This sounds very similar to the HOTOL concept in the early 1980s, and it appears that they are using cryogenic separation. They might save space and weight by using another form of oxygen separation, but they would still need the heat exchangers for making LOX.

ESA study finds in-flight oxidiser collection possible
By Rob Coppinger

In-flight oxidiser collection possible, says ESA study

A European Space Agency-funded study has concluded that air liquefaction plants for a space transportation system’s first-stage carrier aircraft are possible within the mass limits required.

The first stage would collect air, liquefy it and separate the nitrogen, producing 10kg/s (22lb/s) with a 10,000kg (22,000lb) on-board liquefaction plant.

The advantage of such a system is that the preferred liquid-oxygen propellant does not have to be carried from the ground. Once collected, the oxygen-enriched liquefied air is stored in the second-stage reusable orbiter vehicle.

The plant’s main mass drivers are the heat exchangers, of which there would be three. These have been a focus of the ESA study.

The study, involving Universite Libre de Bruxelles (ULB), developed the two-stage launch system concept that incorporates liquefaction.

That system has a dual-hull, hydrogen-fuelled aircraft using six General Electric 90b engines as the carrier aircraft. Between its two fuselages under the wing, it would carry an orbiter vehicle fuelled only with liquid hydrogen with a total mass of 90,000kg.

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