[AS] Fixing Solar Max: 30 Years Since Mission 41C

[Orionid]

Fixing Solar Max: 30 Years Since Mission 41C (Part 1) (1)
By Ben Evans, on April 5th, 2014


Thirty years ago this week, Mission 41C put the shuttle’s capabilities to the test. In a single flight, the reusable vehicle demonstrated its capacity to support satellite deployment and retrieval, rendezvous and proximity operations, untethered spacewalking and robotics … and served as a highlight of the ingenuity of the human spirit. Photo Credit: SpaceFacts.de

Thirty years ago this week, the shuttle launched on arguably its most ambitious mission to date: a mission which would demonstrate the reusable orbiter’s capabilities of rendezvous, retrieval, satellite repair, and spacewalking with the Manned Maneuvering Unit (MMU) “jet backpack” in spectacular fashion and enhance NASA’s confidence in anticipation of future flights to service the Hubble Space Telescope (HST). Originally designated “STS-13,” and later redesignated “STS-41C,” the reader would be forgiven for thinking that the mission might have been dogged with ill-fortune. In fact, for the five-man crew, the question of good or bad luck even factored into their impromptu mission patch. On Mission 41C in April 1984, the astronauts salvaged NASA’s crippled Solar Maximum Mission (SMM) spacecraft—nicknamed “Solar Max”—and after initial difficulties repaired and rejuvenated it during two magnificent EVAs.

Perhaps by design or circumstance, the scheduled launch date for the “unlucky” mission had moved from Friday, 13 April 1984, (according to NASA’s November 1982 shuttle manifest) to Wednesday, 4 April, by the end of 1983. Eventually, Challenger launched on 41C on Friday the 6th. The absurdity of NASA’s efforts to avoid misfortune befalling the flight had already led to the introduction of a bizarre, 13-free numbering system, in which missions would be designated with a series of letters and digits. Although 41C was originally STS-13 in the sequence, the cancellation of two other missions meant that it actually became the 11th flight in shuttle program history. The issue of bad luck was taken a stage further by the mission’s pilot, Dick Scobee, who designed an unofficial crew patch with a menacing black cat, emblazoned with the numeral “13,” surrounded by lightning bolts and a shuttle hurtling into space from beneath its diabolical belly. Scobee’s crewmate, Terry Hart, later admitted that the astronauts had coffee mugs made with the “official” 41C patch on one side … and the “unofficial” one on the other.

When the crew was announced by NASA in February 1983, one of them was unavailable to begin direct training until later that year. Commander Bob Crippen was preparing to lead STS-7 in June 1983 and his stint on the Solar Max repair would make him the first person to fly the reusable spacecraft three times. He would be joined by pilot Scobee and mission specialists Hart, James “Ox” van Hoften, and George “Pinky” Nelson.

In contrast to several other shuttle crews, whose payloads were being endlessly juggled, the two main objectives of 41C—repairing Solar Max and deploying a huge, bus-sized satellite called the Long Duration Exposure Facility (LDEF)—had remained static ever since the flight was approved by NASA Headquarters in August 1982. “Our mission was so specialized,” explained Crippen in a NASA oral history interview, “that when we were going up to get Solar Max … it was not reasonable that we could change it.” LDEF, too, was so large that it would have been difficult to remove it from the manifest and put it onto another flight. In fact, the satisfactory performance of the Canadian-built Remote Manipulator System (RMS) mechanical arm was critical, not just for the Solar Max repairs, but also for the deployment of LDEF.


Mission 41C’s official crew patch included LDEF (center) and Solar Max (lower), together with the MMU-equipped EVA team. Image Credit: SpaceFacts.de

The satellite took the form of a 12-sided structure, and, as its name implied, it was designed to house experiments which required long-term exposure to the hostile environment of low-Earth orbit. No one could possibly have foreseen, at the time of LDEF’s launch, exactly how long it would remain in space before being retrieved by another shuttle mission and returned to Earth. NASA intended to collect the satellite during Mission 51D in February 1985, but that was repeatedly delayed, and by the time Challenger exploded the retrieval had been rescheduled for Mission 61I in September 1986. In fact, it would not be recovered until January 1990, by which point it was only weeks away from an uncontrolled and fiery re-entry. It was a peculiar object, measuring 29.8 feet (9.1 meters) long by 13.8 feet (4.2 meters) wide and weighing 20,990 pounds (9,520 kg). At its most basic, it consisted of an intricate frame of aluminum rings and longerons, loaded with trays for 57 experiments, whose disciplines ranged from materials and structures to power and propulsion and from science and technology to electronics and optics.

Deployment of LDEF occurred 24 hours into Mission 41C, on 7 April 1984, and, although Terry Hart admitted “that was exciting,” it hardly compared with his first and only shuttle launch a day earlier. “It was a clear, cool morning,” he said of Friday the 6th, “and we went through the traditions of having breakfast together and there was always a cake there for the crew before they went out. Next, we went out to the launch pad and up the elevator. As usual, people don’t say much in elevators—whether you’re in a hotel or on the launch pad—and you watch the numbers tick by and, instead of floors, they do everything in feet in the launch pad elevators. When you walk across the gantry to board the shuttle, you can look down into the flame trench. The obvious thing that’s striking you is that this is for real: we’re going to go! Everything was pretty smooth on our launch countdown. We got strapped in and, again, the guys strapping us in were a lot of the same guys that strapped in Al Shepard on his Mercury flight [in May 1961].”

