July 14, 2011

Defending Planet Earth [from space asteroids

Defending Planet Earth [from space asteroids] 15 page presentation from Future of Space Operations talk

4 approaches depending on circumstances

* Civil defense (evacuation, sheltering, first aid, etc.
- Up to 50 meter in diameter?

* Slow Push-Pull (tug, solar heating, albedo change, gravity tractor, et al.)
- Needs decades to operate (plus time to build, etc.)
- Max size 300-600 m diameter
- Gravity tractor closest to ready and least dependent on properties of NEO

* Kinetic Impacts (Super Deep Impact)
- sensitive to porosity of top meters to tens of meters
- momentum transfer efficiency not known
- much wider range of applicability (max size 1 to 1.5 km, shorter warning for small ones)

*Nuclear blast
- standoff blast best
- works up to 10 km and relatively short warning

What Next

* Don Quixote-like mission
- a rendezvous spacecraft at a small NEO followed by a large impactor
- biggest gain in knowledge directly related to mitigation
- Guess $1.5G; Good for international collaboration

* Gravity tractor demonstration
- fewer unknowns other than engineering
- second priority

* Apophis a possible target but any small NEO will do
- Can’t predict which might need to be used first
- Small NEO is by far the most likely
- Warning time very uncertain but short warnings are likely at ~100m diameter or less

Research Needs

- Momentum transfer
- Warning times
- Tails of orbital distribution
- NEO properties - spin and shape, multiplicity, and especially porosity and density
- lots for science but not so much for hazard mitigation
- hence radar programs at Arecibo and Goldstone
- Physics of airbursts
- search strategy - death plunge vs. full survey
- Effects of the wide range of NEO properties on the mitigation strategy
- tsunami generation
- NEO disruption

Planetary Defense and NEO Exploration (26 pages)

The Near-Earth Object Survey spacecraft proposed by Ball Aerospace would prowl for hazardous NEOs and astronaut targets from a Venus-like orbit. The Target NEO workshop recommended NASA compete such a survey telescope as its earliest and highest priority exploration precursor mission. (Ball Aerospace)

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