Gemini 4 was the second crewed mission of the Gemini series and carried James McDivitt and Edward White on a 4-day, 62-orbit, 98-hr flight from June 3 to June
7, 1965. The mission included the first American spacewalk. The objective of
the mission was to test the performance of the astronauts and capsule and to
evaluate work procedures, schedules, and flight planning for an extended length
of time in space. Secondary objectives included demonstration of extravehicular
activity in space, conduct stationkeeping and rendezvous maneuvers, evaluate
spacecraft systems, demonstrate the capability to make significant in-plane and
out-of-plane maneuvers and use of the maneuvering system as a backup reentry
system, and conduct 11 experiments.
Gemini 4 was launched from Complex 19 at 10:15:59 a.m. EST (15:15:59.562 UT) and inserted into a 162.3 x 282.1 km Earth orbit at 10:22:05. The orbit was raised to 166 x 290 km
during the first revolution to attempt a rendezvous with the second stage. This stationkeeping exercise was cancelled early in the second revolution after
depletion of 42% of the fuel, it was determined that use of more fuel would
jeopardize other mission objectives. White then donned special gear and pressurized his suit at 3.7 psi. McDivitt depressurized the cabin, bringing the pressure to zero at 2:33:35 p.m. EST, and the hatch was opened at 2:34. White stood up two minutes later and exited the spacecraft using a hand-held gas gun at 2:46, becoming the first American to walk in space. White was attached to the spacecraft by an 8 meter tether. The gas gun fuel supply was depleted in 3 minutes, after which White pulled on the tether and twisted his body to maneuver around the spacecraft. The extravehicular activity (EVA) lasted 23 minutes, after which White pulled himself back into the spacecraft.
Difficulty was encountered sealing the hatch, but working together the astronauts finally closed it, at 3:10 p.m. EST. Cabin repressurization began at 3:12:50. Drifting flight was maintained for the next 30 hours to conserve propellant. A computer malfunction on the 48th revolution made the planned computer-controlled reentry impossible. A zero-lift ballistic reentry, similar to that used by the Mercury program, was started at the beginning of revolution 62 with retrofire at 11:56:00 a.m. EST on June 7. Gemini 4 splashed down 16 minutes later at 12:12:11 in the western Atlantic, 27.73 N, 74.18 W, 81 km from the target. Total elapsed mission time was 97:56:12. The crew were recovered by helicopter and flown to the aircraft carrier U.S.S. Wasp at 1:09 p.m. and the capsule was recovered at 2:28 p.m.
The experiments performed during the mission were electrostatic
charge (MSC-1), proton-electron spectrometer (MSC-2), triaxial
magnetometer (MSC-3), two-color earth limb photos (MSC-4), inflight
exerciser (M-3), inflight phonocardiogram (M-4), bone demineralization
(M-6), synoptic terrain photos (S-5), synoptic weather photos (S-6),
dim and twilight phenomena (S-28), radiation (D-8), and simple
navigation (D-9). All experiemnts were performed successfully. All
other objectives except the rendezvous and computer controlled reentry
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 6 silver-zinc batteries to a 22- to 30-volt DC two-wire
system. During reentry and post-landing power was supplied by four 45 amp-hr
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.
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.
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.