Exploring the Unknown: Selected Documents in ... - The Black Vault

Exploring the Unknown 351
correctly throughout the remainder of the run. After the NSR maneuver, the range
was approximately 169 nautical miles. The pilot did not re cord anything on the
data sheet until the values began to match the nominal values at approximately
136 nautical miles range. After that, the values were recorded and data points
were frequently called to the ground. The computer solution for the total-velocitychange
for rendez vous was very close to nominal. The target-centered coordinate
plot (see fig. 7.1.2-1) [not included] showed that the NSR maneuver had placed
space craft 6 into the nominal trajectory and that the maximum deviation was
approximately 0.25 mile high with no ellipticity. During this time, the elevation
and azimuth pointers were oscillating approximately +1.5° from the electrical null.
The period of the oscillation was approximately 4 seconds. As the range decreased
to 97 miles, there was a noticeable reduction in the amplitude of the oscillation;
however, the period re mained constant. It should be noted that both the azimuth
and eleva tion readings crossed the null point simultaneously during these oscillations.
At a range of 79 miles, all pointer oscillations ceased and remained steady
throughout the remainder of the rendezvous operation [7-20] and down to a range
of 20 feet. The radar data were continually being plotted and computations made
as spacecraft 6 approached the point of terminal phase initiation.
7.1.2.3.2 Visual acquisition: Visual acquisition of spacecraft 7 occurred
at 5 hours 4 minutes g.e.t., 54 miles slant-range from space craft 6 to spacecraft
7. The target vehicle appeared as a bright star, 0.50 to the right of the boresight
line on the optical sight. The tar get appeared brighter than the star Sirius, and
during postflight com parisons, the flight crew believed it was probably brighter
than the planet Venus. The target stayed in sight because of reflected sunlight
until 05:15:56 g.e.t., or for approximately 12 minutes. Spacecraft 7 was lost in
darkness about 3 minutes prior to the transfer thrust, at a range of approximately
30 miles. The crew, however, could have deter mined a backup solution during
the programmed tracking period prior to transfer, and would have been able to
perform the maneuver without vis ual contact.
7.1.2.3.3 Terminal phase: During the terminal phase, the crew used the
data provided by the IGS (closed-loop) to perform all maneuvers. However, the
pilot did make all backup computations for each maneuver in order to compare
them with the results of the closed-loop solution. The target-centered coordinate
plot revealed very quickly that the relative trajectory was near nominal and that
the transfer thrust would be very close to the planned value of 32 ft/sec along
the line of sight. For the backup procedure, the component normal to the line of
sight was de termined from the time change of the total pitch angle. The ground
solution, transmitted from Guaymas, indicated that the value was 31.5 ft/sec.
The initial time transmitted to the flight crew for the initiation of the terminal
phase was 05:16:54 g.e.t. A short time later this was refined to 05:18:54 g.e.t. The
onboard computer solu tion gave a thrust time of 05:18:58 g.e.t., 4 seconds later
than that computed on the ground.
As the point of terminal phase initiate approached, it became evi dent that
the exact- time to initiate the maneuver would be near the half way point between
two of the computer solutions that are 100 seconds apart. At this point the crew
discussed the situation and decided to take the second of these solutions, if it still
met the basic criteria. This decision was made to insure that transfer would occur