LUNAR ENCOUNTER

After they woke up on the final day of their coast to the Moon, a crew would set about their usual post-sleep chores of reporting their condition to mission control and preparing their breakfast. Normally the spacecraft w’as slowly turning around in its barbecue roll, spreading the heat of the Sun across its surface. While the crew slept, engineers at the ground stations on Earth had taken precise measurements of the spacecraft’s position and velocity to accurately monitor its trajectory. Using this data, FIDO, the flight dynamics flight controller in the MOCR, calculated the amount by which the approach to the Moon needed to be adjusted, if at all. Was the spacecraft coming in too quickly or Loo slowly to pass around the far side at the correct altitude? Was it within the correct orbital plane to pass over the desired landscape? Based on the results of overnight radio tracking, and with the help of the big computers in the real-time computer complex (RTCC), FIDO calculated the details of a burn to be carried out at the fourth opportunity for a mid-course correction, usually scheduled to occur five hours prior to entry into lunar orbit. The details of this corrective burn w’ere read up to the crew1, along with the results of calculations by the Retro flight controller.

While FIDO had been deciding w’here they wanted the spacecraft to fly. Retro was busily working out what to do if something w’ent w’rong. He had Lw’o scenarios to consider: the first was if something were to prevent or impair the LOI burn; and the second was for the situation in w’hich the LOI burn w’as completed successfully but the crew7 were required Lo return Lo Earth at the earliest opportunity. Having decided the manoeuvres that the crew’ should make in these scenarios, it was then important that the details be passed up to the spacecraft while it w’as still in communication with Earth. The mantra was that they should always have the data necessary to get home without further assistance from mission control, in case communications w’ere lost.