Fwd: 30 Years Since STS-6

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From: "Gary Johnson" <gjohnson144@comcast.net>
Date: April 8, 2013 10:29:21 AM GMT-06:00
To: "Gary Johnson" <gjohnson144@comcast.net>
Subject: FW: 30 Years Since STS-6

 

AmericaSpace

For a nation that explores
April 6th, 2013

30 Years Since STS-6: The Rise of the Challenger (Part 1)

By Ben Evans

Challenger rolls in gloomy midwinter fog towards Pad 39A on 30 November 1982. Photo Credit: NASA

Thirty years ago this week, America's second space shuttle thundered into orbit for the first time. Challenger spent five days circling the Home Planet, deployed a giant communications and data-relay satellite for NASA, and saw the first U.S. spacewalk in nearly a decade. The story of Challenger is naturally overshadowed by the dreadful tragedy which befell her in January 1986, but for several years she was the most-flown orbiter in NASA's shuttle fleet and accomplished several significant feats in rendezvous, retrieval, repair, spacewalking, and as a satellite launcher. Yet perhaps Challenger's most remarkable achievement is that she might never have existed at all and, but for a quirk of fate and timing, might have begun and ended her days as a non-descript structural test article.

In April 1981, Columbia became the first shuttle to travel into orbit, and it had long been hoped that her predecessor, Enterprise, would be upgraded to make her spaceworthy. Enterprise had flown a series of captive and free flights over the California desert in the summer of 1977, and lessons learned during her assembly had been incorporated into the design of Columbia. However, it was recognized that Enterprise weighed too much to carry a payload into orbit. She would need a new set of plans to make her capable of flying in space. Moreover, she had no propulsion systems, plumbing, fuel lines, or propellant tanks. Her main engines were dummies, her payload bay had no attachments for cargo, its doors had no opening mechanism or radiators, and her thermal protection system was little more than polyurethane and fiberglass. Inside her cabin, she had no star trackers or heads-up displays, no aft flight deck or overhead windows, no airlock, no middeck lockers, no galley, no cryogenic fuel cells, and her landing gear was operated by explosive bolts. In short, modifying Enterprise for space would be a long, hard road to tread.

Enter Structural Test Article-99.

Structural Test Article (STA)-99 – later to become known as 'Challenger' from February 1979 – during initial construction. Photo Credit: NASA

Since the original contracts for the shuttle were signed in July 1972, virtually all components were tested to handle significant stress. Limited computing power meant that it was difficult to predict mechanical and thermal loads, and NASA built STA-99 as an engineering tool. After its completion in February 1978, it was tested for a year in a steel rig at Lockheed's Plant 42 in Palmdale, Calif., where conditions of launch, ascent, orbital flight, re-entry, and landing were simulated. The decision to modify STA-99 as a "real" orbiter came about because, unlike Enterprise, it was an incomplete airframe and could be more easily upgraded. Traditionally, manned spacecraft had been tested to 140 percent of their design strength, but NASA engineers recognized that this might cause so much damage to STA-99 as to make it inadvisable to do so. Consequently, Tom Moser and his team at the Johnson Space Center in Houston, Texas, developed an analytical computer model to simulate 3,000 measurement points on the airframe. Their results confirmed that it could easily withstand 140 percent loads, with actual stress distributions in critical areas comparing favorably with pre-test data.

On 29 January 1979, it was official. Under a $1.9 billion contract between NASA and Rockwell International, STA-99 would follow Columbia as the second orbiter. Four days later, on 2 February, the structural test article was renamed "Challenger," in honor of a steam-assisted Royal Navy corvette, which undertook a prolonged cruise from December 1872 until May 1876. In support of this expedition, all but two of Challenger's guns were removed and her spars reduced to increase the availability of space for laboratories, additional cabins, and a special dredging platform. Equipped with specimen jars, alcohol to preserve samples, microscopes and chemical apparatus, thermometers, sounding leads, and sediment collectors, the 80,000-mile Challenger Expedition gathered the equivalent of 50 volumes of information about the Atlantic and Pacific Oceans. Sadly, she was broken up for her copper bottom in 1921 and, today, nothing, save her figurehead remains; this is enshrined in the National Oceanography Centre in Southampton, England.

