LMS equipment used in final testing phases of the largest space telescope ever

If everything goes according to plan, in early 2009, the largest space telescope of its kind, the Herschel telescope, will be launched into space atop an Ariane 5 from Europe’s Spaceport in Kourou, French Guiana. Approximately six months later, Herschel will reach its operational orbit around a point in space known as the second Lagrangian point – what astronomers refer to casually as L2. From this distant point in space -- 1.5 million kilometers away from the Earth, Herschel will investigate the history of how stars and galaxies formed and study how they continue to form in the Milky Way and other galaxies.

A project of this magnitude does not happen overnight. For years, the team of experts at ESA (European Space Agency) and European Space Industry have diligently pieced together this precious piece of cargo and packaged it in its spacecraft: a tall tube measuring 7.5 meters high and 4 meters wide with a launch mass of approximately 3.3 tonnes.

The Herschel’s trip to L2 will be a demanding one. The telescope is scheduled to work for three years in an orbit far more distant than that of the Hubble telescope. Not only will it have to withstand very hard environmental conditions during its voyage to L2, it will have to survive the launch itself, where it will be violently shaken and where it will be subjected to extremely high noise levels caused by the rocket engine and aerodynamic effects on the launcher.

This is where the team of vibration and acoustic specialists from European Test Services (ETS) at the European Space Research And Space Technology Centre (ESTEC) Test Centre, in the Dutch coastal town of Noordwijk, step into the picture. Located between Amsterdam and The Hague, ESTEC is the largest ESA complex. A world-class test centre and hub for European space projects, it is most likely home to one of the highest concentrations of rocket scientists in Europe.

“The ESTEC test centre is among the largest facilities in Europe and most likely one of the largest in the world. The mechanical test facilities includes a series of electro-dynamic shakers, HYDRA, the six degree of freedom hydraulic shaker, a state-ofthe-art acoustic facility known as LEAF and a number of physical property measurement machines – all designed to verify the integrity and launch survivability of the structural design of spacecrafts, their subsystems and other individual equipment,” explained Alexander Kübler, Marketing & Sales Manager of test centre operator ETS.

“The HYDRA is quite unique. In the aerospace industry, controls need to be highly reliable and safe. You have to be able to stop the shaker in an extremely smooth way without risk of destroying the satellite. I believe there are not many sites in Europe that can handle this type of tonnage and most of them are used for seismic testing. It is not such a big deal if you break a ton of cement,” added Gaetan Piret Head of the ESTEC Test Centre.

Ensuring the Herschel’s safety

It is here in late June 2008 that the Herschel spacecraft underwent a series of mechanical tests to verify spacecraft compliance with specification requirements, ensuring that the flight model is ready for historic launch in 2009. Testing included acoustic noise tests and more than a week of vibration tests.

The LMS-ETS partnership

To run these mission critical vibration and acoustic tests, you need 150% certainty in your facility’s hardware and software. LMS International and ESTEC-ETS have a very long and successful partnership working together to solve some of the toughest challenges in the aerospace testing industry.

Five years ago, the ESTEC test centre upgraded their in-house system to a LMS installation consisting of state-ofthe-art LMS SCADAS III hardware and LMS vibration control and data-reduction software in the form of the LMS Test. Lab Environmental Testing software. In close collaboration with ESA staff, those standard items were fitted into a customized package for optimal deployment efficiency.

With over 500 channels, the new LMS system combines LMS Test. Lab Environmental software and LMS SCADAS III hardware. The 40-channel vibration control system accurately controls specific load excitation schedules in real time and in closed-loop mode. A master control station manages the overall data acquisition while four mobile stations process all measurement data. Each mobile station can manage signal conditioning, acquisition, raw time data storage and online processing for 128 channels.

