By taking highly detailed images from space, orbiters circling
Mars have revealed a wealth of information about the planet's
atmosphere, topography and subsurface characteristics. They have
also found some incredible resemblances to features here on
Orbiters on future missions will examine the planet's surface
even more precisely. They will also search for evidence of
water's existence both now and in the past, on the surface and
underground. Scientists are looking for
signs of water
since they believe it must be present to sustain life, even one-celled
organisms they think may have lived on Mars at one time.
Orbiters will also play a key role as communications relays for
the assets such as rovers, landers and aerial vehicles on the
surface or in the atmosphere of Mars. Orbiters may also play a
vital role in bringing back samples from the surface of Mars.
The Mars Global Surveyor mission has already achieved all of its science goals, and continues to provide a global characterization of the Martian topography, gravity, magnetic fields, thermal properties, surface composition, internal structure, atmospheric structure, and atmospheric dynamics.
In April, 2001, the 2001 Mars Odyssey orbiter will launch on a journey to Mars to
map the terrain's makeup of minerals and elements
and look for hydrogen, whose presence could be an indication that
water was once present.
Mars Odyssey will also study the variations in the Martian
surface and take pictures that will provide a map of the entire
planet. Instead of getting close-up visible images of a very small
part of Mars like those taken by the Mars Global Surveyor,
which started orbiting the planet in March, 1998, the '01 orbiter will
take visible and infrared images of lower resolution but cover
the entire planet.
The Mars Express Orbiter, a European mission
launching in 2003, will carry an instrument whose radar will
penetrate many miles into the Martian surface to search for
reflections from pools of subsurface water. This radar sounder
instrument, called MARSIS (Mars Subsurface and Ionospheric Sounder),
is a joint project of NASA and the Italian Space Agency (ASI).
The Mars Reconnaissance Orbiter, a NASA
mission launching in 2005, will continue searching for water's
signature by studying the planet's minerals. The '05 orbiter will
also study the climate to see if water is released into the
atmosphere during different seasons of the Martian year. This
orbiter may be equipped with an ultra high-resolution camera
capable of imaging surface features like large rocks that would be
hazardous to landers and interfere with mobility of rovers.
Beyond 2005, orbiters will provide more powerful relay
communications capabilities for vehicles on the Martian surface.
It won't be practical for rovers, busy navigating hazardous terrain,
to point their small antennas towards faraway Earth and transmit
information. Instead, it will be easier for the rover to send data to
a Mars orbiter, which in turn will precisely point a large antenna
at Earth and communicate large volumes of images and other data.
Orbiters will also be used to bring samples back from Mars. Just
as it is not efficient to communicate large volumes of science data
directly from the Martian surface to Earth, it is not practical to
launch a rocket containing samples from the Martian surface and
expect it to navigate itself back to Earth and land safely. Instead,
the preferred solution is to launch a small canister containing
samples into orbit around Mars, have an orbiter rendezvous with
and capture the canister and then eject the orbiter from Mars
orbit back towards Earth.
Entering and Leaving Orbit
In addition to the technologies for orbital imaging,
telecommunications and rendezvous and capture, the technologies
for entering and leaving Mars orbit are vitally important for the
development of low cost missions. Chemical propulsion has been
used on every orbital mission since Mariner 9, the first Mars
orbiter in 1971. In 1997, a new capability called aerobraking
was used not to enter or leave orbit, but to gradually modify
the shape of the orbit by skimming through the high atmosphere.
NASA and CNES, the French space exploration program, are
currently collaborating on the deveopment of aerocapture, a technology
that would send a spacecraft approacing Mars deep into the atmosphere
where it would decelerate by several thousand miles per hour (mph) in
less than ten minutes. It would then emerge into an orbit around Mars.
The aeroshell needed to protect the spacecraft and the
guidance system needed to place it accurately in the right orbit
are the keys to this technology.
Chemical propulsion is a relatively mature technology although new types
of lightweight components will make it possible to place larger payloads
into Mars orbit or to remove larger payloads and send them back to
Earth. Electric propulsion, on the other hand, is an emerging technology
with the prospect of providing large advantages for missions which require a
spacecraft to first orbit Mars, then leave Mars orbit on return to Earth
and then possibly enter orbit around Earth. Electric propulsion was
demonstrated for the first time on a Deep Space mission in 1999. Future
advances in the technology will open up major new opportunities for Mars