Detecting Near Earth Asteroids with a Constellation of Cubesats with Synthetic Tracking Cameras. M. Shao, S. Turyshev, S. Spangelo, T. Werne, C.

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1 Detecting Near Earth Asteroids with a Constellation of Cubesats with Synthetic Tracking Cameras M. Shao, S. Turyshev, S. Spangelo, T. Werne, C. Zhai

2 Introduction to synthetic tracking Synthetic tracking is made possible with new fast low noise cameras + fast computers Increase in sensitivity is proportional to the length of the streaked image Improved detection SNR Improved astrometric accuracy

3 Astrometry on NEOs ~2013 Residuals of optical observations from orbit that used both optical and Radar data RMS 0.2~0.5arcsec ~1200 new NEOs are discovered each year <100 have radar observation. Most NEOs are found then lost. Graph by J. Giorgini, 2013

4 Astrometry of Streaked Images The dominent error source in NEO astrometry is due to the streaked image. Synthetic tracking removes the streak by a shift/add algorithm. But the image that shows the NEO as a point, has the stars streaked. In ccd astrometry one centroids the image using a least sq fit of a PSF and a 2D image. (solving for X,Y, Intensity) In synthetic.tracking we fit a moving PSF to a 3D datacube and we do the Lsfit to X,Y, Vx, Vy, Intensity. reference target Stationary objects on sky target reference Image motion caused by telescope pointing and atmospheric turbulence is mostly common mode, and drop out, for relative astrometry Image position of a streaked image with telescope or atmospheric jitter: astrometric errors are no longer common mode

5 Synthetic Tracking Benefits Ground-based tracking of asteroids limited in accuracy to ~ 0.2 arcseconds (1 μrad) mostly due to image streaking (minor contribution from atmospheric turbulence) Synthetic tracking mitigates image streaking Demonstrated ~ arcsecond astrometry Vastly improved astrometry with Synthetic Tracking can provide precise orbits Conventional Long Exposure Synthetic Tracking ~ 8 mas

6 Combine Emerging Technologies Synthetic tracking allows higher sensitivity. Cubesats offer ultralow cost spacecraft, this combination can result in a range of mission architectures that reduce cost by 5X~10X and reduce the time to survey 90% from 2.5X to 4X. Cubesat office (4X) funded a very brief TeamXc study of a cubesat constellation to find NEOs. 10cm telescope on a Cubesat 1 of 5 cubesats in 0.7AU orbit 2.75 yrs of observing to find 90% of 140m NEOs ~14M for 1 st cubesat ~8~9M/each for duplicates

7 Survey Simulation After several conversations with S. Chesley and P. Chodas, on how to properly do the survey simulation, we re/wrote our simulation code. Parent population Of 200K NEOs 1) Start with parent population 2) Calculate MOID and identify Impactors here defined MOID<0.002AU 3) Searched for impactors using N cubesats

8 Impactor Population

9 Run Simulation 0.5m IR telescope in Venus Orbit Our results consistent With NRC report ~8 years to find 90% Of NEOs It s not hard to change the results by 20% by changing the assumptions in the simulation.

10 Tracklet vs SynTracking When astronomers looked for asteroids with photographic plates, they used a blink comparator Modern asteroid hunters use the 4 image tracklet. (why?) In the absence of stars, expect 8 false positives/frame Diff of 2 frames => 8*7/2=28 vectors But at 21mag and 10sqdeg, there are ~ ½ million stars. A large fraction are just 1 sigma above or below the 5s threshold. (17% prob 1sig) Any star that pops in or out is a possible moving object. Example: 16mPix detector 5s thresh => 8 false positives 1000 s of false positives per frame => tracklet where a 3 rd image at a 3 rd epoch has to be at the right place at the right time. There are so many false positives that the 4 image tracklet is now standard.

