[en] AEA Technology, the commercial arm of the UK Atomic Energy Authority, is conducting an internally funded, detailed definition study of a spacecraft 'bus' and propulsion system for small, economical, off-the-shelf satellites, launched quickly by low cost boosters. These 'lightsats', as they are called, could use an ion thruster to increase payload capability or launcher enhancement. This article discusses the concept and its novel propulsion system, which may fly a demonstration mission later this decade. (Author)

[en] The effect of the velocity program and duty cycle (St_L) on the propulsive efficiency of pulsed-jet propulsion was studied experimentally on a self-propelled, pulsed-jet underwater vehicle, dubbed Robosquid due to the similarity of essential elements of its propulsion system with squid jet propulsion. Robosquid was tested for jet slug length-to-diameter ratios (L/D) in the range 2-6 and St_L in the range 0.2-0.6 with jet velocity programs commanded to be triangular or trapezoidal. Digital particle image velocimetry was used for measuring the impulse and energy of jet pulses to calculate the pulsed-jet propulsive efficiency and compare it with an equivalent steady jet system. Robosquid's Reynolds number (Re) based on average vehicle velocity and vehicle diameter ranged between 1300 and 2700 for the conditions tested. The results indicated better propulsive efficiency of the trapezoidal velocity program (up to 20% higher) compared to the triangular velocity program. Also, an increase in the ratio of the pulsed-jet propulsive efficiency to the equivalent steady jet propulsive efficiency (η_P/η_P,ss) was observed as St_L increased and L/D decreased. For cases of short L/D and high St_L, η_P/η_P,ss was found to be as high as 1.2, indicating better performance of pulsed jets. This result demonstrates a case where propulsion using essential elements of a biological locomotion system can outperform the traditional mechanical system equivalent in terms of efficiency. It was also found that changes in St_L had a proportionately larger effect on propulsive efficiency compared to changes in L/D. A simple model is presented to explain the results in terms of the contribution of over-pressure at the nozzle exit plane associated with the formation of vortex rings with each jet pulse.

[en] We present two objections to Redzic conclusion that in the 'tough variant' of Bell's thread-between-spaceships problem (the ships' acceleration is constant) the stretch of the thread remains finite. First, we show that because of the existence of the horizon for the accelerated observer Redzic drops out an essential part of the thread's history. Second, we show that there is no simple relation between the distance between the spaceship and the physical (leading to strain) stretch of the thread. We also present the correct estimate for the stretch, which shows that the stretch increases infinitely. (letters and comments)

[en] In this paper, we indicate how the great advantages that ICF offers for interplanetary propulsion can be accomplished with the VISTA spacecraft concept. The performance of VISTA is expected to surpass that from other realistic technologies for Mars missions if the energy gain achievable for ICF targets is above several hundred. Based on the good performance expected from the U. S. National Ignition Facility (NIF), the requirements for VISTA should be well within the realm of possibility if creative target concepts such as the fast ignitor can be developed. We also indicate that a 6000-ton VISTA can visit any planet in the solar system and return to Earth in about 7 years or less without any significant physiological hazards to astronauts. In concept, VISTA provides such short-duration missions, especially to Mars, that the hazards from cosmic radiation and zero gravity can be reduced to insignificant levels. VISTA therefore represents a significant step forward for space-propulsion concepts

[en] The vehicle includes pair of compasses with chains for transmission of required motion between motors of the vehicle body and propulsion means with a limited mobility in respect to the body. The aim is to clear varied obstacles without loss of stability for places inaccessible to a human worker after an accident

[en] A stable and compact vehicle is claimed for intervention in buildings becoming inaccessible to workers after an accident. Thrusters can be tilted by rotation when such motion is useful e.g. for obstacles such as stairs, or a pipe on the floor

[en] This paper describes the design and testing of an indirect hanging pendulum thrust balance using a laser-optical-lever principle to provide micro- to millinewton thrust measurement for the development of electric propulsion systems. The design philosophy allows the selection of the total thrust range in order to maximize resolution through a counterbalanced pendulum principle, as well as passive magnetic damping in order to allow relatively rapid transient thrust measurement. The balance was designed for the purpose of hollow cathode microthruster characterization, but could be applied to other electric propulsion devices in the thrust range of micro- to millinewtons. An initial thrust characterization of the T5 hollow cathode is presented

[en] An overview is presented of special propulsion research carried out in Beijing University of Aeronautics and Astronautics of China. The research activities are supported by NSFC (National Natural Science Foundation of China), other governmental agencies and industrial partners, which include experimental, analytical and numerical work related to arcjet thrusters, ion thrusters, plasma sail and other new concept propulsions

[en] We study controllability properties (swimming capabilities) of a mathematical model of an abstract object which 'swims' in the 2-D Stokes fluid. Our goal is to investigate how the geometric shape of this object affects the forces acting upon it. Such problems are of interest in biology and engineering applications dealing with propulsion systems in fluids

[en] The prerequisite for manned space missions in the twenty first century is the advanced high performance transportation. Plasma thrusters are known to provide higher specific impulse than conventional chemical thrusters, and because of this advantage, plasma thrusters have been used on satellites for several decades. For successful deep space missions, an even higher performance propulsion system is required, and the Ion Cyclotron Resonance Heating (ICRH) plasma thruster is one of the candidates. An ICRH thruster can provide not only high specific impulse but also operational flexibility, which is the most important aspect of the thruster. For the feasibility study of the ICRH thruster, a small sized, proof-of-principle-type experiment is currently ongoing under the KAIST-KBSI collaboration research. If it turns out to be successful, a larger scale experiment will be planned at HANBIT magnetic mirror device