A Linear Mode Photon-Counting (Lmpc) Detector Array in a Cubesat to Enable Earth Science Lidar Measurements

A LINEAR MODE PHOTON-COUNTING (LMPC) DETECTOR ARRAY IN A CUBESAT TO ENABLE EARTH SCIENCE LIDAR MEASUREMENTS

Renny Fields1, Xiaoli Sun2, James B. Abshire2, Jeff Beck3, 3 3 1 Richard M. Rawlings , William Sullivan III , David Hinkley

1The Aerospace Corporation, El Segundo, CA 90245 2NASA Goddard Space Flight Center, Greenbelt, MD 20771 3DRS Technologies, C4ISR Group, Dallas, TX 78712

Effort funded under the NASA Earth Science Technology Office InVEST 12 open solitication

1 © The Aerospace Corporation 2015 UNCLASSIFIED AC9 LMPC CubeSat – Aerospace AeroCube-9 (AC-9) LMPC

-Z 3 -Z 5 +Y -X - +X Y

1 & 4 6 BUS Optical Path Optical Path • HgCdTe responds from 0.4 to 4 microns to single 1. Dewar • Filter wheel with 5 settings photons (1000 electrons per photon) 2. Stirling cycle cooler • 3 Bandpass filters • AC9 will use narrowband filters to pass 1.06, 1.55 and 3. IDCA controller • 1 blank (opaque) 2.06 microns for daylight operation 4. FPA conditioning circuits • 1 open • Launch Nov 2016 (delivery Aug 2016) 5. Radiator structure 6. Warm filter and objective lens

HgCdTe electron initiated avalanche photodiode (e-APD) array • Developed by DRS Technologies in Dallas TX Diode Side View Unit Cell Cross Section Top View • 2x8 pixels with built in read-out integrated circuit (ROIC), 20 µm AR Coating N-Type diameter active area, 64 µm pitch, with µ-lens array F/7 optical 5-7 µm P-Type Region path, 7 mm diameter entrance aperture MCT <1 µm epoxy epoxy

Thickness Pre-amp input pad • 90% quantum efficiency CdTe 0.5 mm Passivation • >1000 APD gain, more than sufficient to override ROIC noise Readout IntegratedROIC Circuit (ROIC) • Linear mode photon counting (LMPC) detectors from visible to mid-wave infrared (VIS/MWIR) wavelength range.

2 © The Aerospace Corporation 2015 UNCLASSIFIED UNCLASSIFIED AC9 Why Fly a Linear Mode Photon Counting Detector? LMPC

Tier 1 Tier 2 Tier 3

Decadel Survey ACE LIST PATH SCLP SMAP SWOT GACM

Missions HyspIRI ICESat-II DESDynl 3D=Winds GRACE=II CLARREO ASCENDS

GEO=CAPE      LMPC Impact  0  0  0 0 0       

At least three Tier 1 missions are strongly driven in science capability by photon detection sensitivity • LIST which is strongly related to ICESat & DESDynl will not reach threshold goals without single photon response matched to high power efficient transmitters that respond to 1 micron • While threshold science can be achieved with photomultipliers for CO2 at 1.5 and 2 microns, single photon response will significantly extend the science • The potential for high sensitivity passive arrays across the 0.4-4 micron HgCdTe response shows potential for many other missions as this technology and its support elements mature

3 © The Aerospace Corporation 2015 UNCLASSIFIED UNCLASSIFIED AC9 Packing Density View LMPC

IDCA PAYLOAD • Located centrally inside satellite • Radiator/payload hard mount to body by solid brackets that are mechanically fixed but made from thermally isolating material.

