Experimental Study on the Deflagration Characteristics of the Liquid Propellant Spray Electrical Ignition and the Simplified Model Calculation
The liquid propellant atomization experimental apparatus, single pulse discharge device and the AC (alternating current) sequence discharge device have been designed to explore the electrical ignition method of HANbased liquid propellant. By using of high speed camera system, the electrical ignition experiment study of the HAN-based liquid propellant LP1846 under different injection pressure has been conducted. The results indicate that: the spray can be ignited instantly by single pulse discharge method as the Sauter mean diameter of the LP1846 droplets is in the region of 10~20 μm, but there is deflagration ability; stable ignition can be got by alternating current pulse discharge method as SMD of LP1846 droplets is in the region of 40~50 μm . Based on the experiment, the simplified model of LP1846 atomization pulse discharge ignition delay time has been proposed. The numerical results coincide well with the experimental results.
NONTOXIC ORBITAL MANEUVERING AND REACTION CONTROL SYSTEMS FOR REUSABLE SPACECRAFT
Toxic propellants have a high ground operations cost because of the potential hazards that require extensive safety precautions, particularly for reusable spacecraft. Nontoxic propellants for orbital maneuvering and reaction control systems have received periodic attention since the late 1960s as new reusable vehicles and upgrades to existing vehicles are proposed. This paper discusses the spacecraft requirements that drive propellant selections, the viable candidates for nontoxic propellants, and the system concepts and technologies required. Options for nontoxic propellants are also discussed, which are categorized as monopropellants, storable bipropellants, and cryogenic oxygen-based bipropellants. Monopropellants provide inherently simple systems and are most suited to low total impulse systems. Hydrogen peroxide and kerosene is a promising storable bipropellant in terms of its density, specie c impulse, and low toxicity for long-duration spacecraft on-orbit propulsion systems. This combination can be made hypergolic, which renders it a very effective replacement for currently used storable propellants. The hypergolic characteristics of kerosene with additives and high-concentration hydrogen peroxide are presented in detail. Higher-performance liquid oxygen and alcohol or hydrocarbon fuels are advantageous for reusable propulsion systems that emphasize e uid commonality with other spacecraft systems and for human exploration missions where in-situ propellant production is foreseen. The prospects for further research work on all of these propellants are also discussed.
Live birth in the Devonian period
The extinct placoderm fishes were the dominant group of vertebrates throughout the Middle Palaeozoic era, yet controversy about their relationships within the gnathostomes (jawed vertebrates) is partly due to different interpretations of their reproductive biology. Here we document the oldest record of a live-bearing vertebrate in a new ptyctodontid placoderm, Materpiscis attenboroughi gen. et sp. nov., from the Late Devonian Gogo Formation of Australia (approximately 380 million years ago). The new specimen, remarkably preserved in three dimensions, contains a single, intra-uterine embryo connected by a permineralized umbilical cord. An amorphous crystalline mass near the umbilical cord possibly represents the recrystallized yolk sac. Another ptyctodont from the Gogo Formation, Austroptyctodus gardineri, also shows three small embryos inside it in the same position. Ptyctodontids have already provided the oldest definite evidence for vertebrate copulation, and the new specimens confirm that some placoderms had a remarkably advanced reproductive biology, comparable to that of some modern sharks and rays. The new discovery points to internal fertilization and viviparity in vertebrates as originating earliest within placoderms.