Optomechanical Design and Analysis for Nanosatellite Laser Communications

L. Yenchesky, O. Cierny, P. Grenfell, W. Kammerer, P. Periera, T. Sevigny, K. Cahoy

Space Telecommunications, Astronomy, and Radiation Lab (STAR Lab)

MIT Department of Aeronautics and Astronautics

Overview

1. Introduction

2. Optical Design

3. Structural Design

4. Spacecraft Thermoelastic &

Payload Thermal Model

5. Summary & Future Work

2

Image: P. Grenfell

Introduction

3

Mission Beam Divergence Angle Link Type Ref.

Aerocube 7 A, B, CA: 1260 arcsec (6.11 mrad)B: 180 arcsec (0.873 mrad)C: 540 arcsec (2.61 mrad)

LEO to Ground [1]

CLICK-A 268 arcsec (1.3 mrad) LEO to Ground [2]

OSIRIS 41.2 arcsec (200 urad) LEO to Ground [3]

CLICK-B/C 14.6 arcsec (70.8 urad) LEO to LEO or Ground [4]

LLCD 3 arcsec (15 urad) Lunar to Ground [5]

TerraSAR-X 1.9 arcsec (9 urad) LEO to LEO [6]

SPOT-4 0.74 arcsec (3.6 urad) LEO to GEO [7]

CLICK B/C (LEO Lasercom Crosslink)

4

Communications 20 Mbps or higher, Full-duplex, PPM,1537 / 1565 nm, 14.6” divergence, 200 mW

Crosslink Range 25 km - 580 km (extended goal 10-855 km)

Ranging (no GPS) 0.5 m (extended goal 5 cm w. GPS)

Downlink LEO to a COTS 30 cm diameter telescope (MIT PorTeL)

Size, Power 147 mm x 96 mm x 96 mm,Volume < 2U, Mass < 2 kg, Peak power < 40 W

Beacon 976 nm, 0.75 degree divergence, 500 mW

Attitude ControlBus and payload exchange ADCS information/commands to point coarsely at the other spacecraft.

Fine Steering±1 degree throw MEMS fast steering mirror from Mirrorcle Technologies rejects remaining fine pointing error.

NASA AmesMIT PI: Kerri CahoyUF Co-I: John Conklin

Image: L. Yenchesky

Overview

1. Introduction

2. Optical Design

3. Structural Design

4. Spacecraft Thermoelastic &

Payload Thermal Model

5. Summary & Future Work

5

Image: L. Yenchesky

Optical Paths

6

115 mm Image: L. Yenchesky

Slide: O. Cierny, P. serra [4]

Beacon250 mW, 976

nm22 mrad 1/e2

Transmit200 mW, 1537 nm

120 µrad 1/e2

Receive1563 nm20 mm

aperture

Optical Analysis

7

• Optimization of optics in Zemax → MATLAB– Beacon PSF sizing on quadcell to determine

optimal tracking precision• Tolerancing analysis to determine machining

precision & where kinematic mounts are necessary

Transmit & APD Receive Analysis (1537/1565 nm)

Quadcell Receive Analysis (976 nm)

Beacon PSF on Quadcell (zoom-in)

128 um

Images: O. Cierny

16 um

Optical Mounting

8Images: L. Yenchesky

• Tip/Tilt Kinematic Mounts for an adjustment resolution better than +/- 30 arcsec for the beacon laser and +/- 3 arcsec for the transmit laser.

• X & Y Decenter Kinematic Mounts for an adjustment resolution better than +/- 15 um for both sensors.

