May the (G) Force be with You

We’re going to the moon. In 12 years.

Well, we’ve got some time to kill.

In the meantime, let’s just all pretend that Apollo is still going on.


This is a simple graph of the G forces experienced during the trip from the launch pad to low earth orbit in a Saturn V. I actually thought they went higher than 4-G during the boost. A note mentions that the highest G-forces the astronauts encounter is during re-entry when they hit about 6.5 Gs. Ooftah.

Here are the explanations of the changes in acceleration:

1. Launch with ignition of the S-IC. Note how the acceleration rapidly rises with increasing engine efficiency and reduced fuel load.
2. Cut-off of the centre engine of the S-IC.
3. Outboard engine cut-off of the S-IC at a peak of 4g.
4. S-II stage ignition. Note the reduced angle of the graph for although the mass of the first stage has been discarded, the thrust of the S-II stage is nearly one tenth of the final S-IC thrust.
5. Cut-off of the centre engine of the S-II.
6. Change in mixture ratio caused by the operation of the PU valve. The richer mixture reduces the thrust slightly.
7. Outboard engine cut-off of the S-II at a peak of approximately 2.7g.
8. S-IVB stage ignition. Note again the reduced angle of the graph caused by the thrust being cut by a fifth.
9. With the cut-off of the S-IVB’s first burn, the vehicle is in orbit with zero acceleration.

From the incredible Apollo 15 – Launch and Reaching Earth Orbit page. (via The Eternal Golden Braid)


  1. The NASA scientists in the early seventies sincerely believed that by now, the first Mars mission would be most of a decade in the past. Now we’re in 1957. Sheesh.