11 林新發 dec. 11, 2012 @ ncku 衛星地面站 - 說明衛星地面站之構成、...

11

林新發Dec. 11, 2012 @ NCKU

衛星地面站 -

說明衛星地面站之構成、衛星軌道之估算、與衛星操作之流程

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主題 - 衛星地面站內容 - 說明•衛星地面站之構成 ( 第一部

份 )

•衛星軌道之估算 ( 第二部份 )

•衛星操作之流程 ( 第三部份 )

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第二部份 : 衛星軌道之估算

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Contents• NGS Overview• FDF Overview• FDF H/W and S/W components• FDF Operations Database• FDF Functional Descriptions

– Orbit Propagation– Orbit Parameters/Events Prediction– Tracking Data Processing– Orbit Determination– Orbit Maneuver Planning– Ground Track Plotting– Satellite Orbit/Attitude Monitoring

• FDF Operational procedures• OASYS Demonstration

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NGS Overview (1/2)• The NSPO Ground Segment (NGS)

consists of the following subsystems:– Mission Operations Center (MOC)

– Mission Control Center (MCC)

– Flight Dynamics Facility (FDF)

– Science Control Center (SCC)

– Telemetry, Tracking & Command (TT&C)

– X-Band Antenna System (XAS)

• Three ground stations (TT&C sites) operated remotely from the Satellite Operations Control Center (SOCC).

• XAS station in Hsin-Chu provides remote sensing data acquisition.

• The Operations complex SOCC in Hsin-Chu provides the central control for all FORMOSAT operations and activities.

Hsin-Chu

Chung-Li

Tainan

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NGS Overview (2/2)

TT&C•FORMOSAT Commanding•Telemetry Capture•Acquisition and Tracking

MOC•Command Processing•Telemetry Processing•Spacecraft and Ground Monitoring

FDF

•Orbit and Attitude Determination•Flight Dynamics Simulations

SCC•Science Planning and Scheduling•Science Operations and Monitoring•Science Data Processing•Data Archive and Distribution

MCC•Spacecraft Scheduling and Planning•Instrument Scheduling and Planning•Scheduling Conflict Resolution•Command Load Generation

GCN•Provides Data Flow Between RGS Elements

•Consists of Local Area and Wide Area Networks

XAS•FORMOSAT-2 X-Band Signal Demodulating•Remote Sensing Data Capturing and storing•Acquisition and Tracking

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FDF Overview

• FDF is one of the NGS subsystem. Its main functions are as follows:– Orbit Determination– Orbit Prediction Generation– Launch Planning– Attitude Determination (Optional)– Flight Dynamics Simulator (Optional)

FDF

TrackingData

MOCTT&C

S/C Commands

Telemetry

Ground Equipment

StatusAcquisition DataTelemetry

Real-Time Tracking Data

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FDF Hardware Components

• FS2 Work Stations– fdf3

» Sun Ultra 60» CPU: 450 MHz» Memory: 256 MB

– fdf4» Sun Ultra II» CPU: 198 MHz» Memory: 256 MB

• FS3 Work Stations– fdf5 & fdf6

» Sun Blade 2500» CPU: 1.28GHz (2X)» Memory: 2 Gbytes

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FDF Software Components (1/2)

• OASYS (Orbit Analysis System)– COTS for orbit determination, prediction,

and analysis– Version: 4.3.6 (FS2), 5.2.2 (FS3)

• EPOCH T&C– COTS for satellite telemetry & command

– Version: 2.5.9d

Mainly for Satellite Orbit Estimation

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FDF Software Components (2/2)

• Utility– Tracking (FS2)

» GPS data reformatting» Attitude data conversion

– fetchPVT.pl (FS3)» GOX data fetching

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Software Distribution

• Workstation fdf3 & fdf4– OASYS 4.3.6– EPOCH 2.5.9d– Solaris 7

• Workstation fdf5 & fdf6– OASYS 5.2.2– EPOCH T&C 2.5.9d– Solaris 8

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Operation Database – FS2

• FDF OASYS– rocsat2_v14_4.3.6.bdb

• MCC OASYS– rocsat2.adb– RS2_event_rpt.adb– RS2_rev_rpt.adb– RS2_sun_rpt.adb– alias.adb

