Enthusiasts who have been following NASA's mission plans closely might be a little disappointed with the space agency's latest decision concerning the historic Asteroid Redirect Mission (ARM). The mission, the very name of which held the promise of physically capturing an asteroid, will now simply be plucking a boulder from the surface of a hurtling space rock as it flies by in 2022.

Nature World News had previously reported back in June how the boulder capture scenario was only one of two possible ARM scenarios the agency was considering. The other, which captured the imaginations of young researchers across the nation, concerned physically snagging a very small asteroid with a robotic spacecraft and redirecting its path so that it would be caught in the Moon's orbit. From there, astronauts would have been able to physically step on an asteroid to retrieve samples by hand for the first time in human history.

But while the latter of these two ideas is certainly more exciting, it's important to note that NASA spent a great deal of money simply considering the scientific value and returns of both these plans.

NASA had crowdsourced for conceptual ideas to tackle these endeavors, and had awarded a net total of $4.9 million (USD) to scientific teams conducting relevant studies that addressed the challenges of each mission. As a result, NASA announced Wednesday that the boulder retrieval scenario was far more plausible and cost-efficient. It has since officially become the goal set for the ARM.

"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," NASA Associate Administrator Robert Lightfoot said in a statement. "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."

It's fair to wonder, however, that if the agency is using the ARM to delve into difficult deep space missions, why would it choose the seemingly simpler of the two scenarios? After all, taking a large sample from a large asteroid via unmanned spacecraft is certainly not "redirecting" an asteroid like the mission name implies. (Scroll to read on...)

NASA reports that one of the main benefits of the ARM is that it will allow experts to put advanced Solar Electric Propulsion (SEP) technologies to the test.

The agency describes this as "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."

And while SEP is far slower than conventional chemical propulsion systems, "SEP-powered spacecraft require significantly less propellant and fewer launches to support human exploration missions, which could reduce costs."

And getting the most bang for your buck, at the end of the day, may be what this decision was really all about.

Lightfoot explained in a teleconference on Wednesday that the boulder-snatch concept is expected to cost $100 million more than the bagging concept, largely because it will require some impressive robotics technology as well as a means to bring that boulder back to Earth.

However, he added that it's the safer route. The asteroid capture concept would only have one shot at getting it right. Meanwhile, the boulder retrieval method can make several attempts. (Scroll to read on...)

"I'm going to have multiple targets when I get there, is what it boils down to," Lightfoot said. "That was the better value, in my opinion, for what we're trying to do."

It's also important to note that while the boulder approach will cost an estimated $1.25 billion, the Moon orbit scenario had its own additional costs that could have pushed the agency's wallet. After the small asteroid was successfully redirected, NASA would still have to drop the cash for additional launches to put equipment-toting astronauts on it.

Still, some experts are skeptical that any ARM is worth any cost at all. After all, NASA and Canada are already invested in the OSIRIS-REx mission, which aims to return about 60 grams of samples from the asteroid Bennu by 2023. And Bennu also happens to be one of the three asteroid candidates that NASA is considering for the ARM.

Meanwhile, JAXA, Japan's space agency, just launched Hayubusa 2, which will be bringing several grams of asteroidal material back to Earth in 2020.

It may be that NASA has its hands in too many cookie jars at one time. We won't know for sure that ARM will be worth it until results are in - long after the mission's spacecraft returns with a big old hunk of space rock in tow.

For more great nature science stories and general news, please visit our sister site, Headlines and Global News (HNGN).

 - follow Brian on Twitter @BS_ButNoBS