Moon mission LADEE arrives after an 'amazingly precise' looping flight (+video)
LADEE, NASA's latest mission to the moon, successfully slipped into lunar orbit on Sunday. LADEE's looping trajectory offers a low-cost, dependable path to the moon.
More than 40 years after the last astronaut left the moon, NASA's next (robotic) explorer has arrived in lunar orbit. The Lunar Atmosphere and Dust Environment Explorer (LADEE) arrived right on schedule Sunday morning to investigate the twin mysteries of the moon's atmosphere and dust, after a picture-perfect launch and transit.Skip to next paragraph
In Pictures We love the moon
Subscribe Today to the Monitor
"The launch people really worked well and gave us just an absolutely perfect launch," says Mike Loucks, one of the "astrogators" (space navigators) planning LADEE's trip from the Earth to the moon. "It was just unbelievably precise… which made our job easy after that!" Though the team had prepared contingencies for any number of bobbles or snafus, none were needed.
Throughout the month-long flight, "the onboard propulsion system on the spacecraft has performed flawlessly as well, and been amazingly precise," says Loucks, who with the rest of the LADEE flight team was exempted from the NASA shutdown because their mission had already launched and needed their monitoring and maneuvering. "It's been remarkable."
RECOMMENDED: Are you a space whiz? Take our quiz!
It's tricky to define exactly when LADEE "got to the moon," since the robotic explorer didn't (and won't) land. Maybe when LADEE started orbiting? That happened with the first Lunar Orbit Insertion, or LOI-1, at 3:57 a.m. PDT on Sunday morning. But by then, LADEE had already been in the moon's "field of influence" — where the moon's gravity pulls more strongly than Earth's — for almost a day. Even before that, on October 2, LADEE crossed the midpoint of its final loop, and was closer to the moon than to Earth.
Imagine that the Earth-moon system is a clock, with Earth at the center and the moon at the tip of the second hand, smoothly sweeping around the Earth once a month. To get to the moon when it's at the 12 o'clock position, you need to leave Earth sometime sooner. During the Apollo missions, NASA took a straight shot to the moon, getting there as quickly as possible. In effect, they launched straight "up" the clock face, departing when the moon was at the 11 o'clock position.
LADEE didn't do that. The Apollo astronauts had a quicker flight — three days instead of 30 — but it required breathtaking precision and a mountain of fuel. Instead, LADEE flew along "phasing loops," taking big orbital swings around Earth until it crossed paths with the moon. Using the clock image, picture the little robot swinging out toward the 1 and back to the center, then down to the 4 and back to center, then over to the 8 and back to center, before finally arcing up to the 12 — arriving just as the moon sweeps by.
With this "phasing loop" approach, the astrogators built a nearly infinite amount of flexibility into their mission design. If the initial launch had been a bit low, or high, or fast, or slow, it wouldn't have mattered.
"We use those loops to open up our launch period," explains John Carrico, another flight dynamics expert and astrogator with the LADEE team. "If we had to launch a day late for some reason, we could still go to the moon exactly at the same time… by adjusting the orbit period, the time we spend in each loop."