The Blog

On earth, oxygen comprises 21 percent of the atmosphere. That precise figure is an anthropic constant that makes life on earth possible.

If oxygen were 25 percent, fires would erupt spontaneously; if it were 15 percent, human beings would suffocate.

But oxygen is not the only problem.

Like the atmosphere on earth, a change in one constant on the spacecraft can affect several others that are also necessary for life.

This can be displayed with the incident with Apollo 13.

The explosion creates a shortage not only of oxygen but also of electricity and water. Without oxygen, there will be no way to manufacture air, water, or power.

Since they are in the vacuum of space, there is no source of oxygen from the outside.

Unfortunately, with most automated systems shut down, concentration becomes more and more critical.

Besides slinging around the moon, the crew needs to make several manual course corrections to ensure they hit the right re-entry angle to speed up their trip home.

To do so, they will have to navigate by the stars. But since the debris from the explosion continues to envelop the ship in the vacuum of space, the astronauts cannot distinguish from sunlight reflecting off the debris.

Consequently, they are reduced to using the earth and the sun as navigational reference points by lining them in a spacecraft window.

Using this tedious method, they check their calculations again and again to ensure they are correct. They have little room for error.

In fact, they must aim the ship for reentry at a point no less than 5.5 degrees and no more than 7.7 degrees below the earth’s horizon. Any deviation from this range, and their ship will either skip off the earth’s atmosphere or burn up in too steep a descent.

What is the importance of atmospheric transparency?