Moonwalker Neil Armstrong has made a rare public appearance to honour a Nasa pioneer.
Mr Armstrong, 80, the first person to walk on the moon, presented an award at the US Space & Rocket Centre in Huntsville, Alabama, to Georg von Tiesenhausen, 96, whom the former astronaut warmly called "Dr von T".
Mr Armstrong, who has made infrequent public speeches since landing on the moon in 1969, said: "It's very comfortable for me to be in the company of many old associates."
Standing under a full-size Saturn V test rocket from the Apollo programme, Mr Armstrong praised Mr von Tiesenhausen as a space visionary, a great teacher and a top flight engineer.
"He is and has been a person who imagines what can be, and he has the skills to convert that imagine into reality," he said.
Mr von Tiesenhausen was among dozens of engineers who helped develop V-2 rockets for Germany during the Second World War and moved to the United States after the fighting ended. They formed the backbone of the fledgling US space programme at Huntsville's Redstone Arsenal in the 1950s and 60s.
Working under Wernher von Braun, Mr von Tiesenhausen helped design the battery-powered rover that astronauts drove on the lunar surface during the last three Apollo missions to the moon in 1971 and 1972.
Mr von Tiesenhausen was honoured as both an innovative space designer and an engaged, inquisitive man who still works with students, has an up-to-date mobile phone and knows about pop sensation Lady Gaga.
The German, who received a lifetime achievement award in education from the state-operated space museum, only recently gave up lecturing to students.