1. Satellite Design Lab Aerospace Engineering FOTON: A Software-Defined, Compact, Low-Cost GPS Radio Occultation Sensor Glenn Lightsey and Todd Humphreys, UT Austin Aerospace Dept. GEOScan Planning Workshop | March 27-30, 2011

2. Satellite Design Lab Aerospace Engineering Instrument/Sensor Specifications Mass: 350 g Power: 4.8 W Volume: < 1 U Data rate: 64 kbps (occulation mode), 2.6 kbps (standard) Flight heritage or stage of development: Under development Number of satellites required: at least 1 Accommodation requirements: antenna on anti-ram (possibly also ram) facing surfaces Expected data products: 100-Hz phase, TEC, S4, sigmaPhi, tau0 Data delivery and distribution: Data posted to central server Expected results, contribution, broader impact: Prove the promise of swarms of low-cost GPS occultation sensors for ionospheric and tropospheric science Cost: $10k - $50k per unit, depending on number of units Instrument/Science Team Main contact: Todd Humphreys, University of Texas at Austin (todd.humphreys@mail.utexas.edu) Collaborators: Glenn Lightsey, University of Texas at Austin Mark Psiaki, Cornell Steve Powell, Cornell Chuck Swenson, USU Chad Fish, SDL Sponsors/institutions/individuals with potential interest in funding development of FOTON US Air Force under existing SBIR contract NASA Ames for constellation of cubesats FOTON Sensor Overview Grand Challenges Responsive, flexible occultation science via software-defined GPSRO sensor Exploit emerging technology to maximize science return from GPSRO sensors Signals: GPS L1CA and L2C GPS radio occultation sensors are strongly synergistic with in-situ electron density sensors, electric field sensors, etc. Conceptual Design FOTON Software-defined space weather sensor High-sensitivity occultation returns Scintillation triggering Data-bit wipeoff Open-loop tracking Recording of raw IF data

3. Satellite Design Lab Aerospace Engineering Q: What emerging technologies can be exploited to maximize the science impact of GNSS-based radio occultation over the next decade?

4. MiniaturizationProliferationModernizationEstimation  Smaller, less power-hungry GPSRO devices enable deployment:  As hosted payload on larger SVs (e.g., IridiumNext)  On CubeSats  Shrinking Sensor envelope and cost allows ubiquitous space based sensor networks

5. MiniaturizationProliferationModernizationEstimation  Low cost enables larger constellations (10- 100) of GPSRO-bearing SVs  Redundancy shifts from sensor to swarm  Challenges posed by large numbers of low-cost GPSRO sensors:  Data rate (~300 kB per occulation) may be too high for practical downlink  sensors should be smart, do some preliminary processing onboard  Occultation capture cannot be orchestrated from the ground  sensors must be autonomous  Low cost implies some radiation hardness sacrifice  Low cost implies less rigorous pre-flight qualification testing of each unit Like COSMIC but at a fraction of the cost per GPSRO sensor

6. MiniaturizationProliferationModernizationEstimation  GPS L2C offers a crucial unencrypted second civil signal  Allows tracking of occultations deeper into troposphere  9 L2C-capable SVs now in orbit  20 L2C-capable SVs by 2015  GPS L1 C/A + L2C most promising signal combination for occultations over next decade  GPS L5 and Galileo signals  Also promising after ~2018  P(Y) code may be discontinued after 2021  Software-defined GNSSRO receivers offer complete on-orbit reprogrammability  Reduces operational risk  Enables on-orbit innovation  Allows adaptation to science needs/events (Fig. 1 of Wallner et al., "Interference Computations Between GPS and Galileo," Proc. ION GNSS 2005)

7. MiniaturizationProliferationModernizationEstimation  Challenge: Need good measurement quality despite low-cost and small size of GNSSRO sensors  Climate science requires accurate, consistent measurements  If large, high-gain antennas can’t be accommodated, must make up sensitivity in signal processing  Specialized open-loop tracking required to push deep into troposphere  Phase measurements must be CDGPS-ready to enable precise orbit determination (Topstar receiver by Alcatel fails this req’t)  Challenge: Atmospheric assimilative models should be modified to ingest raw carrier phase and TEC measurements from occultations  Abel transform appears to be an unnecessary step: does not fully summarize the information in the data  Challenge: To ease data downlink burden, ionospheric science parameters such as TEC, S4, tau0, sigmaPhi should be estimated on-orbit

8. Satellite Design Lab Aerospace Engineering Survey of GPSRO Receivers (Flight Qualified or Considered) Chart adapted from Oliver Montenbruck, 2008; Pictures from Gupta, 2009. Javad TR-G2T (Javad) 2561C1,P1,P2, LA,L2C,L5 1m1.6 W 34 g ?-35 C/ + 75 C 10 k$? COTS receivers

9. Satellite Design Lab Aerospace Engineering Since 2008, The University of Texas, Cornell, and ASTRA LLC have been developing a dual- frequency, software-defined, embeddable GPS- based space-weather sensor.

