A novel spacecraft standard for a modular small satellite bus in an ORS environment 7 th Responsive Space Conference David Voss PhD Candidate in Electrical Engineering BUSAT Project Manager Boston University 7 th Responsive Space Conference 1
Outline Project Overview Technology development Mechanical bus Electrical bus Launch vehicle interface Compliance with current standards Current work 7 th Responsive Space Conference 2
Program Overview Standard developed through the Air Force s University Nanosatellite program (UNP) through two student efforts Thunderstorm and Effects Scientific and Technology (TEST) Nanosatellite (UNP 3) The Boston University Student Satellite for Application and Training (BUSAT) (UNP 5) BUSAT involved over 60 undergraduate students at both BU and Taylor 13 student teams Five instrument teams Six subsystem teams Two ground support teams Both programs had a strong science mission as well as a strong technological objective BUSAT with one wall removed Full time student summer staff 7 th Responsive Space Conference 3
Mission Overview Mission Objectives: Primary : To help understand the coupling between the Magnetosphere and Ionosphere Secondary: Create a modular spacecraft bus Tertiary: Create a mesh network between high altitude balloons, ground stations, and BUSAT Instrument payload Imaging Electron Spectrometer (IES): Measure energetic particles in the 50keV to 500keV range Auroral Imager: COTS CCD camera imaging several optical wavelengths characteristic of the Aurora COTS Magnetometer: Honeywell MILSPEC magnetometer with resolution around 100nT Plasma Probe: Measures thermal electrons and ions < 10eV Very Low Frequency (VLF) Receiver Measures the integrated RF energy in six VLF bands (A) (D) (B) (C) (A) 1 (B) (C) (D) 7 th Responsive Space Conference 4
Technology Development Modular Nanosatellite design Standardized, interchangeable subsystem housings Development will allow for a rapid deployment of satellites in response to a loss of space assets Reduce cost of spacecraft development Allow for development of subsystems and instruments prior to a known mission Modular bus design has been prototyped Current status in a Technology Readiness Level (TRL) 5, after environmental testing a TRL 6, and after flight a TRL 7 Goal for a unified bus standard Mesh Networking Technology Demonstration Provides for ad hoc networking between satellites and terrestrial contacts Communication system is completed Currently at a TRL 6 and a TRL 7 after flight Partially assembled BUSAT 7 th Responsive Space Conference 5
Subsystem and Instrument Housing Design Based off of the CubeSat concept Basic 1U dimension is 4in x 4in x 4in Follows the equation x = 4*n+0.5*(n-1), where x is the length of the side, n is the number of 1U cubes Example of a 3U cube in image on the right Instruments and subsystems can be any number of cubes as long as they are an even increment of the 1U size (plus some space) A 3U subsystem cube 1U 1U 1U = 1U 2U 2U 4U = 16 1U cubes = 16U 7 th Responsive Space Conference 6
Primary Structure Subsystems held in place by a primary structure (Exoskeleton) Subsystem structures stacked inside Spacers are used to maintain a gap between the cubes Modules held in place using a compressive force exerted by a Wedge-Lok from Birtcher Inc. Primary structure need not be an even multiple on each side BUSAT s primary structure Spacers used to maintain space between cubes Various subsystem arrangements 7 th Responsive Space Conference Birtcher Wedge-Lok 2 7
Assembly Procedure 7 th Responsive Space Conference 8
Paylaod to Dry Mass Ratio Responses to Common Concerns Concern 1: BUSAT is a heavy design Self shielding useful for COTS components As number of empty cubes are used payload to spacecraft dry mass ratio improves Possible weight reducing technologies used that BUSAT did not implement (i.e. honeycomb primary structure) Concern 2: Thermal design Structure is essentially isothermal Heat conducted 3-dimensionaly through the cubes structure Subsystems or instruments able to be thermally isolated Number of Cubes vs. Payload to Dry Mass Ratio 30.0 25.0 20.0 15.0 10.0 5.0 0.0 0 5 10 15 Number of Cubes used for payload Study by JPL relating Payload Mass to Spacecraft Dry Mass 3 7 th Responsive Space Conference 9
Electrical Bus Design 7 th Responsive Space Conference 10
Electrical Bus Design Central Routing Cube (CRC) allows for complex routing of signals in a simplified PCB format Allows for a variable number of cubes to be added to the system Single cable is used to interface between the subsystem and the CRC The CRC allows for flat sat testing and listening in on instruments and subsystems Physical layer could have been wireless, RS422, SpaceWire CRC could reflect a computer mother board and be a crossover to other standards Central Routing Board, FPGA routing board, and power subsystem 7 th Responsive Space Conference 11
Launch Vehicle Interface BUSAT is designed around a 15in Lightband adapter made by Planetary Systems Corporation Lightband adapter fits on an ESPA ring made by CSA Engineering Various sized Lightbands are available for scalable BUSAT designs Planetary System s Lightband Adapter 4 CSA s ESPA Ring 5 7 th Responsive Space Conference 12
Compliance with Current Standards Space Plug and Play Avionics (SPA) Current design does not meet SPA standards Software system would need to be rewritten to meet the SPA self discovery objective and data transmission protocol BUSAT s mechanical modularity has something to offer the SPA standard BUSAT s physical medium could meet the SPA requirement PC104 standard Commercial embedded systems standard PC104 form factor fits into basic 1U cube size BUSAT utilizes a PC104 power supply, single board computer, and FPGA board CubeSat standard The CubeSat 1U structure is slightly different than the BUSAT 1U Able to accommodate both designs with spacers 7 th Responsive Space Conference 13
Current and Future Work Vibrate structure Investigate the SPA standard for our software protocol and node self-discovery Use optical or wireless signals as the physical data transmission in a Fly-by- Wireless design Additional methods of weight reduction Sin sweep of the TEST satellite a similar bus design Cavity between cubes ideal for wireless transmission 7 th Responsive Space Conference 14
Conclusion Mechanical design strongly complements the SPA s goal It meets many of the objectives of satellites in the 10 kg to 100kg range Although a heavier design BUSAT provides for a simplification in interfaces that complements the ORS objective of a mission definition to launch in 7 days The Air Force s University Nanosatellite Program is an excellent educational program and we thank them for their support throughout this competition 7 th Responsive Space Conference 15
References 1. http://www.bu.edu/cism 2. http://www.birtcherproducts.com 3. Nagler, R. G., & Schule, J. W. (1976). Satellite Capabilities Handbook and Data Sheets. Jet Propulsion Lab., JPL California Institute of Technology. Pasadena, CA 4. Holemans, W. (2004). The Lightband as Enabling Technology for Responsive Space. AIAA 2nd Responsive Space Conference. AIAA 5. http://www.csaengineering.com/ 7 th Responsive Space Conference 16