1. Alessandra Babuscia Jet Propulsion Laboratory – California Institute of Technology Part of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. © 2015 California Institute of Technology. Government sponsorship acknowledged. 1 FISO Telecon 5-6-2015

2.  Introduction and history of the project  Inflatable antenna (version 1)  Design  Fabrication  Tests  Extension to the X-Band  Scalability and comparison with other technologies  Conclusion and future work 2

3.  An increasing number of universities, companies and space agencies are actively designing, developing, launching and operating CubeSats.  CubeSats have mostly been used to perform research in Low Earth Orbit and most of the COTS components available in the market have been designed to that purpose.  A new technological trend is the development of technologies and strategies for potential interplanetary applications of small platforms (CubeSats/Satellites).  One of the most interesting problems is how to allow small satellites to communicate from very far distance in the solar system.  Current work in this area includes developments in antenna design (deployable [1], reflectarray [2], inflatables [3]), amplifiers and transceiver designs [4] [5] [6], coding [7], CDMA [8], multiple spacecraft per antenna [9] and collaborative communication [10].  In this presentation, I will focus on inflatable antenna: an overview of the history of the project, design, fabrication, tests, extension to the X-Band and current status 3

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5. STS 77-1996 Could this model be adapted to CubeSat? 5

6. Babuscia, Van de Loo, et al., 2012 A new design was needed 6

7.  Requirements:  Size of the reflector: at least 1 m diameter  Frequency: S Band (2.4 GHz)  Volume: less than 1U  Mass: less than 1 Kg  Power (for deployment mechanism): less than 1 W  Inflation: simple and “low risk for the main mission” 7

8.  CubeSats are generally launched as auxiliary payloads on the launch vehicle  A pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.  The pressure differential is dangerous, and it could cause accidents that could damage the primary spacecraft  In addition, pressure vessels could occupy a big portion of the CubeSat volume 8

9.  Sublimating powder is a chemical substance such that given a certain change of pressure, it sublimates from a solid to a gas state  Few grams of benzoic acid can inflate an entire balloon  The mechanism is completely passive:  No pressure vessel on board  Simple  It takes less volume than other inflation mechanism 9

10. Echo Balloon 1964 10

11.  Inflatable volume with one side reflective, metalized Mylar (1), other side clear Mylar (2) with a patch antenna (3) at the focus.  Stored in a volume (4) less than 1U in size.  Antenna passively inflated with a small amount of a sublimating powder.  2 versions: conical and cylindrical to minimize deformation of the parabolic shape of the reflective section. Concept design of the inflatable antenna. Conical (left) and cylindrical (right) configurations of the antenna. Radiation 11

12. 12 ~21 dB ~16 dB

13.  Parabolic shape made with four petal-shaped pieces of flat Mylar bonded at edges.  Edges are bonded with epoxy designed specifically for hard-to-bond plastics. Finished reflective Mylar parabolic side Finished antenna with polycarbonate plate. 13

14.  4 possible folding techniques MethodVol. con. (U) Vol. cyl. (U) 10.320.5 20.280.52 30.320.5 40.280.52 Regardless of the method chosen, the antenna can be folded in less than 0.52U 14

15.  The deployment mechanism consists of two plates  The ejector plate  The base plate.  A compression spring is mounted onto each of the 4 rods.  The ejector plate sits on top of the compression springs and slides along the length of the rods.  Nylon wires to hold the ejector plate. 15

16. 16.16 Cylindrical and conical configurations are reached but the reflector is not perfectly parabolic. More pressure measurements need to be performed in the future.

17.  The antenna was tested for EM gain at the JPL anechoic chamber in may 2013.  A specific test stand was designed at MIT to maintain the antenna in the desired aligned position. 17

18. The gain is not the one previously measured on the same patch antenna (previously 6 dB, now 4dB at 2.4 GHz). Possible mishandling of the antenna by another team as well as interactions with the polycarbonate plate are possible causes for the mismatch. As a result, the new performance metric for the test is the delta-gain: 18

19. At 2.4 GHz, the delta gain is ~8.9 dB which is 1.1 dB less than expected. The possible cause is leakage in the antenna due to the impossibility of filling the antenna with helium at the Mesa. An helium pump at the Mesa was later found and used for the cylindrical antenna, but not for the conical. 19

20. The delta gain measured at 2.4 GHz is 6.48 dB, very different from the 15 dB expected. This result was surprising given that the cylindrical antenna was inflated with helium at the Mesa, so leakage was supposed to play a very minor role. The team believed that the issue was due to the addition of the polycarbonate plate. Hence simulations were made to verify this hypothesis. 20

