The United States manned space program has been conducted in three major phases Mercury, Gemini, and Apollo. Each manned flight has led to increased knowledge of the systems and techniques needed to operate successfully in space, and each phase represents a significant advancement over the previous one.

The first man in space was the Russian Yuri Gagarin, who made one orbit of the earth in his Vostok 1 spacecraft on April 12, 1961. The first American spaceman was Alan B. Shepard, Jr., who rode his Mercury spacecraft into space atop a Redstone booster on May 5, 1961. The first American to orbit the earth was John H. Glenn, Jr., who made three orbits in a Mercury spacecraft on Feb. 20, 1962.

To date (August 1, 1968), 19 Americans have been in space, and seven of these have made two space flights. There were six manned flights during the Mercury program and 10 manned flights in the Gemini program.

Eleven Russians have been in space in their nine-launch program. The Russian manned program also has involved three spacecraft, with six flights aboard the one-man Vostok, two flights with the Voskhod (one a three-man and the other a two-man craft), and a single flight with the Soyuz spacecraft.

There have been no fatalities in space, but accidents have marred the advanced programs of both the United States and Russia. Three American astronauts Virgil I. Grissom, Edward H. White, II, and Roger B. Chaffee died in a fire aboard an Apollo spacecraft on the pad at Kennedy Space Center. Grissom, a veteran of two space flights, was pilot of the second Mercury spacecraft and commander of the first Gemini to go into space. White was aboard the second manned Gemini spacecraft in orbit, and made the historic 21-minute "walk in space." The accident occurred on Jan. 27, 1967, as the three men were rehearsing countdown procedures for what was to have been the first Apollo manned launch.

The Russian tragedy occurred during a space mission, but not in space. Cosmonaut Vladimir Komarov died in the Soyuz 1 spacecraft on April 24, 1967, when it crashed during landing. The Soyuz flight, which lasted about 25 hours, had been characterized as successful by the USSR. It had entered the atmosphere and vvas at an altitude of about 4.3 miles when its parachutes became fouled and it plunged to earth. Komarov was the first Russian to go into space twice: he was one of the three cosmonauts aboard the Voskhod 1.


Project Mercury was America's first step into space. The one-man Mercury capsules were designed to


Date Vehicle Astronaut Rev. Hours Description
May 5, 1961 Mercury-Redstone 3 Alan B. Shepard, Jr. * 00:15:22 First American in space; Freedom 7
July 21, 1961 Mercury-Redstone 4 Virgil I. Grissom * 00:15:37 Capsule sank; Liberty Bell 7
Feb. 20, 1962 Mercury-Atlas 6 John H. Glenn, Jr. 3 04:55:23 First American in orbit; Friendship 7
May 24,1962 Mercury-Atlas 7 M.Scott Carpenter 3 04:56:05 Landed 250 miles from target; Aurora 7
Oct. 3, 1962 Mercury-Atlas 8 Walter M. Schirra, Jr. 6 09:13:11 Landed 5 miles from target; Sigma 7
May 15-16, 1963 Mercury-Atlas 9 L. Gordon Cooper, Jr. 22 34:19:49 First long flight; Faith 7

("*" represents suborbital flights)

answer the basic questions about man in space; how he was affected by weightlessness, how he withstood the gravitational forces of boost and entry, how well he could perform. A milestone in applied science and engineering, the Mercury flights proved that man not only could survive, he could greatly increase the knowledge of space.


Gemini was the next step in NASA's program. The goal of these two-man flights was to find out how man could maneuver himself and his craft, and to increase our knowledge about such things as celestial mechanics and space navigation. Gemini has a record of 10 successful manned flights and set many records, including the longest duration (almost 14 days), the first rendezvous by two maneuverable spacecraft, and the first docking.

