LRRP The Next Generation Space Telescope
Simon Lilly University of Toronto


 

THE NEXT GENERATION SPACE TELESCOPE (NGST)

 

Submission to the Long Range Planning Panel

November 27th, 1998

Simon Lilly

University of Toronto

NGST Canadian Project Scientist

 

This document summarizes the NGST project and the prospects for Canadian participation in it. The prospects for a significant Canadian participation in NGST are good, although significant hurdles remain, most notably the approval by the Federal Cabinet of CSA’s overall Long Term Space Plan III – a ten year plan for Canada’s activities in space.


1. THE NEXT GENERATION SPACE TELESCOPE (NGST)

1.1 The NASA NGST mission concept

1.1.1 The Dressler Report "HST & beyond"

The NASA NGST mission concept in its present guise arose in the US in the "HST & Beyond" study, undertaken during 1993–1994 by the "Dressler Committee" (of which I was a member) at the request of AURA, with the concurrence of NASA. The NGST proposed by the Dressler Committee would be much larger, but cheaper, than the 2.5m HST, and would be optimized for the 1-5 micron waveband. Located far from Earth and shielded from the Sun, it would passively cool to much lower temperatures (below 100K) than the HST or any ground-based telescope – giving it a sensitivity in the infrared waveband that exceeds all existing and planned telescopes on the ground and in space by factors that increase from 10-1000 over the 1–30 micron wavelength interval. Like the HST, the NGST was envisaged to be a "facility-class" observatory open to a broad community of scientific investigators.

1.1.2 The "Origins" Science Theme

The science case for the NGST (see Section1.2 below) was centered on the "Origins" theme – the idea that astronomical observations could provide the answers to fundamental questions about our origins within an evolving Universe. We could learn in detail how galaxies such as our own formed in the early Universe and detect the very first generations of stars that illuminated a dark Universe. It would be possible to follow the chemical evolution of the galaxies, tracing the enrichment of the interstellar gas with the elements necessary for Life. The NGST could also study important "Origins" phenomena in our own Galaxy, penetrating dust-enshrouded regions in our own Galaxy to reveal the processes by which stars are formed and to study the evolution of proto-planetary disks. And search for signs of the formation of planetary systems similar to our own. The NGST, the report concluded, would represent a major step towards understanding our cosmic origins and answering many of the most profound questions known to humankind.

1.1.3 Initial feasibility studies

The Dressler Report was enthusiastically received by NASA. During 1996, NASA commissioned three independent studies (by Lockheed, TRW and NASA GSFC) to assess the feasibility of constructing a 6-8m class NGST by 2005 within a Phase C/D construction budget of $US 500M. These studies independently concluded that this was indeed possible if approximately $US 200M was invested in technology development beforehand – leading to a total program cost of about $US 1B including launch and operations (see § 2.4).

The three design concepts shared many novel features. Lightweight deployable optics allowed primary mirror apertures of between 6m and 8m, far larger than the 2.5m HST, to fit within existing launch shrouds. Deep space orbits would place the spacecraft far from Earth, either at the L2 Lagrange point or half-way out to Jupiter on a 1´ 3 A.U. orbit, and would provide for the lowest possible temperatures and maximum infrared sensitivity. Total spacecraft weight of about 3000 kg (1/4 of that of HST) would keep costs down. The designs differed in their approaches to mirror construction, materials, detectors, sunshields, vibration control and choice of launch vehicle. The studies identified a number of areas where some development from available technologies was required, but did not identify any aspect of the mission that required "new discoveries". The results of these studies were summarized in a book "NGST: Visiting a time when galaxies were young" which still provides a good introduction to the project. A copy of this will be provided to the LRPP and it is also available in PDF format at:http://oposite.stsci.edu/ngst/initial-study/

 

The 1996 "in-house" NASA/GSFC NGST observatory concept, illustrating many of the generic features of current designs. A large filled aperture deployable mirror is located behind a very large deployable sunshield (the size of a tennis court) where the telescope assembly can passively cool to 30 K. On the other side of the shield a "warm" spacecraft bus provides housekeeping functions.

