Long-Lost Apollo Rocket Returns to Earth Orbit

WASHINGTON (Reuters) - A long-lost piece of an Apollo rocket has returned to Earth orbit after decades of racing around the Sun, the first time our planet has captured an object from solar orbit, astronomers said on Friday.

Earth's new satellite is most likely the third stage of a massive Saturn V rocket that lifted Apollo 12 astronauts to the moon in November 1969, according to astronomers at NASA's Jet Propulsion Laboratory in Pasadena, California.

Last seen in an elongated 43-day orbit around Earth, the bus-sized rocket stage escaped Earth orbit in March 1971, the laboratory's Paul Chodas said in a statement.

Known now as J002E3 and first seen by an amateur astronomer starting on Sept. 3, the rocket stage probably completed nine or 10 Earth orbits, then swung far enough toward the Sun to be pulled into a Sun-centered orbit, Chodas said.

The transition occurred through a special portal located at the L1 Lagrangian point, where the gravitational pulls of the Sun and Earth are about equal.

"Last week we didn't know for sure that it had been captured, and now there's no doubt that it was captured in April of this year," Chodas said.

"What's more, we are virtually certain that it originally escaped Earth orbit in March 1971 and that it will escape again next June," he said. "It's only a temporary visitor."

There is less than a 1 percent chance that J002E3 will hit either Earth or the moon before its departure from Earth orbit, the statement said. Even if it did, its relatively small size -- about 60 feet long -- means it would not be considered hazardous.

Scientists at the University of Arizona, Tucson, and the Massachusetts Institute of Technology analyzed the object's surface this week to determine it was white paint and not some asteroid-like material.

If it is not from the Apollo 12 rocket, this object might be one of the four 22-foot panels that enclosed lunar modules from six Apollo missions or rocket stages from Soviet or U.S. unmanned lunar missions.

Those are less likely because they seem too small to match the object's observed brightness, and they are not known to have been left in orbits that could have escaped Earth, the statement said.

When J002E3 was circling the Sun, it completed 33 orbits in the time it took Earth to orbit 31 times. It lapped Earth once in 1986, but was not snagged by Earth's gravity; this year it was about to lap Earth again but passed too close to the L1 portal and Earth captured it.

Ok, if its in a 43 day orbit how can it escape the Earth at all let alone next June?

The word "orbit" has many meanings. If it were a nice, circular, stable orbit relatively close to the Earth, then yeah, it'd remain there barring any major disruption.

However, any looping path around a gravitational source can be called an "orbit", and this one is elongated, oblong, and far enough away that the Earth's gravity is only one of the major influences on the path of the piece of debris.

For one thing, it loops across the orbit of the Moon, and sooner or later it'll cross the Moon's orbit while the Moon is nearby, and the Moon will then have a large gravitation effect on it and help slingshot it out of its current path.

What would cause it to accelerate to faster than Earth's escape velocity?

The Moon, for one. Plus, it's far enough away from the Earth that the escape velocity is pretty low, it won't take much of a bump for the Earth to "lose" it again.

Is falling toward the Sun is adding energy to it? But then it gives that energy back during that part of the orbit when it is travelling away from the Sun.

The Sun is yet another influence on it.

Things like escape velocities, stable elliptical or circular orbits, etc., are all simplifications of the more complex analysis of orbital trajectories involving 3 or more objects (the so-called "N-body problem"). Escape velocity, etc., only makes sense when analyzing how two bodies (e.g. a spacecraft and the Earth) interact gravitationally.

Things get a lot weirder and less predictable when 3 or more bodies are considered. Thankfully, in many situations, one can ignore the effects of more distant bodies -- for example, the Moon is not a great consideration when looking at the orbit of the Space Shuttle when it's in its near-Earth orbit (the Moon is too far away).

But whenever the situation requires more than two things to be considered, orbits become much more complicated and can no longer be predicted using simplified concepts like stable elliptical orbits or static escape velocity figures.

For example, check out this page

It contains a Java applet that simulates the motions of multiple bodies interacting gravitationally. It provides a number of "canned" scenarios which show unusual or special-case situations which demonstrate unusual results. I especially like the "PlateSaucer4" scenario which results in nearly square orbits... At least for a while. Some of the orbital scenarios are unstable, like this one, and eventually fall apart. Others are stable, and persist indefinitely even when disrupted by other objects, like the yellow bodies in the "L1-L5 M/m=40" simulation.

Work your way through the examples on that page, and you'll see how an object that is more-or-less in orbit can be "ejected" (or recaptured) due to the influence of other objects.

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