Asteroids are getting a lot of attention, today in particular, because asteroid 2014 YB35 will be coming within 0.03 Astronomical Units (AU) of Earth. There is no reason to be alarmed, as this is a natural occurrence within our Solar System, and NASA is hard at work discovering these Near Earth Objects, or NEOs. Since NASA launched its Asteroid Initiative three years ago, the agency has identified more than 12,000 asteroids, with about 96 percent measuring over 0.6 miles (1 km) in length. None of these objects pose a threat to our home planet; however, they do offer the chance to study these massive space rocks for future deep space missions and deflection techniques if one should threaten Earth. NASA’s Asteroid Redirect Mission (ARM) is currently under development with plans to send a robotic spacecraft to a near-Earth asteroid for a rendezvous and capture mission. The agency originally had an ambitious plan to rendezvous with an asteroid, capture it, and bring it into lunar orbit for exploration by astronauts.
However, on Wednesday, March 25, NASA announced plans to move forward instead with the Robotic Boulder Capture Option (also known as “Option B”) under the ARM. Following Option B, a robotic spacecraft will pluck a boulder from the surface of a near-Earth Asteroid (NEA) and move it into a stable orbit around our Moon. Once the boulder is in stable lunar orbit, astronauts will launch off the agency’s Space Launch System (SLS) rocket and navigate to the orbiting mass aboard the Orion spacecraft. NASA expects this to happen in the mid-2020s, and currently plans for a two-astronaut crew to carry out the mission in a 24-25 day time period.
“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,” explained NASA Associate Administrator Robert Lightfoot. “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.”
A previous AmericaSpace article noted that a decision regarding ARM was to be made in January prior to a Mission Concept Review (MCR) scheduled for February 2015, with only the selected option presenting, but Lightfoot delayed the decision in order to gain a better understanding of some of the issues.
The rejected option, Option A, involves sending a “probe out to capture a small asteroid and tow it back to orbit using an inflatable system.” Both options involve redirecting an asteroid mass into a stable orbit around the Moon.
The Robotic Boulder Capture Option, or Option B, has three primary objectives:
- Return a boulder from the surface of a large Near-Earth Asteroid (NEA) to a stable lunar orbit
- Alter the trajectory of an asteroid of potentially hazardous size (~100+ m diameter)
- Mature key technologies and operations in human-class Mars mission environment
At this time, the agency has a few asteroids in mind for selection but won’t announce the specific asteroid until 2019, about one year before the robotic spacecraft is due to launch. NASA expects to identify up to two prospective asteroids per year until then. Characteristics such as size, rotation, shape, and orbit matter when choosing a valid candidate asteroid. So far, the agency has three candidates for the mission: Itokawa, Bennu, and 2008 EV5.
Option B has identified asteroid candidates based on target availability and boulder size and mass. Asteroid Itokawa is a “valid candidate with hundreds of candidate boulders.” Bennu and 1999 JU3 are “two candidates planned to be characterized by precursors in 2018” by OSIRIS-Rex (Bennu) and Hayabusa 2 (1999 JU3). There is one candidate, 2008 EV5, characterized by radar at ~6000 SNR. Option B plans on at least two more candidates being “sufficiently characterized by radar during the next 4 years: 2011 UW158 and 2009 DL46.” According to the July 2014 presentation on Boulder Size and Mass for June 2019 Launch and February – May 2025 Crew Availability, it was determined that “spherical maximum returnable boulder size ranges from 1.5 m to 4 m enabling a large range of boulder size for retrieval.”
The Hayabusa spacecraft, developed by Japan Aerospace Exploration Agency, known as JAXA, landed on the surface of the asteroid in November 2005 and collected samples to return to Earth in June 2010. The mission confirmed that there were thousands of 2-5 meter boulders existing on the surface of the asteroid and around 20 percent of the surface contains smooth areas with few hazards and wide access to target boulders. Boulders are commonly found on NEAs and are believed to be created by impacts.
When NASA decides on a suitable target, the uncrewed ARM spacecraft will travel to the target asteroid, rendezvous with it, and deploy robotic arms to pluck a boulder from the surface. According to NASA, it will take nearly six years for the robotic spacecraft to move the mass into the Moon’s orbit, known as distant retrograde orbit.
The ARM robotic spacecraft will explore a number of abilities needed for future human missions to space, including a new method of propulsion known as Solar Electric Propulsion (SEP). This new method converts sunlight to electrical power through the use of solar arrays and uses that power to thrust charged atoms to push a spacecraft. This method can move massive cargo very efficiently but moves slower than conventional chemical rocket propulsion. On the flip side, one of the benefits of using a SEP-powered spacecraft is that it requires less propellant and fewer launches to support human exploration and deep space missions. The use of SEP propulsion could significantly reduce costs.
Another ability the ARM spacecraft will test before the asteroid is moved to lunar orbit is planetary defense techniques to aid in deflecting a potential asteroid impact, if one should threaten Earth. There is no threat of an asteroid impacting our home planet for the next century, but in case it does become a possibility, NASA will have the technology to move an asteroid off a collision course with Earth.
“Asteroids are a hot topic,” said Jim Green, director of NASA Planetary Science. “Not just because they could pose a threat to Earth, but also for their scientific value and NASA’s planned mission to one as a stepping stone to Mars.”
The crewed mission to study an asteroid mass in lunar orbit will test many capabilities needed to send humans on deep space missions to Mars and beyond. Some of these include news sensor technologies and a docking system that will attach Orion to the ARM spacecraft carrying the boulder. Astronauts will conduct EVAs, or spacewalks, outside the Orion crew capsule to study and collect samples of the asteroid. They will also wear and test out new spacesuits designed for human exploration in deep space.
Samples collected from the orbiting mass will help astronauts and mission managers determine the best techniques for securing and safely returning samples from future Mars missions. The samples may also provide important data for research or commercial entities interested in mining asteroids for resources.
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