The Roman Space Telescope (RST)

On January 10 2021, I was contacted by Dr. Ed Cheng (note spelling), who is one of the scientist working on RST.  He wanted to know if I was interested in starting a side project that involved controlling LEDs for a in-flight calibration system for the space telescope.  It sounded simple enough and I decided to give it a try.  This calibration system was for the main camera of RST, called the Wide Field Instrument (WFI), which was/is being built by Ball Aerospace.  They subcontracted out the calibration system, called the Relative Calibration System (RCS) to SDL. However, this system was behind schedule, and management wanted to have a backup in case they did not deliver.  There was some political sensitivity, so this side project would be in secret and us two Dr Eds would work this quietly.

I designed and built a simple prototype, and found that my initial design concept was not going to work (using an LM117 as the current regulator).  I learned from this and then switched to a more traditional op-amp based design and drew the schematic and did the simulation analysis.  However, in April 2021, Ed told me the investigation we were doing was being cancelled as SDL showed good progress.

This changed again in June 2021 when SDL revealed at a monthly review to RST management that they were still behind schedule (they had been working on the RCS since Summer 2018).  The SDL subcontract was cancelled, and I was tasked with resuming work on the design, which would now be renamed simplified RCS, or sRCS. 

My role on sRCS would be as Electrical Lead, and I formed a small team of old friends.  My alternate would be Roger Chiei, the FPGA and test GUI was built by Dr. Will Clement.  Our electrical tech would be Ryan Fischer.

The reason SDL could not complete the design in the three preceding years was the large dynamic range and stability needed in the performance of the LED controller.  Starting with a clean slate, I proposed a much simpler design that would be easier to package and build.

The main assembly house that was selected was the Peraton corporation in Beltsville, MD.  That is the location of the image captured above.  In addition to building the flight design



Since the digital interface between sRCS and the instrument is a simple serial connection, I reasoned it would be worth it to build a simulator to start our code development.  That test is shown above, the commercial board that hosts our FPGA code is the very small board on the edge of the blue mat above.  It communicates with the large gold box that is at the center.  This test was initially not successful, but we found the error.  This made this test very valuable and worth while.

The first unit built would be the Engineering Development Unit (EDU) shown above on the test bench.  We had to make some small modifications to tweak the design and this was done on the three flight units that would follow.

In the image above we assembled the complete non-flight system for an early EMI test.  You can see the sRCS electronics as the gold box sitting on the copper bench on the right and this powers the integrating sphere that contains the LEDs.  This sphere sits in a metal cage on the far right of the copper table.

The integrating sphere above holds the 24 LEDs that comprise of the sRCS.  These LEDs are powered by the sRCS electronics.  The light is fired inwards and then come out of the gold cone at the top.  The shortest wavelength light emitted is in the red color.  So many of these cannot be seen by the human eye.

Both flight units were tested together in thermal-vacuum in the setup above.  We were able to confirm good operation over the temperature that is expected on-orbit.

We took a break from work and headed to Aruba for the New Year holiday and then came back to ship the system to Ball Aerospace in Boulder, CO.  The system was loaded onto a tractor trailer and was driven without stop (two drivers) along with a chase car to Boulder.

We delivered the system and oversaw the installation into the WFI instrument that is being built in the cleanroom in Boulder.  You can see the two sRCS electronics units in the bottom part of the instrument above. 


As part of the functional test, we turned the LEDs on, and you can see the red glow in the image above.  Note that it appears in a curved opening, and that is the outline of the imaging detector of the Instrument.  It turns out that my daughter is the one building this detector.  You can see this curved detector array in the logo of the mission that is engraved on the cover of the electronics unit.