Can you steal a spacecraft?  Sure you can, in Science Fiction.  But, way back in 1959, this actually happened. 

The Cold War was raging and the Americans were a long way behind in the space race. Their rivals, the Soviet Union, had put a satellite in orbit and even sent a dog up in a vehicle weighing over a tonne.  Even more impressively, they'd also sent spacecraft to the moon. 

In contrast, the Americans had only managed to send very small probes into space.  The first of these was called Explorer 1.  There's a picture of three men of advancing years responsible for this spacecraft.  Between them they were easily capable of holding their probe above their heads.  The Americans simply couldn't launch the heavy payloads that the Soviet rockets were capable of.

The chilling fact behind this space-based competition was that the Soviet rockets were capable of carrying nuclear weapons.  Essentially, they could send a nuclear weapon to anywhere in the world.  The Americans, in contrast, had to rely on long range bombers and all the attendant risks of interception that went with them.  

In short, there was a gap to be closed.

Fortunately, while there was a technological competition there was an ideological one too.  Both the US and the Soviet Union were looking to score points over the other.  The Soviets were very keen to show how good they were at space technology, to the extent that they would go on world exhibition tours, including going to the United States itself. And the CIA saw an opportunity to sneak a peek at the technology that the Soviets were prepared to send.

Their target was a display of a Lunik (Luna) space probe and part of the rocket that sent it to the Moon.  Looking at that spacecraft wasn't as simple as going into the exhibition after hours and snooping around.  The display was under constant guard.

The weakness they found was the transport of the exhibit on its tour.  The truck carrying the spacecraft was part of a routine shipment, meaning it wasn’t under constant armed guard—just regular transport workers following a schedule.  This allowed the CIA to arrange for the truck to be delayed and redirected through a mixture of bribery, distraction and misdirection.

One night, the truck was diverted to a secure location where engineers and intelligence officers went to work.  The spacecraft was carefully examined, measured, photographed, and reassembled before dawn.  Intelligence experts worked in shifts to get as much information as possible in a few hours.

One of the most critical aspects of the operation was ensuring that the spacecraft was put back exactly as it was found—down to the smallest details.  If anything had been left out of place or damaged, the Soviets might have suspected foul play.  The team ensured that screws, fastenings, and even dust patterns were meticulously restored.

The CIA learned a lot about the design choices of the Soviet engineers, including things like: material selection, instrumentation, electronics and rocket guidance.  Perhaps the most important thing they learned was whether Soviet propaganda matched reality.  In this case, it broadly did, and the Americans knew they had a lot of work to do.

The entire operation was carried out with such precision that the Soviets never realized their spacecraft had been secretly examined. The Lunik was returned exactly as it had been taken, ensuring that no suspicion was raised.

This remains one of the most daring and successful covert intelligence operations of the Cold War, demonstrating how espionage played a major role in the Space Race.