Washington, Feb 7 (IANS): NASA has said it is preparing to send its deep space atomic clock on a test flight in 2018 as a hosted payload on General Atomic's Orbital Test Bed spacecraft aboard the US Air Force Space Technology Program (STP-2) mission.

The the "Deep Space Atomic Clock" (DSAC) aims to provide accurate onboard timekeeping for future missions, NASA said on Tuesday.

"We have lofty goals for improving deep space navigation and science using DSAC," said DSAC's principal investigator Todd Ely of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

JPL scientists have been perfecting the clock for 20 years now.

Currently, most missions rely on ground-based antennas paired with atomic clocks for navigation. Ground antennas send narrowly focused signals to spacecraft, which, in turn, return the signal.

NASA uses the difference in time between sending a signal and receiving a response to calculate the spacecraft's location, velocity and path.

This method, though reliable, could be made much more efficient. For example, a ground station must wait for the spacecraft to return a signal, so a station can only track one spacecraft at a time.

This requires spacecraft to wait for navigation commands from Earth rather than making those decisions onboard and in real-time.

Spacecraft using thw new technology would no longer have to rely on two-way tracking. A spacecraft could use a signal sent from Earth to calculate position without returning the signal and waiting for commands from the ground, a process that can take hours.

Timely location data and onboard control allows for more efficient operations, more precise manoeuvering and adjustments to unexpected situations.

This paradigm shift enables spacecraft to focus on mission objectives rather than adjusting their position to point antennas earthward to close a link for two-way tracking.

Additionally, this innovation would allow ground stations to track multiple satellites at once near areas like Mars, crowded with NASA science missions.

In certain scenarios, the accuracy of that tracking data would exceed traditional methods by a factor of five, NASA said.

DSAC is an advanced prototype of a small, low-mass atomic clock based on mercury-ion trap technology.

While the atomic clocks at ground stations in the Deep Space Network are about the size of a refrigerator, DSAC is about the size of a four-slice toaster, and could be further miniaturized for future missions.

The DSAC test flight will take this technology from the laboratory to the space environment.

While in orbit, the DSAC mission will use the navigation signals from US GPS coupled with precise knowledge of GPS satellite orbits and clocks to confirm DSAC's performance.

The demonstration should confirm that DSAC can maintain time accuracy to better than two nanoseconds (.000000002 seconds) over a day, with a goal of achieving 0.3 nanosecond accuracy.

Once DSAC has proven the technology, future missions can use its technology enhancements, NASA said.