Constellation-X Update

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Constellation-X Update

We include this article because we feel it is of interest to the Chandra community, even though it is not strictly CXC work. In particular, it provides information about programs that will continue the excitement of Chandra. The Chandra Newsletter welcomes contributions from readers in similar areas.

This is the first in what will be a continuing series of updates on the status of the Constellation X-ray Mission (Con-X for short). Con-X is one of the two 'Beyond Einstein Great Observatories' that are central to NASA s Beyond Einstein space science program for the next decade. Con-X grew out of the merger of two 1990's proposals from GSFC and SAO for large area, high throughput spectroscopic missions, and has received strong endorsement from two separate National Academy of Sciences reviews: the Astronomy and Astrophysics Decadal Survey and the Connecting Quarks to the Cosmos Panel. The Decadal Survey ranked Con- X the highest priority large space mission after JWST. Teams at many X-ray astronomy centers throughout the US are now working on instrument and optics development and there is European and Japanese participation on the Facility Science Team (FST). The launch dates of the four-telescope observatory are being evaluated in the context of NASA's new initiatives; our current expectation is for launches in the 2015 timeframe. Please see for all the details!

FIGURE 24: An artist's conception of the 4 Constellation-X telescopes in orbit at L2. In order to meet the effective area requirements and at the same time reduce cost and risk, 4 identical telescopes are planned. They will simultaneously point at the same target.

Recent good news for Con-X is that the Beyond Einstein program was given a new start in FY04. The Beyond Einstein program contains Con-X and LISA (a space based gravitational wave detector) as its two Great Observatories, and also three smaller Einstein Probes. Con-X and LISA both concluded highly successful Technology Readiness and Implementation Plan (TRIP) Reviews in early 2003. These Great Observatories and smaller Einstein Probes all lead to future Vision Missions as laid out in the 2003 NASA/SEU Roadmap. The new start is a major step forward for Con-X, as it represents a shift from the studies and planning phase into the design and eventually construction phase. This good news was tempered by substantial cuts in the FY04/05 budgets due to problems with other NASA Space Science programs and the recent redirection of NASA priorities.

Con-X is envisioned as a high throughput, high-resolution spectroscopy mission, utilizing reflection gratings with CCDs at low energies (< 1.5 keV) and micro-calorimeter arrays at higher energies (Figure 24). An additional set of high-energy mirrors and detectors will extend the response to at least 40 keV, and possibly beyond. The effective area for high-resolution spectroscopy is 100x that of Chandra (Figure 25). The gratings and calorimeter give energy resolution (E/ΔE) in excess of 300 everywhere over the 0.25-10 keV band. Con-X has the resolution and sensitivity to study the effects of strong gravity in hundreds of black holes, to study the nature of dark energy and the structure of the dark matter by tracing clusters of galaxies and the inter-galactic medium out to z ~ 2, to study the formation of supermassive black holes, and to study the life cycle of matter via high resolution spectroscopy of trans-He elements.

The current baseline set of observations used for planning purposes and mission design can be seen on the web at http: //, where you can also find a blank form you may use to design and submit your own observations ( A set of response matrices is on the web page to facilitate simulations. There are a number of observation placeholders yet to be fleshed out, and undoubtedly some great ideas that have been missed. This is a very opportune time to help define the mission requirements. Once construction starts it will be harder to change the mission capabilities.

Studies of the design, fabrication and assembly methods for the large Spectroscopy X-ray Telescope (SXT) are the primary efforts for the next year. While these studies are being led by US teams, international participation here may be fruitful. An industry study of planned fabrication methods and telescope design will be conducted in FY04 and FY05. The SXT itself will be fabricated by a yet to be selected industry partner.

Another of the studies currently underway is a trade between 'in-plane' and 'off-plane' gratings. The mission baseline utilizes the in-plane gratings, though the off-plane gratings may provide higher spectral resolution. Under study is how this choice affects implementation of the CCD detectors, assembly and alignment tolerances, line response functions, throughput, mass budgets, etc. The Con-X gratings team is currently developing integrated grating and optics models to predict performance, and hopes to make their recommendations during 2004.

FIGURE 25: The effective area of Constellation-X (all 4 telescopes) as compared to current missions with similar energy resolution. The Con-X gratings (=RGS) and microcalorimeter (=XMS) combine to give an effective area ~ 30-100x larger than current missions. The Hard X-ray Telescope (HXT) extends the bandpass out to ~ 40 keV, but with lower energy resolution.

On the detector front, the microcalorimeter team has made progress on improving the energy resolution, now down to about 2.5eV. They have also embarked on fabrication of pixel arrays, and conducted tests of multiplexed readouts for the arrays. The CCD efforts are moving towards testing of an event-driven CCD, which hold the promise of improved readout speeds, and higher throughput at low energies (< 0.25 keV).

The FST has been actively updating the mission requirements and observational suite based on new understandings of the technologies and new scientific discoveries. This has been done via numerous trade studies on the effective area, angular resolution, spectral resolution, and sky coverage. Your participation in these trade studies is welcomed, by attending the FST meetings and/or by submitting new observational scenarios via the Con-X web site. The most recent meeting of the FST was in November last year. The presentations at this meeting give a nice summary of the current state of the mission, items under study, and future plans. If you want to be 'in the know' about Con-X, please peruse these presentations at, follow the links at the top of the page to resources and then to meetings .

Finally, the instrument AO (covering the CCD detectors, the gratings, the microcalorimeter, and the HXT optics and detectors) will be open to international participation.

Michael Garcia and Jay Bookbinder for the Con-X Team

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