By the time of launch, the 41C crew had spent 14 months together as a team and all five men would agree that this mission was the mission that everyone wanted. With a background as a pilot in the Air Force Reserve and master’s degrees in mechanical and electrical engineering, Hart had spent his first few years as an astronaut working on new rendezvous procedures. Although rendezvous had been accomplished during the Gemini and Apollo programs, bringing the orbiter alongside Solar Max for repairs was quite different. “The shuttle was this big truck,” he told the NASA oral historian, “and it had a very limited amount of fuel on board, whereas the Apollo command module and Gemini were like sports cars. They could just zip around and change orbits much more readily, especially in close, around an object, they could just kind of move right around with great ease. If we started to do much of that, we’d very quickly run out of fuel and have to de-orbit, so we had to come up with new design trajectories and procedures to accommodate that difference to ensure that we were flying the most fuel-optimal approach during a rendezvous.”

When he was assigned to 41C, Hart’s initial suspicion was that he would be involved in the rendezvous, and not the EVAs, but the word on the astronaut office grapevine was that James van Hoften (nicknamed “Ox,” due to his physical height and size) was too big to perform a spacewalk. Nevertheless, one day Bob Crippen approached Hart and told him that his expertise was needed to perform the RMS work and the rendezvous. The EVAs would be done by van Hoften and Nelson.


The crew of Mission 41C. From the left are Bob Crippen, Terry Hart, James “Ox” van Hoften, George “Pinky” Nelson, and Dick Scobee. Photo Credit: SpaceFacts.de

Throughout 1983 and into the spring of 1984, Hart’s attention was entirely devoted to preparing for the intricate RMS operations in support of the Solar Max repair and the LDEF deployment. “The arm engineers wanted to make sure we properly tested the arm moving such a large object,” he explained, “so they could understand that it was going to be able to do what it was designed to do, so I spent a lot of time working with the engineers to make sure that I was doing everything that they wanted done during testing.” Much of the simulation work was done at the Johnson Space Center (JSC) in Houston, Texas, and at RMS prime contractor Spar Aerospace’s facility in Toronto, Canada, and Hart found himself routinely testing the flex of the arm with the huge LDEF attached and capturing Solar Max in a rotating mode.

One of Hart’s responsibilities during Challenger’s ascent to orbit was to act as a “second flight engineer”; seated behind Dick Scobee, he assisted van Hoften with checking off the milestones and monitoring the procedures needed in the event of problems. There were none. “Off we went,” he said of the 8:58 a.m. EDT liftoff, “right on time on a perfectly clear day. I had a couple of surprises: the shake, rattle and roll of the Solid Rocket Boosters for the first two minutes is a very low-frequency rumble; just a tremendous sense of power. You can look back over your shoulder or look out the top window when you’re in the flight deck and watch the world disappearing behind you. Very quickly, the SRBs taper off and separate and that was the surprise I had, because your G-loading builds up close to 2.5 G as the boosters reach their peak thrust. As the solid rockets burn off and separate, the sensation that you have at that point I wasn’t quite prepared for, because you go from 2.5 G back to about one and a half. The sensation you have is that you’re losing out, that you’re falling back into the water! You don’t think you’re accelerating as much as you should be to get going and, of course, I’d worked on the main engine program anyway, so I was very familiar with what the engines could do or not do. I think in the next minute I must have checked the main engines to make sure they were running, because I’d swear we only had two working: it just didn’t feel like we had enough thrust to make it to orbit! Then, gradually, the External Tank gets lighter and as it does, of course, with the same thrust on the engines, you begin to accelerate faster and faster. After a couple of minutes, I felt like, yes, I guess they’re all working.”

Indeed, Challenger’s fifth launch had proceeded without incident. The External Tank behaved superbly and the performance of the main engines, read NASA’s post-mission report, “appeared to be normal.” The only deviation was when the engines throttled down to 67 percent, rather than the predicted 71 percent, as Challenger passed through maximum aerodynamic pressure (known as “Max Q”), a minute into the flight; this lower level was later attributed to a higher than anticipated SRB impulse during the first 20 seconds. Chase aircraft also revealed that one of the main parachutes on the right hand booster failed to inflate, although both boosters were recovered successfully.

Experiencing the launch from a somewhat different perspective, seated on Challenger’s darkened middeck, next to the side hatch, George “Pinky” Nelson did not have the luxury of viewing the ascent through the wrap-around windows of the cockpit as Crippen, Scobee, Hart, and van Hoften could. Still, he recalled the rapidity of his first ride into orbit. He was also able to peer through a tiny circular window in the side hatch and capture a fleeting glimpse of the enormous, controlled explosion that was underway outside. “I could see the tower go by and the sky and horizon as we ascended,” he told this author in an email correspondence from March 2006. “It was a bit lonely down there, but Crip kept a running commentary on how the launch was going, since we were all rookies, but him. That helped keeping up with the events. My first experience with weightlessness was problematic. I’d had many flights on the KC-135 aircraft and hundreds of hours in the water tank, so was familiar with the sensations of weightlessness. I remember how pleasant a sensation it was and how surprised I was that I didn’t get sick!”


