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 tracking periods by MSFN will provide a precise determination of the spacecraft's orbit and the translunar injection parameters to be inserted into the Command Module computer, which will back up the launch vehicle guidance system for translunar injection.

The actual commit point for translunar injection must occur at least 7 minutes before S-IVB ignition, since this is the period required for the S-IVB restart sequence. This sequence initiation may be inhibited by the crew if it is decided to delay injection until the next orbit, but once the sequence is started on a given orbit it is not possible to delay in jection to the next orbit. The sequence can, of course, be terminated at any time, but the limitations on S-IVB consumables (associated with the chill-down and with the ullage propellants) do not allow a second opportunity.

These considerations of tracking, spacecraft checkout, IMU align­ ment, and data transmission and analysis would, therefore, make it unlikely that translunar injection would be able to occur on the first Pacific opportunity when this injection point lies over the Western Pacific. It may be practical, however, to make the first Pacific opportunity when the injection points are in the eastern part of the Pacific. This is being looked into at the present time and there appears to be no strong reasons why it could not be accomplished. The advantage to planning the mission to inject as early as possible would be to allow maximum time (within the 4½ hour limitation for the S-IVB) to correct a tem­porary malfunction of either the onboard systems or the gound systems.

For purposes of the reference mission description, however, it will be assumed that injection will occur on the second Pacific opportunity, so the spacecraft continues on in earth orbit passing over the Pacific Ocean ship, over the Hawaii station, and finally coming up on the West Coast of the United States. Across the United States, the tracking is continuous by stations at Goldstone, Guaymas, Corpus Christi, and Cape Kennedy.

Since injection is not taking place during the first orbit, then time will be available to perform a series of landmark sighting in earth orbit to test the ability to perform the same type of navigation to be used in lunar orbit. These are not necessary to earth orbit determination since this has all been done by the ground; however, if time, lighting, and cloud cover permit, then a few sightings may be taken as a further checkout of our onboard system. To perform the sightings, it will be necessary to roll the spacecraft 180 degrees from the standard attitude, so that the optics axis is pointing toward the earth. Following the sightings, t hethe [sic] spacecraft is rolled back to its normal attitude.