Vostok 1: First Human Orbit & Ballistic Reentry

Orbit — 108-minute flight, April 12, 1961

Mission Control

Time scale 60×

Flight Data

Altitude

181 km

Velocity

7.80 km/s

G-force

1.0 g

Mission time

T+00:00

How it works

Vostok 1 launched into an elliptical orbit with perigee 169 km, apogee 327 km and inclination 64.95°. Position on the ellipse is found by solving Kepler's equation for eccentric anomaly E from mean anomaly M = 2π t / T (Newton's method), then converting to a radius and speed:

r = a(1 − e·cosE)
v = √( GM · (2/r − 1/a) )      (vis-viva equation)

Pressing Retrofire fires the TDU-1 retrorocket for a ≈41 s burn, cutting velocity by ≈136 m/s and dropping perigee below the surface — the capsule leaves the ellipse and enters the atmosphere. Vostok's descent module was a sphere with no aerodynamic lift, so its trajectory is governed by the ballistic (point-mass) reentry equations:

dv/dt = −D/m − g·sinγ
dγ/dt = (v/r)·cosγ − (g/v)·cosγ
dh/dt = v·sinγ
D = ½·ρ(h)·v²·Cd·A,   ρ(h) = ρ0·e^(−h/H)

with scale height H = 7.2 km. Because the capsule generates no lift to spread the deceleration out, this ballistic entry is steep and violent — the simulation reproduces the historically-recorded peak of roughly 8 g that Gagarin experienced, versus the gentler ~3–4 g of a lifting-body reentry like the Space Shuttle.

Time scale — the real flight took 108 minutes; speed it up to watch a full orbit and reentry in under a minute.
Retrofire — only available once per run; watch the ellipse collapse into a reentry arc.
G-force readout is drag deceleration D/m expressed in multiples of g0 = 9.80665 m/s².

Vostok 1 orbit path Reentry trajectory

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