Projected Flight Hardware Laser

MNG-03E-100

TETHERING AND RANGING MISSION OF THE GEORGIA INSTITUTE OF TECHNOLOGY (TARGIT)

The Development of a CubeSat Sized Imaging LiDAR Lorin Achey1, Caleb Alexander1,2, Saumya Sharma1, Dr. Brian C. Gunter1, Dr. Chris Valenta2

(1) Daniel Guggenheim School of Aerospace Engineering, (2) Georgia Tech Research Institute (GTRI)

OVERVIEW and APPROACH TESTING and RESULTS FUTURE WORK

ACKNOWLEDGEMENTS

The LiDAR System of TARGIT would like to thank Benja-

min Quick and Nathan Meraz for their extensive support

from GTRI. Additionally, Connor Lawson and Byron Davis

brought their vast knowledge from the RANGE mission that

helped shape these designs. Finally, we would like to thank

all of the current and former members of the TARGIT team,

who have enabled our success.

The Tethering and Ranging Mis-

sion of the Georgia Institute of

Technology (TARGIT) is a

nanosatellite (CubeSat) mission,

tentatively slated to launch in late

2019, that strives to provide centi-

meter-level topographical map-

ping of an inflatable target using a

compact LiDAR imager.

The objective of this mission is to develop, and test on-orbit,

a small form factor LiDAR imaging camera. The LiDAR

camera will be the primary payload of this NASA sponsored

CubeSat mission. The LiDAR system will image an inflata-

ble target tethered to the CubeSat starting at three meters

away, and then after the tether is released, will continue

ranging the target until it is no longer detectable.

This mission will raise the technology readiness level of new

silicon photomultiplier arrays by demonstrating their utility

for space applications and will lay the groundwork for future

planetary missions that need imaging technology at lower

cost. The LiDAR subsystem will be suitable for ride-share

applications due to its small form factor and will be a viable

low-cost option for imaging of planetary bodies.

Laser Wavelength and Photodetector Responsivity

Trade Study

SENSL J SERIES % Total @

532 nm

% Total @

905 nm

% Total @

1064 nm

Phobos/Deimos/Class D

Asteroid 1.5 0.18125 0.00142

Europa 29.7 2.775 0.28

Clay 9.9 1.25 0.0851

Clean Snow 17.1 0.75 0.0562

Subsystem Diagram

The trade study determined that a laser wavelength of 532nm

coupled with a SensL J series photodetector was the optimal

combination for imaging of planetary bodies.

The subsystem diagram represents the high level architecture

of the LiDAR system. It includes all of the components as

well as the serial communication methods.

The graph above shows partial results from a radiometry

study used to determine the maximum possible ranging dis-

tance with the selected laser at solar intensities expected on-

orbit. The study confirmed that amplifiers for the SiPM sig-

nals will not be necessary, reducing the complexity, cost, and

volume of custom circuit boards used for flight hardware.

TARGIT CubeSat Expected Volumetric

Constraint of LiDAR

Flight Hardware

Long-Range System

Near-Range System

GOAL: To scale from the one pixel benchtop setup to a 16

pixel flight hardware system. This involves testing and manu-

facturing nanosatellite form factor LiDAR system.

POTENTIAL NEAR-RANGE HARDWARE LIST:

• Initial Trigger: SensL J-Series 30035 TSV Single Cell

• Receiving Array: SensL J-Series 30035 16 Cell Array

• Microcontroller: PSoC5 by Cypress Semiconductor

• ToF Processor: ACAM TDC-GPX (x2 for 16 channels)

• High Speed Comparators

• Receiving and Transmitting Optics

Example 4x4 SensL SiPM Array and Circuit Board

LASER:

• Purchase the Teem Photonics MNG-30E-100 laser for

further testing and integrate into the benchtop setup

DETECTOR ARRAY:

• Scale up from a single pixel SiPM to a 4x4 SiPM Array

for detection of return signals

TIME-TO-DIGITAL CONVERTER:

• Transition from GP-22 to the two 8-channel GP-X’s for

the 4x4 SiPM array

CUSTOM CIRCUIT BOARD FABRICATION:

• Design, fabricate, and test custom boards that will inte-

grate high speed comparators and the 4x4 SiPM array

SOFTWARE/FIRMWARE DEVELOPMENT:

• Software integrating the PSoc5 microcontroller and GP

-X time to digital converter

OPTICAL DESIGN:

• Purchase lens tubes and lenses for transmitting and re-

ceiving optics

• Incorporate a narrowband filter into receiving optics

Initial Benchtop Attempt

The QP50 Photodiode (initial trigger T0) could not produce

a start signal fast enough, due to its slow rise time. This

caused the GP-22 to experience timeout errors before a ToF

could be obtained. The MicroFJ-SMA-60035 SiPM selected

to replaced the QP50, eliminating the rise time issue.

Oscilloscope Capture of Initial Trigger and

Receiving SiPM (Standard & Fast Output)

Current Benchtop Setup

LASER:

• Utilizing a QL532-200 Pulsed 532nm Laser to more

closely resemble the flight hardware that will be used

MICROCONROLLER SELECTION:

• We decided on PSOC for its timing capabilities and

programmable logic with the help of the fast and con-

figurable FreeRTOS as opposed to a slow and cumber-

some full Linux operating system on the BeagleBone

DETECTOR SELECTION:

• MicroFJ-SMA-30035 SiPM selected to detect return

signals due to its sensitivity, quick response time

OPTICS

• Using thin film, retroflective material, which transmits

laser light into the SiPM used to signal the T0

Standard Output

Fast Output