F4IOZOlivier · radio amateur · JN18FS

Into orbit three, two, one… lift-off!

Set the launcher's tilt and thrust, cut the engine at the right moment: does your satellite stay in orbit, fall back, or fly off to the stars? All games

Ready for the countdown?

Three tries per mission. Tilt too early, the air brakes you; too late, you waste your propellant climbing. Cut when the apogee touches the target orbit!

Badges

First satelliteA first time into orbit.
The ISS's neighbourAn orbit within 20 km of the ISS's (420 km).
Spot onA PERFECT try.
ThriftyIn orbit with 15% of the Δv still in the tanks.
Sun-synchronousA GOOD try or better in sun-synchronous orbit.
GeostationaryAn orbit within 1,000 km of 35,786 km.
Mr HohmannA PERFECT try in geostationary orbit: QO-100 says hello.
Bon voyage!Too fast: escape the Earth.
Three out of threeThree GOOD tries or better in a game.
All-rounderFinish a game of each game.

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Falling without ever hitting the ground

A satellite keeps falling towards the Earth, but it goes so fast sideways that the ground curves away beneath it: that is an orbit. Gravity weakens with the square of the distance (1/r²), the speed it takes follows v = √(μ/r), μ = 398,600 km³/s².

At 420 km (the ISS): 7.66 km/s, a lap in an hour and a half. Slower, the satellite falls back into the air; at 10.83 km/s (√2 times as fast), it escapes the Earth for ever.
The launcher first climbs straight up to get out of the thick air, then tilts little by little towards the horizontal: the pitch program. Flat too early, the air brakes it; straight up too long, it spends its propellant against gravity.
Cutting the engine sets the apogee; at the apogee, a second burn raises the perigee and rounds the orbit off. A low orbit takes about 9.3 km/s of Δv in all, losses included.
The sun-synchronous orbit (500 to 800 km) passes near the poles, slightly backwards: the Earth's rotation no longer helps the launcher, it even brakes it a little.
The Hohmann transfer: from 250 km, +2.44 km/s at perigee start an ellipse rising to 35,786 km in 5.3 h; up there, +1.47 km/s make it a circle at 3.07 km/s. A lap there takes 1,436 min, a sidereal day: QO-100 stays over 25.9° E.

The mark: how far the perigee and the apogee are from the target orbit. PERFECT within the mission's tolerance (20 km in low orbit, 250 km in geostationary), then GREAT, GOOD, OK; a bonus for the propellant left.

Simplified, but right Gravity, orbital speed and the Hohmann transfer are the real ones. The rest is simplified: a single stage of constant thrust, an autopilot that only keeps it from sinking while the engine burns, a flight in the orbit's plane, an atmosphere halving every 6 km, the Earth's rotation as a push at the start.