This team, based in the USA give away few details about their "Solaris" X-Prize attempt vehicle. If you look at the team briefing, you find the word "proprietary" against most of the useful details. However, the above picture, and I can't remember where I found it, now, indicates a launch from below water. Interesting.

Well, at least you see that they are intending to paint it black and the exhaust has a very solid sulphurous look to it. There are some pictures on their website, indicating that something has been built and tested, but there no details of a progression to the X-Prize to be had. The fuel for Solaris-X is given as (the unusual) fuming nitric acid as oxidizer and "hydrocarbon X" as fuel. There do seem to be facilities, but there is no "News" section on their website, only some entries in a "Media" section without hyperlinks. One cannot be very hopeful that this team is a serious X-Prize contender, on the available evidence.