RADIATION DETECTOR • Commercially available Teledyne Dosimeter • Uses AC8 Derived daughter PCB • Co-Located with IDCA sensor

ACS COMPONENTS • All ACS components hard mount to body around primary payload

SINGLE STAGE LASER • Output of laser co-bore sighted Sensor with IDCA sensor

4 © The Aerospace Corporation 2015 UNCLASSIFIED UNCLASSIFIED AC9 LMPC Enabling Technology: Linear Mode HgCdTe e-APD

• High, near noiseless, uniform, APD Gain vs. Bias Excess Noise Factor vs. Gain avalanche gain 10000 5 53 Pixels Si Theory for Ideal k = 0 • Gain normalized dark current M = 1270 @13.1 V 4 (McIntyre History-Independent) 1000 6,5 s/mean = 4.5 % 6,0 as low as 100 e/s 3 5,4 3,0 2,7

100 F(M) k=0 • Broad spectral range: UV – 2 ' Gain Measured data k=0.02 MWIR k=0.001 1 10 • High quantum efficiency 0 Beck, et al. 2006 JEM 0 200 400 600 800 1000 1200 • High intrinsic bandwidth (~ 10 1 Gain GHz) 0 5 10 15 Bias (V) • Large dynamic range 8 ns pulse separation Broad Spectral Response • Demonstrated photon counting (ROIC BW limited) 0.03

sensitivity 0.025

0.02 8 ns • Continuous operation with no 0.015 dead time or after-pulsing 0.01

Voltage (V) Voltage 0.005 – Minimum time between 0 0.1 Gain = 254 -0.005 events MBE < ~ 10 ns 0.05 -0.01 0 10 20 30 40 50 60 (limited by current ROIC 0 Time (ns) bandwidth) 0.1 Gain = 514 0.05 0 High SNR Single Photon Sensitivity Amplitude (V) Amplitude

0.1 Gain = 1100 0.05 0 0 50 100 150 200 250 Time (µs)

5 © The Aerospace Corporation 2015 UNCLASSIFIED UNCLASSIFIED AC9 LMPC Blocking Noise from ROIC Glow

16-Pixel-Mean PDE vs. FER Pixel-by-Pixel FER Comparison 1 2000 A8327-14-2 (No metal shield) No mirror blocking metal A8327-14-1 (With metal shield) 1800 With mirror blocking metal 0.8 1600 All pixels: 1400 >50% PDE 0.6 1200

1000 PDE 0.4

FER (kHz) FER 800

600 0.2 400

200 0 3 4 5 6 7 10 10 10 10 10 0 False Event Rate (Hz) 1,1 1,2 1,3 1,4 1,5 1,6 1,7 1,8 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 Pixel

“Tab” No metal shield With Metal metal ROIC FER ≤ 200 kHz for every pixel with shield shield Glow HgCdTe Array HgCdTe Array blocking metal layer, a 1/5 reduction. Photons Multiple metal layers are expected to decrease FER to diode limit (< 20 kHz). Si ROIC Si ROIC

10/27/14 6 © The Aerospace Corporation 2015 Sun et al., ESTF 2014, Paper B4P5 UNCLASSIFIED UNCLASSIFIED AC9 LMPC HgCdTe e-APD Performance Summary LMPC GSFC ACT Program Parameter Specification Oct. 2014 Status Notes 2x8 pixel array, 20 µm Form factor can be changed if Size and form factor Demonstrated dia, 64 µm pitch funds available for a new ROIC

Photon Detection > 40% > 50% (> 65% From optical input to the analog Efficiency 0.9 to 4.2 µm (> 50% goal) demonstrated) outputs

< 500 kHz < 200 kHz Including detector dark current, Dark count rate (<100 kHz goal) demonstrated ROIC and system noise Stray capacitance limiting Pulse pair separation < 10 ns (< 6 ns goal) 9 ns demonstrated bandwidth < 1.0 ns rms ~1.6 ns rms (< 1 ns Improvement with smaller pitch Timing jitter (< 0.5 ns rms goal) rms in 2011 FPA) APDs pixel designs expected. 1.2-1.25 Decreased diode Excess Noise Factor < 1.4 Demonstrated junction width Analog and Linear mode multi-photon Outputs Demonstrated Digital (optional) resolution with analog outputs LN2 Dewar (80K) with May be housed in an existing Housing Demonstrated window, f/1.5 to f/4.9 long lifetime space cryo-cooler All spec’s met, except jitter, at Simultaneity of All specifications met Demonstrated with the same time on the same Specifications at the same time exception of jitter device at the same threshold.

