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The National Aerospace Initiative (NAI): Technologies For Responsive Space Access
Abstract
The Secretary of Defense has set new goals for the Department of Defense (DOD) to transform our nation's military forces. The Director for Defense Research and Engineering (DDR&E) has responded to this challenge by defining and sponsoring a transformational initiative in Science and Technology (S&T) -the National Aerospace Initiative (NAI) -which will have a hndamental impact on our nation's military capabilities and on the aerospace industry in general. The NAI is planned as a joint effort among the tri-services, DOD agencies and National Aeronautics and Space Administration (NASA). It is comprised of three major focus areas or pillars: 1) High Speed Hypersonics (HSH), 2) Space Access (SA), and 3) Space Technology (ST). This paper addresses the Space Access pillar. The NAI-SA team has employed a unique approach to identifying critical technologies and demonstrations for satisfying both military and civilian space access capabilities needed in the fbture. For planning and implementation purposes the NAI-SA is divided into five technology subsystem areas: Airframe, Propulsion, Flight Subsystems, Operations and Payloads. Detailed technology roadmaps were developed under each subsystem area using a time-phased, goal oriented approach that provides critical space access capabilities in a timely manner and involves subsystem ground and flight demonstrations. This S&T plan addresses near-term (2009), mid-term (2016), and long-term (2025) goals and objectives for space access. In addition, system engineering and integration approach was used to make sure that the plan addresses the requirements of the end users. This paper describes in some detail the technologies in NAI-Space Access pillar. Some areas of emphasis are: high temperature materials, thermal protection systems, long life, lightweight, highly efficient airframes, metallic and composite cryotanks, advanced liquid rocket engines, integrated vehicle health monitoring and management, highly operable systems and payloads. Implementation strategies for NAI is also described.
... The RAND Corporation also believed that a TSTO concept close to Sänger II should be a strong contender for the NASP program [1]. Subsequently, additional efforts were conducted to develop a TSTO RLS with air-breathing propulsion on the first stage [10][11][12][13][14][15][16][17][18]. ...
The Skylon concept incorporates the highly innovative synergetic air-breathing rocket engine concept that has the potential to revolutionize the mode of propulsion for transportation of medium-weight payloads to low Earth orbits. An independent partial assessment is provided of the technical viability of the Skylon concept. Pressure lift and drag coefficients derived from Euler simulations for unpowered flight compare very well and fairly well, respectively, with those from engineering methods. The engineering-method coefficients for powered flight are increasingly less acceptable as the freestream Mach number is increased beyond 8.5 because these methods did not account for the increasing favorable (in terms of pressure forces) effect of underexpanded rocket engine plumes on the aft fuselage. At Mach numbers greater than 8.5, the thermal environment around the aft fuselage is a known unknown: a potential design and/or performance risk issue. The adverse effects of shock waves on the aft fuselage and plume-induced flow separation are other potential risks. A preliminary design of Skylon requires the judicious use of a combination of engineering methods, advanced methods based on required physics or analytical fidelity, test data, and independent assessments. The demonstration of a synergetic air-breathing rocket-engine-powered experimental aerospace plane calls for the second revival of the Aerospace Plane Program.
An independent partial assessment is provided of the technical viability of the Skylon aerospace plane concept, developed by Reaction Engines Limited (REL). The objectives are to verify REL's engineering estimates of airframe aerodynamics during powered flight and to assess the impact of Synergetic Air-Breathing Rocket Engine (SABRE) plumes on the aft fuselage. Pressure lift and drag coefficients derived from simulations conducted with Euler equations for unpowered flight compare very well with those REL computed with engineering methods. The REL coefficients for powered flight are increasingly less acceptable as the freestream Mach number is increased beyond 8.5, because the engineering estimates did not account for the increasing favorable (in terms of drag and lift coefficients) effect of under-expanded rocket engine plumes on the aft fuselage. At Mach numbers greater than 8.5, the thermal environment around the aft fuselage is a known unknown−a potential design and/or performance risk issue. The adverse effects of shock waves on the aft fuselage and plume-induced flow separation are other potential risks. The development of an operational reusable launcher from the Skylon concept necessitates the judicious use of a combination of engineering methods, advanced methods based on required physics or analytical fidelity, test data, and independent assessments. Nomenclature Symbols A t = nozzle throat area A e = nozzle exit area C L = pressure lift coefficient C D = pressure drag coefficient C z = pressure moment around z-axis F x = pressure force in x-direction, the direction from nose to tail of Skylon F y = pressure force in y-direction, the vertical direction F z = pressure force in z-direction, the span-wise direction h = altitude J = objective function M ∞ = freestream Mach number M j = Jet Mach number at nozzle exit m a = airflow rate m f = fuel flow rate m e = mass flow rate at nozzle exit p ∞ = freestream pressure P 1t = total pressure at the exit of combustion chamber P e = static pressure at nozzle exit T 1t = total temperature at the exit of combustion chamber T e = static temperature at nozzle exit T rec = freestream recovery temperature T tot = freestream total temperature V e = velocity at nozzle exit
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