https://ntrs.nasa.gov/search.jsp?R=20160010305 2019-05-22T01:40:23+00:00Z Small Satellite Conference 2016 An Optimum Space-to-Ground Communication Concept for CubeSat Platform Utilizing NASA Space Network and Near Earth Network Yen F Wong, Obadiah Kegege, Scott H Schaire, George Bussey, Serhat Altunc Goddard Space Flight Center Yuwen Zhang, Chitra Patel Harris Corp, Information Systems Presenter Scott H Schaire [email protected] EXPLORATION AND SPACE COMMUNICATIONS PROJECTS DIVISION 1 NASA GODDARD SPACE FLIGHT CENTER NASA Near Earth Network/Space Network Overview - The Space Network (SN) Tracking and Data Relay Satellite System (TDRSS) fleet currently consists of nine satellites supported by three tracking stations, two at White Sands, New Mexico, and a third on the Pacific island of Guam - TDRSS supports low earth orbiting satellites including the International Space Station, earth observing satellites, aircraft, scientific balloons, expendable launch vehicles, and terrestrial systems Example SA User 2nd or 3rd (S- Band Fwd & Rtn Gen TDRS Ka-Band Rtn) 2nd or 3rd Gen TDRS - NASA Near Earth Network (NEN) is comprised of Example SA User (S- Band Fwd & Rtn stations distributed throughout the world in locations Ku-Band Fwd & Rtn) SA USER (S- and / or including Svalbard, Norway; Fairbanks, Alaska; Ku-Band) Santiago, Chile; McMurdo, Antarctica; Wallops Island, Virginia. SA USER SA USER (S- and / or (S- and / or Ku-Band) MA User ORION Ku-Band or (S-Band) (S- Band Fwd & Rtn - The NEN supports orbits in the Near Earth region Ka-Band) Ka-Band Fwd & Rtn) from Earth to 2 million kilometers. MA User (S-Band) - NEN and SN assets are assigned to missions WSC based on priorities set by the NASA Science WHITE SANDS, NM Mission Directorate EXPLORATION AND SPACE COMMUNICATIONS PROJECTS DIVISION 2 NASA GODDARD SPACE FLIGHT CENTER NASA Future CubeSat Communication Architecture Study Study Objectives 1. Develop optimum communication concepts for CubeSat platform utilizing TDZ NASA SN and NEN “Mothership” Direct-to- Support via 2. Perform detailed analyses and Ground Through Direct-to- simulations of the proposed communication TDRS Ground architecture configurations. This includes TDW TDE CubeSat swarm, daughter ship/mother ship constellation, NEN S- and X-band direct-to- ground link, TDRSS MA array vs Single Access mode, notional transceiver/antenna WSC configurations, ground asset configurations, GSFC signal trades, space science X-band Service Characteristics downlink 10 MHz channel maximum Support provided via TDRS achievable data rates CubeSat Characteristics Multiple Access (MA) antenna S-band transmit and receive No customer RTN service Hemispheric or patch antenna, i.e. scheduling no rigorous attitude / antenna Global coverage; low latency 3. Explore CubeSat current technologies pointing requirements. capabilities CubeSat Constellation “Mothership” Support via Cubesat Characteristics Mothership: S-band transmit and TDRSS 4. Develop concepts of operations for receive; directional antenna (i.e., Configuration attitude / antenna pointing NASA’s future CubeSat/SmallSat end-to- requirements); high rate burst end communication Constellation Characteristics transmissions; transponder required if TDRSS tracking services One Mothership, however, multiple CubeSats have the ability to fulfill the role of required 5. Provide innovation concepts to meet Mothership Subordinates: Proximity link Two or more Cubesat architectures (Mothership-capable CubeSats, subordinate Cubesats) comm only; GPS position future CubeSat/SmallSat communication determination needs EXPLORATION AND SPACE COMMUNICATIONS PROJECTS DIVISION 3 NASA GODDARD SPACE FLIGHT CENTER NEN CubeSat Support Analysis • NEN Support Link Analysis - CubeSat/SmallSat mission communication requirements including frequencies and data rates can be met by utilizing NEN S and X-band support Links Data Rate Mod & CubeSat Link Coding EIRP Margin S-band 2 kbps BPSK, ½ -1 dBw 40.1 dB Downlink conv + RS S-band 4 kbps BPSK, ½ -1 dBW 36.5 dB Performance Results at 400 km altitude. Downlink conv S-band 256 kbps BPSK, ½ -1 dBW 18.45 dB Downlink conv S-band 513.7 BPSK, RS -1 dBW 14.4 dB Downlink kbps X-band 13.1 Mbps QPSK, 7/8 5 dBW 10.3 dB Downlink LDPC X-band 130 Mbps QPSK, ½ 5 dBW 3.2 dB Downlink conv + RS 11.3 m at AS1, CubeSat PA = 1 W, 0 dBi Antenna Gain (S-band), Antenna Gain = 5 dBi (X-band) Performance Results at 9000 km altitude. EXPLORATION AND SPACE COMMUNICATIONS PROJECTS DIVISION 4 NASA GODDARD SPACE FLIGHT CENTER Near Earth Network (NEN) Upcoming CubeSat Support • NEN will provide first time support to a CubeSat mission, CubeSat Proximity Launch Operations Demonstration (CPOD), when it Date (No launches in 2016 Earlier – Supporting Station: WGS 11m, ASF Mission Than) 11m, MGS 