STS-39 was the twelfth mission of the

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

Space Shuttle ''Discovery'', and the 40th orbital shuttle mission overall. The primary purpose of the mission was to conduct a variety of payload experiments for the

U.S. Department of Defense The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national secur ...

(DoD).

Crew

Crew seating arrangements

Mission highlights

Launch was originally scheduled for March 9, 1991, but during processing work at Pad LC-39A, significant cracks were found on all four lug hinges on the two external tank umbilical door drive mechanisms. NASA managers opted to roll back the vehicle to the

Vehicle Assembly Building The Vehicle Assembly Building (originally the Vertical Assembly Building), or VAB, is a large building at NASA's Kennedy Space Center (KSC), designed to assemble large pre-manufactured space vehicle components, such as the massive Saturn V and th ...

(VAB) on March 7, 1991, and then to Orbiter Processing Facility (OPF) for repair. The faulty hinges were replaced with units taken from orbiter ''Columbia'', and reinforced. ''Discovery'' was returned to the pad on April 1, 1991, and the launch was rescheduled for April 23. The mission was again postponed when, during prelaunch external tank loading, a

transducer A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and contr ...

on high-pressure oxidizer turbopump for main engine number three showed readings out of specification. The transducer and its cable harness were replaced and tested. The launch was rescheduled for April 28. Actual launch occurred at April 28, 1991, 7:33:14 a.m. EDT. Launch weight: . STS-39 was a dedicated U.S. Department of Defense mission. Unclassified payload included Air Force Program-675 (AFP-675); Infrared Background Signature Survey (IBSS) with

Critical ionization velocity Critical ionization velocity (CIV), or critical velocity (CV), is the relative velocity between a neutral gas and plasma (an ionized gas), at which the neutral gas will start to ionize. If more energy is supplied, the velocity of the atoms or mole ...

(CIV), Chemical Release Observation (CRO) and

Shuttle pallet satellite The shuttle pallet satellite was a satellite bus designed to be deployed and then retrieved for return to Earth on NASA's Space Shuttle. It carried a variety of payloads both scientific and military in nature. It was made by Messerschmitt-Bölko ...

-II (SPAS-II) experiments; and Space Test Payload-1 (STP-1). Classified payload consisted of Multi-Purpose Release Canister (MPEC). Also on board was

Radiation Monitoring Equipment Radiation dosimetry in the fields of health physics and radiation protection is the measurement, calculation and assessment of the ionizing radiation dose absorbed by an object, usually the human body. This applies both internally, due to ingested ...

-III (RME-III) and Cloud Logic to Optimize Use of Defense Systems-1A (CLOUDS-1A). STS-39 was the first unclassified Department of Defense (DoD)-dedicated Space Shuttle mission. There had previously been seven Shuttle missions dedicated to the DoD, but those were considered classified and information about the operation or success of the payloads or experiments was not released. For STS-39, only the payload in the Multi-Purpose Experiment Canister (MPEC) was listed as classified. (Bluford reportedly launched the classified payload by himself while, according to another member of the crew, "the rest of us pretended not to notice".) The crew was divided into two teams for around-the-clock operations. Among other activities, the crew made observations of the atmosphere and gas releases, ''Discovery''s orbital environment, and firings of the orbiter's engines, in

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

s ranging from

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

far ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

. As part of the sophisticated experiments, five spacecraft or satellites were deployed from the payload bay, and one was retrieved later during the mission. Carried in the orbiter's cargo bay were: Air Force Program-675 (AFP-675); Infrared Background Signature Survey (IBSS); Space Test Program-01 (STP-01); and the MPEC. Inside the crew cabin were the Cloud Logic to Optimize the Use of Defense Systems-1A (CLOUDS-1A) experiment and the Radiation Monitoring Equipment-III (RME-III). The Remote Manipulator System (

Canadarm Canadarm or Canadarm1 (officially Shuttle Remote Manipulator System or SRMS, also SSRMS) is a series of robotic arms that were used on the Space Shuttle orbiters to deploy, manoeuvre, and capture payloads. After the Space Shuttle ''Columbia' ...