Date Vehicle Astronauts Rev. Hours Description
Mar. 23,1965 Gemini III Virgil Grissom John Young 3 4.9 First manned orbital maneuvers
June 3-7,1965 Gemini IV James McDivitt Edward White 62 97.9 21 -minute "spacewalk " by White
Aug. 21-29,1965 Gemini V Gordon Cooper Charles Conrad 120 190.9 First extended manned flight
Dec. 4-18,1965 Gemini VII Frank Borman James Lovell 206 330.6 Longest space flight; served as Gemini VI-A target vehicle
Dec.15-16,1965 Gemini VI-A Walter Schirra
Tom Stafford
16 25.9 Rendezvous within 1 foot of Gemini VII
Mar.16-17,1966 Gemini VIII Neil Armstrong David Scott 6.5 10.7 First docking, to Agena target; short circuit cut flight short
June 3-6,1966 Gemini IX-A Tom Stafford Eugene Cernan 45 72.3 Rendezvous, extravehicular activity, precision landing
July 18-21,1966 Gemini X John Young Michael Collins 43 70.8 Rendezvous with retrieved package from Agena in space walk
Sept. 12-15,1966 Gemini XI Charles Conrad Richard Gordon 44 71.3 Rendezvous and docking, 161-minute extravehicular activity
Nov. 11-15,1966 Gemini XlI James Lovell
Edwin E. Aldrin
59 94.6 3 successful extravehicular trips, rendezvous and docking, rendezvous with solar eclipse


The Soviet Union opened the space age when it put the first man, Yuri Gagarin, into space in April of 1961. They followed four months later with the 25-hour flight of Gherman Titov.

The Russians waited a year after the Gagarin flight before their next, but that was the first group flight; two spacecraft on successive days. A 10-month lull followed before the second group flight, this time including a woman, Valentina Tereshkova, as one of the cosmonauts.

These six flights were with the Soviet Union's first manned spacecraft, the Vostok. Their second generation spacecraft, the Voskhod, made only two flights about six months apart. The first Voskhod mission, 16 months after the last Vostok flight, carried a crew of three and was the first spacecraft with more than one passenger. The second Voskhod flight carried only two men but featured the first man to leave his spacecraft and "walk" in space.

The Soviet Union's third-generation spacecraft, Soyuz, made its only flight in April of 1967, when Komarov was killed.

Date Spacecraft Cosmonaut Revolutions Hours Description
Apr. 12, 1961 Vostok 1 Yuri Gagarin 1 1.8 First manned flight
Aug. 6, 1961 Vostok 2 Gherman Titov 17 25.3 More than 24 hours in space
Aug. 11, 1962 Vostok 3 Andrian Nikolayev 64 94.4 First group flight
Aug. 12, 1962 Vostok 4 Pavel Popovich 48 71.0 Came within 3.1 miles of Vostok 3 on first orbit
June 14, 1963 Vostok 5 Valery Bykovsky 81 119.1 Second group flight
June 16, 1963 Vostok 6 Valentina Tereshkova 48 70.8 Passed within 3 miles of Vostok 5; only woman in space
Oct. 12, 1964 Voskhod 1 Vladimir Komarov
K. Feoktistov
B. Yegorov
16 24.3 First 3-man craft
Mar. 18, 1965 Voskhod 2 A. Leonov
P. Belyayev
17 26.0 Leonov was first man outside spacecraft in 10-minute "walk"
Apr. 23, 1967 Vladimir Komarov Soyuz 1 17 25.2 Heaviest manned craft; crashed killing Komarov


Many differences in the three manned U.S. spacecraft are readily apparent, such as size and weight. The major differences are in the complexity and refinement of subsystems. Apollo's requirement for hardware "maturity" is significantly higher than for earlier spacecraft programs. Each subsystem has become progressively more complex, with many more demands made upon it and a correspondingly greater capability. Only Apollo has its own guidance and navigation system.

Electrical power is a good example of increased system complexity. Electrical power for Mercury was supplied by six batteries; for Gemini, it was supplied by seven batteries and two fuel cell powerplants; for Apollo, it is supplied by five batteries and three fuel cell powerplants. The three systems do not sound too different physically. In operation, however, the differences are considerable.

