satellite

import "github.com/joshuaferrara/go-satellite"

Intro

I decided to port the SGP4 library to GoLang as one of my first projects with the language. I've included a test suite to ensure accuracy.

Usage

Constants

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const DEG2RAD float64 = math.Pi / 180.0

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const RAD2DEG float64 = 180.0 / math.Pi

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const TWOPI float64 = math.Pi * 2.0

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const XPDOTP float64 = 1440.0 / (2.0 * math.Pi)

func ECIToLLA

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func ECIToLLA(eciCoords Vector3, gmst float64) (altitude, velocity float64, ret LatLong)

Convert Earth Centered Inertial coordinated into equivalent latitude, longitude,
altitude and velocity. Reference: http://celestrak.com/columns/v02n03/

func GSTimeFromDate

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func GSTimeFromDate(year, mon, day, hr, min, sec int) float64

Calc GST given year, month, day, hour, minute and second

func JDay

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func JDay(year, mon, day, hr, min, sec int) float64

Calc julian date given year, month, day, hour, minute and second the julian date
is defined by each elapsed day since noon, jan 1, 4713 bc.

func Propagate

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func Propagate(sat Satellite, year int, month int, day, hours, minutes, seconds int) (position, velocity Vector3)

Calculates position and velocity vectors for given time

func ThetaG_JD

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func ThetaG_JD(jday float64) (ret float64)

Calculate GMST from Julian date. Reference: The 1992 Astronomical Almanac, page
B6.

type LatLong

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type LatLong struct {
	Latitude, Longitude float64
}

Holds latitude and Longitude in either degrees or radians

func LatLongDeg

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func LatLongDeg(rad LatLong) (deg LatLong)

Convert LatLong in radians to LatLong in degrees

type LookAngles

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type LookAngles struct {
	Az, El, Rg float64
}

Holds an azimuth, elevation and range

func ECIToLookAngles

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func ECIToLookAngles(eciSat Vector3, obsCoords LatLong, obsAlt, jday float64) (lookAngles LookAngles)

Calculate look angles for given satellite position and observer position obsAlt
in km Reference: http://celestrak.com/columns/v02n02/

type Satellite

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type Satellite struct {
	Line1 string
	Line2 string
}

Struct for holding satellite information during and before propagation

func ParseTLE

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func ParseTLE(line1, line2 string, gravConst Gravity) (sat Satellite)

Parses a two line element dataset into a Satellite struct

func TLEToSat

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func TLEToSat(line1, line2 string, gravConst Gravity) Satellite

Converts a two line element data set into a Satellite struct and runs sgp4init

type Vector3

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type Vector3 struct {
	X, Y, Z float64
}

Holds X, Y, Z position

func ECIToECEF

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func ECIToECEF(eciCoords Vector3, gmst float64) (ecfCoords Vector3)

Convert Earth Centered Intertial coordinates into Earth Cenetered Earth Final
coordinates Reference: http://ccar.colorado.edu/ASEN5070/handouts/coordsys.doc

func LLAToECI

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func LLAToECI(obsCoords LatLong, alt, jday float64) (eciObs Vector3)

Convert latitude, longitude and altitude into equivalent Earth Centered
Intertial coordinates Reference: The 1992 Astronomical Almanac, page K11.

func NewSpacetrack

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func NewSpacetrack(username, password string) *Spacetrack

Initialise a spacetrack API for fetching TLEs

func Spacetrack.GetTLE()

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func (s *Spacetrack) GetTLE(catid uint64, ts time.Time, gravConst Gravity) (Satellite, error)

Get an initialized Satellite based on the latest TLE before the given time.