Dilute Aperture Visible Nulling Coronagraphic Imager DAVi NCI

Dilute Aperture Visible Nulling Coronagraphic Imager (DAVi. NCI) DAVi. NCI IWA = 38 mas @800 nm, 0. 5 um to 1. 7 um converage (25%BW) Science of an 8 m telescope at the cost of a 2. 5 m telescope M. Shao , B. M. Levine, G. Vasisht, C. Zhai, J. Sandhu JPL, B. F. Lane, Draper Labs, R. Woodruff, G. Vasudevan, Lockheed-Martin, R. Samuele, Northop Grumman, K. Havey, ITT, M. Clampin, R. Lyon, NASA/GSFC, O. Guyon, U. Arizona, V. Tolls, SAO, © 2008 California Institute of Technology. Government sponsorship acknowledged.

Outline • Instrument and Mission Overview - 4 1. 1 m telescopes, inside of a 4. 5 m fairing. Nulling coronagraph • Equal collecting area to a 2. 2 m telescope, but telescope costs much lower than a filled aperture on axis 2. 2 m telescop - Team X cost ~1. 15 B total cost, includes launch vehicle and 5 years of mission operations. Cost roughly equal to a ~2. 5 m coronagraph • Science Case DAVi. NCI - 38 mas IWA @ 800 nm (Inner Working angle ~25 mas @ 500 nm) - Exo-Earth science equal to ~8 m 2 l/D coronagraph , or 76 m occulter (vs 50 m) at 166, 000 vs 72, 000 km. - Science instrument R~80 spectrometer 0. 5 um to 1. 7 um, 25%BW at a time. • Team X study • Technology needs and status - Detecting a planet with 1% False Alarm - vis nulling coronagraph testbed, segmented MEMs Deformable Mirror 03 October 2020 2

DAVi. NCI: Dilute Aperture Visible Nulling Coronagraph Imager • Main mission - • • Image and take spectroscopic measurements for Earth-like exo-planets up to 150 nearby stars Reduce costs by using four 1. 1 m telescopes (spatially separated to create a dilute aperture array) to produce the resolution of a large aperture telescope The payload acts as a coronagraph by using interferometry to null the central star’s signal DAVi. NCI • Astrophysics Strategic Mission Concept Studies (ASMCS) Flagship class mission ($1. 2 B) 03 October 2020 3

DAVi. NCI Concept 4 x 1. 1 m telescopes based on Next. View CRS Sun Shade provides thermal insulation, while allowing the target to be observed within ~45 deg of the Sun, any target is observable 75% of the time. Sun shade Spectra of Exo-Earth in Winter and Summer DAVi. NCI Three-axis stabilized spacecraft bus Spacecraft in 5 m Fairing 03 October 2020 NGST 4

B=2. 2 m Baseline 4. 2 m Tip-Tip At its longest baseline, Davinci has an Inner Working Angle of IWA~38 mas @ 780 nm DAVi. NCI Roughly equal to ~8 m coronagraph working at 2 l/D 03 October 2020 5

Discovery Space DAVi. NCI # Stars ~ IWA-3 4 x 1. 1 m DAVi. NCI and 8 m telescope with 2λ/D Coronagraph 4 m telescope with 2λ/D Coronagraph DAVi. NCI 2 m telescope with 2λ/D Coronagraph Max star-planet sep > IWA*1. 2 03 October 2020 6

Imaging Planets with a Nulling Coronagraph DAVi. NCI • Because of the null pattern an image needs ~3 rotations to produce an “normal” looking image of all the planets outside the IWA. • In the presence of a significant exo-zodi signal, one approach is to difference two images at two different epochs when the planets have moved. - Without zodi subtraction the angular resolution of the image may need ~3 airy spots between the planet and star. 7

