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November 10, 2009

MESSENGER sends greetings from Mercury

Beate Czogalla

A short while ago the MESSENGER spacecraft had another close encounter with our solar system’s innermost planet, Mercury. MESSENGER — another one of those infamous NASA acronyms — stands for Mercury Surface, Space Environment, Geochemistry and Ranging mission. It was launched in 2004 and has since then traveled throughout our celestial neighborhood in a carefully choreographed path that will eventually take it to Mercury at the proper angle and velocity to go into orbit around the planet. Since then it has come tantalizingly close to its goal twice, only to slingshot around Mercury again and sail back out into space.

It seems quite strange that a spacecraft destined for Mercury should pass by its target three times and take around six years to get there. Why didn’t they just send it straight there?

Well, it’s complicated. First and foremost, it’s a money-saving plan. When you launch a rocket into space you want to get it up to the proper speed early on, then discard the fuel tank and let it coast the rest of the way at a good clip. When you get close to the end you step on the brakes — in space travel this means firing rocket engines against the direction you’re traveling in order to slow down, and then either let the craft be captured by the planet’s gravity to go into orbit or slow it down even further in order to land. All of that takes a lot of extra equipment and fuel.

MESSENGER is a project for patient people who can wring every advantage of a drop of propellant out of a rocket — and do it in exchange for a longer trip.

A long-time favorite of many science fiction shows — and actually used frequently in space travel (remember Apollo 13?) — the slingshot maneuver whips a spacecraft around a planet, using its gravity to alter its course and gain momentum for an increase in velocity. You need to know your math and your orbital mechanics to do this rather complicated process, but it’s usually worth it. Fuel saved is mass saved is money saved!

Secondly, Mercury is a tricky planet to get to. Close as it is to the sun it orbits much faster than the Earth. It’s like trying to shoot a flying bullet — there is no margin for error. So why not give yourself more time to line up your spacecraft perfectly so when the big day comes you’ve got all your ducks in a row and your orbital insertion will be like dotting the proverbial “i”?

In this third flyby MESSENGER made some very cool discoveries — despite the fact that due to a solar eclipse it only got half the observation time it should have had. Stunning images of craters within craters were radioed back to Earth along with new evidence that Mercury is not the dead planet it was once thought to be: recently active volcanic features have spewed differently colored material onto the surface.

Keep up with MESSENGER at http://messenger.jhuapl.edu/

Beate Czogalla is the associate professor of theater design in the Department of Music and Theater at Georgia College & State University. She has had a lifelong interest in space exploration and has been a solar system ambassador for the Jet Propulsion Laboratory/ NASA for many years. She can be reached at our_space2@yahoo.com

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