Issues in Firing Safety

Analysis of Single Point Failure (SPF) modes in current firing systems yields an unacceptably high probability of failure resulting in an unplanned launch. The following is a Safety Checklist that Firelinx has implemented:

  • Firing circuits are switched at both power and ground
  • Firing circuits shunted at the capacitor bank (input to firing switches)
  • Circuitry is thermally and electrically isolated from the case
  • Interlocks and detection circuits allow detection of driver stuck on failure before firing
  • Intelligent switches prevent control glitches on firing circuits
  • Double pull-downs on switch control lines prevent open circuit SPF (Single Point of Failure)
  • Continuity Test
    1. Separate power supply and path
    2. Intrinsically Safe (No SPF) design
    3. Multiplexed testing limits the total current path to safe levels
    4. Detect partial failure of continuity test safety circuitry
  • On-board power system with wired backup prevents communications ringing, allows for graceful degradation, backup in the case of a wire break
  • Keyed access and unique ID encryption keys prevent unauthorized access
  • Transmission packets with CRC (Cyclic Redundancy Check) and encryption make the probability of random interference or tampering vanishingly small
  • On-board clock masters with time code comparison and intelligent jump logic make the probability of timing errors vanishingly small.
  • Module IDs are always unique
  • Capacitor bank power is isolated from the primary supply by a SEPIC (Single-Ended Primary Inductance Converter) boost converter
  • Software/Hardware interlocks remove software SPFs
  • Heartbeat signal provides synchronization and shutdown in the case of LOPC (Loss of Positive Control)
  • No Relays
  • Separation of applied power and control signals

The following paper summarizes the results of our research into the most common SPF sources and discusses solutions that can be implemented in firing systems to remove failure scenarios. In particular, a thorough redesign of the standard methodology for performing continuity testing can reduce the probability of inadvertent launch during testing.

Issues in Firing System Safety 110927