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Operation Database – FS3

• FDF OASYS– FMx_v01.bdb

• MCC OASYS– FMx.adb– RS3_event_rpt.adb– RS3_rev_rpt.adb

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FDF Functional Descriptions

• Orbit Propagation• Orbit Parameters/Events Prediction• Tracking Data Processing• Orbit Determination• Orbit Maneuver Planning• Ground Track Plotting• Satellite Orbit/Attitude Monitoring

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Orbit Propagation (1/9)

• Propagate a set of orbit elements through a time-span to derive an orbit ephemeris

• An ephemeris is the time history of the satellite state (mass, orbit elements, and attitude) propagated forward or backward from a set of orbit elements

• Time epoch types– UTC.YmdHMS, UTC.YjHMS, GPS.YmdHMS,…

• Orbit element types– Kepler, ECI, ECF, Geodetic, Brouwer Mean,

Norad…• Attitude types

– Quoternion, Euler angles

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Orbit Propagation (2/9)

• Time Epoch Types– UTC is the universal time coordinate.– GPS is the global position system time.– Currently GPS time is ahead of UTC by 16 seconds.

GPS – UTC = n SEC

Now (2012-12-11) n=16

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Orbit Propagation (3/9)

• ECI/ECF Coordinate Frame– Earth Center Inertial frame (ECI): X points to star Aries – Earth Center Fixed frame (ECF): X points to longitude 0° in

equator

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Orbit Propagation (4/9)

• ECI Keplerian Orbital Parameters

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Orbit Propagation (5/9)

• Attitude Types – Quotation is a 4-element state vector describing

the attitude relative to a coordinate frame.» [q1, q2, q3, q4)] = [ê*sin(/2), cos( /2)]» Ê is the unit vector of the rotation axis is the rotation angle

– Euler angles are the three rotation angles of the three orthogonal axes of a frame deriving the attitude relative to the frame.

» Final attitude is sensitive to the rotational sequence of the three axes (,,).

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Orbit Propagation (6/9)• The ephemeris is propagated from a state at

some epoch to another epoch by Cowell’s method.– The basic idea is that the equation of motion including

all perturbations, ks is integrated stepwise.

– The satellite state (r, v) for the desired epoch is then calculated using suitable methods of numerical integration.

(r, v)integration

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Orbit Propagation (7/9)

• The perturbing forces considered in OASYS are:– earth gravational field (n x m) spherical harmonic expansion,– point mass solar gravity,– point mass lunar gravity,– solar radiation pressure,– atmospheric drag, and – continuous thrust and/or discrete impulse

Added

Perturbing forces acting on a satellite

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Orbit Propagation (8/9)

• The degree of fidelity of the model is controllable– Each of the force components can be toggled ON or

OFF– The degree and order of the earth gravity field can

be specified• Values affecting the force model stored in

the on-line database– the field coefficients– satellite area elements– reflectivity– drag coefficient – thruster characteristics, and– other astrophysical constants

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Orbit Propagation (9/9)• Two Numerical Integrators for high fidelity dynamics

– Bulirsch-Stoer (based on the Modified Midpoint Method and Rational Function Extrapolation)

» is adaptive in step size and order– Runge-Kutta 5/6

» is adaptive in step size only

• Several Semi-Analytic Propagators, e.g.– Kepler

» the classical 2 body solution– Brouwer Mean

» reflect gravitational potential terms through J3, third body effects are NOT included

– Norad SGP-4» Include third body (sun, moon) and the effects of atmospheric drag

• The Semi-Analytic Propagators sacrifice precision for speed of propagation– useful for long-range mission planning,

» especially for eclipse or sensor interference estimation.

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Orbit Parameters/Events Prediction (1/2)

• Predict various orbit data for mission or contingent operations at user specified data rate and time span.

• Orbit parameters/events can be tabled or plotted.

• Orbit parameters/events such as:– ECI/ECF x/y/z/Vx/Vy/Vz– Sma, e, i, , , f– Longitude, latitude, altitude, Sun beta angle– Local time/longitude of descending/ascending node– In-track/cross-track/along-track error– Azimuth/elevation/range/range rate

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Orbit Parameters/Events Prediction (2/2)

• Parameter Trending Example

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Tracking Data Processing (1/4)

• Process tracking data for Orbit Determination• Data types

– GPS position/velocity– Range rate by Doppler– Elevation/azimuth angle

• Processing types– Data fetching– Data filtering– Data reformatting

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Tracking Data Processing (2/4)

Z

Y

X

(x,y,z)

(Vx,Vy,Vz)

• GPS position/velocity

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Tracking Data Processing (3/4)

• Range Rate– Range Rate = (R2-R1)/(t2-t1)

(from Doppler frequency shift measurement to obtain the range rate data)

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Tracking Data Processing (4/4)

• El/Az Angle– Elevation = angle above horizon

Azimuth = angle from north

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Orbit Determination (1/4)

• Orbit determination is an orbit differential correction with tracking data.