7 © The Aerospace Corporation 2015 UNCLASSIFIED UNCLASSIFIED AC9 Physical Dimensions of the Cooler and Cold Filter Performance LMPC

Basic Dimensions of the Integrated Detector Cooler Assembly

3.131”

Ø1.52 9” 1.887”

0.602” 4.214” LMPC QE, CubeSat Coldfilter - Incident Background Count Rate: 102.45 kHz at f/7.0 30 8.373” 10 1 Cold filter transmission Spectral Radiance 0.9 25 10 APD QE The background count rate was calculated 0.8 using: 0.7

* sr * m)) * sr * 20 • Materion’s measured cold filter 2 10 transmission 0.6

15 • QE from previous LMPC APD array 10 0.5 (analysis uses 300 K blackbody temperature, 0.4 2 10 dual stacked cold filters, f/7, and a (64 µm) 10 2.25 µm cutoff 0.3 Filter Filter Transmission & QE detector.) 0.2

Spectral radiance (ph / (s * m * / (s (ph radiance Spectral 5 10 0.1

0 The total expected 0 1 2 3 4 5 6 background count rate Wavelength (µm) is 103 kHz Stacked filter transmission is very good (>90%) at 1064 nm, 1572 nm, and 2060 nm

8 © The Aerospace Corporation 2015 UNCLASSIFIED UNCLASSIFIED AC9 Overall System Block Diagram LMPC

Analog board Digital board

Analog Power Supplies Digital Power Supplies

Photon Counters Capacitive Isolators Pre-Filter Linear Capture Zynq 7020 SoC (ARM + FPGA) High-speed Main Vehicle Bus MainVehicle Capture & MUX DRSSensor Connector Control and Status (Power, analog outputs,status) (Power, (Power, GPS Time, Tx2/Rx2, Tx1/Rx1) Tx2/Rx2, Time, GPS (Power,

Flash FPGA ARM (QSPI, LPDDR2 LPDDR2 µSD, Atmel)

9 © The Aerospace Corporation 2015 UNCLASSIFIED UNCLASSIFIED AC9 Three Data-Capture Subsystems LMPC 16x Analog Signals from DRS HgCdTe detector 8 GB 8 MB 16+ MB 16 µSD Backup Boot Photon Counters (16 Channel) Card Flash Flash 16 Low-pass Filter Thresholds 2×LTC2605 e.g. LFCN-105 (16-bit DAC×16) (F3db=180 MHz) 16

Comparators (ADCMP605) 16 Zynq-7020

Linear-mode (16 Channel) 16 16 Main Low-pass AD9249 FPGA ARM Bus (F3db= 7 MHz) (65MSPSx16) (Isolated)

High-speed (Single Channel)

MUX MUX 1 16 AD9286 1 2 GB 1 GB (500MSPS×1) LPDDR2 LPDDR2 (667 MT/s) (667 MT/s) 16:1 MUX (ADG782) Note: I2C/SPI control signals omitted for clarity

AC9 Mission Specific Hardware Solar Cells (14V, 0.5A string, 4 strings) Comm Laser • Spectrolab • Aerospace Design • Maturity: TRL6 • Single Stage, nominal 2W optical output

Payload Batteries Sun /Earth Sensor Assembly 5W constant Payload Solar • Molicel IBR18650BC • Maturity: TRL8 Cells • Maturity: TRL6 Sensor (8W sunlit) • Power: 90% efficient Sun Sensor Assembly 29 PCB Avionics Solar • Maturity: TRL9 Software Cells STAR Camera (x2) . (2W orbit avg) • CMOS (VGA) Laser Power • Maturity: TRL6 DRS Hardware • 21 deg lens

