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Space watch on which way the winds blow
A SATELLITE that will be able to measure the winds in earth’s atmosphere from orbit is being built under UK leadership for launch in 2007.
The Aeolus wind-sensing spacecraft — named after the Greek gods’ mortal “keeper of the winds” — will be the first to provide, from space, detailed global surveillance of winds. It promises both better weather forecasting and greater understanding of our planet.
Under a contract worth 180 million euros from the European Space Agency (ESA), EADS Astrium — the UK arm of the European EADS Space group — has already completed the design phase and now takes overall responsibility for building the spacecraft. The company has been appointed prime contractor for a project that will see some 50 companies in 12 European countries supply various equipment and services.
Astrium in the UK will also be specifically responsible for assembling the 500-kilogram payload to the spacecraft platform, based on that of ESA’s Mars/Venus Express missions. In addition, it will provide the spacecraft’s attitude and orbit control system as well as its propulsion sub-system and thermal control system. The UK firm has also been given responsibility for the ground processor which will use the raw data from Aeolus to determine the wind patterns and speeds.
Evert Dudok, EADS Astrium’s director of Earth Observation, Navigation and Science, said: “This is a unique and challenging mission which EADS Astrium is looking forward to undertaking, in partnership with ESA, to provide a long-term European capability that will be of great benefit to mankind.”
Initially called the Atmospheric Dynamics Mission (ADM), the renamed Aeolus programme will have a cost of some 300 million euros. The spacecraft will weigh about 1.5 tonnes at launch in October 2007. With an expected lifetime of three years, it will be placed in a sun-synchronous orbit at an altitude of 400 kilometres, enabling it to collect information from anywhere on our planet.
In this type of near-polar orbit that maintains an almost constant angle with the sun/earth axis, a satellite always flies over a given point on earth at the same time, simplifying comparisons of data and the monitoring of fast-changing phenomena.
Aeolus will provide global observations of “three-dimensional wind fields” across earth’s surface with a vertical resolution that will satisfy the requirements of the World Meteorological Organisation in both climate research and operational forecasting, and with a speed accuracy of two metres a second.
That will be a big improvement on wind-profiling that relies on ground-based cloud-tracking radars, weather balloons launched from scattered locations and observations by instrumented research and commercial aircraft — leaving large areas, especially over the oceans, under clear skies and in the tropics, where wind profiles are not regularly monitored.
With Aeolus, measurements will be taken every 0.1 of a second and then averaged over a seven-second period (during which time the satellite will have travelled 50km) to obtain wind profiles from altitudes from zero to 30km. This is equivalent to launching one balloon every 28 seconds, on a global basis, for three years.
The mission is expected to increase scientists’ knowledge, and improve the forecasting, of extreme weather events such as storms, and phenomena caused by global warming and/or the effects of pollution.
Aeolus’ only instrument, the Atmospheric Laser Doppler Lidar Instrument (Aladin), supplied by EADS Astrium, France, will gather data by measuring the Doppler shift (change in frequency) between transmitted laser pulses and the returning pulses of light backscattered at different levels in the atmosphere. As well as the wind strength/direction profile created by programming the levels studied, moisture and dust can also be detected.
The UK companies E2V and SIRA are responsible for providing the instrument detector and detector electronics unit.
Martin Jones, head of Space Programmes at the UK’s Meteorological (Met) Office, feels the satellite instrument could become an important new tool for weather forecasters globally. He said: “Direct measurements of wind over the oceans and the tropics could give us the next breakthrough in improving our hurricane and typhoon forecasts.”
One important advance would be the near real-time availability of Aeolus data, especially when studying tropical cyclones that cause great economic and physical damage. Flexible programmability for five-day autonomous operation will enable the satellite to focus on specific altitudes in regions of special interest such as developing storms.
The UK’s Natural Environment Research Council (NERC) is responsible for the UK’s subscription to the ESA’s environmental science programmes.
NERC’s director of Earth Observation, Dr Stephen Wilson, said the council’s “watchword” was the idea of “earth system science” — understanding the environment as a complex and interacting system as a whole, Aeolus would not only help the weather-watchers but also advance scientists’ understanding of such global phenomena as the el Nino effect.
Professor Jose Achache, director of Earth Observation Programmes at the ESA, said the World Meteorological Organisation had given sensors to measure global wind profiles a top priority. “The wind-lidar mission has been studied for about 20 years now but technology was not yet matured enough for an implementation,” he said.
“Finally, Europe has developed the demanding technology and thus can go ahead with the full-scale satellite programme. Aeolus is planned as a pre-operational spacecraft to demonstrate the actual utility of global wind profiles for weather prediction and other atmospheric science uses. We expect that a series of Aeolus-type spacecraft will follow to suit the operational use for routine weather forecasting.”
Mike Healy — Astrium UK’s director of Earth Observation, Navigation & Science — pointed out that the space-borne laser system had only been made possible by the development of detector concepts patented by Astrium’s optics group in France together with technology developed in the UK by the then EEV company. He added: “There are of course technical challenges with Aeolus — including how to handle the one kilowatt of power from the laser and the five-day autonomy requirement which leads to significant cost savings in the ground segment.
“Even at the start of the definition phase 15 months ago, there were doubts that the technology was robust and reliable enough. By clever system design we have overcome these concerns and achieved this to a precise schedule that we committed to those 15 months ago. We have done this through sound project management and good team work, including critical contributions from our other core team members,” he said.
Pointing out that the company was also the prime contractor for the ESA’s immensely successful Envisat spacecraft — at present monitoring the global environment from orbit — he said: “Aeolus is in fact one of a number of high-profile contracts that continue to reaffirm EADS Astrium UK as a major player in European space.” — LPS/ Dawn Feature
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