The LMS acquisition systems display real-time measurement results and deliver electronic data immediately after

the test, mostly on USB sticks or DVDs although the system still has the capacity to produce printed plots extremely fast. Truly revolutionary, these mobile processing stations offer maximum test flexibility: they can be divided over multiple simultaneous test programs or united into a single mega-unit for 400- 500 channel projects.

“The old system was installed in 1985 and it survived until 2002. Towards the end, we were limited by the number of channels – only 256 -- and the analogue back-up recording on tape. It was obviously time for an upgrade,” explained Mr. Piret. “We knew what we wanted: 500 channels; a highly reliable system without data loss; time domain throughput on all channels; processed data available immediately after the test. LMS created four independent yet interlockable systems that could be used separately or together. This gives us a tremendous amount of flexibility as a test centre.”

Across the board improvements in mobility, flexibility and time-savings

This new system as well as a key software upgrade and several add-ons like the animation module have changed the concept of testing and data acquisition at the ESTEC Test Centre. With the mobile system, the operator moves physically with the rack and can easily interact with other operators on the floor.

“During tests, you only need one operator with the master control panel. You don’t need four operators – one in front of each rack talking with walkie-talkies. The days of walkie-talkies are long gone,” quips Steffen Scharfenberg in charge of mechanical testing at ESTEC.

This new mobility is an aspect that translates to improved flexibility as well. The previous system was one big and solid permanent system. Today, the data acquisition system looks like four small refrigerators on wheels. The units can easily be split up or combined for 512 channel functionality.

“We can easily handle two test campaigns simultaneously. This wasn’t the case with the old system. In addition,

the system’s impressive bandwidth and dynamic range, along with direct charge-type sensors support on the

LMS Scadas III hardware and analysis capabilities allows us to use it as a highchannel count transient recorder for pyro-shock testing,” added Mr. Piret.

The time-crunching patch panel concept

Another aspect of flexibility which led to massive time-savings is the patch panel concept. When thinking about the new system, Gaetan Piret came up with the idea to move the connector set-up along with the satellite when moving from the clean room where set-up takes place to the actual shaker. “For vibro-acoustic test, there is

physically 100m between the two facilities. In the past, this meant disconnecting 200 cables, reconnecting 200 cables on the other side and double-checking them. In short about 2 days of work for only 200 channels,” said Gaetan Piret.

Now thanks to the patch panel concept, the team only does the connection job once saving significant time from the tedious set-up process. “With the new 500-channel system and patch panels, we only have 16 master cables to connect instead of 500 individual ones. To reconfigure now it takes a couple of hours instead of what would have been 4 days or more,” adds Steffen Scharfenberg.

Data delivery in 30 minutes

On the data processing side, the team sees some significant improvements as well. Being a 100% online system, LMS Test.Lab delivers the frequency domain results right after the test. The data is ready without any additional post-processing. As a back-up, the time domain data as available as well.

“After a large test, we can usually deliver the data on a USB stick in about 30 minutes for 500 channels. This of course includes the quality control we perform before handing it over to the customer,” stated Jean-Sébastien Servaye, ETS Data Handling Manager at ESTEC. “That can be challenging since the customer usually wants the data immediately,” adds Steffen Scharfenberg. “The best point about LMS Test.Lab is that we have everything in the system: configuration, conditioning and data acquisition. You don’t have to translate the data. It is very seamless – easy even,” states Jean-Sébastien Servaye.

Future-proof super-safe testing

With most of Europe’s complex satellite test campaigns and even other types of testing such as aircraft and shipping manufacturers finding their way to Noordwijk, the ESTEC test centre has clearly become a benchmark in safety, quality and efficiency. “In regards to security – most likely the most important factor at the test centre – the operator really appreciated the self-check feature in LMS Test.Lab control. It concisely gives a forecast of how the spacecraft will behave in regards to the response of the each channel during the sine sweep or random excitation. In a sense, it is another set of eyes in these missioncritical tests to guarantee the safety of priceless aerospace cargo,” concludes Jean-Sébastien Servaye.

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