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Mars Climate Orbiter MOI Timeline


The Mars Climate Orbiter is just 9 days from entering orbit around Mars.
This event, called Mars Orbit Insertion (MOI), will occur on September 23, 1999,
when the spacecraft approaches its closest point to the planet coming 
in over the northern hemisphere. The spacecraft will fire its 640-newton
main engine for 16 minutes 23 seconds to brake into an elliptical
capture orbit.  Below it the timeline for the key events during
the orbit insertion.

                     Mars Climate Orbiter MOI Timeline
                             September 23, 1999
                   All times in Earth Receive Time (ERT).
           One way light time from Mars is 10 minutes 55 seconds.

                         Event                    PDT    EDT    UTC
       Orbiter stows solar array                 01:41  04:41  08:41

       Orbiter turns to correct orientation
       to begin main engine burn                 01:50  04:50  08:50

       Orbiter fires pyrotechnic devices
       which open valves to begin                01:56  04:56  08:56
       pressurizing the fuel and oxidizer tanks

       Main engine burn starts,
       fires for 16 minutes 23 seconds.          02:01  05:01  09:01

       Orbiter passes behind Mars,
       out of view from Earth                    02:06  05:06  09:06

       Main engine burn ends                     02:17  05:17  09:17

       Orbiter turns to orientation which will
       allow Earth contact                       02:19  05:19  09:19

       Orbiter comes out from behind Mars,
       flight controllers regain contact         02:27  05:27  09:27

       Solar array unstows                       02:30  05:30  09:30

Mars Climate Orbiter was launched on December 11, 1998 from a Delta II launch
vehicle at Cape Canaveral Air Station, Florida.  The spacecraft carries
instruments to seek clues to the history of climate change on Mars,
and will map the Martian surface and profile the structure of the atmosphere.

The orbiter, along with the Mars Polar Lander, are the second installment in 
NASA's long-term program of robotic exploration of Mars, which was initiated 
with the 1996 launches of the currently orbiting Mars Global Surveyor and the 
Mars Pathfinder lander and rover.

The 1998 missions will advance our understanding of Mars' climate history
and the planet's current water resources by digging into the enigmatic
layered terrain near one of its poles for the first time. Instruments
onboard the orbiter and lander will analyze surface materials, frost,
weather patterns and interactions between the surface and atmosphere to
better understand how the climate of Mars has changed over time.

Key scientific objectives are to determine how water and dust move about the
planet and where water, in particular, resides on Mars today. Water once
flowed on Mars, but where did it go? Clues may be found in the geologic
record provided by the polar layered terrain, whose alternating bands of
color seem to contain different mixtures of dust and ice. Like growth rings
of trees, these layered geological bands may help reveal the secret past of
climate change on Mars and help determine whether it was driven by a
catastrophic change, episodic variations or merely a gradual evolution in
the planet's environment.

Today the Martian atmosphere is so thin and cold that it does not rain;
liquid water does not last on the surface, but quickly freezes into ice or
evaporates and resides in the atmosphere. The temporary polar frosts which
advance and retreat with the seasons are made mostly of condensed carbon
dioxide, the major constituent of the Martian atmosphere. But the planet
also hosts both water-ice clouds and dust storms, the latter ranging in
scale from local to global. If typical amounts of atmospheric dust and water
were concentrated today in the polar regions, they might deposit a fine
layer every year, so that the top meter (or yard) of the polar layered
terrains could be a well-preserved record showing 100,000 years of Martian
geology and climatology.

Next week, Mars Climate Orbiter will fire its main engine to put itself into 
an elliptical orbit around Mars. The spacecraft will then skim through Mars' 
upper atmosphere for several weeks in a technique called aerobraking to 
reduce velocity and circularize its orbit. Friction against the spacecraft's 
single, 5.5-meter-long (18-foot) solar array will slow the spacecraft as it 
dips into the atmosphere each orbit, reducing its orbit period from more than 
14 hours to 2 hours.

Finally, the spacecraft will use its thrusters to settle into a polar,
nearly circular orbit averaging 421 kilometers (262 miles) above the
surface. From there, the orbiter will await the arrival of Mars Polar Lander
and serve as a radio relay satellite during the lander's surface mission.
After the lander's mission is over, the orbiter will begin routine
monitoring of the atmosphere, surface and polar caps for a complete Martian
year (687 Earth days), the equivalent of almost two Earth years.

