© The Aerospace Corporation 2015

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, Richard M. Rawlings3, William Sullivan III3, David Hinkley1 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

AC9 LMPC

2 © The Aerospace Corporation 2015

UNCLASSIFIED

UNCLASSIFIED

HgCdTe electron initiated avalanche photodiode (e-APD) array •  Developed by DRS Technologies in Dallas TX •  2x8 pixels with built in read-out integrated circuit (ROIC), 20 µm

diameter active area, 64 µm pitch, with µ-lens array F/7 optical path, 7 mm diameter entrance aperture

•  90% quantum efficiency •  >1000 APD gain, more than sufficient to override ROIC noise •  Linear mode photon counting (LMPC) detectors from visible to

mid-wave infrared (VIS/MWIR) wavelength range.

AR Coating

5-7 µm P-TypeMCT

N-TypeRegion

<1 µm

0.5 mm

Thic

knes

s

CdTePassivation

ROIC

epoxy epoxy

Unit Cell Cross Section

Pre-amp input pad

AR Coating

5-7 µm P-TypeMCT

N-TypeRegionN-TypeRegion

<1 µm

0.5 mm

Thic

knes

s

CdTePassivation

ROIC

epoxy epoxy

Unit Cell Cross Section

Pre-amp input pad

Diode Side View

Readout Integrated Circuit (ROIC)

Top View

LMPC CubeSat – Aerospace AeroCube-9 (AC-9)

+X -Z -

Y -X

-Z +Y

1 & 4

5

2

6

3

Optical Path Optical Path BUS 1. Dewar 2. Stirling cycle cooler 3.  IDCA controller 4. FPA conditioning circuits 5. Radiator structure 6. Warm filter and objective lens

•  HgCdTe responds from 0.4 to 4 microns to single photons (1000 electrons per photon)

•  AC9 will use narrowband filters to pass 1.06, 1.55 and 2.06 microns for daylight operation

•  Launch Nov 2016 (delivery Aug 2016)

•  Filter wheel with 5 settings •  3 Bandpass filters •  1 blank (opaque) •  1 open

AC9 LMPC

3 © The Aerospace Corporation 2015

UNCLASSIFIED

UNCLASSIFIED

Why Fly a Linear Mode Photon Counting Detector?

Tier 1 Tier 2 Tier 3 Decadel Survey Missions

ICE

Sat

-II

CLA

RR

EO

SM

AP

DE

SD

ynl

Hys

pIR

I

AS

CE

ND

S

SW

OT

GE

O=C

AP

E

AC

E

LIS

T

PATH

GR

AC

E=I

I

SC

LP

GA

CM

3D=W

inds

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

AC9 LMPC

4 © The Aerospace Corporation 2015

UNCLASSIFIED

UNCLASSIFIED

Packing Density View

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.

ACS COMPONENTS •  All ACS components hard mount

to body around primary payload

RADIATION DETECTOR •  Commercially available Teledyne

Dosimeter •  Uses AC8 Derived daughter PCB •  Co-Located with IDCA sensor

SINGLE STAGE LASER •  Output of laser co-bore sighted

with IDCA sensor Sensor

AC9 LMPC

5 © The Aerospace Corporation 2015

UNCLASSIFIED

UNCLASSIFIED

Enabling Technology: Linear Mode HgCdTe e-APD

•  High, near noiseless, uniform, avalanche gain

•  Gain normalized dark current as low as 100 e/s

•  Broad spectral range: UV – MWIR

•  High quantum efficiency •  High intrinsic bandwidth (~ 10

GHz) •  Large dynamic range •  Demonstrated photon counting

sensitivity •  Continuous operation with no

dead time or after-pulsing –  Minimum time between

events MBE < ~ 10 ns (limited by current ROIC bandwidth)

Excess Noise Factor vs. Gain

0

1

2

3

4

5

0 200 400 600 800 1000 1200Gain

F(M)

6,56,05,43,02,7k=0k=0.02k=0.001

'

Si

Measured data

Theory for Ideal k = 0 (McIntyre History-Independent)

1

10

100

1000

10000

0 5 10 15

Bias (V)G

ain

APD Gain vs. Bias

53 Pixels M = 1270 @13.1 V s/mean = 4.5 %

Beck, et al. 2006 JEM

0

0.05

0.1

0

0.05

0.1

Ampl

itude

(V)

0 50 100 150 200 250

0

0.05

0.1

Time (µs)

Gain = 254

Gain = 514

Gain = 1100

High SNR Single Photon Sensitivity

0 10 20 30 40 50 60-0.01

-0.005

0

0.005

0.01

0.015

0.02

0.025

0.03

Time (ns)

Volta

ge (V

)

8 ns

8 ns pulse separation (ROIC BW limited) Broad Spectral Response

AC9 LMPC

6 © The Aerospace Corporation 2015

UNCLASSIFIED

UNCLASSIFIED

Blocking Noise from ROIC Glow

10/27/14 Sun et al., ESTF 2014, Paper B4P5

Si ROIC

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 2,80

200

400

600

800

1000

1200

1400

1600

1800

2000

Pixel

FER

(kH

z)

No mirror blocking metalWith mirror blocking metal

FER ≤ 200 kHz for every pixel with blocking metal layer, a 1/5 reduction. Multiple metal layers are expected to decrease FER to diode limit (< 20 kHz).

