FOTON sensor

Report
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
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.
Instrument/Sensor Specifications
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Conceptual Design
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FOTON
Software-defined space
weather sensor
High-sensitivity
occultation returns
Scintillation triggering
Data-bit wipeoff
Open-loop tracking
Recording of raw IF data
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
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Main contact: Todd Humphreys, University of Texas at Austin
([email protected])
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
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Chuck Swenson, USU
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Chad Fish, SDL
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
Modernization
 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
Estimation
Miniaturization
Proliferation
Modernization
Estimation
 Low cost enables larger constellations (10100) 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 
Like COSMIC but at a fraction
sensors should be smart, do some
of the cost per GPSRO sensor
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
Miniaturization
Proliferation
Modernization
Estimation
 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)
Miniaturization
Proliferation
Modernization
 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
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-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 dualfrequency, software-defined, embeddable GPSbased 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
CASES Follow-On: FOTON GPSRO
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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 lowend Size/Weight/Power and Cost
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Aerospace Engineering
Characteristic
NovAtel OEMV-3
FOTON
BRE Pyxis-RO
Flight Heritage
Precursor OEM4-G2L flown on
CanX-2
Plans for 2013-14 flight
Precursor IGOR flown on CHAMP,
GRACE, COSMIC
Size/Weight/Power
8.2 x 12.5 x 1.3 cm / 75 g / 2.1 W
8.3 x 9.6 x 3.8 / 350 g / 4.8 W
19 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 Fix
2.25 min. for OEM4-G2L on
CanX-2 with aiding scripts
10 seconds with appx. time
~14 min. for IGOR
Precision
0.5 mm carrier phase
< 0.5 mm carrier phase
< 0.5 mm carrier phase
Antenna Inputs
1
1-2 (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
Yes
Raw L1/L2 IF data
capture?
No
Yes
No
On-board orbit
determination
No
Yes
Yes
Data-bit wipeoff for
robust tracking?
No
Yes
No
On-board
Estimation of Space
Weather Products?
No
S4, TEC, sigmaPhi, tau0, SPR
No
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 Iridiumhosted 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:
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Characteristic
Value
Power
2.1 W
Mass
75 g
Size
85x125x13 mm
Signals
L1, L2,L2C,L5
Meas. rate
100 Hz
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
Satellite Design Lab
Aerospace Engineering

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