Some of the early design issues with reusable vehicles

Some of the early design issues with reusable vehicles, and that shown to be enormous challenges, were stability, control, aerodynamic heating and hypersonic flow fields [1]. X-1A and X-1B proved inadequate stability at Mach 2.44. At this speed, the aircraft diverged and spun to almost the impossibility of landing safely. X-2 experienced inadequacy of aerodynamic control at 126,200 feet altitude and a speed of Mach 3. The aircraft diverged out of control and it could not be recovered [2]. These control difficulties experienced by the early X-planes later led to thruster reaction pitch, yaw and roll, while aerodynamic heating issues led to the development of new alloys to stand up to high temperatures during the high speed flights [3] With the stability issues encountered by X-1 and X-2 at lower Mach speeds than expected, NACA suggested the replacement of the supersonic airfoil with a wedge shaped vertical tail. This kind of tail would give a higher maneuverability to control the vehicle if it diverged, as well as directional stability [4]. Such design changes (thruster reaction and wedge shape tail) would be implemented in the X-15 in order to achieve a speed of over Mach 3. To deal with the heat, designers chose a hot structure and the plane was meant to fly at the maximum heat tolerance of the alloys, which was expected to be around Mach 7. Although X-15 was designed to fly “fast and hot - the faster, the hotter, the better” [5], and not necessarily high, the X-15 managed to reach above the atmosphere. It was then noticed that over 200,000 feet altitude there was no more any kind of aerodynamic reaction control [6]. Despite the fact that human space flight was not yet considered at that time, another important issue discussed was reentry, both in regard to heating and stability.

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Notes:

[1] Armstrong, Neil A. The X-15. Next Generation Suborbital Research Conference (NSRC), 2012. YouTube (accessed September 9, 2012).

[2] Ibid.

[3] Jenkins, Dennis R. Space Shuttle - The History of the National Space Transportation System. World Print Ltd, Hong Kong, 2010, 5.

[4] Ibid, 6.

[5] Armstrong, Neil A. The X-15. Next Generation Suborbital Research Conference (NSRC), 2012. (accessed September 9, 2012).

[6] Jenkins, Dennis R. Space Shuttle - The History of the National Space Transportation System. World Print Ltd, Hong Kong, 2010, 5.

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References

Armstrong, Neil A. The X-15. Next Generation Suborbital Research Conference (NSRC), 2012.

Jenkins, Dennis R. Space Shuttle - The History of the National Space Transportation System. World Print Ltd, Hong Kong, 2010.