Hubble Servicing Mission 4 Blog

Name: Udo Rapp

Title: Engineering Support for the Solar Array Drive Electronics (SADE).

What is your area of expertise?

My expertise is the Solar Array Drive Electronics (SADE) that controls all rotations of the solar arrays.

What made you choose this field?

I have been leading projects designing drive electronics for all kind of mechanisms on satellites for many years. I feel this is a quite interesting job as you are always working on projects where you can directly see the effects and the operation of the electronics; if the mechanism performs its tasks and movements as intended and with the required accuracy, you did a good job!

What are the challenges for the Drive Electronics for the Solar Arrays?

Well, the SADE (Solar Array Drive Electronics) for the Hubble Space Telescope has to perform suitably to specific requirements. It receives rotation commands from the spacecraft whenever a re-positioning of the solar arrays to point to the Sun is requested. The major requirement is then to calculate an extremely smooth velocity profile (plan for movement) and to control the solar arrays’ rotation accurately according to this profile. It has to be noted that the SADE was designed and built around the year 1980, where much effort had to be spent to build up all of the functions without the benefit of advanced processors and software that we know today.

How have the solar arrays and the drive mechanisms and electronics performed? We are closely watching all solar array positions and telemetry during the mission to ensure that no excessive slippage occurs which potentially might disturb the astronauts during their EVA work. From time to time the solar arrays have to be re-positioned, for example, to point the solar arrays to the Sun for battery charging or to provide the astronauts access to other locations on the telescope. All of this is operating perfectly.

How do you feel about supporting what many call the most powerful astronomical tool of our time?

It feels very special looking at the history of this project as it is very unique - the only space telescope that can be serviced by astronauts. It was launched in 1990 and has been operating well since that time. It’s been serviced and maintained several times in-orbit and it continues to deliver great pictures and science data from our distant past. Hubble is very special and unique for me.

Do you have a favourite HST image?

Not really. They all present colourful, sometimes very surprising views of the Universe, so it is hard for me to choose one favourite from so many great images.

Have you worked all of the servicing missions?

No. I started working on this project shortly after its launch in 1990 and I was involved in all serving mission preparations since then. However, this is the first time that I have had the opportunity to support a servicing mission at the operation control centre in GSFC (Goddard Space Flight Center) directly.

What has been the most exciting part of SM4 for you so far?

For me, the first egress of the astronauts during their first EVA (spacewalk) day was very exciting! To see them beginning their work and knowing that they were going to start all the work that’s been planned for months and years in painstaking detail felt very special.

What has been the most stressful part of SM4 for you so far?

We are crossing fingers. As I said before, everything is operating very well and there has been no stressful part at all. However, as we are working on 12-hours shifts throughout the mission, it still turns out to be a strenuous job.

What is next for you?

Continuing to monitor all solar array telemetry during Sm4 and, after the mission, I am responsible for several drive electronics projects in our company which will keep me busy for the next several months.