It's a mission where failure will be success -- and that's exactly what NASA engineers are hoping for.
They anticipate failures in six experiments on the NASA Space Radiation Electronics Testbed, a payload now orbiting Earth aboard the Space Technology Research Vehicle-1-d. The satellite was launched Nov. 15 on an Ariane 5 rocket from French Guiana.
Managed by the Marshall Space Flight Center in Huntsville, Ala., the experiments will enable engineers to better evaluate the effects of space radiation on advanced microelectronics. Radiation can cause trouble for printed circuit boards and other electronic equipment on satellites.
"It may sound strange, but we're actually hoping electronic components will fail," said Donna Hardage, project manager for the NASA Space Radiation and Electronics Testbed at the Marshall Center. "That's the best way we can accurately know their limits.
"We're monitoring and evaluating several commercial off-the-shelf electronic components to determine how they hold up under the severe exposure to radiation," Hardage added.
Engineers will use telemetry data received from the satellite to improve designs for spacecraft circuitry. The experiments also will help meet NASA's goals of reducing costs, weight, power requirements and production time for future spacecraft while improving their reliability.
The experiment package is part of a joint mission involving NASA, the U.S. Department of Defense's Ballistic Missile Defense Organization, the U.S. Air Force, the United Kingdom's Defence Evaluation and Research Agency and several other international organizations.
The mission -- planned to last for at least one year -- is corresponding with the solar maximum that occurs every 11 years -- a period when solar and radiation activity is at its peak. As it circles the Earth every 10.5 hours, the satellite passes through the Van Allen Belts, zones of intense radiation trapped in Earth's magnetosphere and extending several thousands miles into space.
There, the satellite encounters the trapped proton region and the inner and outer electron belts. Charged particles in these belts cause serious problems for satellite operations - such as deterioration of components and interruption of electronic signals.
The package is about the size of a 40-quart ice chest and weighs 220 pounds (100 kilograms.) The satellite is in a highly elliptical orbit to expose it to greater radiation. The orbit is 385.3 miles (620 kilometers) at perigee, its closest point to the Earth, and 24,230 miles (39,000 kilometers) at apogee, its farthest point from Earth.
"We're pushing these components to their limits. If they survive, that tells us a lot. But if they fail, it tells us even more," Hardage said. "All of the commercial off-the-shelf items have been tested on the ground, but with exposure to only one energy range and just one energy particle," she said. " We want to see how they respond to continual radiation as well as events such as solar flares and cosmic rays."
Engineers will use the collected data to improve models for designing and manufacturing electronics for space missions. The investigators are expected to publish the results in the spring of 2002. Here are brief descriptions of the experiments:
- The dosimetry experiment measures the amount of radiation on the components. Monitoring parameters include ionizing dose, temperature, particle energy, and charging effects. The experiment also evaluates the effectiveness of composite material and conformal coating shielding technologies on the components.
- The commercial off-the-shelf analog experiment measures the impact of continual exposure to low-level radiation and of solar flares and cosmic rays (transient single event effects) on commercial analog devices - those that operate or display information continuously like a thermometer or voltmeter. Engineers hope to reduce the uncertainties regarding performance of these devices when exposed to space radiation.
- The commercial off-the-shelf digital experiment measures the impact of the radiation environment on commercial digital devices, such as stacked memories, ferroelectric memories, field programmable gate arrays and flash electrically erasable programmable read-only memories. Such devices are found in everyday items ranging from cellular telephones to the cable box connected to a television. Engineers will evaluate these microelectronic components for future space applications.
- The commercial off-the-shelf photonics experiment is a two-part study that measures enhanced proton displacement effects, single event transients and total ionizing dose/displacement damage effects on high rate, state-of the-art commercial optocouplers -- devices that bridge gaps between incompatible wire communications systems. The engineers are also getting information from, and evaluating components identical to those on the Hubble Space Telescope. Hubble -- one of the largest and most complex satellites ever built -- has been orbiting Earth since 1990.
- The pulse height analysis experiment measures the radiation environment of the satellite. The device will monitor the amount of radiation from solar flares and cosmic rays. The data will be used to update the engineering models for electronic components in space applications and help to improve predictions about the rate of these occurrences.
NASA's Space Environments and Effects program, managed by the Marshall Center, provides funding for government agencies to periodically update and validate new engineering models for electronics based on data gathered from space.
Other major participants in the program include NASA Headquarters, Washington, D.C.; Goddard Space Flight Center, Greenbelt, Md.; Jet Propulsion Laboratory, Pasadena, Calif.; Langley Research Center, Hampton, Va.; and the Aerospace Corporation, El Segundo, Calif.
The Space Technology Research Vehicle is funded by the U.S. Department of Defense's Ballistic Missile Defense Organization, Washington, D.C., with development and integration performed by the U.S. Air Force Research Laboratory, Kirtland Air Force Base, New Mexico.
The United Kingdom's Defence Evaluation and Research Agency, in Farnborough, England, was responsible for the payload integration and launch of the Space Technology Research Vehicle-1-d.