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Planetary defense

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Planetary defense, is the technical concept referring to the protection a planet such as the Earth from extraterrestrial threats such as asteroids and comets. There are multiple proposed Asteroid mitigation strategies.

Potential extraterrestrial threats

Near-Earth objects (NEOs) are asteroids, comets and large meteoroids whose orbits bring them close (perihelion distance < 1.3 AU) to Earth's orbit,[1] and which may therefore pose a collision danger. If a large asteroid or comet impacts the Earth, such an impact event might bring about the end of civilization. These threats can be distinguished by other planetary threats such as climate change or volcanic eruptions.

History of recent activities

In a 1992 report to NASA,[2] a coordinated Spaceguard Survey was recommended to discover, verify and provide follow-up observations for Earth-crossing asteroids. This survey was expected to discover 90% of these objects larger than one kilometer within 25 years. Three years later, another NASA report[3] recommended search surveys that would discover 60-70% of short-period, near-Earth objects larger than one kilometer within ten years and obtain 90% completeness within five more years.

In 1998, NASA formally embraced the goal of finding and cataloging, by 2008, 90% of all near-Earth objects (NEOs) with diameters of 1 km or larger that could represent a collision risk to Earth. The 1 km diameter metric was chosen after considerable study indicated that an impact of an object smaller than 1 km could cause significant local or regional damage but is unlikely to cause a worldwide catastrophe.[2] The impact of an object much larger than 1 km diameter could well result in worldwide damage up to, and potentially including, extinction of the human race. The NASA commitment has resulted in the funding of a number of NEO search efforts that are making considerable progress toward the 90% goal by 2008.

Over the past few years, there have been several meetings of world experts on this topic. The 2004 Planetary Defense Conference was held beginning on 23 February 2004 to discuss detection, deflection, policy, law, and disaster preparedness. There was a follow-up 2007 Planetary Defense Conference, held from March 5-8, 2007 in Washington, D.C. that also addressed similar issues.

Detection

The first step in defending against Near-Earth objects is detection and threat analysis. There are several world-wide programs for detection. Most of these programs are currently (as of early 2007) by NASA's Near Earth Object (NEO) program office as part of their Spaceguard programs. These detection and analysis programs include:

Near-Earth Object Survey Act

U.S. Representative George E. Brown, Jr. (D-CA) was quoted as voicing his support for planetary defense projects in Air & Space Power Chronicles, saying "If some day in the future we discover well in advance that an asteroid that is big enough to cause a mass extinction is going to hit the Earth, and then we alter the course of that asteroid so that it does not hit us, it will be one of the most important accomplishments in all of human history."

Because of Congressman Brown's long-standing commitment to planetary defense, a U.S. House of Representatives' bill, H.R. 1022, was named in his honor: The George E. Brown, Jr. Near-Earth Object Survey Act. This bill "to provide for a Near-Earth Object Survey program to detect, track, catalogue, and characterize certain near-earth asteroids and comets" was introduced in March 2005 by Rep. Dana Rohrabacher (R-CA). It was eventually rolled into S.1281, the NASA Authorization Act of 2005. Presently, it is law.

The following text became law as part of the NASA Authorization Act of 2005 passed by the Congress on December 22, 2005, and subsequently signed by the President:

The U.S. Congress has declared that the general welfare and security of the United States require that the unique competence of NASA be directed to detecting, tracking, cataloguing, and characterizing near-Earth asteroids and comets in order to provide warning and mitigation of the potential hazard of such near-Earth objects to the Earth. The NASA Administrator shall plan, develop, and implement a Near-Earth Object Survey program to detect, track, catalogue, and characterize the physical characteristics of near- Earth objects equal to or greater than 140 meters in diameter in order to assess the threat of such near-Earth objects to the Earth. It shall be the goal of the Survey program to achieve 90% completion of its near-Earth object catalogue (based on statistically predicted populations of near-Earth objects) within 15 years after the date of enactment of this Act. The NASA Administrator shall transmit to Congress not later than 1 year after the date of enactment of this Act an initial report that provides the following: (A) An analysis of possible alternatives that NASA may employ to carry out the Survey program, including ground-based and space-based alternatives with technical descriptions. (B) A recommended option and proposed budget to carry out the Survey program pursuant to the recommended option. (C) Analysis of possible alternatives that NASA could employ to divert an object on a likely collision course with Earth. The result of this directive was a report presented to Congress in early March 2007. This was an Analysis of Alternatives (AoA) study led by NASA's Program Analysis and Evaluation (PA&E) office with support from outside consultants, the Aerospace Corporation, NASA Langley Research Center (LaRC), and SAIC (amongst others).

Mitigation techniques

Various techniques have different trade-offs with respect to metrics such as overall performance, cost, operations, and technology readiness. There are various methods for changing the course of an asteroid/comet. These can be differentiated by various types of attributes such as the type of mitigation (deflection or fragmentation), energy source (kinetic, electromagnetic, gravitational, solar/thermal, or nuclear), and approach strategy (interception, rendezvous, or remote station). For more description of mitigation techniques please see Asteroid mitigation strategies.

