FLIGHT DYNAMICS OPERATIONS
FOR THE
INTERSTELLAR BOUNDARY EXPLORER
Lisa Policastri
Lisa@AppliedDefense.com
AGI Users’ Conference Tour, Greenbelt, MD
12 July 2010
IBEX Background
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NASA Small Explorer Program (SMEX)
Southwest Research Institute, principal investigator
Launched from Kwajalein Atoll on 19 October 2008
Launched on Pegasus with STAR-27 SRM
Highly elliptical orbit, approximate:
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Apogee altitude of 48 Re
Perigee altitude of 7,000 km
Period of 8 days
Operational lifetime of at least two years
Three orbit-raising maneuvers to achieve mission orbit
Spinning spacecraft, sun-pointed
Tracked by Universal Space Network (USN) + APL
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IBEX Orbit
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IBEX’s Science Objectives
• IBEX's sole, focused science objective is to discover the
global interaction between the solar wind and the
interstellar medium
• IBEX achieves this objective by taking a set of global
energetic neutral atom (ENA) images that answer four
fundamental science questions:
• What is the global strength and structure of the termination
shock?
• How are energetic protons accelerated at the termination shock?
• What are the global properties of the solar wind flow beyond the
termination shock and in the heliotail?
• How does the interstellar flow interact with the heliosphere
beyond the heliopause?
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IBEX Flight Operations Team
• Mission Operations Center (MOC) at Orbital
Sciences in Virginia
• Flight Dynamics (FDG) operations at Applied
Defense Solutions in Maryland
• Program Management at Southwest
Research Institute in Texas
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IBEX Flight Dynamics Info
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Flight dynamics operations at ADS
Three tracking contacts every orbit
One attitude maneuver every orbit
Orbit determination after each contact
Product delivery requirements per orbit
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Acquisition files: TLEs and INP2s…
Ephemeris predicts…
Ground station view periods
Star tracker outage predictions
Orbit events information
And more!
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IBEX Flight Dynamics Group
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Lisa Policastri (FD lead)
Ryan Lebois
John Carrico
Marissa Intelisano
Craig Nickel
Mike Loucks (Space Exploration Engineering)
FDG activities 40 hours per week total
max!
• Must have efficient & reliable tools &
software!!!
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IBEX Flight Dynamics Software
• Satellite Tool Kit (STK) 8.1.3
• Astrogator + Professional Edition + Integration +
Attitude
• Recently added STK/Communications!
• Orbit Determination Tool Kit (ODTK) 5.1.2
• Microsoft Excel 2007
• WSFTP 2007
• Scripts & Utilities (custom workflows)
AGI software + custom workflows supports
all flight dynamics operational needs for
IBEX
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Equipment
• Desktop
• Antec Quad-Core Xeon Processor
• Configured for all flight dynamics activities
• Backed up to ADS secure server
• Network Connection
• SFTP
• e-mail
• Blackberry
• Modem
• Communicating with friends at the MOC
• Backup laptop
• Dell Precision M4300 Laptop
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Operational Flow Stages
“High Level”
Planned
Maneuvers
ODTK
STK
Tracking
Measurements
Utilities
QC
Data Products:
•Definitive Ephemeris with
Covariance
•Predict Ephemeris with
Covariance
•TLEs & INP2s
•View period predicts
•Star tracker outage predicts
•Orbit events files
•Long-term analysis
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Planned Maneuvers - Validate
• Mother-of-all IBEX STK scenarios
• Originally called “IBEX ATS” scenario
• Script that reads in ATS files
• Models spacecraft attitude
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Attitude Check
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Pre-screen Tracking Files
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Grab
Load
Preview
Time period?
Correct IDs?
Gaps with file?
Missing files?
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Pre-Processing Tracking Measurements:
ODTK Preview
• Measurements are preprocessed in ODTK
• Displayed summary information about each
measurement file
• Tracking station identification
• Start and stop times of the measurements
• Number of valid measurements in the file
• Warning if the measurements are:
• Out of order, then run ODTK “Sort UTDF Observation
File” Utility
• Not valid
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Pre-Processing Tracking Measurements:
UTDF Reader
• Read binary measurement files in the UTDF format.
• “Tracking and Acquisition Handbook for the Spaceflight Tracking
and Data Network,”
• Displayed about measurements:
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Ground station identification codes
Record date and time
Tracking mode: program track or auto-track
Doppler is valid or invalid
• Allows editing of data in binary files, if records showed to
be mis-tagged or out of order.
