Freedom 7 spacecraft pre-launch activities

Mercury Spacecraft #7, which became known as Freedom 7, was delivered from the McDonnell Aircraft Corporation plant in St. Louis, Missouri to Hangar S at Cape Canaveral on 9 December 1960. Upon delivery, the instrumentation system and selected items of the communication system were removed from the capsule to be bench treated. During this bench-test period, the capsule underwent rework which included the cleaning up of dis­crepancy items deferred from St. Louis and making changes to the capsule that were required to be made prior to beginning systems tests.

Systems test were begun as soon as all instrumentation and communications compo­nents were reinstalled in the capsule. These tests required a total of 46 days. During this period the electrical, sequential, instrumentation, communication, environmental, reaction control, and stabilization and control systems were individually tested. Included in the test of the environmental system were two runs in an altitude chamber with an astronaut installed in the capsule.

At the completion of systems tests, another work period was scheduled in which the landing bag system was installed on the capsule. Following this work period, a simulated flight test was performed, followed by the installation of pyrotechnics and parachutes. The capsule was then weighed, balanced, and delivered to the launching pad to be mated with the Redstone booster. Nineteen days were spent on the launching pad, prior to launch, test­ing the booster and capsule systems, both separately, and as a unit. Also, practice inser­tions of an astronaut into the capsule were performed during this period.

Simulated flight 1 with the booster was accomplished at the completion of systems tests on the launching pad. A change was then required in the booster circuitry which necessi­tated another simulated flight test (simulated flight 2). The capsule-booster combination was then ready for flight. The flight was postponed several days due to weather; however, this allowed time for replacing instrumentation components which were malfunctioning. A final simulated flight was then run (simulated flight 3). The capsule was launched two days after this final test.

MODIFICATIONS MADE

During capsule systems tests and work periods, both in Hangar S and on the launching pad, modifications were made to the capsule as a result of either a capsule malfunction or an additional requirement placed on the capsule. The most significant modifications made to Spacecraft 7 while at Cape Canaveral were as follows:

(a) Manual sensitivity control and a power cut-off switch were added to the VOX (Voice – Operated Transmitter) relay.

(b) A check valve was installed between the vacuum relief valve and the snorkel inflow valve.

(c) The cabin pressure relief valve was replaced with one which would not open until it experienced an equivalent head of 15 inches of water.

(d) Screens were added at the heat barriers upstream of the thrust chambers (downstream of the solenoid valves).

(e) The high-thrust pitch and yaw thrusters were welded at the juncture between the thrust chambers and the heat barriers.

(f) The cables to the horizon scanners in the antenna canister were wrapped with reflective tape to minimize radio-frequency (RF) interference from capsule commu­nications components.

(g) The retro-interlock circuit was bypassed by installing a jumper plug in the amplifier-calibrator.

(h) Permission relays were installed to both the capsule-adapter ring limit switches and the capsule-tower ring limit switches.

(i) Capacitors were installed in the circuits to the orbit attitude, retro-jettison, and impact inertia arm time delay relays.

(j) Capsule wiring was changed to extend the periscope at 21,000 feet.

(k) The potting on the capsule adapter umbilical connectors was extended 0.75 inches from both connector ends and the connector was wrapped with asbestos and heat reflective tape. Also, the fairings over these connectors were cut away and a cover was added which provided more clearance between the fairings and the connectors.

(l) The lower pressure bulkhead was protected from puncture damage that might result from heat sink recontact. Aluminum honeycomb was added, bolts reversed, and brackets with sharp protrusions were potted solidly with RTV-90 and plates between the brackets and the bulkhead.

(m) Pitch indicator markings were changed from -43 to -34 degrees for retro-attitude indication