Pictured from the perspective of the departing crawler, the 41C stack has just been deposited on Pad 39A in March 1984. Photo Credit: SpaceFacts.de

On his first voyage into space, Nelson adapted well to the new environment. Unfortunately, the same could not be said for Terry Hart. Mission 41C marked the shuttle’s first “direct insertion” ascent. In other words, only one Orbital Maneuvering System (OMS) engine firing—rather than two—was needed to circularize Challenger’s orbit at an altitude of around 330 miles (530 km). Previously, when less performance data was available for the main engines and some targeting precision was lacking, an initial OMS burn was made to raise the apogee, followed by another, half an orbit later, to raise the perigee and circularize the orbit. On 41C, however, the ascent was to achieve an initial orbit with an apogee at the desired altitude without performing the OMS-1 burn, and the OMS-2 burn provided circularization. This enabled the engines to provide more energy and permit the easier use of on-board software.

The high orbit was needed for the rendezvous with Solar Max and also simplified the post-insertion procedures for the astronauts. “It’s a much easier task from a crew standpoint,” explained Bob Crippen, “because you’re pretty busy there right after main engine cutoff and this took away some work, so it was a neat thing to try.” As Crippen, Scobee, and van Hoften busied themselves with readying their ship for orbital operations, Hart was granted the opportunity to unstrap and leave his seat to photograph the jettisoned External Tank as it tumbled Earthward. It was perhaps fortuitous that the LDEF deployment was still a day away, because Hart’s initial euphoria turned rapidly into a severe dose of space sickness.

“I had never had any motion sickness,” he recalled years later. “I was a fighter pilot and could do anything in an airplane. I had a light airplane I used to do aerobatics in and nothing ever bothered me in terms of flying or riding a boat or a train or a car or whatever. I wasn’t weightless for more than three minutes and I knew I was in trouble! I could just tell my whole gastro-intestinal system was going into high-speed reverse and I didn’t understand it because, psychologically, I was elated. Maybe I got up too quick and started moving around or started looking out the window too soon, but for the whole first day I was really out of it.

“There were some things I had to do that first day, but they were minimal,” Hart continued. “I had to unstow the RMS and barely made it through that. I really was totally incapacitated for the first day and I tried the usual drugs that they give you to help, but I had it so bad that nothing helped at all. That night, when we got ready to go to sleep, I was exhausted, really depleted. I remember falling asleep and was asleep for maybe a half hour, when I dreamt that I was falling and I remember reaching out to grab something and I did it with such force that I ripped my sleeping bag. I don’t think the other guys were asleep yet, but if they were, I woke them up when I yelled out. That was kind of a low spot and, after that, I acclimatized. I had some kind of fundamental neurological brainstem reaction to a fear of falling. I think my initial sickness, after three or four minutes of weightlessness, was something that triggered my basic instincts of falling, even though it wasn’t conscious. I couldn’t detect it consciously and I think it stayed with me for that first night. The next day, I was able to do all my duties, but it was just a terrible experience. I never heard anyone else relate such a bad experience.”

[Orionid]

Fixing Solar Max: 30 Years Since Mission 41C (Part 1) (2)


Challenger rockets into orbit on 6 April 1984. Photo Credit: SpaceFacts.de

Fortunately, by Day Two, Hart had recovered sufficiently to take the lead in the LDEF deployment, successfully releasing it into space at 12:19:27 p.m. EDT, as Challenger travelled “upside down,” her open payload bay facing Earthward. To activate its many investigations, he firstly grappled the satellite by its so-called Experiment Initiation System fixture and then regrappled LDEF’s second grapple fixture to actually pick it up and deploy it. “The concern,” he remembered, “was that I was going to get it stuck, then we couldn’t close the payload bay doors and couldn’t come home. Crippen and I were trained on the RMS, with him watching and making sure everything was going well. First, I had to lift it out “straight” and then the arm did everything it was supposed to do. I put it back in the payload bay, just to make sure it would go back in before I lifted it out one more time to deploy it. We left it out on the arm and did some slow maneuvers to verify all the dynamics that the engineers wanted to understand about lifting heavy objects out of the Shuttle. Then, we very carefully deployed it. It wasn’t detectable at all when I released it; totally steady and we very carefully backed away and got some great photographs.” As LDEF drifted serenely into the inky blackness, Crippen and Scobee pulsed the shuttle’s thrusters to increase their distance from the satellite, confirming the separation rates using the Ku-band radar.

Pinky Nelson’s assignment to perform two EVAs, with van Hoften, in support of Solar Max had come at a restless time for himself. “This was the mission I wanted,” he said of 41C, “because it had EVAs. I remember meeting with Crippen shortly after that, in one of the little conference rooms at JSC, where he doled out the assignments and gave me the role of flying the MMU, which made my year! Here was a mission with four military pilots and they decided to let me fly the maneuvering unit. Training for that mission was really fun. It was really the most complicated spacewalk that had ever been conceived and a real precursor to the much more complicated work they’ve done on the Hubble Space Telescope. We worked hard to choreograph this repair and we had it down to a dance. We knew all the steps and who was where when, what tools were needed and how we moved things.”

