Gemini 9A

Description

Gemini 9A was the seventh crewed Earth-orbiting spacecraft of the Gemini series. It carried astronauts Tom Stafford and Gene Cernan. Primary mission objectives were to demonstrate (1) rendezvous techniques and docking with a target vehicle to simulate manuevers to be carried out on future Apollo missions, (2) an ExtraVehicular Activity (EVA) spacewalk to test the Astronaut Maneuvering Unit (AMU), and (3) precision landing capability. Scientific objectives included obtaining zodiacal light and airglow horizon photographs. Two micrometeorite studies were to be carried out, and there were also one medical and two technological experiments.

Mission Profile

The mission was originally scheduled for launch (as Gemini 9) on 17 May but was postponed when the Gemini Agena Target Vehicle failed to achieve orbit due to a booster failure earlier that day. The replacement Augmented Target Docking Adapter (ATDA) was launched successfully into Earth orbit on 1 June, but telemetry indicated that the shroud had failed to jettison properly. Gemini 9 was to launch shortly thereafter but ground equipment failure resulted in a postponement until 3 June.

Gemini 9A was launched on 3 June from Complex 19 at 8:39:33 a.m. EST (13:39:33.335 UT) and inserted into a 158.8 x 266.9 km orbit. After three orbital maneuvers, rendezvous within 8 meters of the ATDA was achieved on the third revolution. It was confirmed that the launch shroud on the ATDA had failed to deploy and was blocking the docking port. The flight plan was then revised to include two equiperiod passive rerendezvous maneuvers in place of the docking. The first, using optical techniques without on-board radar, was completed at 3:15 p.m. EST, and the second, a rendezvous from above simulating rendezvous of an Apollo command module with a lunar module after abort from the Moon, was completed at 6:21 a.m. EST on 4 June and final departure from the ATDA took place at 7:38 a.m. The scheduled EVA was postponed due to crew fatigue and the second day was devoted to experiments.

On 5 June at 10:02 a.m. EST the Gemini capsule was depressurized and the hatch above Cernan opened. Cernan was out of the spacecraft at 10:19, attached by an 8 meter long tether which was connected to Gemini's oxygen supply. He had no gas maneuvering unit as was used on Gemini 4. He retrieved the micrometeorite impact detector attached to the side of the capsule and then moved about the spacecraft. He had great difficulty manuevering and maintaining orientation on the long tether. He took photographs of Gemini from the full length of the tether and finally moved to the back of the capsule where the Astronaut Maneuvering Unit (AMU) was mounted. He was scheduled to don the AMU, disconnect from the Gemini oxygen supply (although he would still be attached to the spacecraft with a longer, thinner tether) and move to 45 meters from the capsule. The task of donning the AMU took "four to five times more work than anticipated", overwhelming Cernan's environmental control system and causing his faceplate to fog up, limiting his visibility. It was also discovered that the AMU radio transmissions were garbled. These problems caused Stafford to recall Cernan to the spacecraft. He reentered the spacecraft at 12:05 p.m. and the hatch was closed at 12:10. Cernan was the third person to walk in space and his total time of 2 hours, 8 minutes was the longest spacewalk yet.

Retrofire occurred at the end of the 45th revolution on 6 June at 8:26:17 a.m. EST. Splashdown was at 9:00:23 in the western Atlantic at 27.87 N, 75.00 W, 550 km east of Cape Kennedy and 0.7 km from the target point. The astronauts stayed inside the spacecraft and were brought aboard the recovery ship U.S.S. Wasp at 9:53 a.m. Total mission elapsed time was 72:20:50. Of the primary objectives, three rendezvous techniques were demonstrated, although docking could not be achieved due to the failure of the augmented target-docking shroud to jettision. Testing of the AMU was not completed. The Agena micrometeorite experiment hardware was lost when the Agena target vehicle failed to achieve orbit. Other experiments functioned normally.

The Astronaut Maneuvering Unit (AMU)

The AMU was a 75 kg backpack, 81 cm high, 56 cm wide, and 48 cm deep, mounted on the rear of the Gemini capsule adapter section. It had a form-fitting seat, a 45 meter nylon tether, and self-contained life-support, communications, telemetry, propulsion, and manual and automatic stabilization systems. The propulsion system consisted of 12 small thrusters mounted on the corners of the pack using a hydrogen peroxide fuel supply and thruster controls on two sidearm supports. The backpack could be accessed by a spacewalking astronaut who would move to the back of the craft, put on the backpack, and disconnect the spaceship tether and oxygen supply before using the AMU.

Spacecraft and Subsystems

The Gemini spacecraft was a cone-shaped capsule consisting of two components, a reentry module and an adaptor module. The adaptor module made up the base of the spacecraft. It was a truncated cone 228.6 cm high, 304.8 cm in diameter at the base and 228.6 cm at the upper end where it attached to the base of the reentry module. The re-entry module consisted of a truncated cone which decreased in diameter from 228.6 cm at the base to 98.2 cm, topped by a short cylinder of the same diameter and then another truncated cone decreasing to a diameter of 74.6 cm at the flat top. The reentry module was 345.0 cm high, giving a total height of 573.6 cm for the Gemini spacecraft.