For the orbiter Challenger, ground evaluations, practice landings, and structural test articles were no substitute for actually operating in space. Before she could be declared ready for flight, Challenger required substantial disassembly and rework at Rockwell International's Palmdale plant in November 1979. Her payload bay doors, aft body flap, and elevons were removed and returned to their vendors for refurbishment, followed by her vertical stabilizer in January 1980. She had been built with a simulated crew cabin, which required the two halves of her forward fuselage to be opened to remove it for modifications. In July 1981, after its own series of improvements, the aft fuselage returned to Palmdale. In physical appearance, the rebuilt Challenger looked similar to Columbia. External appearances, though, proved deceptive. "Challenger would end up some 2,889 lb lighter," wrote Dennis Jenkins, "in spite of having additional operational equipment installed and the more robust structure." This saving was also achieved through the absence of ejection seats, the replacement of several hundred thermal protection tiles with new insulating blankets, the removal of a number of tube-supporting frames, the use of lightweight "honeycomb" for her landing gear doors and vertical stabilizer, and the incorporation of less weighty main engine heat shields.

By December 1982, most of the preparations in support of Challenger's maiden voyage, STS-6, had already been completed; in fact, attached to her External Tank and boosters and partially enshrouded in a gloomy midwinter fog, she crept out to Pad 39A on 30 November. Once there, a critical exercise lay ahead: the Wet Countdown Demonstration Test, which was scheduled to culminate on 18 December in a 15-second firing of her three main engines. This Flight Readiness Firing (FRF) was needed to demonstrate the engines' ability to throttle and gimbal under hydraulic command, just as they would be required to do during launch. Preparations for the FRF proceeded in a manner not dissimilar to a real countdown.

Challenger's three main engines roar to life, though imperfectly, on 18 December 1982 for the first Flight Readiness Firing of STS-6. Photo Credit: NASA

With a minute to go before engine ignition, the NASA commentator picked up the coverage: "T-1 minute and counting … the firing system that releases the sound suppression water onto the pad has been armed … T-50 seconds and counting … T-45 seconds and counting … T-40 seconds and counting; SRB development flight recorders are being turned on … T-37 … gaseous oxygen vent arm will not be retracted on this particular test … T-31 seconds, we have a Go from LPS [Launch Processing System] for auto-sequence start … [Challenger's] four primary flight computers taking over control of the terminal count … final LPS command for engine start will occur at approximately ten seconds … T-15 seconds and counting … "

At this stage, the relative silence and serenity on the pad changed markedly. First, the sound suppression water began to gush across the launch pad from four gigantic "rainbirds." "T-10 … Go for main engine start … we have main engine start … " All at once, a sheet of orange flame gave way to a trio of shock diamonds from the three main engines, combined with a thunderous roar and vast cloud of smoke. The engines ignited in a ripple-like sequence, starting up at 120-millisecond intervals, reaching 90 percent of rated performance within three seconds and hitting the 100-percent mark precisely as the countdown clock touched zero: "T-0, engines throttled at 100 percent, all engines up and burning … T+5 seconds, engines continuing to burn … T+10 seconds … twelve … first [engine] cutoff at T+15 seconds … [Number One] engine cutoff … and engines Two and Three also cutoff at 16.8 seconds … T+25 seconds; GLS [Ground Launch Sequencer] safing now in progress … "

Challenger's main engines were capable of achieving 104 percent thrust—a 4 percent increase over Columbia—which enabled her to transport heavier payloads aloft. In fact, for each one-percent of performance increase over rated thrust, the new shuttle gained 990 pounds of additional payload-to-orbit capability. Challenger's higher thrust was accomplished by incorporating redesigned components into each engine. Such changes became necessary in anticipation of higher temperatures, pressures, and pump speeds that they would encounter at the greater thrust levels. A series of test firings, lasting over 62,000 seconds, had been performed to validate the engines in readiness for their first orbital mission; additionally, the main injectors employed stronger liquid oxygen posts and modified fuel pre-burners to overcome turbine blade erosion and thicker tubes and coolant supply lines to handle higher aerodynamic loads at liftoff.

However, their performance during the FRF was not entirely successful.

As they blazed at full power on 18 December 1982, engineers detected levels of gaseous hydrogen in Challenger's aft compartment which significantly exceeded allowable limits. When it became impossible to pinpoint the cause or location of a leak, the decision was taken to perform a second FRF. New instrumentation was installed both inside and outside the aft compartment to determine whether the hydrogen was leaking from an internal or external source. Suspicion focused initially on the latter possibility, because vibration and current had found their way into the aft compartment, behind the engines' heat shields. By the beginning of 1983, launch was not anticipated before 1 February, at the earliest. However, the second test firing on 25 January, during which the engines were run at 100 percent for 23 seconds, again revealed the presence of leaking hydrogen gas.

