Reliability is very important when designing a space board. NASA launched Voyager One 36 years ago, and it's still flying. If you want to fly in the air for 36 years, your circuit must be quite trustworthy. Flexible plate can bear more dynamic force than traditional plate, and eliminate high fault interconnection point.
The spacecraft is mainly affected by various dynamic forces during take-off. Dynamic force is the bane of traditional boards, and vibration causes up to 20% faults. Flexible and rigid flexible plates are distorted during operation and can be bent thousands of times before failure occurs. This will help the flex plate bend rather than break, and continue to work under harsh conditions.
Connections, such as solder joints, crimp, are also the main risk of failure. These attachments can also be destroyed by dynamic forces. Flexible circuits eliminate this risk by eliminating connections, and most of the connections on the flexible board are made in the substrate. In order to connect failure, the whole PCB will have to fail. Therefore, the flexible circuit almost eliminates the fault point of your circuit board.