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Development of an All‐Cubesat Low‐Earth‐Orbit Optical Network

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Development of an All‐Cubesat Low‐Earth‐Orbit Optical Network CubeSat Laser Communication Crosslink Pointing Demonstration Richard Welle, Christopher Coffman, Dee Pack, and John Santiago The Aerospace Corporation 6 August 2019 © 2019 The Aerospace Corporation Space-to-Space Laser Illumination Demo AeroCube-7 (OCSD) • 1.5U and 2.6 kg • 0.02 degree pointing ISARA • 10 MP cameras + HD video • 3U and 5 kg • Warm-gas propulsion • 0.2 degree pointing • Laser rangefinder • Ka-band antenna (primary payload) • Laser communications transmitter • Cameras: vis, SWIR InGaAs, LWRI • 1064 nm microbolometer • 0.06 degree divergence Mission Goal: Demonstrate a Mission Goal: Demonstrate optical practical, low cost Ka-band High Gain downlink (lasercomm) of 50 Mb/s Antenna (KBA) on a 3U CubeSat and perform proximity operations Mission of Opportunity: Demonstrate optical crosslink pointing between two CubeSats in LEO: laser from AeroCube-7 is pointed at ISARA satellite and recorded by SWIR camera 2 Why Laser Communication? • Potential to reduce complexity and mass of space-based communication networks – Enabler for CubeSat-scale, low-cost, high-density LEO relay network • Previous demonstrations of space-based laser communication used terminals with a mass of ~30 kg and cost in excess of $20M per terminal – Much of the cost is in the two-axis pointing system – Far too massive and expensive for high-density LEO constellation • Current optical systems rely on GEO relay to get signal to ground – Requires massive/expensive terminal on LEO satellites to reach GEO • Body pointing presents a simple, low-cost, alternative to two-axis gimbal systems OCSD CubeSat laser terminal OPAL laser terminal NASA Photo 15 cm 3 Why Crosslinks? Applications • High-volume, short-range download from satellites in LEO EO satellite • Low-latency download from satellites in LEO Optical links • Low-latency Earth-to-space-to- Relay satellite Earth data transfers Relay satellite Requirements Cloud • Lasers • Detectors Ground • Pointing and tracking station • Data handling/management Ground station Earth 4 Optical Communication and Sensor Demonstration (OCSD) Laser Downlinks and Proximity Operations Retroreflector Hi-Res Camera Two 1.5-unit CubeSats launched in November 2017 with five goals: LED Beacon (Achieved) (In progress) Steam Thruster • Demonstrate optical communications from a CubeSat to a Star ground station from low Earth orbit at rates between 5 and 50 Camera Mb/s (actual result was 200 Mb/s) • Demonstrate relative maneuvering to within 200 meters 2-Axis Sun Sensor • Demonstrate tracking of a nearby cooperative spacecraft using a commercial off-the-shelf (COTS) laser rangefinder GPS • Demonstrate orbit control using variable drag Antenna • Demonstrate propulsive orbit control using a steam thruster RF Comm. Antenna Steam Thruster Communications Laser Laser Rangefinder Stowed Wing Earth Horizon 2-Axis Sun Sensor Sensor (4 x 16 array) OCSD is supported through NASA’s 5 Small Spacecraft Technology Program Integrated Solar Array and ReflectArray (ISARA) A CubeSat with a hosted payload Hosted Payload: Primary Mission: Ka-band communications CubeSat Multispectral Observation System (CUMULOS) Reflectarray Sensitive to OCSD laser wavelength Reflectarray Feed SWIR Camera InGaAs 640x512 Visible Camera CMOS 1280x1024 LWIR Camera Microbolometer 640x512 Standard-Gain Antenna Secondary payload included on a “do no harm basis.” Turned on after completion of primary mission. 