Twenty-five years ago, next week, one of the most complex space shuttle missions in history got underway with a spectacular liftoff from Pad 39A at the Kennedy Space Center (KSC) in Florida. As outlined in yesterday’s AmericaSpace history article, the eight-day STS-39 was the longest shuttle mission ever conducted for the Department of Defense, whilst its seven-man crew—Commander Mike Coats, Pilot Blaine Hammond, and Mission Specialists Lacy Veach, Rick Hieb, Greg Harbaugh, Don McMonagle, and the first African-American spacefarer, veteran astronaut Guy Bluford—was the largest ever flown on a military flight. Theirs would involve the deployment and retrieval of a free-flying satellite, laden with infrared sensors for atmospheric and other research, as well as a multitude of experiments mounted inside Shuttle Discovery’s cavernous payload bay.
When Bluford, Veach, and Hieb were assigned to STS-39 in May 1989, their principal payload consisted of Air Force Project-675 (AFP-675), together with the Infrared Background Signature Survey (IBSS). The five AFP-675 experiments were the Cryogenic Infrared Radiance Instrument for Shuttle (CIRRIS)—previously flown on STS-4 in June-July 1982—together with the Far Ultraviolet Camera (FARUV), the Uniformly Redundant Array (URA), the Horizon Ultraviolet Program (HUP), and the Quadropole Ion Neutral Mass Spectrometer (QINMS). Primary targets included Earth’s upper atmosphere, its aurorae and astronomical objects, as well as analyzing the spectrum of gases released from or around the shuttle itself, as part of efforts to better understand the difficulties of identifying spacecraft with remote sensors and distinguishing them from natural phenomena.
Of the experiments, CIRRIS and HUP had flown before. The former sought to obtain simultaneous spectral and spatial measurements of atmospheric “airglow” and emissions from terrestrial aurorae; in fact, STS-39’s launch was precisely timed to ensure proper visibility of auroral displays. On its first flight, CIRRIS was unable to operate properly, due to a jammed lens cap, but on STS-39 it was expected to answer fundamental questions about the optimum atmospheric “windows” for detecting cold-body targets, together with background radiance levels in various regions, the spatial structure of the background, and the variability of Earth’s limb emissions during auroral events. The results of these experiments were anticipated to contribute substantially to the development of new surveillance systems. Such was the sensitivity of CIRRIS that it demanded a so-called “gravity gradient” attitude, in which the shuttle occupied a tail-to-Earth orientation, minimizing its use of thrusters. Meanwhile, HUP would monitor the spectral characteristics of Earth’s horizon at ultraviolet wavelengths and measure contaminants in the payload bay.
The remaining AFP-675 experiments were devoted to ultraviolet and X-ray research. Of these, FARUV observed both natural and man-made emissions in near-Earth space, including atmospheric airglow, diffuse northern and southern aurorae, and chemical and particulates in the environment around the shuttle. In the latter case, firings by Discovery’s Reaction Control System (RCS) and Orbital Maneuvering System (OMS) and “surface glow” effects were of significant interest. At the same time, FARUV was to be directed towards astronomical objects, including diffuse nebulae, the Milky Way “background,” neighboring galaxies and starfields. Finally, URA was employed for X-ray studies of astronomical sources, whilst QINMS would explore the levels of contamination in the payload bay and gather data as the shuttle passed through the auroral zone and polar latitudes.
The second major payload, IBSS, was mounted atop the triangular Shuttle Pallet Satellite (SPAS), which had earlier flown aboard STS-7 in June 1983. For STS-39, the SPAS was dominated by the barrel-shaped IBSS cryostat, which sought to obtain scientific data for use in the development of missile defence sensors. Flying freely from the shuttle at various ranges, IBSS-SPAS would make spectral, spatial, and temporal radiometric observations of the orbiter’s exhaust plumes and replications of booster firings. Interactions of these plumes with the ionosphere would be analyzed, as would the region around the engine nozzles.
A crucial element of this activity was the Chemical Release Observation (CRO), which involved the deployment of three subsatellites from the shuttle at rates of about 3.3 feet (1 meter) per second, enabling them to separate until they trailed IBSS-SPAS by 30-125 miles (50-200 km). Signals transmitted from Vandenberg Air Force Base, Calif., would expel chemicals—nitrogen tetroxide, unsymmetrical dimethyl hydrazine, and monomethyl hydrazine, all used as station-keeping propellants—from the satellites, which would quickly vaporize. These would be simultaneously observed by IBSS-SPAS, by sensors at Vandenberg and aboard tracking aircraft, following Discovery’s flight path. It was hoped that this combined data would enable characterization of interactions of the chemicals with Earth’s upper atmosphere.
Elsewhere, the Critical Ionisation Velocity (CIV) experiment involved the ejection of pressurized xenon, neon, carbon dioxide, and nitric oxide gases from four canisters in the payload bay, at different angles to the orbiter’s own velocity, in order to enhance ionization with the thin upper atmosphere. This was expected to enable researchers to examine a theory which held that gases could be “ionized” if passed through a magnetized plasma and their kinetic energy caused to exceed their ionization potential. “Ions so created,” noted NASA’s STS-39 press kit, “would then flow along the local magnetic lines of force and generate emissions which can be detected by space-borne sensors, thereby permitting tracking of the vehicle releasing the gases.”
