Going For 8 Meters
Partly in response to the Dressler Report, Joe Rothenberg (then GSFC Director) and Ed Weiler (NASA HQ) encouraged a GSFC/STScI collaboration to study a passively cooled successor to the Hubble. John Mather and Peter Stockman were the two Project Scientists and John Campbell (HST Project Manager) led the initial engineering effort. As the Project grew, Bernie Seery replaced Campbell and led the project through the early formative years.
Dan Goldin, the NASA director at that time, gave a presentation pushing his "Faster, better, cheaper" motto at the AAS meeting. He was disappointed by the lack of development in space telescope technology, both for astronomy as well as for the military. He urged the astronomical community to think big, challenging them to come up with an 8m telescope design at a lower cost than previous telescopes.
Combining Goldin's challenge with the realization that a lot of science needed to be and could be done at high redshifts (z=1-5 and higher), more radical telescope designs were studied. The higher redshifts goal pushed explorations of very low infrared backgrounds, meaning observatory orbits much further away from earth.
Portions of the very early designs from Pierre Bely and Peter Stockman implementing new concepts for NGST that are now still recognizable, like a large deployable mirror (then still at 8m), L2 point orbit, and an "open telescope design" (no external baffle) with passive cooling behind a large multi-layer sunshield. This concept was still envisioned with one large near-IR camera in the focal plain.
Four corporations joined the feasibility study, and came up with designs that were generally very similar:
- NASA/Goddard with a telescope at L2, with a large sunshield and a deployable 8m mirror,
- TRW with a telescope at L2, with a large sunshield and an articulated 8m mirror,
- BALL Aerospace with a telescope at L2, with a large sunshield and a deployable 8m mirror, and
- Lockheed with a monolithic 4m mirror at 3AU (which provides low background, but also low solar power and more data transmission problems).
The trade studies suggested that these designs could be developed for about $500 million, under the assumption that the whole telescope would be built by one contractor, as would the science instruments. The idea of one contractor, like many other assumptions going into the studies, turned out not to be feasible, especially for the instruments.
Based on these studies, a comprehensive report was written, titled Next Generation Space Telescope, Visiting a Time When Galaxies Were Young. This report also presented a technological roadmap for the succesful development of NGST in the next decade.
In the meantime, more detailed simulations were conducted to provide a better scientific basis for NGST and to drive its instrument capabilities. For example, Myungshim Im simulated deep images for an 8m NGST, suggesting feasibility to detect galaxies out to redshifts of 15, if they exist. These simulations highlighted the need for diffraction limited operation to a high wavelength in order to be feasible, and a strong push for mid-IR capabilities. The simulations from, for instance Massimo Stiavelli, indicated the need for Multi-Object Spectroscopic capability for NGST. Where the followup of deep HST imaging like the Hubble Deep Fields was possible from the ground with 8m class ground-based telescopes, this will no longer be true for the very high redshift galaxies that will be discovered by NGST. If any science has to be done on very high redshift galaxies beyond morphology and position on the sky, NGST will have to do the spectroscopy itself, because most of the flux will be redshifted to wavelengths out of reach of ground-based telescopes.
Buoyed by all these studies, NASA agreed to fund additional studies that further refined the technical and financial requirements for building the telescope.