WASHINGTON — Scientists at the Johns Hopkins University Applied Physics Laboratory (APL) and two NASA field centers have teamed to conceive a robotic mission to visit an asteroid in advance of a future manned asteroid mission prescribed by U.S. President Barack Obama.

For the past five years, NASA has been working on the Constellation program to send astronauts back to the Moon by 2020. Obama in February proposed canceling the cash-hungry program in favor of a new set of initiatives that includes sending astronauts to the international space station on commercial taxis and eventually starting a new heavy-lift rocket development. In April, Obama called for sending astronauts to visit a near-Earth object by 2025.

Laurel, Md.-based APL was the first organization to build a satellite to orbit and land on an asteroid. The lab’s Near Earth Asteroid Rendezvous (NEAR) Shoemaker spacecraft made history when it orbited the asteroid 433 Eros and then touched down on its surface in 2001. The Japanese Hayabusa spacecraft that orbited and landed on an asteroid in 2005 is the only other craft to do so.

APL over the past several months has worked with NASA’s Johnson Space Center in Houston and Goddard Space Flight Center in Greenbelt, Md., to conceive of a follow-on mission to NEAR Shoemaker that would help set the stage for a human asteroid mission. The team has designed the so-called Next Gen NEAR mission to visit one of many candidate asteroids that reside between seven and 16 months from Earth, said Andy Cheng, chief scientist of APL’s Space Department. The envisioned car-sized spacecraft, with proper funding, could launch on a medium-class rocket as early as 2014, Cheng said in an Aug. 31 interview.

Next Gen NEAR is designed to use commercially available subsystems and lightweight scientific instruments including a camera, composition-measuring spectrometers and surface interaction experiments with flight heritage. The satellite would be small enough for NASA to include a tagalong spacecraft on the rocket, much as NASA did with the Lunar Reconnaissance Orbiter mission when it added the $80 million Lunar Crater Observation and Sensing Satellite.

Just as NASA sent robotic probes to the Moon before landing astronauts there for the first time during the Apollo program, the agency has said it will send an unmanned spacecraft to visit whichever asteroid is eventually chosen for a manned mission.

“A robotic mission must go to the asteroid before a manned mission, because otherwise you’re taking a tremendous amount of risk to go to an unknown object,” Cheng said. “You don’t know what you can do there; you don’t know if the experiments you bring are going to work or what hazard you might face.”

The near-zero gravity conditions found on asteroids make their operating environment more similar to the international space station than the Moon, said Paul Abell, a space scientist at Johnson who also worked on the NEAR Shoemaker mission. Instead of actually landing on the asteroid’s surface, the spacecraft would fly alongside it and penetrate the surface with probes.

The precursor mission’s primary objectives are to characterize the surface material and determine whether and how a future mission could attach itself to the asteroid.

“Sending a human mission is a little different than sending a robotic mission,” Abell said. “With a human mission, you’re probably talking about doing some close proximity operations, getting very close to the surface with the spacecraft and then deploying astronauts for [extra-vehicular activities], and then maybe deploying other robotic devices like rovers.

“Because of the microgravity environment, they’re going to be interacting with it but not walking across it. Think of it like underwater cave diving.”

The Next Gen NEAR mission concept has been briefed internally to NASA leadership, and has not yet been approved or funded in any way. APL, Johnson and Goddard believe the mission could be executed within the budgetary constraints of a Discovery-class mission, currently capped at $425 million, not including launch. NASA’s 2011 budget proposal includes funding for a new class of Exploration Precursor Robotic Missions, but lawmakers so far have resisted fully funding the program.