Moonshot is a simplified but physically grounded simulation of a lunar free-return trajectory. While some scales are compressed for playability, the underlying physics uses real values from our solar system. This page explains both what the game simulates and the broader science of orbital mechanics.
Everything in this game is governed by Newton's Law of Universal Gravitation: every object with mass attracts every other object with mass.
F = G × M × m / r2Where G = 6.674 × 10-11 N·m2/kg2 is the gravitational constant, M and m are the masses of two bodies, and r is the distance between their centers. In the game, this determines how strongly Earth and the Moon pull on your capsule at every moment.
The visual scale is compressed so both Earth and Moon are visible on screen. All distances, velocities, and gravitational forces use the real values above.
An orbit is simply falling toward a body while moving sideways fast enough to keep missing it. The balance between your velocity and the gravitational pull determines the shape of your path.
To orbit Earth at its surface (ignoring atmosphere), you'd need to travel at about 7,900 m/s. At the Moon's distance, orbital velocity drops to about 1,020 m/s. The further you are from a body, the slower you need to go to maintain orbit.
v = sqrt(G * M / r)Depending on your speed and direction, orbits can be:
In Moonshot, your capsule follows an elliptical or hyperbolic path that gets bent by both Earth's and the Moon's gravity.
When only two bodies interact (like a satellite orbiting Earth), the math has exact solutions — Kepler's laws describe every possible orbit. But add a third body — in our case, the Moon — and there is no general closed-form solution. This is the famous three-body problem.
The only way to predict what happens is to simulate it step by step, which is exactly what Moonshot does. The game calculates the gravitational pull from both Earth and the Moon on your capsule 60 times per game-second, updating position and velocity each time. This is the same fundamental approach NASA uses, just with fewer decimal places.
The simulation uses Velocity Verlet integration, a method that conserves energy better than simpler approaches like Euler's method. At each step:
This two-stage approach means the simulation stays accurate even during close encounters with the Moon, where gravity changes rapidly.
Getting to the Moon isn't about pointing at it and firing. In reality, a spacecraft first enters low Earth orbit (~200 km altitude, ~7,800 m/s), then performs a trans-lunar injection (TLI) burn to boost into a high elliptical orbit whose apoapsis reaches the Moon's distance.
In Moonshot, we simplify this: you launch directly from Earth's surface at the full velocity. The optimal launch speed in the game is around 11,100 m/s — just under Earth's escape velocity of 11,186 m/s. This puts you on a trajectory that reaches the Moon's orbit without quite escaping Earth's gravity, allowing the Moon to bend your path.
The angle matters because the Moon is a moving target. It orbits Earth every 27.3 days, so you need to lead it — launching ahead of where the Moon currently is. In the game, angles around 40–55° tend to produce the best encounters.
A gravity assist (or slingshot) uses a body's gravity to change a spacecraft's speed and direction without using fuel. As your capsule approaches the Moon, the Moon's gravity accelerates it; as it recedes, gravity decelerates it. But because the Moon is moving, the net effect can add or subtract energy.
In Moonshot, the slingshot around the Moon is what bends your trajectory back toward Earth on a free-return trajectory — one where no additional burns are needed to get home. This is the same principle used by Apollo 13 after its service module explosion: the crew swung around the Moon and let gravity carry them home.
The closer you pass to the Moon, the stronger the gravitational deflection. A pass at 100 km sharply bends your trajectory; a pass at 9,000 km barely curves it. This is why Moonshot rewards close approaches — they demonstrate precise orbital mechanics control.
A free-return trajectory is a flight path that uses the Moon's gravity to return the spacecraft to Earth without any course corrections. It's the safest possible lunar trajectory because if anything goes wrong, you're already heading home.
The entire Artemis I mission in Moonshot is based on this concept: you must find the exact launch parameters that send the capsule past the Moon and back to Earth, with no mid-course burns allowed.
In reality, free-return trajectories are a narrow family of solutions. Slight changes in velocity (even 1 m/s) can mean the difference between a clean return and a decades-long orbit. The game captures this sensitivity — the success window is only about 20–30 m/s wide.
In mission planning, each body is considered to dominate a sphere of influence (SOI) — the region where its gravity is the primary force. Earth's SOI extends about 925,000 km; the Moon's is about 66,000 km.
Real mission software often uses "patched conics" — solving two-body problems within each SOI and stitching them together at boundaries. Moonshot instead simulates all gravitational forces simultaneously, which is more physically accurate but makes the math harder (and the three-body problem inescapable).
For playability, Moonshot makes several simplifications:
Real lunar missions involve layers of complexity beyond this simulation:
This game was inspired by the Artemis program and NASA's return to the Moon.
Special thanks to the crew of Artemis II, the first crewed mission to the Moon in over 50 years:
Their mission — a lunar flyby and return, just like the one you're simulating — represents humanity's next step back to the Moon and forward to Mars.
And to everyone at NASA, the Canadian Space Agency, the European Space Agency, JAXA, and the thousands of engineers, scientists, and dreamers who make it possible: thank you.
Ad astra.