Overview

1. Introduction

2. Optical Design

3. Structural Design

4. Spacecraft Thermoelastic &

Payload Thermal Model

5. Summary & Future Work

9

Image: L. Yenchesky

BC Payload Design

10

Image: T. SevignyImage: L. Yenchesky

Slide: O. Cierny [4]

CSA

C

Structural Analysis

Static Analysis for 30 G Loading

Static Direction

Margin of Safety (MOS)

X 21

Y 44

Z 16

MOS > 0 Requirement

Satisfied

11

Images: L. Yenchesky

Typical launch static structural loading range:

4.55 - 11 G [9-11]

Structural Analysis

Resonant Freq Analysis

Mode No. Freq (Hz)

1 888

2 955

3 1023

4 1030

5 1089Typical launch random structural

vibration range: 100 - 250 Hz [9-11]

12

Image: L. Yenchesky

Modes 1 & 2

Modes 3 & 4

Mode 5

Factor of safety > 3

Fastener Analysis

13

Fastener Analysis [12]

Mounted Element

Mass (g)

Joint Separation

MOS

Pure Shear MOS

Pure Tensile

MOS

Payload 1500 16 27 14

Bench Assm. 471 19 40 21

Camera 179 60 103 55

TelescopeAssm.

18 251 467 245

Quadcell Assm.

15 511 868 466

MOS > 0 Requirement Satisfied

Image: L. Yenchesky

Overview

1. Introduction

2. Optical Design

3. Structural Design

4. Spacecraft Thermoelastic &

Payload Thermal Model

5. Summary & Future Work

14

Image: L. Yenchesky

Spacecraft Thermoelastic Analysis

15

Images: L. Yenchesky, W. Kammerer

• Assessment of pointing error due to thermoelastic expansion of S/C body• Relative alignment between S/C star tracker and CLICK apertures• 300 arcsec thermoelastic aperture

misalignment requirement to meet.• Thermal Desktop → FEMAP → MATLAB

Spacecraft Thermoelastic Analysis

16

Images: L. Yenchesky

99th percentile estimates (9 arcsec) well within allocations (300 arcsec)

Future Work - Payload Thermal Model

• Primarily passive bench thermal design– reduction of thermal gradients– temperature stability on optical bench

• 2 Cases– Standby mode– Full-duplex transmit mode

• Thermal and thermoelastic analysis results are in-progress.

17

Image: W. Kammerer

Payload Thermal Desktop Model

18

● Compact < 1.5U lasercom terminal design for 70.1 urad narrow beam laser communications crosslinks and downlinks > 20 Mbps

● Precision kinematic optical design allows optical system calibration on the ground.

● Structural analysis of payload structure and fasteners shows that the current design meets MOS & modal requirements.

● Thermoelastic analysis of 3U structure yields up to 9 arcsec of aperture misalignment, well within the 300 arcsec allocation.

Future work:

● Finalized Thermal & Thermoelastic analysis of payload structure.

● Engineering model assembly & integration.

● Engineering model vibrations and thermal vacuum testing.

Summary & Future Work

4/24/2018

Questions

19

4/24/2018 20

[1] Janson, S., Welle, R., Rose, T., Rowen, D., Hardy, B., Dolphus, R., … Hinkley, D. (2015). The NASA Optical Communications and Sensor Demonstration Program : Initial Flight Results. 29th Annual AIAA/USU Conference on Small Satellites.

[2] Payne, C., Aguilar, A., Barnes, D., Diez, R., Kusters, J., Grenfell, P., … Cahoy, K. (2018). Integration and Testing of the Nanosatellite Optical Downlink Experiment. 32nd Annual AIAA/USU Conference on Small Satellites.

[3] Schmidt, C., Brechtelsbauer, M., & Rein, F. (2014). OSIRIS Payload for DLR’s BiROS Satellite. Conference on Space Optical Systems. Retrieved from http://elib.dlr.de/89346/

[4] Serra P., Cierny O., Diez R., Grenfell, P., Gunnison, G., Kammerer, W., Kusters, J., … , Stupl, J. (2019). Optical Communications Crosslink Payload Prototype Development for the Cubesat Laser Infrared CrosslinK (CLICK) Mission. 33rd Annual AIAA/USU Conference on Small Satellites.

