between the
United States and the Soviet Union was
largely the Cold War played out in space,
with the early victories to the Soviets
and the ultimate prize to the Americans.
Significant successes by one or the other
could be trumpeted as evidence of the
superior technology of that state, and by
extension the superiority of its political
and economic system.
Although that ideological spirit
has largely faded now, it persisted for
many years. The US was very keen to
complete its first soft landing on Mars
on July 4, 1976, the 200th anniversary
of the Declaration of Independence.
Operational difficulties spoilt that dream
and the landing of Viking 1 was delayed
until the 20th (a significant-enough date
given that exactly five years before, Apollo
11 had touched down on the Moon).
But the July 4 link to Mars was
firmly established 21 years later in
1997, when the first successful Mars
mission since the two Vikings in 1976
— was Mars Pathfinder — landed in
much the same area as Viking 1. It
was a trailblazer in many ways. It was,
for example, an embodiment of a newNASA strategy of “cheaper, faster,
better,” and therefore much less costly
than comparable earlier missions. And
after being slowed by a heatshield,
parachute and retrorockets, the craft’s
landing was cushioned by airbags to
protect it from damage; another first.
And it carried a passenger — a
10-kilogram, shoebox-sized rover called
Sojourner, ready to roam across the
surface on its tiny wheels. This was a
‘proof of concept’ for the use of rovers
to explore other worlds, though the
Soviets had deployed similar machines
on the Moon in the 1960s. It was the
forerunner of the much larger rovers
Spirit, Opportunity and Curiosity on
later missions to Mars.
Most of the scientific smarts of the
mission were in Sojourner. The lander
that brought it down was equipped
merely to take pictures and sample the
weather. Of course it worked hard at
that, taking 16,500 photographs and
gathering 8.5 million measurements
of air pressure, temperature and wind
speed over three months.
Sojourner rolled out on sol 2 (ie.
day two on Mars). It was no speedster,
moving at about 1 centimetre per
second, but over the 80 sols of its active
life it travelled about 100 metres, never
far from the lander. It was no dumb
robot either, with software to help it
find its way around obstacles, rather
than wait for instructions from Earth,more than 20 minutes away by radio.
In its quest for knowledge, it fronted
up to a number of nearby rocks, named
after cartoon characters such as Yogi Bear
and Scooby Doo, to sniff their mineral
content. Alpha particles were fired
into the rocks, stimulating x-rays at
frequencies characteristic of the various
chemical elements. It was slow work,
taking 10 hours to analyse one rock, but
all of the elements found on Earth, other
than hydrogen, were detected.
This was a pioneering enterprise,
designed to see what might be achieved
with the larger and much better-
equipped missions then being planned,
and which we have since seen come to
fruition. As is often the case with such
missions, it exceeded its design lifetime
of about one month; the rover continued
to run for nearly three months.
Twenty years after Mars Pathfinder
fell silent, it was spotted from above
by the cameras of a newer spacecraft,
the Mars Reconnaissance Orbiter. The
lander was renamed the Sagan Memorial
Station in honour of the US scientist
Carl Sagan, who had done so much to
raise public interest in astronomy and
also made major contributions to our
understanding of the way the planets
have come to be as they are.■ DAVID ELLYARD presented SkyWatch
on ABC TV. His StarWatch StarWheel
has sold over 100,000 copies.DISCOVERIES by David EllyardThe first wheeled vehicle on Mars, Sojourner,
spent three months exploring the surface.NASA/JPL