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Similarly, the addition of a payload specialist requires a serial effort. A payload specialist must be trained, and procedures must be developed and equipment stored for him in an interrelated and serial manner. Often, the activities have to be accomplished in an extremely short timeframe which leaves the crew feeling more time-constrained and less well-prepared than would have been the case had there been a mechanism for schedule relief.

The freeze point goal for the definition of the payload specialists for any given mission is L-5 months. Missions STS 41-C through STS 61-C were reviews to define when payload specialists were assigned in relation to the freeze point (fig. 11). A total of 16 payload specialists were added to these flights ranging from no earlier than L-9 months to L-7 weeks. Seven of the 16 payload specialists were added after the L-5 freezing point, two additions being external in nature and the remaining five resulting from payload requirements.

e. KSC Orbiter Processing

The following only reflects the impact of manifest changes on KSC operations. The flight production template is designed for a start of Orbiter processing at launch minus 2 months. The impact of late changes on KSC Orbiter processing is a function of the type change and when prior to launch the changes are made. In general, changes made prior to Cargo Integration Review (CIR) are transparent and result in little additional work.

Between CIR and Launch Site Flow Review (LSFR) the impact of changes varies depending on the type payload. For example:

1. Primary payload changes involve significant impact. A delta  review is required for engineering hardware. The time available to develop and review documentation is greatly reduced, and the amount of overtime is increased. They also force other tasks to be reprioritized. 

2. Secondary payload (mounted in the payload bay) changes can generally be accommodated with minor impacts.

3. Middeck payload changed result in no impact.

After LSFR, the impact of changes become more acute as follows:

1. Primary payload changes can be made only if a like payload is substituted for an existing payload. Other changes would result in a launch delay or heavy overtime and a very short preparation cycle. 

2. Secondary payload changes can be done for certain predefined gas containers or predefined payloads requiring only structural interfaces.