Space simulator manual

Getting started: a first mission

1. Open the simulator and keep Earth: 400 km orbit selected. It is the easiest scenario for trying out manoeuvres. Earth launch starts from the surface with a two-stage launcher instead.
2. Check Start UTC and press Start scenario. Wait until “Native ephemerides” appears at the top. The mission opens paused.
3. In the Flight panel, choose the Earth as Reference body, Prograde as Thrust direction and set the Throttle. Press Ignite engine, then Resume.
4. Watch Propellant, Delivered Δv and Altitude. Press Pause and Shut down engine when you want to end the burn.
5. Set a Horizon of a few days and press Calculate in the Forecast section to compare the unpowered trajectory with the one under the current controls.

The date and coordinates received from Planetarium become starting values. Latitude and longitude only give the Earth launch site: they are not the ship's position in space.

Guided Earth–Moon mission (for the classroom)

The 🎓 Guided Earth–Moon mission button, at the top of the panel, takes the ship from Earth orbit to an orbit about 100 km above the Moon in seven stops: Earth orbit, launch window, departure burn, journey, course correction, approach and braking. Each stop explains what happens and why, shows the values to watch and has a single button that performs the manoeuvre with the simulator's ordinary controls: the flight is the same one you would fly by hand. The stops that let time run stop by themselves at the right moment. At departure you can choose 🧑‍🚀 Do it yourself: the ship stops at the ignition point, the pupil fires and stops the engine while watching the apoapsis climb towards the computed target (time slows down near the target) and compares the result with the computer’s; if it is too far off they can try again. At the end the Moon is framed close up with the current orbit in yellow.

Each stop also offers a question for the class and a “Did you know?” about the Apollo missions. The whole mission takes a few minutes; if a correction or a braking burn fails, the guide explains it and offers to advance one hour and try again. The link /simulatore/?guida opens the simulator with the guide ready, to share with students.

The teacher’s guide offers objectives by level, a 50-minute lesson plan, the answers to the questions and a printable pupil sheet.

Manual piloting

Reference body sets the body against which direction and telemetry are read. Destination sets the body whose distance and arrival are tracked. Changing the reference does not teleport the ship.

Prograde and retrograde

Thrust along the velocity relative to the chosen body, or against it. In Earth orbit a prograde burn usually raises the orbit; a retrograde one lowers it.

Radial and anti-radial

Thrust outwards along the body–ship line, or towards the body.

Normal and anti-normal

Thrust perpendicular to the local orbital plane. It changes the inclination, often at a high Δv cost.

Fixed

Pointing commanded by right ascension and declination in J2000 axes. The ship turns at most 2° per second: after an attitude change the thrust does not point in the new direction at once.

Time rate speeds up the simulation to seven days per second, but the simulator slows down automatically during launch, burns and approaches: the instrument bar then shows the actual rate and the reason. Separate stage becomes available for the launcher once the current stage has run out of propellant.

The instrument bar above the view sums up altitude, speed, propellant, Δv left and time rate, with the engine and pause buttons. Keyboard shortcuts, when you are not typing in a field:

Forecast, view and telemetry

Calculate propagates two copies of the current state: one with the engine off (grey line) and one that keeps the chosen direction and throttle until the propellant runs out (orange line). With the engine off the two lines coincide. The real flight is not changed. The light blue line is the path already flown; green, purple and red-orange are the verified departure, the correction and the braking of assisted navigation.

Use Camera to follow the ship, the Earth, the Sun or the destination. Drag the view to rotate it and use the wheel to zoom. The rendering uses a local scale so that very different distances stay visible; telemetry values come from the physical model. Sunlight lights one hemisphere of every body and leaves the other in shadow; ☀ Sun behind moves the camera to the Sun's side.

On a phone the view has a single bar at the top (camera, altitude, propellant, engine, pause); Legend opens from the bottom-left corner and lists only the lines on screen; the ⛶ button shows the view full screen (Esc or the same button to leave). With the phone held sideways the view goes full screen by itself once the mission has started.

View from the ship

From the ship (key 5) shows what the pilot sees: the camera sits on the ship and looks along its attitude, with celestial north up. Drag to look around, use the wheel to narrow or widen the field of view and double-click to look ahead again. The Prograde and Retrograde marks show the direction of motion relative to the reference body. In this view bodies have their real angular size: far from the planets they look like points. The stars are the real ones (Bright Star Catalogue and Hipparcos down to magnitude 8, about 41 000) in J2000 coordinates; the planets have the maps and IAU rotation used by the planetarium. Near the Earth a more detailed map is loaded and, below about 2 000 km, tiles down to about 0.6 km per pixel (NASA Blue Marble).