The rationale for NGST is to achieve dramatically reduced backgrounds by eliminating the atmospheric OH emission in the 0.8-2.0 micron waveband and the atmospheric and telescope thermal emission in the 2.0-10.0 micron waveband. In terms of the reduced background alone, the sensitivity gain of NGST over ground-based 8-m telescopes such as Gemini range from a factor of a few in the visible to over 10,000 at 10 microns. While ground-based 8-m telescopes may match NGST's spatial resolution in the near-infrared with adaptive optics, this will likely be confined to small isoplanetic patches and to wavelengths longward of 1 micron. Relative to other space observatories, NGST will have a sensitivity 100 times greater than the cryogenic SIRTF telescope at wavelengths below 10 micron. At longer wavelengths, where the gains are smaller, NGST has 10 times better resolution.

As a result of further studies, the NGST mission concept has now solidified around a number of specifications, consistent or exceeding the requirements envisioned by the Dressler Report. An important realization has been that a "mid-IR compatible" NGST (with zodiacal background limited performance to 10 mm and dramatic performance gains still to 30 microns) is not significantly more expensive that a "near-IR optimized" NGST limited to 1–5 microns, since the telescope naturally cools to 30 K. The current specifications of NGST are listed below:

 Parameter  Specification
 Primary mirror aperture  8m filled aperture (=50m**2 area)
 Mass  3000 kg
 Orbit  Remote (non-servicable), probably L2
 Background  Limited by natural Zodiacal background to 10 microns
 Operating wavelength less than or equal to 0.6 microns to at least 10 microns, desired extension to 30 microns
 Science instrumentation  TBD 1999, but including wide-field imagers and spectrographs
 Observatory lifetime  5-10 years

As a result of the initial studies, NASA adopted NGST as a major component of its "Astronomical Search for Origins" (ASO) program, along with the Space Interferometer Mission (SIM) and, in the longer term, the Terrestrial Planet Finder (TPF) and ultimately the Terrestrial Planet Imager (TPI). These latter missions are aimed at the grand vision of discovering and studying habitable extra-solar planetary systems. They will require arrays of large aperture telescopes operating as interferometers in the near- and mid-infrared spectral regions. They will utilize many of the key technologies that will be developed for the NGST.

1.2 NGST Scientific Objectives – the Ad Hoc Science Working Group and the Design Reference Mission

In 1997, NASA formed the NGST Ad Hoc Science Working Group (ASWG). Initial membership was by competitive application from the US community (as an aside I was the only non-US scientist selected). Subsequently, the leads of the six US instrument studies have been added. Following the emergence of the NASA-ESA-CSA partnership on NGST (see Section 2.3 below), four European members have been added and I have been designated as the official Canadian member. The task of the ASWG is to define the "Design Reference Mission" (DRM), a program of scientific observations against which different designs and concepts may be assessed. The DRM is a "best guess" as to what programs the NGST will be used for in ten years time -- the actual programs of observations will of course be determined by the succesful observing proposals -- and currently consists of five major science themes. Within each theme, the relative importance of different observational programs or capabilities has been developed by teams within the ASWG (I lead the "Origin and Evolution of Galaxies" team). The overall balance between different science themes reflects a consensus of the whole ASWG and the areas of star and planet formation have been substantially augmented over that envisioned in the original "Visiting a time when galaxies were young" book.

The broad nature of the investigations in each of these science areas (and their nominal contribution to the DRM) is summarized below.

The ASWG has attempted to ascribe "scientific value" of the different potential wavelength ranges and instrument capabilities, which will be traded against their costs, as the latter become better defined from technical studies.


2 NGST IN THE UNITED STATES

2.1 US Funding and Approval status

NGST is budgeted within NASA’s ASO program. The budget plan for NGST (which has been agreed with NASA Headquarters and the OMB) utilizes the HST funding "wedge" – NGST takes the place of HST as the latter mission ramps down. The major expenditure with NGST occurs in the Phase C/D construction period 2003-2007, which commences after the last HST servicing mission. Thus, while NASA’s overall budget is approved every year by Congress, it is my understanding that no "new money" is required for NGST to proceed and it is in this sense an "approved" program. The high public and political esteem for HST in the US make it unlikely that the continuing HST/NGST budget line will be negatively impacted. It is nevertheless regarded as very important that the NGST be highly ranked by the US National Academy Decadal Review (the Taylor/McKee Report) that will take place in the next 12 months.