Ox van Hoften was also elated by the assignment to Mission 41C. Years later, he speculated that Bruce McCandless, who had worked extensively on developing procedures for the Solar Max repair—and who performed the first untethered spacewalk with the MMU jet backpack in February 1984—was “unhappy” that he did not receive the assignment. “He went up and did the first flight,” van Hoften told the NASA oral historian, “but the real mission was not to just go out and fly the MMU around; it was to go out and fix the satellite.” At first, it seemed that van Hoften himself might not be making the EVAs. “About that time,” he explained, “they started running into money crunches and they said that they wanted to limit the space suit sizes, because originally the [space suit] that they made was meant for everybody. It was supposed to be from the 5th percentile female to the 99th percentile male. Well, I was the biggest guy they ever had, so at some point they decided they weren’t going to make extra-large suits anymore; they were just going to make small, medium and large, and those of us on the fringes weren’t going to get to do it.” It was a disappointment, but van Hoften still had a spot on what he described as “one of the premier missions.” At length, it was George Abbey who came to the rescue, insisting that van Hoften should do the EVAs with Nelson and ordering that a pair of extra-large suits should be manufactured.

For the next 14 months, the crew trained with an almost obsessive focus, totally immersed in the minutiae of the mission, and van Hoften is not alone in having lamented the effect that this imposed on families, particularly wives and children. “But the nice part,” he told the oral historian, “is that everyone is kind of in that boat, so there’s a whole community there to support everybody.” Every week, Nelson and van Hoften would don training versions of their suits and descend into the water tank at JSC to simulate removing equipment from Solar Max and installing new components … and their families were invited into the space centre to watch them at work. By the late spring of 1984, they were ready.


Equipped with a Manned Maneuvering Unit (MMU), astronaut George “Pinky” Nelson approaches the slowly-spinning Solar Max on the morning of 8 April 1984. Photo Credit: SpaceFacts.de

Not only had they nailed down the mission to perfection, but, in Bob Crippen’s case, even the pre-flight photographs turned into something of an art form. “I remember the day we posed for our crew picture,” recalled Terry Hart, “and all put our blue flight suits on and took maybe 20 pictures, trying to get the right expressions on our faces! Then, the tradition is that you bring them down to the astronaut office and ask the secretaries to pick which one is best. In one of them, one of us would be winking or our smile would be crooked or something like that. Every one of us had maybe a 50 percent “hit” rate on the pictures, having the right expression on our face. Then we looked at Crippen, who’d been in the public eye from STS-1 until this mission. Every photograph had the same expression on Bob Crippen’s face! He had it down pat. He knew exactly how to smile!”

As Nelson and van Hoften worked in the WET-F tank to perfect their orbital repair work, Crippen, Scobee, and Hart busied themselves with rendezvous procedures in the shuttle simulator. In Hart’s case, the RMS was another of his responsibilities. This had given trouble on its previous mission, when the wrist yaw joint failed. Although the cause of that failure was still unknown when 41C lifted off, the faulty arm (serial number 201) had been replaced by another (serial number 302) and verified on the ground.

Despite the importance of deploying LDEF, it was overshadowed by the repair of NASA’s malfunctioning Solar Max. In fact, virtually every shuttle flight since November 1982 had helped to lay the groundwork for the reusable spacecraft’s most ambitious mission so far. Extensive tests had been undertaken to validate the RMS, requiring it to manipulate larger and more bulky payloads, and three spacewalks had verified the performance of the suits, tools, and MMUs, together with the ability of astronauts to work effectively with them. In particular, Nelson and van Hoften paid a great deal of attention to the MMU assisted spacewalks undertaken on Challenger’s 41B mission. Crippen and Scobee, meanwhile, perfected the challenging rendezvous technique.

Their quarry—Solar Max—had launched atop a Thor-Delta rocket from Cape Canaveral Air Force Station, Fla., in February 1980, and was to spend a decade (essentially a full “solar cycle”) utilizing a battery of gamma ray, X-ray, ultraviolet, and other instruments to provide broad spectral coverage of the mechanisms responsible for causing solar flares. Ironically, only months after the MMU fabrication contract had been awarded to Martin Marietta, an unfortunate series of circumstances conspired to lead to the backpack’s first operational use. One of Solar Max’s instruments, a white light coronagraph and polarimeter, provided by the High Altitude Observatory of Boulder, Colo., worked satisfactorily from March to September 1980, then suffered an electronics failure which left it inoperative. Then, in December, a fuse blew in Solar Max’s attitude control system, causing it to “wobble” and rendering it incapable of pointing precisely toward the Sun.

