Apollo abort modes
Encyclopedia
During the launch of an Apollo spacecraft
by the Saturn V
rocket, the flight could be aborted to rescue the crew if the rocket failed catastrophically. Depending on how far into the flight the crew were, they would use different procedures or modes. None of the abort modes ever had to be used.
Houston's announcements of the current abort mode and the spacecraft commander's acknowledgements belong to the few things being said on the radio link during the first minutes of flight.
If the rocket failed during the first phases of the flight, the Emergency Detection System
(EDS) would automatically give the command to abort. The reason is that life-threatening situations can develop too fast for humans to discuss and react to. In the later, less violent phases of the ascent, the EDS was turned off and an abort would have to be initiated manually.
). Mode three (III) and up are variations of jettisoning only the failing rocket stage, using the other stages to continue into Earth orbit. Once there, a backup Earth orbit mission could be performed so that the flight was not entirely in vain. In all cases, the Command Module (CM) with the astronauts performs a splashdown by:
The EDS is enabled for the pad abort (beginning 5 minutes prior to launch) through abort mode IB phases. Beginning in mode IC, the EDS is switched off and aborts must be commanded manually.
Apollo spacecraft
The Apollo spacecraft was composed of five combined parts designed to accomplish the American Apollo program's goal of landing astronauts on the Moon by the end of the 1960s and returning them safely to Earth...
by the Saturn V
Saturn V
The Saturn V was an American human-rated expendable rocket used by NASA's Apollo and Skylab programs from 1967 until 1973. A multistage liquid-fueled launch vehicle, NASA launched 13 Saturn Vs from the Kennedy Space Center, Florida with no loss of crew or payload...
rocket, the flight could be aborted to rescue the crew if the rocket failed catastrophically. Depending on how far into the flight the crew were, they would use different procedures or modes. None of the abort modes ever had to be used.
Houston's announcements of the current abort mode and the spacecraft commander's acknowledgements belong to the few things being said on the radio link during the first minutes of flight.
If the rocket failed during the first phases of the flight, the Emergency Detection System
Emergency Detection System
An Emergency Detection System is a system that is used on manned rocket missions. It monitors critical launch vehicle and spacecraft systems and issues status, warning and abort commands to the crew during their mission to low Earth orbit. It can trigger the Launch Abort System which will take the...
(EDS) would automatically give the command to abort. The reason is that life-threatening situations can develop too fast for humans to discuss and react to. In the later, less violent phases of the ascent, the EDS was turned off and an abort would have to be initiated manually.
Overview
Of the five abort modes, the modes up to two (II) are variations of jettisoning the entire rocket followed by an immediate landing in the sea (splashdownSplashdown (spacecraft landing)
Splashdown is the method of landing a spacecraft by parachute in a body of water. It was used by American manned spacecraft prior to the Space Shuttle program. It is also possible for the Russian Soyuz spacecraft and Chinese Shenzhou spacecraft to land in water, though this is only a contingency...
). Mode three (III) and up are variations of jettisoning only the failing rocket stage, using the other stages to continue into Earth orbit. Once there, a backup Earth orbit mission could be performed so that the flight was not entirely in vain. In all cases, the Command Module (CM) with the astronauts performs a splashdown by:
- dumping the hypergolic fuel overboard since the toxic substance would be an unnecessary risk to recovery personnel
- if high enough, deploying high-speed parachutes (drogue parachuteDrogue parachuteA drogue parachute is a parachute designed to be deployed from a rapidly moving object in order to slow the object, or to provide control and stability, or as a pilot parachute to deploy a larger parachute...
) - jettisoning the drogues and deploying the main parachutes
- splashing down in the sea and waiting for recovery team to arrive.
Details
Apollo's planned-for abort modes were, in chronological order:- Pad abort: If the rocket failed in the last five minutes before launch, the CM and the launch escape system (LES, see figure) would separate from the remainder of the rocket below with the LES propelling itself and the CM beneath it upward and eastward to the sea using a small solid-fuelled engine (the pitch control motor) at the top of the tower on the launch escape system. The launch escape tower would then be jettisoned in anticipation of the parachute deployment and the CM would splash down. (Preparation for a pad abort is seen in Apollo video footage: five minutes before launch, the umbilical arm connecting to the CM retracts and swings clear of the rocket. It does so because the swing arm must be out of the way in case the EDS decides to abort.)
- Pad Abort Test-1Pad Abort Test-1 (Apollo)Pad Abort Test 1 was the first abort test of the Apollo spacecraft on November 7, 1963.-Objectives:Pad Abort Test 1 was a mission to investigate the effects on the Apollo spacecraft during an abort from the pad. The launch escape system had to be capable of pulling the spacecraft away from a...
