Gene P. Menees

Design and Performance Analysis of a Conical Aerobrake Orbital Transfer Vehicle Concept

A Shuttle-compatible systems design based on the core concept of attachable modules for the major vehicle components is proposed. The principal features include a disposable cargo/extra-propellant tank module; a porous, radiative, back-scattering drag-brake surface material of thin silica cloth; and a lightweight carbon-composite support structure. The mission payload capability for delivery, retrieval, and combined operations is determined for a broad range of missions including NASA/DOD requirements and extending through cislunar space. The effects of finite-rate surface catalysis, negative lift, and multiple atmospheric passes in reducing the aerothermodynamic heating rates are also investigated. In addition, the structural and thermal protection problems of the drag-brake support apparatus are analyzed, and recommendations are proposed for future design refinements.

Analytical and experimental validation of the Oblique Detonation Wave Engine concept

Wave combustors, which include the oblique detonation wave engine (ODWE), are attractive propulsion concepts for hypersonic flight. These engines utilize oblique shock or detonation waves to rapidly mix, ignite, and combust the air-fuel mixture in thin zones in the combustion chamber. Benefits of these combustion systems include shorter and lighter engines which require less cooling and can provide thrust at higher Mach numbers than conventional scramjets. The wave combustors ability to operate at lower combustor inlet pressures may allow the vehicle to operate at lower dynamic pressures which could lessen the heating loads on the airframe. The research program at NASA-Ames includes analytical studies of the ODWE combustor using Computational Fluid Dynamics (CFD) codes which fully couple finite rate chemistry with fluid dynamics. In addition, experimental proof-of-concept studies are being performed in an arc heated hypersonic wind tunnel. Several fuel injection design were studied analytically and experimentally. In-stream strut fuel injectors were chosen to provide good mixing with minimal stagnation pressure losses. Measurements of flow field properties behind the oblique wave are compared to analytical predictions.

Nitric Oxide Formation by Meteoroids in the Upper Atmosphere

Abstract The process of nitric oxide formation during atmospheric entry of meteoroids is analyzed theoretically. An ablating meteoroid is assumed to be a point source in a uniform flow with a continuum regime evolving in its wake. The amount of nitric oxide produced by high-temperature reactions of air in the continuum regime is calculated-by numerical integration of chemical-rate equations. This is accomplished by assuming that flow properties are constant across the reacting region, the radius of the region being determined from considerations of shock-wave formation and molecular diffusion. The results, when summed over the observed mass, velocity, and entry-angle distributions of meteoroids, provide annual global production rates of nitric oxide as a function of altitude. The peak production of nitric oxide is found to occur at altitudes between 9 × 104 and 105 m, the total annual rate being about 4 × 107 kg. The present results suggest that the large concentration of nitric oxide observed below 9.5 × 104 m could be attributed to meteoroids instead of photodissociation of nitrogen into metastable, 2D-state atoms, as has been previously hypothesized.

Numerical Simulations of a Pulsed Detonation Wave Augmentation Device

We present here the concept of a hybrid engine for Single Stage To Orbit (SSTO) air-breathing hypersonic vehicle. This concept relies on the use of pulsed detonation waves, both for thrust generation and mixing/combustion augmentation. We describe the principles behind the engine concept, which we call the Pulsed Detonation Wave Augmentor (PDWA). We demonstrate the principles of operation for two possible configurations through numerical simulations. We also attempt a first approximation to engine design, and propose various applications.

A multi-temperature TVD algorithm for relaxing hypersonic flows

In this paper, the extension of a multispecies TVD algorithm, second-order accurate for real-gas flows to a multitemperature formulation is described. The convection algorithm is coupled to internal relaxation processes, and the features of the coupling are examined. The first version consists of a three-temperature model, where translational-rotational, vibrational, and electronic energy modes are separately convected. Although several species are present, there is only one vibrational temperature in this model. The second version generalizes to a vibrational temperature for each molecular specie, with additional couplings between species. The algorithms are applied to a generic two-dimensional flow field, and results are compared with experimental observations.

