Approximately Up Thrust-to-Weight Calculator

Every Approximately Up crash story starts the same way: “I thought it would fly.” Thrust-to-weight ratio (TWR) is the quickest sanity check between a successful launch and a pad explosion. This page explains TWR in the context of Earth’s gravity, vacuum hops to the Moon, and heavy delivery missions — then lets you plug in numbers with the interactive calculator below.

What is thrust-to-weight ratio?

TWR compares total thrust along an axis to weight (mass × gravity). In simple terms:

TWR = thrust ÷ (mass × gravity)

When TWR = 1.0, thrust exactly balances weight — you hover in ideal conditions. Above 1.0 you accelerate upward; below 1.0 you cannot lift off vertically without help (slings, ramps, or cheating physics with a bug).

Approximately Up uses realistic-ish scaling: atmospheric thrusters depend on air density, electric thrusters push in vacuum, and gravity changes per planet. TWR on Earth is not TWR on the Moon. Always use the gravity of the world where you start a vertical burn, or the heaviest gravity along your landing leg.

Why TWR matters in Approximately Up

The game sells first-person flight across huge distances. Underpowered ships still move — slowly — which wastes time, drains RCS propellant on attitude fixes, and annoys co-op partners. Overpowered ships lift fast but snap frames if you punch throttle without dampers.

Common TWR failures:

1. Earth pad with cargo — mission components push mass up; atmospheric count unchanged.
2. Moon landing — two electric thrusters vertical is a strategy, but only if TWR with lunar gravity clears 1.0 when pulsed.
3. Wrong thruster type — atmospheric TWR is meaningless in vacuum; electric TWR is meaningless for dense-atmosphere takeoff unless you hybridize.

Cross-check part choice on Thruster tier list after running numbers here.

Target TWR bands (rule of thumb)

These are planning guides, not in-game hard limits:

Phase	Vertical TWR target	Notes
Earth liftoff	1.3 – 2.0+	Extra thrust improves acceleration and handles wind-up lag
Lunar landing pulse	1.0 – 1.5	Lower gravity helps; pulse electric vertical thrusters
Vacuum cruise	N/A (horizontal)	Focus on forward thrust and burn time, not vertical TWR
Heavy delivery	1.5+ on source planet	Cargo spikes mass — recalc every mission

Add margin if your ship drags cables or lands with partial fuel tanks. RCS mass counts toward weight even when idle.

Step-by-step: calculate before you wire

1. Estimate total mass — frames, thrusters, batteries, cargo, crew (if counted).
2. Pick gravity — Earth baseline first; swap to Moon or other worlds from Planets map.
3. Sum thrust — only thrusters firing on the axis you care about (vertical for liftoff).
4. Divide — thrust ÷ weight.
5. Adjust — add atmospheric clusters on Earth or reposition electric thrusters before launch.

In co-op, assign a engineer to update the spreadsheet while the pilot tests in fly mode — see Co-op guide.

Interactive calculator

Use the widget below to test scenarios. Enter mass in kilograms (or your preferred unit if the tool converts), local gravity, and installed thrust. Tweak values when you add a window block or second battery rack.

Worked example (conceptual)

Suppose your Earth lander masses 8,000 kg and Earth gravity is roughly 9.81 m/s². Weight ≈ 78,480 N. If combined vertical atmospheric thrust is 120,000 N, TWR ≈ 1.53 — enough to lift with moderate acceleration. Add 2,000 kg mission cargo without new thrusters and TWR drops to about 1.22 — still flying, but sluggish; co-op friends will notice.

Move the same hull to the Moon with ~1.62 m/s² gravity and weight falls sharply; two electric thrusters vertical often suffice because weight dropped even if thrust is lower in vacuum.

TWR vs other metrics

TWR is not the whole story:

• Approach velocity needs velocity meter readouts, not TWR alone.
• Landing height uses altimeter thresholds.
• Trip time depends on forward thrust and route length.
• RCS handles rotation; do not count RCS thrust as primary vertical lift unless you know what you are doing.

Use TWR as a gate: if vertical TWR fails, fix before adding sensors or logic gates.

Demo limits and full release

The demo grants limited electric thrusters — you cannot infinitely stack thrust to fix bad TWR. The full release promises more planets and parts; recalc when new engines unlock after Demo vs full release.

Related pages

• Tools hub — other planners
• Thruster tier list — which engines to count in thrust sum
• Getting Started — first missions and unlocks
• Codes — no codes replace good TWR

Run the calculator every time someone says “one more frame block won’t matter.” Approximately Up rewards ships that lift approximately enough — this tool helps you land on the right side of that joke.