FORMATION FLYING, AROUND THE MOON AT 3,600 MPH – The act of two or more aircraft flying together in a disciplined, synchronized manner is one of the cornerstones of military aviation, as well as just about any organized air show. But as amazing as the U.S. Navy’s elite Blue Angels or the U.S. Air Force’s Thunderbirds are to behold, they remain essentially landlocked, anchored if you will, to our planet and its tenuous atmosphere. What if you could take the level of precision of these great aviators to, say, the Moon?
“Our job is to ensure our two GRAIL spacecraft are flying a very, very accurate trail formation in lunar orbit,” said David Lehman, GRAIL project manager at JPL. “We need to do this so our scientists can get the data they need.”
Essentially, trail formation means one aircraft (or spacecraft in this case), follows directly behind the other. Ebb and Flow, the twins of NASA’s GRAIL (Gravity Recovery And Interior Laboratory) mission, are by no means the first to synch up altitude and “air” speed while zipping over the craters, mountains, hills and rills of Earth’s natural satellite. That honor goes to the crew of Apollo 10, who in May 1969 performed a dress rehearsal for the first lunar landing. But as accurate as the astronauts aboard lunar module “Snoopy” and command module “Charlie Brown” were in their piloting, it is hard to imagine they could keep as exacting a position as Ebb and Flow.
“It is an apples-and-oranges comparison,” said Lehman. “Lunar formation in Apollo was about getting a crew to the lunar surface, returning to lunar orbit and docking, so they could get back safely to Earth. For GRAIL, the formation flying is about the science, and that is why we have to make our measurements so precisely.”
As the GRAIL twins fly over areas of greater and lesser gravity at 3,600 mph, surface features such as mountains and craters, and masses hidden beneath the lunar surface, can influence the distance between the two spacecraft ever so slightly.
How slight a distance change can be measured by the science instrument beaming invisible microwaves back and forth between Ebb and Flow?
How about one-tenth of one micron? Another way to put it is that the GRAIL twins can detect a change in their position down to one half the width of a human hair (0.000004 inch). Any change in separation between the two twins greater than this will be duly noted aboard the spacecraft’s memory chips for later downlinking to Earth. Working together, Ebb and Flow will make these measurements while flying over the entirety of the lunar surface.
Why would scientists care about such a tiny change of distance between two spacecraft?
“From the data collected during these minute distance changes between spacecraft, we will be able to generate an incredibly high-resolution map of the Moon’s gravitational field,” said MIT’s Maria Zuber, principal investigator of the GRAIL mission. From that, we will be able to understand what goes on below the lunar surface in unprecedented detail.”
“Next time you look up and see the Moon, you might want to take a second and think about our two little spacecraft flying formation, zooming from pole to pole at 3,600 mph,” said Lehman. “They’re up there, working together, flying together, getting the data our scientists need. As far as I’m concerned, they’re putting on quite a show.”
You can contact Bob Eklund at firstname.lastname@example.org, or visit his website at www.bobeklund.com.