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

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First Steps into Space: Projects Mercury and Gemini
[2]
Whereas radar computer guidance will be the primary onboard mode
for the terminal rendezvous phase of Flight No. 6; the radar optical and optical
guidance modes will be primary for Flights 8 and 9 respectively. The Gemini radar
optical and optical guidance modes are very similar to the LEM Manual Alternate
guidance modes outlined in Grumman Aircraft Engineering Corporation Report
No. LED-540-3, Back-up Guidance Requirements, July 9, 1963. The basic feature
of the terminal homing phase in these rendezvous maneuvers is that the LEM and
Gemini essentially fly a collision course to their respective rendezvous target. This
characteristic is achieved by keeping the inertial rate of the Line of Sight (LOS) to
the target below a given threshold value. Following the LOS rate reduction, range
rate with respect to the target is measured and thrust applied along the LOS
direction until range rate is reduced to a pre-determined value appropriate to the
range at which thrust was initiated. This procedure is repeated several times from
the initial range of 20 NM down to the docking phase. A mission profile for Flight
No. 8, employing radar optical guidance, is shown in Enclosure 5[not included].
The mission profile for Flight No. 9 will be basically the same; however, the optical
sight will be used in place of the radar.
When viewed against the malfunctions encountered with the Automatic
Stabilization Control System in Project Mercury, it is difficult to over-emphasize
the vital importance of simulating and testing the manual alternate modes
provided to accomplish critical maneuvers such as rendezvous. The success of
Project Mercury was due in large part to its manual modes. Since the Gemini
manual modes require the greatest degree of astronaut participation, they will
also provide the greatest degree of astronaut training.
In NASA Project Apollo Working Paper No. 1083, Study of Earth Orbit
Simulation of Lunar Orbit Rendezvous, July 24, 1963, it is concluded that it would
be desirable to perform an earth orbit simulation of lunar orbit rendezvous since
this will provide a realistic assessment of the guidance techniques and demonstrate
the ability to perform the critical lunar orbit rendezvous maneuver. Enclosures 6 and
7[not included], taken from Working Paper No. 1083, show the close comparisons
of earth orbit and lunar orbit rendezvous trajectories and closing times.
By Flights 10 and 11, or earlier, we plan to flight test the feasibility of the
LEM lunar orbit direct rendezvous mode in earth orbit if possible. In this mode,
the catch up or parking orbits are essentially by-passed and terminal rendezvous is
initiated near first apogee as shown in Enclosure 8. In order to insure its successful
completion, the astronauts should be ready to take over manual control of the
spacecraft at any time should the automatic system falter. This will require a high
degree of training and proficiency on the part of the astronauts. While it is true
that Gemini does not employ the same guidance hardware as Apollo; Gemini may
be in a unique position, based on present plans, to flight test direct rendezvous
in earth orbit. In addition, in terms of schedules, Gemini is in a relatively good
position to influence Apollo [3] rendezvous techniques with flight test results.
Gemini’s first rendezvous flight takes place approximately two years prior to
the first manned Apollo flight and its first direct rendezvous flight takes place
approximately two years prior to the first lunar rendezvous flight.