Lightfoot said Option B, the boulder concept, was more intriguing in terms of advancing future technologies. However, Option B is more complex because it requires the capture vehicle to land on a target asteroid before capturing its boulder. NASA expects both concepts to cost less than $1.25 billion, with Option B requiring an additional $100 million. Those mission costs do not include a launch vehicle. Lightfoot said possible rocket choices include NASA's Space Launch System, a United Launch Alliance Delta IV Heavy, or SpaceX's Falcon Heavy. Launch dates are expected to be evaluated during the Mission Concept Review. A crewed asteroid visit would take place using the NASA's Orion spacecraft, launched via the Space Launch System.

An independent cost estimate is expected to evaluate whether the $1.25 billion ARM budgets are accurate. During today's teleconference, Lightfoot indicated such an assessment might not be made until after one of the options are selected. "We're required to do an independent cost assessment going into the MCR," he said. "And that's one of the reasons we want to limit the options that go into the MCR. That's one of the bigger drivers, because the independent cost assessment takes awhile."

According to notes from a July 2014 meeting of the NASA Advisory Council, Chair Steve Squyres asked NASA's Deputy Associate Administrator for the Human Exploration and Operations Mission Directorate Greg Williams when an independent cost estimate for ARM would take place. "Williams replied that it would occur before the down-select," say the meeting notes.

Editor's note: The Planetary Society conditionally supports NASA's Asteroid Redirect Mission, pending a rigorous, independent cost estimation.