All was not lost, however, because it had been designed as one of several Multi-Mission Modular Spacecraft (MMS), part of NASA’s vision to permit certain satellites to be serviced by the shuttle. Measuring 13.1 feet (four meters) long and fitting into a circular envelope some 7.5 feet (2.3 meters) in diameter, the 5,100-pound (2,315-kg) Solar Max had two sections: a payload module, laden with eight powerful solar instruments, and the MMS for attitude control, power, communications, and data handling functions. In view of its problems, Solar Max was placed into a slowly spinning “safe” mode, which it maintained for three years, and although three of its instruments returned valuable data, the primary mission was effectively suspended. Its Hard X-ray Imaging Spectrometer malfunctioned in June 1981 and was left useless. However, by keeping the spacecraft rotating at one degree per second and aiming its solar panels constantly in the direction of the Sun, NASA engineers kept it alive in a dormant state. In the meantime, as efforts got underway to build a replacement electronics box for the white light coronagraph and polarimeter, it was decided to incorporate changes into the new device to improve the instrument’s imaging resolution (which had begun to degrade as early as July 1980) and permit space-to-ground communications through the Tracking and Data Relay Satellite (TDRS) network.


Cursed by bad luck? Although Mission 41C was the 11th shuttle flight, it was still saddled with the internal NASA designation of “STS-13.” On 8 April 1984, the crew’s mission to capture and repair Solar Max seemed doomed to failure. Image Credit: SpaceFacts.de

By the morning of 8 April 1984, after executing a series of thruster firings to set up an approach to their target, the 41C crew glimpsed Solar Max as a steadily brightening star. Crippen halted Challenger about 230 feet (70 meters) from the slowly spinning satellite, as Nelson and van Hoften completed donning their spacesuits. They entered the payload bay at 9:18 a.m. EDT. “There’s no comparison to getting into a suit and being outside,” said van Hoften. “It was just a whole new world. You open the hatch and you look out and … there goes Africa! It’s just so distracting that it took probably 20 minutes until you start saying ‘Hey, we’ve gotta get back on track here.’ But it was just amazing. We had done so much work in the water tank, but in zero gravity it’s really a lot different.” The plan was for Nelson, designated “EV1,” to fly the MMU out to the satellite and dock himself to its mid-section using a Trunnion Pin Attachment Device (TPAD).

Although Solar Max was not spinning too fast for Hart to grapple it with the RMS, “we felt it was more prudent to have Pinky fly over with a backpack, dock himself to the satellite, stabilize it and then I could grab it with the arm.” “Donning the MMU went very smoothly,” Nelson recalled, “just like training. Ox and I had practiced so intensely that it was more like a well-choreographed dance than anything else. Once I left the docking station in the payload bay, the MMU flew just like the simulator at Martin Marietta in Denver, where we trained. I had been very well briefed by Bruce McCandless about the few differences between the simulator and the real unit, such as “chatter” when accelerating, so I didn’t experience anything unexpected.”

Precisely on time, after a 10-minute solo flight, Nelson arrived in Solar Max’s vicinity and used the MMU’s thrusters to gently match its rotation. Unfortunately, when he moved in to mate his TPAD with the satellite, it did not clamp properly into place. “We didn’t know what was wrong,” explained Hart, “but, being mechanical engineers, we said ‘If a small hammer doesn’t work, use a bigger hammer!’ So Pinky went in twice as fast the next time and he hit again and bounced right off again.” A third try, which imparted yet more force, also failed. Had the TPAD been affected by the cold of orbital darkness? Its temperature after removal from the payload bay storage locker had not been maintained, but pre-flight tests and actual flight experience on Mission 41B determined that it was capable of withstanding at least a few hours in the frigid darkness.

Low temperatures did not seem to be a contributory factor. Furthermore, when Nelson pushed the TPAD against Solar Max, its trigger activated and released a pair of jaws in an attempt to grab onto its quarry. This ruled out a malfunction in the docking hardware. However, as the first EVA continued, the crew saw another problem brewing: Nelson’s efforts had jostled Solar Max out of its previously slow spin and Crippen asked him to grab a solar panel to steady it. The gyroscopic effect of this action worsened matters, and, with his MMU’s nitrogen supply running low, Nelson returned to Challenger. Instead of revolving gently, like a top, Solar Max was now tumbling unpredictably around all three axes.

Four tries by Hart to grapple it with the RMS proved fruitless, and Crippen opted to withdraw to a distance of about 100 miles (160 km) until a new strategy could be thrashed out. “The grappling pin I had to grab was underneath one of the large solar panels, so I could only get [the arm] there under certain conditions,” recalled Hart, “and it was very hard to predict how it was doing. I got close to it and I was maybe a foot away from getting it, but I’d reach some limit on the elbow or the wrist. I couldn’t go far enough or fast enough to get it. It may be a good thing, because the satellite was tumbling so much that if I had gotten it, it may have actually broken the arm! Crippen, rightfully, said ‘King’s X. Let’s go back.’ We got the Shuttle back in position in front of the satellite and then we stabilized everything. We had fuel left, but not enough to do what we were doing anymore.”

Privately, the astronauts were convinced that they had blown it and that the mission was a failure. “I could see myself spending the next six months in Washington,” Crippen told the NASA oral historian, “explaining why we didn’t grab that satellite!”