6 Crosslink Geometry Apparent elevation angle between OCSD and airglow layer Local horizontal at CUMULOS OCSD Airglow CUMULOS Earth Ra 7 16000 AC-11 to ISARA OCSD to ISARA Orbital Dynamics 14000 12000 • OCSD to ISARA 10000 crosslink pointing tests are possible for ~8 days 8000 every 6 weeks Range (km) 6000 • R3 to ISARA crosslink pointing tests are 4000 possible for ~24 hours every five days 2000 0 5/15/19 5/25/19 6/4/19 6/14/19 6/24/19 7/4/19 7/14/19 7/24/19 8/3/19 8/13/19 5000 Date 4500 AC-11 to ISARA 4000 OCSD to ISARA 3500 3000 2500 Range (km) 2000 1500 1000 500 0 0 10 20 30 40 50 60 70 8 Time (h) Centerline Beam Flux Can we see it? • Compared expected centerline laser intensity to integrated IR intensity of reference star Alpha Tau (Aldebaran) • All three lasers are at least as bright as Alpha Tau out to maximum crosslink range CUMULOS SWIR image (subtracted) • OCSD-B is an order of 1.0E+00 magnitude brighter at 4000 km 1.0E-01 OCSD-B 1.0E-02 OCSD-C R3 1.0E-03 Alpha Tau 1.0E-04 1.0E-05 Intensity (W/m2) 1.0E-06 1.0E-07 1.0E-08 0 1000 2000 3000 4000 5000 9 Range (km) ISARA Illuminated by AC7-B, Raw Image 9 January 2019 Lots of hot pixels (common to using InGaAs camera in space) Hot Pixels Star Date/Time: 2019-01-09 19:13:16Z Range: 1996 km AC7-B Laser AeroCube-7B (SCC #43042) ISARA (SCC #43050) ISARA_CUMULOS_CrossLink_04_1346_0 10 Image Series: 9 Combined Images Subtraction Removes (Most) Hot Pixels The camera is tracking AC7. With both AC7 and ISARA moving, the stars Hot Pixels move across the frame but AC7 remains stationary. The Earth limb remains stationary because AC7 and ISARA are in the same orbit plane Star Star AC7-B Laser Star brightness varies due to changes in camera settings 11 ISARA Illuminated by AC7-B, Hot Pixels Subtracted 9 January 2019 Stars Date/Time: 2019-01-09 19:13:16Z Range: 1996 km AC7-B Laser AeroCube-7B (SCC #43042) ISARA (SCC #43050) ISARA_CUMULOS_CrossLink_04_1346-1351_0 12 IR Starfield Image 1351 subtracted from image 1346 Nu Tucanae Alpha Tucanae DM Tucanae Bright visible stars are not necessarily bright in IR Some very dim visible starts are bright in IR AC7 Beta Gruis Alnair (Alpha Gruis) Pi Gruis Delta Gruis Image subtraction causes stars to appear as two spots, one bright and one dark, with constant offset 13 Starfield Identification infrared visible The CUMULOS SWIR camera sees the infrared sky, which is very different from the visible sky. Beta Gruis Delta Gruis Pi Gruis Alpha Gruis (Alnair) Atlas image obtained as part of the Two Micron All Sky Survey (2MASS), The Digitized Sky Survey was produced at the Space Telescope Science a joint project of the University of Massachusetts and the Infrared Institute under U.S. Government grant NAG W–2166. The images of these Processing and Analysis Center/California Institute of Technology, funded surveys are based on photographic data obtained using the Oschin Schmidt by NASA and NSF. Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission 14 of these institutions. ISARA Illuminated by AC7-B, Dark Subtracted 15 March 2019 Date/Time: 2019-03-15 14:51:53Z Range: 2292 km AC7-B Laser AeroCube-7B (SCC #43042) ISARA (SCC #43050) R Doradus ISARA_CUMULOS_CrossLink_10_1839_0 15 Beam Profile OCSD commanded to sweep beam across CUMULOS at 2292 km range 16 What Next? Following up on a mission of opportunity • OCSD-to-ISARA crosslink pointing tests provided proof-of-principle demonstration for CubeSat-scale optical crosslinks – Open-loop pointing for communication • <1-mrad accuracy by both transmitter and receiver – Beam-profile measurement technique that avoids atmospheric effects • Future experiments – Identify alternate cameras – Beam profile measurements • OCSD B and C • R3 – More-challenging orbits • Higher slew rates • More frequent opportunities 17 Acknowledgments Multiple missions of opportunity • The OCSD spacecraft were built by Aerospace with support from NASA’s Space Technology Mission Directorate through the Small Spacecraft Technology Program • The ISARA program was led by JPL, with support from NASA’s Space Technology Mission Directorate through the Small Spacecraft Technology Program; JPL and Aerospace collaborated on the build of the ISARA spacecraft • The CUMULOS payload was built by Aerospace and hosted on ISARA with permission from NASA and JPL • The work described in this presentation was funded by The Aerospace Corporation’s Independent Research and Development program 18.
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