High radiation doses have the potential to adversely affect electrical devices used in satellites, space probes, rockets, landers and other equipment. The effects of ionizing radiation on integrated circuits and other components can range from temporary malfunctions to permanent damage. In some cases, radiation damage is caused by a high-energy burst. In others, equipment suffers from cumulative radiation damage and the gradual degradation of micro-electronics.
Instantaneous Radiation Damage
Any device or material used in space missions is at risk for instantaneous radiation damage. Single event effects (SEEs) take place when an ionizing particle passes through a micro-electric device and deposits a charge that is large enough to adversely affect the device. Single event effects in aerospace technology can wreak havoc on costly and sensitive equipment.
This can include issues like data corruption, noise on images, system shutdown or reset, circuit damage, or “part tolerance exceeded” situations. SEEs can also cause catastrophic part failure as a result of conditions like single event latchup.
Cumulative Radiation Damage
Long-term, cumulative radiation damage can result in the parametric degradation of electronics and materials. This can include the degradation of optical components and the degradation of solar cells. The total ionizing dose (TID) experienced by the materials can produce variations in parameters like threshold voltage or leakage current. It can also affect the way a device functions.
Trapped protons, trapped electrons and solar protons are the most common sources of TID exposure. Devices and materials that are likely to experience these types of exposure—especially for extended time periods—should undergo thorough pre-launch TID testing.
It is critical that manufacturers and other stakeholders understand the displacement damage dose (DDD) and displacement damage effects associated with any device or material they intend to use in the space environment.
Radiation Hardness Assurance
Radiation hardness assurance (RHA) is defined as all of the activities necessary to ensure that all of the materials and electronics (primary systems, subsystems, boxes, boards, miscellaneous piece parts, etc.) used in the space radiation environment can withstand the radiation doses to which they will be exposed. This includes everything from how equipment is designed and manufactured, to how it is tested.
A number of steps are taken to ensure that a space resource, such as a spacecraft, is radiation hardened (or rad-hard). Both the external environment that the craft will operate in and its internal environment must be defined. Based on this information, necessary hardness levels and design margins must be established.
Then the aerospace design must be evaluated, including screening of the parts list and radiation characterization. If problems exist, mitigation tactics must be devised. Finally, performance testing must be performed, with any anomalies identified, documented and resolved. At that point, the spacecraft or other technology to be used in space is considered ready for its mission.
A Hard Lesson in the Need for Radiation Hardness
In 1962, the Telstar satellite was put into orbit and subsequently became the first satellite to fail as a result of total ionizing dose exposure. Launched the day after the high-altitude test of a nuclear weapon called the Starfish that created an artificial electron belt, Telstar experienced a total dose 100 times greater than it would have otherwise. The Starfish test inadvertently claimed many other satellites, as well, in the months that followed.
While this type of incident is unlikely to happen today, the fact remains that space technology must be manufactured and tested to withstand both instantaneous radiation damage and cumulative radiation damage in the space radiation environment.