Source: https://www.americaspace.com/2014/04/05/fixing-solar-max-30-years-since-mission-41c-part-1/

[Orionid]

Fixing Solar Max: 30 Years Since Mission 41C (Part 2)
By Ben Evans, on April 6th, 2014


Backdropped by the glorious Earth, Challenger drifts serenely with Solar Max secured in her payload bay. Photo Credit: SpaceFacts.de

Thirty years ago today (6 April 1984), the shuttle launched on arguably its most ambitious mission to date: a mission which would demonstrate the reusable orbiter’s capabilities of rendezvous, retrieval, satellite repair, and spacewalking with the Manned Maneuvering Unit (MMU) “jet backpack” in spectacular fashion and enhance NASA’s confidence in anticipation of future flights to service the Hubble Space Telescope (HST). Originally designated “STS-13,” and later redesignated “STS-41C,” the reader would be forgiven for thinking that the mission might have been dogged with ill-fortune. In fact, for the five-man crew, the question of good or bad luck even factored into their impromptu mission patch. On Mission 41C in April 1984, astronauts Bob Crippen, Dick Scobee, Terry Hart, James “Ox” van Hoften, and George “Pinky” Nelson salvaged NASA’s crippled Solar Maximum Mission (SMM) spacecraft—nicknamed “Solar Max”—and after initial difficulties repaired and rejuvenated it during two magnificent EVAs.

As described in yesterday’s AmericaSpace article, the mission began with little magnificence, for spacewalker Pinky Nelson had been unable to dock his Trunnion Pin Attachment Device (TPAD) onto the slowly spinning satellite on 8 April and his actions had actually jostled it and made matters worse. It was impossible for Hart to extend the shuttle’s Canadian-built Remote Manipulator System (RMS) mechanical arm to grapple the satellite. This required 41C commander Bob Crippen to withdraw Challenger to a distance of about 100 miles (160 km), as mission managers discussed their next move.

Overnight, as the astronauts slept, engineers at NASA’s Goddard Space Flight Center in Greenbelt, Md., which operated the satellite, battled to regain control, but since its solar panels were no longer pointing toward the Sun, battery power was gradually dwindling away without recharging. The engineers switched off as many systems as possible, including heaters, but still had only six to eight hours of battery life left. When it became clear that Solar Max’s magnetic torque bars were now slowing the rotation, Goddard implemented a new technique, using a different method of sensing its position. This made the bars more effective in “pushing off” against Earth’s magnetic field, and the satellite quickly stabilized itself. Then, just as battery life was running out, it came around in its orbit in such a way that the electricity-generating panels faced sunward once more and began to recharge. When the crew awoke on the morning of 9 April, the satellite’s batteries were powered and it was rotating serenely at half a degree per second.

Fuel reserves in Challenger’s propellant tanks were low, at 13 percent, prompting Bob Crippen to quip that it really was STS-13 now! “Then we talked about what we had to do and Mission Control worked out the available fuel,” said Terry Hart in a NASA oral history interview, “but we took an extra day and decided we would do a second rendezvous. This time, Pinky and Ox would stay inside the orbiter and I would try to capture it with the arm.” It also became clear during the second spacewalk precisely why Nelson’s attempts to capture Solar Max had been thrice frustrated: a small grommet, just 0.8 inches (20 mm) high and 0.25 inches (6.4 mm) thick, had obstructed the full penetration of the TPAD onto the satellite’s trunnion pin. The grommet, which was installed near the pin, helped to hold part of Solar Max’s gold-colored thermal insulation blanket in place.


Challenger rockets into orbit on 6 April 1984. Photo Credit: SpaceFacts.de

“What no-one noticed,” explained Hart, “is that one of the blankets had been put on with a little fiberglass standoff that the grommets would fit over. The engineering drawings didn’t specify where those standoffs could be, so when they assembled the satellite, the technicians just put one wherever the grommet was. They glued it onto the metal frame, then stuck the blanket on. That was the correct thing to do, because no-one envisioned using that pin for anything.” A use for the pin did emerge, however, a year after Solar Max’s launch, when the option of a shuttle repair was first explored in depth, “but when they were designing the TPAD,” Hart continued, “no-one noticed that there was a grommet there. When Pinky went to dock, it interfered with the docking adaptor.”

It turned out that, if Nelson had made his approach to the pin within a very narrow pitch angle “corridor,” he might have succeeded and captured Solar Max. However, during his second EVA, he took measurements of where the grommet was and the obstruction it posed, and found that it stuck out 0.6 inches (1.5 cm) too far. The TPAD, clearly, would not work. Either way, Challenger’s on-board fuel was now too low to support a rescue if Nelson’s MMU happened to fail. Instead, Crippen would fly close enough to Solar Max for Hart to grapple it with the mechanical arm.

Early on 10 April, on his first attempt, Hart successfully grappled the Solar Max satellite with the RMS and anchored it onto a Flight Support Structure (FSS) at the rear end of the payload bay. “It was a dramatic moment for Mission Control,” he remembered later. “We were euphoric when we succeeded. We really felt that the mission was at risk, which it was, and we were really on a mission that was demonstrating the flexibility and usefulness of the Shuttle to do things like repair.”

The spectacular success, sadly, would prove to be the MMU’s death knell.

