NASA is continuing to work on one of its most ambitious projects to date, and it is now offering money to companies, universities, and organizations to help find answers to the biggest technical hurdles that lie ahead. The mission itself sounds like it's ripped from the pages of a science-fiction novel — it calls for an unmanned vehicle to capture a small asteroid and tow it into the Moon's orbit, where it will be used for landing and training exercises by astronauts. The agency hopes that it will capture the asteroid in 2019 or 2020 in time for a manned mission in 2025 or later.

But first, there are a number of questions that need to be answered. And that's what today's call for proposals — known as a Broad Agency Announcement (BAA) — is for. There are five main areas where NASA's looking for help, and perhaps the most important is the asteroid capture system itself. The robotic ship, under current plans, would use an inflatable bag to capture the asteroid, roughly four to ten meters (roughly 13 to 32 feet) in diameter.

The agency is also accepting proposals for a suite of sensors designed for the mission, as well as finding ways to repurpose existing vehicles for the mission. It's all a long ways out, but this is one of the key steps in advancing the mission closer to reality. And if the asteroid mission isn't exciting enough for you, take note that the lessons learned on this journey are directly connected to any future manned missions to Mars.