11 Tracklet vs Syn Tracking 2 How many potential tracklets? With 2 images it s (2000*1999)/2, 3 images ~2000^3/6 ~1 billion tracklets, with 4 images ~1 trillion tracklets. Tracklet processing requires keeping track of 100 s of thousands of mostly false positives to find the 1 true moving object. Synthetic tracking has been advertised as a way to increase sensitivity for moving objects, but it is also a substitute for tracklet ID of moving objects. (Detection at the Cramer Rao limit) Synthetic tracking doesn t keep track of tracklets. Most problems in conventional NEO search don t exist in Syn tracking. Galaxies don t move. Stars that pop-in/out they average to a constant when averaged over 50 images. By not keeping track of tracklets, we don t need to send down (~50,000?) false positives that are potential NEOs.

12 5 Cubesat Constellation Orbit is 0.7AU sma Ecc = 0.1 Inclin =0 Purple lines show 1 month of orbital motion Calculate apparent magnitude Distance NEO-Sun Distance NEO-Cubesat Phase angle correction Code for calculating streak losses was written but was not exercised because with syn tracking it doesn t matter and for 140m asteroid it s not a big effect for NEOCam/B612 But for smaller NEOs (30m streak losses approach 99%)

13 Mission time If you have 1 S/C and it fails after 3 or 6 years into a 10yr mission, that s catastrophic. If you start with 6 and 2 fail, you don t care N Cubesat Constellation Survey Time vs #cubesats 90% of 140m NEOs Results consistent with conventional wisdom (NRC report) There is an advantage for a Venus like orbit # cubesats The survey can be done faster with more cubesats, until we get to 5. (if we start with 5 and one fails, it s no big deal)

14 FOV/Sky Coverage Conventional Wisdom is you want a camera with a large FOV, as large as possible. To cover as much of 40,000 sqdeg/day as possible. Not always true When the sky coverage/day exceeds a certain amount, there is no benefit to increasing sky coverage. The reason is that the 140m NEO sky changes on a time scale of ~3 months. If you cover 40,000 sqdeg/day then on the next day, you re finding zero new asteroids. The simulation shows saturation ~1400sqdeg/day. That s roughly 1 Panstarrs. Adding 100 more ground based observatories will NOT reduce the time to find 90% of NEOs. Adding a space observatory in Earth orbit to existing ground facilities is much less effective than adding a space telescope NOT in Earth orbit.

15 90% of Smaller (50m) NEOs? From NRC report, combining two major Facilities. 1) Dedicated LSST to search NEOs AND 2) IR space telescope in Venus Orbit Find 90% of 50m NEOs in ~14 years 2 nd gen Constellation of 8 cubesats 15cm telescopes, 8K*8K sensor Find 90% of 50m NEOs in ~4.2 years The switch to a constellation of syn tracking cameras is a paradigm shift, once the shift is made, there is no turning back.

16 Astrometry, Orbit Determination The rationale for finding 90% of xxx meter NEOs is for planetary protection. But for planetary protection, it s important to get the orbit with sufficient accuracy to know whether the NEO will actually hit the Earth. At what probability would this discover trigger a multi billion effort to deflect the asteroid? 100%, 10% 1%? If error (in 10~20yrs) Is 640,000km there s a 1e-4 chance of an impact Earth Radius ~6400km

17 # NEA with X or more observations Orbital Error Propagation NEOs observed by 1 spacecraft over 15 yrs total 10 observations at 2 arcsec/each obs Number of NEA that have more than X observations # of observations of over time 0 (90%) ~4600 Impactors in the simulation, 2500 of them have > 10 observations over 15 years. Very preliminary results

18 # NEA with X or more observations Constellation Improves Orbit Determination Several telescopes distributed around the solar system means the NEO is observed over a large fraction of its orbit Number of NEA that have more than X observations # of observations of over time 0 (90%) Number of obs over ~4yrs

19 Summary Synthetic tracking is a technique that allows long integrations on moving objects to increase sensitivity. (at the expense of observing time) Small telescopes can be used, fit into cubesat/small sat form factor. The use of cubesat spacecraft components dramatically lowers the cost of a mission. So low it allows one to think of using multiple cubesats. (that make up for longer integration time) The distributed nature of the telescopes reduces the time needed to find 90% of NEOs of any size, provides much higher orbit determination accuracy Last of all NEOs much smaller than 140m can cause significant damage. A distributed array of telescopes is the only way to find these smaller (~50m) NEOs in a timely manner.