The greatest demand on the Mercury system was to supply power to sustain the 4,265-pound spacecraft and its single astronaut for a day and a half (the 34-hour flight of Gordon Cooper). In Gemini, the electrical power system had to provide sufficient power to operate a typical 7,000-pound craft containing two astronauts for as long as two weeks (the 14-day flight of Frank Borman and James Lovell). In Apollo, the system is designed to support a 100,000- pound spacecraft carrying three men for up to two weeks.


Mercury Gemini Apollo
Height 26 ft 19 ft 82 ft
Diameter 6.2 ft 10 ft 12 ft 10 in.
Launch weight 4265 lb at launch
2987 lb in orbit
2422 lb at recovery
8360 lb 109,500 lb at launch
100,600 lb injected
Crew 1 2 3
Major components Manned capsule (6 ft 10 in.) Entry (manned) module (11 ft 4 in.) Command module (10 ft 7 in.) (top of apex cover)
Adapter (4ft 3in.) Adapter module (7ft 6in.) Service module (24ft 2in.) (top of fairing)
Launch escape tower (16 ft 11 in.) Lunar module (22 ft 11 in.) (legs folded) Launch escape system (33 ft) Adapter (28 ft)
Abort Launch escape rocket and tower to carry manned capsule to safety Ejection seat for each astronaut up to about 70,000 ft; malfunction detection system Launch escape rocket and tower (similar to Mercury but about twice the size); emergency detection system
Communications UHF and HF for voice; UHF for telemetry; C-band and S-band tracking radar UHF primary for voice with HF backup; C-band tracking beacon; rendezvous radar; 300 flight measurements telemetered to ground VHF-AM primary for near earth; S-band primary for deep space; rendezvous radar; 700 flight measurements telemetered to ground
Docking None Index bar (to fit in notch on target vehicle) and latches Probe and docking ring on CM, drogue on LM
Earth Landing 4 chutes: main, drogue, reserve, pilot 3 chutes: main, drogue, pilot, and ejection seats 8 chutes: 3 main, 2 drogues, 3 pilot
Mercury Gemini Apollo
Electrical Power 6 batteries: 3 main auxiliary, 2 standby, and 1 isolated 2 small fuel cells; 2 cryogenic tanks, 4 entry batteries, 3 pyro batteries 3 large fuel cells; 4 cryogenic tanks; 3 entry batteries; 2 pyro batteries
Environmental Control Suit cooling and oxygen loop, cabin cooling loop (water coolant); cabin pressurized to 5 psi; no space radiators Suit cooling and oxygen loops; redundant cabin cooling loops (silicon ester coolant); cabin pressurized to 5 psi; space radiators, coldplates for operating equipment; shirtsleeve environment Four major loops: oxygen, suit circuit, water, and coolant (water-glycol); space radiators and coldplates; cabin pressurized to 5 psi; shirtsleeve operations
Guidance and Control Attitude control equipment (2 attitude gyros, 3 rate gyros, logic and programming circuits); automatic system using 12 small H2O2 thrusters and manual system using 6 small H2O2 thrusters; horizon sensors, periscope Small computer (4,000-word memory), horizon sensor, no redundancy; 16 orbital attitude maneuvering system thrusters of 25 to 100 lb (No redundancy); 16 entry control thrusters (redundant systems of 8 25-lb engines); inertial platform, rendezvous radarLarge computer (39,000-word memory), telescope and sextant; semiautomatic operation; optical, inertial, and computer systems; attitude control through stabilization and control systems; 16 SM reaction control engines (100- lb) redundant systems, 12 CM reaction control engines in redundant systems; separate guidance and control systems in LM.
Propulsion 3 posigrade rockets for separation from booster, 3 retrograde rockets for entry from orbit 4 retrograde rockets for entry (2,500 lb each) Restartable service propulsion engine (20,000 Ib); liquid propellant rodset propulsion with unlimited restart and thrust vector control (automatic and manual)

Copyright 1997-2005 by John Duncan
Comments and questions welcome. All photographs contained on these pages are the author's, unless otherwise noted. No unauthorized reproduction without permission.

Last update: August 2002