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

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Russian HOTOL. However, NPO Molnyia provided a unique approach to space access by
decoupling the attachment to a few fixed base operations and opening up space access
to a global clientele, and not from a remote nation, but from Russia. NPO Molnyia's
approach also removed the noise and smoke from a rocket launch to a mundane takeoff
of a turbofan-powered transport.
The upper payload limit of the An-225 is 300 metric tons for the structural mounts on
the top of the fuselage. With a conventional rocket, that limit was reached for the
Russian HOTOL at 5.45 metric tons, not the 7 tons desired. With the addition of an air­
breathing rocket to the initial part of the trajectory and the FDL-7/Model 176
configuration, that limit now is not reached with even an 11-ton payload .
The An-225 has the empennage modified from the An-124 single vertical and horizontal
to an 'H' configuration. This permits the powered hypersonic glider to easily lift off the
top of the vehicle, as the MBB Sanger wind tunnel test demonstrated. A second
modified transport would be modified to carry the liquid hydrogen and liquid air to fuel
the hypersonic vehicle, along with maintenance and support crew. The intent was to
use the automatic launch checkout the author witnessed at Baikanour in 1988, wherein
a Soyuz that arrived on its train carrier at 0500 hours launched carrying a Progress
capsule at 1715 hours the same day. That should make a local launch possible within
hours of arriving at the specified airport launch departure site. Again, we can thank the
Russian design bureaus for arriving with a concept that might be the first economically
viable global launch concept not tied to a fixed geographical launch site that employs
robust, proven carrier aircraft.
As illustrated in Figure 31, a LACE system operating to mach 5.5 that has the same
operational weight empty and ?-metric ton (15,435-lb) payload as an all-rocket reduces
the liftoff gross weight of a HOTOL concept operating from atop a transport by 150
metric tons (330,000 lb). That enables a transport launch platform to carry an orbital
launcher with a functional payload greater than 11 metric tons (24,225 lb). Payloads
greater than 11 tons are determined by the size of the launcher atop the transport.
The launcher can become too large for the transport to maintain stability and control.
The exhaust temperature and therefore velocity of a LACE rocket are less than those of
a hydrogen/oxygen rocket, resulting in a quieter launch and making launch from a
transport more favorable. The LACE-powered vehicle is physically smaller than the
rocket vehicle because the propellant weight and volume are less. The green line in
Figure 31 is the propellant weight for the sized LACE orbital launcher. The important
thing to remember is that the air-breathing rocket motor is the same as the all-rocket
motor; only the propellant mix is different.
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