Instrument reference information July 1 2015 The information in this file is excerpted from the SDT report dated March 10 2015 Spergel et al arXiv150303757 and from the February 13 2015 SDT briefing to Paul Hertz Both are accessible from the WFIRST site ID: 306068
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Slide1
WFIRST Instrumentreference information
July
1,
2015Slide2
The information in this file is excerpted from the SDT report dated March 10, 2015 (Spergel et al. arXiv:1503.03757) and from the February 13, 2015 SDT briefing to Paul Hertz. Both are accessible from the WFIRST site: http://wfirst.gsfc.nasa.gov
Extensive information on WFI
optical characteristics
is available
hereSlide3
WFIRST-AFTA Observatory ConceptKey Features
Telescope:
2.4m aperture primary
Instruments
Wide Field Imager/Spectrometer & Integral Field UnitInternal Coronagraph with Integral Field SpectrometerOverall Dry Mass: ~4060 kg (CBE)Structure: high stiffness composites; modular packaging for avionicsGN&C/Propulsion: inertial pointing, 3-axis stabilized, mono-prop system for stationkeeping & momentum unloadingData Downlink Rate: Continuous ~600 Mbps Ka-band to dedicated ground stationC&DH: low rate bus for housekeeping and spacecraft control, high speed bus for science dataPower: ~2400 W average power (CBE)GEO orbitLaunch Vehicle: Delta IV HeavyGSFC: leads mission, wide field instrument, spacecraftJPL: leads telescope, coronagraph
3
02-13-15
WFIRST-AFTA SDT Final Report Briefing to HertzSlide4
WFIRST-AFTA Payload Layout
4
02-13-15
WFIRST-AFTA SDT Final Report Briefing to Hertz
Wide Field Instrument
Coronagraph Instrument
Instrument CarrierSlide5
WFIRST-AFTAPayload Optical Block Diagram
5
02-13-15
WFIRST-AFTA SDT Final Report Briefing to HertzSlide6
Optical Field LayoutThe Wide Field Instrument (WFI) has two science channelsA Wide Field Channel (WFC) with two modes dependent on element wheel position
Wide Field Imaging Mode (WIM)
Wide Field Spectroscopy Mode (WSM)
An Integral Field Unit (IFU) channel viewing two fields
3”x3.15” and 6x6.3” FOVsThe Coronagraph Instrument (CGI) is a small field system in a separate field of viewContains an imager and a Integral Field Spectrometer (IFS) viewing the same field602-13-15WFIRST-AFTA SDT Final Report Briefing to Hertz
Channel Field Layout for WFIRST-AFTA InstrumentsSlide7
Telescope Reuse7
02-13-15
WFIRST-AFTA SDT Final Report Briefing to HertzSlide8
Wide Field Instrument OverviewKey Features
Wide field channel instrument for both imaging and spectroscopy
3 mirrors, 1 powered
18 4k x 4k HgCdTe detectors cover 0.76 - 2.0
mm0.11 arc-sec plate scaleSingle element wheel for filters and grismGrism used for GRS survey covers 1.35 – 1.89 mm with R = 461l (~620 – 870)IFU channel for SNe spectra, single HgCdTe detector covers 0.6 – 2.0 mm with R between 80-120802-13-15
WFIRST-AFTA SDT Final Report Briefing to Hertz
Focal Plane Assembly
Optical Bench
Cold Electronics
Cold Optics Radiation Shield
Element WheelSlide9
WFI FiltersSlide10
WFI detector performanceDetector technology development requirements. The right two columns summarize the results from the two lots of
prototype detectors available in late 2014.Slide11
IFU Layout - Slicer
11Slide12
IFU Layout – Relay to Spectrum
12Slide13
Coronagraph Instrument Overview
13
02-13-15
WFIRST-AFTA SDT Final Report Briefing to Hertz
Temperature293 K
for instrumentTemperature~165
K for camerasData Volume
~30 Gbits/day Imaging
0.43 – 0.97 microns, 4.8"
FoV
0.009" pixel scale, 1K×1K
EMCCD
Integral
Field Spectrograph
0.60 – 0.97 microns R~70Slide14
Primary Architecture:
Occulting Mask Coronagraph = Shaped Pupil + Hybrid Lyot
14
02-13-15
WFIRST-AFTA SDT Final Report Briefing to Hertz
SP and HL masks share very similar optical layouts
Small increase in overall complexity compared with single mask implementation
In “SP mode” provides the simplest design, lowest risk, easiest technology maturation, most benign set of requirements on the spacecraft and “use-as-is” telescope. This translates to low cost/schedule risk which is critical for the independent CATE process.
In “HL mode”, affords the potential for greater science, taking advantage of good thermal stability in GEO and low telescope jitter for more planet detections in a shorter timeSlide15
Model contrast performanceModel-predicted contrast for the HLC in the presence of LOS jitter. Jitter values represent the variation after control by the LOWFS, which is
expected
to reduce
rms
jitter to a fraction of a milli-arcsecond. Model-predicted contrast for the SPC in the presence of LOS jitter. The LOWFS is expected to reduce jitter seen by the coronagraph to a fraction of a milli-arcsecond. Slide16
CGI FiltersCoronagraph mask/filter sets for each configuration. The table shows the number of masks or filters required in each configuration at leach location in the optical
beamtrain
.
Bandpass
filters for planet imaging, spectroscopy, and dust debris disk imaging.Slide17
CGI IFS specificationsSlide18
CGI Detector Performance Requirements18
02-13-15
WFIRST-AFTA SDT Final Report Briefing to Hertz
Specification
Expected
Value
Requirement
Unit
Notes
Active Pixels
1024 x 1024
1024 x 1024
---
---
Pixel Pitch
13 x 13
13 x 13
microns
Effective area:
177.2mm
2
Effective Read
Noise
0.2
0.2
e-
Achieved using EM gain
Saturation
Signal per Pixel
50863
N/A
e-
EM amp
full well @ 1 MHz vertical frequency
Dark
Current
9
x 10
-5
1
x 10
-4
e-/
pix/sec
Temp 165K, inverted
mode operation
Clock-Induced Charge
(
CIC
) @ 5
s
0.0013
0.0018
e-/
pix/frame
10 MHz
horizontal frequency; 1 MHz vertical frequency; EM gain = 1000
QE at
660
,
770
,
890
nm
88, 68, 28
88, 68, 28
%
At
165KSlide19
CommContinuous downlink to dedicated ground station, same concept as SDOS-band omni antennas for uplink and housekeeping data downlink
Ka
-band for science data is ~600 Mbps
GSFC developed transmitter (update of SDO design) with a capability of 1.2
Gbps (prototype on schedule for completion in early 2015)Attitude Control/Prop3-axis stabilized using 4 reaction wheels with thruster unloading14 mas drift & 14 mas jitter, RMS/axisFGS uses guide window data from wide field focal planeMono-prop system for station-keeping, momentum unloading and end of life disposalSpacecraft Overview1902-13-15
WFIRST-AFTA SDT Final Report Briefing to Hertz