One of the early conclusions that our Association of Space Explorers (ASE) Committee on Near Earth Objects (NEOs) made as we began to wrestle conceptually with the challenge of deflecting an incoming potential impactor was that a successful NEO deflection would require a “deflection campaign” rather than a “deflection mission.”1 The context of this discussion was the general endorsement by the emergent planetary defense community of the kinetic impact concept as the default deflection technique for most anticipated asteroid impacts. The resultant NEO momentum change from a kinetic impact would change the arrival time of the NEO at the nominal NEO/Earth impact point such that its arrival time would either precede or occur subsequent to the Earth passing through the intersection thus avoiding a potentially catastrophic collision.
While the viability of the kinetic impact technique has been validated with the success of the DART mission2 , a successful campaign may nevertheless require a sequence of such missions for larger NEO threats. Even in the case where a single impact may be sufficient, multiple missions may need to be planned to address the possibility of an initial mission failure.
As important as the deflection mission(s), per se, may be, a precursor observer spacecraft mission may be even more important. The criticality of an observer satellite in such a campaign cannot be overstated. Sequentially, an observer spacecraft would perform a critical sequence of operations designed to maximize the success of any deflection campaign; among others these operations would include:
- On arrival, determination of a precise orbit for the NEO (and thereby confirming whether or not a deflection is needed3)
- Determining the size and other key NEO characteristics to assist in design and execution of a follow-on impactor mission, if required
- Providing direct guidance and navigation assistance to the impactor mission, if required
- Observing and imaging the kinetic impact, per se, to evaluate impact success
- Determining a precise post-deflection NEO orbit (including evaluation of any potential keyhole encounter)
- And, assuming a gravity tractor capability, execution of a precision deflection trim maneuver to avoid a future keyhole passage should such an orbital trajectory result from the kinetic impact missions
Citations & Notes
- ASE Asteroid Threats: A Call For Global Response. Appendix II, Key Concepts in Asteroid Threat Mitigation. Association of Space Explorers Near-Earth Object Committee. 2008.
- While the kinetic impact (KI) technique is generally preferred by the planetary defense community, a variety of nuclear explosive techniques are also in consideration. In general the use of these options, as in KI, would also require consideration of multiple missions to insure success.
- In most instances a precursor mission would be launched while the probability of impact is less than 100%; e.g. 1 in 10. In a case such as this, the probability is then 9 in 10 that an impact is not imminent and thus a deflection mission is not required.