Detector Spacecraft Research Articles

Diffractive–refractive X-ray optics for very high angular resolution X-ray astronomy

The 0.5 arcsec angular resolution of the Chandra X-ray Observatory is possibly the best that a grazing incidence telescope with substantial collecting area will ever attain. We describe a telescope consisting of a diffractive and refractive doublet that transmits rather than reflects X-rays. Therefore, its angular resolution is relatively insensitive to figure errors and surface roughness, the factors that limit grazing incidence telescopes. When the focal length of the refractive component is minus twice that of the diffractive the chromatic aberration that is inherent in the diffractive and refractive components individually will compensate each other within a limited but not insignificant energy band. We consider a system with a long focal length, about 5000 km, to allow the refractive lens to be thin and transmit X-rays. The long focal length requires very long distance formation flying between an optics spacecraft and a detector spacecraft that must be aligned to better than a few centimeters. Solar orbit is a likely site. We simulate an imaging system where chromatic aberration is corrected to first order at 6 keV. The angular resolution is expected to be better than 0.3 miliarcsec within a 10% bandwidth. The components are lightweight, and can probably be made in a machine shop.

Studying the evolution of the hot universe with the X-ray evolving universe spectroscopy mission – XEUS

Europe is one of the major partners building the International Space Station (ISS) and European industry, together with ESA, is responsible for many station components including the Columbus Orbital Facility, the Automated Transport Vehicle, two connecting modules and the European Robotic Arm. Together with this impressive list of contributions there is a strong desire within the ESA Member States to benefit from this investment by utilizing the unique capabilities of the ISS to perform world-class science. XEUS is one of the astronomical applications being studied by ESA to utilize the capabilities of the ISS. XEUS will be a long-term X-ray observatory with an initial mirror area of 6 m 2 at 1 keV that will be expanded to 30 m 2 following a visit to the ISS. The 1 keV spatial resolution is expected to be 2–5″ half-energy-width. XEUS will consist of separate detector and mirror spacecraft (MSC) aligned by active control to provide a focal length of 50 m. A new detector spacecraft, complete with the next generation of instruments, will also be added after visiting the ISS. The limiting 0.1–2.5 keV sensitivity will then be 4 × 10 −18 erg cm −2 s −1, around 200 times better than XMM-Newton, allowing XEUS to study the properties of the hot baryons and dark matter at high redshift.

Correction: Gamma-Ray Observations of Orbiting Nuclear Reactors

The Perspective "Gamma-ray observations of orbiting nuclear reactors" by Joel R. Primack (28 Apr., p. 407) incorrectly identified the Gamma-Ray Spectrometer on the Solar Maximum Mission satellite as having been blinded by radiation from Soviet satellites. The seventh paragraph should have read, in part, "Gamma-ray detectors are surrounded by charged-particle detectors, so that events initiated by gamma rays can be distinguished from background events initiated by electrons. But positrons can annihilate on other parts of the gamma-ray detector spacecraft such as the SMM shield, and the resulting 511-keV gamma rays can appear to be astronomical gamma-ray signals. The SMM-GRS picked up such signals an average of eight times per day for much of 1987 and early 1988, each time causing brief interference with astronomical observations. The data storage capacity of the Gamma-ray Burst Detector (GBD) on the Japanese Ginga satellite was sometimes saturated by such events, so that it could take no more data until the next pass over its ground station (which could be on the same orbit or as many as 14 orbits later); this effectively blinded the GBD about 20% of the time. The sensitive detectors aboard Gamma Ray Observatory ...." [The remainder of this paragraph is as published.]