European Asteroid Smasher Could Bolster Planetary Defense

Planetary Defense is a concept very few people heard of or took seriously – that is until last week’s humongous and totally unexpected meteor explosion over Russia sent millions of frightened residents ducking for cover, followed just hours later by Earth’s uncomfortably close shave with the 45 meter (150 ft) wide asteroid named 2012 DA14.

This ‘Cosmic Coincidence’ of potentially catastrophic space rocks zooming around Earth is a wakeup call that underscores the need to learn much more about the ever present threat from the vast array of unknown celestial debris in close proximity to Earth and get serious about Planetary Defense from asteroid impacts.

The European Space Agency’s (ESA) proposed Asteroid Impact and Deflection Assessment mission, or AIDA, could significantly bolster both our basic knowledge about asteroids in our neighborhood and perhaps even begin testing Planetary Defense concepts and deflection strategies.

After two years of work, research teams from the US and Europe have selected the mission’s target – a so called ‘binary asteroid’ named Didymos – that AIDA will intercept and smash into at about the time of its closest approach to Earth in 2022 when it is just 11 million kilometers away.

“AIDA is not just an asteroid mission, it is also meant as a research platform open to all different mission users,” says Andres Galvez, ESA studies manager.

Asteroid Didymos could provide a great platform for a wide variety of research endeavors because it’s actually a complex two body system with a moon – and they orbit each other. The larger body is roughly 800 meters across, while the smaller one is about 150 meters wide.

Didymos with its Moon
Didymos with its Moon. Credit: ESA

So the smaller body is some 15 times bigger than the Russian meteor and 3 times the size of Asteroid 2012 DA14 which flew just 27,700 km (17,200 mi) above Earth’s surface on Feb. 15, 2013.

The low cost AIDA mission would be comprised of two spacecraft – a mother ship and a collider. Two ships for two targets.

The US collider is named the Double Asteroid Redirection Test, or DART and would smash into the smaller body at about 6.25 km per second. The impact should change the pace at which the objects spin around each other.

ESA’s mothership is named Asteroid Impact Monitor, or AIM, and would carry out a detailed science survey of Didymos both before and after the violent collision.

“The project has value in many areas,” says Andy Cheng, AIDA lead at Johns Hopkins’ Applied Physics Laboratory, “from applied science and exploration to asteroid resource utilisation.” Cheng was a key member of NASA’s NEAR mission that first orbited and later landed on the near Earth Asteroid named Eros back in 2001.

Recall that back in 2005, NASA’s Deep Impact mission successfully lobbed a projectile into Comet Tempel 1 that unleashed a fiery explosion and spewing out vast quantities of material from the comet’s interior, including water and organics.

NASA’s Deep Impact images Comet Tempel 1 alive with light after colliding with the impactor spacecraft on July 4, 2005.  ESA and NASA are now proposing the AIDA mission to smash into Asteroid Didymos.  CREDIT: NASA/JPL-Caltech/UMD
NASA’s Deep Impact images Comet Tempel 1 alive with light after colliding with the impactor spacecraft on July 4, 2005. ESA and NASA are now proposing the AIDA mission to smash into Asteroid Didymos. CREDIT: NASA/JPL-Caltech/UMD

ESA has invited researchers to submit AIDA experiment proposals on a range of ideas including anything that deals with hypervelocity impacts, planetary science, planetary defense, human exploration or innovation in spacecraft operations. The deadline is 15 March.

“It is an exciting opportunity to do world-leading research of all kinds on a problem that is out of this world,” says Stephan Ulamec from the DLR German Aerospace Center. “And it helps us learn how to work together in international missions tackling the asteroid impact hazard.”

The Russian meteor exploded without warning in mid air with a force of nearly 500 kilotons of TNT, the equivalent of about 20–30 times the atomic bombs detonated at Hiroshima and Nagasaki.

Over 1200 people were injured in Russia’s Chelyabinsk region and some 4000 buildings were damaged at a cost exceeding tens of millions of dollars. A ground impact would have decimated cities like New York, Moscow or Beijing with millions likely killed.

ESA’s AIDA mission concept and NASA’s approved Osiris-REx asteroid sample return mission will begin the path to bolster our basic knowledge about asteroids and hopefully inform us on asteroid deflection and Planetary Defense strategies.

Ken Kremer

Near-Earth asteroid Eros imaged from NASA’s orbiting NEAR spacecraft. Credit: NASA
Near-Earth asteroid Eros imaged from NASA’s orbiting NEAR spacecraft. Credit: NASA

An Elegant Proposal for Near Earth Asteroid Deflection

Although the chances of an asteroid hitting Earth appear to be small for any given year, the consequences of such an event would be monumental. The science community has come up with some ideas and proposals for ways to mitigate the threat of an incoming asteroid hitting the Earth. Some proposals suggest almost Hollywood type theatrics of launching nuclear weapons to destroy the asteroid, or slamming a spacecraft into a Near Earth Object to blow it apart. But other ideas employ more simple and elegant propositions to merely alter the trajectory of the space rock. One such plan uses a two-piece solar sail called a solar photon thruster that draws on solar energy and resources from the asteroid itself.

Physicist Gregory Matloff has been working with NASA’s Marshall Spaceflight Center to study the two-sail solar photon thruster which uses concentrated solar energy. One of the sails, a large parabolic collector sail would constantly face the sun and direct reflected sunlight onto a smaller, moveable second thruster sail that would beam concentrated sunlight against the surface of an asteroid. In theory, the beam would vaporize an area on the surface to create a ‘jet’ of materials that would serve as a propulsion system to alter the trajectory of the Near Earth Object (NEO.)

Changing the trajectory of a NEO exploits the fact that both the Earth and the impactor are in orbit. An impact occurs when both reach the same point in space at the same time. Since the Earth is approximately 12,750 km in diameter and moves at about 30 km per second in its orbit, it travels a distance of one planetary diameter in about seven minutes. The course of the object would be altered, or either delayed or advanced and cause it to miss the Earth.

But of course, the arrival time of the impactor must be known very accurately in order to forecast the impact at all, and to determine how to affect its velocity.

Additionally, the solar photon thruster’s performance would vary depending on the unique makeup of each NEO. For example, asteroids with a greater density, radius or rate of rotation would cause decreased performance of the solar photon thruster in acceleration and deflection.

Even though the solar photon thruster appears to be efficient in its performance, Matloff said that more than half of the solar energy delivered to the “hotspot” on the NEO would not be available to vaporize and accelerate the jet due to other thermodynamic processes such as conduction, convection, and radiation. As expected, a larger collector sail radius would increase the amount of energy available, and would increase acceleration of the NEO. Matloff said this system allows the sail craft to “tack” against the solar-photon breeze at a larger angle than conventional single solar sails can achieve.

This system of sails would not be attached to the NEO, but would be kept nearby the NEO “on station” either with its own thrusting capability or by auxiliary electric propulsion. More studies would be needed to ascertain if a supplementary propulsion system would be necessary.

The sails used in the study were both inflatable. However, Matloff believes it might be worth considering a small rigid thruster sail, which might simplify deployment and reduce occultation.

Said Matloff, “Hopefully, future design studies will resolve these uncertainties before application of NEO-diversion technology becomes necessary.”