Apollo (spacecraft)
Apollo had one job, stated as a deadline: land American astronauts on the Moon before the end of the 1960s, and bring them home alive. It was not one ship but a stack of separate machines, built once, used once, then left behind piece by piece. One section carried the crew. Another supplied the ship's power and propulsion. A third was built to land on the Moon and come back up again. Two more pieces rode along that rarely make it into a simple retelling of the story. One shielded the lander during the violence of launch. The other stood ready to pull the crew to safety if the launch itself went wrong. NASA's engineers reached this five-piece design through an approach called lunar orbit rendezvous. Two docked spacecraft would travel together to the Moon and settle into lunar orbit. One would separate and descend to the surface while the other stayed circling above. After the descent, the two would find each other again, dock, and begin the trip home. Not every piece of that stack was built to make the whole journey. Some were designed, from the very start, to be discarded somewhere between the launch pad and the Moon.
Three astronauts lived and worked inside a pressurized cabin built by North American Aviation, later renamed North American Rockwell, for the length of an Apollo mission. It served as both control center and living quarters. Inside were the crew couches, the control and instrument panel, and the Primary Guidance, Navigation and Control System that flew the ship. Communications gear, an environmental control system, and batteries were packed in alongside a heat shield bonded to the hull. A reaction control system gave the crew the ability to adjust the capsule's orientation in flight. Five windows let the astronauts look outside. Two hatches, one forward for docking and one on the side, gave them a way in and out. A parachute recovery system waited folded inside for the final minutes of a mission. Of every section bolted into the Apollo stack, this capsule alone was built to come back to Earth's surface intact.
The astronauts' drinking water came from an unlikely source: the fuel cells that generated electricity for the ship. Those cells combined hydrogen and oxygen, producing water as a byproduct that also fed the environmental control system. The same oxygen supplied the crew's breathing air. Unlike the crew capsule, this section of the spacecraft was left unpressurized, built around a main propulsion engine and a tank of hypergolic propellant. Capable of firing more than once, that engine pushed the spacecraft into lunar orbit and pulled it back out again. It also corrected the ship's course during the days between Earth and the Moon. A separate reaction control system handled smaller adjustments to attitude and direction. Radiators on the exterior dumped waste heat into space, and a high gain antenna kept the ship in contact with Earth. On Apollo 15, 16 and 17, this module also carried a scientific instrument package, including a mapping camera and a small sub-satellite released to study the Moon. It stayed bolted to the command module for nearly the whole mission, breaking away only in the final minutes before reentry into Earth's atmosphere.
Grumman Aircraft Company designed and built the lander that flew somewhere no earlier spacecraft had gone. It moved only through the vacuum of space, never through an atmosphere, earning it a description as the first true 'spaceship.' The lander split into two pieces: a descent stage and an ascent stage. On Apollo 15, 16 and 17, it kept two astronauts alive on the surface for four to five days at a stretch. The descent stage carried the landing gear, a landing radar antenna, the descent propulsion system, and the fuel needed to set the craft down. Its cargo compartments held science packages known as ALSEP, along with tools and lunar sample collection boxes. On Apollo 14, one of those compartments carried a hand-pulled cart called the modularized equipment transporter. Apollo 15, 16 and 17 carried something larger instead: the Lunar Rover, plus a surface television camera. Once the astronauts finished their work on the surface, the descent stage stayed behind. Only the ascent stage carried the crew back into space. Its own rocket engine and propellant pushed it up to rendezvous in lunar orbit with the command and service module. Its cabin held instrument panels, guidance systems, radar and communications antennas, and an overhead hatch that doubled as a docking port.
A conical structure made of aluminum honeycomb just 1.7 inches thick connected the service module to the Saturn rocket's S-IVB stage, built once again by North American Aviation. Four fixed panels, each 7 feet long, bolted to the Instrument Unit atop the S-IVB. Hinges linked them to four longer panels, 21 feet each, that opened outward from the top like petals of a flower. A thin skin of cork, between 0.03 and 0.2 inches thick, covered the exterior and was painted white to keep thermal stress down during the climb through the atmosphere.
Because a failed separation could strand a crew in orbit with no way home, engineers layered the release system with redundancy. It used multiple signal paths, multiple detonators, and multiple explosive charges. If one charge's detonator failed, the detonation of another charge would set it off anyway. In flight, the astronauts pressed a button on the control panel labeled 'CSM/LV Sep' to trigger separation. Detonating cord fired around the flange joining the service module to the adapter, and along the seams between the four panels, blowing the connections apart. Pyrotechnic thrusters at the base of the panels then rotated them outward on their hinges at 30-60 degrees per second.
On every flight through Apollo 7, the panels stayed hinged to the S-IVB stage and swung open to a 45-degree angle, exactly as designed. During Apollo 7, the crew practiced a rendezvous with the discarded S-IVB and its dummy docking target. One panel failed to open the full 45 degrees. Astronaut Wally Schirra likened the sight to the 'angry alligator' the crew of Gemini 9 had once faced. The incident triggered a redesign: engineers added a spring-loaded hinge release. It snapped the panels open and pushed them away from the S-IVB at roughly 8 kilometers per hour. That cleared the panels out of the way before the astronauts turned the command and service module around to dock with the lander.
Four attachment points held the lander to the lower panels. Once the crew docked and fired the separating charges, a guillotine device cut the last umbilical line. Springs then pushed the lander free to continue toward the Moon. Fully assembled, the whole adapter stood 28 feet tall and weighed 4,050 pounds. It enclosed 6,700 cubic feet of space, though only 4,900 cubic feet of that was usable.
