However, as NASA moved to ballistic capsules during Project Mercury, funding for research into winged vehicles slowly disappeared, and LACE work along with it.
[dubious – discuss][citation needed] Conceptually, LACE works by compressing and then quickly liquefying the air.
The LACE design then blows the compressed air over a heat exchanger, in which the liquid hydrogen fuel is flowing.
It will be seen that heat-exchanger limitations always cause this system to run with a hydrogen/air ratio much richer than stoichiometric with a consequent penalty in performance[1] and thus some hydrogen is dumped overboard.
[4] This term implies that unless the lift-to-drag ratio (L/D) and the acceleration of the vehicle as compared to gravity (a/g) are both implausibly large for a hypersonic air-breathing vehicle, the advantages of the higher Isp of the air-breathing engine and the savings in LOx mass are largely lost.
LACE was studied to some extent in the United States of America during the late 1950s and early 1960s, where it was seen as a "natural" fit for a winged spacecraft project known as the Aerospaceplane.
As the aircraft climbed and the atmosphere thinned, the lack of air was offset by increasing the flow of oxygen from the tanks.
This makes ACES an ejector ramjet (or ramrocket) as opposed to the pure rocket LACE design.
However, as NASA moved to ballistic capsules during Project Mercury, funding for research into winged vehicles slowly disappeared, and ACES along with it.