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Low Graphics

Monday, 18 March, 2002, 10:43 GMT

Tom and Jerry on weighty mission

Tom and Jerry will fly at a separation of 200 km

Two satellites called Tom and Jerry have

launched on a mission to investigate the Earth's

shifting water masses and map their effects on

the planet's gravity field.

A Rokot vehicle carrying the US-German satellites

blasted off from the northern Russian city ofPlesetsk on Sunday. The satellites were

successfully inserted into a 500-kilometre- (300-

mile-) high polar orbit

Tom and Jerry, which each weigh 500 kilograms

(1,100 pounds), will circle the planet 16 times a

day and fly 200 kilometres (120 miles) apart.

Their monthly gravity maps will be up to 1,000

times more accurate than those currently in use.

Best yet

The Rokot lifted clear of the launch pad at 1221

hours (0921 GMT). It should have gone up on

Saturday but the take-off was postponed due to

unfavourable weather.

The twin satellites are

WATCH/LISTEN

ON THIS STORY

The BBC's Jane BePowellThe mission will lyears

See also:

21 Nov 01 | Sci/TNew gravity map r

18 Mar 02 | Sci/TeMystery force tugsprobes

Internet links:

Nasa gravity map

Grace

The BBC is not respfor the content of exinternet sites

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ot lifted clear of the launch pad at 1221

921 GMT). It should have gone up on

y but the take-off was postponed due to

rable weather.

The twin satellites are

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the products of a

German-American

project known as

Grace (Gravity

Recovery And Climate

Experiment).

The $127m spacecraftwill fly in tandem to

create what scientists

expect will be the most

accurate map ever of

the Earth's

gravitational field.

The strength of the field varies from place to

place due to differences in the density and types

of materials that make up the Earth.

Water flow

The five-year mission - put together by the

American space agency (Nasa) and the German

Centre for Air and Space Flight - will chart large-

scale movements of water around the planet.

These shifts in mass result in measurable -

although tiny - differences in the planet's

gravitational field.

The satellites have been built to sense these

minute variations. Regions of slightly stronger

gravity will affect the lead satellite first, pulling it

slightly away from the trailing satellite.

Scientists will record the constantly changing

distance between the two spacecraft, using an

extremely sensitive microwave ranging system.

This information will be combined with data fromprecise navigational instruments to construct a

detailed Earth gravity map.

Links to more Sci/Tech stories

In This Section GO

Current gravity mapsshow the Earth to be verylumpy

ucts of a

American

nown as

ravity

And Climate

nt).

7m spacecrafttandem to

hat scientists

ill be the most

map ever of

h's

onal field.

ngth of the field varies from place to

e to differences in the density and types

ials that make up the Earth.

low

year mission - put together by the

n space agency (Nasa) and the German

r Air and Space Flight - will chart large-

vements of water around the planet.

ifts in mass result in measurable -

tiny - differences in the planet's

onal field.

llites have been built to sense these

ariations. Regions of slightly stronger

ill affect the lead satellite first, pulling it

way from the trailing satellite.

s will record the constantly changing

between the two spacecraft, using an

ly sensitive microwave ranging system.

rmation will be combined with data fromavigational instruments to construct a

Earth gravity map.

ore Sci/Tech stories

Section GO

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