Cosmic Velocity - First to Knot (UK)

The first cosmic velocity (escape velocity from Earth's surface to orbit) is approximately 7,900 m/s (7.9 km/s), the minimum speed needed to achieve Earth orbit.

v₁ = √(GM/r) where G is gravitational constant, M is Earth's mass, r is Earth's radius. Approximately 7.9 km/s.

To km/h: × 3,600. To mph: × 17,672. 7.9 km/s = 28,440 km/h = 17,672 mph.

Minimum speed for satellites, space station orbit, and low Earth orbit (LEO) calculations.

ISS orbits at ~7.66 km/s. Below this speed, you fall back to Earth. Above it, you stay in orbit (if horizontal).

Confusing with escape velocity (second cosmic velocity, 11.2 km/s) — orbital velocity is lower.

Remember: ~8 km/s for orbit, ~11 km/s to escape. v₁ is minimum for orbit, not escape.

The UK knot is a historical variation of the knot based on the British nautical mile (6,080 feet) rather than the international nautical mile (6,076.12 feet).

1 UK knot ≈ 1.853184 km/h = 0.5148 m/s. Slightly faster than the international knot (1.852 km/h).

To international knots: × 1.00064. To km/h: × 1.853. To m/s: × 0.5148.

None in modern use. Only relevant for interpreting historical British naval records.

The difference between UK and international knots is only 0.064% — barely noticeable but important for precise navigation.

Assuming all old British ship logs use the same knot as today — they don't, but the difference is tiny.

Historical only. Effectively identical to modern knot. Only matters for historical maritime research.