[5] Khatri, F. I., Robinson, B. S., Semprucci, M. D., & Boroson, D. M. (2015). Lunar Laser Communication Demonstration operations architecture,. Acta Astronautica, 111, 77–83. https://doi.org/10.1016/j.actaastro.2015.01.023

[6] Buckreuss, S., Balzer, W., Muhlbauer, P., Werninghaus, R., & Pitz, W. (2003). The terraSAR-X satellite project. IGARSS 2003. 2003 IEEE International Geoscience and Remote Sensing Symposium. Proceedings (IEEE Cat. No.03CH37477), 5(C), 3096–3098. https://doi.org/10.1109/IGARSS.2003.1294694

[7] Perez, E., Bailly, M., & Pairot, J. M. (1989). Pointing Acquisition And Tracking System For Silex Inter Satellite Optical Link. SPIE 1989 Technical Symposium on Aerospace Sensing, 1111. https://doi.org/10.1117/12.977988

[8] Grenfell P., Aguilar A., Cahoy K., Long M. (2018). Pointing, Acquisition, and Tracking for Small Satellite Laser Communications. 32nd Annual AIAA/USU Conference on Small Satellites

[9] (2015) Minotaur IV V VI User’s Guide, Release 2.2.

[10] Legier, R. (2016) Ariane 5 User’s Manual.

[11] (2013) General Environmental Verification Standard.

[12] Chambers, J. (1995) NASA Preloaded Joint Analysis Methodology for Space Flight Systems Memorandum.

References

4/24/2018

Backup

21

Motivation

22

• To enable new distributed & coordinated sensing missions

• There is a need for:– Mbps-rate full-duplex crosslinks– Precision ranging and timing

• Goal: Development of miniaturized optical transceivers based on COTS components & compatible with CubeSat SWaP constraints

Distributed sensing

networks

CLICK Payloads

23

CLICK-A• Single 1.2 U, 800 g, <15 W payload• 200 mW avg. Tx, 1.3 mrad beam• Uplink beacon at 976 nm for PAT

– Up to ±3° bus pointing error rejection capability

• Rate-scalable M-ary PPM downlink– 40 Mbps with 1 m Rx telescope– 10 Mbps with 30 cm telescope

• Primary success criteria:– Validate laser transmitter– Validate fine-pointing stage– Validate optical GS– Successful >10 Mbps downlink

CLICK-B/C

• Pair of 1.5 U, ~1700 g, <25 W payloads• 200 mW avg. Tx, 70 urad divergence• 25 cm receive aperture• 500 mW beacon at 976 nm for PAT• Full-duplex PPM crosslinks 1537/1565 nm

– 50 Mbps, 4-PPM, <450 km– 25 Mbps, 16-PPM, <920 km

• 200 ps timing accuracy & time transfer

• Primary success criteria:– >20 Mbps full-duplex @ 580 km– <0.5 m ranging w/o GPS @ 580 km

AB C

1537 nm Transmit

1565 nm Receive

1550

nm

Dow

nlin

k

Concept of Operations

24

PAT Staging & Budget

25

Credit: M. Long

Image: P. Grenfell

Payload Architecture

26

Optical Path

27

Configuration

28

MEMS FSM

APD

Telescope

Camera

Beacon

Quadcell DichroicsTx Laser

29

Zemax® Optical Raytracing

Optical Modeling

S/C Thermoelastic

30

3U Spacecraft Thermal Model

Optical Ground Terminal

31

• MIT-developed Portable Telescope for Lasercom (PorTeL)

• Based on ⌀28 cm Celestron CPC1100

• Fitted with a custom backend & star camera

• Rapid setup and pointing calibration based on star camera quaternion solution (<15 min)

Credit: K. Riesing [2,3]

Image: T. Sevigny

CLICK B/C Coarse PAT

32

Images: P. Grenfell

CLICK B/C Fine Tracking Flow

33

Image: P. Serra

Optomechanical Design Elements

34

assembly alignment & calibration

thermoelastic effects

structural modes & static loading

fastener analysis

Images: L. Yenchesky, D. Barnes

Optomechanical Engineering

35

• Sub-field of optical engineering where optics are integrated into a mechanical structure to form an instrument

• Requires integrated models for optical systems performance prediction

• Often includes all phases ofmission developing, including I&T

115 mm

Image: L. Yenchesky