PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = " initial draft based on information collected from the MARIE team website Steven Joy, 2002-06-01; Major revision by the P.I. Cary Zeitlin, 2002-09-11; Minor edits Mark Sharlow, 2002-09-11; Minor edits and reformatting Mark Sharlow, 2002-11-14;" OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = ODY INSTRUMENT_ID = MAR OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "MARS RADIATION ENVIRONMENT EXPERIMENT" INSTRUMENT_TYPE = "CHARGED PARTICLE TELESCOPE" INSTRUMENT_DESC = " Scientific Objectives and Overview: =================================== Mars is substantially exposed to the harshest elements of space weather. Unlike Earth, which sits inside a protective magnetic field called the magnetosphere, Mars does not have a global magnetic field to shield it from solar flares and cosmic rays. Another factor is the lack of atmosphere. Mars' atmosphere is less than 1% as thick as Earth. These two factors make Mars vulnerable to space radiation. The Marie instrument was designed to measure the amount of harmful radiation in the Mars environment. The particles which are thought to be most harmful to humans fall mostly in the energy range of 30 MeV to thousands of MeV per nucleon. These are the particles with enough energy to damage human DNA. The MARIE instrument is designed to measure particles in the range of 15 MeV to 500 MeV/n. The data gathered in several detector elements is combined to identify the species of the incident particles and their energies in this range. The MARIE Instrument was developed by NASA Johnson Space Center. The development process was a coordinated effort of NASA/JSC, Lockheed-Martin and Battelle. Battelle developed the CPU, power boards, A detector, B detector and C detector boards. Lockheed was tasked with development of the position sensor devices (PSD), the instrument packaging, system integration, software development and certifying the instrument for flight. NASA/JSC provided the project management and coordination of the contractors. If a particle enters the MARIE detector telescope within the 60 degree cone defined by the A1 and A2 detectors, and has enough energy to reach the A2 detector, it is considered a coincident event. On coincident events, all detector boards are polled by the CPU and the data for this event is recorded. The readout for each detector records a pulse height that is proportional to the amount of energy deposited in the detector. The PSD's also record the position of the strike within the detector. The minimum proton energy required to form an A1A2 coincidence corresponds to a proton with range greater than the sum of the thickness of A1, PSD1, PSD2, and a minuscule part of the A2 thickness. This adds up to 0.374 g/cm2 of Si and corresponds to a proton energy of 19.8 MeV. So protons above this energy will be recorded by the telescope; more energy per nucleon is required for higher-charged particles. If one takes into account the thin aluminum case that surrounds MARIE, the minimum proton energy is 30 MeV. The angular response functions are calculated for those particles that give an A1A2 coincidence and also pass through PSD1 and PSD2 detectors, since they are the only particles that can provide the incidence angle of the charged particle. Note that not all particles that give rise to A1A2 coincidence pass through PSD1 and PSD2 because the position sensitive detector are slightly smaller in size. A new particle identification algorithm is being developed to determine incident angles for particles that miss the PSDs or have their positions mis-reported by the PSDs. (The latter are common, owing to spurious detector noise.) If a particle hits only one of the A-detectors, the event is discarded because the angle of impact and energy loss in the other detector boards is not known. Also, any particle entering the bottom of the telescope will not register an event on the C-detector due to the directional properties of the C-detector. The chassis box of MARIE is made from machined aluminum with an alodine coating. The exterior surfaces are painted white. Input voltage to MARIE is 28 VDC and power requirements are 3 watts for survival mode and 7 watts for nominal operation.There are no external controls. All control is from the orbiter through an RS-422 interface. Calibration: ============ Data obtained during the cruise phase of the 2001 Mars Odyssey mission have been used to calibrate the data. Pulse height spectra in the range 0 to 4096 have been scaled to yield distributions of apparent charge, Z. Calibration factors for each detector were determined by forcing the obvious high-energy proton peak in each distribution to have its center at Z = 1. Operational Considerations: =========================== During Odyssey's daily DSN session, MARIE is off for 1-2 hours, causing small gaps in coverage. When the recorded data volume approaches the capacity of MARIE's local storage, data acquisition is halted until the next download opportunity. When all data have been downloaded, the storage area is erased and the instrument reset. This sequence of events causes relatively long outages, on the order of 1 to 2 days. Detectors: ========== Each of the two A detector assemblies contains a 25.4 x 25.4 x 1 mm ion-implanted silicon solid state detector, detector signal amplifiers, detector high voltage supply and the interface circuitry between the detector and the MARIE CPU. The MARIE CPU controls the interface circuitry including high voltage control, collecting digitized signal amplitude data and controlling signal coincidence timing sources. The two A-detectors are used to define a coincidence event. These detectors are operated near 160 V. Each of the four B-detector assemblies contains a 5 mm thick lithium-drifted silicon solid state detector, detector signal amplifiers, detector high voltage supply and the interface circuitry between the detector and the MARIE CPU. The MARIE CPU controls the interface circuitry including high voltage control and collecting digitized signal amplitude data. These detectors are operated near 350 V. The C detector consists of a Schott-glass Cherenkov detector and a Hamamatsu photo multiplier tube (PMT). When a charged particle with velocity greater than [velocity of light / glass refractive index] hits the Cherenkov detector, the detector releases a photon light burst proportional to the energy of the particle which struck it. The photo