Delivered Δv / ideal Δv left

Change of velocity already provided by the engines / theoretical capacity left with the remaining propellant. The value left does not guarantee that a manoeuvre is feasible at the right moment.

Periapsis / apoapsis

Nearest / farthest point of the orbit relative to the reference body. An escape orbit has no finite apoapsis.

Radial / tangential speed

Components of the velocity relative to the chosen body. The radial speed tells whether you are moving away or closing in.

Assisted navigation to Mars and the Moon

This mode starts from the ship in a 400 km Earth orbit. It proposes an initial trajectory, then lets you verify and apply each manoeuvre. A numbered list shows the current step and, under each disabled button, the reason. Lambert and Hohmann estimates are preliminary: the verification uses finite burns and the simulator's complete gravity field.

1. Choose the Destination, the goal Flyby or Estimated circular orbit, the departure interval and the minimum and maximum days of flight. Press Search windows.
2. Press Use this window on a candidate. The mission is reset to the ship in Earth orbit at the chosen departure epoch; save first if you want to keep the previous flight.
3. Press Verify finite burn (optional). Read the closest approach, cost, final propellant and outcome. “Missed encounter” means the candidate does not arrive without further action.
4. Press Execute estimated departure. It is a real simulated burn: it uses propellant and moves time forward.
5. During the transfer, beyond one million km from the Earth (50 000 km towards the Moon), press Calculate course correction and then Execute estimated correction, only if the result and the remaining propellant are adequate. You can recalculate it after other manoeuvres.
6. During the approach, within one million km of Mars or 100 000 km of the Moon, press Verify periapsis braking. Execute verified braking is enabled only when the propagation confirms a bound orbit and a safe periapsis for two hours.

The altitude set in the planner is used for the preliminary estimate; the final orbit altitude depends on the actual encounter. The comparison between the manual flight and the plan appears when the flight reaches the selected arrival epoch.

Mission to the Moon

Choose Moon as destination: the search switches to flights of a few days (3 to 5 days proposed, 1 to 10 allowed) over a departure interval of up to 31 days. Each candidate starts from the low orbit the ship would have at that epoch and aims at a point beside the Moon, at the chosen altitude. The departure costs about 3.1 km/s, insertion into a low lunar orbit about 0.8 km/s.

The initial arc only considers the Earth's gravity, so without a correction the ship usually grazes or hits the Moon. The correction is enabled beyond 50 000 km from the Earth and up to six hours before arrival; it adjusts the trajectory until the predicted perilune is close to the chosen altitude. Braking is enabled within 100 000 km of the Moon, during the approach; the lowest accepted perilune is 50 km. There is no landing.

Saving and resetting

Save keeps the mission in this browser. Load restores the last local save. Reset returns the scenario to its initial state; it does not undo a single manoeuvre. If you change browser or device, or clear the site data, the local save will not be available.

The manual opens in a new tab, so you can read it without interrupting the mission left in the simulator.

What is simulated

The ship is propagated numerically under the gravity of the Sun, the Moon and the eight planets. Body positions come from the native Planetarium astronomy engine. The engines apply finite thrust: they burn propellant, reduce the mass and change the trajectory. An Earth launch also includes the planet's rotation, the atmosphere and drag.

The model does not include landing on other bodies, lift, winds, heating, pressure-dependent engine performance or attitude thrusters. Attitude is kinematic. Assisted navigation does not guarantee an arrival: it checks candidate manoeuvres and reports when an encounter or a capture fails. Do not use the results to plan real missions.

Common problems

“Astronomy engine unavailable”

Check the connection and try again. The flight cannot start without native ephemerides for the chosen epoch.

No launch windows found

Widen the departure interval or the range of flight days. Windows depend on the positions of the bodies at the chosen epoch.

The candidate misses the destination

This can happen: Lambert only gives a first estimate. Execute the departure and calculate a correction once away from the Earth; always check propellant and closest approach.

A correction or braking button is disabled

The geometric, timing or propellant conditions are not met yet: the reason is written under the button.

I only see one line

At first there is only the path already flown. With the engine off the two forecasts coincide; the other lines appear during assisted navigation.