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August 02, 2011

Europe's Plan to Move An Asteroid


Arxiv - Measurement requirements for a near-Earth asteroid impact mitigation demonstration mission

A concept for an Impact Mitigation Preparation Mission, called Don Quijote, is to send two spacecraft to a Near-Earth Asteroid (NEA): an Orbiter and an Impactor. The Impactor collides with the asteroid while the Orbiter measures the resulting change in the asteroid's orbit, by means of a Radio Science Experiment (RSE) carried out before and after impact. Three parallel Phase A studies on Don Quijote were carried out for the European Space Agency: the research presented here reflects outcomes of the study by QinetiQ. We discuss the mission objectives with regards to the prioritisation of payload instruments, with emphasis on the interpretation of the impact. The Radio Science Experiment is described and it is examined how solar radiation pressure may increase the uncertainty in measuring the orbit of the target asteroid. It is determined that to measure the change in orbit accurately a thermal IR spectrometer is mandatory, to measure the Yarkovsky effect. The advantages of having a laser altimeter are discussed. The advantages of a dedicated wide-angle impact camera are discussed and the field-of-view is initially sized through a simple model of the impact.

MIT Technology Review has coverage

In 2002, the European Space Agency began a program called Don Quijote to find out how best to perform such a deflection. Don Quijote involves sending two spacecraft to a near Earth asteroid; one to smash into it and the other to watch while in orbit above the impact crater. The goal is to change the asteroid's semimajor axis by more than 100 metres and to measure the change with an accuracy greater than 1 per cent.



Full 29 page paper

Many important lessons were learnt during the course of this study. These include:

• Solar radiation pressure uncertainty due to degradation of spacecraft optical surfaces: For low mass asteroids such as 2002 AT4, to measure harmonics above J2, one must do RSE drift-bys for gravity field as early as possible, or perform measurement of SRP in orbit and/or in cruise.

• To fulfil the primary mission objective, a sensitive thermal infrared spectrometer is required to measure the Yarkovsky effect. More complex modelling is required to determine performance requirements.

• A laser altimeter has many advantages and aids achieving the primary objective (increased spatial resolution, smaller data volume than trying to do the same with imagery, fewer operational constraints, etc.).

• To interpret the impact and extrapolate for any particular NEA, via assessment of properties of first few metres (~ crater depth), the payload needs to include:
– an impact camera (modelling ejecta dynamics required)
– a polarimetry filter on at least one of the cameras

Future NEO impact mitigation demonstration missions will need to take into account the issues highlighted by this work.

Other Work on Asteroid Deflection

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

Dr. Matloff favors diverting rather than exploding them because the latter could create another problem — debris might bathe Earth in a radioactive shower.

Dr. Matloff’s research indicates that an asteroid could be diverted by heating its surface to create a jet stream, which would alter its trajectory, causing it to veer off course. In 2007, with a team at the NASA Marshall Space Flight Center in Huntsville, Alabama, he investigated methods of deflecting NEOs. The team theorized that a solar collector (SC), which is a two-sail solar sail configured to perform as a concentrator of sunlight, could do the trick. Constructed of sheets of reflective metal less than one-tenth the thickness of a human hair, an SC traveling alongside an NEO for a year would concentrate the sun’s rays on the asteroid, burn off part of the surface, and create the jet stream.

There have been disagreements about the best way to deflect asteroids. There is option of a nuclear bomb or gentler non-nuclear methods. David Dearborn, a research physicist at the Lawrence Livermore National Laboratory in Livermore, says that if an asteroid was expected to collide with Earth within the next 50 years, using nuclear explosives to divert or disperse the hostile space rock could be the best alternative.

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