Institute for Space Systems Operations * 2001 Annual Report * 94-96
Lawrence S. Pinsky, Ph.D., Professor and Chair, Department of Physics, University of
Houston
Thomas L. Wilson, Ph.D., Earth Science and Solar System Exploration Division, NASA-JSC
Victor Andersen, Post-Doctoral Aerospace Fellow
Kerry Lee, Doctoral Student, Department of Physics
| Abstract--The Mars Radiation Environment Experiment (MARIE) was launched April 7, 2001, and inserted into orbit around Mars in October 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 and has a resolution capable of measuring the flux of charged particles from about 20-450 MeV/A. The experiment experienced an equipment failure in August and has been inoperable since. However, some data were taken prior to that failure, and the analysis of those data is proceeding. Plans exist to attempt to restore the experiment to full functioning capacity when the spacecraft's orbit around Mars is stabilized after other mission-critical events have occurred. The original NASA PI for the experiment, Dr. Gautam Badhwar, tragically passed away last August, and there has been a transition in the responsible NASA personnel on the project. However, commitments have been reaffirmed to continue the involvement of the UH student supported in the project with ISSO funds as he continues to pursue his Ph.D. dissertation research. |
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 then spent about two months aerobraking to achieve 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 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 surface and solar energetic particle events (SEPs) and galactic cosmic rays (GCRs). Data collected by MARIE will be used to model the effects of the atmosphere of Mars in order to predict radiation doses. MARIE is an energetic particle spectrometer that is described in the next section.
Instrument Description
The MARIE instrument 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 directly 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, such that 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" brass sheets in the detector stack. There is one sheet located on each side of
the two A detectors. This material was inserted to reduce the background noise.
Figure 1. Detector array schematic of MARIE
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 seven watts of power. Its outside dimensions are 29.4 × 23.2 × 10.8 cm. An isometric view is shown in Fig. 2.
Figure 2. An isometric view of MARIE
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 were made to the values for voltage
bias in the spectrometer. These changes altered triggering thresholds which affected
particle energy cutoffs.
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 Janni1 to a power law Rp = kEn, where the values of k and n are material-dependent. The data spread above the solid lines are 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.
Figure 3. Particles stopping in detector B1.
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 
where DE is the measured energy loss, and
is determined by forcing the proton peak to a value of Z = 1. The resolution of this plot
will improve when the A detectors are included in the measurement.
Figure 4. Charge plot showing H and He.
Figure 5. Charge plot showing Z > 4.
References
1J. Janni. "Proton Range-Energy Tables, 1 keV-10GeV, Part I and II," Atomic
Data and Data Tables 27 (1982).
Publications
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 Conf., League City, TX, March 11-15, 2002
Presentations
Lee, K., L. Pinsky, G. Badhwar, T. Cleghorn, T. Beyers, R. Dunn, C. Chambellan, J. Bahr,
F. Riman, J. Flanders and P. Delaune. "Measurement of the Galactic Cosmic Ray
Particle Energy Spectra in Earth-Mars Transit and Mars Orbit," Int'l. Conf. on
Environmental Systems, San Antonio, TX, July 15-18, 2002.
Funding and proposals
"Analysis of Data from the Mars '01 MARIE Experiment." Aug. 1, 2001-July 31,
2002, NAG9-1347, $25,894.
"Analysis of the MARIE Data Including A Study of the Radial Dependence of Solar
Energetic Particle Events," July 1, 2002-June 30, 2005, NASA NRA-01-OSS-01=Mars
Odyssey Participating Scientist, $356,400; pending.
"Determining the Radial Dependence of Particle Intensities from Coronal Mass
Ejections," Jan. 1, 2002-Dec. 31, 2003, ARP, $103,000.
Theses or student reports
Lee, K. Dissertation in progress.
PDF (152K)
Table of Contents
Institute for Space Systems Operations - 2001
Annual Report
Copyright © 2002
|
|
