This is one of the several combined turbofan and rocket space-plane proposal amongst the X-Prize entries. The Cosmos Mariner's flight programme would consist of an ascent to 40,000 feet, using the turbofan engines, followed by ignition of the rocket motors in a 130-second burn. The rocket motor would be shut down at 200,000 feet and the Cosmos Mariner would coast to the apogee, a little over 100km.

No built components or tests had been announced as of Oct 2004 and the images of the Cosmos Mariner are clearly computer-generated. A cutaway of the design concept can also be seen on Lone Star's website. The news items displayed on the website run from the years 1997 to 2000 in descending order, and there is a cryptic announcement referring to restrictions on future release of information due to "on-going negotiations".

In 2006, the web site has not changed in two years or so. Now, in 2009, Lonestar seem no longer to have a web site, so it would seem that the project has come to an end. If anyone can supply information about what happened to it, Spacefleet would be grateful.