[Note that this article is a transcript of the video embedded above.]

In May of 1992, the Space Shuttle Endeavour launched to low earth orbit on its very first flight. That first mission was a big one: the crew captured a wayward communications satellite stuck in the wrong orbit, attached a rocket stage, and launched it back into space in time to help broadcast the Barcelona Summer Olympics. Endeavour went on to fly 25 missions, spending nearly a year total in space and completing 4,671 trips around the earth. But even though the orbiter was decommissioned after its final launch in 2011, it had one more mission to complete: a 12 mile (or 19 kilometer) trip through the streets of Los Angeles to be displayed in the California Science Center. Endeavour’s 26th mission was a lot slower and a lot shorter than the previous 25, but it was still full of fascinating engineering challenges. This October marks the 10 year anniversary of the nearly 3-day trip, so let’s reminisce on this incredible feat and dive into what it took to get the orbiter safely to its final home. I’m Grady, and this is Practical Engineering. On today’s episode, we’re talking about the Space Shuttle Endeavor Transport project.

As midnight approached on October 11, 2012 the Space Shuttle Endeavour began its harrowing (if somewhat sluggish) journey from LAX airport to the California Science Center near downtown LA. Although Endeavour traveled into space 25 times, launched a number of satellites, visited Mir, helped assemble the International Space Station, and even repaired the Hubble Telescope, it was never designed to navigate the busy streets of an urban area. But, despite spending so much of its career nearly weightless, it was too heavy for a helicopter, and it couldn’t be dismantled without causing permanent damage to the heat tiles, so the Science Center decided to foot the roughly $10 million it would take to move the shuttle overland. The chilly late night departure from the hangar at LAX was the start of the transport, but Endeavour’s journey to Exposition Park really started more than a year beforehand.

In April 2011, NASA awarded Endeavour to the California Science Center, one of only four sites to receive a retired shuttle. The application process leading up to the award and the planning and engineering that quickly followed were largely an exercise in logistics. You see, Endeavor is about 122 feet (37 meters) long with a 78 foot (24 meter) wingspan, and with 58 feet (18 meters) to the top of the vertical stabilizer during transport. It also weighs a lot, around 180,000 pounds (80,000 kg), about as much as a large aircraft. Transporting the shuttle through Los Angeles would not be a simple feat. So, the Science Center worked with a number of engineering firms in addition to their heavy transport contractor (many of whom offered their services pro bono) to carefully plan the operation.

The most critical decision to be made was what route Endeavor would take through the streets of LA. The Shuttle couldn’t fit through an underpass, which meant it would have to go over the 405, the only major freeway along its path. It also would face nearly countless obstacles on its journey, including trees, signs, traffic signals, and buildings. 78 feet is wider than most two-lane city streets, and there are a lot of paths in Los Angeles that a Space Shuttle could never traverse. And this isn’t a sleepy part of the city either. Exposition Park and the Science Center are just outside downtown Los Angeles. The engineering team looked at numerous routes to get the Shuttle to its destination, evaluating the obstacles along the way. They ultimately settled on a 12 mile (or 19 kilometer) path that would pass through Inglewood and Leimert Park.

On the NASA side, they had been stripping the Shuttle of the toxic and combustible fuel system used for the reaction control thrusters and explosive devices like hatch covers to make the vehicle safe for display at a museum. With Endeavor attached to the top of a 747 jet, NASA made a series of low altitude flyovers around California to celebrate the shuttle’s accomplishments and retirement before landing and offloading the vehicle at LAX, a short distance but a long journey away from its final destination. Three weeks later, the last leg of that journey began.

