Advanced manned launch systems studies underway at the NASA Langley Research Center are part of a broad effort examination of options for the next manned space transportation system to be developed by the United States. One promising concept that uses advanced technologies is a fully reusable, single-stage horizontal-takeoff vehicle that uses airbreathing propulsion. This paper discusses some potential ascent issues that could influence the design of this class of launch vehicles. Two issues are identified. The first issue is that the drag losses due to aerodynamic trim can require a significant fraction of the total energy required to achieve orbit. The second issue is the difficulty in achieving precision insertions with a vehicle that coasts unpowered from a high dynamic pressure to orbit.
A cNomenclature engine capture area, m 2 sensed acceleration, 'g • drag coefficient, nondimensional, = (drag/^S) lift coefficient, nondimensional, = (lift/q^S) pitching-moment coefficient, nondimensional, = (pitching moment/^ Sc) thrust coefficient, nondimensional, = = mean aerodynamic chord, m = altitude, m = specific impulse, s = roll rate gain, s = pitch rate gain, s = pitch acceleration gain, s 2 = yaw rate gain, s = angle-of-attack error gain, nondimensional = integral of angle-of-attack error gain, s -1 = sideslip angle gain, nondimensional = roll error gain, nondimensional = roll rate, deg/s = pitch rate, deg/s = time derivative of dynamic pressure, Pa/s = commanded dynamic pressure, Pa = dynamic pressure, Pa = product of dynamic pressure and angle of attack, Pa-deg = yaw rate, deg/s = reference area, m 2 = inertial velocity, m/s = Earth relative velocity, m/s = angle of attack deg = commanded angle of attack, deg = nominal angle of attack, deg = sideslip angle, deg = flight-path angle, deg j c = commanded flight-path angle, deg AApogee = change in apogee at orbital insertion as compared with optimal trajectory, km AC D = drag coefficient increment due to elevon deflection, nondimensional, = (drag increment/0oo S) AC L = lift coefficient increment due to elevon deflection, nondimensional, = (lift increment/tfooS) AC m = pitching moment coefficient increment due to elevon deflection, nondimensional, = (pitching-moment increment/^ Sc) APayload = change in delivered payload as compared with optimal trajectory, kg APerigee = change in perigee at orbital insertion as compared with optimal trajectory, km ATime = change in orbital insertion time as compared with optimal trajectory (positive longer), s AJ'aero =velocity loss increment due to aerodynamics, m/s AK circ = instantaneous velocity required to circularize, m/s A^cor = velocity loss increment due to Goriolis effect, m/s APgrav = velocity loss increment due to gravity, m/s A Pideai = ideal velocity increment, m/s AJ"ioss = total velocity loss increments, m/s A thrust = velocity loss increment due to reduced thrust induced by atmospheric pressure, m/s AK tv = velocity loss increment due to thrust vector misalignments, m/s da = aileron deflection, = [(de l -de r )/2)], ...
