In July 1969, four faculty members traveled from College Park to Kennedy Space Center in Florida to provide last-minute instruction to a noteworthy pupil: an Apollo 11 astronaut about to become one of the first humans to set foot beyond Earth.
Just days later, lunar module pilot Buzz Aldrin would be following mission commander Neil Armstrong onto the moon’s surface to deploy a UMD-led experiment. The suitcase-size array of retroreflectors—painstakingly crafted hunks of glass able to reflect light directly back to its source from any angle—would serve as a target for powerful lasers on Earth and provide the first accurate measurements of the distance between the planet and its satellite. In a meeting with Aldrin, then-Assistant Professor Douglas Currie, an expert in laser light, asked if the former fighter pilot with a Ph.D. in astronautics had any questions.
At a later lunar workshop, Currie recalls, Aldrin scoffed about the procedural instructions, “Ahh, it was so easy I decided I could give it to Armstrong.”
But the wisecracking astronaut had done his homework, and for the last 55 years, that array and two more placed by successive Apollo missions have yielded a wealth of data for NASA’s Lunar Laser Ranging experiment, helping scientists detect our moon’s liquid core, bolstering Einstein’s theory of general relativity and providing a better understanding of the evolution of the Earth-moon system, among other discoveries.
In an undated photo, Currie (seated) discusses the project with Apollo astronauts and astronomers at the McDonald Observatory in Texas.
Now the university has done it again with the launch early Wednesday of the Next Generation Lunar Retroreflector as part of a mission scheduled to touch down on the moon on March 2. This time, Currie is principal investigator for the retroreflector project, a position held on the Apollo 11 project by the late physics Professor Carroll Alley.
There are no astronauts to train for this mission; the chunky “corner cube” retroreflector will arrive aboard an uncrewed craft launched by the company Firefly Aerospace as part of NASA’s Commercial Lunar Payload Services program and remain atop the lander for its operational life. (Subsequent reflectors to be developed by NASA with UMD’s help, based on Currie’s general design, are expected to be set up by astronauts in NASA’s Artemis program, which aims to return to the moon later this decade.)
“When NASA announced back in 2004 they were going back to the moon, I said that instead of an array of 100, we need to have one big one, and I’ve been playing with that since then,” says Currie, now a professor emeritus and senior research scientist in the Department of Physics.
He and NASA hope the next-gen device boosts precision in distance measurements by perhaps a factor of 30, from several centimeters of uncertainty to less than one millimeter.
The imprecision of the current device stems from the fact that observers watching from the ground don’t know if a laser pulse bounces back from a reflector on the near corner or the far corner of the array, which are at slightly different and constantly changing distances from the ground because of the moon’s slight back-and-forth movement relative to Earth. Having just one mirror removes uncertainty, Currie says.