10. Satellite Design Lab Aerospace Engineering CASES Receiver (2011)

11. Antarctic Version of CASES  Deployed late 2010  Remotely reprogrammable via Iridium  Automatically triggers and buffers high- rate data output during intervals of scintillation  Calculates S4, tau0, sigmaPhi, SPR, TEC

12. Satellite Design Lab Aerospace Engineering CASES Follow-On: FOTON GPSRO  Size: 8.3 x 9.6 x 3.8 cm  Mass: 350 g  Power: 4.8 W  Reprogrammable from ground  Dual frequency (L1CA, L2C)  Software can be tailored for occultation and space weather sensing:  Scintillation triggering  Open-loop tracking  Recording of raw IF data  Data bit wipeoff Goal: Deliver high-end GPSRO benefits at low- end Size/Weight/Power and Cost Prototype FOTON receiver Now undergoing testing

13. CharacteristicNovAtel OEMV-3FOTONBRE Pyxis-RO Flight HeritagePrecursor OEM4-G2L flown on CanX-2 Plans for 2013-14 flightPrecursor IGOR flown on CHAMP, GRACE, COSMIC Size/Weight/Power8.2 x 12.5 x 1.3 cm / 75 g / 2.1 W8.3 x 9.6 x 3.8 / 350 g / 4.8 W19 x 13.3 x 10 cm / 4.5 kg / 25 W Cost< $10k$10-50k~$500k Signals Tracked/ Num. of channels GPS L1CA, L2C, L2P(Y), L5 72 channels GPS L1CA, L2C 60 channels GPS L1CA, L2C, L2P(Y), L5 48 – 128 channels Radiation Hardness~ 6krad~5-10krad? (can be upgraded)100 krad? Time to First Fix2.25 min. for OEM4-G2L on CanX-2 with aiding scripts 10 seconds with appx. time~14 min. for IGOR Precision0.5 mm carrier phase< 0.5 mm carrier phase Antenna Inputs11-2 (2 antenna option increases SWAP) 4 On-orbit Reconfigurable? Only baseband processor firmware Completely reconfigurable downstream of ADC Baseband processor firmware + extra space in FPGA (used to demonstrate L2C on IGOR) Open-Loop Tracking? Not natively. May be possible to drive open loop tracking via API. Yes Raw L1/L2 IF data capture? NoYesNo On-board orbit determination NoYes Data-bit wipeoff for robust tracking? NoYesNo On-board Estimation of Space Weather Products? NoS4, TEC, sigmaPhi, tau0, SPRNo

14. Satellite Design Lab Aerospace Engineering Commercialization Path for FOTON  Startup Company Created in Austin for licensing and commercialization of university space technology  Air Force SBIR Phase 1 Awarded (2/11-11/11)  SBIR Phase 2 (if awarded) 2012-2014  FOTON GPSRO CubeSat on-orbit demonstration planned in 2013-2014 FOTON will be ready for selection as a GEOScan payload on IridiumNext

15. Satellite Design Lab Aerospace Engineering Concern: Our experience with Iridum interference at two Antarctic stations indicates that this may be a more serious problem for Iridium- hosted GPSRO than earlier studies suggest.

16. Satellite Design Lab Aerospace Engineering More Information http://radionavlab.ae.utexas.edu

17. Satellite Design Lab Aerospace Engineering Backup Slides

18. Satellite Design Lab Aerospace Engineering A Closer Look: NovAtel OEMV-3  High-quality device, proven manufacturer  OEM4-G2L flew on CanX-2  CanX-2 adaptations:  Disable altitude and velocity restrictions  Upload startup scripts to speed acquisition  Set sampling rate to 100 Hz  Set elevation mask to -45 deg  Reduce carrier phase smoothing of code measurements CharacteristicValue Power2.1 W Mass75 g Size85x125x13 mm SignalsL1, L2,L2C,L5 Meas. rate100 Hz