Triton made a first round COTS submission to NASA in 2006, based on the Stellar-J. However, they did not progress to the semi-final.
[quote author=Sep/Oct 2005 AIAA Houston - Horizons Newsletter]
The Stellar-J is a winged first stage vehicle built around kerosene liquid rocket engines and air breathing propulsion. Conventional jet engines power the Stellar-J to stratospheric, subsonic, cruise followed by rocket ignition and continued climb. This first stage ascent is performed with a pull-up terminating in staging conditions similar to existing vertical launchers. Descent follows a profile similar to the X-15, X-34 or the Space Shuttle at high angle of attack until reaching subsonic speeds in which jet cruise or glide descent to an airfield are options. Like a fighter aircraft that carries a range of different ordinance on wing pylons, the Stellar-J carries upper stages or modules within a payload envelope. Triton Systems LLC, a small aerospace startup is pursuing its design.
Commercial aviation stands as proof of routine jet-powered stratospheric, subsonic flight. Unless designing for around-the-world cruise, mass fractions of aircraft seldom approach those of ballistic rockets, but state of the art intermediate values make this flight regime attractive as the start of first stage flight. If one third of the delta velocity required for orbital flight (~30Kfps) is obtained in first stage, 1500 fps can be derived from jet cruise speed at altitude. After first stage rocket burn (adding ~8500 fps ideal velocity), upper stages can be released for continuation to orbital missions. The scalability of the concept parallels commercial jet aircraft: takeoff weights from 35 to 350 tons. In the course of designing Stellar-J vehicles around multiples of available engines, we have developed design, trajectory, mission, and performance data for 35, 70, and 350-ton configurations. At 350 tons the larger Stellar J configurations compare in mass to jumbo jets - or the Soyuz launch vehicle. As a result of discussions with potential customers, we include designs for recoverable orbiters for manned and unmanned sortie flights or rendezvous with space platforms and space stations.
Those jet engines look awfully large and turbofan-ish. I'm also wondering if they'll have spikes or ramps to process the air or heat exchangers like Skylon's SABRE engine or JAXA's precooled turbojet hypersonic engine. I think our best bet for a TSTO spaceplane is something with Burt Rutan's feathering and SABRE or JAXA engines, really. Otherwise, the design looks okay, but not awesome. Needs moar spatula nose that fairs into a compression ramp for scramjets on the belly, X-43 style.