Twenty years ago, on 30 September 1994, the crew of Shuttle Endeavour rocketed into orbit—six weeks later than originally planned—on an 11-day mission to support the second Space Radar Laboratory (SRL-2). As described in yesterday’s AmericaSpace history article, the mission, STS-68, featured the Shuttle Imaging Radar (SIR-C) and the X-band Synthetic Aperture Radar (X-SAR) and sought to perform radar imaging of most of Earth’s surface. Following on from SRL-1, which had flown earlier in the year, it was hoped that SRL-2 would allow surface changes to be monitored between the spring and the fall. However, STS-68 fell foul to the shuttle program’s last Redundant Set Launch Sequencer (RSLS) abort, a harrowing on-the-pad shutdown of Endeavour’s three main engines … just 1.9 seconds before the scheduled liftoff on 18 August.
In the wake of such an engine abort, it was necessary that Endeavour be rolled back to the Vehicle Assembly Building (VAB) for repairs. Since the Mission Management Team regarded an RSLS contingency as equivalent to an actual launch this mandated a complete re-inspection of all main engines in the VAB engine shop, creating a delay of approximately six weeks. For STS-68 mission specialist Dan Bursch, who had just earned the unenviable reputation of becoming the only astronaut in history to sit through two RSLS aborts in his career, his crewmates teased him mercilessly. No one would be coming to another of his launch attempts, they told him.
In the hours and days which followed, the attention of technicians focused upon a problem with the No. 3 Space Shuttle Main Engine’s (SSME) High Pressure Oxidizer Turbine (HPOT). One of its sensors detected a dangerously high discharge temperature, which exceeded Launch Commit Criteria (LCC) rules, and Endeavour’s computers halted the countdown after the Engine Start Command (ESC) had been issued. “From ESC+2.3 seconds through ESC+5.8 seconds,” explained NASA’s STS-68 post-flight report, “the HPOT discharge temperature must not exceed 1,560 degrees R[ankine]. The SSME HPOT discharged temperature Channel A attained 1,576 degrees R. The Channel B measurement attained 1,530 degrees R and that was also higher than predicted.” (Normal HPOT discharge temperatures were around 1,400 degrees R.)
As a result, the No. 3 engine was commanded to shut down at 4.72 seconds after ignition, followed, within the next couple of seconds, by its No. 1 and 2 counterparts. Although the No. 3 engine had been used on two previous shuttle missions, its HPOT was new and was undertaking its first flight. By 24 August, the STS-68 stack was back inside the VAB, where all three main engines were removed and replaced with a flight-qualified trio earmarked for Atlantis’ forthcoming STS-66 mission in November. Endeavour returned to the launch pad on 13 September, with a new flight date scheduled no earlier than the 30th. In the meantime, the troublesome No. 3 engine was transported to NASA’s Stennis Space Center in Hancock County, Miss., for an extensive period of evaluation on the test stand. It was fired for 340 seconds without difficulty on 4 September. “The liftoff could have taken place and the engine could have functioned normally,” Flight International noted, “but conservative launch rules had been built into the on-board launch computer.”
For the astronauts, it seemed their best bet of getting off the ground was to convince Endeavour than the unlucky Dan Bursch was not aboard. As a result, when the STS-68 crew—Commander Mike Baker, Pilot Terry Wilcutt, Payload Commander Tom Jones, and Mission Specialists Jeff Wisoff, Steve Smith, and Bursch—arrived at the Kennedy Space Center (KSC), a couple of days before launch, Bursch ensured that he climbed out of his T-38 jet in an appropriate “Groucho Marx” disguise. Things did not seem to be going well, for all of them, save Wisoff, had colds.
In spite of the jinxed nature of their flight, 30 September turned out to be charmed and Endeavour rose perfectly at 7:16 a.m. EDT, just as the 2.5-hour launch window opened. “The expression Kicked off the pad,” Wilcutt related with a hint of humor at the post-mission press conference, “is an accurate one!” Upon arrival in orbit, Jones expressed satisfaction that he had taken anti-nausea medication before launch, but poor Steve Smith fell victim to the malaise within a couple of hours. Dan Bursch, the designated medical officer, offered a Phenergan shot, which seemed to do the trick. It was perhaps fortuitous that Smith, Bursch and Jones—the STS-68 blue shift—bedded down for their first abbreviated sleep period, shortly after reaching space. Activation of the SRL-2 payload and its inaugural observations were conducted under the auspices of the red shift, with Wisoff taking charge of the radar instruments.
Endeavour flew over many of the same sites that its predecessor SRL-1 did, enabling the SIR-C and X-SAR research teams to examine seasonal changes. In addition to its enormous scientific yield, the first radar mission had demonstrated that it could acquire high-resolution data and could endure adjustments to its timeline to cater for new events on the ground. For example, SRL-1 observed severe floodwaters in the mid-western United States and in Thoringen, Germany, as well as taking three different views of Tropical Cyclone Odille as it formed and contorted in the Pacific Ocean. Snow and ice classification maps had been assembled from data over a supersite at Oetztal in Austria and the late-summer flight of STS-68 offered a chance to observe the Patagonian district of southern Chile, home to the largest glaciers and ice fields in South America.
