Documents / Report
This Defense Intelligence Reference Document, prepared by the Defense Intelligence Agency and dated 8 March 2010, was produced under the Advanced Aerospace Weapon System Applications (AAWSA) Program. It gives a historical and technical review of how to reach space and return. It covers hypersonic gliders, air-breathing and rocket propulsion, thermodynamics and materials, and launch options. It argues that reliable, schedulable access to low Earth orbit is mainly a hardware and propulsion problem rather than a technology one.
“Lockheed”5 pages
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Gross weight trends are shown for five different takeoff wing loadings for horizontal
takeoff and landing (HTOL). Solutions for constant wing loading are shown for values
of tau from 0.2 to 0.063. The curves sweep upward between tau = 0.2 and tau =
0.063 and are variable tau solutions for a fixed takeoff wing loading. The curve for 200
lb/ft2 never converged at tau = 0.063 and is almost vertical. So if 185 knots is an
acceptable takeoff speed, then the maximum weight ratio without significant weight
penalty over vertical takeoff is about 5.6 (40 years ago, Dwight Taylor of McDonnell
Aircraft determined the point to be a weight ratio of 5.5). This excludes conventional
rockets but does permit high-performance air-breathing rockets and the KUN cycle.
The point at which the VTOHL and HTOL modes have the same gross weight is then the
maximum weight ratio for which there is no penalty for horizontal takeoff. For
example, at a takeoff wing loading of 976 kg/m 2 (200 lb/ft2 ), the point at which the
VTDHL and HTDL modes have the same gross weight is for a weight ratio of 5.5, or an
air-breathing speed of mach 6 ± 0.3. For a takeoff wing loading of 610 kg/m 2 (125
lb/ft2), the VTDHL/HTOL boundary is now a weight ratio of 4.3, or an air-breathing
mach 10.5 ± D.S. This wing loading would be consistent with that of commercial
transports and is also correct to air launch horizontal landing at about mach 0.72 and
35,000 feet. For a takeoff wing loading of 464 kg/m 2 (95 lb/ft2), the VTOHL/HTOL
boundary is now a weight ratio of 3.4, or an air-breathing mach 13 ± 1.0.
For an air-breathing rocket, a mass ratio of 5.0 is achievable, resulting in a gross
weight of about 230 tons. This is less than half the 480 tons for an all-rocket case.
However, if a horizontal takeoff requirement is imposed a priori, the lowest wing
loading for which a practical solution exits is 610.2 kg/m 2 . At that point, the gross
weight for the horizontal takeoff solution is about 800 tons, almost twice the all-rocket
value. If a study team is not aware of the comparison to vertical takeoff, it may draw
the improper conclusion that the propulsion system caused the divergent solution. For
lower wing loading, the solution curve becomes vertical, and the solution will not
converge. The conclusion is that if the weight ratio is greater than 4.3, the best vehicle
configuration is vertical takeoff or an air-launched configuration (all of the vehicles have
a horizontal landing mode). If the goals are the lowest gross weight and the smallest
sized vehicle, then it is important to let the characteristics of the converged solution
themselves determine the takeoff and landing modes. To translate the takeoff wing
loading into takeoff speed and the landing wing loading (operational weight empty plus
10-percent margin, so the launcher can return with payload and fuel residuals
onboard), use legacy correlations from McDonnell Advanced Engineering. The
equations for landing and takeoff speeds are given below:
( VTo)k ~J227.114•LTO[It)(',
( VLD), ~JI73.675•LLD ~·no\', 173.675• LTO
WR
(4)
As pointed out previously, an a priori selection of horizontal takeoff (HTO) can have a
very deleterious effect on the weight and size of an SSTO launcher. For example, a
VTDHL air-breather propulsion concept should have a gross weight of 300 to 325 metric
tons at takeoff, compared with 750 tons for an all-rocket VTOHL propulsion concept. A
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Report, from the dia collection. The PDF is mirrored here; the original link is above. 56 pages are in the text index: search them above, or from the library's search.