Precise pointing and stabilization performance for the balloon-borne imaging testbed: 2015 test flight

Balloon-borne astronomy offers an attractive option for experiments that require precise pointing and attitude stabilization, due to a large reduction in the atmospheric interference observed by ground-based systems as well as the low-cost and short development time-scale compared to space-borne systems. The Balloon-borne Imaging Testbed (BIT) is an instrument designed to meet the technological requirements of high-precision astronomical missions, and is a precursor to the development of a facility-class instrument with capabilities similar to the Hubble Space Telescope. The attitude determination and control systems (ADCS) for BIT, the design, implementation, and analysis of which are the focus of this paper, compensate for compound pendulation effects and other sub-orbital disturbances in the stratosphere to within 1–2′′ (rms), while back-end optics provide further image stabilization down to 0.05′′ (not discussed here). During the inaugural test flight from Timmins, Canada in September 2015, BIT ADCS pointing and stabilization performed exceptionally, with coarse pointing and target acquisition to within <0.1° and fine stabilization to 0.68′′ (rms) over long (10–30 min) integrations. This level of performance was maintained during flight for several tracking runs that demonstrated pointing stability on the sky for more than an hour at a time. To refurbish and improve the system for the three-month flight from New Zealand in 2018, certain modifications to the ADCS need to be made to smooth pointing mode transitions and to correct for internal biases observed during the test flight. Furthermore, the level of autonomy must be increased for future missions to improve system reliability and robustness.

A discussion on advanced methods of energy conversion- Magnetohydrodynamic power generation - The prospects for closed cycle m .p.d power generation

The basic features of closed cycle m.p.d. systems are described, introducing the three main combination cycles (direct nuclear, indirect nuclear, indirect fired) which could be adopted for commercialpower stations. Because of the high temperatures and attendant problems associated with thermal ionization of the working gas plasma, emphasis is placed upon achieving non-equilibrium ionization. This phenomenon is generally applicable only in closed cycle systems employing certain gases as the working fluid: the basic theory and required operating parameters of several techniques for inducing non-equilibrium ionization are reviewed. Matching a heat source, whether based on combustion or nuclear energy, to the m.p.d. stage imposes a number of restrictions. Nuclear reactors to provide temperatures suitable for m.p.d. systems (perhaps up to 1800 °G) have yet to be developed, but design criteria can be formulated. Cycle studies to specify operating parameters (including temperature, pressure, associated steam cycle, etc.) are presented. The technical feasibility of an indirect fired heat exchanger is considered. Over-all system performance, development time scale and incentives are also examined. In the United Kingdom, experimental research and development towards closed cycle m.p.d. power generation is mainly in progress at International Research and Development Co. Ltd and at A.E.R.E., Harwell. Details of the programmes are given and achievements in terms of experimental data are presented. Finally, the prospects for closed cycle m.p.d. power generation are reviewed.