Presentation on theme: "DAViNCI 1 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."— Presentation transcript:
DAViNCI 2 February 5, 2014 Outline Instrument and Mission Overview m telescopes, inside of a 4.5m fairing. Nulling coronagraph Equal collecting area to a 2.2m telescope, but telescope costs much lower than a filled aperture on axis 2.2m telescop -Team X cost ~1.15 B total cost, includes launch vehicle and 5 years of mission operations. Cost roughly equal to a ~2.5m coronagraph Science Case -38 mas 800nm (Inner Working angle 500nm) -Exo-Earth science equal to ~8m 2 /D coronagraph, or 76m occulter (vs 50m) at 166,000 vs 72,000 km. -Science instrument R~80 spectrometer 0.5um to 1.7um, 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
DAViNCI 3 February 5, 2014 DAViNCI: Dilute Aperture Visible Nulling Coronagraph Imager Main mission -Astrophysics Strategic Mission Concept Studies (ASMCS) Flagship class mission ($1.2 B) 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 stars signal
DAViNCI 4 February 5, 2014 DAViNCI Concept Sun shade Spacecraft in 5m Fairing 4 x 1.1m telescopes based on NextView CRS Three-axis stabilized spacecraft bus 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. Spectra of Exo-Earth in Winter and Summer NGST
DAViNCI 5 February 5, 2014 B=2.2m Baseline 4.2m Tip-Tip At its longest baseline, Davinci has an Inner Working Angle of 780nm Roughly equal to ~8m coronagraph working at 2 /D
DAViNCI 6 February 5, 2014 Discovery Space DAViNCI Max star-planet sep > IWA*1.2 4x1.1m DAViNCI and 8m telescope with 2λ/D Coronagraph 4m telescope with 2λ/D Coronagraph # Stars ~ IWA -3 2m telescope with 2λ/D Coronagraph
DAViNCI 7 Imaging Planets with a Nulling Coronagraph 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.
DAViNCI 8 February 5, 2014 DAViNCI Science Case DAViNCI, with 4x1.1m telescope has the same science potential (for 1AU) as a 7~8m (PIAA) coronagraph. -Davinci 38mas 780nm (Oxygen) -Spectroscopy from 0.5um to 1.6um. (25% BW at a time) # targets at 1.6um is ~ 1/8 of the number of targets at 0.8um. -# potential targets ~ IWA -3 How many targets are needed? -Whats a good guess on eta_earth? (30% of stars have sub-Neptune planets (5~50 Mearth), from 0.03 to 0.3AU) ~10% of stars have a terrestrial planet in the HZ. DAVINCI has significantly less collecting area (roughly equal to HST) than a GIANT filled aperture coronagraph. But its adequate for a search of 100~150 Earths -An is 29.5 mag. HST ACS (F606W) takes 4.5hrs to get a SNR=6 image of a 29.5mag star. ACS Our calculations show ~10 Hrs to detect an 10pc for DAViNCI
DAViNCI 9 February 5, 2014 Science I Photon throughput has 3 components -Optics/detector efficiency -Coronagraphic mask IWA (70%) -Lyot mask efficiency (no glass in primary if photons dont get to detector) DAVINCI has ~100% Lyot efficiency -In a Lyot coronagraph, working at 2~4 /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/FB1 ~ 4 /D -With 100% Lyot efficiency, DAVINCI has roughly ~1/2 the sensitivity of the TPF-C FB1, 8m*3.5m coronagrah -DAVINCI sensitivity is comparable to a 4m Lyot coronagraph because of 100% Lyot efficiency The Major advantage of DAVINCI is that it has an inner working angle of 780nm (Oxygen line) equal to an 8m coronagraph working at 2 /D.
DAViNCI 10 February 5, 2014 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: Mission Lifetime: 5 years -Observation strategy: Planet Detection, orbit determination (or confirmation of SIM orbit) Exo-Earth Spectroscopy 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.
