WFIRST-AFTA Ops Concept Overview - PowerPoint Presentation

Slide1

WFIRST-AFTA Ops Concept Overview

DRAFT

1Slide2

Multiple surveys with different requirements to implement the various science programs

High Latitude Survey (HLS): ~2,400 deg2 imaging and spectroscopic sky survey for BAO/RSD & WL (dark energy science), also used for archival studies by guest investigators

Supernova (SN) Survey: Multiple visits to SN fields at high ecliptic latitudes to discover and track SN

(dark energy science)Exoplanet Microlensing Survey: Multiple visits to microlensing fields near Galactic bulge to monitor planetary microlensing eventsExoplanet Coronagraph Survey: Observe nearby stars to find and characterize both previously known and new planetsGuest Observer: Allocated time for proposers to observe targets anywhere within the field of regard

Survey Strategy

2Slide3

The high latitude, supernova, and exoplanet microlensing surveys will all use the wide field instrument

HLS imaging survey uses the wide field imager

HLS spectroscopy survey uses the wide field grism

SN survey uses the wide field imager for discovery and the wide field IFU to type SN, measure redshifts, and obtain lightcurvesIFU may also be used in parallel with HLS imaging or spectroscopy to support photometric redshift calibrationMicrolensing survey uses the wide field imagerThe exoplanet coronagraph survey uses the coronagraph instrumentImager is for finding planets and for photometric characterization and the IFS is for spectroscopic characterization

The guest observer program can use either instrumentThe wide field instrument will operate during coronagraph observations

Needed for fine guiding, but will also take deep imaging exposures

Coronagraph observations are not currently planned during wide field instrument observationsAre there reasons to leave the coronagraph powered on during wide field observations for thermal or reliability reasons?

Implementation of Surveys

3Slide4

The HLS covers ~2,400 deg

2 over ~2 years in both imaging (~1.3

yrs

) and spectroscopy (~0.6 yrs) modes and is spread out over the 6 year missionHLS footprint is in regions of high Galactic latitude and is within the LSST footprint (or other deep visible survey) for photometric redshifts.In imaging mode, perform 2 passes over the survey footprint in each of the 4 imaging filters (J,H,F184 [for shapes] and Y [for photo-z’s]There is a “leading” and “trailing” pass in each filter to provide roughly 180˚ roll (but exactly 180˚ not desired) for data set self-calibration (current ops plan

has ~150˚, will be optimized later)Each pass includes four ~184 sec exposures (with five exposures in the J band, since we are attempting WL shape measurement in this band and it has the tightest sampling requirements)

Each exposure is offset diagonally by ~slightly more than a chip gap. This pattern is repeated across the sky in both the X and Y directions spaced by the field size.

90% of imaging field sees ≥5 randomly dithered exposures (≥920 sec total) in Y, H, F184 bands, ≥6 exposures (≥1104 sec total) in J band

No requirement on roll alignment between passes in different filtersIn spectroscopy mode, perform 4 passes total over the survey footprint

The grism has 2 “leading” passes and 2 “trailing” passes

to provide roughly 180˚ roll (but exactly 180˚ not desired) to enable the single grism to rotate relative to the sky and provide counter-dispersion (current ops plan has ~150˚, will be optimized later)Each pass includes two ~362 sec exposures with a small offset to cover chip gapsThe 2 “leading” passes (and 2 “trailing”) are rotated from each other by ~5˚90% of spectroscopy field sees ≥6 randomly dithered exposures (≥2172 sec total)Zero order galaxy provided in J,H or J,F184 bands by WL imaging passesThere is no direct requirement for absolute pointing accuracy (either initial or revisit). The chief consideration is minimizing the overlap of adjacent fields needed to avoid gaps in the survey. An absolute pointing accuracy corresponding to 1% of the size of an SCA (~4.5 arcsec) is a representative value.

High Latitude Survey

4Slide5

HLS (Imaging) Mapping

(view in slide show mode)

5

Perform 1

st

pass mapping of a super field in the 1

st

filter

4 exposures with a gap filling offset between each

Perform 1

st

pass mapping of a super field in the 1

st

filter

Perform 1

st

pass mapping of a super field in the 2

nd

filter

Perform 1

st

pass mapping in the remaining two filters

Perform 2

nd

pass mapping in the 1

st

filter ~6 months (or N years + 6 months) later

Perform 2

nd

pass mapping in the 2

nd

filter ~6 months (or N years + 6 months) later

Perform 2

nd

pass mapping in the remaining 2 filters ~6 months (or N years + 6 months) laterSlide6

HLS (Spectroscopy) Mapping

(view in slide show mode)

6

Perform 1

st

pass of a super field

2 exposures with a gap filling offset

Perform 2

nd

pass of a super field at a slight roll

Perform 3

rd

pass of a super field ~6 months (or N years + 6 months) later

Perform 4

th

pass of a super field at a slight roll ~6 months (or N years + 6 months) laterSlide7

The Type Ia supernova survey

observes for a total of 6 months but is carried out over a total of 2 years in separate 1-year periods.

