Papers by Graham Dorrington
AIAA Journal, 2010
Computational models are developed to predict the natural convection heat transfer and buoyancy f... more Computational models are developed to predict the natural convection heat transfer and buoyancy for a Montgolfiere under conditions relevant to the Titan atmosphere. Idealized single and double-walled balloon geometries are simulated using algorithms suitable for both laminar and (averaged) turbulent convection. Steady-state performance results are compared to existing heat transfer coefficient correlations. The laminar results, in particular, are used to test the validity of the correlations in the absence of uncertainties associated with turbulence modeling. Some discrepancies are observed, which appear to be primarily associated with temperature nonuniformity on the balloon surface. The predicted buoyancy for both the single-and double-walled balloon in the turbulent convection regime, predicted with standard two-equation turbulence models, showed similar trend as with the empirical correlations. There was also good agreement with recently conducted experiments in a cryogenic facility designed to simulate the Titan atmosphere.
Possible Architectures for Near-Future Venus Atmosphere in situ Missions
Rationale for In-Situ Exploration of the Marius Hills Pit
Buoyancy estimation of a Montgolfière in the atmosphere of Titan
The Aeronautical Journal, 2013
Prediction of the buoyancy of a thermal balloon, or Montgolfière, intended to float in the atmosp... more Prediction of the buoyancy of a thermal balloon, or Montgolfière, intended to float in the atmosphere of Titan is discussed. A laboratory based experiment designed to measure the buoyant lift of an electrically-heated, single-wall, natural-shape balloon is described. The experimental results presented closely match an analytical model employing established heat transfer correlations with selected parameter values. When the model is extrapolated to the cryogenic conditions representative of Titan’s lower troposphere, using the same correlations and parameters, the estimated buoyancy is found to be substantially higher than has been previously predicted. To account for the buoyancy difference, it is suggested that the internal free convection heat transfer rate is significantly lower than has been assumed in previous studies. To substantiate this result, it is recommended that further experiments should be performed at higher Rayleigh numbers.
Performance of non-rigid airships operating in the neutral buoyancy condition
The Aeronautical Journal, 2007
The feasibility of using neutrally-buoyant (or fully-buoyant) airships for passenger and cargo tr... more The feasibility of using neutrally-buoyant (or fully-buoyant) airships for passenger and cargo transportation is investigated. The drag coefficients of rigid and non-rigid airships are deduced from flight data. Comparisons are made with empirical drag formulas and previous wind tunnel data. Some general trends for airship drag are derived. The mass breakdown of non-rigid airships with hull volumes up to 35,000m3 is analysed using parametric equations. The maximum feasible airspeed and useful load carrying capacity of projected airships are calculated. ‘Specific productivity’ is found to be lower than values achievable with fixed-wing aircraft, but ‘fuel-specific productivity’ is found to be competitive, confirming results of a previous NASA study. The use of gaseous hydrogen and fuel cells is briefly discussed.
Preliminary thrust tests carried-out on a 0.5 metre diameter, helical rotor based on a sketch by ... more Preliminary thrust tests carried-out on a 0.5 metre diameter, helical rotor based on a sketch by Leonardo da Vinci are presented, along with the results of computational flow simulation. Some of the key geometric variables that define the helical rotor and their influence on the maximum achievable thrust level are also discussed. It is concluded that with sufficient input power, da Vinci's helical rotorcraft could achieve hovering flight; however, the technical challenges involved in a developing a free-flight hovering demonstrator would be formidable.
Use of small lighter-than-air vehicles for mobile access to the upper canopy
In recent years there has been growing recognition of the ecological importance of tropical fores... more In recent years there has been growing recognition of the ecological importance of tropical forest canopies. However, scientific studies of canopies has been hindered by the problem of gaining access to this so-called "High Frontier." Ingenious solutions have been found to the problem of gaining access to limited areas of canopy by using ropes, walkways and cranses, e.g. the "Spiders Web" technique invented by Perry.
