flight dynamics operations for the interstellar boundary explorer

FLIGHT DYNAMICS OPERATIONS FOR THE

INTERSTELLAR BOUNDARY EXPLORER

Lisa [email protected]

AGI Users’ Conference Tour, Greenbelt, MD12 July 2010

IBEX Background• 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:

• 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

www.AppliedDefense.com

IBEX Orbit


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?


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


IBEX Flight Dynamics Info • 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

• Acquisition files: TLEs and INP2s…• Ephemeris predicts…• Ground station view periods• Star tracker outage predictions• Orbit events information• And more!


IBEX Flight Dynamics Group• 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!!!www.AppliedDefense.com

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


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


Operational Flow Stages “High Level”


ODTK

STK

Utilities

Planned Maneuvers

Tracking Measurements

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

QC

Planned Maneuvers - Validate• Mother-of-all IBEX STK scenarios

• Originally called “IBEX ATS” scenario• Script that reads in ATS files• Models spacecraft attitude


Attitude Check


Pre-screen Tracking Files• Grab • Load • Preview• Time period?• Correct IDs?• Gaps with file?• Missing files?


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


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:

• 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)


ADS UTDF Reader


ODTK Configuration• Continuous ODTK scenario• Ground stations geodetics• Biases and bias sigma estimates

• For each measurement type • For each station• From measurement statistics• Refined over time as needed


Running ODTK Filter• Run ODTK Filter• ODTK Static Product Builder: custom graph & report product list

• 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


Doppler Residual Ratios Example

• Bias Sigma, half-life, and white noise sigma adjusted if:• 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


Example of Histogram of Residual Ratios

• Hawaii station• Filtered Doppler measurements (14,835 samples)


Filter 3-Sigma Position Covariance


Radial uncertainty is blue, in-track is red, cross-track is black

Filter 3-Sigma Velocity Covariance



Current Measurements by Altitude


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


Smoother 3-Sigma Position Covariance



Smoother 3-Sigma Velocity Covariance



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

• .Filrun• .Smtrun• .Difrun


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


Filter-Smoother Position Consistency Check


• 3-sigma bounded• Radial uncertainty is blue, in-track is red, cross-track is black

Filter-Smoother Velocity Consistency Check


• 3-sigma bounded• Radial uncertainty is blue, in-track is red, cross-track is black

Ephemeris with Covariance• Each ODTK filter run & smoother run produced ephemeris files

• With 6 x 6 position & velocity covariance• STK .e file format• Contain definitive and predict points

• Smoother ephemeris files contain: • Definitive ephemeris from filter restart point until time of the last

measurement • Four orbits of predictions

• Smoother ephemeris files imported into STK • 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


Smoother Definitive & Predict Ephemeris with Covariance


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


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


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


TLE Generator Utility


• Allow for easy generation of multiple TLEs from the same ephemeris file

• Sets up satellite object with TLE for quality checking

TLE Quality Check Example


• STK Chain “Angle Between” graph• TLE only valid:10 Apr 2009 23:00 to11 Apr 2009 06:30 UTC

INP2 Angle Generator Utility• Allow for easy generation of multiple INP2s• Sets up sensor objects for quality checking


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


Example #1, Nominal Case


Example #2 (…Not Nominal)


Orbit Events Reports from STK

• IBEX Crossing Times Report• At what time does each integer Re altitude occur?

• 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?• STK satellite Apogee and Perigee Times custom report

• Needed for scheduling contacts and science


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


Additional Reporting from STK• View Periods• Star Tracker Outages


Long-Term Analysis• Come to Toronto in August!


Where is FDG?• The FDG configuration is mobile (Thanks Jason)!• Besides the ADS MOR and Orbital MOC:

• 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!!!!


flight dynamics operations for the interstellar boundary explorer

Documents

ibex orbitwww

interstellar flow

termination shock

global strength

global interaction

global properties

solar wind flow

focused science objective