) in the payload bay was used to deploy the Shuttle Pallet Satellite-II (SPAS-II), on which the IBSS was mounted. Among other observations, the SPAS-II/IBSS watched ''Discovery'' as it performed some orbital maneuvers including the "Malarkey Milkshake". The "Malarkey Milkshake" was an orbital maneuver wherein ''Discovery'' rotated out-of-plane, fired one

Orbital Maneuvering System In spaceflight, an orbital maneuver (otherwise known as a burn) is the use of propulsion systems to change the orbit of a spacecraft. For spacecraft far from Earth (for example those in orbits around the Sun) an orbital maneuver is called a ' ...

(SSOMS) engine to move to a different orbital track, rapidly turned around 180° using

Reaction control system A reaction control system (RCS) is a spacecraft system that uses thrusters to provide attitude control and translation. Alternatively, reaction wheels are used for attitude control. Use of diverted engine thrust to provide stable attitude contr ...

RCS thrusters and returned to its original orbital track. This rapid sequence of maneuvers was named after the leader of the

Johnson Space Center The Lyndon B. Johnson Space Center (JSC) is NASA's center for human spaceflight (originally named the Manned Spacecraft Center), where human spaceflight training, research, and flight control are conducted. It was renamed in honor of the late U ...

(JSC) guidance team which developed it (see NASA Press Kit p. 26) The deployment of IBSS was delayed a day, until Flight Day Four, to give priority to the completion of the CIRRIS (Cryogenic Infrared Radiance Instrumentation for Shuttle) experiment which was depleting its

liquid helium Liquid helium is a physical state of helium at very low temperatures at standard atmospheric pressures. Liquid helium may show superfluidity. At standard pressure, the chemical element helium exists in a liquid form only at the extremely low temp ...

coolant supply faster than expected while making observations of auroral and airglow emissions. As usual, crew members faced some unexpected challenges during the mission. After working only about four hours, two

tape recorder An audio tape recorder, also known as a tape deck, tape player or tape machine or simply a tape recorder, is a sound recording and reproduction device that records and plays back sounds usually using magnetic tape for storage. In its present- ...

s could not be reactivated. The tape recorders were designed to record observations made by three instruments on AFP-675. In a complicated two-hour bypass repair operation, the astronauts had to route wires and attach a splice wire to a

Ku-band The Ku band () is the portion of the electromagnetic spectrum in the microwave range of frequencies from 12 to 18 gigahertz (GHz). The symbol is short for "K-under" (originally german: Kurz-unten), because it is the lower part of the ori ...

antenna system so the data could be sent directly to a

ground station A ground station, Earth station, or Earth terminal is a terrestrial radio station designed for extraplanetary telecommunication with spacecraft (constituting part of the ground segment of the spacecraft system), or reception of radio waves fro ...

. The high

orbital inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth ...

of the mission, 57.01° with respect to the

equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...

, allowed the crew to fly over most of

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

's large land masses and observe and record environmental resources and problem areas. STS-39 landed on May 6, 1991, at 2:55:35 p.m. EDT, at Runway 15,

Kennedy Space Center The John F. Kennedy Space Center (KSC, originally known as the NASA Launch Operations Center), located on Merritt Island, Florida, is one of the National Aeronautics and Space Administration's (NASA) ten field centers. Since December 1968 ...

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

. Landing was diverted there because of unacceptably high winds at the planned landing site,

Edwards Air Force Base Edwards Air Force Base (AFB) is a United States Air Force installation in California. Most of the base sits in Kern County, but its eastern end is in San Bernardino County and a southern arm is in Los Angeles County. The hub of the base is E ...

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

. Landing weight: . Rollout distance: , rollout time: 55 seconds.

Gallery

File:STS-39 launch.jpg, Launch of STS-39 Image:STS-39 SPAS-II.jpg, SPAS-II

References

External links

NASA mission summary

NASA Press Kit

STS-39 Video Highlights
{{Orbital launches in 1991 Space Shuttle missions Spacecraft launched in 1991 Department of Defense Space Shuttle missions