The sensors aboard IBSS-SPAS would acquire spectral data on these chemical releases, as well as Earth’s surface under various conditions of light and darkness, hard earth and water, and clouds and cloudlessness. Additional measurements of the so-called “orbiter glow”—the phenomenon in which rarefied atmospheric gases struck the shuttle’s surfaces, particularly its tail, causing visible and infrared radiance—would be pursued, as part of ongoing efforts to understand their cause and precise nature. During two days of free flight, IBSS-SPAS would observe over 60 orbiter maneuvers.
This made STS-39 by far the most complex Department of Defense mission ever undertaken by the shuttle. In fact, its complexity was such that the crew was split into two 12-hour shifts (“red” and “blue”), working around the clock, to complete all of the objectives. As the commander, Coats was not assigned to either shift, but tended to align his work schedule with the red team. He was joined by Hammond, Veach, and Hieb, whilst McMonagle led the blue shift, joined by Bluford and Harbaugh. “We had to do rendezvous, multiple translation manoeuvres, extended station-keeping and deployment and retrieval of the SPAS with the RMS,” recalled Bluford in his NASA oral history. “This involved precision orbiter maneuvering, IBSS-SPAS commanding, CIRRIS and IBSS observation sequences and multi-body management in a very intensive timeline. A lot of co-ordination was required on the flight deck, synchronizing orbiter and SPAS maneuvers and documenting key events. There was approximately 36 hours planned for rendezvous and proximity operations.” On each shift, the payloads, Remote Manipulator System (RMS) mechanical arm and the orbiter itself often had to be managed simultaneously.
A 24-hour operation required the astronauts to “sleep-shift” in the final weeks before launch. In fact, a new sleep regime had been implemented by NASA prior to the dual-shift STS-35 mission, whose crew spent the final week before launch awake all night in an all-white room, under harsh fluorescent lighting, to adjust their irregular sleep cycles. “Their exposure to bright light will be timed so that sunlight will not disrupt their bodies’ shifted circadian rhythm,” noted Flight International before STS-39, “when they emerge from the crew quarters during the day for training. The astronauts’ body clocks will be ‘reset’ in such a way that the Sun will be interpreted as evening light, rather than morning light, because the body’s circadian rhythm is apparently synchronized with sunrise and sunset.”
By the time STS-35 flew in December 1990, NASA anticipated STS-39 to launch in late February or early March of the following year. It was during the lead-up to STS-35 that Guy Bluford suffered a herniated disk in his back. Physical therapy worked well for a while, but when he continued to experience problems during one of his training sessions it was considered prudent to take a closer look. “I started sensing numbness in my right shin,” Bluford remembered, “and found that I couldn’t stand for any longer than 30 minutes, before my leg started aching.” (When the crew had their official photograph taken, Bluford was positioned at the far right side, so that he could stand close to a chair.)
The only option was an operation and there was talk about removing Bluford from STS-39, but judicious rescheduling of crew tasks by Mike Coats allowed for his crewmate to undergo the operation and rejoin the mission. In total, Bluford was out of work for barely two weeks and, within a month, was fit and healthy for flight. Years later, he believed that Rob Crombie—an Air Force Manned Spaceflight Engineer (MSE), who had trained extensively with the crew—would “probably” have flown in his stead if the result of the operation had been different. “He would have done an excellent job,” Bluford told the NASA oral historian, “if the circumstances dictated.”
Unfortunately, in late February 1991, cracks were found in four hinges associated with the two umbilical door drive mechanisms between the External Tank (ET) and the shuttle itself. These doors were required to close after the ET was jettisoned, eight minutes into the ascent, in order to ensure that the Thermal Protection System (TPS) on Discovery’s belly would not be compromised during re-entry. The scheduled 9 March launch was canceled and the STS-39 stack was rolled back to the Vehicle Assembly Building (VAB) for repairs, with a new attempt to get Discovery into space not expected before the end of April. During this period, door hinges from her sister orbiter, Columbia, were reinforced and installed, and by 1 April the STS-39 stack was back on Pad 39A.
Launch was originally expected around 23 April, but a troublesome transducer on one of the High Pressure Oxygen Turbopumps (HPOT) on Discovery’s cluster of three Space Shuttle Main Engines (SSMEs) forced a delay of several more days. At length, in the small hours of 28 April, the astronauts departed the Operations & Checkout (O&C) Building, clad in their bulky orange partial-pressure suits, bound for the pad. The STS-39 crew was the tallest shuttle crew yet launched—ranging from Lacy Veach at 5 feet 10 inches (1.78 meters) to Rick Hieb at 6 feet 3 inches (1.9 meters)—but according to Mike Coats “we still looked like seven orange billiard balls out there.”
