LMS equipment used in final testing phase of largest space telescope ever built

If all goes according to plan, the Herschel telescope, the largest space telescope of its kind, will be launched in early 2009 on an Ariane 5 rocket from the European Space Agency's Kourou launch site in French Guiana. In about six months, Herschel will reach orbit around the second Lagrange point in space, also known as the L2 point by astronomers. From this point in space, 1.5 million kilometers from Earth, Herschel will investigate the history of how stars and galaxies formed, and how they in turn formed the Milky Way and other galaxies.

Such a major project is not achieved overnight. Expert teams from ESA (European Space Agency) and the European space industry have worked hard for many years to assemble the various expensive structural components and load them onto the spacecraft. It is a tall cylinder about 7.5 meters high and 4 meters wide, with a launch mass of nearly 3.3 tons. Herschel's journey to the L2 point will be extremely challenging. The Herschel telescope is planned to be in an orbit more distant than the Hubble telescope for three years. Not only will Herschel have to withstand the harsh environmental conditions of the voyage to L2, but also the strong vibrations that it will be subjected to during launch, as well as the extremely high noise levels generated by the rocket engines and the aerodynamics of the launch vehicle. This is exactly why the vibration and acoustics expert group of the European Test Services (ETS) at the European Space Research and Space Technology Centre (ESTEC) in the Dutch coastal town of Noordwijkr has been involved in the project. ESTEC, located between Amsterdam and The Hague, is the largest ESA joint venture. As a world-class test centre and hub for European space projects, it is likely to be home to one of the highest concentrations of rocket scientists in Europe.

"The ESTEC test centre is the largest in Europe and possibly one of the largest in the world. The test equipment includes a range of electrodynamic shakers, such as the 6-DOF hydraulic shaker HYDRA, a state-of-the-art acoustic facility called LEAF, and a large number of physical characterization test equipment - all designed to verify the structural design integrity and launch survivability of spacecraft, their subsystems and other individual equipment," explains Alexander Kübler, Marketing and Sales Manager at the ETS Test Centre Operations.

Gaetan Piret, head of the ESTEC test center, adds: "HYDRA is unique. In the space industry, the control must be highly safe and reliable. It is necessary to be able to brake the shaker very smoothly to avoid any risk of damaging the satellite. I believe that there are only a few institutions in Europe that have this amount of equipment at their disposal, and most of them are used for seismic testing."

Ensuring the safety of Herschel

At the end of June 2008, the Herschel spacecraft underwent a series of mechanical tests to verify that the spacecraft meets the technical requirements to ensure that the flight model is ready for the historic launch in 2009. The tests included acoustics, noise tests and vibration tests for more than a week.

LMS-ETS partners To perform critical vibration and acoustic testing tasks, 150% confidence in the hardware and software is required. LMS International and ESTEC-ETS have a long and successful partnership in jointly meeting the tough challenges of space testing.

Five years ago, the ESTEC test center underwent an internal system upgrade, which will use LMS equipment, including the best-in-class LMS SCADAS III hardware and LMS Test.Lab environmental testing software for vibration control and redundant data reduction. In close cooperation with ESA staff and in order to adopt the software more efficiently, these standard features were integrated into a customized package.

The new LMS system combines LMS Test.Lab Environmental software and LMS SCADAS III hardware with more than 500 channels. The 40-channel vibration control system accurately controls the excitation process of specific loads in real-time and closed-loop mode. The main control station manages the overall data acquisition, while the four mobile stations process all test data. Each mobile station can manage 128 channels of signal conditioning, acquisition, raw time data storage and online processing. The

LMS acquisition system displays real-time test results and transmits electronic data immediately after the test, mainly via USB stick and DVD for storage, although the system can also quickly generate printed charts. The real innovation is that these mobile processing stations provide maximum testing flexibility: they can be divided into multiple simultaneous test tasks or combined into a 400 to 500 channel data acquisition system.

"The old system was installed in 1985 and used until 2002. In the end, we were limited in the number of channels (only 256 channels) and the tape-like data backup. It was clear that it was time for an upgrade," explains Mr. Piret. "We knew what we wanted: 500 channels; a highly reliable system with no data loss; time domain output capability on all channels; and immediate processing of the data after the test. LMS created four independent interlocking systems that can be used separately or together. This gives us great flexibility in the test center."