DAViNCI 11 February 5, 2014 DM3 Fiber Bundle Array Phase Plates Null Beam Combiner Assembly Combiner/Nuller Instrument DM1 T1 / T2 Nuller Bright T1-2 Dark T3-4 Dark Science Camera WFS Camera1 Phase stepping dither Shutters DM Control Single fibers with matched properties as the fiber bundle Lens compensator Phase Plates DM2 T3 / T4 Nuller Bright Shutter Phase Plates WFS Camera2 DM Control Pupil Remap Lens To Pupil Geom Mechanism ACS Camera Pupil Geom. Camera ACS Camera output with pupil camera allows Phase diversity WFS as well! Filters Translation Stage slit Beam launcher Dichroic mirror
DAViNCI 12 February 5, 2014 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 1.1ms is less than ½ the cost of a 2.2m. -DAViNCI 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 DAViNCI. Instrument (Nulling coronagraph) is roughly the same complexity/cost of a Lyot coronagraph with DMs for phase and amplitude control. -DAViNCI instrument maybe more expensive because of the very wide 0.5um ~ 1.7um wavelength coverage. (rather than 0.5um~0.8um) Spacecraft -(Vibration) requirements similar to other coronagraphs -Thermal stability requirements ~100X less sensitive than coronagraphs that use telescope rotation for speckle subtraction. (Post coronagraph inteferometer)
DAViNCI 13 February 5, 2014 DAViNCI Team X Cost (round 2) Team X Instrument Study 2009
DAViNCI 14 February 5, 2014 Technology Status/ Near Future Plans Define Starlight suppression versus Contrast -Starlight suppression of = contrast of , Finding a planet in a sea of Speckles, and measuring its orbit -Measuring the planets 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 dont know if that spectrum belongs to a HZ planet. In fact we dont know that we havent 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)
DAViNCI 15 Steps to Direct Detection Starlight suppression -Optically remove starlight High contrast (dark hole) -Remove starlight where the planet is supposed to be Speckle subtraction -Subtract out the residual speckles even in the dark hole there are speckles If we have suppression 1 st airy ring < 2x /D < 2x ~8x contrast Trauger et al 2006
DAViNCI 16 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 are 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) 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 the 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.
DAViNCI 17 Why Do We Need 1% FAP? Planet is outside the IWA most of the time but observable only 32% of the time. 30 deg inclination is the Average inclination IWA ~ 0.7* Max star-planet sep => planet is observable over ~32% of its orbit. 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.
DAViNCI 18 There Will Be Lots of 1~30 Mearth Planets Mordasini, et. al. 2009a In one image, the true earth could be inside the IWA, or have its 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 its 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
DAViNCI 19 Statistics of Dark Hole in Image Plane Speckles are caused by gaussian random phase and amplitude errors. ~30pm rms ~ 3e-4 amplitude errors. -Average speckle background ~4e-10. Speckle statistics -Exponential intensity distribution (not gaussian) -Mean speckle = std(speckles) -Probability of a bright (4~5X mean) speckle much higher than for gaussian distribution.
DAViNCI 20 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 ~ 12X the Average speckle, there is a ~1% false alarm probability. Detecting a planet 1.2e-10 as bright as the star with 1% FAP requires the average speckles to be suppressed to ~1e-11. -A threshold of 1.2e-10 means that a planet a flux of 1.2e-10 will be detected 50% of the time.
DAViNCI 21 Speckle Subtraction and Wavefront Stability Starlight suppression to 1e-11 contrast is extremely difficult and has not been demonstrated. 1e-11 optical contrast is not needed if we can measure (and subtract) out the speckle pattern in post processing. There are two techniques -Telescope roll (Occulter roll?) Speckles have to be stable as you roll the telescope -Post coronagraph WFS. (DAViNCI) 1% FAP means detection threshold has to be set ~12X the rms fluctuations in the Differenced image. IWA Positive image Negative image 4e-10 speckles to be stable to 1e-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. SIM optics are stable to ~40pm/90sec. Cumulative Prob Brightest Speckle pair Diff Image
DAViNCI 22 To reduce the wavefront/thermal stability requirement. DAViNCI 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.) Proper operation of this approach to speckle subtraction can relax the stability requirement of the telescope by up to 1000X. (to SIM-like requirements) Instead of asking the telescope wavefront to Be stable to 2.5 pico-m for a few hrs, DAViNCI 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 2.5pm stability. Post Coronagraph WFS for PSF Estimation (Speckle Sub) See poster by Sandhu et al.
DAViNCI 23 Visible Nuller (DAViNCI & EPIC) testbed In air test ~3months, in vacuum test ~3months from now. Measure surface of DM (deformable mirror) -Current mirror has significant scalloping -Noise in the wavefront measurement is ~1.4nm rms for a 0.5 sec integration. (and 5*5 sampling of each DM actuator) -Sensing per actuator < 0.5nm rms (0.5s) Need <30 sec to get noise down to 100 picometers/DM actuator Recent activities -Characterizing DM (influence fn, gain) Future activities -Test image plane contrast -New DM, Fiber bundle amp+phase control -Recently started assembly of Vac test setup Unpowered DM 1024 element Spare MEMs DM with ~40 dead actuators Diff of 2 phase maps 5*5
DAViNCI 24 Next Gen Components Near Ready Two new components are needed in vac nulling testbed Coherent fiber bundle (Fiberguide industries) ~1um 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. The MEMs continuous face sheet DMs have ~20~30nm rms errors within 1 actuator. Due to stresses in the face sheet thats part of the manufacturing process. Segmented DM ~ 6nm rms (BMCorp)
DAViNCI 25 February 5, 2014 Summary Dilute aperture coronagraphs can obtain images at 800nm 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, 38mas) in a small package -Spectroscopy to 1.6um for ~20 targets. -Much much lower cost than a comparable 7-8m coronagraph working at 2 /D. Leverage technology from SIM Technology progress: have demonstrated suppression laser light, which is whats needed for ~ 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 2.5pm/4hrs. DAViNCI 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 100~200M would be much less expensive than an external occulter.