• Estimate orbit elements at user-specified epoch time and coordinate system

• Estimate by using least squares algorithm• Estimate measurement biases and/or

dynamics coefficient• Procedure of the OD

– Preview pre-OD measurement residuals– OD with the primary tracking data– Review post-OD measurement residuals

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Orbit Determination (2/4)

• Least-squares Algorithm– Least-squares algorithm is similar to the curve fitting

to minimizes the sum of squared residuals, a residual being the difference between an observed measurement and the estimated measurement.

– The target function is the sum of squared covariance-weighted measurement residuals.

– The minimization algorithm is batch non-linear least squares using singular value decomposition (SVD).

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Orbit Determination (3/4)

estimated measurement

Res1

t1 t2

Res2

• Measurement Residuals– Measurement residual is the difference between

actual measurement and estimated measurement

Actual measurement

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Orbit Determination (4/4)

• The estimated parameters include– the orbital elements, at epoch T, in any supported

element set;– biases, in the dynamical model including atmospheric

drag coefficient bias, solar pressure coefficient bias, and thrust efficiency; and

– measurement biases, for each measurement type from each tracking antenna.

• The measurement types include– GPS, range, range rate, azimuth and elevation.

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Orbit Maneuver Planning (1/4)

• Change or maintain satellite orbit for different mission phases.

• Maneuver can be divided into two types– In-plane: sma and/or eccentricity maneuver– Cross-plane: inclination maneuver

• Onboard thruster ignition provides force to deliver V for the maneuver.

• Attitude maneuver is usually required to align thrusters with the V before orbit maneuver.

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Orbit Maneuver Planning (2/4)

• Orbit maneuver plan includes several data:– Ignition start time– Ignition stop time– Burn duration– Thrust force– Fuel Isp– Fuel mass– Orbit elements changed

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Orbit Maneuver Planning (3/4)

Io

Vo2*a

o

AscendingNode

DescendingNode

dvV

• SMA Maneuver– Can be conducted anywhere in the orbit

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Orbit Maneuver Planning (4/4)

Io

Vo2*a

o

AscendingNode

DescendingNode

V dv

• Inclination Maneuver– Can only be conducted at ascending or

descending node

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Ground Track Plotting (1/2)

• Plot or animate the ground track of multiple satellite orbits in a world map

• Satellite and ground station coverage can be displayed.

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Ground Track Plotting (2/2)

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Satellite Orbit/Attitude Monitor (1/2)

• Monitor satellite real-time orbit/attitude telemetry during station contacts.

• Monitor GPS x/y/z/Vx/Vy/Vz/sma…• Monitor attitude roll/pitch/yaw angle

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Satellite Orbit/Attitude Monitor (2/2)

• Epoch Monitoring Viewer Example

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• Separation vector propagation• Update F10.7 solar flux index• Orbit determination & ephemeris generation• Contact event generation• NORAD file generation• ASCII ephemeris generation• Update table of leap second• Update ut2_minus_utc &

polar_motion_coefficients• Orbit altitude maneuver plan generation• Beta event generation• TBB event generation• Update MCC OASYS database

FDF Ops Procedures (1/15)

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FDF Ops Procedures (2/15) –Separation Vector Propagation

• This SOP propagates the separation vector delivered by launch vehicle to derive an orbit ephemeris and a state vector for satellite acquisition after launch vehicle separation.

• The separation vector is usually in UTC time and ECF position/velocity frame.

• The state vector to acquire a satellite is usually in NORAD 2-line elements format.

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FDF Ops Procedures (3/15) – Update F10.7 Solar Flux Index

• This SOP retrieves F10.7 value through internet website.

• F10.7 value is an index for the air drag magnitude of a day. It is related to the solar activity intensity of the day. The more intense the solar activity, the greater the F10.7 value and the air drag force in the space.

• F10.7 value shall be updated in the daily orbit propagation operations.

