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Aviation History
1961
1961 - 1360.PDF
464 FLIGHT, 21 September 1961 Space Research in the USA THE 1961 WILBUR WRTGHT LECTURE, BY DR ABE SILVERSTEIN ALTHOUGH officially not a part of the Anglo-American Aero-nautical Conference, the 49th Wilbur Wright Memorial Lecture of the Royal Aeronautical Society on September 12 attracted manyof the delegates attending the joint meeting, and the three presidents of the sponsoring societies—Air Marshal Sir Owen Jones of theRAeS, Dr H. Guyford Stever of the IAS and Air Commodore W. P. Gouin of the CAI—were on the platform as the speaker wasintroduced. He was Dr Abe Silverstein, Director of Space Flight Programs of the US National Aeronautics and Space Administra-tion, and his subject was Research in Space Flight Technology. After the lecture, a vote of thanks to Dr Silverstein was proposedby Mr B. S. Shenstone, president-elect of the Society, who con- gratulated the speaker on having presented a wide view of anenormous subject, without mathematics or excessive detail. This was followed by a reception in the Society headquarters at 4Hamilton Place. Extracts from Dr Silverstein's paper follow: Propulsion The burden of providing increased space-flight capability for thefuture [said Dr Silverstein] falls most heavily on the shoulders of those responsible for the development of the propulsion andassociated launch-vehicle systems. The higher the total velocity to be imparted, the greater is the premium on high propulsive per-formance. In the lunar landing and return mission, in which a total velocity of about 56,000ft/sec is required, a multi-stage, all-solid fuelled rocket vehicle may require as much as 40,000.0001b thrust in the first-stage rocket, and the launch vehicles may weigh25,000,0001b. In contrast, a three-stage launch vehicle with liquid- propellant first and second stages, and a nuclear heat exchangerocket as a third stage can accomplish the same mission with about 0.1 of this launch thrust and weight. Many analytical investigationshave shown the large gains in performance possible from the use of liquid hydrogen either in combination with liquid oxygen orfluorine in a chemical rocket or used as the propulsion fluid in the nuclear rocket. NASA has initiated development of 15,0001band 200,0001b liquid-hydrogen engines, and. in a co-operative effort with the US Atomic Energy Commission, a heat-transfer nuclearrocket engine. The use of liquid hydrogen as a fuel, with its tem- perature of 425 F below zero, a density only one-fifteenth that ofwater and a coefficient of expansion ten times that of most liquids, introduces a host of challenging research problems. The multifoil technique appears to offer considerable promise forlong-term protection of liquid hydrogen in space, but many prob- lems yet remain to be solved. Suggestions have been made forimproving the effectiveness of the multifoils by use of surface coatings with a low solar absorptivity. By a combination ofproperly designed radiation shields, by orientation of the vehicle so that the engine faces the Sun, and by arranging the tanksproperly behind the engine, calculations indicate that the hydrogen loss in space due to thermal radiation from the Sun can be reducedto a value as low as 0.003 per cent per day. Meteoroids The greatest hazard for long-time storage of pro-pellants in space is tank puncture from meteoroids. Information is scarce on the density, composition, velocity, size, and directionof the meteoroids, as well as on the type of damage incurred by the materials that are impacted. Both problems are under study, andmicrophones have been installed on many of the satellites that have been orbited to measure the frequency and momentum of theimpacting meteoroids. A recent summary of the data by C. W. The lecturer, Director of Space Flight Programs for NASA, pictured before his delivery of the 1961 Wilbur Wright lecture "Flight" photogra;. h McCraken, including results from Explorer VIII, shows a lowerincidence of heavier meteoroids, and consequently a lower hazard to space vehicles, than had previously been predicted from extrapoi-ated data. The experimental programme on meteoroid impact is being extended by flights with the S-55 satellite launched by theScout vehicle. Weightless Flight Tank venting, pressurization, and enginere-starting during coasts in orbit or flight through space introduce the question regarding the location of the propellant and pro-pellant vapours during this weightless period of flight. The normal hydrostatic and convective forces are absent, and surface-tensionforces prevail. The NASA Lewis Research Center has initiated an interesting approach in which the fluid surface-tension forces areused to position the liquid mass during the weightless period. The liquid/vapour surface tends to form a sphere. Unfortunatelythis sphere has no preferred location, and could easily come to rest over the pump inlet. If, however, a structure is erected from thebottom of the tank such that the bubble cannot find enough clear space for a spherical shape to form, it should tend towards the least-surface-area shape imposed by the configuration of the structure. Pumping Of greatest importance to the development of the liquid-hydrogen engine is the establishment of sound design methods for the pumps. Considerable progress has been made in understandingthe phenomena of pumping liquid hydrogen, and the problem can be illustrated by referring to tests (NASA Lewis Research Center)on a research model of a three-stage axial-flow pump. This pump embodies concepts developed for turbojet engines,yet is a relatively new approach to liquid pump design. The three typical stages are the inducer, an intermediate stage,and a high-pressure stage. The inducer is designed particu- larly to minimize the adverse effects of cavitation with enoughpressure-rise to recondense any vapours formed and prepare the fluid for the succeeding stages. Nuclear Rocket Propulsion For review a sketch of the nuclear rocket engine system is shown(Fig 1). Hydrogen is pumped from the propellant tank to the jet nozzle, where it is used to cool the walls of the latter. The hydrogenis stored as a liquid at about — 422 F at the entrance to the double- walled nozzle. After cooling the walls, the hydrogen cools thereflector of the reactor, which is used to conserve the neutrons required to produce the fission process. The reflector, therefore,helps to reduce the size of the reactor core and the amount of ura- nium required. The hydrogen then passes through the reactor corewhere it comes in contact with the uranium fuel. The capture of neutrons by the uranium causes fission of the uranium nucleus,releasing the large fission heat energy. This energy is transferred to the hydrogen flowing through the reactor, and the hot hydrogengas is then accelerated through the jet nozzle, producing thrust. Development of the technology of the nuclear rocket is under wayin a joint AEC-NASA Rover programme. Reactors will be de- Fig / A simplified schematic diagram of a nuclear rocket engine Fig 2 Minimum lift/drag ratio leads to reduced weight and heating ./^.RELATIVE/ HEAT LOAD .5 1.5
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