McDivitt Couldn’t Tell Whether the Guidance Instrument Was Right

On the third day of the Gemini 4 mission, Jim McDivitt switched on the spacecraft’s guidance instrument. He compared its reading with what he saw outside the window. This time, the two matched.

The guidance instrument helps the crew determine which way the spacecraft is pointing. That matters when they need to set the spacecraft on course for its return to Earth. But for most of the flight, McDivitt couldn’t check whether the instrument was reliable. He had to rely on it without knowing whether it was accurate.

An Instrument He Couldn’t Check

McDivitt described the problem at a postflight briefing attended by fellow astronaut Edward White. He explained that he hadn’t had enough time to use the instrument and compare its reading with what he saw through the window. For most of the mission, then, he didn’t know whether he could trust its reading.

He also hadn’t been able to properly align and check the instrument at the start of the flight. As far as he was concerned, it remained an open question. Only on the third day did the astronauts manage to switch it on and compare its reading with the view outside.

The Window Settles It

McDivitt compared the instrument’s reading with the spacecraft’s appearance outside the window. The directions matched. At last, he had a reason to trust the instrument. He said that by the time they were ready to return, he felt confident in it.

White agreed with McDivitt’s account. The two also said they’d lost several bets about the instrument. They didn’t say what they had bet on, but the wagers suggest that even among the astronauts, its accuracy had been an open question.

What We Still Don’t Know

The passage doesn’t specify exactly what the astronauts saw outside the window. It describes only the comparison between the instrument’s reading and the view, and notes that the directions matched.

For most of the flight, they had no answer. Then the window and the instrument finally pointed in the same direction. And when you’re on your way back to Earth, how much is a moment like that worth?