10m CPOD/PONSFD (A – Service Provided: S-Band Telemetry and B) 2016 – Data Rates: 1 Mbps or 500 kbps SOCON 2017 – Service Duration: L+30 days to L+6 iSAT 2017 months (possible extension of up to CryoCube 2018 L+12 months) Lunar Ice Cube 2018 BioSentinel 2018 CUTIE 2018 Burst Cube 2019 RadSat 2019 Propulsion Pathfinder (RASCAL) TBD CSIM TBD KitCube TBD PIC/USIP TBD TRYAD/PULSAR TBD EXPLORATION AND SPACE COMMUNICATIONS PROJECTS DIVISION 5 NASA GODDARD SPACE FLIGHT CENTER TDRSS CubeSat Support Analysis • CubeSat TDRSS support will be • A CubeSat constellation demonstration limited by lower data rate due to power mission using MA, consuming TDRS constraint on the spacecraft. Unused Time, and scheduled through the Demand Access System at White • TDRSS can provide global coverage to Sands would be endorsed by the SN. CubeSat with low latency. It is ideal for emergency support. A CubeSat could • CubeSat TDRSS S-band Single send status alerts instantly without Access (SSA) and Ka-Band SA waiting until a ground station is in view. support need a high gain antenna on board the S/C to produce positive link • TDRSS legacy Multiple Access (MA) is able to support CubeSat data rate at 1 • TDRSS will provide 100% coverage kbps with practical S/C power amplifier for LEO CubeSat 5 W and a zero dBi antenna gain. • The new MA Direct Access System (DAS) can have over 100 in-beam MA users without too significant of a mutual interference at this data rate EXPLORATION AND SPACE COMMUNICATIONS PROJECTS DIVISION 6 NASA GODDARD SPACE FLIGHT CENTER CubeSat Constellation CDMA Trade Study • Solve for the most appropriate • Study results indicate : CDMA signal • With the CDMA signal design, the characteristics/design and constellation daughter/mother CubeSat orbit for daughter mother architecture is able to produce adequate constellation inter-satellite link daily data volume if the daughter and communications that will be able mother CubeSats are in a coordinated to downlink adequate daily data orbit (for instance, formation flying) volume to the ground • If the daughter/mother CubeSats are in • The mothership CubeSat an un synchronization orbit, in order to downlink a meaningful/adequate daily (provided by the mission) will be a volume of science data, the use of a store-forward relay to downlink the mother ship CubeSat as a store-forward science data to the ground either relay requires intelligent protocols through NEN direct to ground link capable of performing efficient at X-band or through TDRSS K- management and operation control of band single access (KSA) signal flow for the inter-satellite links • CubeSat inter-satellite link intelligent protocols are under development EXPLORATION AND SPACE COMMUNICATIONS PROJECTS DIVISION 7 NASA GODDARD SPACE FLIGHT CENTER Power and Bandwidth Efficient Signal Techniques for Earth Science CubeSats High Data Rates CubeSat Space Science NEN X-band 10 MHz Earth Science CubeSats Channel Downlink Maximum Achievable High Data Rate Data Rate with High Order Modulation and • Due to the limited power and mass for Bandwidth Efficient Coding Study CubeSat spacecraft, power and bandwidth efficient signal techniques are recommended Summary of the study results for use to achieve CubeSat high data rate Max Implementation Modulation Coding Data Comment requirements loss at 10-5 BER Rate • 7/8 LDPC code with low overhead to There is significant positive link margin increase bandwidth efficiency is 7/8 16 assuming a CubeSat equivalent isotropically OQPSK 3.6 dB recommended for CubeSat NEN S-band 5 LDPC Mbps radiated power (EIRP) with 8.0 dBW (2 Watt TX Power). MHz channel communication links to 7/8 23.6 8PSK 4.1 dB Same as in OQPSK achieve high data rate LDPC Mbps • CCSDS and DVB-S2 signal schemes are > 6 dB For the 6 dB implementation loss case, it was recommended for CubeSat high rate assumed that the CubeSat transmitter distortions are the same as defined in the missions Space Network Users Guide (SNUG). S-band Single Access Return (SSAR) user 7/8 28 16 APSK distortions were used except with a lower LDPC Mbps ~ 5 dB Power Amplifier (PA) nonlinearity. For the 5 dB case, it was assumed the CubeSat transmitter had less distortions than the SNUG defined SSAR user distortions amount and lower PA nonlinearity >> 6dB 7/8 30 32 APSK should not be considered because 32 APSK LDPC Mbps it has minimum benefits on data rate. ~ 5 dB > 6 dB Considering 16 APSK can achieve the same 7/8 28 16 QAM data rate with less stringent constraints, 16 LDPC Mbps ~ 5 dB QAM should not be considered. EXPLORATION AND SPACE COMMUNICATIONS PROJECTS DIVISION 8 NASA GODDARD SPACE FLIGHT CENTER CubeSat Ka-Band End-to-End Communication Analysis Achievable Data Rate at Ka-Band Ground Antenna LEO Data Rate QPSK* Data Rate LEO DVB-S2 ** ASF 1.2