Apollo 13 "Houston, we're got a problem."

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Italian press reaction was typical of world-wide concern.

Other nations offering assistance included France, Britain, Holland, Italy, Spain, Ger- many, Brazil and Uruguay.

At 7:21 p.m. Tuesday, the spacecraft swung behind the Moon, lost contact with Earth and passed 164 miles above the lunar surface. Haise and Swigert, who had never been so close and might never get closer, snapped photos like a couple of tourists. At 7:49 the spacecraft emerged on the other side and was again picked up by tracking stations.

This conversation took place:

SC--Houston, Aquarius.

CAPCOM--Aquarius, Houston.

SC--The view out there is fantastic... You can see where we're zooming off.

Apollo 13 was headed homeward. Moments later the 15-ton spent third stage of the Saturn V launch vehicle crashed into the Moon, as planned.

It occurred at 8:09 p.m. EST, April 14. The S-IVB struck the Moon with a force equivalent to 11 1/2 tons of TNT. It hit 85 miles west northwest of the site where the Apollo 12 astronauts had set up their seismometer. Scientists on Earth said, "the Moon rang like a bell."

Back in November 1969, the Apollo 12 astronauts had sent their Lunar Module crash- ing into the Moon following their return to the command craft after the lunar landing mission. That Lunar Module struck with a force of one ton of TNT. The shock waves built up to a peak in eight minutes and con- tinued for nearly an hour.

The seismic signals produced by the impact of s-IVB were 20 to 30 times greater and four times longer than those resulting from the LM crash. Peak intensity occurred in 7 minutes.

The information from these two artificial moonquakes led to reconsideration of theories proposed about the lunar interior. Among puzzling features are the rapid build- up to the peak and the prolonged reverbera- tions. Nothing comparable happens when objects strike Earth.

One theory is that the signal is scattered and repropagated in very deep rubble. An- other holds that the velocities of seismic waves from these impacts are comparable to meas- urements of velocities in crystalline rock. So the crystalline material which the astronauts found so abundant on the Moon's surface may extend very deep into the Moon.

Houston reported the lunar impact of the S-IVB to the spacecraft:

CAPCOMN--By the way, Aquarius, we see the results now from 12's seismometer. Looks like your booster just hit the Moon, and it's rocking a little bit.

SC--Well, at least something worked on this flight... I'm sure glad we didn't have an LM impact, too.