The Early Years
In 1989 Riccardo Giacconi, then director of STScI, realizing that large space science projects take about 20 years from first development to launch, suggested that a workshop should be held about a followup to HST. The Next Generation Space Telescope Workshop, organized by Garth Illingworth and Pierre Bely was hosted by STScI with support from NASA/Goddard. It focused on the science drivers and technical capabilities of an HST follow-up telescope at the end of the HST lifetime, which was then estimated to be 2005. An obvious science driver was studying galaxies at high redshift, which was at that time a redshift of about 1.
At the end of the workshop, it was proposed that NASA should investigate the feasibility of an 8m passively cooled near-IR telescope, in a high earth orbit, or a similar telescope based on the moon.
The discovery of thespherical aberration problem of the Hubble Space Telescope's primary mirror effectively stopped all development of the NGST. NASA encountered a number of other problems at the same time. While all effort was put into fixing HST and working around the spherical aberration problem, nobody dared think about the long term future.
The Association of Universities for Research in Astronomy Inc. (AURA) and NASA chartered the "HST and Beyond" committee, chaired by Alan Dressler, to consider the needs of the astronomical community after the nominal mission lifetime of HST, ending in 2005. The committee came up with three recommendations:
- Extend the lifetime of HST to 2010 to allow a overlap and smooth transition to the new telescope,
- Study the feasibility of a 4m space telescope in a low background orbit,
- Support science based on the Origins theme, i.e. investigations that seek to understand the formation processes of galaxies, stars, planets and life.
Motivation for the visiting time when galaxies were young slogan of the report came from deep HST images that still clearly showed structure in cluster galaxies at a redshift of 0.4, even with spherical aberration. Furthermore, there were strong indications that galaxies were visible in these images out to redshifts of a few. This had not been expected of the 2.4m Hubble Telescope, extrapolating ground based experience of galaxies extended over 1 arcsec or more to high redshift. Galaxies turned out to be more compact and have more structure, therefore they could be resolved to very high redshift with HST, as the Hubble Deep Fields later showed. This opened up investigations of much higher redshift galaxies and indeed opened up the possibility of visiting time when the galaxies where young.
Based on these developments, a space telescope was proposed called "Hi-Z", which had a monolithic 4m mirror, was still fully baffled and was envisioned to be in a 1x3 AU elliptical orbit.