Nasa missions on their way into space

The two probes were launched on a Delta II rocket

Two Earth-monitoring spacecraft have been launched by the US space agency Nasa.

The missions are a satellite known as Jason-1 that will monitor the oceans and a probe to study an uncharted area of space just above the Earth's atmosphere.

They were launched aboard the same rocket from the Vandenberg Air Force base in California on Friday.

Nasa said it was a flawless lift-off.

Timed will monitor the inner boundary of space

Jason-1 is Nasa's newest oceanography satellite. It will monitor global interactions between the sea and the atmosphere.

Scientists hope the probe will improve forecasting of weather events like El Nino and increase understanding of ocean circulation and seasonal changes.

It will also measure wave heights and wind speed over the ocean.

Gary Kuntsmann, Jason-1 project director at Nasa's Jet Propulsion Laboratory in Pasadena, California, said: "The prime objective is to continue long-term data collection for the ocean surface topology measurements that the science community needs to accurately forecast and predict long-range climate changes."

Surveying Earth

Meanwhile, a joint US/French mission, known as Timed (Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics mission) will study the boundary between space and the Earth's atmosphere.

This area, some 64 to 177 kilometres (40 to 110 miles) above the planet's surface, has been difficult to observe in the past.

It is too high for conventional aeroplanes and balloons but too low for direct satellite measurements.

The spacecraft will send back pictures of the region, known for producing beautiful auroras, and measure temperature, pressure, winds, and chemical composition.