2.2 Major US NGST activities in 1998

Two major pre-Phase A studies of NGST have just been completed (Fall 1998) by Ball Aerospace and TRW. These further developed the NGST architectures that had been outlined in the initial studies. Lockheed has also conducted parallel studies using internal funds. Competitive Phase A studies are due to commence early next year.

In addition, major technology development contracts have been let in 1997-8 in those technology areas perceived to be most critical to the success of NGST. These are:

Finally, STScI has been designated as both the operations and science center for NGST and is now involved in the planning for the operations phase of NGST.

2.3 International partnership

It has always been recognized that the $500M cost-cap on the US contribution to the Phase C/D construction budget was a significant constraint and that a more capable observatory could be built if this cost-cap could be augmented. Accordingly, both ESA and CSA are planning to participate in the NGST (see Section 3 below for more details of Canadian plans). In both cases, and as with the ESA contribution to HST, this would take the form of a "contribution in kind" with an agreed monetary value to the project.

In the case of the Europeans, $US 200M contribution to NGST is planned (this is linked also to the run-out costs of the HST after the present NASA-ESA HST agreement expires), taking the place of an F-class mission in the Horizon-2000+ plan. CSA (which had no HST participation) is planning to participate at the $US 50M level. ESA is currently undertaking studies of both the whole spacecraft architecture (750 kecu) and of MOS/IFS instrumentation (175 kecu). A further study for visible wavelength instrumentation is imminent. CSA studies are described below.

2.2 Top-level Budget and Schedule

 NGST top-level budget  $US M (1996)
 Technology development  160
 Nexus PF-3 mission  50
 Phase C/D construction (US)  500*
 Launch  100
 Operations  225
 Total US contribution 1035
 Proposed ESA contribution  200
 Proposed CSA contribution  50
 Total from all partners  1285
 * capped, but could be raised by ESA and CSA contributions  

NGST NASA/ESA/CSA top-level schedule  
 Pre-Phase A studies complete  09/98
 Phase A start  03/99
 NASA/ESA/CSA MOU's signed  03/99
 NASA/ESA/CSA instrument allocatons  07/99
 NASA/ESA/CSA spacecraft allocations  11/99
 Phase B start (2 primes)  10/00
 NASA/ESA/CSA definite agreements  10/00
 Prime contractor select  06/01
 Phase C/D construction  11/03
 Launch  09/07
 Phase E operations  01/08


3 NGST IN CANADA

3.1 Background

NGST represents a much larger space astronomy project than any that CSA has undertaken hitherto, and it is fortunate that the opportunity to participate in the NGST arose at precisely the time that the CSA was formulating a new ten-year plan for Canadian space activities (known as the Long Term Space Plan III or LTSP-III). The LTSP-III represents a fundamental change of CSA’s activities away from a "project-oriented" approach to a "program oriented" approach. A continuing space astronomy program, and NGST in particular, are part of the proposed program.

In 1996, the Joint Sub-Committee on Space Astronomy (JSSA) and CSA were informed about the "HST and beyond" study, its favourable reception by NASA and the possibility that CSA might be able to participate in what appeared to be set to become the forefront space astronomy mission of the first decades of the next century. During 1996-1997 it became increasingly clear that this possibility enjoyed wide-spread support amongst the Canadian astronomical community, and the JSSA subsequently adopted participation in NGST as a major component of its proposed ten-year program in space – the other elements being participation in the ESA FIRST/Planck mission and in a to-be-defined second generation space-VLBI mission.

Preliminary informal discussions with the project by myself and others in the astronomical community led to the formulation of a brief 5-page "proposal" to CSA for participation in NGST. This was submitted by the JSSA as part of its LTSP-III submission in September 1997 (available on the Web at http://www.astro.utoronto.ca/~lilly/NGST/5page.html). A formal invitation from NASA to CSA was also secured, and a two-day meeting in Ottawa in December was organised during which the CSA Space Science Directorate and relevant Canadian industries were fully briefed by the NGST project on all aspects of the program.

