Faster detection of weak objects with the LSST telescope

The Large Synoptic Observing Telescope (LSST) is an advanced type of telescope that can reach 3.2 billion pixels because it combines a huge 8.4-meter primary mirror with the largest digital camera in the world, improving its performance. field of view. This combination would detect pale objects with particularly short exposure times, twenty times faster than what is achievable at the present time.

These advances would give him the opportunity to observe the entire sky twice a week. Every night, more than 30 terabytes of data would be generated, processed and stored. The LSST was to have its first look at the sky in 2015 from the summit of a mountain on the Chilean Andes and get fully operational in 2017.

Large Synoptic Survey Telescope (LSST)

The large synoptic topographic telescope

Every night, the LSST can record hundreds of images from the sky because of its exposure time of only 15 seconds. In fact, it would give a film from the sky, but the most important capability of the LSST is that it can detect and track objects close to the Earth that could pose a risk of collision.

In addition, it can capture ephemeral cosmic events that can be ignored by conventional telescopes. In the end, the LSST would be used to create a 3D map of the universe with unprecedented details. Scientists and astronomers hope to use it to locate dark matter and characterize the properties of dark energy, which remain for the moment theoretical.

Extraordinary optical properties

The impressive structure of the LSST, which includes the 8.4 meter mirror, incorporates the main and tertiary mirrors of the telescope into a single piece of glass. This gives the LSST several extraordinary optical properties. The grinding of mirror surfaces was to be completed in January 2012. The process involved the removal of more than 11,000 pounds of material. It would take more than two years.

The mirror of 8.4 meters in the polishing cell

As mentioned, the mirror is large. Therefore, contraction and expansion due to temperature differences in the different sections can have a substantially negative effect on the final accuracy of the grinding and polishing operations.

Such a negative effect can be disastrous because of the time required to complete the process. It is overcoming this problem that Omega Engineering has been able to make a significant contribution to the success of its business.

The LSST design team wanted to use a custom thermal control system installed at the back of the mirror to maintain a uniform temperature throughout the entire structure at all times.

Precision thermocouples had to be glued to the mirror in the front, rear and middle planes at 146 locations. If a temperature difference was observed between any of the monitored sites, the temperature control system would react to correct it. The specification required differential temperature measurements to be reproducible and accurate to 0.1 degrees Celsius.

High quality thermocouples

The best way possible to achieve such performance is to use high quality thermocouples, all made with yarn from the same batch. Omega Engineering was different from other vendors that the LSST team contacted in their willingness and willingness to meet all the special requirements of this application.

Omega Engineering already had significant quantities of thermocouple wires from the same batch because of its large insulating extrusion operation. After a review of Omega's production capacity and quality assurance procedures, a green light was given and the project began.

Rear surface of the 8.4 meter mirror

Thermocouples provided were Omega type^® Products of the 5TC series, the only difference being that they were made from a single batch of special error limit thermocouple wires. In addition, they received special handling and packaging, in accordance with the specifications of the LSST team. The drivers of all units were terminated with Omega strain relief connectors and they were rolled up into large rolls.

In doing so, a great uniformity is obtained between the numerous thermocouples. It has also improved temperature measurements and traceability on the large number of locations involved. The explanation, reported by the LSST team, is that the temperature monitoring system, using the^® thermocouples, meets the requirements of the system at 0.1 degrees Celsius.

Once the telescope is complete, the same thermocouples will be used for continuous thermal monitoring of the mirror. During use, relevant data can be used by the digital processing package to compensate for distortion caused by mirror expansion and contraction under real-world conditions.

The success of this project has attracted Omega's interest and it has been requested to provide additional thermocouples from the same batch for test and measurement applications in other phases of the project.

Conclusion

Omega Engineering is pleased to play an important role in the successful rectification and polishing of the 8.4-meter LSST mirror. Omega's commitment to providing the products and services its customers need is evident through this application. A custom engineering capability and extensive experience in meeting specific customer needs have made Omega the reliable choice for test and instrumentation applications.

This information has been obtained, revised and adapted from documents provided by OMEGA Engineering Ltd.

For more information on this source, please visit OMEGA Engineering Ltd.