The first generation of Tracking and Data Relay Satellites (TDRS) were designed to support the communications and data-relay needs of the shuttle and several other low-orbiting spacecraft. Image Credit: NASA

Several more days of troubleshooting eventually identified a cracked weld in tubing leading to the uppermost (Number One) engine, which was promptly removed on 4 February. A replacement was delivered, but initial inspections in the VAB uncovered a leak in an inlet line to its liquid oxygen heat exchanger. Before it could even be installed onto Challenger, the "replacement" was itself replaced by a third engine. After more checks, including a 500-second, full-flight-duration test firing, it was dispatched from Mississippi to Florida on 3 March and fitted a week later.

Unfortunately, while this work was ongoing, painstaking efforts were underway to ensure that the other two original engines did not exhibit any leaks—and the bad news seemed to be that they did! Towards the end of February, hairline cracks were found in one of the fuel lines to the left-hand (Number Two) engine, and borescope observations of the right-hand (Number Three) engine revealed a similar problem. Both were removed, returned to the VAB and repairs were conducted. With the arrival of the replacement engine from Mississippi, all three were installed by mid-March and verified as being ready to support a launch. The leaks from the Number Two and Three engines were apparently caused by a generic "seepage" in an inconel-625 tube situated in their ignition systems. It apparently occurred underneath a protective sleeve brazed onto a small hydrogen line which sent fuel to the engine's augmented spark igniter. The sleeve was designed to counter possible chafing. After practicing cutting off the sleeve on the Mississippi plant's test stand, Rocketdyne technicians replaced it with a non-sleeved inconel-625 tube on each of Challenger's engines.

By the time their orbiter was finally declared "flight ready," the four-man crew of STS-6 had already performed their Terminal Countdown Demonstration Test, and, on 5 February, the payload for their five-day mission—the first in a series of large Tracking and Data Relay Satellites (TDRS), attached to an Inertial Upper Stage (IUS) booster—was transferred to the launch pad and inserted into the payload bay. The impressive TDRS/IUS combo filled three-quarters of the bay and was by far the largest payload carried by the shuttle. After deployment, ten hours into the mission, the two-stage, solid-fueled IUS would boost the TDRS into a geostationary transfer orbit and finally circularize that orbit at 22,000 miles above Earth. Before launch, the satellite was alphabetically designated "TDRS-A," but when fully operational it would be numerically renamed "TDRS-1."

In spite of the engine leaks, the payload had originally been moved to the pad a couple of days after Christmas, but when it became clear that Challenger would not be flying in January 1983 and another FRF would be needed, it was returned to the Vertical Processing Facility for temporary storage. By the end of the first week in February, it was back at Pad 39A and ensconced in the Payload Changeout Room of the Rotating Service Structure for installation aboard the shuttle. Then, on 28 February, strong winds whipped across the launch area and breached a weather seal between the changeout room and Challenger's payload bay, depositing a fine layer of particulate material on the satellite's solar array deployment springs. This resulted in an additional delay from 26 March until 4 April.

After thorough inspections, TDRS-A was removed and carefully cleaned, before being replaced aboard the shuttle on 19 March. The plan was to follow up with the second TDRS in the summer of 1983. They would provide near-continuous voice and data relay traffic between Mission Control and future shuttle crews, as well as support an ambitious series of future scientific missions, including the Hubble Space Telescope. Unfortunately, a long and difficult road would have to be travelled before TDRS-A could enter operational service.

 

Copyright © 2013 AmericaSpace - All Rights Reserved

 

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AmericaSpace

For a nation that explores
April 7th, 2013

30 Years Since STS-6: The Mission of the 'Geritol Bunch' (Part 2)

By Ben Evans

 

It was Paul Weitz (seated left) who decided on the F-Troop moniker for his crew, whose number included (left to right) Don Peterson, Story Musgrave, and Karol "Bo" Bobko. Photo Credit: Joachim Becker/SpaceFacts.de

Thirty years ago this week, the youngest member of the United States' shuttle fleet took to the skies on her maiden voyage. As described in yesterday's history article, Challenger had risen from the bones of a structural test article—used to establish baseline thermal and mechanical stress data—and been extensively upgraded to render her capable of traveling into space. Four years later, on 4 April 1983, she was finally ready to go. Juxtaposed against Challenger's youth, however, were the combined ages of the four men who would ride STS-6, call her home for five days, spacewalk from her, and launch a giant NASA communications satellite. Commander Paul Weitz had wryly dubbed his crew "The F-Troop" … but the jokesters in the astronaut office countered with their own moniker: Geritol Bunch.

