NASA has announced more details about its Asteroid Redirect Mission (ARM), which no longer includes an attempt to capture an entire asteroid. Instead, an uncrewed spacecraft will travel to one of three candidate asteroids in 2020. When the craft arrives in 2022, it will use robotic arms to pick and secure a small boulder from the asteroid, and will spend a number of years towing the boulder into a stable orbit between the Earth and the Moon.
Humans will visit the boulder in 2025
The space agency plans to send a team of astronauts to study the boulder in 2025 using the Orion capsule, the same spacecraft that should eventually bring the first humans to Mars. They will also be tasked with returning samples to Earth. Asteroids are rocky and full of precious metals, which means they can teach us a lot about the formation of our solar system, as well as provide material value. The three being considered — Itokawa, Bennu, and 2008 EV5 — have all been closely studied or even visited by other spacecraft, so the mission should be less risky than sending a probe to explore a comet that's a half-billion miles away.
The mission plan NASA discarded involved the much greater task of "lassoing" an entire asteroid. The jettisoned mission required a bigger spacecraft and more moving parts — specifically an inflatable module to surround and seal the space rock inside before towing it to a similar spot.
The challenges NASA faces in executing a mission like this will help us develop important skills that could one day be useful in a trip to Mars, according to the agency. Despite that inspirational claim, ARM has had somewhat of a tumultuous history. Vox's Joseph Stromberg points out that the mission was originally proposed in part to give the Space Launch System (NASA's next giant rocket meant to bring humans to space) something to do in the time between its creation and potential missions to the Moon or Mars — not the most inspiring start. ARM has also been a target of House Republicans both on the floor and in op-ed pages because many would rather see NASA return to the Moon instead. As a result of that either/or argument, ARM has not received any specific budgeting. Considering that the agency won't make a final asteroid selection until 2019, even this version of ARM is a long way from being rock solid.