Observers, mission planners, and other interested users
are invited to use the following tool to identify future observing
opportunities for those near-Earth objects that may be well-suited to
future human space flight round trip rendezvous missions.
Please consider the assumptions and caveats
(listed below) related to these data to assist in their proper interpretation.
A table showing NHATS-compliant NEAs that can be filtered using
various constraints and sorted by various fields is available at the
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 NEOs, particularly Near-Earth Asteroids (NEAs)
that might be accessible by future human space flight 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.
Hence, it is prudent to monitor these NEA discoveries daily and run
an analysis to determine if any among them warrant additional study as they
might become attractive mission targets.
Brent Barbee (GSFC) has developed a 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 filters
(see below for subscription option).
The results of this daily analysis are then immediately uploaded to the
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.
Alan Chamberlin (JPL) was largely responsible for creating this NHATS website.
Assumptions and Caveats for NHATS-Compliant NEAs
- The list of potential mission targets should not be interpreted as a complete
list of viable NEAs for an actual human exploration mission. As the NEA orbits
are updated, the viable mission targets and their mission parameters will change.
To select an actual target and mission scenario, additional constraints must be
applied including astronaut health and safety considerations, human space flight
architecture elements, their performances and readiness, the physical nature of
the target NEA, and mission schedule constraints.
- The target NEAs in these tables were identified using a Lambert solution
technique. Since no mid course maneuvers, gravity assists or continuous
thrust options (e.g. solar electric propulsion) were considered, there are
certain to be additional mission options that do not appear within this table.
- The trajectory filter parameters were purposely chosen to be highly
inclusive in order to provide a broad spectrum of mission possibilities. To
pass the trajectory filter and be characterized as NHATS-compliant,
a NEA must offer at least one round trip
trajectory solution that satisfies the following constraints:
- Earth departure date between 2015-01-01 and 2040-12-31
- Earth departure C3 less than or equal to 60 km2/sec2
- Total mission delta-V (dV) less than or equal to 12 km/s.
The total delta-V includes the Earth departure maneuver from a 400 km altitude
circular parking orbit, the maneuver to match the NEA's velocity at arrival,
the maneuver to depart the NEA and, if necessary,
a maneuver to control the atmospheric re-entry speed during Earth return.
- Total round trip mission duration less than or equal to 450 days
- Minimum stay time at the NEA of 8 days
- Earth atmospheric entry speed less than or equal to 12 km/s at an
altitude of 125 km
- Trajectories are computed using the method of embedded trajectory grids.
This provides a comprehensive analysis by stepping through, at 8-day intervals,
all combinations of departure dates, outbound flight times, stay times, and
inbound flight times. The trajectory calculations are performed using
patched conics with Lambert solutions for the spacecraft and with full precision
ephemerides for the Earth and NEAs obtained from
JPL's Horizons system.
- The observability of each NEA is analyzed by generating its geocentric
ephemeris through to the year 2040.
- Optical observing constraints vary widely from observatory to observatory.
The constraints used for the NHATS table were purposely chosen to represent
programs with access to large-aperture telescopes, in order to include even the
difficult observational opportunities. The optical constraints are as follows:
- The magnitude has to reach 24.0 or brighter
- The angular distance from the Sun (solar elongation) has to exceed 60 degrees
- The 3-sigma plane-of-sky uncertainty must be less than 1.5 degrees over a 3-day period
- The object must be at least 5 degrees away from the galactic equator
- Observations are excluded for the 4-day period around each full moon
The peak visual magnitude (Vp) during the tracking opportunity is shown as a guide
- Many asteroids with poorly-determined orbits violate the plane-of-sky
uncertainty constraint soon after discovery; these objects are considered
lost. A secondary filter is then applied to simulate a serendipitous
re-discovery of such an object by one of two asteroid survey programs. The survey
programs are simulated by removing the plane-of-sky uncertainty constraint and
imposing the following survey constraints:
- To simulate current programs, a limiting magnitude of 21.5 and minimum solar
elongation of 70 degrees are used
- To simulate the proposed LSST survey, a limiting magnitude of 24.0 is used, starting
in the year 2021, and sky coordinates must be within the LSST survey region
The dates of possible survey recoveries are shown in the table with leading and
trailing '?' in order to indicate that these are far from certain.
- Radar tracking opportunities for Arecibo and Goldstone are determined by
calculating the daily signal-to-noise ratio (SNR) values using the best known
physical parameters for the asteroid (primarily size and rotation period), as
well as the actual parameters for these antennas. The radar constraints are as
- The SNR must be at least 10
- Either the 3-sigma plane-of-sky uncertainty must be less than 0.75 arc-min, or
- There must be an optical observing opportunity shortly before, with magnitude
brighter than 21.5 and plane-of-sky uncertainty less than 3 degrees, 3-sigma.
This is meant to simulate the optical astrometry often requested to lower the
pointing uncertainty and make the radar experiment possible.
The entry in the table shows the date of the peak SNR, and the estimated SNR value
follows in square brackets.
Subscribe to NHATS Update Notices
If you'd like to subscribe to the NHATS email daily notification service,
visit the following link to signup.