: Launch Escape System (LES) abort test from launch pad with Apollo Boilerplate BP-6. - Pad Abort Test-2Pad Abort Test-2 (Apollo)Pad Abort Test 2 was the follow-on second abort test to Pad Abort Test 1 of the Apollo spacecraft.-Objectives:Apollo Pad Abort Test 2 was the fifth of six unmanned Apollo missions that flight tested the capability of the launch escape system to provide for safe recovery of Apollo crews under...
: LES pad abort test of near Block-I CM with Apollo Boilerplate B-23A.
- Pad Abort Test-1
- Mode I: Abort using the LES, from launch until LES jettison 30 seconds after S-IIS-IIThe S-II was the second stage of the Saturn V rocket. It was built by North American Aviation. Using liquid hydrogen and liquid oxygen it had five J-2 engines in a cross pattern...
ignition.- Mode IA (one alpha): During the first 42 seconds of flight (up to 3000 m), the rocket is still relatively upright and an abort is much like a pad abort. The main and pitch control motors move the CM out of the flight path of the possibly exploding rocket. Fourteen seconds into the abort, the LES tower is jettisoned, leading to splashdown.
- Mode IB (one bravo): From 3000 m to 30.5 km (117 seconds after launch), the rocket is tilted eastwards far enough that firing the pitch control motor is unnecessary. After the LES main motor moved the CM away from the rocket, the tower would deploy canards (small wings at the tip). They would force the CM-LES combination to fly with the CM bottom forward (blunt-end forward or BEF attitude), necessary because the parachutes stowed at the CM top can only be deployed in a downwind direction.
- Mode IC (one charlie): From 30.5 km until the LES is jettisoned, turning the CM-LES combination around into the CM-forward position would still be necessary, but in the now thin air the canards are useless. Instead, the small engines of the CM's reaction control system (RCSReaction control systemA reaction control system is a subsystem of a spacecraft whose purpose is attitude control and steering by the use of thrusters. An RCS system is capable of providing small amounts of thrust in any desired direction or combination of directions. An RCS is also capable of providing torque to allow...
) would do the job. During One-Charlie, the first staging occurs, that is the jettisoning of the spent first stage (S-ICS-ICThe S-IC was the first stage of the Saturn V rocket. The S-IC first stage was built by The Boeing Company. Like the first stages of most rockets, most of its mass of over two thousand metric tonnes at launch was propellant, in this case RP-1 rocket fuel and liquid oxygen oxidizer...
) and ignition of the second stage (S-IIS-IIThe S-II was the second stage of the Saturn V rocket. It was built by North American Aviation. Using liquid hydrogen and liquid oxygen it had five J-2 engines in a cross pattern...
). One-Charlie ceases about 30 seconds after the staging when the LES is jettisoned.
- Mode II: Abort early during S-II burn. With the LES gone, the Command/Service ModuleApollo Command/Service ModuleThe Command/Service Module was one of two spacecraft, along with the Lunar Module, used for the United States Apollo program which landed astronauts on the Moon. It was built for NASA by North American Aviation...
(CSM) would separate as a whole from the rocket and use its large engine and RCS engines to move clear of the rocket and align itself. The CM would then separate from the SM and splash down.
- Mode III, also known as Contingency Orbit Insertion (COI) or S-IVB to COI: In case of an S-II failure, it would simply be jettisoned early. For the first time in the flight, the rocket is now high and fast enough that the third stage (S-IVBS-IVBThe S-IVB was built by the Douglas Aircraft Company and served as the third stage on the Saturn V and second stage on the Saturn IB. It had one J-2 engine...
) engine, followed by the Service ModuleApollo Command/Service ModuleThe Command/Service Module was one of two spacecraft, along with the Lunar Module, used for the United States Apollo program which landed astronauts on the Moon. It was built for NASA by North American Aviation...
(SM) engine, has enough power to place the spacecraft in Earth orbit. The spent S-IVB would not have fuel to perform trans lunar injectionTrans Lunar InjectionA Trans Lunar Injection is a propulsive maneuver used to set a spacecraft on a trajectory which will arrive at the Moon.Typical lunar transfer trajectories approximate Hohmann transfers, although low energy transfers have also been used in some cases, as with the Hiten probe...
, so only an earth orbit mission would be performed.
- S-IVB to orbit: As in Mode III, the failing S-II would be jettisoned early, but Earth orbit insertion is now possible by the S-IVB alone. Other than not using the SM engine, this is identical to a Mode III abort. This abort mode ends with normal S-II jettison.
- Mode IV: Abort during S-IVB burn. Should the S-IVB fail, the Service ModuleService moduleA service module is a spacecraft compartment containing a variety of support systems used for spacecraft operations. Usually located in the uninhabited area of the spacecraft, the service module is jettisoned upon the completion of the mission, and usually burns up during atmospheric reentry...
engine can now place the CSM in Earth orbit to perform an Earth orbit mission.
The EDS is enabled for the pad abort (beginning 5 minutes prior to launch) through abort mode IB phases. Beginning in mode IC, the EDS is switched off and aborts must be commanded manually.