The area of research known as “Planetary Defense” is largely concerned with identifying and tracking asteroids that could impact Earth. The vast majority of asteroids that pose such a risk are known as “Near Earth Asteroids/Objects” or NEAs and NEOs. Some of them are unknown, un-cataloged, and untracked, but are presumed to orbit in Earth-like orbits, and periodically cross Earth’s orbit in a possibly threatening manner.

In order to reduce the cost of such a NEO-detection mission, both the mass and complexity of the detecting instrument and the spacecraft must be reduced. Spacecraft that leave Earth’s orbit around the Sun must carry a substantial amount of propulsion capability, typically 2 to 5 km/s for orbits being considered by such missions.

A NEO search mission could be accomplished with a spacecraft of mass under 50 kg, with 10 kg of payload, using a propulsion system of Isp 8,000, if the propulsion system mass (sans propellant) remained under 5 kg. This is made possible by micro-electrofluidic-spray propulsion (MEP). With MEP, a propulsion system can be assembled of micro-components that in total is under 5 kg without indium metal propellant, and is composed of MEP thruster-chips arrayed by the many dozens to fashion a thruster of finite thrust without tanks, valves, lines, plenums, and other accouterments of ion propulsion. Such a system with 5 kg of indium propellant can provide a 50-kg spacecraft more than 10 km/s of delta-v.

Rather than a very narrow-angle-field, cooled, infrared sensor such as used for WISE, this mission will use visual bands and a wider field camera (e.g., 15°). Such a camera, using refractive optics, can be assembled from commercially available parts and subsequently space rated. This can produce a very effective instrument inexpensively. The change in search strategy is accomplished by virtue of the fact that the instrument is not scanning, but is able to rapidly scan and re-scan large areas of the sky, and automatically detect and immediately retrack potential NEOs.

By this strategy, the cost of the spacecraft has dropped by a factor of 5 to 10 relative to a conventional mission. With ample delta-v capability, this mission can not only discover objects, but can then match orbits with them, rendezvous, and perform reconnaissance, perhaps even making physical contact with the surface.

The Hunter Seeker mission concept combines aspects of two important classes of missions: the NEO discovery mission and the asteroid surveyor. Yet, the cost of this mission is as much as an order of magnitude less than the combined cost of these two missions, at near $100 million.

The key novelty is the drastically reduced mass and resulting cost, and the ability, via MEP, to not only discover, but visit such NEOs. Another novelty is the arraying of MEP micro-thrusters for thruster vector control with no moving parts, e.g., gimbals.

This work was done by Joseph E. Riedel, Young H. Lee, and David J. Eisenman of Caltech for NASA’s Jet Propulsion Laboratory. NPO-49435

This Brief includes a Technical Support Package (TSP).
NEO Hunter Seeker Micro-Spacecraft and Mission Concept

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This article first appeared in the February, 2016 issue of NASA Tech Briefs Magazine.

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