PERIAPSIS

Goal

Kaleva went dark. Your crew eats a day of supplies every day. Salvage drifts on its own orbits all over the system — reach it and grab it before the beacons die. Your score is how many days you survive.

Controls

On a phone: hold BURN, steer with ⟲ ⟳, tap the mode strip, tap ◆ beacons, pinch to zoom.

The physics is real

• Every body pulls on you, always. Your ship is integrated with an adaptive Dormand–Prince 5(4) solver in the gravity of the star, all planets and moons. Planets ride fixed Kepler orbits; tides and three-body effects are real.
• The cyan line is your future, computed with the same physics. Pe/Ap markers show periapsis and apoapsis; violet ghosts show encounters.
• Rocket equation. Δv = Isp·g₀·ln(m_wet/m_dry). Every kilo of supplies, armour or tank costs Δv.
• Orbits are counter-intuitive. Burn prograde and the far side of your orbit rises. A lower orbit is faster — to catch something ahead of you, slow down.
• Oberth effect. Burns are most effective deep in a gravity well, at periapsis.
• Gravity assists trade momentum with a moving moon or planet: free Δv.
• Aerobraking. Dip into an atmosphere to shed speed for free — drag ∝ ρv², heating ∝ ρ^½v³.
• Heat. Sunlight falls off as 1/r². Radiators reject σT⁴. Fly too close to Ukko and the hull cooks.
• Flares. Ukko's particle storms travel outward at ~1500 km/s. Hide in a body's shadow (cyan cones) or in Kaleva's magnetosphere.
• Debris damage scales with your speed relative to the local orbiting particles. Match their orbit and rings become safe.
• Ion engines run on sunlight: thrust ∝ 1/r², zero in shadow.
• Set up burn is an intercept assistant: it searches a single prograde/retrograde burn with two-body Kepler math. You still fly it in the full n-body simulation — the cyan line tells the truth.