Aladin’s Magic Laser Lamp

Measuring cyclones: ESA’s Aeolus wind mission will provide timely and accurate profiles of the world’s winds and further information on aerosols and clouds. (Source: ESA / ATG Medialab)

The launch of Aeolus – ESA’s mission to map Earth’s wind in real-time – is getting tantalizingly close, with the satellite due for lift-off next week from Europe’s Spaceport in Kourou, French Guiana. With the wind in their sails, mission teams are busily preparing this unique satellite for its upcoming journey.

Aeolus will carry a sophisticated atmospheric laser Doppler instrument, dubbed Aladin. Combining two powerful UV lasers, a large telescope and extremely sensitive receivers, it is one of the most advanced instruments ever put into orbit. Lift-off is set for 21 August at 21:20 GMT on a Vega rocket.

“Aeolus’ arrival at the launch site marks the end of sixteen years of intensive planning, testing and construction, by literally generations of engineers and scientists” says Juan Piñeiro, spacecraft operations manager for Aeolus. “We now look forward to seeing the skill and dedication of these countless individuals come to fruition, as Aeolus takes flight and we begin receiving evidence that the satellite can fulfil its very ambitious mission objectives.”

The Aeolus satellite carries a complex instrument: Aladin, the first wind lidar in space. (Source: ESA / ATG Medialab)

Currently, one of the biggest challenges in making accurate weather predictions is gathering enough information about Earth’s wind. Aeolus will be the first-ever satellite to directly measure winds from space, at all altitudes, from Earth’s surface through the troposphere and up thirty kilometers to the stratosphere – providing information that will significantly improve the quality of weather forecasts.

Paolo Ferri, head of mission operations at ESA adds, “The Aeolus mission will be a wonderful addition to our fleet of satellites that continually observe Earth bringing us incredible insights into our planet, in particular into the complex world of atmospheric dynamics and climate processes – systems that not only affect our everyday lives but also have huge consequences for our future.”

Aeolus will orbit continuously from pole to pole in a ‘sun-synchronous’ orbit – passing over any given point on Earth’s surface at the same local time each revolution, always maintaining the same orientation in relation to the Sun. Specifically, Aeolus will follow a ‘dawn/dusk’ orbit, appearing to follow the borderline between sun and shade, day and night on Earth, meaning its solar panels will always receive the same amount of light from the Sun.

The Atmospheric Laser Doppler Instrument, Aladin for short, comprises a powerful laser, a large telescope and a very sensitive receiver. The laser system generates a series of short light pulses in the ultraviolet spectrum at 355 nm, which is used because the backscatter from atmospheric molecules at this short wavelength is particularly strong.

The complex system of laser sources and amplifiers is packaged closely together. There are two small lasers to fix the frequency of the emitted pulses, a laser oscillator to generate pulses, two amplifier stages that boost the energy of the light pulses to the required value and a frequency convertion crystals stage to produce the correct wavelength. Aladin is dominated by a large telescope, which measures one and a half meters across. It is used to collect the backscattered light from the atmosphere and then directs it to the receiver. Although large, it is made of lightweight ceramic material so it weighs only 55 kg.

Aeolus measurement geometry: The wind is observed orthogonal to the satellite ground-track, pointing 35º off-nadir, away from the Sun. (Source: ESA / ATG Medialab)

The telescope is pointed 35 degrees away from the orbit plane in order to transmit and receive light perpendicular to the speed of the satellite. This allows Aladin to determine the east-west horizontal component of the atmosphere. The receiver analyses the Doppler shift of the backscattered signal with respect to the frequency of the transmitted laser pulse.

Two optical analyzers measure the Doppler shift of the Rayleigh and Mie scattering from molecules, aerosols and water droplets picked up by sensitive photo-detectors. The wind profiles are accumulated over at least twenty individual measurements before being downlinked to ground for further averaging.

In preparation for this unique mission, teams at ESA’s European Space Operations Centre in Germany have spent months practicing to handle any possible scenarios in a series of launch simulations in the Main Control Room. Once a satellite has been launched into space, it goes through the critical and complex ‘launch and early orbit phase’, during which control systems and, later, instruments, are progressively switched on and their health and proper functioning assessed.

This is a risky time when the satellite is unusually vulnerable – not yet fully functional but still exposed to the hazards of space. Pier Paolo Emanuelli, flight director for Aeolus, describes this unique period: “Every satellite has its own unique objectives, orbit and quirks, and Aeolus is no exception. Teams of highly trained engineers, flight dynamics specialists and experts in control systems and ground stations have been practicing exactly what Aeolus needs to do, when, and how they will instruct it to do so.” (Source: ESA)

Links: Observing the Earth > Aeolus, European Space Agency, Paris, France

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