Advances in X-ray astronomy require high spatial resolution and large collecting area. Unfortunately, X-ray
telescopes with grazing incidence mirrors require hundreds of concentric mirror pairs to obtain the necessary
collecting area, and these mirrors must be thin shells packed tightly together... They must also be light enough to
be placed in orbit with existing launch vehicles, and able to be fabricated by the thousands for an affordable cost.
The current state of the art in X-ray observatories is represented by NASA's Chandra X-ray observatory with 0.5
arc-second resolution, but only 400 cm<sup>2</sup> of collecting area, and by ESA's XMM-Newton observatory with 4,300
cm<sup>2</sup> of collecting area but only 15 arc-second resolution. The joint NASA/ESA/JAXA International X-ray
Observatory (IXO), with ~15,000 cm<sup>2</sup> of collecting area and 5 arc-second resolution which is currently in the
early study phase, is pushing the limits of passive mirror technology. The Generation-X mission is one of the
Advanced Strategic Mission Concepts that NASA is considering for development in the post-2020 period. As
currently conceived, Gen-X would be a follow-on to IXO with a collecting area ≥ 50 m<sup>2</sup>, a 60-m focal length and
0.1 arc-second spatial resolution. Gen-X would be launched in ~2030 with a heavy lift Launch Vehicle to an L2
orbit. Active figure control will be necessary to meet the challenging requirements of the Gen-X optics. In this
paper we present our adaptive grazing incidence mirror design and the results from laboratory tests of a prototype
The International X-ray Observatory (IXO) is a collaborative effort between NASA, ESA, and JAXA. The IXO science
goals are heavily based on obtaining high quality X-ray spectra. In order to achieve this goal the science payload will
incorporate an array of gratings for high resolution, high throughput spectroscopy at the lowest X-ray energies, 0.3 - 1.0
keV. The spectrometer will address a number of important astrophysical goals such as studying the dynamics of clusters
of galaxies, determining how elements are created in the explosions of massive stars, and revealing most of the "normal"
matter in the universe which is currently thought to be hidden in hot filaments of gas stretching between galaxies. We
present here a mature design concept for an Off-Plane X-ray Grating Spectrometer (OP-XGS). This XGS concept has
seen recent significant advancements in optical and mechanical design. We present here an analysis of how the baseline
OP-XGS design fulfills the IXO science requirements for the XGS and the optical and mechanical details of this design.
Over the last two years, we have studied system concepts for the International X-ray Observatory (IXO) with the goal of
increasing the science return of the mission and to reduce technical and cost risk. We have developed an optical bench
concept that has the potential to increase the focal length from 20 to 25 m within the current mass and stability
requirements. Our deployable bench is a tensegrity structure formed by two telescoping booms (compression) and a
hexapod cable (tension) truss. This arrangement achieves the required stiffness for the optical bench at minimal mass
while employing only high TRL components and flight proven elements. The concept is based on existing elements, can
be fully tested on the ground and does not require new technology.
Our design further features hinged, articulating solar panels, an optical bench fully enclosed in MLI and an instrument
module with radially facing radiator panels. We find that our design can be used over a wide range of sun angles, thereby
greatly increasing IXO's field of regard, without distorting the optical bench. This makes a much larger fraction of the
sky instantaneously accessible to IXO.
Successfully developing and launching the next large X-ray observatory in a cost constrained environment will require a
close partnership between scientists and engineers in academia, government and industry. We outline a set of design
principles governing a sustainable development model that enables breakthrough scientific capability while maintaining
credible commitment to tight cost constraints. We further aim for flexibility in a changing funding environment and
responsiveness to new technology development. We bring in lessons learned from developing the Chandra X-ray
observatory, the Lunar Crater Observation and Sensing Satellite (LCROSS) and include results of recent architecture
studies. From the perspective of the builders of CGRO, Chandra and other high energy observatories, we summarize our
progress towards a robust yet flexible development model that provides the highest probability for the next X-ray
observatory to move from detailed concept studies to in orbit science operation.