DAVi. NCI Science Case • DAVi. NCI, with 4 x 1. 1 m telescope has the same science potential (for Earths @ 1 AU) as a 7~8 m (PIAA) coronagraph. - Davinci 38 mas IWA @ 780 nm (Oxygen) - Spectroscopy from 0. 5 um to 1. 6 um. (25% BW at a time) # targets at 1. 6 um is ~ 1/8 of the number of targets at 0. 8 um. - # potential targets ~ IWA-3 • How many targets are needed? - What’s a good guess on eta_earth? (30% of stars have sub-Neptune planets (5~50 Mearth), from 0. 03 to 0. 3 AU) ~10% of stars have a terrestrial planet in the HZ. DAVi. NCI • DAVINCI has significantly less collecting area (roughly equal to HST) than a GIANT filled aperture coronagraph. But it’s adequate for a search of 100~150 Earths - An Earth @10 pc is 29. 5 mag. HST ACS (F 606 W) takes 4. 5 hrs to get a SNR=6 image of a 29. 5 mag star. ACS 83620 - Our calculations show ~10 Hrs to detect an Earth @ 10 pc for DAVi. NCI 03 October 2020 8

Science I • Photon throughput has 3 components - Optics/detector efficiency - Coronagraphic mask transmission @ IWA (70%) - Lyot mask efficiency (no glass in primary if photons don’t get to detector) • DAVINCI has ~100% Lyot efficiency DAVi. NCI - In a Lyot coronagraph, working at 2~4 l/D, there is a mask at a reimaged pupil (Lyot stop) that “blocks” the starlight diffracted by the coronagraphic mask. Lyot efficiency of TPF-C/FB 1 ~ 30% @ 4 l/D - With 100% Lyot efficiency, DAVINCI has roughly ~1/2 the sensitivity of the TPF-C FB 1, 8 m*3. 5 m coronagrah - DAVINCI sensitivity is comparable to a 4 m Lyot coronagraph because of 100% Lyot efficiency • The Major advantage of DAVINCI is that it has an inner working angle of ~38 mas @ 780 nm (Oxygen line) equal to an 8 m coronagraph working at 2 l/D. 03 October 2020 9

Team X Mission Study Summary • 1. 5* Cost of Probe Class Mission • High Level Mission Description - Launch Vehicle: Atlas V 521 Orbit: Earth-Trailing Launch Date: 2020 Mission Lifetime: 5 years Observation strategy: • Planet Detection, orbit determination (or confirmation of SIM orbit) • Exo-Earth Spectroscopy DAVi. NCI • Instrument Description - 4 element dilute aperture imaging interferometer using (‘COTS’ telescopes) on (Dual) Variable baselines - Dual nullers for deep and wide null with imager and (R=80) spectrometer See Poster by Levine et. a. l. 03 October 2020 10

Combiner/Nuller Instrument Shutters T 1 / T 2 Nuller Shutter Phase stepping dither Phase Plates Bright DM 1 DM 2 Bright Phase Plates T 1 -2 Dark ACS Camera output with pupil camera allows Phase diversity WFS as well! T 3 / T 4 Nuller Dichroic mirror ACS Camera Pupil Remap Lens Pupil Geom. Camera T 3 -4 Dark DM 3 Beam launcher Null Beam Combiner Assembly DM Control DAVi. NCI To Pupil Geom Mechanism DM Control Fiber Bundle Array Single fibers with matched properties as the fiber bundle Filters Lens compensator WFS Camera 1 03 October 2020 WFS Camera 2 slit Translation Stage Science Camera 11

Cost Advantages of Dilute/Segmented Aperture Telescopes • Mulitple telescopes are cheaper - Telescopes #2, 3, 4 are ~ 50% of the cost of #1. - If cost ~ D 2. 5 then 4 1. 1 m’s is less than ½ the cost of a 2. 2 m. - DAVi. NCI telescopes are On-Axis (not off-axes unobscured) • Technology for diffraction limited segmented and dilute aperture telescopes was demonstrated on Keck >10 years ago. (JWST) - Technology for SIM (picometer level dilute aperture telescope/interferometer in space) is also in hand. - There is a known ~fixed cost for the metrology and structure/mechanisms for DAVi. NCI. • Instrument (Nulling coronagraph) is roughly the same complexity/cost of a Lyot coronagraph with DM’s for phase and amplitude control. - DAVi. NCI instrument maybe more expensive because of the very wide 0. 5 um ~ 1. 7 um wavelength coverage. (rather than 0. 5 um~0. 8 um) DAVi. NCI • Spacecraft - (Vibration) requirements similar to other coronagraphs - Thermal stability requirements ~100 X less sensitive than coronagraphs that use telescope rotation for speckle subtraction. (Post coronagraph inteferometer) 03 October 2020 12