Improved mobility, flexibility and time savings

The new system with key software upgrades and additional modules such as animation have changed the concept of testing and data acquisition at the ESTEC test center. With the mobile system, the operator physically moves with the launcher and can easily interact with other operators on the ground. [page]

"In testing, only one operator is needed at the main control panel. No more four operators talking on walkie-talkies at each launcher. The days of walkie-talkies are gone forever," says Steffen Scharfenberg, head of mechanical testing at ESTEC.

This new mobility is also an aspect of improved flexibility. The previous system was a bulky, fixed, permanent system. Now, the data acquisition system looks like four small refrigerators on wheels. The units can be easily separated or combined to form a 512-channel data acquisition system.

"Unlike the old system, we can easily run two tests at the same time. In addition, the system's impressive bandwidth and dynamic range, the charge-type sensors supported by the LMS Scadas III hardware and the analysis capabilities allow us to use it as a high-channel-count transient recorder for burst shock tests," added Mr. Piret.

Time-saving patch panels

Patch panels can save a lot of time. When considering the new system, Gaetan Piret came up with the idea of ​​moving the satellite and its connector assembly from the clean room where the assembly was set up to a real vibration table.

"For vibration and noise testing, the physical distance between the two devices is 100 meters. In the past, this meant separating 200 cables and reconnecting them on the other side and carefully checking them. In short, it would take two days of work just for 200 channels," said Gaetan Piret.

Herschel will be launched on an Ariane 5 rocket, along with ESA's Planck spacecraft. Shortly after launch, the two spacecraft will separate and independently travel to different orbits around the second Lagrange point in the Earth-Sun system.
Herschel will provide an unprecedented view of the cold Universe, filling a gap in observations from the ground and earlier such space missions. Infrared radiation can penetrate the clouds of gas and dust that block objects from optical telescopes, providing insights into star-forming regions, the center of the Milky Way and planetary systems. Space dust obscures colder objects such as small stars and molecular clouds, and even galaxies, which are almost non-luminous in the optical range, but are still visible in the infrared region. Observations in the infrared range thus provide us with a view of the unknown universe. [page]

Thanks to the patch panel, the team now only has to make the connections once, saving valuable time from the tedious setup process. “With the new 500-channel system and patch panel, we only have to make 16 main cables instead of 500 individual cables to make the connections. What used to take four days or more can now be done in just a few hours,” adds Steffen Scharfenberg.

Data delivery in 30 minutes

There have also been some significant improvements in data processing. As a 100% online system, LMS Test.Lab delivers frequency domain results immediately after the test. The data does not require any additional post-processing. At the same time, time domain data is available as a backup.

“After a large test, we are usually able to deliver data for 500 channels via USB stick in 30 minutes. This of course includes our quality control before delivery to the user,” states Jean-Sebastien Servaye, ETS Data Processing Manager at ESTEC.

In a typical test, Herschel is subjected to transverse sinusoidal vibrations in the frequency range of 4-100 Hz.
For this vibration test, the spacecraft model is mounted on an electrodynamic shaker at the ESTEC test center.
Over a period of about 80 seconds, the shaker frequency is gradually and steadily increased from 4 Hz to 100 Hz, with
four vibration tests performed in each of the three axes of the Herschel spacecraft.

“This presents a challenge, as customers often want data immediately,” adds Steffen Scharfenberg. “The great thing about LMS Test.Lab is that the system includes configuration, signal conditioning and data acquisition very well. You don’t have to do data conversion. It’s very accurate and easy to use,” says Jean-Sebastien Servaye.

Proactive, safe and reliable testing

With Europe’s growing number of complex satellite test missions, as well as other types of testing (e.g. for spacecraft), the ESTEC test center in Noordwijk has clearly become a benchmark for safety, quality and efficiency in testing. “As for safety, which is probably the most important factor in a test center, operators benefit greatly from the self-checking function in LMS Test.Lab Control. It concisely predicts the response that each channel will get under swept-sine or random excitation, and these responses describe the behavior of the spacecraft. In a sense, it is an important reflection of the safety of expensive space equipment in mission-critical testing,” concludes Jean-Sebastien Servaye. (end)