First Results From the GPS Compact Total Electron Content Sensor (CTECS) on the PSSCT-2 Nanosat

Transcription

1 First Results From the GPS Compact Total Electron Content Sensor (CTECS) on the PSSCT-2 Nanosat Rebecca Bishop 1, David Hinkley 1, Daniel Stoffel 1, David Ping 1, Paul Straus 1, Timothy Burbaker 2 1 The Aerospace Corporation, 2 Pennsylvania State University PSL/SSAL 16 August 2012 The Aerospace Corporation 2012

2 Outline Introduction PSSCT-2 Mission CTECS Sensor CTECS Operations Review of GPS Radio Occultation Data Examples Future CTECS Flight Opportunities Air Force XR SENSE mission GEOScan or other hosted sensor opportunities Summary 2

3 PicoSat Solar Cell Testbed-2 (PSSCT-2) STP mission Purpose: Demonstrate new s/c subsystem technology including quadruple-junction solar cells, 3-axis attitude control system, adaptive communications radio. Nanosat: 5 x5 x10 Primary Payload: Compact Total Electron Content Sensor (CTECS)- a GPS radio occultation instrument. PSSCT-2 launched 20 July 2011 from the Space Shuttle STS-135 mission. Supported by Air Force Space and Missile Center Development and Planning Directorate (SMC/XR) and STP program Left: Completed PSSCT-2 Nanosatellite Right: Launch of PSSCT-2 from the Space Shuttle STS- 135 (Courtesy of NASA) 3

4 Altitude PSSCT-2 Mission Continued. Released into a circular orbit at initial altitude of 380 km. Orbit decayed in 4.5 months and re-entry occurred 8 December On-board rockets were fired, temporarily raising orbit. Attitude control provided 3-axis stability (1 ) and magnetic alignment Sun and earth sensors Magnetometer Torque coils Reaction Wheels Angular rate sensor Downlink Rate: kbps Altitude Perigee Apogee 4 Date

5 Compact Total Electron Content Sensor (CTECS) Hardware consists of NovAtel OEMV-2 receiver, custom designed antenna Low-noise-amplifier (LNA), cables Receiver: CTECS tracks L1, L2, L2C Also GLONASS capable but not used. Modified internal software Allows multiple sampling rate Specific commands for occultation use 16 MB of on-board data storage dedicated for CTECS Radiation tests: Radiated with 20, 30, 50 MeV protons, Primary errors were power resets. Rarely checksum errors in data stream during serial comm observed Receiver recovered from both error types without assistance. Failure at 20 krad (serial comm lost) 5 Completed CTECS sensor. The antenna is mounted in the bracket facing into the page.

6 Compact Total Electron Content Sensor (CTECS) Continued. Antenna/LNA Initially several COTS antennas tested L1 and/or L2 tuning off by several MHz given their narrow-band performance Lower gain than desired. Custom antenna designed by The Aerospace Corporation Dual patch antenna with a stripline 90 internal hybrid. 7.6 x7.6 x 1 cm Hemispherical gain pattern with 10 db gain reduction at 90 form antenna boresight. Bandwidth centered on L1/L2 is 20 MHz Gain: L1= 6.2 dbic and L2 = 6.4 dbic LNA mounted directly to back of antenna Gain: L1 = 28 db, L2 = 20 db Noise Floor: L1=2.0 db, L2 = 2.1 db 6 Topside of CTECS sensor assembly showing the antenna

7 On-orbit GPS Sensors GPS Radio Occultation (GPSRO) Occulting: Latin: Hidden, concealed, secret Occultation: an an event that that occurs when one one object is is hidden by by another another object that object passes that between passes between it and the it and observer. the observer. As the GPS constellation satellite Tangent point As the GPS constellation satellite passes below below the the horizon, the the signals are are refracted. v GPS Measuring the the refraction of of the the LEO L1/L2 L1/L2 signals signals is is used used to to calculate calculate TEC, electron density profiles, TEC, and scintillation electron density in theprofiles, and ionosphere. scintillation in the v leo ionosphere. Parameters measured: Figure Figure From 4. From Zhen Zhen Zeng (HAO/COSMIC) Parameters L1/L2 measured: pseudorange L1/L2 phase L1/L2 pseudorange L1/L2/L2C phase 6 7

