June 1994: The original hardcopy of this Guide included a number of line drawings and illustrations of Mars Observer, its instruments, and orbit plans. These figures are not going to be reproduced for this on-line version, but .gif images of various features are included here where relevant. The 1994-1995 Curriculum Guide will have .gif images of line drawings of new Mars mission spacecraft. -- K. Edgett.
The Mars Observer Primary Mission goes for 687 days, until sometime in November 1995. Once the Primary Mission is completed, Mars Observer may go into what is called the Extended Mission if the spacecraft and instruments are functioning well and if there is enough fuel to control the spacecraft's altitude and orientation. Additionally, the Extended Mission phase is contingent upon continued funding by the U.S. Congress. On a positive note, most sucessful U.S. planetary spacecraft have had an Extended Mission period, the Viking 1 lander had an extended mission of 6 years, and Voyager 2's extended mission included the Uranus and Neptune encounters!
The mission will provide scientists with a global portrait of Mars as it exists today, using instruments similar to those now used to study Earth. The seven instruments have been selected so that observations from one provide a complimentary approach to mission objectives. For example, the composition of the surface will be addressed by both the Gamma Ray Spectrometer (chemical composition) and the Thermal Emission Spectrometer (mineral composition).
The interdisciplinary investigations of the Mars Observer mission also will combine data from more than one instrument to explore questions that cross boundaries between scientific disciplines and individual investigations. The six interdisciplinary investigations are:
The mission is expected to provide a major increase in the amount of scientific data available for Mars. During the 687-day mission, Mars Observer will return about 120 megabytes of data per day, for a total of 80 to 90 gigabytes (about 600 billion bits of information). This amounts to more scientific data than has been returned by all previous planetary missions except the current Magellan mission to Venus (which itself has returned considerable amounts of data).
<--- Mars Observer assembly at G.E., 1992
Prior to launch, the spacecraft plus its fuel weighed about 2,573 kg (5,672 lbs). The spacecraft is designed to last 3 years and is equipped with one large solar array (for power), consisting of six 183 by 219 by 9.1 -cm (6 x 7.2 x 0.3 ft) solar panels.
<--- Mars Observer flight plan
Launch Configuration: At the time of launch in September 1992, the spacecraft's main communication antenna, the magnetometer boom, gamma ray spectrometer boom, and the solar array were folded up tight and close to the spacecraft.
Cruise Configuration: During the cruise phase, the 11-month (Sept. 1992 - Aug. 1993) journey to Mars plus the 3-month orbit insertion phase (Aug. 1993 - Oct. 1993), the spacecraft booms were partially extended.
Mapping Configuration: After Mars Observer reaches its circular, polar mapping orbit in November 1993, the solar array and high-gain antenna are fully unfolded, and the instrument booms are extended. Owing to calibration procedures, the gamma ray spectrometer boom won't be completely extended until around March 1994.
<--- Mars Observer Instruments
<--- Thermal Emission Spectrometer
The spectrometer, a Michelson interferometer, will determine the composition of surface rocks and ice and map their distribution on the martian surface. Other capabilities of the instrument will investigate the advance and retreat of the polar ice caps, as well as the amount of radiation absorbed, reflected, and emitted by these caps. The distribution of atmospheric dust and clouds will also be examined over the 4 seasons of a martian year.
Click HERE for a line drawing of the TES from Christensen et al., 1992, Journal of Geophysical Research paper.
Click HERE for an example of terrestrial mineral spectra illustrated in the paper about TES by Christensen et al., 1992, Journal of Geophysical Research.
By observing the number and energy of these gamma rays, it is possible to determine the chemical composition of the surface, element by element. The GRS also can measure the presence of water frozen in the polar caps and as ground ice if it is within 1 meter of the surface.
Low-resolution global images of Mars-- a daily "weather map"-- will also be acquired each day using two wide-angle cameras operated at 7.5 kilometer (4.7 miles) resolution per picture element (pixel). These same cameras will acquire moderate-resolution photographs at 240 meters (787 feet) per pixel.
A separate camera will obtain very high resolution images at 1.5 meters (4.6 feet) per pixel for features of special interest. To create these images, each of these camera systems uses the motion of the spacecraft in combination with what is called a line array of several thousand detectors.
The low-resolution camera system will capture global views of the martian atmosphere and surface so that scientists may study the martian weather and related surface changes on a daily basis. Moderate-resolution images will monitor changes in the surface and atmosphere over hours, days, weeks, months, and years. The high-resolution camera system will be used selectively because of the high data volume required for each image.