The adaptor module was an externally skinned, stringer framed structure, with magnesium stringers and an aluminum alloy frame. The adaptor was composed of two parts, an equipment section at the base and a retrorocket section at the top. The equipment section held fuel and propulsion systems and was isolated from the retrorocket section by a fiber-glass sandwich honeycomb blast shield. The retrorocket section held the re-entry rockets for the capsule.

The reentry module consisted mainly of the pressurized cabin which held the two Gemini astronauts. Separating the reentry module from the retrorocket section of the adaptor at its base was a curved silicone elastomer ablative heat shield. The module was composed predominantly of titanium and nickle-alloy with beryllium shingles. At the narrow top of the module was the cylindrical reentry control system section and above this the rendezvous and recovery section which holds the reentry parachutes. The cabin held two seats equipped with emergency ejection devices, instrument panels, life support equipment, and equipment stowage compartments in a total pressurized volume of about 2.25 cubic meters. Two large hatches with small windows could be opened outward, one positioned above each seat.

Control, Propulsion, and Power

Attitude control was effected by two translation-maneuver hand controllers, an attitude controller, redundant horizon sensor sytems, and reentry control electronics, with guidance provided via an inertial measuring unit and radar system. The orbital attitude and maneuver system used a hypergolic propellant combination of monomethylhydrazine and nitrogen tetroxide supplied to the engines by a helium system pressurized at 2800 psi. Two 95 lb translation thrusters and eight 23 lb attitude thrusters were mounted along the bottom rim of the adaptor, and two 79 lb and 4 95 lb thrusters were mounted at the front of the adaptor. Power was supplied by a fuel cell power system to a 22- to 30-volt DC two-wire system. During reentry and post-landing power was supplied by four 45 amp-hr silver-zinc batteries.

Communications

Voice communications were performed at 296.9 MHz with an output power of 3 W. A backup transmitter-receiver at 15.016 MHz with an output power of 5 W was also available. Two antenna systems consisting of quarter-wave monopoles were used. Telemetry was transmitted via three systems, one for real time telemetry, one for recorder playback, and a spare. Each system was frequency-modulated with a minimum power of 2 W. Spacecraft tracking consisted of two C-band radar transponders and an acquisition-aid beacon. One transponder is mounted in the adaptor with a peak power output of 600 W to a slot antenna on the bottom of the adaptor. The other is in the reentry section, delivering 1000 W to three helical antennas mounted at 120 degree intervals just forward of the hatches. The acquisition-aid beacon was mounted on the adaptor and had a power of 250 mW.

Reentry

At the time of reentry, the spacecraft would be maneuvered to the appropriate orientation and equipment adaptor section would be detached and jettisoned, exposing the retrorocket module. The retrorockets consisted of four spherical-case polysulfide ammonium perchlorate solid-propellant motors mounted near the center of the reentry adaptor module, each with 11,070 N thrust. They would fire to initiate the spacecraft reentry into the atmosphere, with attitude being maintained by a reentry control system of 16 engines, each with 5.2 N thrust. The retrorocket module would then be jettisonned, exposing the heat shield at the base of the reentry module. Along with the ablative heat shield, thermal protection during reentry was provided by thin Rene 41 radiative shingles at the base of the module and beryllium shingles at the top. Beneath the shingles was a layer of MIN-K insulation and thermoflex blankets. At an altitude of roughly 15,000 meters the astronauts would deploy a 2.4 meter drogue chute from the rendezvous and recovery section. At 3230 meters altitude the crew releases the drogue which extracts the 5.5 meter pilot parachute. The rendezvous and recovery section is released 2.5 seconds later, deploying the 25.6 meter main ring-sail parachute which is stored in the bottom of the section. The spacecraft is then rotated from a nose-up to a 35 degree angle for water landing. At this point a recovery beacon is activated, transmitting via an HF whip antenna mounted near the front of the reentry module.

Gemini Program

The Gemini program was designed as a bridge between the Mercury and Apollo programs, primarily to test equipment and mission procedures in Earth orbit and to train astronauts and ground crews for future Apollo missions. The general objectives of the program included: long duration flights in excess of of the requirements of a lunar landing mission; rendezvous and docking of two vehicles in Earth orbit; the development of operational proficiency of both flight and ground crews; the conduct of experiments in space; extravehicular operations; active control of reentry flight path to achieve a precise landing point; and onboard orbital navigation. Each Gemini mission carried two astronauts into Earth orbit for periods ranging from 5 hours to 14 days. The program consisted of 10 crewed launches, 2 uncrewed launches, and 7 target vehicles, at a total cost of approximately 1,280 million dollars.