1. Characterizing Small, Dim Near-Earth Asteroids with Coherent Doppler Ladar Bijan Nemati bijan.nemati@jpl.nasa.gov M. Shao, C. Zhai, S. Turyshev Jet Propulsion Laboratory, California Institute of Technology 9/30/2013 9/30/2013 - B. Nemati, JPL (ISAL)Asteroid Initiative Idea Synthesis Workshop1

2. Introduction By equipping a 4 meter-class, ground-based telescope with laser active illumination and adaptive optics we can have a facility that can comprehensively investigate asteroids down to a few meters in size, capable of: 1.Detection, Astrometry, Precise Orbit, Spin rate (out to 40 LD) with Synthetic Tracking sensitive out to 10m NEO @ 40 LD (3.6 m tel, 2 min) 2.Size Estimation with Incoherent LADAR 3.Imaging with Inverse Synthetic Aperture LADAR (ISAL) – Coherent Doppler Laser Radar 4.Mass and density estimation from Astrometry, over weeks 9/30/2013 - B. Nemati, JPL (ISAL)Asteroid Initiative Idea Synthesis Workshop2 Passive (sunlight) Active (Laser) Combined Earth moon NEO trajectory NEO facility Imaging via ISAL at < 1 LD Detection & Astrometry via Synth Tracking at 40 LD Size determination via Incoherent Imaging mass determination using size and extended astrometry

3. Implementation Telescope – 4 m class telescope – A single telescope can be used to both transmit and receive (monstatic operation) Because fast switching between transmit and receive mode is possible with a laser Laser system – 1 kW laser at 2 um (coherent) for (imaging, size) chirp system capable of ~20 GHz/s – 5 kW laser at 1 um (Incoh., AM mod.) for (range,size) Adaptive optics – Diffraction limitted transmitter – phase matching of LO and return Acquistion, Tracking, and Astrometry System – High speed camera and GPU for “synthetic tracking” – Synthetic tracking enables precision astrometry AMOSS 3.6 m Telescope AFRL Maui, HI NEO track shift/add velocity vector frame 1 frame 2 frame 3 frame 4 Synthetic Tracking JPL is in collaboration with USAF on an ISAL project with their 3.6 m telecope 9/30/2013 - B. Nemati, JPL (ISAL)Asteroid Initiative Idea Synthesis Workshop3

4. Operational Scenario 1.Discover – Detection (10 m NEO out to 40 LD, further for larger NEO’s) Using synthetic tracking, detect small asteroids down to 100X current rate) – Astrometry to get precise orbits (< 10 mas) Put the beam on the target Determine target orbit so it is not subsequently “lost” – Photometry to get spin rate 2.Estimate Size – Actively illuminate to get size estimate Visibility drop in chirped AM modulated Incoherent LADAR Doppler Broadening with Coherent LADAR 3.Image – ISAL in chirped mode (at < 1 LD) 4.Measure Mass and Density – via photon pressure, using Astrometry + Size 9/30/2013 - B. Nemati, JPL (ISAL)Asteroid Initiative Idea Synthesis Workshop4

5. NEA far away (40 LD) – Synthetic Tracking Detection – Synthetic Tracking allows detection of 10 m object at 40 LD Astrometry – The beam size, from diffraction, is ~ 2um/4m ~ 100 mas To put the most power on the target, need to point to ~ 20mas – We have recently demonstrated 7 mas relative astrometry of 19 mag asteroid GAIA will get everything brighter than 20 mag to < 1 mas on its first release Once GAIA numbers are available our relative astrometry becomes absolute – absolute astrometry necessary for orbits, to keep track of the asteroid long term 9/30/2013 - B. Nemati, JPL (ISAL)Asteroid Initiative Idea Synthesis Workshop5 NEO track shift/add velocity vector frame 1 frame 2 frame 3 frame 4 Synthetic Tracking