“Tab” metal shield

Si ROIC

HgCdTe Array HgCdTe Array

16-Pixel-Mean PDE vs. FER Pixel-by-Pixel FER Comparison

All pixels: >50% PDE

ROIC Glow Photons

No metal shield With Metal shield

103 104 105 106 1070

0.2

0.4

0.6

0.8

1

False Event Rate (Hz)

PDE

A8327-14-2 (No metal shield)A8327-14-1 (With metal shield)

AC9 LMPC

7 © The Aerospace Corporation 2015

UNCLASSIFIED

UNCLASSIFIED

Parameter GSFC ACT Program Specification Oct. 2014 Status Notes

Size and form factor 2x8 pixel array, 20 µm dia, 64 µm pitch Demonstrated Form factor can be changed if

funds available for a new ROIC

Photon Detection Efficiency 0.9 to 4.2 µm

> 40% (> 50% goal)

> 50% (> 65% demonstrated)

From optical input to the analog outputs

Dark count rate < 500 kHz (<100 kHz goal)

< 200 kHz demonstrated

Including detector dark current, ROIC and system noise

Pulse pair separation < 10 ns (< 6 ns goal) 9 ns demonstrated Stray capacitance limiting bandwidth

Timing jitter < 1.0 ns rms (< 0.5 ns rms goal)

~1.6 ns rms (< 1 ns rms in 2011 FPA)

Improvement with smaller pitch APDs pixel designs expected.

Excess Noise Factor < 1.4 Demonstrated 1.2-1.25 Decreased diode junction width

Outputs Analog and Digital (optional) Demonstrated Linear mode multi-photon

resolution with analog outputs

Housing LN2 Dewar (80K) with window, f/1.5 to f/4.9 Demonstrated May be housed in an existing

long lifetime space cryo-cooler

Simultaneity of Specifications

All specifications met at the same time

Demonstrated with exception of jitter

All spec’s met, except jitter, at the same time on the same device at the same threshold.

LMPC HgCdTe e-APD Performance Summary

AC9 LMPC

8 © The Aerospace Corporation 2015

UNCLASSIFIED

UNCLASSIFIED

Physical Dimensions of the Cooler and Cold Filter Performance

Basic Dimensions of the Integrated Detector Cooler Assembly

4.214”

Ø1.529”

8.373”

0.602”

3.131”

1.887”

The background count rate was calculated using: •  Materion’s measured cold filter

transmission •  QE from previous LMPC APD array (analysis uses 300 K blackbody temperature, dual stacked cold filters, f/7, and a (64 µm)2 detector.)

Stacked filter transmission is very good (>90%) at 1064 nm, 1572 nm, and 2060 nm

The total expected background count rate

is 103 kHz

0 1 2 3 4 5 6

105

1010

1015

1020

1025

1030

Wavelength (µm)

Spec

tral r

adia

nce

(ph

/ (s

* m2 *

sr *

m))

LMPC QE, CubeSat Coldfilter - Incident Background Count Rate: 102.45 kHz at f/7.0

0 1 2 3 4 5 60

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Filte

r Tra

nsm

issi

on &

QE

2.25 µm cutoff

Cold filter transmission Spectral Radiance APD QE

AC9 LMPC

9 © The Aerospace Corporation 2015

UNCLASSIFIED

UNCLASSIFIED

Overall System Block Diagram

Analog Power Supplies

FPGA LPDDR2

ARM LPDDR2

Flash (QSPI, µSD,

Atmel)

Photon Counters

Linear Capture

High-speed Capture & MUX

Capacitive Isolators

Pre-Filter

Mai

n Ve

hicl

e B

us

(Pow

er, G

PS

Tim

e, T

x2/R

x2, T

x1/R

x1)

DR

S S

enso

r Con

nect

or

(Pow

er, a

nalo

g ou

tput

s, s

tatu

s)

Zynq 7020 SoC (ARM + FPGA)

Control and Status

Digital Power Supplies

Analog board Digital board

AC9 LMPC

10 © The Aerospace Corporation 2015

UNCLASSIFIED

UNCLASSIFIED

High-speed (Single Channel)

Linear-mode (16 Channel)

Photon Counters (16 Channel)

Three Data-Capture Subsystems

Zynq-7020

AD9249 (65MSPSx16)

AD9286 (500MSPS×1)

ARM

2 GB LPDDR2

(667 MT/s)

1 GB LPDDR2

(667 MT/s)

16x Analog Signals from DRS HgCdTe detector

MU

X

Main Bus

(Isolated)

8 GB µSD Card

Low-pass Filter e.g. LFCN-105 (F3db=180 MHz)

