SimTX Guide/Satellites: Difference between revisions

Revision as of 19:59, 24 October 2026

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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

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

The new satellite's details open after the launch.

Orbit presets

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

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

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.

Select the satellite in the Stations tab.
Under Passes, choose one of your ground stations in Seen from.
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:

In the Transmit or Receive tab, choose a satellite under Track a satellite.
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

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

In the satellite's details, press Deorbit…. The globe shows where it will fall.
Check when and where it reenters, the burn and the sessions that will end.
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.

@@ Line 1: / Line 1: @@
 {{SimTX Guide navigation}}
-A '''satellite''' is a station in orbit, designed and launched by a SimTX user. Every satellite belongs to an account; there are no built-in ones. Like a ground station it has antennas and radios, and many sessions can use it at the same time.
+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.
-A satellite is '''sealed''' at launch. Its orbit, antennas, radios and attitude can't be changed afterwards; only the name, callsign and visibility can. To change anything else, deorbit it and launch a new one.
+== Launch a satellite ==
+# In the '''Stations''' tab, select '''Mine''' and press '''Launch satellite'''. The globe shows the orbit as you design it.
+# '''Orbit''': choose a preset and adjust it (see below). Press '''Next: Payload'''.
+# '''Payload''': set the antennas, radios, attitude, name, callsign and visibility. Press '''Next: Launch'''.
+# '''Launch''': check the summary, tick '''Sealed after launch''' and press '''Launch satellite'''.
-== Launch a satellite ==
+The new satellite's details open after the launch.
-In the '''Stations''' tab, select '''Mine''' and press '''Launch satellite'''. The '''Launch a satellite''' workspace opens beside the globe, which shows the orbit as you design it. There are three steps: '''Orbit''', '''Payload''' and '''Launch'''. Use '''Next''' and '''Back''' to move between them.
-=== Orbit ===
+=== Orbit presets ===
-Choose a starting point:
 {| class="wikitable"
 ! Preset !! Orbit
@@ Line 19: / Line 21: @@
 |-
 | '''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.
 |}
-'''More orbits''' adds '''Polar''', '''Equatorial''' and '''Molniya'''. Changing a value that a preset fixes turns the design into '''Custom'''.
+'''Polar''', '''Equatorial''' and '''Molniya''' are under '''More orbits'''. Editing a value that a preset fixes switches to '''Custom'''.
-The controls describe the orbit in plain terms:
+=== Orbit controls ===
-* '''Altitude''': how high the satellite flies, from 200 to 40,000 km. A higher satellite moves more slowly, sees a larger area and stays in view longer, but is farther away, so its signal is weaker. Choose '''Circular''' for one altitude, or '''Elliptical''' to set the '''Lowest point''' and '''Highest point''' and whether the highest point is over the '''North''' or the '''South'''.
+{| class="wikitable"
-* '''Inclination''': the tilt of the orbit against the equator. At 0° the satellite stays over the equator; at 90° it passes over both poles. Above 90° it moves against the Earth's rotation. The track reaches north and south up to the latitude of the inclination (or 180° minus it).
+! Control !! Meaning
-* '''Sun-synchronous''': the app sets the inclination for the altitude, slightly more than 90°, so that the satellite passes each place at the same local time.
+|-
-* '''Geostationary''': at about 35,800 km over the equator the satellite turns with the Earth and stays fixed in your sky. Set the longitude under '''Parked over longitude'''. From a given place it is either always in view or never.
+| '''Circular''', '''Elliptical''' || One altitude, or a '''Lowest point''' and '''Highest point''' with the highest point over the '''North''' or '''South'''.
-* '''Molniya''': a long, elliptical orbit at 63.4° whose high point hangs over high northern latitudes for hours on each orbit. Set the longitude under '''Highest point over longitude'''.
+|-
-* '''Starting point''': where the first orbit begins, as latitude and longitude, heading '''Northbound''' or '''Southbound'''. '''Pick on globe''' places it by clicking the globe; '''Over my station…''' starts it over one of your ground stations.
+| '''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.
+|}
-'''Orbital elements''' shows the orbit as numbers and lets you type them directly. '''Back to guided controls''' returns to the controls above.
+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.
-The figures beside the form update as you design: '''Orbit takes''' (the period), '''Speed''', '''Footprint radius''' (how far from the point below it the satellite is in view), '''Max Doppler''', '''Coverage''', and how often it passes over each of your ground stations. If the orbit can't be flown, for example because the lowest point is too low, a warning says why.
 === Payload ===
-* '''Antennas''': one to four. Satellite antennas are fixed to the body and work in free space; '''Rotation on the body''' turns an antenna on the body.
+{| class="wikitable"
-* '''Radios''': up to eight, each with a '''Power cap'''. Small satellites run 1 to 10 W. '''Link check''' estimates how strong the satellite would be at a ground station at 30° elevation on 437.8 MHz.
+! Section !! Contents
-* '''Attitude''': how the satellite holds itself. '''Earth-pointing''' keeps one face toward the ground, with a '''Yaw''' angle. '''Spinning''' spins for stability, sweeping its antenna pattern past you; set the '''Spin rate''' and what it '''Spins around'''. '''Fixed in space''' holds one direction among the stars.
+|-
-* '''Name and visibility''': the satellite's '''Name''' and '''Callsign''', and '''Public''' or '''Unlisted'''. A public satellite is shown on the map, and anyone signed in can receive from it. An unlisted satellite can only be used by you, though others still hear it transmit.
+| '''Antennas''' || One to four antennas, fixed to the body. '''Rotation on the body''' turns an antenna on the body.
+|-
-=== Launch ===
+| '''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.
-Check the summary. Each line has an '''Edit''' link back to its step. Tick '''Sealed after launch''' and press '''Launch satellite'''. The new satellite's details open.
+|-
+| '''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 to see:
+Select a satellite in the '''Stations''' tab.
-* '''Right now''': altitude, speed, the point it is over, footprint radius and how long an orbit takes;
+* '''Right now''': altitude, speed, the point below it, footprint radius and orbit time.
-* '''On this station''': the sessions running on it;
+* '''On this station''': sessions running on it.
-* '''Passes''' and '''Doppler now''' (see below);
+* '''Passes''' and '''Doppler now'''.
-* its antennas and radios.
+* '''Edit''' changes the name, callsign and visibility.
-'''Edit''' changes only the name, callsign and visibility.
 == Passes ==
-A '''pass''' is the time a satellite is above your horizon. It starts when the satellite rises (AOS, acquisition of signal) and ends when it sets (LOS, loss of signal). The '''elevation''' is how high above the horizon it is, from 0° at the horizon to 90° straight overhead. A pass with a high maximum elevation is longer and closer, so the signal is stronger. A pass that stays a few degrees above the horizon is short and weak.
+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.
-In the satellite's details, the '''Passes''' panel lists the next passes over one of your ground stations, chosen under '''Seen from'''. Each row shows the time in UTC, the highest elevation and the direction it crosses the sky. Select a pass to see a 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.
+# Select the satellite in the '''Stations''' tab.
+# Under '''Passes''', choose one of your ground stations in '''Seen from'''.
+# 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.
-Passes also appear elsewhere:
+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 '''Mine''' list shows the next pass of each satellite over your first ground station;
-* a ground station's details list the '''Satellites over this station''';
-* in the '''Transmit''' and '''Receive''' tabs, choosing a satellite under '''Track a satellite''' shows the next pass.
-All times are UTC in simulation time, the clock shown 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.
-Passes are predicted against a flat horizon. Hills and mountains around a station can hide a satellite that is low in the sky, so a low pass, or the first and last minutes of a pass, may be silent.
+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 moves at several kilometres per second. While it comes toward you its signal arrives higher in frequency, and while it moves away, lower. On 70 cm the shift reaches several kilohertz during a pass. The '''Doppler now''' panel in the satellite's details shows the current shift for a frequency you enter.
+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, choose the satellite under '''Track a satellite''' in the '''Station''' section of the '''Transmit''' or '''Receive''' tab. '''Correct Doppler''' turns on with it:
+To correct it:
-* when receiving, the tuning follows the shift, so the satellite stays at the same place in your SDR program;
+# In the '''Transmit''' or '''Receive''' tab, choose a satellite under '''Track a satellite'''.
-* when transmitting, the frequency is shifted the other way, so the signal arrives on frequency at the satellite.
+# Leave '''Correct Doppler''' ticked.
-On a ground station with a rotator, choosing a satellite also makes the antenna follow it; see [[SimTX Guide/Rotators and tracking]].
+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 ==
-A satellite appears in '''Transmit from''' and '''Receive at''' like a ground station.
+Choose the satellite in '''Transmit from''' or '''Receive at'''.
-* '''Transmitting from a satellite''' sends a downlink: the signal leaves the satellite's antenna at its position in orbit, and moves with it.
+* Transmitting from it sends a downlink from the satellite's position in orbit.
-* '''Receiving at a satellite''' hears the uplink: the signals that reach the satellite's antenna in orbit.
+* Receiving at it hears the uplink, the signals that reach the satellite.
-On a satellite the tracking control is called '''Doppler-correct toward''' and takes one of your ground stations. A transmission from the satellite is then corrected to arrive on frequency at that station, and reception at the satellite is corrected for signals from it.
+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.
-Other people hear a public satellite by receiving at their own ground station while it passes, or receive at it directly as a '''Public station'''.
 == Deorbit ==
-A deorbit is a real retrograde burn, not a deletion.
+A deorbit is a retrograde burn that brings the satellite down.
-# In the satellite's details, press '''Deorbit…'''. The app works out where and when the satellite will reenter and shows the fall on the globe.
+# In the satellite's details, press '''Deorbit…'''. The globe shows where it will fall.
-# The confirmation shows how long until it reenters and over which place, the size of the burn and how many sessions will end.
+# Check when and where it reenters, the burn and the sessions that will end.
-# Press '''Fire deorbit burn''' to confirm, or '''Cancel'''. The burn can't be undone.
+# Press '''Fire deorbit burn'''. The burn can't be undone.
-After the burn the satellite is marked '''Deorbiting'''. It keeps working on its falling orbit: sessions run, passes are listed and others can still use it. The '''Reentry''' panel counts down to the moment it reaches 80 km and burns up. At that moment its sessions end and it disappears from the map.
-== See also ==
+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.
-* [[SimTX Guide/Stations]]
-* [[SimTX Guide/Rotators and tracking]]
-* [[SimTX API/Satellites]]: the orbit model and satellites in the developer reference.
 [[Category:SimTX Guide]]