The orbiter carries two science instruments: the Pressure Modulator Infrared
Radiometer, a copy of the atmospheric sounder on the Mars Observer
spacecraft lost in 1993, and the Mars Color Imager, a new, light-weight
imager combining wide-and medium-angle cameras. The radiometer will measure
temperatures, dust, water vapor and clouds by using a mirror to scan the
atmosphere from the Martian surface up to 80 kilometers (50 miles) above the
planet's limb.

Meanwhile, the imager will gather horizon-to-horizon images at up to
kilometer-scale (half-mile-scale) resolutions, which will then be combined
to produce daily global weather images. The camera will also image surface
features and produce a map with 40-meter (130-foot) resolution in several
colors, to provide unprecedented views of Mars' surface.

Mars Polar Lander, launched a month after the orbiter, will
arrive on December 3, 1999, two to three weeks after the orbiter has finished
aerobraking. The lander is aimed toward a target sector within the edge of
the layered terrain near Mars' south pole. 

Like Mars Pathfinder, Mars Polar Lander will dive directly into the Martian
atmosphere, using an aeroshell and parachute scaled down from Pathfinder's
design to slow its initial descent. The smaller Mars Polar Lander will not
use airbags, but instead will rely on onboard guidance and retro-rockets to
land softly on the layered terrain near the south polar cap a few weeks
after the seasonal carbon dioxide frosts have disappeared. After the heat
shield is jettisoned, a camera will take a series of pictures of the landing
site as the spacecraft descends.

As it approaches Mars about 10 minutes before touchdown, the lander will
release the two Deep Space 2 microprobes. Once released, the projectiles
will collect atmospheric data before they crash at about 200 meters per
second (400 miles per hour) and bury themselves beneath the Martian surface.
The microprobes will test the ability of very small spacecraft to deploy
future instruments for soil sampling, meteorology and seismic monitoring. A
key instrument will draw a tiny soil sample into a chamber, heat it and use
a miniature laser to look for signs of vaporized water ice.

About 100 kilometers (60 miles) away from the microprobe impact sites, Mars
Polar Lander will dig into the top of the terrain using a 2-meter-long
(6-1/2-foot) robotic arm. A camera mounted on the robotic arm will image the
walls of the trench, viewing the texture of the surface material and looking
for fine-scale layering. The robotic arm will also deliver soil samples to a
thermal and evolved gas analyzer, an instrument that will heat the samples
to detect water and carbon dioxide. An onboard weather station will take
daily readings of wind temperature and pressure, and seek traces of water
vapor. A stereo imager perched atop a 1.5-meter (5-foot) mast will
photograph the landscape surrounding the spacecraft. All of these
instruments are part of an integrated science payload called the Mars
Volatiles and Climate Surveyor.

Also onboard the lander is a light detection and ranging (lidar) experiment
provided by Russia's Space Research Institute. The instrument will detect
and determine the altitude of atmospheric dust hazes and ice clouds above
the lander. Inside the instrument is a small microphone, furnished by the
Planetary Society, Pasadena, CA, which will record the sounds of wind gusts,
blowing dust and mechanical operations onboard the spacecraft itself.

The lander is expected to operate on the surface for 60 to 90 Martian days
through the planet's southern summer (a Martian day is 24 hours, 37
minutes). The mission will continue until the spacecraft can no longer
protect itself from the cold and dark of lengthening nights and the return
of the Martian seasonal polar frosts.

The Mars Climate Orbiter, Mars Polar Lander and Deep Space 2 missions are
managed by the Jet Propulsion Laboratory for NASA's Office of Space Science,
Washington, DC. Lockheed Martin Astronautics Inc., Denver, CO, is the
agency's industrial partner for development and operation of the orbiter and
lander spacecraft. JPL designed and built the Deep Space 2 microprobes. JPL
is a division of the California Institute of Technology, Pasadena, CA.

For more information on the Mars Climate Orbiter and Mars Polar Lander 
missions, please visit our website at:

http://mars.jpl.nasa.gov/msp98

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