University of Texas at Austin

Thursday, July 2, 2009

Apollo 11 and the Texas laser rangers

To mark the 40th anniversary of the Apollo 11 moon landing, Further Findings is highlighting ways The University of Texas at Austin and its people touched or were touched by the mission. Know of others? Let us know.

Peter Shelus was visiting The University of Texas at Austin campus in 1971, attending an astronomy conference. More important, he was looking for a job.

He was completing a post-doc assignment at the Manned Space Center (now Johnson Space Center) in Houston and job prospects weren’t great. NASA was laying off scientists and engineers as the basic Apollo program wound down.

It was a Friday afternoon and Shelus waited for the elevator in the Castilian apartment building. But before the doors opened, Darrell Mulholland from the university approached Shelus and said, “I hear you’re looking for a job.”

Besides a slow elevator, Shelus can also thank Neil Armstrong and Buzz Aldrin for the job he’s had for 38 years.

The retroreflector placed on the moon by the Apollo 11 astronauts.

The retroreflector placed on the moon by the Apollo 11 astronauts.

During their first moonwalk in July 1969, the Apollo 11 astronauts placed a retroreflector package, a complex mirror system, on the moon’s surface. A laser beam directed from Earth at the retroreflector would bounce off of it and back to Earth. The 240,000-mile round trip takes about 2.5 seconds. Oh, and then there was science to do with the data collected.

Shelus’s job was to process the information coming from the new Lunar Laser Ranging Station at McDonald Observatory, the source of the laser beam.

Since then, four other retroreflectors have been placed on the Moon. Two by other Apollo missions 14 and 15 and two French-made mirrors carried to the surface by Soviet Union soft landers.

Now, in a matter of bittersweet timing, The University of Texas at Austin’s role in the lunar laser ranging project is ending as the 40th anniversary of Apollo 11 is marked.

The National Science Foundation (NSF), which provided support for the project when NASA dropped it more than 15 years ago, has notified Shelus that the $135,000 for the McDonald Laser Ranging System (MLRS) won’t be renewed.

“We’re essentially going out of business by probably the end of the calendar year,” Shelus said.

He understands the NSF decision—for the most part.

“We know what the lunar science is, we know the MRLS is on its last legs,” he acknowledged. The system is 20 years old and has had few upgrades.

What’s more, a brand new station is coming online in New Mexico and a French installation will re-open after shutting down for refurbishing.

Still, Shelus would like to keep his project going for another two years to collect data that overlap across the three laser stations.

“I’ve been here since 1971 so I’ve been here almost the entire 40 years. It’s been a fantastic ride,” he said. “We’ve put good data on the table, we’ve kept the experiment going and there are no regrets.”

The precise measurements of the moons orbit enabled a range of science projects.

One of the biggest science accomplishments was to test the Equivalence Principal, one of the fundamental concepts in which Albert Einstein built the General Theory of Relativity.

Among specific findings, according to NASA, the laser ranging project showed that:

• the moon is spiraling away from Earth at a rate of 3.8 centimeters a year because of the Earth’s ocean tides.

• the moon probably has a liquid core.

• the universal force of gravity is very stable. Newton’s gravitational constant G has changed less than one part in 100-billion since the laser experiments began.

Just because the Moon will no longer be a target, it doesn’t mean that the Laser Ranging Station is shutting down. Shelus and Jerry Wiant, the project’s engineer, and Randy Ricklefs, the software expert, still have work to do. Ken Harned and Anthony Garcia are observers on the laser.

The station is part of a worldwide network of lasers that bounce laser beams off satellites. What’s more, it will be involved with the two moon missions, LCROSS and LRO, launched by NASA in June.

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» Apollo 11 and the Texas laser rangers



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