Collaborative Engineering Creates Innovative Cryocooler Isolation System for ASTRO-H Mission
3 December 2015
1. Tell us a little bit about yourself, education, and work at Moog?
I joined Moog in June 2006 as an engineer in the Design and Analysis Department. I was part of a team that designed, fabricated, and tested over 20 isolation systems, including SoftRide. I’m currently in the role as Business Development Manager for Moog Mountain
View operations. I’ve been in this position for two years and am still learning the ropes.
I have a BSME from Kansas State University. While my degree was critical to being a part of the Moog Mountain View team, my background in structures and finite element analysis (FEA), -(garnered from being mechanical design lead on the solar car team)-, was key to joining this highly technical team of subject matter experts.
2. How did Moog become involved in the Astro-H mission? What have we contributed to the program?
The primary sensor of the Astro-H mission is the Soft X-Ray Spectrometer (SXS). The detector in the SXS instrument is approximately the size of a human thumb nail. It measures the energy from x-rays directly. In order to measure these energy signatures, the instrument needs to be cooled to 50 mK. That is cold!
Often Moog provides vibration isolation systems to reduce jitter on optical payloads. For Astro-H, the detector needed to be so cold, any mechanical vibration would heat the sensor beyond its operational range. Further, the exact instruments that enable second stage cooling of the instrument, the cryocoolers, also produce the mechanical disturbance that inhibits the sensor function.
JAXA (Japan Aerospace Exploration Agency) initially reached out to Moog in the summer of 2013 requesting information on our passive component isolation systems. We suggested a small study contract to evaluate if our structural dynamics capabilities and isolation system expertise would provide the necessary energy attenuation from the cryocooler to the SXS instrument.
3. What is so special about this system?
The technical team at Moog is impressive. What Moog has done for the Astro-H is pretty amazing. Our team of highly talented structural analysts were able to design an isolation system that, at times, had highly incompatible requirements. From design space limitations to exceedingly high design loads – the team persevered and provided JAXA exactly what they needed.
From the beginning we recognized the challenge of this system. Not only were we required to meet extremely stringent attenuation requirements on-orbit, we were also required to limit displacements and loads during launch; two completely different environments with completely different objectives. Therefore, we implemented an entirely passive, two – stage, bilinear, isolation system that reduced displacement during launch and mitigated energy transfer on-orbit. Further, we needed to move the heat dissipated by the cryocoolers to other areas of the spacecraft. The system required heat transfer paths, thermal straps that were flexible enough to not influence vibration attenuation, strong enough to survive launch, and conductive enough to move heat as quickly as possible. This system is critical to an industry that wants risk reduction, cost reduction, less complexity, yet maintains performance. No other competitor has this type of isolation system.
We were driven by customer schedule and a set of requirements that were the most challenging we had ever seen. Yet, we were able to give the performance needed, while packaging it into a system that was never designed to accommodate more hardware. Through ingenuity and determination, the team has designed an isolation system that is the first of its kind.
4. What were the challenges while creating this system?
The challenges were many. However, at each stage we were able to move forward with new design techniques, better testing, and exceptional coordination with the customer.
Displacement During Launch
One key aspect of any mechanical isolation system is that it introduces compliance into the structure. Therefore, during high energy loading – like launch – one would expect to see large displacements across the isolators. The lower the frequency, the higher the displacement. The cryocoolers had loop heat pipes (LHP) to transfer fluids to and from the instrument. These LHPs were rigid metallic tubes that ran as flanking paths across the vibration isolation system. They were sensitive to excessive displacements. This is the primary reason Moog implemented a secondary isolation system. The secondary system was much stiffer and limited the displacement of the primary load path during launch loading
The original infrastructure, designed by JAXA suppliers, did not anticipate the necessity for an isolation system under the cryocoolers. Therefore, Moog needed to design around existing infrastructure (wire harnessing, LHPs, sensors) as well as tuck the isolation system as closely to the cryocooler as possible.
The cryocooler removes heat from the LHP and moves it to the surrounding structure where it will not interfere with sensor performance. However, Moog’s vibration isolation systems are very good thermal isolation systems. For Astro-H, this is a less than ideal situation. The cryocoolers will not function at peak performance if the heat sticks around. Moog's design necessitated flexible, heat-conducting thermal straps. We ultimately selected graphite fiber thermal straps (GFTS) due to their heritage, minimal weight, and high efficiency. Their flexibility reduces impact to overall mechanical vibration isolation performance while dumping the heat in order to have the cryocoolers function properly.
5. What was it like working with another Moog operating group?
This program is a classic example of how Moog can work across operating groups to provide the customer with the necessary resources. Without the help from the Industrial Group and Space and Defense Group (SDG) we would not have had the capability to perform critical performance testing on the cryocooler isolation system. Moog Industrial helped facilitate high energy 6-DOF testing of the cryocooler isolation system in Ann Arbor Michigan over a very tight schedule.
Blog by John Howat | SDG, Senior Project Engineer