Subsequently, in March 1998, CSA (in the form of Dr. Bob Hum, Director of Space Science Programs) verbally undertook to the NGST project to participate "provided that the anticipated LTSP-III funding was secured from the Canadian Government". CSA has since taken part in regular three-monthly "NGST Partnership" meetings with NASA and ESA. An MOU has been drafted and co-ordinated schedules agreed. The draft MOU envisages a $US 50M contribution to NGST in return for a minimum 5% share of NGST observing time for the Canadian astronomical community. CSA also plans to support a number (TBD) of Canadian technical/astronomer positions at the STScI through the operations phase.

Mr. Russ Alexander of CSA has been appointed CSA Project Manager for the NGST Program and I have been designated as Canadian Project Scientist.

3.2 Current funding and approval status

Participation in NGST is part of the CSA LTSP-III, which is now with the Cabinet for approval. It is anticipated that the funding level of LTSP-III will be announced in the February 1999 Federal budget. If the LTSP-III funding is secured in February 1999 at approximately the requested level, then, on the assumption that suitable Canadian contributions to the project can be identified (see below), the intention is that CSA will sign the MOU in March 1999 and proceed with defining the Canadian contribution(s) later in the year. A final definite commitment from CSA must be in place by the Fall of 2000.

3.3 The process of identifying the Canadian contributions to NGST

Canada is a minority partner in NGST and has an aerospace industrial sector that, while excellent in some areas, is less diverse than that in the US or Europe. Furthermore, the Canadian astronomical community does not have an extensive heritage of participating at a technical level in large space astronomy missions. Thus, identifying the Canadian contribution(s) to NGST remains a significant challenge. Because the procurement of the international contributions to NGST will differ from that of the rest of the program, they need to be defined early in the program – within the next 12 months. The schedules of the studies in the different communities have been synchronized to allow this to happen. The process of allocating elements of the mission to the partners will be as follows.

In the area of science instrumentation, the results of the various concept studies being carried out in the US, Europe and Canada will be submitted to a "Joint Scientific Review Board" (JSRB - composition TBD) in June 1999. The JSRB will make generic recommendations on the complement of science instruments for NGST and will evaluate issues such as scientific suitability, technical risk, and cost estimates. Following this review, in the August 1999 timeframe, NASA, ESA and CSA will then allocate amongst themselves elements of the instrument package, which will then be developed and procured by the respective agencies. Integration of the NGST Integrated Science Instrument Module (ISIM) will then be undertaken by NASA GSFC.

In the area of spacecraft components, areas of European and Canadian expertise will be advertized at the next "NGST Technology Challenge" meeting that will be held in September 1999 at Wood’s Hole. Following these presentations, and once the instrumentation allocation is known, spacecraft components will then be allocated to the partners. To minimize the complexity of integration, these will ideally be "black-box" components.

Over the next nine months, three different instrumentation initiatives are being pursued within Canada (see below). In some cases, these are, or may develop into, collaborations with study teams in the US or Europe. Given the technical, scientific and political uncertainties of the instrument allocation process, this strategy is designed to ensure that Canada has a place in NGST science instrumentation. In parallel, two areas of Canadian technical expertise in the "spacecraft" area are being developed as potential Canadian contributions to NGST. These are also described below.

3.4 Current Canadian NGST activities (1998-1999)

3.4.1 Canadian NGST instrumentation initiatives

Three separate initiatives have developed in Canada in response to the NGST opportunity. These are just now getting under way (November 1998) and are as follows:

These are all now being funded by CSA (either through the science lead or the industrial partner) at an initial $65,000 level. Proposals are currently being prepared for additional study work, particularly involving development or prototyping of specific hardware aspects of the studies.

3.4.2 Canadian NGST spacecraft initiatives

CSA is currently funding studies of two "spacecraft" technical areas.