An umbilical line was connected to the satellite to feed it with power from the orbiter, and it was pivoted around so that Nelson and van Hoften, during their second spacewalk, which began at 3:58 a.m. EDT on 11 April, could reach and fix its broken attitude control system and the main electronics box of the disabled coronagraph and polarimeter. These repairs were originally meant to occupy one EVA apiece, but with the condensed and rescheduled flight plan it was decided to attempt both during the same excursion. Replacement of the attitude control box, which had been responsible for crippling the $240 million project more than three years earlier, took just 45 minutes.

Standing on the end of the RMS, his feet anchored in restraints, van Hoften removed a pair of screws, pulled the box out smoothly, and plugged in a new unit. The second procedure of fixing the main electronics box to the coronagraph and polarimeter, which was not designed for replacement in orbit, was expected to be a longer and trickier task. Nonetheless, with surprising dexterity and outstanding skill, van Hoften pulled back a panel covering the box, cut and taped back a layer of insulation, removed two dozen screws, and cut several wires. Nelson then took over, installing the new electronics box using large, gold-plated beryllium clips, instead of tiny screws, for the connectors. An hour after their second task had begun, the two men were finished and were able to place a baffle cover over the X-ray polychromator to vent its exhaust gases away from Solar Max’s other instruments.


Thirty years ago this week, Mission 41C put the shuttle’s capabilities to the test. In a single flight, the reusable vehicle demonstrated its capacity to support satellite deployment and retrieval, rendezvous and proximity operations, untethered spacewalking and robotics … and served as a highlight of the ingenuity of the human spirit. Photo Credit: SpaceFacts.de

The second EVA had lasted six hours and 44 minutes, which, together with their two-and-a-half-hour outing on 8 April, brought Nelson and van Hoften’s spacewalking time to more than nine hours. “The repair itself was a kick,” Pinky Nelson recalled years later. “It was so much easier to work in space than it is on the ground. Ox and I, and T.J. Hart running the arm, just kind of did this repair. It was a piece of cake! It was so much fun riding on the end of the arm and much easier than working underwater.” The pilots, too, were just as excited, particularly Scobee, who persuaded his crewmates to don T-shirts for the space-to-ground press conferences, emblazoned with the legend, Ace Satellite Repair Company.

Finally, after a day of checkout in the payload bay, on 12 April 1984 Hart grappled the satellite with the RMS and deployed it back into space. By this time, in view of the additional day of planning needed to retrieve Solar Max, the mission had been extended by 24 hours and rescheduled to land on “unlucky” Friday, 13 April, after all. Yet, despite the huge success of the repair, bad luck had one more card to play. Much to Crippen’s chagrin, the planned landing at the Kennedy Space Center (KSC) was postponed and finally cancelled due to showers in Florida, obliging the crew to land at Edwards Air Force Base.

For Terry Hart, who had already decided before the mission that this would be his only space mission, the re-entry came after a sleepless last night in orbit, soaking up as much of the experience as possible. Pinky Nelson, who had ridden into orbit on the middeck, changed places with Hart on Challenger’s flight deck for the return to Earth. “I didn’t have a lot of time, since we were busy on the flight, but the last night on-orbit, I had no duties at all,” recalled Hart. “I just figured that I wasn’t going to sleep at all. I’d turned down a second mission [the Spacelab-D1 flight] and was going back to AT&T Corporation, so I was damned if I was going to sleep. I stayed up all night and looked out the window while the rest of the crew was sleeping and watched the Himalayas go by and other parts of the world that I didn’t see during the regular shifts.”

Re-entry the following morning, he remembered, “was a wonderful thing. Watching the fireball around the vehicle was breathtaking. The engineer side of me wanted to see the G build-up, but I had a camera and remember just letting it go and it would sit there, of course, when we were weightless. As we started to hit the upper parts of the atmosphere, I watched the camera accelerate forward as I let go, because the vehicle was decelerating. I was downstairs, but I was able to stick my head up every once in a while before I strapped in and looked out and could see the fireball overhead ‘flickering,’ a very impressive experience coming through that, but very smooth and quiet all the way down.”


Declaring themselves the “Ace Satellite Repair Company,” the five men of Mission 41C celebrate their success. From the left are Dick Scobee, George “Pinky” Nelson, James “Ox” van Hoften, Terry Hart, and Bob Crippen. Photo Credit: SpaceFacts.de

True to the weather forecasters’ predictions, an ominous thunderstorm arrived over KSC’s Shuttle runway at precisely the time that Bob Crippen might otherwise have been landing there. “My family were in Cape Canaveral,” continued Hart, “and we were landing in California, but it was beautiful. When I got out of my seat, I felt like I was using almost all of my strength just to get up! I was used to moving my body around with just my fingertips and now, all of a sudden, I had to exert all this force to get up. We didn’t want to fall down the stairs on national television, so we were all doing deep knee bends to make sure we got our blood flowing again.” Van Hoften, in the flight engineer’s seat, recalled watching the effects of the super-heated plasma, whilst Nelson’s enduring memory was how strong the sense of gravity felt on his body after a week of weightlessness. Yet Crippen’s touchdown was perfect. “I’d done so many approaches and landings in the simulator, the Shuttle Training Aircraft and the T-38 jets,” Nelson said, “that the landing felt very normal. It was disappointing that my family could not be there.”

