Getting a chance to see a Space Shuttle orbiter in person can be awe inspiring. These huge airplane-like spacecraft ferried hundreds of people to the most dangerous environment imaginable, carrying huge telescopes, space station modules, and satellite payloads while protecting its human passengers from the extremes of space. Six of these unique spacecraft were built: Enterprise, Columbia, Challenger, Discovery, Atlantis, and Endeavour. But no two space shuttles turned out just the same. In honor of the 40th anniversary of Space Shuttle Discovery’s first mission, STS-41D, let’s take a look at features that distinguish the vehicle we love so much here at the Smithsonian from the others.

Tiles

For anything to survive a trip through Earth’s thick atmosphere, it needs protection from the heat generated by friction when traveling through this dense protective shell. The space shuttle’s thermal protection system (TPS) provided that barrier in the form of reinforced carbon-carbon panels, heat resistant glass-coated silica tiles, additional white silica tiles, and woven silica blankets. Few places on the orbiter are not covered at all. The pattern of tiles, though, is unique to each orbiter because of changes to the tiles after each mission. Whole maps existed for each Space Shuttle orbiter, allowing engineers to fabricate tiles of the required shape and depth for the coded locations.

However, following missions, damage might happen to any number of tiles, meaning they either had to be repaired or replaced, slightly changing the “map” after every mission. The appearance of the tiles gives away these changes. Some tiles are heavily streaked with gray or have visible signs of repairs, while others appear perfectly black. Almost all of them have a specific serial number printed on them, and only a few are missing a distinguishing white circle at the center where waterproofing solution was inserted (the blank ones were replacements after STS-133, Discovery’s final mission). The tiles are porous, so water getting inside them could freeze and make the tile crack. The blankets are also obviously discolored in different areas in differing intensities on each vehicle too. The dingy looking streaks generally go in the same upward angle from the side of the forward fuselage towards the back of the payload bay doors, but it’s not exactly the same on the three remaining flown vehicles (Enterprise never launched to space and does not have real tiles).

File URL

So, the outside of each orbiter looks slightly different based on experience, but there are some distinctive patterns in the tiles as well. Near the flight deck windows, each orbiter has a black tile coming off the corner of the middle window. In the case of Discovery though, there’s an additional three black tiles coming down from the starboard middle window (Window #5). Some have speculated that these were intentionally meant to give a “teardrop” appearance, perhaps as Discovery was the orbiter selected to fly first after the losses of Challenger in 1986 and Columbia in 2003. These were not later additions but errors in manufacturing during Discovery’s original build in 1983. The TPS around the windows is otherwise consistently a ring of black tiles followed by white tiles. Since tiles were manufactured to fit into very specific locations, it would not matter if it was the wrong type of tile but rather its size and shape that would matter most.

File URL

BLT

No, Discovery doesn’t make sandwiches or have a way to cook bacon. But it does have a very special thermal tile that has the name BLT (Boundary Layer Transition). Towards the end of the Space Shuttle program, engineers, mostly from the NASA Langley Research Center, wanted to see what changes might occur during reentry by intentionally disrupting the flow of plasma on the underside of the orbiter’s wings. Engineers needed to test this on repeated missions, and Discovery became the primary vehicle for tests over four missions, though Atlantis and Endeavour also flew missions with a BLT tile (which you can still see on the underside of their port wings). Information from embedded sensors and telemetry data gathered from a jet aircraft flying next to the orbiter during landing would indicate how changing the flow of plasma altered the vehicle’s stability. Changing the size of this raised bump, as well as vehicle speed and altitude, from one mission to the next gave engineers information to augment data gathered during the loss of Columbia in 2003. In that case, plasma flow was drastically disrupted by a hole on the port wing leading edge, causing the vehicle to spin out of control and break apart. The BLT tests provided information for future missions on the effect of surface disruptions during reentry, making it possible to determine a safe course of action if damage was found on the thermal protection system.