Volcanic sites were a key objective. Already, on SRL-1, the radars had observed Mount Pinatubo in the Philippines—which erupted in mid-1991, affecting global stratospheric temperatures and aerosol levels—and several locations in the Galapagos Islands. Imagery of Pinatubo during the summer monsoon season, when new mud flows were predicted to occur, was high on SRL-2’s list of priorities … but, early in the flight, a serendipitous observation of another eruption, in the Russian Far East, was made.
Klyuchevskaya Sopka is the highest mountain on the Kamchatka Peninsula and the highest active volcano in the whole of Eurasia; it burst into fiery life shortly after Endeavour entered orbit, giving the STS-68 crew a surprise. They saw its tremendous black plume on the horizon, “ahead” of their flight path. At first, it looked like a vast thunderhead. Mike Baker was the first to recognize it as a volcano. Jeff Wisoff was amazed. “It shows how much change nature can produce in a short period of time,” he recalled in a Smithsonian interview. “You had this huge eruption, but then by the end of the flight it had largely stopped erupting. There was still a small smoke trail, but it had re-snowed on top of the soot. In the span of ten days, it was almost white again!”
Tom Jones, too, remembered the event lucidly in his book, Skywalking. In his recollection, it was the red team of Baker, Wilcutt, and Wisoff who called the blues up to the flight deck to see the eruption. Like Wisoff, Jones thought at first that it was an anvil-shaped thunderstorm, or a clump of dust lofted by high winds, but the smoke-free nature of the surrounding terrain (and the location, Kamchatka) quickly assured them that it was a volcano. Jones had seen it before, during the SRL-1 radar passes, but less than six months earlier Klyuchevskaya had been silent and still under a blanket of April snow. Now, at the end of September, it was in full fury. “We soon had every camera … zeroed-in on the eruption,” Jones wrote, “as Endeavour gave us a dramatic, down-the-throat view of this impressive geology lesson.” In another example of responding to unforeseen events on the ground, the SRL-2 investigators reprogrammed several radar passes over the coming week to scan the eruption site as many as three times per day, and Jones hoped that their work might lead to the implementation of permanent, Earth-orbiting satellites to watch for volcanic events.
By the sixth day of STS-68, as expected, consumables remained at a level sufficient to enable the Mission Management Team to formally extend the flight an additional 24 hours. Endeavour would now land on 11 October. (She would actually touch down at Edwards Air Force Base, Calif., at 10:02 a.m. PDT, after thick cloud at KSC forced NASA to switch landing sites.) The radar’s filing-cabinet-sized payload recorders performed well, although one had to be removed and replaced after it failed to play back properly. Rerouting the data stream between the remaining machines, the repair by Smith and Wisoff was scheduled over a comparatively “empty” Pacific orbital pass. “With the radar inactive over the ocean,” wrote Jones, “Steve and Jeff were well into the repair before we made landfall again. An hour later, the swap was complete and the pair had stowed their wrenches and screwdrivers with almost no loss in science data.”
Orbital life aboard Endeavour herself was exceptionally smooth … and humorous for the irreverent STS-68 sextet. During training, at reviews of the food menus, Mike Baker had expressed his fondness for smoked turkey, which he enjoyed folding into tortillas. Now, in space, this love would return to haunt him. “When Bakes asked what was for dinner, the answer nearly always was … smoked turkey,” wrote Tom Jones. “Noticing our escalating laughter, by the third day our commander was convinced he was the victim of a practical joke instigated either by us or some of his 1985 astronaut classmates. We maintained our innocence and post-flight investigation showed the on-board turkey surplus was his own doing!” To be fair, an entire pantry of other goodies awaited them—shrimp cocktails, horseradish, beef tips and mushrooms, spaghetti and meat sauce, buttered asparagus, strawberries, chocolate puddings—but Jones could not help but wonder what turkey-loving Baker ate for his Thanksgiving meal.
Overall, more than 110 hours of radar observations were acquired in 950 data takes, recorded on 199 digital tapes, and covered an area of over 32 million square miles (83 million square km). One of the bonuses of flying the mission a second time was the ability to use “interferometry” during the final three days of STS-68 and SIR-C/X-SAR data was used to record topographical changes between April and October in California’s Long Valley Caldera and Hawaii’s Kilauea. “Mission Control and our crew combined to perform the most precise orbital manoeuvres ever seen in the shuttle program,” explained Jones, “putting Endeavour in an orbit for the first six days that nearly matched our SRL-1 flight path.” At times, the respective flight paths differed by less than 30 feet (10 meters).
Also flawless were operations with the Measurement of Air Pollution by Satellite (MAPS), which gathered 256 hours of data and achieved a 100-percent success rate. However, the MAPS results reinforced the STS-59 consensus that although carbon monoxide concentrations in the southern hemisphere were relatively low, with exceptionally clean air, the situation worsened in the northern hemisphere, with the highest concentrations to the north of the 40-degree latitudinal band. MAPS also observed intentionally-set fires, monitored by scientists from the University of Iowa and the Canadian Forest Service, to assess their wind fields, thermal evolution, and carbon monoxide emissions and calibrate SRL-2 infrared data. “These fires,” noted NASA in one of its STS-68 news releases, “were planned in advance of the mission and would have been set for forest-management purposes, even if the shuttle mission were not in progress.” Other “controlled” observations included an experimental “spill” of diesel oil and algae products in the North Sea to test SRL-2’s capacity to differentiate between the spill and naturally-produced film caused by the products of fish and plankton.
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 30th anniversary of Mission 41G, an ambitious shuttle flight in October 1984 which featured the first spacewalk by an American woman.