There are many types of methods that have been proposed to change the course of an asteroid. These include the following:

  • Mass Drivers: Setting up "mass drivers" on the object to scoop up dusty material and shoot it away, giving the object a slow, steady nudge.
  • Flying a big sheet of reflective aluminized PET film to wrap itself around the asteroid, acting as a "solar sail" to use the pressure of sunlight to shift the object's orbit.
  • Dusting the object with powdered chalk or soot to perform a similar adjustment, utilising the Yarkovsky effect.
  • Magnetic Flux Compression
  • Gravitational tractor
  • NEO Painting
  • NEONet
  • Laser ablation
  • Solar Mirror / Concentrator
  • Space Pebbles
  • Chemical Propulsion
  • SpaceTug (VASIMR)
  • Propulsive Tug NEPTug (Ion or Hall)

Detonating an explosive nuclear device above the surface (or on the surface or beneath it) of an NEA would be one option, with the blast vaporizing part of the surface of the object and nudging it off course with the reaction. This is a form of nuclear pulse propulsion.

The hurling of a massive object at the NEA, such as another near-earth object, is another violent possibility. A small asteroid or large mass in a stable high-Earth orbit would have tremendous kinetic energy stored up. With the addition of some thrust from mounted rockets (plasma or otherwise) , it could be used like a stone from a slingshot to deflect the incoming threat. Another possibility is to use a mass driver on the moon to take advantage of its orbital velocity and inexhaustible supply of "rock bullets".

However, it is becoming increasingly obvious that many asteroids are "flying rubble piles" that are loosely glued together, and a nuclear detonation might just break up the object without adjusting its course. In some ways, being struck with a loose cloud of smaller asteroids is worse than being struck with just one big one.[citation needed] The amount of energy released by either type of collision is essentially the same, given the physics of kinetic and potential energy.

Planetary Defense in Science Fiction

Another interpretation of planetary defense is that it may involve the defense of the planet against an alien invasion. This is a less probable event than an asteroid or comet impact upon the Earth and should be viewed as a more speculative event and more typically belongs in the science fiction realm. Planetary defenses are a recurring theme in science fiction, usually designed to repel an invasion of a planet by an external force; human or otherwise. An example would be during the Earth Alliance Civil War on the television series Babylon 5, whereby the loyalist forces used orbital planetary defense platforms to defend Earth from the separatist forces.

Planetary defenses are not limited to one pre-defined type, some are space or orbital based platforms or ships like in the previously stated example. Another example of planetary defense platforms is Cairo station, which is from the Halo 2 game and the Halo novels. As well as serving as docking stations for UNSC ships, MAC stations such as Cairo Station also possess a massive MAC coilgun, which serve to ward off assaulting enemy fleets via long-range bombardments. UNSC worlds often possess multiple MAC stations in orbit, to provide overlapping fields of fire against either human or alien invaders. There are also weapon systems based on the surface of planets occasionally, as in Stargate SG-1 where the hero uses an Ancient weapon in Antarctica to destroy the villain's invading fleet from the ground; others are simpler, including ground based fighters, as in the case in Star Wars Episode IV: A New Hope where single-manned fighters defended a rebel base against a moon-sized Death Star. In addition, in the novel The Armageddon Inheritance from the author David Weber's Empire From the Ashes trilogy, Antarctica possesses a core-tap generator, which yanks large energy reserves from hyperspace and projects it around Earth as a planetary shield. While serving to ward off enemy fleets and bolster Earth's defenses against most conventional assaults, it proved insufficiently powerful against large asteroids and small moons, as when in the book the moon Iapetus was hurled at Earth to "crack it open like a bullet through butter." However, when combined with the planetary defense platforms in place, planetary shields can be very necessary to planet-wide protection.

The Posleen novels also called the Legacy of the Aldenata series by John Ringo describe in detail a planetary defense scenario using alien technology to construct a fleet of starships. Similar themes can be seen in the japanese anime series The Super Dimension Fortress Macross and its Robotech american adaptation. Both Macross and Robotech also include a "Grand Cannon" massive energy weapon based in the northern hemisphere that is used for planetary defense. Doc Travis S. Taylor's Warp Speed and The Quantum Connection books (known as The Warp War Series) gives examples of developing planetary defense systems based on warp technologies. The Von Neumann's War series by John Ringo and Travis S. Taylor also develops an organization designed to develop planetary defense strategies from present day technologies.

Relevant conferences

References

  1. ^ Glossary of Astronomical Terms:Near-Earth Object
  2. ^ a b Morrison, D., 1992, The Spaceguard Survey: Report of the NASA International Near-Earth-Object Detection Workshop, NASA, Washington, D.C.
  3. ^ Shoemaker, E.M., 1995, Report of the Near-Earth Objects Survey Working Group, NASA Office of Space Science, Solar System Exploration Office

Further reading

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