The F-Troop nomenclature came from a television series about an aging cavalry unit and was reflective of the fact that the men of STS-6 were the sixth ("F") shuttle crew, as well as honoring their military heritage. Weitz even had tongue-in-cheek photographs produced, including a crew portrait with the quartet clad in Civil War attire: cavalry hats, braces, red and white neckties, swords, a Winchester lever-action rifle, a bugle, and a flag, emblazoned with the legend "F-Troop." (According to STS-6 Mission Specialist Don Peterson, the sword once belonged to a lieutenant in Napoleon's army.) Another image of the crew had them wearing vintage spectacles. In truth, the aged cowboy image was appropriate, because Weitz, Peterson, and crewmates Karol "Bo" Bobko and Story Musgrave were the oldest spacefaring crew to date, with a combined age of 191 years! Behind their backs, other astronauts snickered that they were "The Geritol Bunch"—after the dietary supplement famously associated with aging—but Peterson, for one, did not remember that nickname with as much fondness. "Maybe that was something everybody said about us when we weren't around," he told the oral historian, "but when we were in orbit, somebody was talking about 'how old you guys are'. We had a bunch of F-Troop pictures and I couldn't resist, so I said, 'We're not going to show these to anybody under 35 when we come back! You wise-asses won't see them!"

The STS-6 participate in a training session in the flight deck simulator. In the front seats are Weitz (left) and Bobko, with Musgrave in the center flight engineer's position and Peterson to his right. Photo Credit: NASA

When he was assigned to STS-6 in March 1982, it seemed inconceivable that Peterson and fellow Mission Specialist Musgrave would prove to be the first men to perform an EVA from the shuttle. The problems encountered by STS-5 crewmen Bill Lenoir and Joe Allen changed all that, and in late November 1982, Flight International reported that it was "likely" that the EVA would be rescheduled to STS-6. NASA was well aware that the new space suits needed to be thoroughly tested in readiness for the Solar Max satellite repair—an ambitious shuttle mission, scheduled for early 1984—and it was decided to defer Lenoir and Allen's EVA to STS-6. According to NASA, the addition of the spacewalk caused the STS-6 mission to be extended from an original two days to five days.

"It didn't give us much time to train," Peterson recalled. "I didn't have much experience in the suit, but the advantage was that Story was the astronaut office's point of contact for the suit development, so he knew everything there was to know. He'd spent 400 hours in the water tank, so he didn't really have to be trained!" By his own admission, Peterson's EVA training "was pretty rushed." He recalled being underwater on a mere 15-20 occasions. However, the tasks for their excursion were relatively straightforward evaluations of the performance of the suit and of the airlock; if any of the equipment tests went awry, he and Musgrave could quickly curtail their spacewalk and return to Challenger's cabin.

For the spacewalk on STS-6, Musgrave would take the lead as "EV1," wearing red stripes on the legs of his suit, and although it was scheduled to last for barely four hours, the preparation and conduct of the excursion consumed the crew's entire working day on 6 April 1983. Aided by Pilot Karol "Bo" Bobko, who would choreograph the spacewalk, Musgrave and Peterson rose early that morning to begin readying their suits and equipment in Challenger's airlock. They spent three and a half hours "pre-breathing" to avoid an attack of the bends and clear dissolved nitrogen from their blood.

Challenger roars into orbit on her maiden voyage. Photo Credit: NASA

Since reaching orbit, two days earlier, on 4 April, Weitz, Bobko, Peterson, and Musgrave had repeatedly checked their equipment for the long-awaited EVA: testing a third, "spare" upper torso in accordance with flight rules, verifying that oxygen regulators and fans operated normally, inspecting for leaks and confirming that communications were satisfactory. In fact, the only problem raised was a need to replace some flat floodlight batteries. With everything in place, suit donning began and, in true F-Troop fashion, it ran as crisply as a military campaign. At length, at 4:05 p.m. EST, Musgrave initiated the final depressurization of the airlock and, 16 minutes later, pushed open the outer hatch into the payload bay. The plan called for three hours of activities, but he and Peterson had up to six hours' worth of consumables. Entering the overwhelmingly floodlit bay for the first time, one of his first comments, somewhat understatedly, was that "it's so bright out here!"

Their time outside may have been limited, but the experience would remain with both men for the rest of their lives. "You remember little things like sound," Musgrave told a post-flight press conference. "Even though there's a vacuum in space, if you tap your fingers together, you can hear that sound because you've set up a harmonic within the space suit and the sound reverberates within it. I can still 'hear' that sound today. But the main impression is visual: seeing the totality of humanity within a single orbit. It's a history lesson and a geography lesson; a sight like you've never seen."

