Can a TWR below 1 be useful?

Yes, for in-space manoeuvres. Ion engines have tiny TWR (0.001 or less) but accumulate large delta-v over time.

Why not maximise TWR?

Very high TWR means excessive acceleration, which wastes fuel fighting drag in the lower atmosphere and stresses the structure.

Yes. As fuel burns the mass decreases while thrust stays roughly constant, so TWR increases throughout the burn.

Calculate the thrust-to-weight ratio of a rocket: TWR = thrust / (mass * g), determining if it can lift off.

Thrust

Total Mass

Surface Gravity

m/s2

Thrust-to-Weight Ratio

1.4128

Net Vertical Acceleration4.0481 m/s2

Thrust-to-Weight Ratio vs Thrust

The TWR determines whether a vehicle can lift off and how quickly it accelerates.

TWR = F / (m * g)

*F* = engine thrust in newtons

*m* = total vehicle mass

*g* = local gravitational acceleration

TWR must exceed 1.0 for liftoff. Most launch vehicles aim for 1.2 to 1.8 at ignition.

Saturn V first stage: 7 607 000 N thrust, 549 054 kg.

Total velocity change.

Engine efficiency.

Required fuel for a mission.