Challenger made landfall at 5:38:06 a.m. PDT (8:38:06 a.m. EDT) on the Edwards dry lakebed, Runway 17, completing a mission of almost exactly seven days. As 41C’s epic voyage ended, Solar Max’s rejuvenated voyage of exploration had scarcely begun. After a four-week checkout, it set to work on what would turn into more than five years of observations of changes in the Sun’s energy output. Its coronagraph and polarimeter, repaired by Nelson and van Hoften, resumed work in June 1984 and, despite a few interruptions, continued to capture images of the solar corona during the “daytime” portions of the satellite’s orbit until the end of the mission. Minor problems arose for most of January 1986, when Solar Max suffered a loss of memory in its on-board computer. Observations were again interrupted in December of that year, when the coronagraph’s dedicated tape recorder failed, only coming back online in March 1987, thanks to the use of a backup device. Nevertheless, the satellite continued operating—in spite of atmospheric friction gradually dragging its orbit downward—almost until the end of the decade.

Other scientific results included the surprising discovery that the Sun is much brighter during periods at which “sunspot” activity on its surface reaches its peak. Solar Max’s instruments confirmed that, although the sunspots themselves are dark, they are surrounded by bright “faculae,” which more than offset the dimming effects of these Earth-sized blotches. By the time the satellite’s mission ended in mid-November 1989, just two weeks before it re-entered the atmosphere, it had chalked up an impressive tally of a quarter of a million images of the Sun’s corona and over 12,000 recorded solar flares. Additionally, its gamma ray spectrograph made important contributions to the international study of Supernova 1987A, which had provided astronomers with their first “local” opportunity to examine such a major stellar event since 1604. It also detected 15 observed gamma ray bursts from deep space.


Challenger lands safely at Edwards Air Force Base on Friday, 13 April 1984, concluding a flight which turned bad luck into good luck with the triumphant repair of Solar Max. Photo Credit: SpaceFacts.de

If Mission 41C was stricken with bad luck at all, the greatest victim must have been the MMU jet backpack first tested by Bruce McCandless two months earlier. Admittedly, it had performed admirably and could hardly be blamed directly for the failure of the TPAD. Indeed, it would prove its worth in November 1984 when, flown by Joe Allen and Dale Gardner, it was instrumental in the retrieval of the errant Palapa-B2 and Westar-6 communications satellites. However, what 41C did prove was the crisp maneuverability of the orbiter itself and the precise handling characteristics of the RMS. It was, observers said later, Hart’s small grab, rather than Nelson’s free flight, which had pulled success from the jaws of what might have been an ignominious defeat.

In the fall of 1989, there was an effort to fly the MMU again. A proposal was solicited from Martin Marietta for recertification and refurbishment for one shuttle mission. It came in at $6.1 million, which was deemed too expensive, and despite some small sums for clean room environmental storage, “just in case,” they were eventually retired. Today, the MMU flight unit first used by Bruce McCandless hangs in the Smithsonian. The other backpack was loaned to NASA’s Marshall Space Flight Center in Huntsville, Ala., for possible future use as a “flying testbed” for autonomous rendezvous and docking systems. Both units were mothballed until such time as their unique capabilities were needed again.

They never were.

Perhaps, through the drawbacks it uncovered with the multi-million-dollar backpack, 41C proved to be an unlucky mission after all.

Source: https://www.americaspace.com/2014/04/06/fixing-solar-max-30-years-since-mission-41c-part-2/

[Orionid]

SpaceX just launched the 1st US astronaut mission to embrace the 'unlucky' number 13 since the Apollo era
By Robert Z. Pearlman Published October 1, 2026

NASA pushes past its historic triskaidekaphobia and sets aside superstition.


From right to left, Canadian Space Agency astronaut Joshua Kutryk, NASA astronauts Jessica Watkins and Luke Delaney and Roscosmos cosmonaut Sergey Teteryatnikov pose next to their Crew-13 mission insignia inside their quarters at NASA’s Kennedy Space Center in Florida on Tuesday, Sept. 29, 2026. (Image credit: NASA/Kim Shiflett)

(...) "I never thought of it in a superstitious sense, that we would have a problem on 13," said Haise, the mission's lunar module pilot, in a 50th anniversary interview with collectSPACE.com in 2020. "I had no sense at all, nor do I relate to the launch time [13:13 CST] and all the other thirteens that people have tried to tie to things as being connected with the flight."

Jim Beggs reportedly felt differently. The NASA administrator when the agency reached its next 13th numbered mission in 1984, Beggs was against tempting fate.

"'There's not going to be [another] Apollo 13 or a Shuttle 13," he said, according to Bob Crippen, commander of the space shuttle's STS-41C mission, in a NASA oral history interview.

Giving in to triskaidekaphobia — the fear of the number 13 — Beggs ordered NASA to adopt a new but convoluted numbering system for all shuttle missions after STS-9.

"Hence, what would have been STS-13 became STS-41-C, where the '4' was the fiscal year [1984], the '1' was the launch site [Kennedy Space Center in Florida] and 'C' the order of launch [C was the third planned flight of the year]," said Crippen. (...)
https://www.space.com/space-exploration/human-spaceflight/spacex-just-launched-the-1st-us-astronaut-mission-to-embrace-the-unlucky-number-13-since-the-apollo-era