• Allows exporting of information
• Auto-track records (angle measurements)
• Doppler measurements
• STK Sensor Pointing files (auto-track)
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ADS UTDF Reader
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ODTK Configuration
• Continuous ODTK scenario
• Ground stations geodetics
• Biases and bias sigma estimates
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For each measurement type
For each station
From measurement statistics
Refined over time as needed
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Running ODTK Filter
• Run ODTK Filter
• ODTK Static Product Builder: custom graph & report product list
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Histograms of residual ratios per station, per measurement type
Measurement Residuals per station, per measurement type, +/- 3 sigma
Measurement Residuals all stations, per measurement type, +/- 3 sigma
Residual Ratios (normalized residuals), per measurement type
Position uncertainty
Velocity uncertainty
Measurements locations along orbit as a function of spacecraft altitude
Measurements locations along orbit as a function of spacecraft true
anomaly
Measurement summary
• Results in histograms, residuals, and residual ratios are examined to
determine if the Gauss-Markov parameters needed adjustment
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Doppler Residual Ratios Example
• Bias Sigma, half-life, and white noise sigma adjusted if:
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Too much “white space” in the residual ratios graph
Histograms were not showing Gaussian distributions
• Measurements with residuals outside of +/-3 sigma were not
accepted by filter
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Example of Histogram of Residual Ratios
• Hawaii station
• Filtered Doppler measurements (14,835 samples)
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Filter 3-Sigma Position Covariance
Radial uncertainty is blue, in-track is red, cross-track is black
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Filter 3-Sigma Velocity Covariance
Radial uncertainty is blue, in-track is red, cross-track is black
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Current Measurements by Altitude
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Running ODTK Smoother
• Each successful filter run followed by
corresponding smoother run
• Smoother refines the state & covariance from
the filter
• Provides improved orbit accuracy with a
smoothed ephemeris & covariance
• Solves for maneuvers
• Products generated after each smoother run
• Smoothed position uncertainty
• Smoothed velocity uncertainty
• Maneuver summary reports
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Smoother 3-Sigma Position Covariance
Radial uncertainty is blue, in-track is red, cross-track is black
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Smoother 3-Sigma Velocity Covariance
Radial uncertainty is blue, in-track is red, cross-track is black
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Running Filter & Smoother
• Modified State Diff tool
installed w/ ODTK
• Automates file naming
and storage
• Automates pointing to
various files for:
• Smoother (rough file)
• Static Product Builder
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.Filrun
.Smtrun
.Difrun
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Filter-Smoother Differencing
• Position and velocity consistency tests are an
important quality check
• If differences in the filtered and smoothed
ephemeris solutions were outside of three
sigma, go back and re-examine data
• Differencing process is handled by the ODTK
“State Difference” utility
• Position and Velocity Consistency graphs are
generated
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Filter-Smoother
Position Consistency Check
•3-sigma bounded
•Radial uncertainty is blue, in-track is red, cross-track is black
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Filter-Smoother
Velocity Consistency Check
•3-sigma bounded
•Radial uncertainty is blue, in-track is red, cross-track is black
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Ephemeris with Covariance
• Each ODTK filter run & smoother run produced ephemeris files
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With 6 x 6 position & velocity covariance
STK .e file format
Contain definitive and predict points
• Smoother ephemeris files contain:
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Definitive ephemeris from filter restart point until time of the last
measurement
Four orbits of predictions
• Smoother ephemeris files imported into STK
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Spacecraft position graphically displayed
Position covariance ellipsoids displayed in 3-D
Compare differences in solutions
Graph the angle between spacecraft position
Look for covariance in ground station FOV
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Smoother Definitive & Predict Ephemeris
with Covariance
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Predict Ephemeris Delivered
• Smoother (or filter) ephemeris files used for
generating the official delivery of predicted
ephemeris
• State at last measurement used in STK/Astrogator for
initial state
• Prediction files needed for scheduling ground
station contacts
• Prediction files used to create acquisition data
for the ground stations
• INP2 angle files
• TLEs
• SPICE
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Acquisition Data Types
• TLEs primary (initially)
• Selected years ago for pointing antennas
• Tested for a typical nominal operations cases
• INP2 angle files
• Contain azimuth & elevation angles at specified time steps over a
period of time
• Highly elliptical orbits
• STK Access Custom report style
• SPICE predict ephemeris for APL station
• IIRV for NASA stations
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Current Acq Data Deliveries
• Always deliver a TLE and INP2 file set
• INP2 near perigee (270 to 110 degrees true anomaly)
every 1 second
• INP2 for all other locations, every 5 sec
• All Q/C against predicted ephemeris
• TLE only valid when angle from the ground station
between the predict ephemeris and the TLE is less
than 0.2 degrees
• INP2 must match with original ephemeris to within 0.2
degrees from the ground stations
• Deliver IIRV to NASA when needed for NASA
Ground Network contacts
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TLE Generator Utility
• Allow for easy generation of multiple TLEs
from the same ephemeris file
• Sets up satellite object with TLE for quality
checking
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TLE Quality Check Example
• STK Chain “Angle Between” graph
• TLE only valid:10 Apr 2009 23:00 to11 Apr 2009 06:30 UTC
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INP2 Angle Generator Utility
• Allow for easy generation of multiple INP2s
• Sets up sensor objects for quality checking
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INP2 Angle File Quality Check Example
• Angle between ground station sensor boresight & satellite
• Alaska INP2: 10 Apr 2009 23:00 to 11 Apr 2009 06:30 UTC
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Example #1, Nominal Case
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Example #2 (…Not Nominal)
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Orbit Events Reports from STK
• IBEX Crossing Times Report
• At what time does each integer Re altitude occur?
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Astrogator Stop & Continue for each Re integer
Astrogator Summary Report
Convert to txt format
• Needed for scheduling contact times and attitude/ Sun
repointing maneuvers
• IBEX Apogee & Perigee Times Report
• At what time does IBEX go through Apogee &
Perigee?
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STK satellite Apogee and Perigee Times custom report
• Needed for scheduling contacts and science
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Tracking Schedule Variations
• Varies uniquely for each orbit
• Based on both the visibility times and when the
ground stations are available
• If contacts were simply not possible near
perigee, the orbit uncertainty will increase
dramatically
• Antenna nulls
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Additional Reporting from STK
• View Periods
• Star Tracker Outages
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Long-Term Analysis
• Come to Toronto in August!
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Where is FDG?
• The FDG configuration is mobile (Thanks Jason)!
• Besides the ADS MOR and Orbital MOC:
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Southwest airlines flight #2892 on March 18 2009
“Superprom 16”, Baldwin MD
Red Sky Grill/Hooters, Laurel MD
Point Mugu CA (NAVSOC)
My parents’ house, Baltimore MD
Mountain View CA (NASA Ames)
BWI Airport
Spaceflight Mechanics Meeting 2009, Savannah GA
Greene Turtle, Laurel MD
Las Vegas Airport
Game Sports Bar, Fulton MD
Many many hotels!!!!
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