multiplier tube receives the light pulse and translates it into an electronic pulse which is amplified by the tube and read by the electronics on the C-detector board. The C-detector assembly contains the PMT, detector signal amplifiers, detector high voltage supply and the interface circuitry between the detector and the MARIE CPU. The MARIE CPU controls the interface circuitry including high voltage control and collecting digitized signal amplitude data. Each of the two position sensitive detector (PSD) assemblies contains 25.4 X 25.4 mm position sensitive detector. These are double-sided silicon strip detectors with 24 strips on each side, with a 1 mm pitch. The strips on one side are oriented so as to be orthogonal to the strips on the other side. The active area of these detectors is 24 mm x 24 mm. Hits from all four strip planes define the particle's incident angle. From the front of the device, particles entering the detector pass through detector A1, PSD1, PSD2, A2, B1, B2, B3, B4, and C. Depending on the angle of incidence and scattering within the detector, some of the downstream detectors (B's and C) may be missed on any given event. Electronics: ============ The Central Processing Unit (CPU) board has an Intel 80C188 microprocessor, detector interface circuitry and data communication hardware for transferring data to the spacecraft from the 80 MB flash memory. The flash memory holds the program code and any data which has not been transferred to the spacecraft. The power from the spacecraft is nominally 28 volts. The Marie instrument has Interpoint DC-DC converters to convert the power to a usable level. Each detector has its own card, with all of the electronics associated with the detector on it, including a 12 bit analog-to-digital (ADC) converter, and Field Programmable Gate Array (FPGA) The power, mode control and data download of the MARIE instrument are controlled by the Odyssey spacecraft. Commands are sent from the ground to the spacecraft central processing unit (CPU) to power on MARIE and to change modes. Location: ========= The MARIE instrument frame is illustrated by this diagram: _______________ HGA \ / .. `._________.' Science || ._______________.Science deck Orbit || | ^+Xsc | Velocity || | | | ^. || | | ^+Xmarie .' MARIE FOV `. || | |+Zsc /|| .' (68 deg cone) `. ||@| <-----o ..'._|_. .' || +Ysc / | | |.' || | _.' <----o o--------> MARIE FOV || | _.' +Ymarie _.`. boresight Solar || ..'_____________. `. Array .. Bottom Deck `. `. / / --------> / Aerobraking V Nadir Velocity Actual keywords defining MARIE instrument frame and incorporating MARIE mounting alignment information are provided in reference [1]. The MARIE FOV (field of view), as defined in [2], is a 68-degree cone centered around the -Y axis of the MARIE instrument frame. The set of keywords in the data section above defines MARIE FOV as a circle with a half-angle of 34 degrees and boresight direction along the -Y axis of the MARIE instrument frame. The following data for the FOV geometry were extracted from the SPICE instrument kernel for MARIE, provided by the NAIF Node of the Planetary Data System [3]. (The text of this section also was adapted from that SPICE kernel.) These data are included here for the benefit of those familiar with the use of SPICE kernels. INS-53040_FOV_FRAME = 'M01_MARIE' INS-53040_FOV_SHAPE = 'CIRCLE' INS-53040_BORESIGHT = ( 0.0000000000000000 -1.0000000000000000 0.0000000000000000 ) INS-53040_FOV_BOUNDARY_CORNERS = ( 0.0000000000000000 -0.8290375725550400 +0.5591929034707500 ) Operational Modes: ================== The instrument has only two modes, Science Mode and Survival Mode. Science Mode: When placed in Science mode, the MARIE acts as an autonomous data acquisition device. Data is collected until the spacecraft issues a mode change command to move to survival mode. Survival Mode: From survival mode, the spacecraft can issue commands to download data, change parameters, power down or return to Science Mode. During the data download, the spacecraft controls the download process and downlinks the data to the ground. Measured Parameters: ==================== The detector is composed primarily of three types of silicon detectors: the A detectors, which are square in cross-section (25.4 mm on a side) and 1 mm in depth; the B detectors, circular, 63.5 mm diameter and 5 mm thick; and the PSDs, or position-sensitive detectors. The PSDs are square double-sided strip detectors with 24 mm strips on each side (the strips on one side are orthogonal to those on the other side), and have a thickness of 0.3 mm. There are two A detectors, A1 and A2; sandwiched in between them are PSD1 and PSD2; behind A2, there are the B detectors, B1 through B4. Downstream of B4 is a circular piece of quartz, 10 mm thick, that radiates photons (Cerenkov radiation) generated by the passage of high-velocity particles through it. The photons are reflected by a 45 deg mirror into a photo multiplier tube that sits out of the path of particles that hit the detectors. MARIE is triggered by a coincidence of hits in detectors A1 and A2. Once triggered, the data acquisition system records 12-bit digitized outputs which are proportional to the energies deposited in the A and B detectors. A two-byte data word is stored for each of these channels. The pulse height from the phototube is similarly digitized in 12 bits and stored. Readout of the PSDs is more complex. Each PSD has two orthogonal sides, referred to as columns and rows. The following description applies to each side of each detector. Onboard hardware analyzes the signals from each of the 24 strips and finds the two largest pulse heights. For each, the pulse height is digitized in 8 bits (256 channels) and stored, along with the strip number. The largest pulse height and position are referred to as 'event1', the second-largest as 'event2.' The event2 data are usually noise. Four quantities are stored for each side of each detector, so that a total of sixteen words (thirty-two bytes) of PSD data are stored on each event. The eight-bit pulse heights are referred to as 'magnitudes' The positions are valid only when in the range 1 to 24. References: =========== 1. M'01 Frames Definition Kernel (FK), latest version as of March 6, 2001 2. 'MARIE ICD', MSP01-98-0016, June 23, 1999 3. MARIE Instrument Kernel (TI), March 6, 2001" END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "MSP01-98-0016" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END