Free Newsletters - Space - Defense - Environment - Energy - Solar - Nuclear
..
. 24/7 Space News .




PHYSICS NEWS
The Earth Is Not Round
by Launchspace Staff
Bethesda MD (SPX) Oct 19, 2010


File image.

Some 50 years ago, when the first artificial satellite was launched, it was generally thought the Earth was spherical in shape. Of course, the existence of surface anomalies such as mountains, valleys and ocean floor contours were well known, but not well understood in terms of their effects on satellite orbits near the Earth.

Studies of the moon's motion had given some indication that the Earth's mass distribution is not quite spherical, but the moon is far from the planet and anomalies tend to be attenuated at long distances.

As more low-Earth satellites were launched in the 1960s and 70s, precision tracking studies led to a better understanding of how the Earth's mass distribution impacts satellite orbits. Gravity models were refined and new insights were developed about how best to deal with gravity anomalies.

Today, these non-spherical elements of Earth's gravity field are well understood and used to design many space missions.

Noting that the geodetic shape of the Earth does not represent the gravitational field shape, we can summarize the non-spherical elements of Earth's gravity as follows.

If the Earth had a uniformly homogenous mass distribution, it would have to be slightly bulging at the equator and slightly oblate about the equator. In other words, the Earth can be thought of as a basketball that is unevenly bulging about its waist. While the non-spherical elements are small they do have profound implications on how we conduct many space missions.

One important result was the discovery of sun-synchronous orbits, i. e., orbits that combine altitude and inclination in such a way that satellites in these orbits repeat passes over any given point on the Earth's surface at the same local mean solar time.

This is desirable for satellites such as those used for earth observations, because the surface illumination angle will be the same every time such a satellite passes overhead. Consistent lighting offers real advantages for satellites that image terrestrial locations.

Non-spherical elements of the gravity field can also be detrimental for certain orbital missions. One important example is the gravity-induced east-west drift of geostationary satellites. Such satellites are placed in an equatorial orbit that matches the Earth's rotation rate, thus, rendering them "stationary" relative to the Earth. If there were no perturbing forces, these satellites would naturally remain stationary.

Unfortunately, this is not the case. The non-circular shape of the equatorial gravity field causes geostationary satellites to drift to the east or to the west, depending on their chosen longitudinal location.

Overall, perturbing gravitational and non-gravitational forces have a variety of important implications for space missions. In order to better understand space mission design and orbital mechanics, consider Launchspace's courses on these topics.

.


Related Links
Launchspace
The Physics of Time and Space






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





PHYSICS NEWS
Putting A Spin On Light And Atoms
Berkeley CA (SPX) Sep 21, 2010
Magnetometers come in many shapes and sizes - an ordinary hand-held compass is the simplest - but alkali-vapor magnetometers are extrasensitive devices that measure magnetic fields using light and atoms. They can detect archaeological remains and mineral deposits underground by their faint magnetic signatures, among a host of other scientific applications. Researchers from the U.S. Departm ... read more


PHYSICS NEWS
NASA Awards Contracts For Innovative Lunar Demonstrations Data

NASA Thruster Test Aids Future Robotic Lander's Ability To Land Safely

NASA official: Moon still matters

China Scouts Moon Landing Sites

PHYSICS NEWS
Emerging Underground Aquifers Formed Martian Lakes

Revealing More About The Atmosphere Of Mars

Rover Nears 15 Miles Of Driving On Mars

Long-Lived Mars Odyssey Gets New Project Manager

PHYSICS NEWS
NASA Selects 215 Small Business Research And Technology Projects

A New System For Locating And Capturing Satellites In Space

Sciencespace Hotel Project To Be Launched After Contract Is Signed - Energia

British media join forces against Murdoch BSkyB takeover

PHYSICS NEWS
International Crews for Shenzhou

China Eyes Extended Mission Beyond Moon

China's second lunar probe enters moon's orbit: state media

Lunar Probe And Space Exploration Is China's Duty To Mankind

PHYSICS NEWS
Counting Down For ESA MagISStra Mission To Space Station

Glamorous spy sees Russian rocket blast off for ISS

Russian rocket blasts off carrying three astronauts to ISS

Russian manned spacecraft docks with ISS: official

PHYSICS NEWS
ILS Proton Successfully Launches XM-5 Satellite

Ariane Moves Into Final Phase Of Globalstar Soyuz 2 Launch Campaign

Arianespace Hosts Meeting Of Launch System Manufacturers

Political Obstacles For Sea Launch Overcome

PHYSICS NEWS
How To Weigh A Star Using A Moon

Doubt Cast On Existence Of Habitable Alien World

Time to find a second Earth, WWF says

Backward Orbit In A Binary System

PHYSICS NEWS
TerraSAR-X And TanDEM-X Flying In Close Formation

TechDemoSat-1 To Demonstrate UK Innovation In Space

Apple net profit up 70 percent, 4.19 million iPads sold

Space Debris' Enviromental Impact




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement