Editing SimTX Guide/Satellites

{{SimTX Guide navigation}}
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 ===
[[File:SimTX Guide Satellites orbit step.webp|thumb|center|800px|alt=Launch a satellite, Orbit step: preset cards Space station, Sun-synchronous, Geostationary and Custom, the More orbits link, altitude and inclination sliders at 420 km and 51.6°, the starting point, and orbit time, speed, footprint radius and max Doppler; the globe shows the new orbit.|The Orbit step of Launch a satellite with the Space station preset, and the planned orbit on the globe.]]
{| class="wikitable"
! 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 ===
{| class="wikitable"
! 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 ===
[[File:SimTX Guide Satellites payload step.png|thumb|center|777px|alt=Payload step with a Turnstile antenna, a 5 W radio with a link check of -105 dBm, the attitude options Earth-pointing, Spinning and Fixed in space, a Yaw field, and Back and Next: Launch buttons.|The Payload step with one antenna, one radio with its link check, and the attitude choices.]]
{| class="wikitable"
! 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 ==
[[File:SimTX Guide Satellites passes.png|thumb|center|380px|alt=Passes panel seen from Demo hilltop listing six passes with time, highest elevation and direction; the 46° pass is selected, with its sky plot and its rise, highest, set, duration and Doppler figures.|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.

# 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 ==
[[File:SimTX Guide Satellites deorbit.webp|thumb|center|800px|alt=Satellite details with a Deorbit Nightjar-1 card: reentry in 29 min over 79.0° N, 100.4° E, a 179 m/s retrograde burn, one session ending at reentry, Cancel and Fire deorbit burn; the globe shows a red dashed path to a Reentry 05:59 UTC marker.|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.
# 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.

[[Category:SimTX Guide]]