What input does the calculator require?

It requires a valid two-line element set: TLE line 1 and TLE line 2.

What happens if I leave the propagation time empty?

The calculator propagates the satellite at the TLE epoch.

Which orbital elements are displayed?

It displays the six classical Keplerian elements, plus derived semi-major axis and orbital period.

Can I calculate visibility from a ground location?

Yes. Enter observer latitude and longitude to calculate azimuth, elevation, and visibility.

How is Doppler shift calculated?

Enter a transmit frequency in MHz along with an observer location and propagation time to calculate the Doppler shift.

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Astronomy

Keplerian Orbital Element / TLE / SGP4 Satellite Position Calculator

Parse a TLE, show the six Keplerian elements (with derived semi-major axis & period), propagate with SGP4 for ECI position, sub-satellite point, ground track, elevation visibility and Doppler shift

Details

What this tool helps you do

For amateur-satellite operators (AMSAT / SatNOGS), CubeSat teams and space-awareness educators. Paste a two-line TLE: fields are parsed and checksums validated; the six classical Keplerian elements are shown with the semi-major axis and orbital period derived from mean motion; SGP4 propagates the satellite's ECI position at a chosen time, computes the geodetic sub-satellite point, a one-orbit ground track, azimuth/elevation and visibility against a ground observer, and the Doppler shift for a transmit frequency. Based on satellite.js (WGS72 SGP4). Pure local computation, no network.

Execution

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Fill in the form, run the tool, and review the result in one place.

Prepared example runs

Click an example to fill the form automatically. File inputs still need an upload.

2 examples

ISS position and ground track at epoch

Propagate the ISS TLE at its epoch to show the sub-satellite point, altitude and a one-orbit ground track.

{
  "type": "html"
}

Doppler shift for a 437.8 MHz downlink

Compute elevation, visibility and the Doppler shift for an observer during an ISS pass on the 70 cm amateur band.

{
  "type": "html"
}

Inputs

Set the required fields, then run the tool.

7 options

ContentPaste or type the main input values.3

TLE line 1textareaRequiredTLE line 2textareaRequiredPropagation time (UTC)textOptional

SettingsAdjust formats, ranges, numbers, and modes.4

Observer latitudenumberOptionalObserver longitudenumberOptionalTransmit frequency (MHz)numberOptionalGround-track samplesnumberOptional

Result

Ready for a run

Run the tool to preview files, text, structured data, or streamed output here.

Samples

Keplerian Orbital Element / TLE / SGP4 Satellite Position Calculator

What this tool helps you do

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Prepared example runs

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Key facts

Overview

When to use

How it works

Use cases

Examples

1. ISS position and one-orbit ground track

2. Doppler estimate for a 437.8 MHz downlink

FAQ

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