NASA spacecraft shrinking orbit for Mars 2020

NASA's atmosphere-sniffing MAVEN Mars mission is tightening its orbit around the Red Planet to prepare for the US space agency's rover which is scheduled to launch next year.

The operation will reduce the highest point of the MAVEN spacecraft's elliptical orbit from 6,200 to 4,500 kilometres above the surface and prepare it to take on additional responsibility as a data-relay satellite for the Mars 2020 rover.

"The MAVEN spacecraft has done a phenomenal job teaching us how Mars lost its atmosphere and providing other important scientific insights on the evolution of the Martian climate," said Jim Watzin, director of NASA's Mars Exploration Programme.

"Now we're recruiting it to help NASA communicate with our forthcoming Mars rover and its successors," said Watzin.

While MAVEN's new orbit will not be drastically shorter than its present orbit, even this small change will significantly improve its communications capabilities.

"It is like using your cell phone. The closer you are to a cell tower, the stronger your signal," said Bruce Jakosky, MAVEN principal investigator from the University of Colorado, Boulder.

A strong telecommunications antenna signal is not the only benefit of a tighter orbit. Coming in about 1,500 kilometres closer also will allow the MAVEN orbiter to circle Mars more frequently -- 6.8 orbits per Earth day versus 5.3 previously -- and thus communicate with the Mars rovers more frequently.

While not conducting relay communications, MAVEN will continue to study the structure and composition of the upper atmosphere of Mars.

"We're planning a vigorous science mission far into the future," Jakosky said.

The MAVEN mission was designed to last two years in space, but the spacecraft is still operating normally. With the mission managing its fuel to last through 2030, NASA plans to use MAVEN's relay capability as long as possible.

The MAVEN orbiter carries an ultra-high-frequency radio transceiver -- similar to transceivers carried on other Mars orbiters -- that allows it to relay data between Earth and rovers or landers on Mars.

The MAVEN spacecraft already has served occasionally as NASA's communication liaison with the Curiosity rover.

Over the next few months, MAVEN engineers will use a navigation technique known as aerobraking -- like applying the brakes on a car -- to take advantage of the drag of the Red Planet's upper atmosphere to slow the spacecraft down gradually, orbit by orbit.

This is the same drag you would feel if you put your hand out of the window of a moving car.

Based on the tracking of the spacecraft by the navigation team at NASA's Jet Propulsion Laboratory in Pasadena, California, and at Lockheed Martin in Littleton, Colorado, engineers will begin carefully lowering the lowest part of the spacecraft's orbit into the Martian upper atmosphere over the next couple of days by firing its thrusters.

The spacecraft will circle Mars at this lower altitude about 360 times over the next 2.5 months, slowing down slightly with each pass through the atmosphere.

While it may seem like a time-consuming process, aerobraking is the most efficient way to change the spacecraft's trajectory, said Jakosky.