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

FOTON Sensor Overview

Satellite Design Lab Aerospace Engineering Grand Challenges

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Responsive, flexible occultation science via software-defined GPSRO sensor

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Exploit emerging technology to maximize science return from GPSRO sensors

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Signals: GPS L1CA and L2C GPS radio occultation sensors are strongly synergistic with in-situ electron density sensors, electric field sensors, etc.

Instrument/Sensor Specifications

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Mass: 350 g

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Power: 4.8 W Volume: < 1 U

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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

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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

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Cost: $10k - $50k per unit, depending on number of units Conceptual Design

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FOTON

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Software-defined space weather sensor

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High-sensitivity occultation returns

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Scintillation triggering Data-bit wipeoff Open-loop tracking Recording of raw IF data Instrument/Science Team

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Main contact: Todd Humphreys, University of Texas at Austin ([email protected])

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Collaborators:

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Glenn Lightsey, University of Texas at Austin

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Mark Psiaki, Cornell

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Steve Powell, Cornell Chuck Swenson, USU Chad Fish, SDL

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Sponsors/institutions/individuals with potential interest in funding development of FOTON

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US Air Force under existing SBIR contract

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NASA Ames for constellation of cubesats

Q: What emerging technologies can be exploited to maximize the science impact of GNSS-based radio occultation over the next decade?

Satellite Design Lab Aerospace Engineering

Miniaturization Proliferation

  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

Modernization Estimation

Miniaturization Proliferation Modernization Estimation

   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  must be

autonomous

sensors  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

Miniaturization Proliferation Modernization

       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

Estimation

(Fig. 1 of Wallner et al., "Interference Computations Between GPS and Galileo," Proc. ION GNSS 2005)

Miniaturization Proliferation Modernization

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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

Estimation

Survey of GPSRO Receivers (Flight Qualified or Considered)

Javad TR-G2T

(Javad) 256 1 C1,P1,P2, LA,L2C,L5 1m 1.6 W 34 g ?

-35 C/ + 75 C 10 k$ ?

COTS receivers Chart adapted from Oliver Montenbruck, 2008; Pictures from Gupta, 2009.

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.

Satellite Design Lab Aerospace Engineering

CASES Receiver (2011)

Satellite Design Lab Aerospace Engineering

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

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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 Prototype FOTON receiver Now undergoing testing Goal: Deliver high-end GPSRO benefits at low end Size/Weight/Power and Cost

Satellite Design Lab Aerospace Engineering

Characteristic NovAtel OEMV-3 FOTON BRE Pyxis-RO Flight Heritage Size/Weight/Power Cost

Precursor OEM4-G2L flown on CanX-2 8.2 x 12.5 x 1.3 cm / 75 g / 2.1 W < $10k Plans for 2013-14 flight 8.3 x 9.6 x 3.8 / 350 g / 4.8 W $10-50k Precursor IGOR flown on CHAMP, GRACE, COSMIC 19 x 13.3 x 10 cm / 4.5 kg / 25 W ~$500k

Signals Tracked/ Num. of channels Radiation Hardness Time to First Fix Precision Antenna Inputs On-orbit Reconfigurable?

GPS L1CA, L2C, L2P(Y), L5 72 channels ~ 6krad 2.25 min. for OEM4-G2L on CanX-2 with aiding scripts 0.5 mm carrier phase 1 Only baseband processor firmware GPS L1CA, L2C 60 channels ~5-10krad? (can be upgraded) 10 seconds with appx. time < 0.5 mm carrier phase 1-2 (2 antenna option increases SWAP) Completely reconfigurable downstream of ADC GPS L1CA, L2C, L2P(Y), L5 48 4

Open-Loop Tracking?

Raw L1/L2 IF data capture?

On-board orbit determination Data-bit wipeoff for robust tracking?

On-board Estimation of Space Weather Products?

Not natively. May be possible to drive open loop tracking via API.

No No No No Yes Yes Yes Yes No Yes No S4, TEC, sigmaPhi, tau0, SPR No – 128 channels 100 krad?

~14 min. for IGOR < 0.5 mm carrier phase Baseband processor firmware + extra space in FPGA (used to demonstrate L2C on IGOR) Yes

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

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.

Satellite Design Lab Aerospace Engineering

More Information

http://radionavlab.ae.utexas.edu

Satellite Design Lab Aerospace Engineering

Backup Slides

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

Characteristic Value

Power 2.1 W Mass Size Signals Meas. rate 75 g 85x125x13 mm L1, L2,L2C,L5 100 Hz

Satellite Design Lab Aerospace Engineering