[meteorite-list] Responding to Potential Asteroid Redirect Mission Targets

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?release=2014-052

Responding to Potential Asteroid Redirect Mission Targets
Jet Propulsion Laboratory
February 14, 2014

One year ago, on Feb. 15, 2013, the world was witness to the dangers presented 
by near-Earth Objects (NEOs) when a relatively small asteroid entered 
Earth's atmosphere, exploding over Chelyabinsk, Russia, and releasing 
more energy than a large atomic bomb. Tracking near-Earth asteroids has 
been a significant endeavor for NASA and the broader astronomical community, 
which has discovered 10,713 known near-Earth objects to date. NASA is 
now pursuing new partnerships and collaborations in an Asteroid Grand 
Challenge to accelerate NASA's existing planetary defense work, which 
will help find all asteroid threats to human population and know what 
to do about them. In parallel, NASA is developing an Asteroid Redirect 
Mission (ARM) -- a first-ever mission to identify, capture and redirect 
an asteroid to a safe orbit of Earth's moon for future exploration by 
astronauts in the 2020s.

ARM will use capabilities in development, including the new Orion spacecraft 
and Space Launch System (SLS) rocket, and high-power Solar Electric Propulsion. 
All are critical components of deep-space exploration and essential to 
meet NASA's goal of sending humans to Mars in the 2030s. The mission represents 
an unprecedented technological feat, raising the bar for human exploration 
and discovery, while helping protect our home planet and bringing us closer 
to a human mission to one of these intriguing objects.

NASA is assessing two concepts to robotically capture and redirect an 
asteroid mass into a stable orbit around the moon. In the first proposed 
concept, NASA would capture and redirect an entire very small asteroid. 
In the alternative concept, NASA would retrieve a large, boulder-like 
mass from a larger asteroid and return it to this same lunar orbit. In 
both cases, astronauts aboard an Orion spacecraft would then study the 
redirected asteroid mass in the vicinity of the moon and bring back samples.

Very few known near-Earth objects are ARM candidates. Most known asteroids 
are too big to be fully captured and have orbits unsuitable for a spacecraft 
to redirect them into orbit around the moon. Some are so distant when 
discovered that their size and makeup are difficult for even our most 
powerful telescopes to discern. Still others could be potential targets, 
but go from newly discovered to out of range of our telescopes so quickly 
there is not enough time to observe them adequately.

For the small asteroids that do closely approach Earth, NASA's Near-Earth 
Object Program has developed a rapid response system whose chief goal 
is to mobilize NEO-observing assets when an asteroid first appears that 
could qualify as a potential candidate for the ARM mission.

"There are other elements involved, but if size were the only factor, 
we'd be looking for an asteroid smaller than about 40 feet (12 meters) 
across," said Paul Chodas, a senior scientist in the Near-Earth Object 
Program Office at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "There 
are hundreds of millions of objects out there in this size range, but 
they are small and don't reflect a lot of sunlight, so they can be hard 
to spot. The best time to discover them is when they are brightest, when 
they are close to Earth."

Asteroids are discovered by small, dedicated teams of astronomers using 
optical telescopes that repeatedly scan the sky looking for star-like 
objects, which change location in the sky slightly over the course of 
an hour or so. Asteroid surveys detect hundreds of such moving objects 
in a single night, but only a fraction of these will turn out to be new 
discoveries. The coordinates of detected moving objects are passed along 
to the Minor Planet Center in Cambridge, Mass., which either identifies 
each as a previously known object or assigns it a new designation. The 
observations are collated and then electronically published, along with 
an estimate of the object's orbit and intrinsic brightness. Automatic 
systems at NASA's Near-Earth Object Program Office at JPL take the Minor 
Planet Center data, compute refined orbit and brightness estimates, and 
update its online small-body database. A new screening process for the 
asteroid redirect mission has been set up which regularly checks the small-body 
database, looking for potential new candidates for the ARM mission.

"If an asteroid looks as if it could meet the criteria of size and orbit, 
our automated system sends us an email with the subject "'New ARM Candidate,'" 
said Chodas. "When that happens, and it has happened several dozen times 
since we implemented the system in March of 2013, I know we'll have a 
busy day."

Remember, things have to happen quickly because these small NEOs are only 
visible to even the most powerful of telescopes for a short period of 
a few days during their flyby of Earth. After receiving such an email, 
Chodas contacts the scientists coordinating radar observations at NASA's 
Deep Space Network station at Goldstone, Calif., and the Arecibo Observatory 
in Puerto Rico, to check on their availability. These are massive radar 
telescopes (the width of the Goldstone dish is 230 feet, or 70 meters, 
and the Arecibo dish is a whopping 1,000 feet, or 305 meters, wide). They 
have the capability of bouncing powerful microwaves off nearby asteroids, 
providing size and rotation information, and at times, even generating 
detailed images of an asteroid's surface. If these radar telescopes can 
see an asteroid and track it, definitive data on its orbit and size will 
quickly follow.