The

imager is used for SN discovery and the IFU spectrometer is used to type SN, measure redshifts, and obtain lightcurvesSupernova observations take place with a five-day cadence, with each interval of observations taking a total of 30 hours of combined imaging and spectroscopy.Fields are located in low dust regions ≤20˚ off an ecliptic poleExample 3-tiered survey with each tier optimized for a different redshift range

Tier 1 for z<0.4: 27.44 deg2 in Y and J bandsTier 2 for z<0.8: 8.96 deg

2

in J and H bandsTier 3 for z<1.7: 5.04 deg2 in J and H bandsTier 3 is contained in Tier 2 and Tier 2 is contained in Tier 1

Need SN mapping strategyGap filling

Revisit accuracy

TBDDither with 30 mas accuracyIFU exposure times are tailored for each individual supernovaFinal revisit for each target for spectroscopy after SN fade for galaxy subtraction, some may occur after the dedicated 2 year period, but are accounted for in the example observing scenarioWeekly interaction with the ground after visiting discovery fields to schedule follow ups on SN candidatesType Ia Supernova Survey7Slide8

Supernova Field Mapping

8Slide9

Example Weekly Discovery and Follow up Timeline

9

Sun

Mon

Tues

Wed

Thurs

Fri

Sat

3/4 Day Cadence

5 Hour SNe Discovery

2 Hour

Candidate SN Spectroscopic

Follow-Up

Data Downlink/Uplink

Data Downlink Only

Weekly Obs. &

New SNe Spec. Obs.

New SNe Spec. Obs.

Prior concept for slit spectrometer ops on JDEM Probe. I expect there will be a similar plan for discovery and follow up with an IFU, but need inputs from SN group.Slide10

The

exoplanet microlensing survey observes 10 fields in the Galactic bulge for continuous 72-day seasons, interrupted only by monthly lunar avoidance cutouts (~4 days/month).

The plan includes 6 seasons,

with >2 years between the first and last season. The Galactic Bulge is observable for two 72-day seasons each year.In each season, the 10 fields are revisited on a 15 min cadence, viewing in

a single wide filter (W149) for light curve tracking. F

or

one exposure every 12 hours, a narrow, blue filter (Z087) is used to measure the color of the microlensing source star.Fields are revisited to an accuracy of ~110 mas (1

pixel rms) TBD; no precise dithers

Data latency for notifications to other assets?

Exoplanet Microlensing Survey10Slide11

Detecting Planets with a Microlensing Survey

11Slide12

Current example observing schedule has observations scheduled

in 26 blocks of 2 weeks each, interspersed throughout the mission.Portions of each block are dedicated to detecting a planet (imaging) and characterizing a planet (spectroscopy).

The targets are around nearby stars (within ~10 parsecs) and are distributed around the field of regard.

The current operations planner assesses the availability of each potential target star during each block of coronagraph observing time. Out of a catalog of 239 potential target stars, in each of the 26 coronagraph observing blocks we find at least 24 to be continuously viewable over the full 2-week period with no violations of the Earth, Moon, or Sun pointing constraints. Exoplanet Coronagraph Survey

12Slide13

Acquire a dark hole on a nearby bright star

Acquire star in tip/tiltMeasure and remove low order WFEMeasure and remove high order WFE

Verify dark hole

Slew to target starThermal loads change in this processAcquire targetImager is coarse sensorLOWFS is the fine sensorApply tip/tilt control to set the target on occulter1

st order correction of low order wavefrontIntegrateEach band and each sensor

Strawman

Observing Scenario

13Slide14

Allocated time throughout the 6-year mission for proposers to observe targets anywhere within the field of regard

The GO program by definition cannot be “allocated” at this stage in the project.The scheduling of HLS observations can be re-organized based on the content of the GO program. Currently, we have simply required that the time not used for other programs be ≥1.25 years, and that all portions of the sky are visible in multiple years during otherwise-unallocated time.

In computing the unallocated time, we subtract the penalty for a typical 90° slew from each unallocated window. (This way, the slewing penalty between any two programs is charged against the time allocation of one of the programs but not both.)

