NASA asteroid redirect mission decides that less is more
Meteorologist/Science Writer
Saturday, April 4, 2015, 1:58 PM - Worried about NASA's plan to pull a massive asteroid back to Earth for study? Well, after weighing all their options, the team has decided for a "less is more" approach, opting to retrieve a small boulder rather than the whole rock.
A little over two years ago, NASA began developing plans for a mission that would fly out to a nearby asteroid, capture it, and tow it back to Earth for study. Placed into orbit around the Moon, this asteroid could be visited by astronaut teams, who would fly there on the Orion spacecraft, to study its composition. The basic idea behind the mission was to provide us with more information about the nature of these objects, so that we can better defend Earth from random strikes, while at the same time testing out technologies for the future.
"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 press conference on Wednesday. "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."
That's right. Rather than constructing a spacecraft that can tow an entire asteroid back with it, the new plan is to send a spacecraft that will land on a near-Earth asteroid, retrieve a small boulder from the surface and bring that smaller rock back instead.
No doubt this switch in the plan will bring some relief to those who have been anxious about the consequences of a mishap with the mission, but at the same time, this has now become a much more manageable idea.
According to NASA:
The agency plans to announce the specific asteroid selected for the mission no earlier than 2019, approximately a year before launching the robotic spacecraft. Before an asteroid is considered a valid candidate for the mission, scientists must first determine its characteristics, in addition to size, such as rotation, shape and precise orbit. NASA has identified three valid candidates for the mission so far: Itokawa, Bennu and 2008 EV5. The agency expects to identify one or two additional candidates each year leading up to the mission.
The leading contender at the moment, according to those in attendance at the news conference, is 2008 EV5 - a C-type, or carbonaceous asteroid (one of the most common, essentially a dark rock in space) roughly 450 metres across, and which periodically comes as close to Earth as about 2 million kilometres (or over 5 times farther than the distance to the Moon). The boulder that will be retrieved for study will likely be more in the range of a few metres across. Thus, if the unthinkable happened, and this rock entered Earth's atmosphere, it would be far less dangerous, likely exploding harmlessly, far above the surface (for comparison, the Chelyabinsk superbolide was caused by an object roughly 20 metres across).
WATCH BELOW: NASA astronauts blast off to rendezvous with the ARM spacecraft, examine its 'charge', retrieve samples, and return to Earth.
Once the spacecraft lands, retrieves the boulder and takes off again, there is one aspect to the mission it will perform before returning home. It is expected to spend up to 8 months in orbit around the object, as shown below, to investigate one of the methods of planetary defense scientists have come up with to protect us against asteroid impacts.
Asteroid Redirect Mission (ARM) planetary defense demonstration will orbit the asteroid to test a concept known as a 'gravity tractor'. Credit: NASA
The combined mass of the boulder and spacecraft will test a method known as an 'enhanced gravity tractor'. Since all objects exert a gravitational force on all other objects, the closely-orbiting spacecraft should be able to demonstrate how it can cause a slight diversion in the asteroid's path. Adding the mass of the boulder to the 'equation' should enhance the effect.
This method could become a standard for planetary defense, if we are giving plenty of lead time before an impending asteroid impact, since it minimizes payload weight (and thus cost) for a launch, while maximizing the effect on the object we are trying to deflect.
Source: NASA | NASA ARM | JPL Small Object Database