For its ride, the shuttle would sit on top of the Overland Transporter, a massive steel contraption built by NASA in the 1970s to move shuttles between Palmdale and Edwards Air Force Base. Even though it was designed for the shuttle program, this was Endeavour’s first ride on the platform. Before this move, the transporter had been parked in the desert for the last 30 years since the last shuttle was assembled in Palmdale in 1985. Just like the Shuttle Carrier Aircraft, a modified Boeing 747 that ferried the shuttles on its back, and the main fuel tank that attached to the orbiter during launch, the overland transporter used ball mounts that fit into sockets on the shuttle’s underside (two aft and one forward). The contractor used four Self-Propelled Modular Transporters (or SPMTs) to support and move the shuttle. These heavy haul platforms have a series of axles and wheels, all of which can be individually controlled to steer left or right, crab sideways, or even rotate in place (all of which were needed to get this enormous spaceship through the narrow city streets). The SPMTs used for the Endeavour transport also included a hydraulic suspension that could raise or lower the Shuttle to keep it balanced on uneven ground and help avoid obstacles. Each of the four SPMTs could be electronically linked to work together as a single vehicle. An operator with a joystick walked alongside the whole assembly, controlling the move with the help of a team of spotters all around the vehicle. And yes, it was slow enough to walk next to it the entire trip.

About 6 hours into the move, the Shuttle pulled up to the shopping center at La Tijera and Sepulveda Eastway, the first of several stops to allow the public a chance to see the spectacle while also giving crews time to coordinate ahead of the move. Huge crowds gathered all along the route during the move, especially at these pre-planned stops. In fact, the transport project may be one of the most recorded events in LA history, a fact I’m sure gave a little bit of trepidation to the engineers and contractors involved in the project.

Even though this move was pretty unique, super heavy transport projects aren’t unusual. We move big stuff along public roadways pretty regularly when loads are quote-unquote “non-divisible” and other modes of transportation aren’t feasible. I won’t go into a full engineering lesson on roadway load limits here, but I’ll give you a flavor of what’s involved. Every area of pavement sustains a minute amount of damage every time a vehicle drives over. Just like bending a paperclip over and over eventually causes it to break, even small deflections in asphalt and concrete pavements eventually cause them to deteriorate. Those tiny damages add up over time, but some are more tiny than others. As you might expect, the magnitude of that damage is proportional to the weight of the vehicle. But, it’s not a linear relationship. The most widely used road design methodology estimates that the damage caused to a pavement is roughly proportional to the axle load raised to the power of 4. That means it would take thousands of passenger vehicles to create the same amount of damage to the pavement as a single fully-loaded semi truck. And it’s not just pavement. Heavy vehicles can cause embankments to fail and underground utilities like sewer and water lines to collapse.

Because heavy vehicles wear out roadways so quickly, states have load limits on trucks to try and maintain some balance between the benefits of the roadway to commerce and the cost of maintenance and replacement. If you want to exceed that limit, you have to get a permit, which can be a pretty straightforward process in some cases, or can require you to do detailed engineering analysis in others. Of course, nearly every state in the US has different rules, and even cities and counties within the states can have requirements for overweight vehicles. Most states also have exemptions to load limits for certain industries like agricultural products and construction equipment. But, curiously, no state has an exemption for space shuttles. So, in addition to picking a route through which the orbiter could fit, a big part of the Endeavor transport project involved making sure the weight of the shuttle plus the transporter plus the STMPs wouldn’t seriously damage the infrastructure along the way. The engineering team prepared detailed maps of all the underground utilities that could be damaged or crushed by the weight of the orbiter, and roughly 2,700 steel plates borrowed from as far as Nevada and Arizona were placed along the route to distribute the load.

Another place where Endeavour’s weight was a concern was the West Manchester Boulevard bridge over the 405. Around 6:30 PM, 19 hours into the move, Endeavour pulled up to the renowned Randy’s Donuts, its astronomically large donut a perfect prop for photos of such an enormous spacecraft. Photographers had a heyday, and they had time to line up their shots perfectly because there was plenty of work to be done to prepare for the next leg. The shuttle’s permit wouldn’t allow it to be carried over the bridge using the four heavy SPMTs. Instead, they would have to lift it off the transporters and lower it onto a lightweight dolly to get over the 405. The SPMTs were sent over the bridge one at a time ahead of the shuttle. Then, longtime donor and Science Center partner, Toyota, got a chance to shine. The dolly was attached to a stock Toyota Tundra pickup truck that slowly pulled the shuttle across the bridge. Toyota got a nice commercial out of it, and that pickup still sits outside the Science Center as part of a demonstration about leverage (although sadly, it was broken when I was there). By midnight, the shuttle was over the bridge and crews were working to reconnect the SPMTs so that the journey could continue.

