NASA Wednesday announced more details in its plan for its Asteroid Redirect Mission (ARM), which in the mid-2020s will test a number of new capabilities needed for future human expeditions to deep space, including to Mars. NASA also announced it has increased the detection of near-Earth asteroids by 65 percent since launching its asteroid initiative three years ago.

For ARM, a robotic spacecraft will capture a boulder from the surface of a near-Earth asteroid and move it into a stable orbit around the moon for exploration by astronauts, all in support of advancing the nation's journey to Mars.

"The Asteroid Redirect Mission will provide an initial demonstration of several spaceflight capabilities we will need to send astronauts deeper into space, and eventually, to Mars," said NASA Associate Administrator Robert Lightfoot.

"The option to retrieve a boulder from an asteroid will have a direct impact on planning for future human missions to deep space and begin a new era of spaceflight."

The agency plans to announce the specific asteroid selected for the mission no earlier than 2019, approximately a year before launching the robotic spacecraft. Before an asteroid is considered a valid candidate for the mission, scientists must first determine its characteristics, in addition to size, such as rotation, shape and precise orbit.

NASA has identified three valid candidates for the mission so far: Itokawa, Bennu and 2008 EV5. The agency expects to identify one or two additional candidates each year leading up to the mission.

Following its rendezvous with the target asteroid, the uncrewed ARM spacecraft will deploy robotic arms to capture a boulder from its surface. It then will begin a multi-year journey to redirect the boulder into orbit around the moon.

Throughout its mission, the ARM robotic spacecraft will test a number of capabilities needed for future human missions, including advanced Solar Electric Propulsion (SEP), a valuable capability that converts sunlight to electrical power through solar arrays and then uses the resulting power to propel charged atoms to move a spacecraft.

This method of propulsion can move massive cargo very efficiently. While slower than conventional chemical rocket propulsion, SEP-powered spacecraft require significantly less propellant and fewer launches to support human exploration missions, which could reduce costs.

Future SEP-powered spacecraft could pre-position cargo or vehicles for future human missions into deep space, either awaiting crews at Mars or staged around the moon as a waypoint for expeditions to the Red Planet.

ARM's SEP-powered robotic spacecraft will test new trajectory and navigation techniques in deep space, working with the moon's gravity to place the asteroid in a stable lunar orbit called a distant retrograde orbit. This is a suitable staging point for astronauts to rendezvous with a deep space habitat that will carry them to Mars.

Before the piece of the asteroid is moved to lunar orbit, NASA will use the opportunity to test planetary defense techniques to help mitigate potential asteroid impact threats in the future. The experience and knowledge acquired through this operation will help NASA develop options to move an asteroid off an Earth-impacting course, if and when that becomes necessary.

In 2005, NASA's Deep Impact comet science mission tested technology that could assist in changing the course of a near-Earth object using a direct hit with a spacecraft. The ARM robotic spacecraft opens a new and second option for planetary defense using a technique called a gravity tractor. All mass exerts and experiences gravity and, in space, the gravitational attraction even between masses of modest size can significantly affect their motion.

This means that by rendezvousing with the asteroid and holding a halo orbit in the appropriate direction, the ARM robotic spacecraft can slowly pull the asteroid without touching it. The effectiveness of this maneuver is increased, moreover, if mass is moved from the asteroid to the spacecraft by the capture of a boulder.

It will take approximately six years for the ARM robotic spacecraft to move the asteroid mass into lunar orbit. In the mid-2020s, NASA's Orion spacecraft will launch on the agency's Space Launch System rocket, carrying astronauts on a mission to rendezvous with and explore the asteroid mass. The current concept for the crewed mission component of ARM is a two-astronaut, 24-25 day mission.

This crewed mission will further test many capabilities needed to advance human spaceflight for deep space missions to Mars and elsewhere, including new sensor technologies and a docking system that will connect Orion to the robotic spacecraft carrying the asteroid mass. Astronauts will conduct spacewalks outside Orion to study and collect samples of the asteroid boulder wearing new spacesuits designed for deep space missions.

Collecting these samples will help astronauts and mission managers determine how best to secure and safely return samples from future Mars missions. And, because asteroids are made of remnants from the formation of the solar system, the returned samples could provide valuable data for scientific research or commercial entities interested in asteroid mining as a future resources.

In 2012, the president's NASA budget included, and Congress authorized, $20.4 million for an expanded NASA Near-Earth Object (NEO) Observations Program, increasing the resources for this critical program from the $4 million per year it had received since the 1990s. The program was again expanded in fiscal year 2014, with a budget of $40.5 million. NASA is asking Congress for $50 million for this important work in the 2016 budget.

"Asteroids are a hot topic," said Jim Green, director of NASA Planetary Science. "Not just because they could pose a threat to Earth, but also for their scientific value and NASA's planned mission to one as a stepping stone to Mars."

NASA has identified more than 12,000 NEOs to date, including 96 percent of near-Earth asteroids larger than 0.6 miles (1 kilometer) in size. NASA has not detected any objects of this size that pose an impact hazard to Earth in the next 100 years. Smaller asteroids do pass near Earth, however, and some could pose an impact threat. In 2011, 893 near-Earth asteroids were found. In 2014, that number was increased to 1,472.