Discovery roared aloft at 7:33 a.m. EDT on the 28th. From his seat, Blaine Hammond was happy to see a totally nominal ascent, which he joked later made most of the last 12 months of training “wasted.” Immediately after achieving orbit, Coats, Hammond, Veach, and Hieb set to work activating and checking out the multitude of payloads aboard their ship. For AFP-675, this was problematic: two tape recorders stopped working after four hours of running, which required a complicated bypass, in which the astronauts rerouted wires and attached a splice to the shuttle’s Ku-band communications antenna to achieve a direct-to-ground data downlink.
Having also activated the Space Test Payload (STP) in the payload bay, the red team ended their shift and passed the baton over to the blue shift of McMonagle, Bluford and Harbaugh. In order to conserve electrical power on what would turn out to be Discovery’s longest voyage to date—predicted to exceed its previous “personal best,” Mission 51A, by about eight hours—the crew also placed vehicle systems into a “Group B Power-Down” mode, ahead of the IBSS-SPAS deployment on the third day of the flight.
However, the deployment was postponed by 24 hours, in order to allow AFP-675 to acquire more data before its supply of cryogenic coolant expired. Finally, at 4:18 a.m. EDT on 1 May, IBSS-SPAS was released into free flight by the RMS. Over the course of the next two days, the astronauts pulsed Discovery’s OMS engines 16 times and her RCS thrusters a total of 41 times. Due to their complexity, the OMS burns were performed at shift changeovers, when all seven crew members were awake. From afar, IBSS-SPAS monitored the engine bursts, as well as CIV gas releases and the CRO subsatellite deployments.
Immediately after deployment, Coats and Hammond fired the RCS thrusters to raise their orbit slightly above IBSS-SPAS, causing the shuttle to drift about 7 miles (10 km) “behind” the satellite and enabling “far-field” observations to begin. During this time, it observed Discovery performing a rapid sequence of maneuvers which the crew had nicknamed “The Malarkey Milkshake,” in honor of the head of the guidance team, Rockwell International engineer John Malarkey. (Malarkey served as STS-39’s Orbit 2 Rendezvous officer.) The milkshake involved Discovery rotating out of plane: firing one of her OMS engines for 20 seconds to propel the orbiter “northwards,” off its previous ground track, without altering its altitude. Immediately after this burn, the crew performed a “fast-flip” yaw maneuver, using the RCS to align Discovery’s nose 180 degrees to the “south.” A single-engine OMS braking burn then returned the orbiter to its original ground track.
With the completion of the far-field observations, Coats and Hammond performed a retrograde RCS firing to slightly lower their orbit, causing them to move to a position 1.2 miles (2 km) “behind” IBSS-SPAS. At length, late on 2 May, the red team extended the RMS to grapple IBSS-SPAS and berth it back in the payload bay at 7:15 p.m. EDT. A second phase of operations, involving the unberthing of the payload by the RMS, but no deployment, began at around midday on the 3rd and lasted for approximately 23 hours.
One other, far quieter, activity was the deployment of STS-39’s only classified payload, ejected by Bluford from a Multi-Purpose Experiment Canister (MPEC) on 5 May. Years later, he joked that his crewmates disappeared downstairs to the middeck and “pretended” not to notice as he remained on the flight deck to oversee the deployment. In truth, only Bluford and Coats were privy to the classified nature of the payload and other than the name of its stated sponsor (the Air Force Space Systems Division) its purpose remains unclear to this day.
With so many complex objectives, there was precious little time for levity. However, on a couple of occasions, the astronauts were able to offer some televised insights into life in orbit. At one stage, Mike Coats decided to give a demonstration of how to prepare food in the galley on Discovery’s middeck and Capcom Kathy Thornton suggested making a peanut butter sandwich. “And I had to laugh, ‘cos that’s the one thing I cannot stand to eat is peanut butter!” Coats remembered later. “But I broke out a tortilla and made a peanut butter jelly sandwich. Fortunately, Blaine [Hammond] will eat anything and everything. After I put it together, I floated it to Blaine and he ate it right there, on TV. That’s about as close as I’ve ever come to being sick on-orbit!”
The challenging mission of STS-39 had one additional challenge in store, however, when the planned landing at Edwards Air Force Base, Calif., was called off, due to unacceptably high crosswinds. As a result, for the second time in less than six months, a returning orbiter was directed to the Kennedy Space Center (KSC) in Florida. Descending through the heartland of America, and even overflying a commercial airliner at one point, Discovery alighted on Runway 15 at 2:55 p.m. EDT on 6 May. The landing did not go well. Touching down at 240 mph (387 km/h)—the second-fastest shuttle landing, eclipsed only by STS-3—the right-hand main gear hit the runway 200 feet (60 meters) before the left-hand gear, causing one of the right-side tires to shred.
This is part of a series of history articles, which will appear each weekend, barring any major news stories. Next week’s article will focus on the 55th anniversary of Freedom 7, which saw Al Shepard become America’s first spacefarer.