Short answers, pulled from the story.
A boilerplate spacecraft is a nonfunctional craft built to match the size, weight, and shape of an actual spacecraft. It lets engineers test launch vehicle configurations, escape systems, recovery procedures, and transportation logistics before any flight-ready hardware is at risk. NASA used boilerplate vehicles across the Mercury, Gemini, Apollo, Space Shuttle, and Artemis programs.
The term originated at the Norfolk Naval Shipyard in Virginia during development of the Little Joe series of seven launch vehicles. One test capsule in that series had a conical section made of boilerplate steel, the same heavy-gauge material used in ship construction. Engineers extended the name to all prototype capsules in the program, even those built from other materials, and the term became standard across the industry.
Big Joe 1, designated BJ-1, was a boilerplate Mercury capsule launched from Cape Canaveral on the 9th of September 1959 atop an Atlas rocket. The test evaluated heat shield performance, flight dynamics during reentry over the South Atlantic, capsule flotation and recovery procedures, and the overall rocket and capsule control systems.
BP-1227 was lost at sea in early 1969 during recovery training by an Aerospace Rescue and Recovery Squadron, most likely between the Azores and the Bay of Biscay. The Soviet fishing trawler Apatit recovered it off Gibraltar in June 1969 and transferred it to Murmansk. The USCGC Southwind returned it to the United States in September 1970, and it now stands in Grand Rapids, Michigan, as a time capsule.
Challenger began as STA-099, the Structural Test Article, which rolled out in February 1978 as a complete orbiter airframe built for vibration testing. After eleven months of testing, converting the prototype orbiter Enterprise into a flight vehicle proved too expensive, and accumulated design changes made it impractical. STA-099 was upgraded to a flight-ready orbiter instead and rolled out as Challenger in June 1982.
SpaceX launched the Dragon Spacecraft Qualification Unit to orbit on the 4th of June 2010, on the maiden flight of the Falcon 9 rocket. Orbital Sciences Corporation launched the Cygnus Mass Simulator on the first Antares flight on the 21st of April 2013. Both were boilerplate units built to the outer mold line and mass distribution of their respective spacecraft.