Transterrestrial Musings  


Amazon Honor System Click Here to Pay

Space
Alan Boyle (MSNBC)
Space Politics (Jeff Foust)
Space Transport News (Clark Lindsey)
NASA Watch
NASA Space Flight
Hobby Space
A Voyage To Arcturus (Jay Manifold)
Dispatches From The Final Frontier (Michael Belfiore)
Personal Spaceflight (Jeff Foust)
Mars Blog
The Flame Trench (Florida Today)
Space Cynic
Rocket Forge (Michael Mealing)
COTS Watch (Michael Mealing)
Curmudgeon's Corner (Mark Whittington)
Selenian Boondocks
Tales of the Heliosphere
Out Of The Cradle
Space For Commerce (Brian Dunbar)
True Anomaly
Kevin Parkin
The Speculist (Phil Bowermaster)
Spacecraft (Chris Hall)
Space Pragmatism (Dan Schrimpsher)
Eternal Golden Braid (Fred Kiesche)
Carried Away (Dan Schmelzer)
Laughing Wolf (C. Blake Powers)
Chair Force Engineer (Air Force Procurement)
Spacearium
Saturn Follies
JesusPhreaks (Scott Bell)
Journoblogs
The Ombudsgod
Cut On The Bias (Susanna Cornett)
Joanne Jacobs


Site designed by


Powered by
Movable Type
Biting Commentary about Infinity, and Beyond!

« Beware Of Falling Cows | Main | Bad Economic News »

Lumpy Planet

Everyone (well, OK, not everyone, but most people interested in this kind of stuff) is familiar with "mascons" (mass concentrations) on the moon, that cause perturbations and instability in the orbits of objects around it. Interestingly, though, the earth's gravitational field isn't all that symmetric, either, based on results from the GRACE satellites. I think that it's kind of amazing how sensitive these detectors are:

The concept is simple. The two satellites, each about three metres long, follow each other in identical orbits roughly 400 kilometres above the Earth and 210 kilometres apart. Microwave instruments measure the distance between them, precisely enough to detect variations smaller than one percent of the width of a human hair.

"[It's as though] you have two automobile-sized things, one in Los Angeles and one in San Diego, and you're measuring the distance between them to the size of a red blood cell," says Watkins.

As one satellite and then the other passes through wrinkles in the Earth's gravity field, they speed up or slow down slightly, shifting the distance between them. By measuring these tiny yo-yos, scientists can calculate the gravity field that produced them, mapping the entire Earth about once a month.

But the dispersions are much smaller, relative to the size of the body, so it doesn't create the same levels of perturbations that can result in instability. Pretty cool graphic.

Posted by Rand Simberg at November 07, 2007 07:49 AM
TrackBack URL for this entry:
http://www.transterrestrial.com/mt-diagnostics.cgi/8448

Listed below are links to weblogs that reference this post from Transterrestrial Musings.
Comments

Back in 1960-62 when I was going through MIT's Aero and Astro program, the consideration of mascons on Earth was quite common with the understanding that position errors of up to about a quarter of a mile were possible due to deviations of the local vertical around mascons. They alluded to geographic surveys that were used to evaluate guidance error inputs for ballistic missiles, notably submarine-launched missiles or air-launched missiles like Skybolt. It will be interesting to see whether the mascons are stationary, or whether they move around.

Posted by John F at November 7, 2007 07:30 PM

I remember reading that during or shortly after Apollo there was a proposal for a Lunar Orbiting Space Station, dubbed LOSS. But past a point they realized that lunar mascons would perturb the orbit to the point where eventually the low parts of the orbit would be below the tops of mountains. Then someone couldn't be restrained from saying, "LOSS would have been a true loss".

But a station at L-1 would provide fine access to the moon.

Posted by Mike Combs at November 8, 2007 05:54 AM

You know looking at that map the areas of high gravity seem to correlate with highly religious regions. Whether the presence of God is collecting energies or the higher energies are making people all the crazier remains to be seen.

Posted by Josh Reiter at November 12, 2007 12:57 AM


Post a comment
Name:


Email Address:


URL:


Comments: