University of Houston • University of Houston-Clear Lake • ISSO Annual Report Y2002—pp. 97-100

Analysis of the Mars Odyssey MARIE Experiment Data

Lawrence S. Pinsky (UH) and Thomas L. Wilson (NASA-JSC)

Abstract
The MARIE [Mars Radiation Environment Experiment] was launched April 7, 2001, and inserted into orbit around Mars in October 2001 as part of the Mars Odyssey 2001 spacecraft payload. The purpose of the experiment is to evaluate the radiation environment in the vicinity of Mars in order to plan the design of future manned spacecraft and missions to that planet. The experiment consists of a charged particle telescope with a resolution capable of measuring the flux of charged particles from about 20-450 MeV/A. The experiment experienced an equipment failure in August, 2001 and was inoperable until March, 2002, after the spacecraft had been stabilized in its Science Orbit around Mars. Approximately one year’s worth of data have been received, and the analysis is ongoing. UH personnel funded in part by ISSO are participating in the analysis.

IN THE EFFORT TO EXPLORE MARS, THE MARS ODYSSEY SPACECRAFT was launched on April 7, 2001, and arrived in orbit at Mars on October 23, 2001. The spacecraft spent about two months aerobraking to get into a two-hour circular science orbit. One of the three scientific instruments on board is the Mars Radiation Environment Experiment (MARIE), in which the University of Houston group plays a supporting role in the analysis of the data. The principal function of MARIE is to characterize the space radiation environment of Mars and determine the risk it poses to human exploration. Primary radiation sources to be measured are solar energetic particle events (SEPs) and galactic cosmic rays (GCRs) along with the albedos they cause from the Martian atmosphere and surface. Data collected by MARIE will be used to model the effects of the atmosphere of Mars in order to predict radiation doses.

Instrument Description
The MARIE instrument is an energetic particle spectrometer. It functions much like a telescope, as shown in Fig. 1. It consists of six silicon detectors, two position sensitive detectors (PSDs), and a Cerenkov detector. Starting from the top in Fig. 1, detector A1 is a square silicon detector 25.4 ´ 25.4 ´ 1 mm. Next are the position sensitive detectors PSD1 and PSD2, which are identical in design. Each consists of two silicon strip detectors placed one on top of the other, with the strips oriented perpendicular to one another for x-y position sensitivity. Each strip detector has 24 1-mm width strips, so that the dimensions of the PSDs are 24 ´ 24 ´ 0.3 mm. The next detector, A2, is identical to A1. The four B detectors (B1, B2, B3, B4) are identical circular silicon detectors with a diameter of 63.5 mm and thickness of 5 mm. The last detector is the C detector complex, which consists of a Cerenkov detector, made of sapphire (45 mm diameter and 10 mm thickness) followed by a reflector and a photomultiplier tube. In addition to these detectors, there are four 0.001 in. brass sheets in the detector stack. One sheet is located on each side of the two A detectors. This material was inserted to reduce background noise.

The trigger for this instrument is an A1 A2 detector coincidence. This means that an ion or charged nucleus must enter the 60 degree field of view (FOV), in either the forward (top to bottom) or backward (bottom to top) direction and have enough energy to penetrate the A1 and A2 detectors. It is not necessary for the particle to go entirely through both detectors; it only has to penetrate one and then deposit a small amount (enough to be detected by the electronics ~35 keV) in the other. If both A1 and A2 have a signal, then a reading from every detector is recorded to disk as a single event.

MARIE weighs 3.3 kilograms and uses 7 watts of power. Its outside dimensions are 29.4 ´ 23.2 ´ 10.8 cm. An isometric view is shown in Fig. 2.

Preliminary Data Results
Data were taken during the Earth-Mars transit phase from April-August 2001. During this time MARIE was calibrated and several adjustments to the values for voltage bias in the spectrometer were made. These changes altered triggering thresholds which affected particle energy cutoffs.

During mid-August the instrument failed to respond to commands. At the same time the Odyssey team was preparing for orbit insertion and aerobraking; therefore, recovery efforts were put on hold until after a stable science orbit was reached. The instrument was recovered in March 2002 and has continuously provided data from Mars orbit.

Figure 3 shows a scatter plot of the measured energy loss in A2 and B1 for particles that did not completely penetrate B1. The solid lines are theoretical curves based on a best fit of the proton range-energy data of Janni (1982)1 to a power law Rp = kEn, where the values of k and n are material-dependent. Data spread above the solid lines is due to the path-length variation caused by finite opening-angle of the telescope. The solid line has been calculated using normal incidence, and thus minimum path length.