Chodas may also contact selected optical observatories run by professionals 
or sophisticated amateurs, who may be able to quickly turn their telescopes 
to observe the small space rock.

"The optical telescopes play an important role, as their observations 
can be used to improve our prediction of the orbital path, as well as 
provide data that helps us establish the rotation rate of an asteroid," 
said Chodas.

Chodas also reaches out to the NASA-funded Infrared Telescope Facility 
(IRTF) in Mauna Kea, Hawaii. If the IRTF can detect the space rock, it 
can provide a wealth of detailed data on spectral type, reflectivity and 
expected composition.

"After one of these alerts, there is a lot of calling and emailing going 
on in the beginning," said Chodas. "Then, we just simply have to wait 
to see what this worldwide network of assets can do to characterize the 
physical attributes of the potential ARM target."

Scientists estimate that several dozen asteroids in the 20-to-40-foot 
(6-to-12-meter) size range fly by Earth at a distance even closer than 
the moon every year. But only a fraction of these are actually detected, 
and even fewer are in orbits that are good candidates for ARM. Roughly 
half will pass Earth on the daytime side and are impossible to find in 
the bright glare of sunlight. Even so, current asteroid surveys are finding 
tens of asteroids in this size range every year, and new technology is 
coming online to make detection of these objects even more likely.

"The NASA-funded Catalina Sky Survey, which has made the majority of NEO 
discoveries since its inception in 2004, is getting an upgrade," said 
Lindley Johnson, program executive for the Near-Earth Objects Program 
at NASA Headquarters in Washington. "We also will have new telescopes 
with an upgraded detection capability, like PanSTARRS 2 and ATLAS, coming 
online soon, and the Defense Advanced Research Projects Agency's new Space 
Surveillance Telescope will give us a hand as well."

As part of its effort to find asteroids hazardous to Earth and destinations 
for future robotic and human exploration, NASA's NEO program will continue 
to search for even better potential targets for ARM. Also, NASA's WISE 
spacecraft has been reactivated and rechristened NEOWISE and could be used 
to characterize potential ARM targets.

In an attempt to leave no space-stone unturned, the agency is also combining 
public-private partnerships, crowdsourcing and incentive prizes to enhance 
existing efforts. Through its Asteroid Grand Challenge, NASA is reaching 
out to any and all who may have the next pioneering idea in asteroid research.

Of course, all this looking up and out and into the dim recesses of the 
solar system requires funding. NASA is already spending $20 million per 
year in the search for potentially hazardous asteroids through the Near 
Earth Object Observation Program. NASA's FY 14 budget included $105 million 
to plan for the capture and redirection of an asteroid, increase innovative 
partnerships and approaches to help us amplify efforts to identify and 
track and characterize asteroids, and conduct studies for mitigating potential 
threats.

We are learning a lot more about space rocks than we ever had before and 
along with that the rate of discoveries will continue to climb. And of 
those, only a portion of the new asteroids discovered is destined to have 
the right stuff for an asteroid retrieval mission -- the right size and 
the right orbit to satisfy mission requirements for the asteroid redirect 
mission.

The Near-Earth Object Program Office reports that, with current asteroid 
surveys already in place, about two potential candidates suitable for 
the asteroid redirect mission are discovered every year. The rate of discovery 
is projected to at least double as new imaging assets come online.

Does Chodas think there is a perfect target asteroid out there for an 
asteroid redirect mission?

"Absolutely. There are a lot of asteroids out there, and there are a lot 
of dedicated people down here, looking for them," said Chodas. "You put 
the two together and it's only a matter of time before we find some space 
rocks that fit our needs."

NASA's Near-Earth Object Program at NASA Headquarters, Washington, manages 
and funds the search, study and monitoring of asteroids and comets whose 
orbits periodically bring them close to Earth. JPL manages the Near-Earth 
Object Program Office for NASA's Science Mission Directorate in Washington. 
JPL is a division of the California Institute of Technology in Pasadena.

More information about asteroids and near-Earth objects is available at: 
http://neo.jpl.nasa.gov/, http://www.jpl.nasa.gov/asteroidwatch and via 
Twitter at http://www.twitter.com/asteroidwatch.

DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.
agle at jpl.nasa.gov

2014-052