The Combined Release and Radiation Effects Satellite (CRRES) microelectronics experiment package was the first microprocessor-based microelectronics test system that has been flown in space. The Microelectronics & Photonics Test Bed (MPTB) is a follow-on experiment which will evaluate a new generation of microelectronics devices. Candidate devices include 32 bit microprocessors, 16 megabit dynamic memories, field programmable gate arrays, devices fabricated using emerging high speed GaAs and InP technologies, etc. Selected commercial, linear and 3.3 V devices are also being considered. In addition, MPTB will feature the photonic subsystem experiment described in this paper.
Predictions of the devices and subsystems in a space radiation environment will be made before launch based on ground test results and detailed device or system radiation models. The ground and space segment experiments will be performed using the same hardware and software to the extent possible to help ensure comparable results. The current space radiation environment models will be used to make the initial device or system predictions, but they will be updated based on the on-orbit dosimetry once it is available. Finally, new models and testing protocols will be developed using MPTB results. The test bed will be available for a 1997 launch. The currently baselined orbit is ideal for a radiation effects experiments. The orbit is highly elliptical and will pass through both the proton and electron belts frequently. Experimenters will have the opportunity to monitor single event effects in both cosmic ray and trapped proton environments. The MPTB experiment panel will be mounted to the exterior of the spacecraft for maximum exposure to the radiation environment.
The MPTB will provide a detailed characterization of the radiation environment. A four channel proton spectrometer will measure the proton environment. A linear energy transfer (LET) monitor will also be provided to correlate with the single event effect (SEE) measurements on the devices and the STAR-FODB experiment. Most SEE phenomena have cross sections which can be directly related to the LET of the incident radiation. The LET monitor is a solid state microdosimeter which measures pulse height spectra of a large number of sensitive volumes which are comparable in size to those of modern microelectronic devices. Modifications to the instrument are being considered to allow the characterization of very low proton LETs which can cause bit errors in the photodiodes employed in the STAR-FODB experiment. The proton and cosmic ray dosimetry will be known as a function of time with at least a 128 msec resolution so that a particular single event error can be correlated with each type of radiation. In addition, calibrated PMOS dosimeters located throughout the experiment panel will be used to monitor the total ionizing dose, and will be interrogated once or twice per orbit. Several of these dosimeters will be mounted on the STAR-FODB experiment card.
The single most important dosimetry information for the STAR-FODB experiment is the proton LET and spectral information. Message errors in the FODB will be dominated by the proton flux as opposed to heavy ion events due to the sensitivity of the receiver to direct proton ionization events. Note that whereas the typical SEE critical charge is described in pC, bit errors in photodiodes can be caused by fC of deposited charge during link operation at relevant optical powers.
A description of NASA/GSFC's experiment as planned is available.
For more information about MPTB, please contact Art Campbell of Naval Research Lab.
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