NASA performed the first Near-Earth Object Human Space Flight Accessible Targets Study (NHATS) in September/October of 2010, and 666 of the known near-Earth asteroids (NEAs) were identified as meeting the NHATS criteria for mission accessibility (classifying those NEAs as "NHATS-compliant"). These are asteroids in near-Earth orbits that are more dynamically accessible (requiring less time and energy to visit) than round-trip spacecraft missions to Mars.

At that time, just over 7,000 NEAs had been discovered, while today we know of over 12,000 NEAs, an increase of 70%. The percentage increase in the number of accessible asteroids in the catalog has been even greater: On January 18, 2015 - a little over four years since the NHATS assessments began - the 1332nd NHATS-compliant asteroid was identified, doubling the number of known accessible NEAs.

The sizes of these asteroids range from as small as a few meters to as large as a few kilometers. While all these asteroids are more dynamically accessible than a round-trip mission to Mars, many of them (hundreds) require less energy to visit (round-trip) than does the lunar surface, and dozens of them require less energy to visit than does a low orbit around the Moon.

NASA uses the automated NHATS system to monitor the NEA population for mission accessibility. This monitoring assists the identification of attractive destinations for future robotic and crewed missions.

Brent Barbee (GSFC) developed the process that automatically downloads orbital information on newly discovered NEAs from the JPL Small Bodies Database (SBDB) on a daily basis. He then performs trajectory calculations using the method of patched conics for the spacecraft and with full precision ephemerides for the Earth and NEOs obtained from JPL's Horizons system to determine which among them may meet the NHATS accessibility constraints.

The results of this daily analysis are then immediately uploaded to the NHATS table. A process generated by Paul Chodas (JPL) then provides, for each NHATS-compliant NEA, the details of future observation opportunities that might allow the NEA orbit to be improved with follow-up optical astrometric data.

Some of these observing opportunities would also allow the NEA's physical nature to be characterized using photometric and spectroscopic observations.

In cases where there are future close Earth approaches, radar astrometric and physical characterization observations may be possible; these opportunities are listed as well. Working closely with Brent Barbee and Paul Chodas, Alan Chamberlin (JPL) was largely responsible for creating this Accessible NEAs website.

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Number of Known Accessible Near-Earth Asteroids Doubles Since 2010