App note from International Rectifier on various solid state relay circuits. Link here (PDF)
Manufacturers of satellites, satellite launch vehicles, and tactical weapon systems face many challenges when designing electro-mechanical relays (EMR) into their systems. Some method of “cushioning” must be employed in order to prevent false relay operation when encountering shock and vibration. In addition, “hash filters” are sometimes necessary to debounce the contacts, thus adding space and weight. However, Solid State Relays (SSR) are immune to the shock and vibration levels normally encountered, and do not need contact filters. Hence, the use of Solid State Relays in place of the mechanical type leads to a more reliable end product.