From: Jet Propulsion Laboratory
Posted: Wednesday, March 21, 2012
Observers, mission planners, and other interested users are invited to use a new website tool to view a list of near-Earth asteroids that are among the most accessible for future robotic or human space flight round-trip rendezvous missions. For each of up to several hundred asteroids listed, the following information is available:
* Absolute magnitude (H).
* Estimated diameter (meters).
* Minimum delta-V mission and the corresponding round trip flight time. Delta-V, in km/s, is defined here as the total velocity change required for the spacecraft to depart from a 400 km circular Earth orbit, rendezvous with the NEA and return to Earth with an entry velocity less than the specified threshold of 12 km/s.
* Minimum mission duration time (round trip time in days) and the corresponding mission delta-V.
* The number of viable trajectories found for that NEA, which is a proxy for its accessibility.
* The next optical observing opportunity and the peak apparent visual magnitude.
* The next Arecibo radar observing opportunity and the corresponding signal to noise ratio (SNR).
* The next Goldstone radar observing opportunity along with the corresponding SNR.
* Metric for orbit accuracy (Orbit Condition Code).
* Orbit solution ID.
Users can customize the table of accessible NEAs by specifying limits on total delta-V, mission duration, stay time at the asteroid, launch date interval, asteroid absolute magnitude, and orbit condition code. The table can be sorted on almost all the bulleted items above.
Clicking on each object's designation takes the user to an object-specific page, which provides additional details, including a plot showing total mission delta-V for each combination of mission duration and launch date (2015 - 2040). Another click on the object's designation opens a new window that provides orbital and physical data for the object.
The Near-Earth Object Human Space Flight Accessible Targets Study (NHATS) began in September 2010 under the auspices of NASA Headquarters Planetary Science Division of the Science Mission Directorate in cooperation with the Advanced Exploration Systems Division of the Human Exploration and Operations Mission Directorate. Its purpose was to identify any known Near-Earth Objects, particularly Near-Earth Asteroids (NEAs) that might be accessible by future human spaceflight missions. The Goddard Space Flight Center (GSFC) and the Jet Propulsion Laboratory (JPL) independently performed the first phase of the NHATS study in parallel to validate the results.
NEAs are discovered almost daily, and often the time just after discovery is also the optimal time to provide follow-up observations to secure their orbits and characterize their physical nature. These follow-up observations are particularly important for those NEAs that could become potential future mission targets. The goal behind this website is to monitor these NEA discoveries daily and determine if any among them warrant additional study as they might become attractive mission targets.
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.
Website tool is available here: http://neo.jpl.nasa.gov/nhats/
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