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

Text

This text came with the file. It may have mistakes. When the text and the image disagree, the image is right.

UNCLASSIFIED//EAR Q6fi1Clt.k Ulilii QptL\f
overhaul was necessary. It, too, met its end in a government-terminated program, lost
to future space launcher designers.
Two air-breathing rocket propulsion systems permit examination of a rocket-powered
vehicle as an operationally viable commercial system with low-noise airport operation,
reduced operational weight, and global deployability for a space-based FedEx or UPS
(cargo is economically viable, passengers yet to be determined). The earliest of these
is a rocket system that operates as an air-breathing rocket below mach 5.5. This
concept dates to the late 1950s and the Marquardt Company. The termination of the
first aerospace plane halted this work, but John Ahern 15 continued his work, as did John
Leingang16 at the U.S. Air Force Aero Propulsion Laboratory. Much of Leingang's work
was kept out of the technical literature in the 1960s, so this is a current reference
establishing that earlier work. John Ahern was one of the first analyzers of the Liquid
Air Cycle Engine (LACE) concept, and one who identified the sources of irreversibility
and approaches to minimize them. In Russia, Keldesh Institute independently began,
conducting experiments with LACE systems, as reported at the 2002 conference
sponsored by the Association Aeronautique et Astronautique de France and also by
Rudakov17• 18 and Balepin. 19 In Japan, NAL Mitsubishi and ISAS conducted experiments
that were leading to an air-breathing rocket system, and an impressive, ice-free, 1­
cubic-meter liquefying heat exchanger was demonstrated for the NASP visiting team in
1988. 20, 21 With only one hydrogen test stand in Sendi, LACE development was
deferred until the problems with the H-1 engine were solved. However, by then
interest was lost. In India, research organizations used all of the published LACE
documents to arrive at a credible system configuration and performance. 22
Unfortunately, India at the time did not have the manufacturing skill and methods to
make a functional LACE System.
There are two types of air-breathing rockets, both of which are based on using the
recoverable energy in the liquid hydrogen to drive the systems, as diagrammed in
Figure 29. In both systems, the liquid hydrogen absorbs the thermal energy in the inlet
air stream to reduce the air temperature to nearly saturation in an upstream heat
exchanger. In the LACE, as the name implies, a second heat exchanger liquefies the
cold gas and a turbopump pressurizes the liquid air to the correct working pressure
required by the rocket motor. The thermal energy is picked up by the hydrogen in
cooling the gas, and the rocket (including the combustion chamber) is used to drive the
expansion turbines powering the turbopumps (left sketch in Figure 29). In the
Japanese system, a low-pressure ratio compressor pressurizes the cold gas before it
enters into the downstream heat exchanger, increasing the quantity of liquid air
produced per unit liquid hydrogen. With a heat exchanger in the rocket motor
combustion chamber, there is sufficient thermal energy to power the expansion
turbines compressing the saturated or liquid air and deeply cool or liquefy the incoming
air to at least mach 5.5. In the deeply cooled system (Rudakov and Balepin), a
turbocompressor compresses the cold gas to the injection pressure required by the
rocket motor. The thermal energy picked up by the hydrogen in cooling the gas and
the rocket (including the combustion chamber) is used to drive the expansion turbines
powering the turbocompressor (right sketch in Figure 29) . One of the difficulties with
Bond's HOTOL (horizontal takeoff and landing) engine compared with Rudakov and
Balepin was that HOTOL avoided the combustion heat exchanger at the expense of
having the air-breathing rocket operate to less than mach 4, increasing the to-orbit
weight ratio and gross weight and thereby making the concept less viable. In both
UNCLASSIFIED/,,roA. OfifilCIOk flili ODIL¥
26