Click HERE for a line drawing of the MOC presented by Malin et al. in their 1992 Journal of Geophysical Research paper.
The measurements will be used to derive atmospheric pressure and determine temperature, water vapor, and dust profiles from near the surface to as high as 50 miles above the surface. Using these measurements, global models of the martian atmosphere, including seasonal changes that affect the polar caps, can be constructed and verified.
Click
HERE for a line drawing of the MOLA presented in a 1993 edition of
Each time the spacecraft passes behind the planet or reappears on the opposite
side, its radio beam will pass through the martian atmosphere briefly on its way
to Earth. The way in which the radio waves are bent and slowed will provide data
about the atmospheric structure at a much higher vertical resolution than any
other Mars Observer experiment.
During that part of the orbit when the spacecraft is in view of the Earth,
precise measurements of the frequency of the signal received at the ground
tracking stations will be made to determine the velocity change (using the
Doppler effect) of the spacecraft in its orbit around Mars. These Doppler
measurements, along with measurements of the distance from the Earth to the
spacecraft, will be used to navigate the spacecraft and to study the planet's
gravitational field.
Gravitational field models of Mars will be used along with topographic measurements
to study the martian crust and upper mantle. By the end of the mission, as a result
of the low altitude of the orbit and uniform coverage of Mars Observer,
scientists will have obtained unprecedented global knowledge of the martian
gravitational field.
The landers will carry instruments to directly sample both the atmosphere and
surface. The landers will send data to Earth via the Mars 94 orbiter,
using Mars Observer's MBR antenna as a back-up.
If it is still operating on an extended mission, Mars Observer's
MBR may also support the Russian Mars 96 mission, which is planning
to send a balloon to be released in the martian atmosphere in 1997.
Funding and scheduling of the Mars 96 mission are currently uncertain,
and there is still some question as to whether Mars 94 will actually be
launched in 1994. If not, the spacecraft will have to wait for the next launch
window in 1996.
The spacecraft, instruments, and mission were designed so that sufficient resources,
especially power and data rate, are available to power all instruments as they collect
data simultaneously and continuously on both the day and night sides of the planet.
The camera system takes photos only on the day side and will acquire additional
images every three days during real-time radio transmissions to the Deep Space
Network.
The rotation and orientation of the spacecraft are controlled by horizon sensors,
a star sensor, gyroscopes and reaction wheels, as is common for Earth-orbiting
satellites. The horizon sensors, adapted from a terrestrial design, continuously
locate the horizon, providing control signals to the spacecraft. The star sensor
has been used for attitude control during the 11-month cruise and as a back-up for
the horizon sensors during the mapping orbit.
Once during each 118-minute orbit, the spacecraft will enter the shadow of Mars
and rely on battery power for about 40 minutes. The battery is charged by the
spacecraft's large solar panel, which generates more than a kilowatt of power
when it is in the sunlight.
Control of the spacecraft and instruments is accomplished through the use of
onboard microprocessors and solid-state memories. Scientific and engineering
data are stored on tape recorders for daily playback to Earth. Additional
data operations will allow information to be returned in real-time from
selected instruments whenever Earth is in view.
The lifetime of the spacecraft will most likely be determined by the supply
of attitude-control fuel and the condition of the batteries.
The DSN antennas and facilities are located in Pasadena and Goldstone, California;
Canberra, Australia; and Madrid, Spain. It is necessary to have three such
facilities scattered around the Earth to ensure continuous coverage of the sky.
The instrument scientists remain at their home institutions, from which they
can access Mars Observer data via a project database at JPL. Using
workstations and electronic communications links, scientists will also be
connected to the mission planning activities at JPL.
In the same way, data products returned to the JPL database from the home
institution for each of the instruments will be sent electronically to other
investigators at their home institutions. This will allow scientists to have
ready access to science data without moving to JPL for the duration of the
mission (as was common in the past).
More than 60 workstations will be connected to the project database at JPL,
a centralized repository for downlink science and engineering telemetry data,
ancillary data including navigation information, and uplink command and
sequence data. This database, with about 30 gigabytes of on-line storage,
will be electronically available to the science instrument investigators via
NASCOM data links.
During the mapping phase, the instrument investigations will return processed
science data products to the database at JPL for access by the interdisciplinary
scientists and other investigation teams.
