Gemini 11

Description

Gemini 11 was the ninth crewed Earth-orbiting spacecraft of the Gemini series, carrying astronauts Charles "Pete" Conrad and Richard Gordon. The 3-day mission was designed to achieve a first orbit rendezvous and docking with the Agena target vehicle, to accomplish two ExtraVehicular Activity (EVA) tests, to perform docking practice, docked configuration maneuvers, tethered operations, parking of the Agena target vehicle and demonstrate an automatic reentry. There were also eight scientific and four technological experiments on board. The scientific experiments were (1) synergistic effect of zero-g and radiation on white blood cells, (2) synoptic terrain photography, (3) synoptic weather photography, (4) nuclear emulsions, (5) airglow horizon photography, (6) UV astronomical photography, (7) Gemini ion wake measurement, and (8) dim sky photography.

Mission Profile

Gemini 11 was launched on 12 September 1966 at 9:42:26 a.m. EST (14:42:26.546 UT) from Complex 19 and inserted into a 160.5 x 279.1 km Earth orbit at 9:48:28. Five spacecraft maneuvers were made to rendezvous with the Gemini Agena Target Vehicle 11 (GATV-11) at 11:07 a.m. (1:25 Ground Elapsed Time, GET). The GATV-11 had been launched an hour and a half before Gemini 11. Docking was completed at 11:16 a.m. on the first orbit, consuming less fuel than expected. Each astronaut then conducted two docking exercises with the GATV, and then a maneuver at 2:14:14 p.m. brought the docked spacecraft into a 287 x 304 km orbit. The sleep period was spent in docked configuration.

On 13 September at 9:44 a.m. EST (24:02 GET) the Gemini cabin atmosphere was evacuated and the hatch opened to begin Richard Gordon's scheduled 107 minute EVA. He was out of the hatch at 9:51, attached by an umbilical cord. He set up a movie camera and retrieved the micrometeorite experiment. The next task, detaching one end of the 30 meter tether from the Agena and attaching it to the Gemini spacecraft docking bar, proved to be exhausting and overstressed Gordon's life support system. After attaching the tether, Gordon stopped to rest astride the GATV, but the heavy perspiration inside the suit obscured his vision and finally blinded his right eye. Conrad ordered him to cancel the power tool evaluation and return to the cabin. Gordon returned to the cabin at about 10:12 a.m. and closed the hatch at 10:17 a.m. so the cabin could be repressurized. At 11:19 a.m. the hatch was opened again to jettison some excess equipment.

Following the sleep period, the Agena primary propulsion system was fired for 25 seconds at 2:12:41 a.m. EST on 14 September, raising the docked spacecraft apogee to 1374.1 km. (A record altitude for an astronaut mission that would stand until Apollo 8 went to the Moon.) After two orbits the Agena was fired again for 22.5 seconds to lower the Gemini-Agena back down to a 287 x 304 km orbit. At 7:49 a.m. Gordon opened his hatch to begin a 2 hour 8 minute standup EVA during which he conducted photographic experiments. The hatch was closed at 9:57 a.m. and shortly afterwards the spacecraft were undocked and Gemini 11 moved to the end of the 30 meter tether attaching the two spacecraft. At 11:55 a.m. Conrad initiated a slow rotation of the Gemini capsule about the GATV which kept the tether taut and the spacecraft a constant distance apart at the ends of the tether. Oscillations occurred initially, but damped out after about 20 minutes. The rotation rate was then increased, oscillations again occurred but damped out and the combination stabilized. The circular motion at the end of the tether imparted a slight artificial "gravitational acceleration" within Gemini 11, the first time such artificial gravity was demonstrated in space. After about three hours the tether was released and the spacecraft moved apart. A fuel cell stack failed at 4:13 p.m., but the remaining stacks took over the load satisfactorally. At 4:22 a.m. on 15 September a final rerendezvous maneuver without use of the rendezvous radar, which had malfunctioned, was accomplished.

Retrofire occurred at the end of the 44th revolution at 8:24:03 a.m. EST on 15 September. This was the first closed-loop, automatic reentry (guided by computer commands directly to the thrusters) in the U.S. space program. Splashdown in the western Atlantic at 24.25 N, 70.00 W, 4.9 km from the target point, occurred at 8:59:35 a.m. EST. The crew was picked up by helicopter and brought to the U.S.S. Guam at 9:23 a.m. and the spacecraft was recovered at 9:58 a.m. Total mission elapsed time was 71:17:08. All primary objectives were accomplished, and the last rerendezvous added to the mission plan due to the favorable fuel supply. Power tool evaluation was not performed due to early termination of EVA and the airglow horizon photography was only partially done due to a fault in the camera. All other experiments were successfully completed.

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.