STS-39

Key takeaways

STS-39 belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect STS-39 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of STS-39 from memory before moving on to harder problems.

Reference excerpt

STS-39 was the twelfth mission of the NASA 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 (DoD).

Crew

Crew seat assignments

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 (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 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: 112,207 kg (247,374 lb). 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 (CIV), Chemical Release Observation (CRO) and Shuttle pallet satellite-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-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 wavelengths ranging from infrared to far ultraviolet. 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) 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 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 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 recorders 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 antenna system so the data could be sent directly to a ground station. The high orbital inclination of the mission, 57.01° with respect to the equator, allowed the crew to fly over most of Earth'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, Florida. Landing was diverted there because of unacceptably high winds at the planned landing site, Edwards Air Force Base, California. Landing weight: 102,755 kg (226,536 lb). Rollout distance: 2,877 m (9,439 ft), rollout time: 55 seconds.

Gallery

Illustrations

Worked examples

Example 1 — a first encounter with STS-39

Start with the simplest possible case. Write down what STS-39 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to STS-39 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about STS-39 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of STS-39

In research: STS-39 appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses STS-39 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: STS-39 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Department of Defense Space Shuttle missions, Space Shuttle missions, Spacecraft launched in 1991, so understanding it makes those chapters shorter.
In everyday life: Look for STS-39 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study STS-39 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what STS-39 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain STS-39 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is STS-39 in simple terms?

STS-39 was the twelfth mission of the NASA 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.

Why does STS-39 matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study STS-39?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on STS-39.