BENT-BICONIC SINGLE-STAGE-TO-ORBIT VEHICLE CONCEPTUAL STUDY

A new design concept is proposed for an all-propulsive, vertical-takeoff/horizontal-landing, reusable single-stageto-orbit space transportation system. The vehicle is to carry an unmanned payload of 11 tons to a 400-km orbit inclined at 51 deg. It is shaped in a bent-biconic geometry, has no wings but horizontal and vertical stabilizers, and relies on a para-wing for landing. Its tripropellant propulsion system uses both RP1-LOX and LH2-LOX. The vehicle is sized and the weights of its components are estimated using an existing methodology. The ascent and entry flight scenarios are calculated, and their features are compared with those of the existing reference winged-body design. The bent-biconic design is found to be competitive with the reference design in its performance. The new design is advantageous in that it can avoid aerodynamic instabilities at transonic speed range and is free from the problem of excessive heating at the wing leading edge as a result of shock/boundary-layer interactions, leading to a lighter liftoff weight. However, the viability of this new design is dependent on further development of para-wing technology.

NO(x) reduction additives for aircraft gas turbine engines

The reduction of oxides of nitrogen (NO(x)) emissions from aircraft gas turbine engines is a vital part of the NASA High Speed Research Program. Emissions reductions are critical to the feasibility of future High Speed Civil Transports which operate at supersonic speeds in the stratosphere. It is believed that large fleets of such aircraft using conventional gas turbine engines would emit levels of NO(x) that would be harmful to the stratospheric ozone layer. Previous studies have shown that NO(x) emissions can be reduced from stationary powerplant exhausts by the addition of additives such as ammonia to the exhaust gases. Since the exhaust residence times, pressures and temperatures may be different for aircraft gas turbines, a study has been made of additive effectiveness for high speed, high altitude flight.

Atmospheric entry of Mars-return nuclear-powered vehicles due to accidental termination of operations

The entry of nuclear reactors into Earths atmosphere resulting from an accidental or inadvertent abort of a space vehicle powered by nuclear-thermal rockets is investigated. The study is made for a typical piloted Mars mission vehicle incapacitated by an accident or malfunction during the Earth-arrival phase of the Mars-return journey due to simultaneous, multiple failures of its component systems. A single accident/abort scenario resulting in three entry possibilities is considered for a nominal hyperbolic in-bound approach velocity of 8 km/sec. The most severe case involving a direct entry is then analyzed over a broad range of approach velocities extending to 12 km/sec to include sprint-type missions. The results indicate that the severe surface heating, stagnation pressures, and g-loads are greater than 150 kW/sq cm, 300 atm, and 800-g, respectively. The wall heat transfer rate exceeds the value that can be accommodated by a carbon heatshield through radiation equilibrium prior to sublimation at 5500 K. These conditions are beyond our previous experience in crew safety, structural design, and thermal protection.

Comparative flight strategies for ascent from Martian surface to orbiter rendezvous

Flight maneuvers and strategies to transport a vehicle from the Martian surface to orbiter rendezvous are analyzed to determine the most fuel-efficient method. Both endo- and exo-atmospheric flight strategies are considered for orbiter rendezvous into parking orbits of arbitrary inclination. It is found that optimal mass efficiency is achieved where the orbiter inclination is equal to or exceeds the latitude of the launch site. It is shown that high aerodynamic lifting capability improves performance for low circular orbit (LCO) rendezvous. It is suggested that the synergetic ballistic-projecting technique is best for optimal LCO rendezvous and that the all-thrust technique with plane change at apoapsis is best for optimal high elliptical orbit rendezvous.

Synergetic plane-change capability of a conceptual aeromaneuvering-orbital-transfer vehicle

The flight strategy for a general low-earth orbit plane-change is analyzed for a conceptual, high-lift, aeromaneuvering-orbital-transfer vehicle, and applied to the important case of the 45 deg plane-inclination change. The study focuses on two principal methods: (1) the procedure to obtain a change in the inclination of the vehicles orbital plane, and (2) the full rendezvous procedure. Optimal trajectories for minimal propellant use during the synergetic aerotransit are developed, which incorporate best estimates of constraints imposed by reusable thermal-protection requirements and human tolerance to g-load levels. The performance capability for one-way payload delivery to the target orbit is analyzed in detail and the capability for return to the base orbit demonstrated.