Near Earth Survey Telescope (NEST) NEO Survey Concept

1. Near Earth Survey Telescope (NEST)NEO Survey Concept NEST Led by JHU/APL, a Joint Study with GSFC and JSC November 15, 2010

2. NEO Survey Mission Objectives • Search for NEOs potentially suitable for human exploration missions • Search for NEOs that potentially impact Earth • Physical characterization • Refine orbital trajectory • Measure physical properties (mass, size and rotation) • Measure composition and internal structure (requires spacecraft visit) • Objectives for human exploration precursors and for planetary defense are overlapping

3. Human Spaceflight (HSF) Survey Objectives • The number of known targets meeting HSF accessibility criteria, with size > 30 m, is few or zero • Ground-based surveys will not discover suitable targets in timefor HSF in 2025-2030 time frame • These targets have Earth-like orbits, are almost always in the daytime sky, and have long synodic periods • They are discovered when close to Earth, and there is typically not enough time to target a mission • A dedicated space-based NEO survey is needed to discover such targets sufficiently in advance of close encounter to Earth • Suitable targets for HSF are also of interest for planetary defense

4. We need to find affordable targets for 2025-2030 HSF: • When: 2015 - 2020 • From where: space • How:either searching close to Sun in the sky, or searching from <1 AU orbit The plot at the left shows the position of 20 ‘affordable’ NEAs 10 years before (open symbols) and 5 years before (closed symbols) Earth close approach. None of these objects is in the night sky at 10 and 5 years prior to their discovery periods. CONCLUSION: For missions in 2025 – 2030, a platform in space is needed to find the most affordable targets in a timely manner.

5. Searching close to Sun in the sky:Sweet Spot Surveys from near the Earth Sweet Spot (leading) Sun Sweet Spot (trailing) Red dots, NEOs. Green dots, main belt asteroids • View the region ~40° - 70° angular distance from Sun, ± 20° from ecliptic (“sweet spot”) • Asteroids in accessible orbits are always near 1 AU and close to the ecliptic, and they must pass through the sweet spots in the years before Earth close approaches • Two sweet spots (leading, trailing) • Expect ~200 m objects to be ~24 mag in sweet spot • Typically they will be detected at ~1 AU distance

6. Searching from ~0.7 AU heliocentric orbit • Searching from trailing Venus orbit (viewing away from sun) • Targets are generally outside the observatory orbit • Observatory orbits the Sun faster than Earth: catch targets with long synodic period relative to Earth • Targets are generally detected <1 AU from the observatory under optimal lighting conditions • This option is recommended by the Defending Planet Earth study for planetary defense • Searching from trailing Venus orbit can be done with optical or with mid-IR telescopes

7. NEO Survey Telescope (NEST) Constraints • Low mission cost (less than Discovery mission) • Includes launch vehicle (smallest suitable) • Launch readiness in 2015 • High technical maturity (current state-of-art) • Discover and characterize NEOs for human exploration • More than double the known inventory of objects within 2 yr of operation • Include follow-up characterization of all discovered objects (orbit trajectory, rotation rate, etc.)

8. Telescope Trade Space • Our strategy is to target an optimized mission that meets ESMD’s needs for identifying and characterizing NEOs for potential human exploration • Looking for the most cost efficient solution to meet these needs • Considered the “good enough” solution rather than the “be all things to everyone” or Cadillac solution that attempts to detect all NEOs

9. Camera Assumptions CCD camera, 16 Mpx assumed, passively cooled Telescope conventional R-C, 90 cm aperture Filter wheel Limiting magnitude ~24

10. Characterization • Both search scenarios are assumed to use continuous search sequence • Continuous search sequence is modular (can change number of patches observed in each successive search) • Allows for characterization of selected objects with extended observations • Measure colors, rotations • Characterization interrupts continuous search

11. NEO Search Simulations • Simulations done with the known MPC distribution, 7103 NEOs known as of end of August 2010, and with debiased distributions (following the model of Bottke et al. 2002) • Two NEO size distributions considered, a “low” case and a “high” case • 0.7AU/opposition search and Earth/sweet spot search • Inputs are the date of the search (assumed instantaneous) and the observer position (various positions along Earth orbit or 0.7 AU orbit, depending on the case; data from JPL Horizons, geodetic centers of the planets) • Simulation finds sky positions of all the objects at the search date and then finds if they are within the search area seen by the observer; also calculates apparent magnitude of each object in the search area of sky

12. High population Low population

13. Survey Performance Examples 40% completion in 2yr • The actual population of NEOs at sizes down to 50 m is highly uncertain • Two models used, assuming high and low population assumptions • The actual population of highly accessible NEOs with Earth-like orbits is even more uncertain • The Earth-based sweet spot survey is more efficient for larger objects (> 140 m), the trailing Venus/opposition survey is more efficient for smaller objects • Similar discovery rates in the two cases • Population uncertainty is more significant • In two years, a survey will increase total number of objects known with 0.8<a<1.2 and e<0.2 by 3 to 5 times • Survey is likely to discover several tens of targets suitable for human exploration.

14. NEO Survey Simulations • Survey simulations performed for two NEST concepts (Sweet Spot & Opposition) • Two models used, assuming high and low population assumptions • Estimates for detected NEOs are increasingly uncertain for each successive row in the table below (represented by deepening shades of gray) • Due to lack of knowledge of NEO population with Earth-like orbits obtained from current and past ground-based surveys • 10 to several 10s of affordable NEOs in 2025-2030 should be discovered by either survey type • Estimated from the currently known population and scaling is uncertain ≤ 180 day round trip Re-entry speed ≤ 11.8km/s *mean H = 21.7 (150m @ 14% albedo) **mean H = 23.0 (90m @ 14% albedo) 14

15. NEST Mission and Spacecraft Summary NEST mission cost without launch vehicle is ~$300 M to ~$350 M Launch vehicle capability can be as small as Taurus II Nominal 48 month development for 2015 launch, with 2 year prime mission The 0.7 AU option is slightly more expensive than the L2 option

16. Survey Mission Opportunities NEO survey mission is an excellent opportunity for international cooperation No new technology development is required Between COROT and GAIA in technical requirements