Through the night, Endeavour continued its trip eastward, passing the Inglewood City Hall. By 9:30 the next morning, the shuttle had reached its next stop, The Forum arena, where it was greeted by a marching band and speeches by former astronauts. But even though the shuttle was stopped, the crews supporting the move (both ahead of and behind the orbiter) continued working diligently. During preparation for the move, the engineers in charge had used a mobile laser-scanner along the route to create a 3D point cloud of everything that could be in the way. Rather than use crews of surveyors to walk the route and document potential collision points, which would have taken months, they used a digital model of the shuttle to perform clash detection on a computer. This effort allowed the engineering team to optimize the path of the shuttle and avoid as many traffic signals, light poles, street signs, and parking meters as possible. In some cases, the Shuttle would have to waggle down the street to clear impediments on either side, sometimes with inches to spare. The collision detection also helped engineers create a list of all the facilities that would need to be temporarily removed along the way by the Shuttle delivery team. Armies of workers ahead of the move used that list to dismantle and lay obstacles down, and armies of workers behind the move could immediately reassemble them to minimize disruptions, outages, and street closures.

By around noon on Saturday (36 hours into the move), the Shuttle had reached one of the most challenging parts of the route: Crenshaw Drive. This narrow path has apartment buildings tight to the street, narrow straights for an overland space shuttle. Endeavour’s next stop was scheduled for 2PM at Baldwin Hills Crenshaw Plaza, only about 3 miles or 5 kilometers away. But, as the shuttle continued its northward crawl, it encountered several unexpected obstacles, mainly tree branches that had been assumed to be out of the way. By 5PM, the shuttle was still well south of the party as chainsaw crews worked to clear the path, but event organizers decided to go ahead with the performances. The Mayor took the stage to welcome Endeavour to Los Angeles, but the shuttle was still too far to be seen.

Later that night, Endeavour finally made the difficult turn onto Martin Luther King Jr. Boulevard for its final eastward trek, dodging trees all along the way. The trees were probably the most controversial part of the entire shuttle move project, with around 400 needing to be cut down along the route (often in the median between travel lanes). Many in the affected communities felt that having a space shuttle in their science museum wasn’t worth the cost of those trees, several of which were decades old. To try and make up for the loss, the Science Center pledged to replace all the trees that were removed two-to-one and committed to maintain the new trees for at least two years, all at a cost of about $2 million. But the tall pines along MLK Boulevard were planted in honor of the famed civil rights leader and deemed too important to remove. Instead, the shuttle zigzagged its way between the trees on its way to the Science Center.

Endeavour continued inching eastward toward Exposition Park on the last leg of its journey, facing a few delays from obstacles, plus a hydraulic leak on one SPMT. But, by noon that Sunday, the shuttle was making its turn into Exposition Park to a crowd of cheering spectators. It hadn’t hit a single object along the way. With an average speed of about 2 miles or 3 kilometers per hour, on par with the rest of LA’s traffic, the orbiter was nearing the end of its voyage and achieving the dream of any multi-million dollar engineering project: to come in only 15 hours behind schedule. By the end of the day on Sunday, the shuttle was safely inside its new home at the California Science Center.
It took only a few weeks for the center to open the space to the public, and 10 years later, you can still go visit Endeavour today (and you should!). Here’s a dimly lit picture of the channel’s editor (and my best friend) Wesley and me visiting in 2018. The shuttle sits on top of four seismic isolators on pipe support columns so that it can move freely during an earthquake. But the current building is only meant to be temporary. The Shuttle’s final resting place, the Samuel Oschin Air and Space Center, broke ground earlier this year. Eventually, Endeavour will be moved the short distance and placed vertically, poised for launch complete with boosters and main fuel tank in celebration of all 26 of its missions: 25 into space and 1 through the streets of Los Angeles.