The scientists involved with the Mars Observer instruments are listed
on the following page [Hardcopy only!]. Note that there are some guest
investigators from Russia and other European countries.
The Titan III rocket can carry payloads over 31,000 lbs to low-Earth orbit and
up to 11,000 lbs into geosynchronous transfer orbit. The Titan III is a member
of the Titan launch vehicle series that has been used by the US Air Force and
NASA for more than 25 years, including the Gemini program, the Voyager,
and Viking spacecraft. The core vehicle consists of two
liquid-propellant boosters that are the central propulsion element. The
fuels are "Aerozine 50" and nitrogen tetroxide. Twin 10.2-foot diameter
solid rocket boosters are attached to the sides of the core vehicle to
provide additional thrust during lift-off.
The Transfer Orbit Stage (TOS) is a single-stage, solid propellant vehicle
used to propel a spacecraft from low-Earth orbit toward its ultimate
destination. This can be a higher orbit about the Earth or an interplanetary
course. Twenty minutes after separation from the Titan III, Mars Observer's
TOS fired for about 150 seconds, bringing the spacecraft up to a speed of about
25,575 miles per hour. After the firing, the TOS separated from Mars Observer
and spacecraft was on its way to the Red Planet.
Once Mars Observer is in its mapping orbit, the spacecraft will be checked-out
and instruments will be calibrated. Mapping begins shortly afterward, with some
instruments starting around November 24, 1993, and others starting in December 1993
or January 1994.
Radio Science
The radio science investigation will use the spacecraft's telecommunication
system and the giant parabolic (dish) antennas of NASA's Deep Space Network to
probe the martian gravity field and atmosphere. These measurements will help
scientists determine the structure, pressure, and temperature of the martian
atmosphere.
<--- Testing Radio Boom at G.E., 1992Magnetometer and Electron Reflectometer (MAG/ER)
Mars is now the only planet in the Solar System, except Pluto, for which a
planetary magnetic field has not yet been detected. In addition to searching for
a martian planetary magnetic field, this instrument also will scan the surface
material for remnants of a magnetic field that may have existed in the distant past.
The magnetic field generated by the interaction of the solar wind with the upper
atmosphere of Mars will also be studied.Mars Balloon Relay (MBR)
The spacecraft carries a radio system supplied by the French Centre National
d'Etudes Spatiales (CNES, the French space agency) to support the Russian
Mars 94 mission. Mars 94 consists of an orbiter and small landers
and is expected to be launched in October 1994 (reaching Mars around September 1995).
Mapping Cycle
In it's near-circular mapping orbit, Mars Observer will rotate once per
orbit to keep the instruments pointed at the planet. This will allow all instruments
to view the planet continuously and uniformly during the entire martian year.
<--- M.O.'s Solar Panels, men for scale
Science Operations
The Mars Observer mission operations at the Jet Propulsion Laboratory
(JPL) will be supported by NASA's Deep Space Network (DSN) and the JPL Advanced
Multimission Operations System. The 34-meter, high-efficiency subnetwork, the
newest of the DSN antenna subnets, provides daily uplink and downlink
communications with the spacecraft at X-band frequencies of 8.4 gigahertz.
The 70-meter antenna network also provides periodic very-long-baseline
interferometry and real-time, high-rate telemetry and radio science support
to the mission.
<--- JPL as seen from the air
(NASA/JPL)
Mars Observer Launch
Mars Observer was launched from the Kennedy Space Center in Florida on
September 25, 1992. It was launched aboard a Titan III rocket built by the
Martin Marietta Corp. of Denver, Colorado. Mars Observer was attached
to a Transfer Orbit Stage (TOS) rocket which propelled it out of Earth orbit
once it was in space. The TOS was designed and built by Orbital Science Corp.
of Fairfax, Virginia. The TOS used for the Mars Observer launch was
the first one ever flown in space. 
<--- Mars Observer Launch
(NASA/JPL)
Orbit Insertion Phase
After arrival on August 24, 1993, it will take Mars Observer nearly 3 months
to get into the circular polar orbit it needs to carry out its mission. The figures
[TO BE ADDED TO THIS PAGE DURING SUMMER 1994]
outline the orbit insertion phase of the Mars Observer mission.
These figures were generated by David E. Melendrez, the mission planner for
the Mars Observer Thermal Emission Spectrometer instrument.
<--- Mars Orbit Insertion Logo, 1993
TES 1993-1994 Curriculum Guide / K.S. Edgett /edgett@elvis.mars.asu.edu
