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NASA provided funding to increase the amount of time the Apache Point team could spend firing a laser at the moon.
Source: NMSU Newsroom
Photos: Courtesy
Imagine measuring the distance from Earth to an object on the moon within a space equal to the thickness of a single penny.
That’s what a team from Apache Point Observatory (APO) and New Mexico State University’s Department of Astronomy accomplished as part of a NASA project for the Lunar Laser Ranging Operations program using the 3.5-meter telescope at APO in Sunspot, New Mexico.
“It’s just mind boggling to me that we can measure the distance to an object on the moon to within 1 millimeter,” said Nancy Chanover, NMSU astronomy professor. “I hope that people understand what a technological achievement that is.”
On March 2, 2025, Firefly Aerospace’s Blue Ghost Mission 1 landed on the moon in Mare Crisium, delivering 10 scientific instruments to the lunar surface for NASA as part of the agency’s CLPS (Commercial Lunar Payload Services) initiative. One of those, the Next Generation Lunar Retroreflector, is a more compact and newly designed reflective device that is mounted on the lander’s antenna arm, adding to the set of retroreflectors left on the lunar surface by the Apollo 11, 14, and 15 astronauts. The team at Apache Point located the new retroreflector with their laser on March 20 and has continued ranging to it ever since.
The moon is nearly 240,000 miles from Earth. Accurately measuring the distance to the moon through laser ranging experiments provides unique constraints on the moon’s orbit, its interior structure, and fundamental properties of gravity. It also provides navigational benefits to upcoming spacecraft that will orbit or land on the moon. NASA provided funding to increase the amount of time the Apache Point team could spend firing a laser at the moon. They are now firing the laser approximately three times a week.
The Apache Point team includes Bill Ketzeback, director of operations at Apache Point Observatory; Russet McMillan, night operations manager of the 3.5-meter telescope who has been with the laser ranging project since it began in 2005; and Torrie Sutherland, an observing specialist hired last summer specifically for this project.
The Lunar Laser Ranging Operations program began at Apache Point 20 years ago and is currently under the direction of NASA Goddard Space Flight Center’s Geodesy and Geophysics Laboratory, which contributes to the accurate measurements of the Earth and moon reference frames through the deployment, operation and maintenance of a global network of space geodetic observatories.
Unlike other lunar laser ranging experiments, the NMSU team achieves high precision by detecting multiple reflected laser photons per pulse.
“Our laser pulses 20 times a second, every time it flashes, it sends out about 1017 (or a hundred quadrillion) photons, which are the smallest unit of light, toward the moon,” said McMillan. “It does spread out depending on the conditions in Earth’s atmosphere. It can be a kilometer or a mile wide by the time it reaches this little grapefruit-sized retroreflector sitting on the moon’s surface. So, only a fraction of those photons gets reflected back toward Earth.”
Geodesy is the science of the Earth’s shape, gravity and rotation, including their evolution in time. Space geodesy has revolutionized the study of solid Earth processes through its ability to measure the deformation of the Earth’s surface and the Earth’s gravity field with extraordinary accuracy. The Apache Point Lunar Laser Ranging Station extends this effort out to the moon. Apache Point produces the data used to realize the lunar reference frames that are essential for positioning and navigation application on and around the moon. The data is also essential for studying the internal structure of the Moon as well as fundamental tests of gravitational theories like General Relativity.
Sutherland is excited to be the newest member of the Apache Point Observatory team.
(Left) The Apache Point Observatory 3.5-meter telescope fires a laser to locate retroreflectors on the surface of the moon. (APO photo by Candace Gray)
(Right-Top) Inside the 3.5-meter telescope enclosure at Apache Point Observatory as it fires a laser at the moon. (APO photo by Candace Gray)
(Right-Middle) Technician at Firefly Aerospace measures the fit of the Next Generation Lunar Retroflector payload in the lab before attaching it to the Blue Ghost lunar lander’s antenna arm. (Photo courtesy Firefly Aerospace)
(Right-Bottom) This all-sky view from Apache Point Observatory (APO) in Sunspot, NM, captured the laser beam traveling from the 3.5-meter telescope to the Moon. The optical ALCOR SYSTEMS OMEA 5C all-sky camera provides a current 180 by 180-degree view of the sky, which is normally used by remote observers to assess the weather conditions throughout their observations. On the clear night of April 22, 2025, it caught the laser in action. (APO photo by Amanda Townsend)
“I kind of wear two hats right now,” Sutherland said. “One is helping to run the 3.5-meter telescope, and the other hat is working on this project with the laser. What I do is for that is we work on firing the laser, making sure everything the laser is healthy and working properly and then just searching around the moon while the laser is firing to make sure we get the reflectors.”
Ketzeback explained the difficulty of measuring the light’s travel time round-trip to the moon and back to within 1 millimeter. The high level of accuracy that the NMSU team accomplished is about 10 times higher than other stations have reported, usually to about 1 centimeter – the width of a Cheerio (cereal piece).
“Another challenging aspect of this project, this milestone, has been that while the Earth is moving through space, the moon is moving through space,” Ketzeback said. “The Earth is rotating while the moon tends to move with a slow wobble. So not only did this new reflector go on the moon, but when you’re trying to measure distance to an accuracy of 1 centimeter or better, finding this reflector from this distance is quite challenging.”
The NMSU team will continue to range to this new retroreflector as well as several others left on the Moon during the Apollo and Soviet lunar landers in the 1970’s, and there are also plans to deliver another retroreflector to the lunar surface as soon as late 2025 or early 2026. A third one will be delivered a few years after. Another next step for the team is to improve their ability to range not just to reflectors on the moon, but also retroreflectors on satellites either in orbit around the Earth or someday around the moon.
“We want to keep acquiring measurements the way we’ve been doing since 2005 to build up the longtime baseline that is necessary for studies of the lunar interior and orbit,” Chanover said. “But with this new retroreflector we are also preparing ourselves on the technology side to make sure that we can continue to operate and improve our hardware, to ensure that we’ll be able to do this for many years to come.”