Figures 4 and 5 show the average measured charge from the four B detectors for particles that have enough energy to penetrate all the silicon detectors. The charge measured in each detector is calculated using Z = ÖDE/a, where DE is the measured energy loss, and is determined by forcing the proton peak to a value of Z = 1. The resolution of these plots will improve when the A detectors are included in the measurement.

Acknowledgments
The original NASA PI for the experiment, Dr. Gautam Badhwar, tragically passed away in August, 2001, and Dr. Cary Zeitlin of the Lawrence Berkeley National Laboratory has been appointed as the new PI. Mr. Kerry Lee, a UH graduate student who has been supported in part with ISSO funds, continues to pursue his Ph.D. dissertation research on this project.

References
¹J. Janni. Proton Range-Energy Tables, 1 keV-10GeV, Part I and II. Atomic Data and Data Tables, 27.4 & 5 (1982).

Publications
Andersen, V., K. Lee, L. Pinsky, W. Atwell, T. Cleghorn, F. Cucinotta, P. Saganti, R. Turner, and C. Zeitlin. "Monte Carlo Simulations of the Response of the MARIE Instrument," Proc., 34th Lunar and Planetary Science Conference (LPSC), League City, TX, March 17-21, 2003. (Submitted.)
Cleghorn, T., K. Lee, L. Pinsky, C. Zeitlin, and G. Badhwar. "Initial Results from the 2001 Mars Odyssey Martian Radiation Environment Experiment MARIE," Proc. 33rd Lunar and Planetary Science Conference (LPSC), League City, TX, March 11-15, 2002.
Lee, K., T. Cleghorn, F. Cucinotta, and C. Zeitlin. "Heavy Ion Observations by MARIE in Cruise Phase and Mars Orbit," Advances in Space Research (Proc. 34th COSPAR Scientific Assembly), Houston, TX, Oct. 10-19, 2002.
Lee, K., V. Andersen, W. Atwell, T. Cleghorn, F. Cucinotta, L. Pinsky, P. Saganti, R. Turner, and C. Zeitlin. "Cosmic Ray Flux Measurements Made by MARIE in Mars Orbit," Proc. 28th International Cosmic Ray Conference (ICRC), Tsukuba, Japan, July 31-Aug. 7, 2003. (Submitted.)
Lee, K., V. Andersen, W. Atwell, T. Cleghorn, F. Cucinotta, L. Pinsky, P. Saganti, R. Turner, and C. Zeitlin. "Heavy Ion Flux Comparison of MARIE and ACE/CRIS Instruments," Proc. 34th Lunar and Planetary Science Conference (LPSC), League City, TX, March 17-21, 2003. (Submitted.)
Zeitlin, C., T. Cleghorn, F. Cucinotta, P. Saganti, W. Atwell, V. Andersen, K. Lee, and L. Pinsky. "Overview of the Martian Radiation Environment Experiment (MARIE)," Advances in Space Research, Proc. 34th COSPAR Scientific Assembly, Houston, TX, Oct. 10-19, 2002.
Zeitlin, C., T. Cleghorn, F. Cucinotta, P. Saganti, V. Andersen, K. Lee, L. Pinsky, W. Atwell, and R. Turner. "Results from the Martian Radiation Environment Experiment MARIE," Proc. 34th Lunar and Planetary Science Conference (LPSC), League City, TX, March 17-21, 2003. (Submitted.)

Presentations
"Preliminary Results from MARIE (Martian Radiation Environment Experiment)," International School of Cosmic Ray Astrophysics, Erice, Sicily, Italy, June 2002.

Funding and proposals
"Analysis of Data from the Mars ‘01 MARIE Experiment," NAG9-1347, Aug. 1, 2001-July 31, 2002, $25,894.
"Determining the Radial Dependence of Particle Intensities from Coronal Mass Ejections," ARP, Jan. 1, 2002-Dec. 31, 2003, $103,000.
"Analysis of the MARIE Data Including A Study of the Radial Dependence of Solar Energetic Particle Events," NASA NRA-01-OSS-01=Mars Odyssey Participating Scientist, July 1, 2002-June 30, 2005, $356,400 (pending).

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Institute for Space Systems Operations - Y2002 Annual Report
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