8 History of GPS Occultation Measurements TurboRogue Receiver; 2kg; 8 sat tracked Oersted GRACE-A/B SunSat 1999-present IGOR Receiver (BlackJack); 4.6 kg; 23 W 12 sat tracked TurboRogue Receiver; 2kg; 8 sat tracked TurboRogue III (BlackJack) Receiver; 2kg; 8 sat tracked Novatel OEMV-2 Receiver; 153 g; 12 sat track present 2008-present CANX MetOP-A Novatel OEM4-G2L Receiver/COTS antenna; 2838 g; 12 sat tracked

9 CTECS Observations Because of issues with the attitude control system software, and on-board power, CTECS operations limited to 13.5 hours. 4 hours of CTECS operation was maximum supported by the power system. First satellite lock 8 seconds after turn-on; 4 satellites locked on and tracking within 4 minutes of turn-on Attitude control issues on 8/23, 9/14, 10/20 resulted in poor data quality. Date Duration Mode Clean Occulting Tracks % of Total Satellites Tracked 8/23/11 60 min TEC (1 Hz) 10 40% 9/14/11 90 min TEC (1 Hz) /20/11 4 hours TEC (1 Hz) 28 44% 11/1/11 4 hours TEC (1 Hz) 54 65% 11/15/11 90 min S4 (20 Hz) 5 33% 9

10 Data Examples Yellow indicates occultation portion of track. In this example entire track is 30.6 min long Occultation takes 6 minutes Because of low altitude of orbit, able to observe large amount of density above satellite. Appleton anomaly observed. 10

11 Data Examples Continued. 11

12 Space Environment NanoSatellite Experiment (SENSE) Air Force SMC/XR Program Purpose: Demonstrate the ability to design, build, test, and deliver two complete spacecrafts in an 18- month period.demonstrate the feasibility of using cubesats to provide future operational space weather data. Primary Contractor: Boeing Phantom Works Two 3-U flight cubesats to be built Identical buses At least 2 unique sensors Bus 1: WINCS, CTECS Bus 2: CTIP, CTECS Launch scheduled for late summer 2013 Engineering units assembly in progress. 2 Engineering and 2 Flight Units of CTECS were delivered. Will provide relative TEC, S4, σ ϕ, position information Improvements from PSSCT-2 include 3 sampling rates, data quality flags, integrated antenna/lna 12

13 Summary CTECS was successfully integrated into the PSSCT-2 s/c and released from the STS-135 Space Shuttle Mission CTECS collected 13.5 hours of data Successfully demonstrated the ability of a COTS receiver to make occultation measurements and produce TEC data. Acknowledgment: This work is supported under The Aerospace Corporation's Sustained Experimentation and Research for Program Applications program, the Air Force XR program, and the Space Test Program (STP). 13

14 Sources For History of GPS RO Slide Individual Figures GPS/MET: Courtesy of Jet Propulsion Laboratory SAC-C: Courtesy of the IOCCG (International Ocean Color Coordinating Group) MetOP-A: Courtesy of GEO ( CHAMP: Courtesy of GeoForschungsZentrum (GFZ) GRACE: Courtesy of NASA SUNSAT: Courtesy of Stellenbosch University COSMIC: Courtesy of COSMIC UCAR C/NOFS: Courtesy of AFRL PICOSat-9: Courtesy of SSTL Oersted: Model of the Ørsted Satellite in the Tycho Brahe Planetarium CANX-2: Courtesy of University of Toronto Institute for Aerospace Studies 14