Delayed voice communication

•Future human deep space missions will involve significant speed-of-light communication delays.•Mission simulations found many problems with spoken communication using long delays.•These problems can be addressed with training and special communication techniques.•Text messaging provides a valuable complement to delayed voice.

We present results from simulated deep-space exploration missions that investigated voice communication with significant time delays. The simulations identified many challenges: confusion of sequence, blocked calls, wasted crew time, impaired ability to provide relevant information to the other party, losing track of which messages have reached the other party, weakened rapport between crew and ground, slow response to rapidly changing situations, and reduced situational awareness. These challenges were met in part with additional training; greater attention and foresight; longer, less frequent transmissions; meticulous recordkeeping and timekeeping; and specific alerting and acknowledging calls. Several simulations used both delayed voice and text messaging. Text messaging provided a valuable record of transmissions and allowed messages to be targeted to subsets of the flight and ground crew, but it was a poor choice for high-workload operators such as vehicle drivers and spacewalkers. Even with the foregoing countermeasures, delayed voice communication is difficult. Additional aids such as automatic delay timers and voice-to-text transcription would help. Tests comparing delays of 50 and 300 s unexpectedly revealed that communicating with the shorter delay was just as challenging as with the longer one.