2×LTC2605 (16-bit DAC×16)

Comparators (ADCMP605)

Thresholds

Low-pass (F3db= 7 MHz) FPGA

16

16

16

16

16

16

16

1 1

Note: I2C/SPI control signals omitted for clarity

16+ MB Boot Flash

16:1 MUX (ADG782)

8 MB Backup Flash

AC9 LMPC

11 © The Aerospace Corporation 2015

UNCLASSIFIED

UNCLASSIFIED

Remote  Access

RW  Interface

Solar  H

arne

ss

Payload  Solar  Cells(8W  sunlit)

EPS  (bus)•Maturity:  TRL8FGA

•Maturity:  TRL8

1.0,  1.57,  2.05  micron  light  sources•COTS  LEDs•Maturity:  TRL5

Motorized  Filter  wheel•Aerospace  Design•Maturity:  TRL4

BUS  Batteries•Molicel  18650H  •Maturity:  TRL9

FGA  (GPSRADIO  #1FLIGHT  COMPUTER)

Radio  1  915  MHz

GPS1.57  GHz

Software  

AC9  LED  PCB

Temp  Ha

rness  (6)

Camera  controller•Maturity:  TRL6

Dosimeter• Teledyne•Maturity:  TRL9

IDCA  controller•Aerospace  design•Maturity:  TRL4

EPS

Software

Solar  H

arne

ss

Avionics  Solar  Cells(2W  orbit  avg)

CAMERA  PCB

Software

1235

Legend40-­‐pin  backplane

Temperature  sensor

Custom  Kapton  Harness

Kapton  jumper

Patch  antenna

RF  coax  cable

Wire  harness

IDCA  CONTROLLER  (payload)•Maturity:  New

Radio  #2  (optional)•Software  radio•Maturity:  TRL6

ACSDR

Software

Radio  2  915  MHz

4

Reaction  Wheels•Maturity:  TRL7

Torque  Rods•Aerospace  Design•Maturity:  TRL9

Butterfly  Gyro• STIM210•Maturity:  TRL8

Sun  Sensor  Assembly• Maturity:  TRL9.  

Sun  /Earth  Sensor  Assembly• Maturity:  TRL8

AC9  Mission  Specific  Hardware

DRS  Hardware

3

17

18 1919

0W/0.5W@90min

PHOTON  COUNTING(2x  PCBs)  CAPTURE  AND  PROCESSING  ELECTRONICSSoftware

0W/5W@5min

Dewar  Card  PCB

9W  constant

90%  efficient

STAR  Camera  (x2)•CMOS  (VGA)•Maturity:  TRL6• 21  deg lens

10  MP  Camera  (x2)  CMOS•Maturity:  TRL6• (1)  Nadir  face,  180  deg

SensorPCB

Software

29

Camera  baffle

Wing  Latch

RAP,  SW1,  RBF,  Charge  port

Sun  Sensor  anti-­‐Nadir  Assembly•Maturity:  TRL9.  

EPS-­‐H(IDCA  28V,  20W  Max  output!!)

Software

7

Solar  Cells  (14V,  0.5A  string,  4  strings)• Spectrolab•Maturity:  TRL6

Payload  Batteries•Molicel IBR18650BC  •Maturity:  TRL6• Power:  90%  efficient

Temp  Set  Point

Dewar  card  is  only  on  for  short  periods  of  time

Actual  Temp

28V,  8-­‐12  watts  to  IDCA  Controller

Cryo

Cooler  Pow

er Detector  (inside  Dewar)

8

STD  Bus

Dosimeter  PCB(AC8  derived)Comm with  AUX  on  FGA

Analog  Data

Comm Laser•Aerospace  Design• Single  Stage,  nominal  2W  optical  output

Laser  Power

ACB•Maturity:  TRL8

ACS  PCB

Software

3

10W  constant

2W  constant

Dewar  card  is  only  on  for  short  periods  of  time

5W  constant

9V  or  26V    to  Switch  A

AUX  PCB To  ACB  AUXconnector

System Architecture

AC9 LMPC

12 © The Aerospace Corporation 2015

UNCLASSIFIED

UNCLASSIFIED

•  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

AC9 Launch Options

AC9 LMPC

13 © The Aerospace Corporation 2015

UNCLASSIFIED

UNCLASSIFIED

L1 Requirements No.   Requirement  

1  The  LMPC  shall  measure  near  and  short  wave  IR  sources  with  the  2X8  Mercury  Cadmium  Telluride  (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      

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

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

5   The  vehicle  shall  conform  to  CubeSat  standards  

6  The  LMPC  shall  measure  the  effects  of  space  radiaMon  on  the  dark  current,  APD  gain  and  quantum  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  compaMble  with  an  opMcal  communicaMons  link  

2   Measure  an  atmospheric  gas  absorpMon  line  

AC9 LMPC

14 © The Aerospace Corporation 2015

UNCLASSIFIED

UNCLASSIFIED

Summary •  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