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
Soon after the start of science operations of the <i>Chandra X-ray Observatory</i>, it became apparent that weakly penetrating
(0.1-0.5 MeV) protons in the Earth's radiation belt were causing an unexpectedly rapid increase in the charge-transfer
inefficiency of <i>Chandra's </i>front-illuminated CCDs. Fortunately, the <i>Chandra</i> team developed, implemented, and
maintains a radiation-protection program that successfully reduced the rate of degradation of the CCDs' performance to
acceptable levels. Since implementing this program, the average rate of increase of the charge-transfer inefficiency has
slowed to 3.2×10<sup>-6</sup>/y (2.3%/y) for the front-illuminated CCDs and 1.0×10<sup>-6</sup>/y (5.8%/y) for the back-illuminated CCDs.
This paper reviews the <i>Chandra</i> radiation-management program, reports the current status, and describes changes
planned or implemented since the previous paper on this topic.
After over 6 highly successful years on orbit, the Chandra X-ray Observatory continues to deliver world class science to
members of the X-ray community. Much of this success can be attributed to an excellent space vehicle, however; the
creation of several unique software tools has allowed for extremely efficient and smooth running operations. The
Chandra Flight Operations Team, staffed by members of Northrop Grumman Space Technology, has created a suite of
software tools designed to help optimize on-console operations, mission planning and scheduling, and spacecraft
engineering and trending. Many of these tools leverage COTS products and Web based technologies. We describe the
original mission concepts, need for supplemental software tools, development and implementation, use of these tools in
the current operations scenario, and efficiency improvements due to their use.
The Chandra X-ray Observatory, which was launched in 1999, has to date completed almost seven years of successful
science and mission operations. The Observatory, which is the third of NASA's Great Observatories, is the most
sophisticated X-ray Observatory yet built. Chandra is designed to observe X-rays from high-energy regions of the
universe, such as the remnants of exploded stars, environs near black holes, and the hot tenuous gas filling the void
between the galaxies bound in clusters. The Chandra X-ray Center (CXC) is the focal point of scientific and mission
operations for the Observatory, and provides support to the scientific community in its use of Chandra. We describe the
CXC's organization, functions and principal processes, with emphasis on changes through different phases of the
mission from pre-launch to long-term operations, and we discuss lessons we have learned in developing and operating a
joint science and mission operations center.
The CCDs on the Chandra X-ray Observatory are vulnerable to radiation damage from low-energy protons scattered off the telescope's mirrors onto the focal plane. Following unexpected damage incurred early in the mission, the Chandra team developed, implemented, and maintains a radiation-protection program. This program - involving scheduled radiation safing during radiation-belt passes, intervention based upon real-time space-weather conditions and radiation-environment modeling, and on-board radiation monitoring with autonomous radiation safing - has successfully managed the radiation damage to the CCDs. Since implementing the program, the charge-transfer inefficiency (CTI)
has increased at an average annual rate of only 3.2×10-6 (2.3%) for the front-illuminated CCDs and 1.0×10-6 (6.7%) for the back-illuminated CCDs. This paper describes the current status of the Chandra radiation-management program, emphasizing enhancements implemented since the original paper.
The sensitivity of the Advanced CCD Imaging Spectrometer (ACIS)
instrument on the Chandra X-ray Observatory (CXO) to low-energy X-rays
(0.3 - 2.0 keV) has been declining throughout the mission. The most
likely cause of this degradation is the growth of a contamination
layer on the cold (-60 C) filter which attenuates visible and near-visible light incident on the CCDs. The contamination layer is still increasing 4 years after launch, but at a significantly lower rate than initially. We have determined that the contaminant is composed mostly of C with small amounts of O and F. We have conducted ground experiments to determine the thermal desorption properties of candidate materials for the contaminant. We have conducted experiments to determine the robustness of the thin filter to the thermal cycling necessary to remove the contaminant. We have modeled the migration of the contaminant during this bake-out process to ensure that the end result will be a reduction in the thickness of the contamination layer. We have considered various profiles for the bake-out consisting of different temperatures for the ACIS focal plane and detector housing and different dwell times at these temperatures. The largest uncertainty which affects our conclusions is the volatility of the unknown contaminants. We conclude that bakeout scenarios in which the focal plane temperature and the detector housing temperature are raised to +20~C are the most likely to produce a positive outcome.