The spacewalkers' first task was to tether themselves to slidewires running along the sills of the payload bay walls (one on either side, to prevent mutual interference) and move towards the aft bulkhead, in the process evaluating their ability to handle tools. During the spacewalk, the slidewires were used as part of a safety procedure to prevent Musgrave or Peterson from inadvertently floating away from the shuttle. Meanwhile, the two men began conducting their first "real" evaluations of the new suits: their comfort, dexterity, ease of movement, and the performance of their communications and cooling systems and the payload bay floodlights. One of very few concerns expressed by Peterson after the mission was that "the gloves are hard to work in—extremely stiff—and I had to get my hands strengthened with a little hand exerciser." Despite this, both astronauts reported that the suits' mobility enabled them to satisfactorily accomplish each of their tasks. Most of their work focused on identifying suitable locations from which future spacewalkers could best work on the malfunctioning Solar Max, and on practicing some of the intended repair techniques.

Story Musgrave (left) and Don Peterson perform the shuttle program's first EVA. The large tilt-table, used earlier in the mission to deploy the first Tracking and Data Relay Satellite, is visible in the background. Photo Credit: NASA

This kind of work was essential, not only for the successful reactivation of the $240 million solar observatory, but also for future servicing missions to the Hubble Space Telescope. Musgrave and Peterson finally evaluated the manual system for closing Challenger's payload bay doors in the event of a failure. This involved using a hand-operated winch, attached to the forward bulkhead, and was performed both with and without foot restraints. It was during tests of the winch line that they encountered difficulties. "Story got the rope hung over something," Peterson recalled, "and couldn't release the winch. It was under a lot of tension. There was some talk about how we could get this thing loose so we could get it restored. We couldn't just leave it where it was because it was on the rollers that were used to latch the doors down." After the crew's suggestion to cut the Kevlar line was rejected by Mission Control, Musgrave eventually pried it free with his gloved hands.

At another point during the spacewalk, in what NASA labeled a "high metabolic period," Peterson received a "high O₂ usage" warning on his chest display. Although the message cleared quickly and did not recur, it was attributed to flexure within the suit and his high work rate. "I stopped and said 'I've got an alarm'," Peterson recalled. "Story stopped what he was doing and came over. We were trying to check what was going on and the seal popped back in place and the leak stopped. Now, in those days, we didn't have constant contact with the ground. They weren't watching at the time that happened. By the time we dumped the data from the computers to the ground that showed the leak, we were back inside the orbiter." It seemed that Peterson's alarm was caused by overworking and breathing excessively rapidly; this depleted his oxygen, forced a higher feed level, and triggered the warning. Biomedical data confirmed that his heart rate was around 192 beats per minute whilst cranking the wrench, but Peterson doubted he could have worked so hard as to breathe enough oxygen to set off the alarm. In spite of the problems, both Musgrave and Peterson clearly savored the opportunity to venture outside the vehicle in orbit.

After returning to the airlock, the data on Peterson's alarm was pored over by flight controllers with dismay. "They were upset about it," he said later, and, this being the suit's first outing in space, the astronauts would almost certainly have been directed back to the airlock had the problem occurred whilst in communication with Mission Control. At the time of STS-6, however, the shuttle still relied heavily on a network of ground stations to relay its communications and data traffic during part of each orbit, typically only 20 percent. It was therefore ironic that on STS-6, which, in Peterson's mind, benefitted from having gaps in communications with the ground, the first in a series of huge Tracking and Data Relay Satellites (TDRS) had been deployed to improve communications with future shuttle crews. It was optimistically hoped that, after the launch of a second, identical satellite on STS-8 later in 1983, it would be possible to talk to crews not only during the majority of their orbital time, but also throughout re-entry, eliminating the radio blackout normally experienced during this phase of the mission. Moreover, the existing network of 20-year-old ground stations, which were capable of supporting barely one or two spacecraft at a time, could be retired to save money. Once in place, the TDRS network was expected to be capable of supporting the shuttle and up to 26 other satellites simultaneously.

So it was that the men of STS-6—notwithstanding their ages—contributed enormously to the future of the shuttle program and the future of NASA's space exploration program. For without Musgrave and Peterson's EVA, the increasingly complex future steps in spacewalking, such as the repair of Solar Max, the servicing of the Hubble Space Telescope, and the assembly of today's International Space Station, would have been rendered far more difficult. Without TDRS, the crews of the shuttle and station would be severely limited in their ability to transmit voice and data back to Earth … as would numerous other critical scientific satellites in orbit. The "Geritol Bunch" opened up the shuttle's capabilities to three decades of remarkable accomplishment … and set humanity on a path to the future.

 

Copyright © 2013 AmericaSpace - All Rights Reserved

 

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