Near Earth Survey Telescope (NEST)NEO Survey Concept

Led by JHU/APL, a Joint Study with GSFC and JSC November 15, 2010

NEST

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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

NEO Survey Mission Objectives

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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 time for 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

Human Spaceflight (HSF) Survey Objectives

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We need to find affordable targets for 2025-2030 HSF:When: 2015 - 2020From where: spaceHow: 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.

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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

Searching close to Sun in the sky:Sweet Spot Surveys from near the Earth

Red dots, NEOs. Green dots, main belt asteroids

Sun

Sweet Spot (leading)

Sweet Spot (trailing)

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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

Searching from ~0.7 AU heliocentric orbit

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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.)

NEO Survey Telescope (NEST) Constraints

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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

Telescope Trade Space

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CCD camera, 16 Mpx assumed, passively cooled

Telescope conventional R-C, 90 cm aperture

Filter wheel Limiting magnitude

~24

Camera Assumptions

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1 0 1 0 2 6 k 4 . z m xC o n f i g u r a t i o n 1 o f 1

3 D L a y o u tR i t c h e y - C h r e t i e n T e l e s c o p e1 0 / 2 6 / 2 0 1 0

X

Y

Z

1010

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

Characterization

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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

NEO Search Simulations

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High population

Low population

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Survey Performance Examples

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.

40% completion in 2yr

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NEO Survey Simulations

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≤ 180 day round trip

Re-entry speed ≤ 11.8km/s

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

Survey Duration

NEA Population Filter

Sweet Spot Survey, High NEA Pop.

Sweet Spot Survey, Low NEA Pop.

Opposition Survey, High NEA Pop.

Opposition Survey, Low NEA Pop.

Total Detections (18<H<24)

31,752 8,664 37,641 6,735

NEAs with Earth-like orbits

(0.8 < a < 1.2, e < 0.2)1093* 258 1410** 218

Estimated affordable NEAs in

2025-2030~50 ~10 ~60 ~10

Total Detections (18<H<24)

47,191 12,056 65,494 11,995

NEAs with Earth-like orbits

(0.8 < a < 1.2, e < 0.2)1532 338 2422 374

Estimated affordable NEAs in

2025-2030~65 ~15 ~100 ~15

2 years

4 years

*mean H = 21.7 (150m @ 14% albedo) **mean H = 23.0 (90m @ 14% albedo)

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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

NEST Mission and Spacecraft Summary

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NEO survey mission is an excellent opportunity for international cooperation

No new technology development is required

Between COROT and GAIA in technical requirements

Survey Mission Opportunities

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