STS-133 (Discovery / final flight)

Background

By the time NASA managers confirmed STS-133 as the penultimate mission of the Space Shuttle Program, *Discovery* had already cemented its place as the most accomplished orbiter ever flown. Delivered to Kennedy Space Center in 1983, the vehicle accumulated 38 missions before its final flight, a record unmatched by any other spacecraft in the shuttle fleet. Its career had spanned consequential chapters of spaceflight history: the return-to-flight missions after both *Challenger* and *Columbia*, the deployment of the Hubble Space Telescope, and more than a dozen visits to the International Space Station. Retiring Discovery was therefore not merely a logistical step in winding down the shuttle program — it was the closing of an era.

The primary cargo for STS-133 reflected the maturing character of ISS operations. The Permanent Multipurpose Module (PMM) *Leonardo* — a pressurized logistics container originally built by the Italian Space Agency and previously flown as a reusable Multi-Purpose Logistics Module — had been refurbished and outfitted for permanent attachment to the station. Rather than returning to Earth after a resupply run, *Leonardo* would remain as a lasting addition to the ISS, providing roughly 25 cubic meters of storage volume and freeing up interior space in the station's existing modules. Also aboard was Robonaut 2, a dexterous humanoid robot developed jointly by NASA and General Motors. Designed to assist with both routine and hazardous tasks in microgravity, Robonaut 2 represented the first humanoid robot delivered to the ISS and a step toward integrating capable robotics into long-duration spaceflight.

The crew named to fly this mission brought substantial experience to the flight deck. Commander Steven Lindsey was making his fifth spaceflight; Pilot Eric Boe was on his second. Mission specialists Alvin Drew, Nicole Stott, Michael Barratt, and Steve Bowen rounded out a crew with deep familiarity with ISS operations. Stott and Barratt had each previously lived aboard the station during long-duration expeditions, and Bowen — a last-minute replacement for Timothy Kopra, who was injured in a cycling accident before flight — brought EVA experience that proved essential to the mission's spacewalk objectives.

Launch and Ascent

STS-133 lifted off from Launch Complex 39A at Kennedy Space Center on February 24, 2011, following a lengthy delay from its originally planned late 2010 launch date. Discovery's final ascent was nominal. Approximately eight and a half minutes after liftoff, the orbiter reached a stable low Earth orbit, and the crew began the standard post-insertion checkouts that preceded any rendezvous with the space station.

On Orbit and Station Operations

Discovery closed on the ISS over the following two days, docking with the station at mission elapsed time of roughly 55 hours and 33 minutes. The linkup marked the beginning of an intensive period of joint operations. The crew used the station's Canadarm2 robotic arm to extract *Leonardo* from Discovery's payload bay and berth it to the Earth-facing port of the Unity node, the position it would permanently occupy. Cargo transfer operations moved several thousand kilograms of equipment, spare hardware, and consumables into the station — one of the largest single resupply hauls in shuttle history at that time.

Two spacewalks were conducted during the docked phase. Steve Bowen and Alvin Drew performed both extravehicular activities, completing work on station maintenance tasks including the retrieval of a materials experiment and the routing of cabling to support future station upgrades. Bowen became the first astronaut to perform spacewalks on consecutive shuttle missions as a result of his late assignment to the crew.

Robonaut 2, packed in its own protective case within the newly attached *Leonardo*, was transferred inside the station and installed in the Destiny laboratory module, where it would await activation and testing by subsequent crews. The robot's presence aboard the ISS opened a new line of research into human-robot collaboration in space.

Discovery undocked from the ISS at approximately 250 hours into the mission, drawing the docked phase to a close. The station crew and ground teams had accomplished every primary objective.

Reentry and Landing

Following undocking, Discovery's crew spent additional time conducting on-orbit inspections of the orbiter's thermal protection system — standard post-*Columbia* protocol — before preparing for deorbit. The deorbit burn was executed at mission elapsed time of approximately 306 hours and 6 minutes, committing the vehicle to reentry over the Pacific and a return track toward Florida.

Discovery touched down on Runway 15 at Kennedy Space Center at approximately 307 hours and 4 minutes into the mission, completing its 39th and final flight. It was a characteristically precise landing for an orbiter that had returned from orbit more times than any other. After the wheels stopped, no one at KSC needed to be told that the moment carried unusual weight.

Legacy

Discovery's retirement marked a decisive milestone in the wind-down of the Space Shuttle Program, which would conclude with the landings of *Endeavour* and *Atlantis* later that year. The orbiter's 39 missions, accumulated over nearly 27 years of service, logged more than 148 million miles traveled and carried 252 individuals into space across its career.

The permanent addition of the *Leonardo* module to the ISS gave the station a lasting structural legacy from Discovery's final mission, one that continued supporting research operations long after the shuttle era ended. Robonaut 2 similarly represented a forward-looking payload, with NASA researchers using subsequent years to test its capabilities in the actual environment of the station.

Discovery was subsequently transferred to the Smithsonian National Air and Space Museum's Steven F. Udvar-Hazy Center in Virginia, where it remains on public display. Its preservation ensures that the most-flown orbiter in history occupies not just a chapter in the record books but a permanent place in the physical heritage of human spaceflight.