6. NEA at 12 LD : AM Incoherent LADAR Higher-power (order 5 kW) laser can also be used, for incoherent LADAR On the detector side a photon counting detector would be used The laser is amplitude modulated – Single AM frequency to get radial velocity – Chirp to get range and size look for a drop in the visibility to sense the size Estimates show size determination possible at 25% with 5kW laser in 5 hrs from 3.6 m telescope 9/30/2013 - B. Nemati, JPL (ISAL)Asteroid Initiative Idea Synthesis Workshop6 1

7. NEO near (< 1 LD) : full ISAL imaging Send a chirped laser beam with the telescope Collect the return from the target – use a large telescope to collect more returned power Mix with a “Local Oscillator” – get heterodyne gain Fourier-analyze the mixed signal – width from Doppler broadening gives size – chirped version (when SNR is high) gives image 9/30/2013 - B. Nemati, JPL (ISAL)Asteroid Initiative Idea Synthesis Workshop7 Doppler (cross-range) Range Reflectivity (image) Measured Phasor (amp, phase)

8. Peformance on 10 m class asteroid Assume a 5 kW laser from a monostatic 3.6 m facility Size estimation starts becoming possible at 12 LD (25% ) At 1 LD imaging becomes possible with 1 kW coherent LADAR: – the expected rate of return photons per pixel, assuming an albedo of 0.2, is about 320 ph/s – In a 5x5 pixel image, the expected SNR in each pixel after 1 hr is about 10. 9/30/2013 - B. Nemati, JPL (ISAL)Asteroid Initiative Idea Synthesis Workshop8 Distance, LDSNR (5 hr)Size ErrorRange Err., m 124.025%0.80 105.718%0.56 4363%0.09 21431%0.02 Earth moon NEO trajectory NEO facility Imaging via ISAL at < 1 LD Detection & Astrometry via Synth Tracking at 40 LD Size determination via Incoherent Imaging mass determination using size and extended astrometry

9. Getting the NEA mass Sustained observation over several weeks with astrometry at the few mas level allows us to measure the motion of the asteroid due to solar radiation pressure Astrometry measures the acceleration – and hence the area to mass ratio ISAL measures the area (via Doppler broadening) Together these give the mass Example in backup – 4 mas astrometry over 5 wks of 10 m asteroid with 10 LD impact parameter yields 10% estimate of its mass with synthetic tracking 9/30/2013 - B. Nemati, JPL (ISAL)Asteroid Initiative Idea Synthesis Workshop9 Solar radiation

10. Technology Status We are developing ISAL technology currently at JPL We are able to produce a 100 GHz chirp in 100 ms (1 THz/s) We have achived first light on a ball target We are working near the photon limit Target delay AOM Tunable Laser 99% FREQUENCY MONITOR 90% 10% AOM TRANSMITTER 1% AOM A/D BC A/D signal LO RECEIVER PR target arm LO arm delay LO XMIT RCVR Target Freq/ChirpMonitor Filters prior to ADC A B C 5 MHz 5-pole LC 1 kHz RC return from a ball target (+/- chirps) range 70 GHz chirp in 0.1 sec as measured by freq. monitor 9/30/2013 - B. Nemati, JPL (ISAL)Asteroid Initiative Idea Synthesis Workshop10

11. BACKUP 9/30/2013 - B. Nemati, JPL (ISAL)Asteroid Initiative Idea Synthesis Workshop11

12. NEA < 4 LD : Size via Coherent Doppler mean  speed 9/30/2013 - B. Nemati, JPL (ISAL)Asteroid Initiative Idea Synthesis Workshop12 Asteroid Distance (LD)1234 Integration Time (hr)11510 Size Fractional Precision1.3%8%19%42%

13. Example: mass of 10 m asteroid at 4 LD Asteroid Initiative Idea Synthesis Workshop139/30/2013 - B. Nemati, JPL (ISAL)

14. Size Determination – I 9/30/2013 - B. Nemati, JPL (ISAL)Asteroid Initiative Idea Synthesis Workshop14

15. Size Determination – II 9/30/2013 - B. Nemati, JPL (ISAL)Asteroid Initiative Idea Synthesis Workshop15