DAVi. NCI Team X Cost (round 2) DAVi. NCI Team X Instrument Study 2009 03 October 2020 13

Technology Status/ Near Future Plans • Define Starlight suppression versus Contrast - Starlight suppression of 10 -7 = contrast of 10 -10, 10 -9 • Finding a planet in a sea of Speckles, and measuring its orbit DAVi. NCI - Measuring the planet’s orbit. In the double blind test, we set a threshold of 1% FAP (False Alarm Probability) • If one takes the spectra of a dot in an image, without an orbit. We don’t know if that spectrum belongs to a HZ planet. • In fact we don’t know that we haven’t taken the spectrum of a speckle, that by accident is 6 times brighter than the “average speckle. • Starlight suppression demonstration (in a single mode fiber, 2006) • High Contrast demonstration (vacuum nuller with DM) 03 October 2020 14

Steps to Direct Detection • Starlight suppression If we have 10 -7 suppression - Optically remove starlight • High contrast (dark hole) - Remove starlight where the planet is supposed to be 1 st airy ring < 2 x 10 -9 3 l/D < 2 x 10 -10 • Speckle subtraction DAVi. NCI - Subtract out the residual speckles even in the dark hole there are speckles 6~8 x 10 -10 contrast Trauger et al 2006 15

Detecting Terrestrial Planets in the HZ • Goal is to detect a planet in the presence of speckles with a ~1% false alarm probability. - Conducted simulations on speckle statistics • Brightest speckle vs “average” speckle flux, calculate contrast needed for 1% FAP Planet detection - Speckle subtraction. There a couple of ways to do speckle subtraction, How accurately do we need to subtract speckles, in order to see the planet (with 1% FAP) DAVi. NCI • Simulation (because it was computationally simple) was of a 4 lambda/D lyot coronagraph, gaussian coronagraphic stop and hard edge lyot stop. - Purpose of the simulation was to look at direct detection in the same way that astromery and RV has looked at planet detection. Setting a threshold, that results in 1% FAP, and looking at the implications. • At the threshold of detection the ½ the images of a planet will be above threshold and ½ the images of the planet will be below the threshold. • Also, 1% FAP means a lot of images “by eye” will look like planets, but be below the 1% FAP threshold. 16

Why Do We Need 1% FAP? DAVi. NCI • Planet is outside the IWA most of the time but observable only IWA ~ 0. 7* Max star-planet sep => planet 32% of the time. is observable over ~32% of its orbit. • 30 deg inclination is the “Average” inclination • An orbit within 1 deg of face-on is ~100 times less likely than an orbit within 1 deg of edge on. If we look at 100 stars 4 times a 10% FAP means 40 false alarms. 17

There Will Be Lots of 1~30 Mearth Planets Mordasini, et. al. 2009 a DAVi. NCI • In one image, the true earth could be inside the IWA, or have it’s sun-lite side facing away from us. • At the same time, a non-HZ planet could appear to be in the HZ because of orbit phase and inclin. • A Jupiter, with it’s sun-lite side facing away from us, could appear as bright as the Earth. • A dot in the image could also be a bright speckle A claim that a planet in the HZ has been found NEEDS an orbit A claim that a planet is a terrestrial planet in the HZ needs Astrometry

Statistics of Dark Hole in Image Plane • Speckles are caused by gaussian random phase and amplitude errors. ~30 pm rms ~ 3 e-4 amplitude errors. - Average speckle background ~4 e-10. • Speckle statistics DAVi. NCI - Exponential intensity distribution (not gaussian) - Mean speckle = std(speckles) - Probability of a bright (4~5 X mean) speckle much higher than for gaussian distribution. 19

DAVi. NCI Brightest Speckle in an Image • Probability distribution of the brightest speckle in an image, and the cumulative probability of the brightest speckle. • If we set the threshold of detection at ~ 12 X the “Average” speckle, there is a ~1% false alarm probability. • Detecting a planet 1. 2 e-10 as bright as the star with 1% FAP requires the average speckles to be suppressed to ~1 e-11. - A threshold of 1. 2 e-10 means that a planet a flux of 1. 2 e-10 will be detected 50% of the time. 20