Guest Observer Program

14Slide15

Central Line of Sight (LOS) Field

of Regard (FOR)

15

15

+54˚

Keep-Out

Zone

Observing Zone

Keep-Out

Zone

SNe Fields

SNe Fields

+126˚

Galactic Bulge (Available twice yearly)

SNe Fixed Fields be

±

20

˚

off one of the Ecliptic Poles,

Microlensing can observe Inertially Fixed Fields in the Galactic Bulge (GB) for 72 days twice a year

WL/ BAO-RSD/ GO/Coronagraph Surveys can be optimized within the full Observing Zone

Observing Zone:

54˚-126˚ Pitch off Sun Line

360

˚

Yaw about Sun Line

±15

˚

Roll about LOS

(off max power roll)

GB

The LOS cannot point within

33°

(TBR)

of the limb of the Earth

and 8°

(

TBR

)

of the Moon

. Slide16

Galactic Bulge Viewing

16

Looking down on the ecliptic plane, ~72 day seasons available to view the bulge

Galactic Bulge

36˚

36˚

Ecliptic Plane

Galactic Plane

Galactic BulgeSlide17

Observing timeline with constraints in GEO orbit; initial inclination 28.5°, initial RA of ascending node 228° (over 6 years, precesses to inclination=26.4°, RAAN=188°).

Example Observing Schedule

17Slide18

This timeline is an

existence proof only, not a final recommendation.Unallocated time is 1.43 years (includes GO program)

High latitude survey (HLS: imaging + spectroscopy): 1.96 years

2401 deg2 @ ≥3 exposures in all filters (2440 deg2 bounding box)6 microlensing seasons (0.98 years, after lunar cutouts)SN survey in 0.62 years, field embedded in HLS footprint

1 year for the coronagraph, interspersed throughout the mission

Example Observing Schedule: Properties

18

High Latitude

Survey Area

MicrolensingFields

Ecliptic Plane

Celestial EquatorSlide19

1.2 Gbps

continuous Ka downlink capability from GEOPreliminary analysis indicates at least 16x

microstepping

required to keep jitter down during observationsWide Field Instrument produces ~600 Mbps, assumes 2x lossless compressionCoronagraph data volume 30 Gbits/day plus <1 Gbits/day LOWFS

2 Ka antenna on-board, only one radiating at a timeGround architecture similar to SDO

2 ground stations at White Sands, both within the beam width of the

Ka antennaDownlink

19Slide20

Slew/settle accuracy for each program (when can we start next

obs)FGS opsOrbit maintenance

Momentum unloading

Ground systemAssumes MOC is 8x5Additional Info to Include20Slide21

Blind Acquisition – No guide stars picked out

Directed Acquisition – Pre-planned guide starsField – The projected field of view on the skySuper Field – Multiple deg

2

portion of the sky mapped at one timeSlewsDitherGap fillingX-FieldY-FieldFrame Time – The length of time to read out a single detectorIntegration Time – The effective observation time between the first and last read frame of

each pixel in a detector without any resets in between.

Definitions

21Slide22

Continuous Viewing Zone Analysis

22Slide23

Baseline Cycle 4 orbit is circular GEO

Initial inclination = 28.5˚, RAAN = 236˚

Precession (perturbations from Sun, Moon, and Earth

oblateness through ℓ=4)Field of regardPitch range ±36˚ (angle from Sun = 54-126˚)Telescope LOS to Earth center ≥ 41.7˚ (TBR) (33˚

(TBR) from Earth limb from Len Seale’s stray light analysis + 8.7˚ Earth radius)

Chris ignored the Moon for this analysis (moves at 13˚/day, can avoid with minimal impact)

No constraints on radiator anglesEclipsesEarth eclipse seasons at b<9˚

Also 15 Moon eclipses outside these seasons in 6 year mission (short, can avoid – not discussed here)

Sky Availability-Basic Assumptions

(courtesy Chris Hirata)23Slide24

Earth Cutouts

24Slide25

Earth Cutout Geometry

25Slide26

Sun Cutouts

26

26

+54˚

Keep-Out

Zone

Observing Zone

Keep-Out

Zone

SNe Fields

SNe Fields

+126˚

Galactic Bulge (Available twice yearly)

GBSlide27

Combined Cutouts

27Slide28

Beta Angle over the Mission

28Slide29

Fraction of Sky Available versus

b

29Slide30

The following 7 charts show the combined Earth + Sun viewing constraints at 1 month intervals.

The Sun viewing constraint is periodic every 6 months since the pitch limit is symmetric under positive pitch (away from Sun, up to +36˚) and negative pitch (toward Sun, down to -36˚). Thus the last chart is the same as the first.

In each hemisphere, the region

between the gray curves is allowed by the Sun, and within the blue circles is allowed by the Earth.Maximum viewing fraction (satisfying both constraints) is at low b (April or October).

Combined Cutout Charts

30Slide31

31Slide32

32Slide33

33Slide34

34Slide35

35Slide36

36Slide37

37