Launch Vehicles
Fortescue/Spacecraft Systems Engineering, 2011
ABSTRACT The basic principles which determine launcher design and hence constrain the spacecraft ... more ABSTRACT The basic principles which determine launcher design and hence constrain the spacecraft payload are determined. Some key features of the principal launcher alternatives in Europe and the U.S., namely, the unmanned, expendable Ariane and the manned, substantially reusable, Space Shuttle, are outlined. The equations of motion of the rocket are specialized to the vertical plane, parallel and normal to the flight direction, and to the motion of the center of mass and the pitch rotation. A typical Ariane 2 flight profile for transfer into GTO is illustrated. Some representative mission requirements for spacecraft launches are reviewed. Launch vehicle burnout velocities for spacecraft emplacement are given. Geostationary orbit emplacement, orbital mission performance, and configuration interactions are discussed.
Proceedings of the National Academy of Sciences, 2012
Based on terrestrial laboratory experiments, estimates are presented for the buoyancy of a Titan ... more Based on terrestrial laboratory experiments, estimates are presented for the buoyancy of a Titan Montgolfière with a single-wall natural-shape envelope. Using the experimental results, the internal free convective heat transfer rate derived was found to be significantly lower than has previously been assumed. Preliminary estimates of the down force caused by rain and downdrafts are made. Modulation of buoyancy is also briefly addressed.
Advances in Space Research, 2010
Various balloon systems intended as scientific platforms to float in the atmosphere of Venus at a... more Various balloon systems intended as scientific platforms to float in the atmosphere of Venus at altitudes between about 35 and 65 km are briefly reviewed. Previous predictions of the altitude oscillations of balloons filled with helium gas and water vapor are largely confirmed through numerical simulation and analysis. The need for refined thermal modelling is emphasised. Several novel technical concepts are introduced. It is concluded that phase change balloons would be more suitable than non-condensing super pressure gas balloons when repeated altitude excursions are a mission requirement.
Preliminary evidence for drizzle in the middle cloud layer of Venus
Advances in Space Research, 2013
ABSTRACT Vertical trajectory data from the VEGA 1 and 2 balloon flights in the atmosphere of Venu... more ABSTRACT Vertical trajectory data from the VEGA 1 and 2 balloon flights in the atmosphere of Venus is re-analyzed. A previously employed helium leak rate profile invoked to entirely account for the decrease in equilibrium float altitude of VEGA 2 is questioned and deemed ad hoc. As an alternative, it is proposed that both VEGA 1 and 2 experienced in-flight mass increases due to the deposition of cloud particles onto their envelopes, as well as losing helium at a reduced rate consistent with the pre-flight prediction. Particle deposition rates are estimated and found to be compatible with this alternative scenario. Possible evidence for drizzle is also presented. Preliminary experiments to derive aerosol deposition rate on a flat plate and the maximum feasible liquid mass that may be accumulated on a near-spherical envelope are briefly described. Further experimental work is recommended to constrain the deposition efficiency values involved and the maximum feasible drizzle fluxes that could have been encountered by both VEGA 1 and 2.
Aerospace
Exploring how life is distributed in the universe is an extraordinary interdisciplinary challenge... more Exploring how life is distributed in the universe is an extraordinary interdisciplinary challenge, but increasingly subject to testable hypotheses. Biology has emerged and flourished on at least one planet, and that renders the search for life elsewhere a scientific question. We cannot hope to travel to exoplanets in pursuit of other life even if we identify convincing biosignatures, but we do have direct access to planets and moons in our solar system. It is therefore a matter of deep astrobiological interest to study their histories and environments, whether or not they harbor life, and better understand the constraints that delimit the emergence and persistence of biology in any context. In this perspective, we argue that targeted chemistry- and biology-inspired experiments are informative to the development of instruments for space missions, and essential for interpreting the data they generate. This approach is especially useful for studying Venus because if it were an exoplane...
In 1995 a dirigible (or non-rigid airship) was flown successfully 30 times over a region of tropi... more In 1995 a dirigible (or non-rigid airship) was flown successfully 30 times over a region of tropical rain forest in Borneo. Some comments are made about the rationale for these test flights. Some aspects of the airship's design are outlined, including: the requirements; the configuration and overall size; the seating arrangement and payload capability; details about the quiet electric propulsion system. Some operational characteristics are then described. Special attention is paid to the influence of wind/gusts in tropical forests and the ability to hold station and/or the feasibility of safe landing on the canopy roof. The preliminary scientific objectives of the project are also outlined. For example, some details about the design of an insect suction trap and its deployment are included. Finally, some comments on future planned work as well as suggestions for further technical developments are also given.
Performance of air-breathing single-stage-to-orbit vehicles
Acta Astronautica, 1990
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Papers by Graham Dorrington