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FDF Ops Procedures (4/15) – Orbit Determination & Ephemeris Generation

• This SOP estimates an orbit state and propagates an orbit ephemeris for orbit analysis and prediction.

• OD is usually based on GPS position and/or velocity measurement collected onboard and downloaded in station contacts.

• Range rate is a backup OD measurement when GPS data is not available.

• OD results from azimuth/elevation measurement is usually not good enough for satellite acquisition. It is used for OD comparison only.

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FDF Ops Procedures (5/15) – Contact Event Generation

• This SOP generates the contact events based on the elevation masks of the ground stations.

• The contact events include the time of acquisition of signal, maximal elevation, lost of signal, contact duration, acquisition azimuth, and lost azimuth.

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FDF Ops Procedures (6/15) – NORAD File Generation

• This SOP generates the 2-line text file describing a satellite state vector for a NORAD propagator to propagate an orbit ephemeris for antenna program tracking.

• NORAD file example:

1 28254U 04018A 07065.04166667 .00000000 00000+0 36341-4 0 8652 28254 99.0076 131.9948 0002179 102.7577 185.4502 14.00751160142734

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FDF Ops Procedures (7/15) – NORAD File Description (1/2)

1 28254U 04018A 07065.04166667 .00000000 00000+0 36341-4 0 8652 28254 99.0076 131.9948 0002179 102.7577 185.4502 14.00751160142734

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FDF Ops Procedures (8/15) – NORAD File Description (2/2)

1 28254U 04018A 07065.04166667 .00000000 00000+0 36341-4 0 8652 28254 99.0076 131.9948 0002179 102.7577 185.4502 14.00751160142734

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A FDF Ops Procedures (9/15) – ASCII Ephemeris Generation

• This SOP transforms a binary orbit ephemeris file into an ASCII orbit ephemeris file.

• ASCII ephemeris file is for further orbit parameters/events prediction in MCC subsystem.

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FDF Ops Procedures (10/15) – Update Table of Leap Second

• This SOP updates the table of leap second in OASYS database.

• Whenever there is a UTC leap second announced by the International Earth Rotation and Reference Systems Service (IERS), the leap second table in OASYS shall be updated.

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FDF Ops Procedures (11/15) – Update ut2_minus_utc & polar_motion_coefficients

• This SOP updates ut2_minus_utc & polar_motion_coefficients in OASYS database.

• ut2_minus_utc corrects the tiny time difference between ut2 and UTC time system.

• Polar_motion_coefficients corrects the tiny angle difference (precession and nutation) between the Earth’s rotation axis and north pole axis.

• The update is done about once per half a year.

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FDF Ops Procedures (12/15) – Orbit Altitude Maneuver Plan Generation• This SOP generates an orbit maneuver plan

to change the orbit altitude.• The steps include:

– select orbit position for ignition– select fuel system, thrust type– update fuel mass, pressure, temperature– input target orbit altitude– create thrust profile– create maneuver plan report

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FDF Ops Procedures (13/15) – Beta Event Generation

• This SOP generates the events when the orbital Sun beta angle changes its sign.

• When the sun beta changes sign, FS3 needs to flip or flop its yaw angle to 180° or 0° for optimal sun pointing in solar array power input.

• This event occurs about once per two months.

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FDF Ops Procedures (14/15) – TBB Event Generation

• This SOP generates the entry/exit events when FS3 passes the TBB experiment regions on the Earth.

• The onboard TBB payload needs to change its experiment mode in/out the different regions.

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FDF Ops Procedures (15/15) – Update MCC OASYS Database

• This SOP updates the ASCII database for the OASYS run in MCC.

• Most updates are for the change in AOS/LOS elevation mask, ground station or region characteristics/number.

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OASYS Demonstration (1/7)

• Main Functions• Orbit Ephemeris Propagation• Orbit Determination• Orbit Maneuver Planning• Parameters/Events Generation• Ground Track Plotting

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OASYS Demonstration (2/7) –Main Functions

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OASYS Demonstration (3/7) –Orbit Ephemeris Propagation

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OASYS Demonstration (4/7) –Orbit Determination

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OASYS Demonstration (5/7) -Orbit Maneuver Planning

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OASYS Demonstration (6/7) -Parameters/Events Generation

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OASYS Demonstration (7/7) –Ground Track Plotting

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Thank You for Your Attention!Thank You for Your Attention!