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Space-Deployed Inflatable Dual Reflector Antenna: Design and Prototype Measurements

Jesse Mills

7 August 2019

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© 2019 Massachusetts Institute of Technology RAMS# 1009987 Large Aperture Space Based RF Applications

Small satellite 1 deploys

2 Image region of interest with X-Ku band radar

3 Data downlink to ground/surface station

• Several RF space applications such as SAR imaging, deep space comms and radio navigation • Inflatables provide large apertures in small packed volumes, required surface precision is challenging • Goal: Demonstrate the feasibility of precision large inflatable apertures at X-Ku band for small satellites

SEJS - 2 Dual-Reflector Gregorian Inflatable Antenna Design Dual Reflector Gregorian Design 2.7 m Overall Secondary Diameter Reflector 0.25 m Diameter

Secondary Inflatable Chamber

Antenna Feed

Toroid Inflatable Antenna Prototype in the Compact Range

Primary Primary Reflector 2.4 m Inflatable diameter Chamber

1.1 m Total Height

Novel dual-reflector Gregorian inflatable antenna, designed, fabricated, and characterized

SEJS - 3 Key Design and Fabrication Insights

• Gregorian layout removes satellite body beam RF-Transparent Sections at Interfaces obscuration • Three independent inflation chambers allow for post-fab antenna tuning – Tuned pressures for optimal surface quality – Adjustable focal lengths for secondary – Reverse thermoforming to correct fab defects Wrinkling contained to – Post-deployment primary-secondary alignment RF- transparent sections • Pragmatic mechanical design obviates need for high precision design/fab Post-Fabrication Reverse Thermoforming

Az/ alignment lanyards

Co-alignment of Reflective Surfaces

SEJS - 4 Deployed Area vs. Stowed Volume

Spacecraft Deployed Reflectors (In Orbit & Lab Models) 102

L/Mesh L/Inflatable NASA/ATK S/Mesh Harris ACeS ATK AstroMesh Solar Sail 1 10 X/Mesh Ku/Mesh Ku/Inflatable Ku/MIT LL ) 3 100 Ka/Mesh

(m Ka/Solid Harris V/Solid Vol NA/Solar Sail

-1 Lockheed 10 ATS-6 MIT LL JAXA Ikaros Stowed

DARPA ISAT

10-2 USC AENEAS 1.5U packed volume NASA Nanosail-D NASA IAE

10-3 100 101 102 103 Deployed Area (m2) Demonstrated: Inflatable X-Ku band antenna with stowed volume similar to solar sails

SEJS - 5 Simulated and Measured Gain (1 of 2) Inflatable Gregorian Reflector Antenna

Simulated and Measured Gain at 10 GHz

• Measured antenna gain shows good performance at X-band – 37.6 dBi gain, ~1°beamwidth at 10 GHz – Peak directivity within 4 dB of ideal • Improvement in primary reflector design and fabrication required to achieve directivity within 1 dB of ideal

SEJS - 6 Simulated and Measured Gain (2 of 2) Inflatable Gregorian Reflector Antenna

EM Model of Laser Scanned Surface vs. RMS Surface Error vs. Peak Gain RF Chamber Measurements

Projected performance Current prototype

• 3D laser scans of prototype and root mean square (RMS) surface error analysis helped identify error sources – All errors associated with primary surface shape • Improvements in primary fab design and integration fixtures expected to bring performance within 1 dB of ideal

SEJS - 7 Summary and Path Forward

• Designed, prototyped, and characterized a novel dual-reflector Gregorian multi-chambered inflatable antenna for X-Ku band – Successfully demonstrated good RF performance at X-band, very high deployed area to stowed volume ratio

• Identified for improvements in mechanical design and fabrication design

• Implementation of identified improvements expected to bring X-Ku band inflatable antenna within 1 dB of ideal performance

• Aperture diameters up to 10 meters likely feasible with these design and fabrication approaches at X-Ku band

Enabling technology for SAR imaging, deep space communications and radio navigation on small satellites

SEJS - 8 Questions?

SEJS - 9