This week’s image comes to you from the New Mexico Museum of Space History in Alamagordo, New Mexico — it’s a cutaway of an RL-10 rocket engine:
The RL-10 was the first liquid hydrogen / liquid oxygen engine to fly in space. It’s a turbopump-fed, regeneratively cooled engine with a thrust of 15,000 pounds (66,750 newtons).
The RL-10 was first tested on the ground in 1959, and first flown in 1963 — at the time, built to power the Saturn I S-IV stage. Subsequently, modified versions of the RL-10 have been used on upper stages of the Titan and Atlas rockets, as well as on upper stages of the Delta III and Delta IV rockets. As a result, variants of this engine have been in nearly continuous use for just shy of 50 years.