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Aviation History
1963
1963 - 1238.PDF
66 FLIGHT International, 11 July 196$ Missiles and Spaceflight come with the development of lightweight electromagnets using superconducting materials, the latter having nominally zero elec trical resistance at very low temperatures. To terminate and complete this survey of the re-entry problem, it is necessary to consider certain re-entry configurations other than the straightforward ballistic and winged types already discussed. With the technology at its present stage of development, the most important variation is the semi-ballistic (or semi-lifting) capsule. From the benefits of aerodynamic lift as described, it might be inferred that even a little lift would be advantageous to reduce acceleration loads and control the flight path. This is in fact the case. It is expected that the two-man Gemini capsule will, on re entry, be able to correct a 300-mile undershoot, a 700-mile over shoot and a lateral error of 150 miles in achieving the desired landing site10. As regards acceleration, Chapman suggests5 that an L/D of only 0.25 will be sufficient to reduce the deceleration of orbital entry from 8g to 3g.* Accordingly, a great variety of semi-lifting shapes have been proposed for use as re-entry capsules. These range from blunt, slightly flattened cones to flat, rounded lenticular shapes. In all of them, the advantages gained as a result of lift capability are out of all proportion to the small increase in weight of structure and controls. It must be emphasized, however, that the lift obtained is generally completely inadequate for landing or even low-speed flight. Although some proposals have suggested the use of retract able wings, weight and complexity considerations count heavily against such an idea. It is to be expected that the final descent of a semi-ballistic vehicle will be accomplished by parachute or paraglider. The latter device, developed by F. M. Rogallo in conjunction with NASA and Ryan, warrants further attention since it has also been proposed as a lifting surface for use in the re-entry manoeuvre proper11 (as opposed to mere recovery of the capsule). Designed to give a very large wing area for very low weight, the paraglider consists of a flexible sheet lifting surface of slender planform. It is held in position relative to the airflow by means of rigid leading- edge members and a rigid centre piece, the vehicle capsule being * The same author uses this result to demonstrate just how critical a lifting re-entry is: if even this small amount of lift is applied inadvertently in the opposite direction in this case, downwards), the vehicle will experience a peak deceleration of no less than 20%. suspended on long shroud lines. Control is effected by shifting the centre of gravity relative to the centre of pressure of the lifting surface. Experimental testing has shown the parawing to be a practicable lifting device giving very low wing loadings, and that it is controll able at all speeds and all incidences from 0° to 90°. For re-entry purposes the flexible surface would be made of wire gauze, covered with a high-temperature silicone sealant (since porosity lowers lifting efficiency); the shroud lines and leading edges would have to be large-diameter inflated tubes to combat aerodynamic heating. The whole parawing arrangement would be neatly stowed away during the boost phase, and would be deployed before re-entry commenced. Feasibility studies indicate that a wing loading of less than llb/sq ft is possible, and, with a flightpath angle of 1 °, radiation- cooled re-entry could be made with a long shallow glide, giving a maximum deceleration of less than 2g and a maximum skin temperature of 900°C. Another configuration which achieves similar wing loadings and re-entry performance is the inflatable re-entry glider11,la. This consists of a flexible skin attached to a framework of large-diameter inflatable tubes, the whole structure being folded up in the capsule during the boost phase. When re-entry is to begin, the tubular framework is opened out by inflating with a gas (e.g., helium) or a rigid or non-rigid foam, and the structure takes the form of a large slender lifting surface. As with the tubular leading edges of the parawing, the success of the concept for re-entry largely depends on the development of a suitable flexible heat-resistant coating. One other scheme deserves a brief comment, although it has not been looked at in detail; proposed by Ferri13, it suggests mounting the capsule on the upper surface of a relatively thin but rigid sheet wing made of a good heat-conducting material. Heat from the lower surface is conducted through the material to the cool upper- surface, and the effective radiating area is thus doubled. The stag nation-point heating rate would be reduced to an acceptable value by having the material bent upwards to form large-radius "wrap around" leading edges. REFERENCES 2. Smith, R. H. and Menard, J. A.: Supercircular Entry and Recovery with Manoeuvrable Manned Vehicles. IAS Paper 61-114-1808, 1961. 5. Bensen, O. O. and Strughold, H. (editors): Physics and Medicine of the Atmosphere and Space; Wiley, 1960. 9. Fredette and Orazio: The Drive for Lifting Re-entry Vehicles: Astronautics, August 1961. 10. Gatland, K. W.: Astronatutics in the Sixties, Iliffe, 1962. 11. Rogallo, F. M., et al: Preliminary Investigation of a Paraglider: NASA TN D-443, August 1960. 12. Olstad W. B.: A Study of the Feasibility of Inflatable Re-entry Gliders: NASA TN D-538, October 1960. 13. Radiation Inc: Space Trajectories, Academic Press, 1960. @ MOLYBDENUM (7) L--605 (T) COLUMBIUM ©ZIRCONIA ©TITANIUM ©GRAPHITE Prime contractor for the /SS£T aerothermodynamiclelastic struc tural systems environmental tests) is McDonnell Aircraft Corp. of M Louis. This manufacturer's diagram outlines the form of the main struc ture of the ASSET vehicle, six o which are being constructed W sub-orbital shots down the Atlantic Missile Range boosted by Tnor or Thor Delta. Length and span an respectively to be 68ft 8in ana|W 11 in, and gross 1,0001b to 1,2001b weight
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