SimTX Guide/Satellites

A satellite is a station in orbit that you design and launch. It has antennas and radios like a ground station. At launch it is sealed: its orbit, antennas, radios and attitude can't be changed, only its name, callsign and visibility. To change anything else, deorbit it and launch a new one.

Launch a satellite

1. In the Stations tab, select Mine and press Launch satellite. The globe shows the orbit as you design it.
2. Orbit: choose a preset and adjust it (see below). Press Next: Payload.
3. Payload: set the antennas, radios, attitude, name, callsign and visibility. Press Next: Launch.
4. Launch: check the summary, tick Sealed after launch and press Launch satellite.

The new satellite's details open after the launch.

Orbit presets

The Orbit step of Launch a satellite with the Space station preset, and the planned orbit on the globe.

Preset	Orbit
Space station	Low orbit at 420 km and 51.6° that passes over most of the world.
Sun-synchronous	Crosses each place at the same local time every day.
Geostationary	Stays over one longitude, about 35,800 km up.
Custom	Set altitude, shape and tilt yourself.
Polar	Passes over both poles and sees the whole Earth each day.
Equatorial	Stays over the tropics with frequent passes near the equator.
Molniya	Long, high loops that hang over high latitudes for hours.

Polar, Equatorial and Molniya are under More orbits. Editing a value that a preset fixes switches to Custom.

Orbit controls

Control	Meaning
Circular, Elliptical	One altitude, or a Lowest point and Highest point with the highest point over the North or South.
Altitude	200 to 40,000 km. Higher orbits are slower, see more of the Earth and stay in view longer, but the signal is weaker.
Inclination	The tilt against the equator: 0° stays over the equator, 90° crosses the poles, above 90° runs against the Earth's rotation. The track reaches north and south to the latitude of the inclination. Sun-synchronous sets it for you.
Parked over longitude	Geostationary: where the satellite stays. From a given place it is always in view or never.
Highest point over longitude	Molniya: where its high point hangs.
Starting point	Where the first orbit begins, Northbound or Southbound. Pick on globe or Over my station… places it.
Orbital elements	The orbit as numbers, for typing exact values. Back to guided controls returns to the controls.

Beside the form, Orbit takes, Speed, Footprint radius, Max Doppler, Coverage and the passes per day over each of your ground stations update as you design. A warning appears if the orbit can't be flown.

Payload

The Payload step with one antenna, one radio with its link check, and the attitude choices.

Section	Contents
Antennas	One to four antennas, fixed to the body. Rotation on the body turns an antenna on the body.
Radios	Up to eight radios, each with a Power cap. Small satellites run 1 to 10 W. Link check estimates the signal at a ground station at 30° elevation on 437.8 MHz.
Attitude	Earth-pointing keeps one face down, with a Yaw angle. Spinning spins at a Spin rate around an axis chosen under Spins around. Fixed in space holds one direction among the stars.
Name and visibility	Name, Callsign, and Public or Unlisted. An unlisted satellite can only be used by you, but others still hear it transmit.

Satellite details

Select a satellite in the Stations tab.

• Right now: altitude, speed, the point below it, footprint radius and orbit time.
• On this station: sessions running on it.
• Passes and Doppler now.
• Edit changes the name, callsign and visibility.

Passes

Passes of Nightjar-1 over Demo hilltop, with the sky plot of the selected pass.

A pass runs from AOS, when the satellite rises above your horizon, to LOS, when it sets. Its elevation is its height above the horizon, from 0° to 90° overhead. High passes are longer and stronger than low ones.

1. Select the satellite in the Stations tab.
2. Under Passes, choose one of your ground stations in Seen from.
3. Select a pass in the list to see its sky plot and when it Rises, is Highest and Sets, how long it Lasts and its Doppler range.

For a geostationary satellite the panel says whether it is always in view and where to point. Times are UTC simulation time, as in the map legend.

The next pass also shows in the Mine list, under Satellites over this station in a ground station's details, and under Track a satellite in the Transmit and Receive tabs.

Hills and mountains around a station can hide a satellite that is low in the sky, so the start and end of a pass, or a whole low pass, may be silent.

Doppler

A satellite's signal arrives higher in frequency while it comes toward you and lower while it moves away, by several kilohertz on 70 cm. Doppler now in the satellite's details shows the shift for a frequency you enter.

To correct it:

1. In the Transmit or Receive tab, choose a satellite under Track a satellite.
2. Leave Correct Doppler ticked.

On receive, the tuning follows the shift. On transmit, the signal is shifted so it arrives on frequency at the satellite.

Transmit from or receive at a satellite

Choose the satellite in Transmit from or Receive at.

• Transmitting from it sends a downlink from the satellite's position in orbit.
• Receiving at it hears the uplink, the signals that reach the satellite.

The tracking control is then Doppler-correct toward one of your ground stations: transmissions arrive on frequency there, and signals from there are received on frequency.

Deorbit

The deorbit confirmation for Nightjar-1, with the falling path and the reentry point on the globe.

A deorbit is a retrograde burn that brings the satellite down.

1. In the satellite's details, press Deorbit…. The globe shows where it will fall.
2. Check when and where it reenters, the burn and the sessions that will end.
3. Press Fire deorbit burn. The burn can't be undone.

The satellite is then Deorbiting. It keeps working until it reaches 80 km and burns up; the Reentry panel counts down to that moment. Its sessions then end and it leaves the map.