How fast did Apollo 8 travel?

Answer 1

The speed of an Apollo spacecraft is hard to answer because there are many answers available. The best question would ask something like "What was the maximum speed?", or "what was the average speed during the translunar or transearth phase?" The problem is that the speed of spacecraft was constantly changing.

In order to break out of Earth orbit and reach the moon, an object must travel approximately 24,000 miles per hour. The Apollo spacecraft did just that. However, they didn't maintain that speed. Once they were out of orbit, they simply coasted the entire distance to the moon. Breaking out of Earth orbit does not mean breaking free from Earth's gravity though. The Earth was constantly pulling on the spacecraft, slowing it down. Eventually, the spacecraft got close enough to the moon that that moon's gravity had a stronger effect than the Earth's gravity, pulling the Apollo module forward, causing the module to speed up.

With that in mind, we can provide the speed of Apollo 8 at various events:

At translunar injection, Apollo 8 was traveling at 35, 505.41 ft/sec, or 24,208 mph.

When the spacecraft entered the moon's sphere of influence (when the action of the moon's gravity became stronger than the action of the Earth's gravity on the spacecraft), it had slowed down to 3,261 ft/sec, or 2,223 mph.

When the spacecraft reentered the Earth's atmosphere after returning from the moon, it was traveling at 36,221 ft/sec, or 24,696 mph.