Harness Butterfly Gyro IDCA CONTROLLER • STIM210

Solar 18 19 (payload) 19 • Maturity: TRL8 Wing • Maturity: New Latch EPS-H Radio 1 28V, 8-12 watts to 7 Radio 2 GPS (IDCA 28V, 20W Max 9V or 915 MHz IDCA Controller 915 MHz 1.57 GHz Camera 2W constant output!!) 26V to Camera controller

baffle Solar Harness Software Switch A • Maturity: TRL6 STD Temp Set Point Bus PHOTON COUNTING 5 4 333 2 FGA Actual Temp 8 (2x PCBs) CAMERA PCB ACSDR ACS PCB (GPS RADIO #1 1 EPS Analog Data CAPTURE AND PROCESSING FLIGHT COMPUTER) ELECTRONICS Software Dewar Card PCB Software Software Software Software Software Dewar card is 0W/0.5W@90min only on for short 0W/5W@5min periods of time EPS (bus) 9W constant Dewar card is ACB FGA • Maturity: TRL8 IDCA controller Radio #2 (optional) • Maturity: TRL8 • • Maturity: TRL8 only on for • Aerospace design Software radio RW Detector • Maturity: TRL6 Remote Access (inside Dewar) short periods • Maturity: TRL4 17 Interface of time RAP, SW1, Torque Rods RBF, Cooler Power

• Temp Harness (6) AUX PCB To ACB Aerospace Design Charge port • BUS Batteries AUX 10 MP Camera (x2) Maturity: TRL9 Cryo • Molicel 18650H connector CMOS • Maturity: TRL6 • Maturity: TRL9 Motorized Filter wheel • (1) Nadir face, 180 deg Reaction Wheels 90% efficient • Aerospace Design • Maturity: TRL7 • Maturity: TRL4 Legend 40-pin backplane

Temperature sensor Sun Sensor anti-Nadir 10W constant Custom Kapton Harness Assembly • Maturity: TRL9 Kapton jumper . Dosimeter PCB 1.0, 1.57, 2.05 micron Patch antenna Dosimeter (AC8 derived) light sources • Teledyne AC9 LED PCB RF coax cable Comm with AUX on • COTS LEDs • Maturity: TRL9 FGA • Maturity: TRL5 Wire harness

• NASA CSLI Option 1 • 450 km x 820 km x 99 deg inclined • Aug 2016 delivery to Integrator • Nov 2016 launch • NASA CSLI Option 2 • 600 km SSO 10:30 LTDN • April 2016 delivery to Integrator • July 2016 launch

No. Requirement

The LMPC shall measure near and short wave IR sources with the 2X8 Mercury Cadmium Telluride 1 (MCT) electron Avalanche Photo Diode (e-APD) focal plane array (FPA) for 1 year to support the component needs for future NASA missions

2 The LMPC shall detect laser light from a ground source

The LMPC shall perform a radiometry assessment by scanning the Earth's moon for response 3 calibraon

The LMPC shall conduct a variable radiometric response experiment by imaging the sunlit Earth 4 and clouds (i.e. no laser source)

5 The vehicle shall conform to CubeSat standards

The LMPC shall measure the eﬀects of space radiaon on the dark current, APD gain and quantum 6 eﬃciency of a 2x8 HgCdTe electron Avalanche Photo Diode (e-APD) focal plane array (FPA) in a relevant space environment

No. Goal

1 The LMPC shall be compable with an opcal communicaons link

2 Measure an atmospheric gas absorpon line

• Demonstrate single photon detection in space compatible with dark current • Present status: – Despite the relative early stage of the LMPC ACT-10 2 by 8 array, AC9 will have the ability to resolve a 13kcount or greater increase in dark current induced by the radiation exposure • Developments under other programs have significantly reduced systematic background counts due to ROIC glow and pixel jitter to < 1 ns – The ideal coating performance of the Materion cold filters insures relevant performance at the 3 principal earth science lines – Current performance of AC9 star trackers with potentially 0.01 degree open loop pointing opens relevant optical communication demonstrations – Impact of cryo-cooler vibration on spacecraft • Linear acceleration RMS = [ 0.0133 , 0.0141 , 0.0096 ] g • Angle (jitter) RMS = [ 0.06 , 0.36 , 0.15 ] milli-deg (nominal R_gyro) • Angle (jitter) RMS = [ 0.06 , 0.51 , 0.77 ] milli-deg (bounding case R_gyro)

Even the tight 0.1 degree pointing will not be affected by cryo-cooler vibration