Wind Lidar Working Group, Miami 6 Feb 20071 Status Martin Endemann

Wind Lidar Working Group, Miami 6 Feb 2007

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StatusMartin Endemann


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Aeolus mass is 1.1 t (plus fuel), the solar arrays are about 13 m wide to produce 2.2 kW (orbital average power 1.4 kW).It is compatible with small launchers (Vega, Rokot, Dneper).

It carries a single payload, the Atmospheric LAser Doppler INstrument ALADIN.

The satellite is designed for simple operation (7 day autonomy, 5 day unattended survival), repeating 7-day command cycles.

Aeolus satellite with its ALADIN payload


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…and the Aeolus satellite busFlight Model during integration testing at Astrium Germany, Friederichshafen

Most subsystems have been integrated, Flight software is under testing


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ALADIN is the only payload of Aeolus. Its size is dominated by the large afocal telescope of 1.5 m diameter.

It uses diode pumped Nd:YAG laser to generate UV-light pulses (355 nm) emitted to the atmosphere.

Two transmitter laser assemblies (blue) and the receiver (yellow) are on the structure below the telescope.

A large radiator (mounted on the satellite bus) is coupled with heat pipes to the transmitter lasers.

Star trackers are mounted on ALADIN structure to give best possible pointing reference.

Total mass is 480 kg, power 830 W.

ALADIN Atmospheric Laser Doppler Instrument


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ALADIN optical layout

Transmit/receive telescope:1.5 m diameter, SiC lightweight structure (mass about 75 kg), thermally focused

Transmit/receive optics: high stability optical design, polarizer as T/R switch, 1 focus for chopper location, 1 focus as field stop,background filter (1 nm equivalent bandwidth + prism for broad-band rejection

Rayleigh receiver: Double edge etalons, sequentially illuminated, Outputs focused on single accumulation CCD

Mie receiver: Fizeau interferometer,

thermally stable design, Outputs collimated single

accumulation CCD

Transmitter laser assembly:

Reference Laser Headwith stabilized tunable

MISER lasersseeding the

Power Laser Headwith low power oscillator,

two amplifiers and tripling stage

two redundant laser assemblies in ALADIN


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ALADIN transmitter laser (TXA)

For single mode operation, the laser is injection seeded with output from a frequency stabilized cw Nd:YAG laser which is coupled via single-mode fibres to the power laser head.

The laser is conductively cooled via heat pipes mounted on thermal interface plates.

A diode pumped Nd:YAG laser is generating single frequency pulses at 355 nm wavelength with 120 mJ energy at 100 Hz repetition rate. It is operated in burst mode of 12 s on (5 s warm up, 7 s measurement), and 16 s off to increase life time and reduce power consumption.


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Engineering Qualification Model (EQM) has performed vibration test campaign, but with initial problems.However, these problems have been shown to come from external Ground Support Equipment, not the laser itself. Still, the sensitivity of internal laser alignment on external parts is unhealthy and has lead to a review of some design features…

EQM has performed TV test campaign, but it needs to be repeated, probably due to a workmanship issue…

Flight Model 1 has been integrated and initial tests show good performance. Laser has been closed and is presently undergoing full performance characterization.Dependent on results of design review, some retrofits will be introduced before delivery.

ALADIN transmitter laser (TXA)status (1)


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ALADIN transmitter laser (TXA)the hardware

Flight Model 1 of Power Laser Head during integration at Galileo Avionica, Pomezia (Italy)

Dec 2006


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ALADIN transmitter laser (TXA)the hardware

Flight Model 1 of Power Laser Head during integration at Galileo Avionica, Pomezia (Italy)

Jan 2007


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Reference Laser Heads (RLH) Flight Model 1 has been delivered;FM 2 and FM 3 are in final testing – beautiful units from TESAT

Transmitter Laser Electronics (TLE): FM1 completed, some retrofits required to improve communication to ALADIN Control Electronics


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Lifetime of pump laser diode stacks:After initial testing of various different commercial pump diodes, a manufacturer was selected (Nuvonyx-Europe, France) and Flight Model manufacturing initiated.Extended burn-in was performed to select best diode stacks for flight; lifetime testing is ongoing for final qualification (end Feb 07).

Laser Induced Damage (LID):Lifetime of high power optics is often limited by coating damage. Investigations have shown that damage threshold continues to decrease with the number of pulses fired. A power law has been assumed to extrapolate the damage threshold from a 10.000-on-1 damage curve to end-of-life conditions (5 Gpulses).

Laser Induced Contamination (LIC):Outgassing of organic materials is known to generate absorbing layers on coatings, in particular in vacuum operation.Careful selection of materials and stringent cleanliness control are essential prerequisites for a long laser lifetime.



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Sic secondary

mirror

SiC legs with tubular section

Sic parts linking legs and M2

Titanium brackets SiC Pr imary mirror

Titanium Isostatic mounts

Upper Strut Thermal

Protection

ALADIN transmit/receive telescope

Ultra-lightweight Telescope all in silicon carbide (SiC)

Diameter: 1.5 m

Afocal optics

Mass complete: 75 Kg

First frequency > 60 Hz

Thermal re-focusing capability

Wavefront error: 350 nm (complete telescope)


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status: completed and integrated with ALADIN Structure at Astrium Toulouse

ALADIN transmit/receive telescopeFlight Model


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ALADIN Transmit/Receive Optics (1)

TRO combines the transmittter and receiver optical paths, carries the field-stop, background rejection filter and the laser chopper assembly, and the reference light path from transmitter to receiver.

High stability and minimum wave front errors in a small compact unit are design drivers.

In environmental testing right now.


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ALADIN Transmit/Receive Optics (2)

Flight Model prepared for environmental testing, run by unit manufacturer Kayser-Threde at IABG, Munich.


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ALADIN Receiver OpticsRayleigh & Mie Spectrometers

Rayleigh Spectrometer completed at Oerlikon Space AG (ex Contraves), and delivered to Astrium Toulouse.

Mie Spectrometer under environmental testing


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ALADIN Receiver OpticsRayleigh & Mie Spectrometers

Rayleigh Spectrometer completed with isostatic mounts before integration to Optical Bench Assembly at Astrium Toulouse


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Validation of Performance ModelsALADIN Airborne Demonstrator A2D

The pre-development model of the receiver and one of the breadboard lasers have been combined to a complete wind lidar to fit into the Falcon research plane from DLR together with the CTI 2-um wind lidar.

Proving flights in the Falcon jet have been successfully completed in Oct 2005.

An extended ground-based campaign with other lidars and conventional wind sensors has been completed in Oct 2006. Over 100 hrs of data have been collected and are being evaluated.

However, transmitter laser has to be refurbished. Repeated proving flights planned for April 2007.

First airborne campaign is planned for Sep 2007.


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Aeolus statussummary

First space mission to measure global wind profiles: new technology, new challenges

Hardware manufacturing and integration is well advanced:Aeolus satellite bus mostly integrated,ALADIN structure/thermal/electronics hardware all available

But the critical technologies do need time to chase the new Gremlins away…

Launch in the mean time has officially been slipped to June 2009

Gilles Labruyére 2007Gilles Labruyére 2007

Documents

Wind Lidar Working Group, Miami 6 Feb 20071 Status Martin Endemann