AAWSAP DIRD, Space Access: Where We’ve Been and Where We Could Go, March 2010

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Figure 14 compares the glide ranges and L/D ratios of selected hypersonic gliders. The
shuttle would be in the area of the nominal wing body on the righthand chart. From
Figure 13, the no-waiting cross range (lateral range) is 3,600 to 4,400 nautical miles.
That means the hypersonic L/D ratio needs to be in the 2.7 to 3.2 range. Appendix D
has down and lateral ranges shown as landing ellipses. The key to a successful landing
is a subsonic L/D ratio that is in the 4.5-or-greater range. The NASA round-bottom
configurations were not capable of that subsonic L/D ratio. The X-24B was in that
category and was therefore easily landed compared with the X-24A or Prime vehicles.
These high-performance gliders were unique to the AFFDL. The intent in case of a fire
would be to immediately evacuate to the hypersonic gliders and then depressurize the
station to control any fire (remember that Mercury and Gemini could be depressurized).
A crew could then be launched to recover the operation and repair the station.
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Figure 14. Hypersonic Glider Characteristics
There is always the question about landing these blended bodies. Figure 15 shows the
blended body handling qualities to be very good, and therefore a pilot's fear factor is
less than with the X-15. Bill Dana said the X-24A was difficult to handle when landing
but that he could land the X-24B almost with no hands as it flared automatically. To
the author's knowledge, all of the wind tunnel tests showed inherent static and dynamic
stability over the entire speed range.
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