Richard H. Maurer

Neutron production from polyethylene and common spacecraft materials

We report experimental measurements of neutron production from collisions of neutron beams with polyethylene blocks simulating tissue at the Los Alamos National Laboratory Neutron Science Center and 1 GeV/amu iron nuclei with spacecraft shielding materials at the Brookhaven National Laboratory AGS.

Early Results From the Engineering Radiation Monitor (ERM) and Solar Cell Monitor on the Van Allen Probes Mission

The Engineering Radiation Monitor (ERM) measures dose, dose rate and charging currents on the Van Allen Probes mission to study the dynamics of earths Van Allen radiation belts. Early results from this monitor show a variation in dose rates with time, a correlation between the dosimeter and charging current data, a map of charging current versus orbit altitude and a comparison of cumulative dose to pre-launch modeling after 260 days. Solar cell degradation monitor patches track the decrease in solar array output as displacement damage accumulates.

MArs Neutron Energy Spectrometer (MANES): an instrument for the Mars 2003 Lander.

We describe the instrument design and detector development for MANES which has been selected to fly on the Mars 2003 Lander. Section 1 explains the need for the spectrometer in determining the increased risk of carcinogenesis for astronauts. Section 2 presents the instrument design including an outline drawing, a cross-sectional view and a detailed block diagram. Sections 3 and 4 describe the low and high energy detector components of the spectrometer and present responses to monoenergetic neutron beams. Sections 5 and 6 explain the design approaches to charged particle discrimination and instrument transfer function modeling.

Reliability study of gallium arsenide transistors

GaAs signal transistors of the MESFET and HEMT (high electron mobility transistor) technologies were evaluated in an accelerated life test to determine their reliability for space-borne applications. It was found that GaAs MESFET technology is sufficiently mature and reliable for space systems, but that the GaAs HEMT technology is not. Secondary electron and source current imaging of an NE 202 HEMT which had failed during life testing show a bright spot indicating a subsurface defect. The effect of this defect is to short the transistor so that it cannot be turned off. It is concluded that the subsurface defect causing failure in the NE 202 HEMT was either a latent defect present originally in the GaAs material or created during the aging test by the thermal runaway/bridging phenomenon.<<ETX>>

Radiation Test Results of Candidate Spacecraft Parts for the Applied Physics Laboratory

The radiation responses of candidate spacecraft digital-to-analog converters (DACs) and digital synthesizers are presented. Candidate electronics are evaluated for total ionizing dose and single event effects.

Radiation-Induced Single-Event Effects on the Van Allen Probes Spacecraft

Electronic devices on the Van Allen Probes mission have experienced more than a thousand single-event effects (SEE) during the 4.5 years of transit through the inner and outer earth trapped radiation belts. The majority of these SEE have been due to trapped protons determined by the orbit timing and the dose rate response of the engineering radiation monitor. Fault tolerant systems engineering and spacecraft operation have enabled a successful mission to date without a safe mode or spacecraft emergency.

Successes and challenges of operating the Van Allen Probes mission in the radiation belts

The Van Allen probes team has been successful in monitoring and trending the performance of the mission to date. However, operating two spacecraft in the Van Allen radiation belts poses a number of challenges and requires careful monitoring of spacecraft performance due to the high radiation environment and potential impact on the mostly single string electronics architecture. Spacecraft and instrument telemetry trending is tracked with internal peer reviews conducted twice a year by the operations and engineering teams. On board radiation monitoring sensors are used to evaluate total dose accumulated on board the spacecraft and to assess potential impacts. Single event upsets are tracked and high activity events are logged and analyzed. Anomalous data is compared to radiation and solar event activity to determine if there is correlation. Solar array degradation is monitored in real time using a dedicated monitored solar cell and performance is compared to predicted degradation rates. Examples of the effects of radiation on various subsystems and instruments will be given and the impacts discussed as the Van Allen probes team prepares to take on the challenge of an extended mission of continued operations in the radiation belt.

LEON3FT Proton SEE Test Results for the Solar Probe Plus Program

Abstract: The Solar Probe Plus program requires a low power microprocessor with demonstrated capability to resist SEE in a high proton flux environment. Proton tests conducted at IUCF successfully demonstrated the single bit error correction capability of the LEON3FT. The test setup and results are summarized.

Compact ion and neutron spectrometer (CINS) for space applications

We are developing a combined ion and neutron spectrometer (CINS) for space applications inside interplanetary transport vehicles and on planetary surfaces. Our concept for a charged particle telescope includes thick silicon detectors and both thin and thick scintillators. The neutron spectrometer has been under development since 1997 with versions being flown on aircraft and balloon flights. We present 1) charge and energy spectra for the thick silicon detectors from heavy ion experiments; 2) typical neutron prompt and delayed pulse height spectra from neutron accelerator beam experiments; and 3) simulations from modeling of the compact charged particle telescope showing ion species identification and energy deposition spectra.

Qualification of the NEAR laser transmitter

The qualification of the NEAR laser transmitter is discussed with emphasis placed on the three major problem areas encountered: (1) use and derating of discrete power supply components; (2) application of a non-hermetic, high voltage hybrid to the space environment; and (3) vibration testing of the laser optics train. Summary comments are made with respect to the predictability of these quality/reliability problems.