The Lockheed Propulsion Company built the system meant to pull the crew capsule clear of a launch vehicle before it exploded. Three wires ran down the length of the launch vehicle's exterior, feeding constant signals to the system. If any two of those signals dropped out at once, the system fired automatically, without input from the crew. The Commander could also trigger it by hand, using one of two translation controller handles, switched over to a special abort setting before launch. Activation set off a solid fuel escape rocket and opened a set of canard fins that steered the capsule away from the launch vehicle's path. The danger triggering it could be a fire on the pad, a guidance failure, or a rocket about to explode. Once clear, the escape tower jettisoned and the capsule descended under its normal parachutes. If the emergency happened on the pad, the capsule had to reach enough height for its parachutes to open safely before hitting the ground. Absent any emergency, the tower jettisoned routinely, 20 to 30 seconds after the second stage ignited. A separate solid-fuel motor, built by the Thiokol Chemical Company, fired it away. Four uncrewed Apollo flights and fifteen crewed Apollo, Skylab, and Apollo-Soyuz flights all carried the system aloft. None of them ever needed it.
At the very top of the tower sat the Q-ball, a nose cone fitted with eight pressure-measuring pitot tubes. Those sensors wired into the guidance computers of both the capsule and the Saturn rocket, calculating dynamic pressure and, if an abort happened, the capsule's angle of attack. A styrofoam cover protected the tubes from debris and had to come off seconds before launch, through a mechanism built with layers of redundancy. The cover was split in half and held together by a rubber band two inches long, with a razor blade pinched behind it. A cable ran from that blade, through a pulley on the crane atop the launch tower, down to the 360-foot level. There it connected to a weight resting on a lever. A valve at the Launch Control Center released 600 pounds per square inch of nitrogen gas, tipping the lever and dropping the weight. The falling weight pulled the cable, the cable pulled the blade through the rubber band, and the two halves of the cover fell away. The whole chain existed for one reason: the escape system was armed five minutes before launch. That made the cover's removal a matter of life and death during any pad abort.
A pair of canard fins and a pitch motor steered the capsule off the launch vehicle's line of flight, and off to the side of any pad fire rather than through the middle of it. The main escape motor, mounted in a long tube with four exhaust nozzles under a conical fairing, supplied the force to pull the capsule away. A smaller tower jettison motor, with two nozzles of its own, fired later to throw off the entire escape system once it was no longer needed. A truss of metal tubes, the escape tower itself, connected the motor assembly to the capsule. A fiberglass boost protective cover shielded the parachute compartment and smoothed the airflow over the docking tunnel. Early flight tests found that exhaust from the escape motor eroded the capsule's windows. A wider cover was added afterward, protecting the whole upper surface of the capsule on later missions.
Fully assembled with its tower, the escape system measured 39 feet 5 inches tall and weighed 9,200 pounds. At full power it could produce up to 200,000 pounds of thrust, in a burn lasting just 4 seconds. Engineers tested the system on the ground twice. Pad Abort Test 1 flew an Apollo boilerplate designated BP-6, and Pad Abort Test 2 flew a near-Block-I capsule designated B-23A. Four more tests, grouped under the name Little Joe II, checked the system's performance in flight.
Two uncrewed command and service modules and one uncrewed lunar module rode into low Earth orbit atop Saturn IB rockets. Those flights tested hardware before any crew climbed aboard. A fourth Saturn IB carried up one crewed command and service module for the same kind of low Earth orbit shakeout flight. The larger Saturn V rocket, built for the trip to the Moon, launched two uncrewed command and service modules on high Earth orbit test flights. It then carried the command and service module alone on one crewed lunar mission, without the lander attached. A separate Saturn V flight sent the complete three-piece spacecraft, lander included, into a single crewed low Earth orbit mission. Eight more Saturn V launches carried crews all the way to the Moon. After the Apollo program itself ended, the hardware kept flying. Four more command and service modules launched on Saturn IB rockets: three for Earth-orbiting Skylab missions, and one for the joint Apollo-Soyuz Test Project.
Common questions
What were the three main parts of the Apollo spacecraft?
The Apollo spacecraft was composed of three parts: the command module, the service module, and the Apollo Lunar Module. Two additional components, a spacecraft-LM adapter and a launch escape system, were added to complete the assembled stack for launch.
Who built the Apollo command and service module?
North American Aviation, later renamed North American Rockwell, built the Apollo command and service module.
What company designed and built the Apollo Lunar Module?
The Grumman Aircraft Company designed and built the Apollo Lunar Module, the vehicle described as the first true spaceship because it flew solely in the vacuum of space.
What was the angry alligator incident during Apollo 7?
During Apollo 7, one of the four spacecraft-LM adapter panels failed to open to its full 45-degree angle while the crew practiced a rendezvous with the discarded S-IVB stage. Astronaut Wally Schirra compared the sight to the angry alligator the Gemini 9 crew had once faced, and the incident led to a spring-loaded hinge redesign.
How many crewed lunar missions did the Apollo spacecraft fly?
Saturn V rockets launched eight crewed lunar missions using the complete Apollo spacecraft. Saturn V also launched one crewed lunar mission using only the command and service module and one crewed low Earth orbit mission using the complete spacecraft.
What happened to the Apollo command and service module after the Apollo program ended?
After the Apollo program concluded, four more Apollo command and service modules launched on Saturn IB rockets. Three supported the Earth-orbiting Skylab missions and one flew the Apollo-Soyuz Test Project.
All sources
4 references cited across the entry
- 2Moonport, Ch20-3Roger D. Launius