I have recounted the stories of two large telescopes built for general purpose use, but some large telescopes will certainly be designed for specific purposes. I was one of just 14 participants at the first extrasolar planet detection workshop in 1976. Then in 1985 Roger came to me and he asked, “Could we build a telescope to look for Earth-like planets, and what would we see?” We worked out that there was a right wavelength for it, in the 10 micron region where I’d observed silicates before, and the materials that could be seen in the planet atmosphere were oxygen in the form of ozone, carbon dioxide, and water because water vapor absorbed in that part of the spectrum. It seemed that those would be very useful in showing the presence of photosynthetic life. We started to work out concepts for how to make this observation with huge telescopes in space, because it didn’t seem possible to do it without that. I kept pressing on Roger, “Well, if we can’t make the telescope small, can’t we at least shrink it in one dimension to make it easier to get it up into space?”
It was only after the Mars meteorite had been analyzed in 1995 and people started to be interested in life elsewhere in the Universe that this whole topic came to be of general interest. So Roger and I developed a concept of a linear infrared interferometer to null the radiation of the star, and thus be sensitive to the faint radiation of planets around the star. We developed various concept designs for that and analyzed all kinds of structures and forms for the optics: Roger was totally tied up in making mirrors then, so I became the person helping to develop concepts for space observations to search for life elsewhere.