3.4.3 Canadian NGST Science Steering Committee

A Canadian Science Steering Committee for NGST has been appointed by JSSA on behalf of CASCA. This is primarily an email forum at present within a wider circle including the Canadian Gemini Project Scientist, the Canadian FUSE Project Scientist, the Director of DAO, the astronomer in charge of the Canadian Astronomical Data Center (CADC), the senior Canadian astronomer at CFHT and other particularly interested scientists. This group advises me on Canadian scientific priorities regarding NGST. Membership of the CSSC is as follows:

4. IMPLICATIONS FOR THE LONG RANGE PLANNING PANEL

4.1 HIA involvement in Canadian NGST participation

The involvement of HIA/DAO is, in my view, essential to any viable Canadian participation in the science instrumentation for NGST, and indeed two of the Canadian NGST science instrument leads identified above are HIA/DAO staff members. The need for HIA involvement is, I believe, well recognized by CSA management and, in turn, HIA senior management have been consistently supportive of the NGST initiative within Canada and of the involvement of HIA in that initiative. The CADC (which is currently partly funded by CSA) could also have a role in the operations phase of NGST. HIA support of, or involvement in, NGST science instrumentation should not require NRC funds per se since it should be funded at the necessary level by CSA through contracts/sub-contracts etc.. However such activities will require deployment of skilled manpower. The question of support for Canadian usage of NGST is still open, and may depend on the number and nature of the positions (currently TBD) that CSA supports at STScI, the designated operations center for the NGST mission.

4.2 Complementary Ground-based Facilities

There are, I believe, two important implications for future ground-based (NRC) facilities that are raised by the potential Canadian participation in NGST.

First, NGST is squarely aimed at the "Origins" theme, which itself underlies many of the proposed new facilities in astronomy. In particular, its major science goals – understanding the formation of galaxies in the early Universe and the formation of stars and planets in our own Galaxy – are very complementary to that of the large millimeter array projects (e.g. MMA/LSA). As an example, NGST may be the only telescope able to identify the faintest sub-mm sources detected by MMA/LSA and measure their redshifts and mid-IR spectroscopy with NGST may be the only way to determine the energy sources (starburst or AGN) in such objects. MMA/LSA and NGST are also highly complementary in the study of star-formation. Of the several projects aimed at these general science areas, the MMA/LSA and the NGST are also the only facilities that will have arcsec-level or better resolution (c.f. SIRTF, FIRST, LMT etc). Thus NGST and the MMA/LSA should be viewed as very complementary. Both are emerging as "world-telescopes" and Canadian astronomers would be well placed if they had assured access to both and would find themselves in a seriously uncompetitive situation if they did not.

Second, as presently conceived, NGST represents a new era in space astronomy: When launched, it will be essentially as large as any telescope on Earth and thus, free of the Earth's atmosphere, far more capable. This is quite unlike the case with HST, which, by the time it achieved its full capabilities in 1994, was complemented by ground-based telescopes (e.g. Keck) with 16 times the collecting area. This complementarity has proved very powerful, especially in terms of spectroscopy of the faintest objects detected with HST. There is thus considerable interest in the US, Europe and Canada in building a giant ground-based telescope to complement NGST in the same way, especially in the realm of high-resolution spectroscopy. The aperture of such a telescope would need to be in excess of 25m and designs as large as 100m are being considered (e.g. MAXAT in the US, OWL in Europe and "Next Generation CFHT" report in Canada). Such a facility would again be a "world-telescope", with a cost in the $US 1B area. Participating in this telescope, if built, would be essential if we are to build on our investment in NGST.


List of Acronyms

AGN Active Galactic Nucleus
ASO Astronomical Search for Origins
ASWG Ad Hoc Science Working Group
AURA Associated Universities for Research in Astronomy
CADC Canadian Astronomical Data Center
CASCA Canadian Astronomical Society
CSA Canadian Space Agency
DAO Dominion Astrophysical Observatory
DRM Design Reference Mission
FIRST Far-Infrared Space Telescope
FUSE Far-Ultraviolet Spectral Explorer
GSFC Goddard Space Flight Center
HIA Herzberg Institute of Astrophysics
HST Hubble Space Telescope
ISIM Integrated Science Instrument Module
JSRB Joint Science Review Board
JSSA Joint Sub-Committee on Space Astronomy
LMT Large Millimeter Telescope
LSA Large Southern Array
LTSP Long Term Space Plan
MAXAT Maximum Aperture Telescope
MMA Millimeter Array
MOU Memorandum of Understanding
NASA National Aeronautics and Space Administration
NGST Next Generation Space Telescope
OMB Office of Management and Budget
OWL Overwhelmingly Large Telescope
SIRTF Space Infra-Red Telescope Facility
STScI Space Telescope Science Institute