TES News

August/September 1993, Volume 2, No. 3

Thermal Emission Spectrometer Project Mars Observer Space Flight Facility Department of Geology, Box 871404 Arizona State University Tempe, Arizona 85287-1404, U.S.A.

Return to the Red Planet: Anticipated TES Observations in 1993

A Tale of Two Spectrometers

What is the surface of Mars made of? There are two instruments aboard Mars Observer that are dedicated to determining the mineralogy and chemistry of the martian surface. These are the Thermal Emission Spectrometer (TES) and the Gamma Ray Spectrometer (GRS).

The TES project is directed by Dr. Philip R. Christensen at Arizona State University in Tempe. The TES uses thermal infrared observations to identify different types of minerals on the martian surface.

The GRS project is directed by Dr. William V. Boynton of the University of Arizona in Tucson. The GRS observes the energy of gamma rays emitted from the surface of Mars. The GRS will provide information about the elements that make up the martian soil, such as silicon, aluminum, and oxygen, and is also designed to detect water ice buried at depths of less than 1 meter (3.3 feet). In order to shield it from gamma rays that are generated by the spacecraft's own electrical components, the GRS is located at the end of a 6 m (20 ft) -long boom.

The observations of Mars that these two instruments may make in the latter half of 1993 are intimately linked because of the configuration of the Mars Observer spacecraft during its journey from Earth to the Red Planet...

<--- Figure 1; Mars - Earth Orbits 1993 - 1995

Cruise and Mapping Configurations

Figure 1 shows the orbits of Earth and Mars around the Sun (center). The dashed curve represents the path that Mars Observer took on its 11-month journey to Mars. After arrival on August 24, 1993, Mars Observer spends three months adjusting its orbit until late November 1993, when it will be ready to begin mapping.

Figure 1 also shows the solar conjunction period from December 20, 1993, to January 3, 1994. Solar conjunction occurs when Earth and Mars are on opposite sides of the Sun and radio communications cannot be made. Any mapping that TES or other Mars Observer instruments might do in 1993 will occur mainly before December 20th.

Upon arrival, Mars Observer is still partially folded-up in its cruise configuration (shown in Figure 2). The spacecraft traveled from Earth to Mars in this configuration.

<--- Figure 2; Cruise Configuration

In comparison, Figure 3 shows the spacecraft in its mapping configuration. When Mars Observer was launched, it was folded up in a tight package that could fit inside a Titan III rocket. Once in space, two booms, one carrying magnetometers (to detect magnetic fields) and the other holding GRS, were only extended part way. Likewise, the solar panels and high gain antenna (to communicate with Earth) were partially deployed.

<--- Figure 3; Mapping Configuration

<--- Color version of Figure 3

In the cruise configuration (Figure 2), the GRS boom is folded so that the GRS instrument is held close to the spacecraft. To prevent damage to the GRS, magnetometers, solar planels, or high gain antenna, Mars Observer remains in cruise configuration until it is in a circular polar orbit in mid-November 1993.

Position of GRS Limits 1993 TES Observations

Prior to its arrival at Mars, the TES instrument has been turned on three times. The first was in November 1992, the second time in February 1993. During thse first two turn-ons, the TES looked at space.

The third TES turn-on was August 1, 1993. This time, the spacecraft was oriented so that the TES could see Mars, although the Red Planet was still quite far away (5,100,000 km (3,160,000 mi)). Each time the TES was turned on, the observations were carefully planned in advance to avoid seeing the Gamma Ray Spectrometer.

While Mars Observer is in the cruise configuration (Figure 2), the TES can see the GRS when it looks in a sideways direction. The GRS, like the rest of Mars Observer, is covered with reflective material to insulate the spacecraft against heat from sunlight. This covering on the GRS and its boom might act like a mirror and reflect bright sunlight into the TES. This will no longer be a problem for TES once the GRS boom is rotated into the mapping configuration shown in Figure 3.

The GRS will require calibration testing in its folded-up cruise configuration until at least mid-December. Thus, the GRS position will likely limit TES in November - December 1993 to observe only the night side of Mars, when GRS is in the shade.

The plan (as of August 1993) is for the GRS to rotate out of cruise configuration on December 13, 1993. This rotation must occur at least seven days before solar conjunction begins on December 20th, otherwise the GRS will be rotated in early January 1994.

The TES is also affected by this schedule. Thus, daytime TES observations will probably not begin until the GRS is moved out of cruise configuration. Once TES begins mapping, it is expected to continue in this mode throughout the remainder of the mission, which will last to at least November 1995.

<--- Figure 4; Mars Observer Mission Timeline 1992 - 1996

<--- Mars Observer Titan III Launch, September 1992

Mars Observer TES and Education

TES project at Arizona State University has an active program to enrich education using Mars Observer. If you are an educator, we encourage you to visit us to find out more about what resources are available and when to expect the next teachers' workshop.

The first TES Educators' Workshop was held on February 20, 1993, the second on August 21, 1993. Below are listed some Mars items you may be able to obtain from libraries, bookstores, and other sources.

Mars Observer T-shirts:

Recent Articles:

Recent Books (Fiction):

Text by: K.S. Edgett

Original (hardcopy) Typesetting by: K. Patoni

Original Text:  August 1993

Hypertext:  21 June 1994