21. Vacuum chamber testAnechoic chamber testAnalysis and remodeling CAD Model: No plateCAD Model: Plate added 21

22. CAD Model: No plate CAD Model: Plate added 22

23. CAD Model: No plate CAD Model: Plate added 23

24. 24 Corrections were introduced to take into account the attenuation caused by the polycarbonate plate. The delta gain metric is used to indicate the increase in gain with respect to the standard patch antenna (+ 6 dB) Freq. (GHz) Delta Gain (Conical) measured (dB) with plate correction Delta Gain (Conical)with plate correction (dB) Delta Gain (Cyl) measured (dB) with plate correction Delta Gain (Cyl)with plate correction (dB) 2.358.849.715.3115.4 2.48.9710.215.4815.5 2.458.589.514.7314.2

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26.  A new version of the inflatable antenna was designed to operate at X-band.  A new patch antenna and a new reflector were manufactured.  A professional company was engaged into the manufacturing of the dish to reduce leakage issues.  A new testing plate was designed to attach the patch to the reflector. ParameterValue Antenna size9 x 9 cm Antenna conductive plate size 1.2 x 1.8 cm Impedance50 Ohm Dielectric RT Duroid 5880 (perm=2.2) Frequency8.4 GHz Peak gain8 dBi New inflatable antenna on testing standPatch antenna parameters Test plate 26

27. The simulation was set up at X-Band with the new patch Gain at 8.4 GHz of 34.3 dB. 27

28.  Initial tests at X-band did not yet achieve the desired gain  As a result of the new CIF grant, a structural re-design will focus on improving the antenna characteristics  Developing an accurate pressure vs. shape profile  Develop a system to maintain the antenna at the desired pressure while at the anechoic chamber test facility.  Improvement of the antenna feed to improve the focalization of the beam.  Membrane re-manufacturing.  Control and system analysis for future spacecraft design.  Sublimating powder inflation process studied at ASU  Vacuum chamber experiments  Sublimating powders comparison and selection  Reliability analysis and study of rigidization techniques. 28

29.  The feasibility for the different frequencies:  S-Band (~10 cm wavelength) : very feasible, wrinkles in the order of 1 cm or less can be tolerated, pointing is generally few degrees.  X-Band (3-5 cm wavelength): feasible, wrinkles in the order of 3-5 mm, and pointing becomes more complex (~ 1 deg), although achievable with more refined COTS sensors and actuators.  Ka-Band (less than 1cm wavelength): very hard (tolerance is 1 mm or less). Additionally, pointing becomes more complex and may require customized hardware and algorithms.  For size, the inflatable antenna can be easily scaled up to larger sizes Diameter (m) Mass (Kg)Value (U) 1 0.4 2 1.4 4 5.1 8 20.5 29

30.  X-Band antenna concepts in development are projected to achieve gains ~ 30 dBi, although some of them have less stowing efficiency than the inflatable and they are not easily scalable to higher gain  Reflectarray - ISARA type ( 3 foldable 20 x 30 cm panels)  Folding rib reflector based on Aeneas design (0.5 m for 1.5 U volume)  Miniaturized astromesh reflector (1 m for 3 U volume)  The advancement of the inflatable antenna is given by:  Stowing efficiency: 20:1  Low mass: 0.5 Kg for a 1m dish including canister  Scalability to higher gains  Simplicity of inflation: no pressure vessels, no tank required  One of the biggest challenges is the achievement of the desired efficiency, mostly as a result of the irregularities of the surface. Initial tests performed at X-Band reveals that these irregularities can scatter the gain in multiple directions, hence reducing the gain in the desired direction. Reflector diameter (m) Volume (U)Gain (dBi) at X-Band 10.534 1.5137 21.440 Antenna Type Reflector diameter (m) Volume (U) Stowing Efficiency Folding Rib0.5 m1.55:1 Miniaturized Astromesh 1.0 m310:1 Inflatable1.0 m0.520:1 30

31.  An overview of the inflatable antenna project was presented.  The initial design and test at S-band were presented.  The extension to the X-band was discussed.  Future work includes: testing the new antenna in the anechoic chamber, work on control system and on the deployment and stowage structure. 31

32.  The inflatable antenna team over the years: Mark Van de Loo (MIT), Benjamin Corbin (MIT), Rebecca Jensen-Clem (Caltech), Mary Knapp (MIT), Quantum Wei (MIT), Serena Pan (MIT), Thomas Choi (JPL), Miguel Lorenzo (JPL).  Prof. Sara Seager, Prof. Paulo Lozano, Prof. David Miller and the Space System Laboratory at the Massachusetts Institute of Technology.  Swati Mohan, Kamal Oudrhiri, Neil Murphy and the Center for Academic Partnership at the Jet Propulsion Laboratory.  Jeff Harrel, Robert Beckon, Joseph Vacchione and the antenna testing team at the Jet Propulsion Laboratory.  Kar-Ming Cheung, Polly Estabrook, Fabrizio Pollara and the staff of Section 332 at the Jet Propulsion Laboratory. 32

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