File URL

Velcro

Since visitors can’t climb around inside Discovery, be assured that nearly every working surface in the crew compartment has plenty of VELCRO® to secure small items. Most of that material is blue, and the International Space Station features mostly white squares, though some blue can be found. What I learned from occasional trips inside the orbiter with engineers is that there is also yellow VELCRO® in a few spots. I happened to notice one piece above the window directly in front of the pilot’s seat when we were last on the flight deck in early 2022. These infrequent yellow squares are not standard positions, but in crew preferred locations, making the ones in Discovery reminders of the final crew to fly in 2011. Each crewmember on each mission would have different spots they might find the material useful, so each orbiter would have yellow squares in different locations.

Nicknames

Each orbiter has its own name, like sailing vessels throughout history. Enterprise had been used on an aircraft carrier but was notably selected for its connection to the trailblazing space adventures by the spacecraft of the same name on the television show Star Trek. Columbia, Challenger, Discovery, Atlantis, and Endeavour had all been names used on sailing vessels from the 17th through early 20th centuries. But beyond just formal names like those, like our own personal names, sometimes a nickname is fun to have either as a shortened version of the full name or something related to a thing’s style or character (as a Jennifer, I get referred to as Jen or Jenny, depending on the speaker). Crewmembers who were military pilots often came with call signs when they became astronauts or acquired them while working at NASA (for example, George Nelson is “Pinky,” Kenneth Cockrell is “Taco,” and Pam Melroy is “Pambo”). When Discovery arrived at Dulles Airport in 2012, I learned it also had its own nickname, which was more obvious than I expected: Disco! I can’t imagine that derived from the vehicle’s behavior, but it certainly makes flying on it sound really fun.

History

Not to brag, but Discovery does have the greatest flight history record. We often repeat the same information on tours and in printed materials: 39 missions, 365 total days spent in space. That’s quite a feat for the journeys the orbiter took. But it’s really a testament to the team that made each of those flights possible. Tens of thousands of people were involved in maintaining the vehicle, training the astronauts, preparing the science experiments, building the satellites or telescopes, and managing activities on the ground making sure everything went smoothly. Not enough can be said about their commitment to safety and mission success. And Discovery had many an important mission for which that hard work was tested. For the purposes of this remembrance, let’s look a little at that very first mission, STS-41D.

Discovery was a bit temperamental from the get-go: At its late-June 1984 scheduled launch, one of the engines failed and a pad abort was called at T-6 seconds. Making things worse, an invisible hydrogen fire that started near the engine extended up towards the crew hatch. Unusual measures were required to protect the crew from the fire: Instead of a quick exit to escape baskets that drop away from the launch tower, they waited 20 minutes in the crew compartment to ensure the fuel dissipated. That main engine required replacement, which meant a launch delay from late-June to late-August 1984. On board on launch day was Hank Hartsfield as commander; Michael Coats as pilot; mission specialists Mike Mullane, Steve Hawley, and Judy Resnik; as well as payload specialist Charlie Walker. Payloads included multiple satellites, a solar array test unit, science experiments, and an IMAX camera to film scenes for the first shot-in-space movie, The Dream is Alive. The mission’s six days ended with a safe return, but not without concerns. Engineers identified the first problems with solid rocket booster O-rings after those of STS-41D were recovered in the Atlantic Ocean. The problem would eventually doom Challenger in early 1986. Likewise, though on a later mission, foam from the external tank damaged Discovery’s starboard elevon during launch, the type of damage that prevented Columbia from landing safely in 2003. Discovery though was entrusted with both Return to Flight missions after those tragedies, making it unique amongst all remaining orbiters for the most unpleasant reasons.

Forty years on from that first visit to space, Discovery has now retired peacefully at our Steven F. Udvar-Hazy Center in Chantilly, Virginia, welcoming visitors from around the world to learn about spaceflight. We still keep an eye on her (I don’t often refer to Discovery as “her,” but it feels right sometimes), making sure left-over hydraulic fluid doesn’t drip out and create puddles in the aft compartment. Every so often, we climb into the crew compartment to check that all is well there too.

But in her retirement, as part of the Smithsonian’s collection, she gets to rest after many long and weary days in space, serving her crews well and ensuring the Hubble Space Telescope made it safely to orbit, modules of the International Space Station were connected to each other, and tons of supplies and equipment made it there to support a continued human presence in space. It is an honor and privilege to share Discovery’s story and honor her legacy.