Sol Program

Build it. Fly it. Bring it home.

Play Sol Program — free, in your browser

Run a space program from its first hop to a landing on Titan. Design a real rocket — engines, tanks, boosters, payload — and watch the delta-v and thrust-to-weight decide whether it flies. Then fly it yourself: throttle up, hold a gravity turn, stage when the booster burns out, and circularise at apoapsis. Orbits are true Keplerian conics with apoapsis, periapsis and patched-conic encounters, so a maneuver node shows the exact orbit your burn will produce before you make it. Fourteen missions across nine worlds, from a 25 km hop to Luna, Mars, Phobos, Europa and Titan.

Controls

• W / S — Throttle up and down
• Z / X — Full throttle / cut
• A / D — Pitch the vehicle
• Space — Stage separation
• T — Attitude hold, Tab — hold mode
• M — Map view, C — Camera, N — Maneuver node
• Y — Deploy payload
• , / . — Time warp
• Throttle slider — Engine power
• MAX / CUT — Full throttle and engine shutdown, above and below the slider
• Tilt buttons — Pitch the vehicle
• STAGE — Separate the spent stage
• MAP / CAM / NODE — View and planning
• ◀ ▶ — Time warp

How to Play Sol Program

Every mission starts in the Vehicle Assembly building. Pick a payload that can do what the mission needs, then add stages until the delta-v readout clears the mission requirement and thrust-to-weight is above about 1.2.

Orbit is a speed, not a height. Launch vertically, then pitch over east as you climb so the engine is building horizontal velocity, not just altitude.

Watch apoapsis and periapsis on the HUD. Raise apoapsis on the way up, coast to it with the engine off, then burn prograde there to lift periapsis clear of the atmosphere.

Stage the moment a tank reads empty — an empty tank is dead mass, and the HUD calls the burnout.

Press N to place a maneuver node and drag its handles. The dashed orbit is exactly what the burn will produce, and the panel tells you how long the burn takes so you can start early.

Time warp only works outside the atmosphere with the engine off. It drops back to 1x automatically when it stops being safe.

Sol Program Strategy Guide

1. A gravity turn is cheaper than a vertical climb. Start tipping at about 2 km and be roughly horizontal by 45 km — every degree away from prograde during a burn is delta-v spent on nothing.
2. Burn at the apsis. Raising apoapsis is cheapest at periapsis and vice versa; that is the whole reason a maneuver node has a position as well as a size.
3. Vacuum engines are terrible at sea level and superb above it. The configurator will not stop you putting one on the pad, but the advisory panel will tell you why not to.
4. Tank fabrication research is the best credits you can spend: lighter tanks buy delta-v straight out of the rocket equation, on every vehicle you ever build.
5. For a landing on an airless world, kill horizontal velocity first and descend vertically. Coming down at an angle means the gear takes sideways load it is not rated for.
6. Reentry wants to be shallow. Aim for a periapsis around 20 km rather than driving straight down — the same energy shed over more time is the difference between a capsule and a meteor.
7. Watch the transfer window readout before leaving for another planet. Departing at the wrong phase angle costs far more than waiting does.

Questions & Answers

What is Sol Program?

Sol Program is a free browser-based space program game. You design a multi-stage rocket, fly it off the pad yourself, and take it through fourteen missions from a 25 km hop to a landing on Titan.

Is Sol Program free?

Yes, Sol Program is completely free to play in your browser with no downloads required.

How realistic is the orbital mechanics?

Orbits are real Keplerian conics. The HUD shows apoapsis, periapsis, eccentricity and orbital period, and the drawn trajectory is the same two-body solution the ship actually flies. Patched conics detect encounters, so the map tells you when you will arrive at another world and what your orbit around it will be.

How does rocket staging work?

A vehicle is a stack of stages, each with its own engines, tanks and propellant. Mass, thrust and specific impulse are all simulated, so acceleration rises as propellant burns off and jumps again the moment you drop a spent stage. If you carry an empty tank, you pay for it in delta-v.

What are maneuver nodes?

A maneuver node is a burn planned in advance. Place one anywhere on your orbit, drag its prograde and radial handles, and the map draws the exact orbit the burn will produce — along with the delta-v it needs and how long it will take at full throttle.

What worlds can you visit?

Nine: the Sun, Earth, Luna, Mars, Phobos, Jupiter, Europa, Saturn and Titan. Earth, Mars and Titan have atmospheres that both help and hurt, and Saturn has rings.

Do I need to understand orbital mechanics to play?

No. The first missions teach throttle, staging and the gravity turn one at a time, every mission has a flight director’s note telling you how to fly it, and a failed flight explains exactly what went wrong and what to change.

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