The time-resolved soft x-ray spectrometer (TSXS) aboard on the X-ray Pulsar Navigation Test Satellite is an x-ray timing spectrometer covering the energy range of 0.5 to 10 keV. It is China’s first focusing x-ray telescope launched into space orbit. The optical system of TSXS is an x-ray grazing incidence focusing system with a field of view 15 arc min, which is nested with 4 parabolic mirrors with a focal length of 1150 mm. The focal plane detector of TSXS uses a silicon drift detector. From April to June 2016, ground calibration was carried out on TSXS, including the optical axis determination, calibration of energy linearity and energy resolution, calibration of time resolution and photon arrival time accuracy, and calibration of mirrors’ reflectivity. After the launch on November 10, 2016, the in-orbit calibration and performance verification of the telescope was carried out, including the optical axis determination, the performance of energy response, the performance of time accuracy, the calibration of effective area, and the evaluation of telescope sensitivity. After calibration and verification on the ground and in orbit, the photon energy measurement error of the telescope is better than 0.5% at energies above 1.5 keV, the energy resolution is better than 156 eV at 6.4 keV, the time resolution is <1 μs, the photon arrival time measurement accuracy is <302 ns, and the telescope in-orbit background is <4.16 ± 1.42 × 10 − 3 photons / s (0.5 to 3 keV, 40°N to 40°S, not including South Atlantic Anomaly). The telescope has an in-orbit observation sensitivity of 2.09 × 10 − 3 photons / cm2 / s / keV (0.5 to 3 keV, T = 1000 s, and nσ = 5).
X-ray pulsars were used for spacecraft navigation at the beginning of the discovery as their super stability spin periods (periodic changing rate 10-19-10-21). It is hopeful to get rid of the support of ground facility systems, which can be a real sense of spacecraft autonomous navigation in the large temporal and spatial range. Considering the pulsars radiation luminance, periodic instability and time of approach (TOA) uncertainty, the autonomous navigation accuracy can be achieved the order of kilometer magnitude. This paper reviews the X-ray pulsars navigation principle and the navigation missions in orbit in recent years. Finally, the study progresses of the X-ray pulsar telescope in our team are introduced. These efforts can be usefully for autonomous navigation in the future deep space exploration.
The grazing incidence soft X-ray optical system is the core equipment of future space science missions. The optical system expands the collecting area of x-ray photos and improves the SNR. The effective area calibration is the key indicator for testing and verifying the performance of the grazing incidence optical system. One of the traditional calibration methods uses the wide x-ray beam as the calibration x-ray source. This calibration method requires large ground equipment, high environmental conditions while the x-ray beam is not so parallel that the calibration accuracy is limited. Another effective area calibration method uses the narrow x-ray beam scan the optical system. In this paper, the above two effective area calibration methods of the grazing incidence optical system are modeled mathematically. The factors such as the parallelism of the beam, the uniformity of the beam and the characteristics of optical system are absorbed into the unified mathematical model for describing the effective area. The key factors which affect the effective area calibration accuracy are extracted, and their influences on the calibration result are analyzed. Eventually the two calibration methods accuracy is evaluated and the ways for improving the calibration accuracy are given. The effective area calibration is able to test and verify the collecting ability of x-ray photons of the grazing incidence optical system, which is the basis for the development of soft x-ray optics.
X-ray pulsar navigation has attracted extensive attentions from academy and engineering domains. The navigation accuracy is can be enhanced through design of X-ray mirrors to focus X-rays to a small detector. The Wolter-I optics, originally proposed based on a paraboloid mirror and a hyperboloid mirror for X-ray imaging, has long been widely developed and employed in X-ray observatory. Some differences, however, remain in the requirements on optics between astronomical X-ray observation and pulsar navigation. The simplified Wolter-I optics, providing single reflection by a paraboloid mirror, is more suitable for pulsar navigation. In this paper, therefore, the grazing incidence X-ray mirror was designed further based on our previous work, with focus on the reflectivity, effective area, angular resolution and baffles. To evaluate the performance of the manufactured mirror, the surface roughness and reflectivity were tested. The test results show that the grazing incidence mirror meets the design specifications. On the basis of this, the reflectivity of the mirror in the working bandwidth was extrapolated to evaluate the focusing ability of the mirror when it works together with the detector. The purpose of our current work to design and develop a prototype mirror was realized. It can lay a foundation and provide guidance for the development of multilayer nested X-ray mirror with larger effective area.