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Matthew Greenhouse

Hunt for Exoplanets

Matthew Greenhouse has served on the James Webb Space Telescope senior staff as Project Scientist for the Webb science instrument payload since the very beginning: 1997. At the SpaceInfo Club we had the honor to ask him some questions: enjoy the journey through these amazing experiences!

What inspired you to pursue a career in astrophysics and eventually lead you to work on groundbreaking projects like the James Webb Space Telescope?

I began my journey in geology, earning my degree from the University of Arizona. Afterward, I ventured into planetary geology and eventually transitioned into astrophysics. Pursuing my passion further, I completed my PhD in Physics at the University of Wyoming. Following that, I embarked on postdoctoral positions at the Smithsonian Institution in Washington DC as a Federal Civil Service astrophysicist, and after some time in Europe I completed my journey at the Goddard Space Flight Center. In 1997, I joined the James Webb Space Telescope project right from its inception.

As the project scientist for the James Webb Space Telescope, can you share some of the most challenging aspects you and your team encountered during its development and deployment?

When it came to deciding which field of science to pursue, the National Science Foundation and NASA decided for a groundbreaking mission. The task at hand was daunting. On one hand the scientific demands where so high that we needed to design a telescope with a huge primary mirror, but on the other hand it was so large that it couldn't fit into a rocket, presenting a significant engineering challenge.

The second major hurdle was creating an infrared telescope that could operate at incredibly low temperatures, approximately 50 degrees above absolute zero. This meant finding a solution without relying on traditional mechanical refrigeration methods.

So we came up with very interesting, but still challenging solutions.

Our breakthrough came with the design of a segmented mirror architecture consisting of 18 hexagonal segments. These segments could be mechanized to align seamlessly, a feat never before attempted in space exploration. This solved, at least in theory, the problem of fitting such a large structure into a conventional rocket fairing. Since the telescope is working so well now, we demonstrated that this solution is incredibly valid.

Addressing the cooling problem was equally innovative. Instead of placing the telescope in Earth's orbit, we positioned it at L2, approximately 1 million miles away. This strategic placement ensured that all heat sources—Earth, the Moon, and the Sun—were in the same direction. To counteract this, we devised a giant sunshield to block radiation, allowing for passive cooling. This positioning was a crucial factor in the success of the mission. We had to reduce all the possible sources of heat at their minimum, also considering the radiation emitted by apparently negligible bodies with respect to the Sun, which remains the main source of heat. By doing this, passive cooling can be exploited at its maximum.


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