Speckle Subtraction and Wavefront Stability • Starlight suppression to 1 e-11 contrast is extremely difficult and has not been demonstrated. 1 e-11 optical contrast is not needed if we can measure (and subtract) out the speckle pattern in post processing. • There are two techniques Positive image Negative image IWA Cumulative Prob Brightest Speckle pair Diff Image - Telescope roll (Occulter roll? ) • Speckles have to be stable as you roll the telescope - Post coronagraph WFS. (DAVi. NCI) DAVi. NCI 4 e-10 speckles to be “stable” to 1 e-11 implies the wavefront from the telescope is stable to ~2. 5 picometer over 2~4 hrs as two images are recorded for speckle sub. 1% FAP means detection threshold SIM optics are stable to ~40 pm/90 sec. has to be set ~12 X the rms fluctuations in the “Differenced” image. 21

Post Coronagraph WFS for PSF Estimation (Speckle Sub) Instead of asking the telescope wavefront to Be stable to 2. 5 pico-m for a few hrs, DAVi. NCI measures the speckles simultaneously with the science image. The great advantage is not just from avoiding a new invention, but the testing of a flight telescope to 2. 5 pm stability. DAVi. NCI • To reduce the wavefront/thermal stability requirement. DAVi. NCI measures the residual speckle pattern and the science image simultaneously. • This will be tested in the VIS-Nulling testbed under construction. • The Post corongraph WFS measures the E-field after the coronagraph. (The fft^2 of which should be the residual speckle pattern. ) • Properation of this approach to speckle subtraction can relax the stability requirement of the telescope by up to 1000 X. (to SIM-like requirements) See poster by Sandhu et al. 22

Visible Nuller (DAVi. NCI & EPIC) testbed • In air test ~3 months, in vacuum test ~3 months from now. • Measure surface of DM (deformable mirror) - Current mirror has significant “scalloping” - Noise in the wavefront measurement is ~1. 4 nm rms for a 0. 5 sec integration. (and 5*5 sampling of each DM actuator) - Sensing per actuator < 0. 5 nm rms (0. 5 s) • Need <30 sec to get noise down to 100 picometers/DM actuator Unpowered DM 1024 element Spare MEMs DM with ~40 dead actuators Diff of 2 phase maps 5*5 • Recent activities - Characterizing DM (influence fn, gain) DAVi. NCI • Future activities - Test image plane contrast - New DM, Fiber bundle amp+phase control - Recently started assembly of Vac test setup 23

Next Gen Components Near Ready • Two new components are needed in vac nulling testbed • Coherent fiber bundle (Fiberguide industries) ~1 um spacing of fibers. • Segmented DM, with tip/tilt piston control (delivered from BMC) Delivered DM has 5 dead actuators, which will have to be masked by the lyot stop. DAVi. NCI • The MEMs continuous face sheet DM’s have ~20~30 nm rms errors within 1 actuator. Due to stresses in the face sheet that’s part of the manufacturing process. • Segmented DM ~ 6 nm rms (BMCorp) 24

Summary • Dilute aperture coronagraphs can obtain images at 800 nm of Exo-Earths around ~150 nearby stars at a small fraction of the cost of other visible direct detection concepts. - Very high angular resolution (Small IWA, 38 mas) in a small package - Spectroscopy to 1. 6 um for ~20 targets. - Much much lower cost than a comparable 7 -8 m coronagraph working at 2 l/D. Leverage technology from SIM DAVi. NCI • Technology progress: have demonstrated 10 -7 suppression laser light, which is what’s needed for 10 -9~10 -10 contrast. - A full imaging demonstration experiment has started. • Use similar wavefront control technology to lyot coronagraphs • New approach is speckle subtraction w/o telescope stable to 2. 5 pm/4 hrs. • DAVi. NCI from a cost/science point of view is playing in a different ball park from other (Large) vis coronagraph concepts • The nulling coronagraph architecture is also compatible with on-axis, & segmented telescopes. If a dedicated TPF is never flown, but only as an instrument on a large GP telescope, A nulling coronagraph instrument at 100~200 M would be much less expensive than an external occulter. 03 October 2020 25