Douglas Isbell
Headquarters, Washington, DC                November 13, 1996
(Phone: 202/358-1547)

Diane Ainsworth
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-5011)

Diane Farrar
Ames Research Center, Mountain View, CA
(Phone: 415/604-3934)

RELEASE: 96-236

U.S. SOIL EXPERIMENT READY FOR LAUNCH ABOARD RUSSIA'S 
MARS `96

     An instrument developed by the United States to measure 
the rate at which metals and organics corrode when exposed to 
the Martian environment is set for launch on Nov. 16, aboard 
two small landing stations on the Russian Mars '96 
spacecraft.

     The instrument, called the Mars Oxidant Experiment 
(MOx), was built at the Jet Propulsion Laboratory, Pasadena, 
CA, and is part of expanding U.S.-Russian cooperative  
efforts in space exploration.

     Integration and final testing of the experiment on the 
Russian landers, also referred to as "small autonomous 
stations," was completed in late October at the Lavochkin 
Research and Production Association in Moscow,  where the 
landers were designed and assembled, said Mark Herring, 
manager of the experiment at JPL. Two of the MOx instruments 
will fly on the mission, one on each of its two landers.

     "This was a major engineering milestone for the U.S. 
experiment,  culminating a development effort which started 
in 1992," Herring said. "In the course of integration on the 
landers, the U.S. team was required to take numerous trips to 
Helsinki and Moscow during the past year. We've gained 
valuable experience in what is involved with participation on 
an international mission."

      The goal of the Mars '96 mission, set for launch aboard 
a Russian Proton launch vehicle from Baikonur Cosmodrome in 
Kazakstan, is to investigate  the evolution of the Martian 
atmosphere, surface and interior by acquiring comprehensive 
measurements of the physical and chemical processes that 
occur on Mars today and those that may have taken place in 
the past.

     The Mars Oxidant Experiment was developed to further 
investigate the  presence of a strong oxidizing agent in the 
Martian soil that was inferred from the results of the 
biology experiments onboard the NASA Viking landers in the 
mid-1970s.

     "We hope MOx will be able to tell us more about the 
surprisingly reactive properties of the Martian soil first 
detected by the Viking biology experiments and tell us if 
this reactivity is the cause of the complete absence of 
organics in the surface soil on Mars," said 
Dr. Christopher McKay, project scientist at NASA's Ames 
Research Center, 
Mountain View, CA.

     "If we plan to search for the organic remnants of early 
life on Mars with future missions, then we have to understand 
the processes that are destroying these organics on the 
surface so that we know how deep we have to dig to reach 
unoxidized material," he added. "Viking, for instance, dug 
under a rock as deep as 4 inches (11 centimeters) but found 
only oxidized sand."

     MOx uses chemical sensor technology originally developed 
at the Sandia National Laboratories, Albuquerque, NM. The 
instrument measures  the oxidizing power of the Martian soil 
and atmosphere using a detector that monitors the change in 
reflectivity of a thin chemical film that is exposed  to  the 
Martian environment. The instrument, which weighs only three 
pounds, relies on its own power source  -- a set of batteries  
-- to carry out the measurements.

     Upon landing and deployment, MOx will operate 
autonomously, Herring said, according to a sequence that is 
programmed into its internal "read-only memory." While the 
mission is designed for a one-year lifetime, the operating 
life of MOx will be limited by its battery power source.  
Depending on the actual conditions on the surface of Mars, 
the operating
time will be between 80 and 160 days.

     "The instrument's sensor head is located on a petal of 
each of the two Russian small stations and is comprised of 
eight sensor cell assemblies,  four of which are designed to 
contact the soil and four that will be exposed to the 
atmosphere," Herring said. "Within each cell assembly there 
are six active sensing sites and six reference sites, for a 
total of 96 sites.

     "The active sites are protected by thin membranes of 
silicon nitride, which protect the sensor films from 
premature oxidation," he explained. "These membranes will be 
broken upon deployment, exposing the active films. The 
reference sites will remain permanently sealed. The sensor 
films have been selected to provide a broad range of chemical 
reactions. Each film type is duplicated in the air and soil 
cells."

      Each of the 96 sensor sites is illuminated by two 
light-emitting diodes  (LEDs), one operating at a wavelength 
of 590 nanometers and the other at 870 nanometers. The 
reflected signal will be measured by a silicon photodiode 
detector array. The sensor sites are coupled to the LEDs and 
the detector array through fiber optics.

      A  key feature of the experiment's data transmission 
sequencing is its ability to transmit data three times in 
order to reduce the data loss associated with various 
communications links. During the mission, the experiment team 
will distribute calibration data and mission data sets in 
which data from the instruments are merged with pertinent 
mission
information.

      Another U.S. instrument aboard Mars '96  is the Tissue-
Equivalent Proportional Counter (TEPC).  The TEPC instrument 
was developed at NASA's Johnson Space Flight Center, Houston, 
TX, to measure and store accumulated radiation spectra during 
the interplanetary cruise phase of the mission, as well as 
upon arrival in Mars orbit.  This information should yield 
important insight into the space radiation environment and 
potential health risks involved in future human spaceflight.

     Also aboard the spacecraft, attached to the MOx 
electronics case, is a CD-ROM, entitled "Visions of Mars," 
produced by The Planetary Society,  Pasadena, CA, which is 
analogous to the records carried into space in 1977 by the 
twin Voyager spacecraft. The Mars `96 CD-ROM contains a 
collection of science fiction stories, sounds and artwork 
which chronicle humanity's fascination with Mars over four 
centuries of human history, 10 alphabets,
17 languages and 26 nations. The collection covers the 
earliest references to Mars in science fiction to present day 
stories about the red planet. A label pointing to the 
location of the CD-ROM is mounted on the outside of the 
spacecraft and includes a microdot of 100,000 names of 
Planetary Society members and instructions on how to use the 
CD-ROM.

     If launched on time, Mars `96 will reach the orbit of 
Mars in mid-September 1997, at about the same time as NASA's 
Mars Global Surveyor (MGS) orbiter,  which was launched 
successfully on Nov. 7.  Mars '96 will deploy the two small 
stations and two penetrators on the surface of the planet 
shortly after arriving in Mars orbit. On-time launches of 
both spacecraft will enable MGS to assist in relaying data 
from the Russian small stations once
the MGS primary mapping mission begins in March 1998.

-end-