Re: "I'll put my money on a Skylon."
the main reason why you would have toughened graphite
The main reason you wouldn't is that "toughened graphite" doesn't exist.
is the ease of being able to fix it with a quick space walk with polymer from a tube as the fibres have no specific order
Aerospace grade resin systems typically require hours, if not days, in controlled environments for final cure to their specified strength. You don't squeeze a tube of goop and get a quick super-strong bond. You'd only do that for a cosmetic fix, like a scratch in a gel coat, or some non-strength critical application like encapsulating an electrical connector.
Real composite repairs tend to take three forms where I'm employed:
1) A little dab of adhesive on a carefully cleaned, scuffed, and primed cosmetic scratch
2) A large, carefully applied, overlapping patch of fibers and resin, to be followed by a 7-day cure (or 2-4 hours if the part can go in an oven)
3) No repair, scrap it. Most of our engineering for parts with damage to their fibers is to toss the part rather than repair it. But this is a production environment where we're building stuff, not a situation with fielded hardware.
i doubt the x-37b is made from alloy
Why? The running joke at my aerospace employer (in my materials engineering group, anyway) is, "Sure, you can make your part out of any material you want so long as it's 6061-T6," (a common aluminum alloy and temper.) The data requirements for introducing new materials into flight hardware are ludicrous, designers won't touch new materials until they have well-developed A- and B-basis values for the major properties. Aluminum alloys like 6061 and 7050 have well-known properties and are strong enough, tough enough, and cheap enough for the job.
Aluminum alloys are a workhorse in space. The International Space Station's modules have aluminum pressure vessels (mostly 6000- and 7000-series alloys) and even aluminum Whipple armor panels. The shuttle used aluminum for its frame - a major design driver in its heat shielding was to keep interior temperatures low enough that aluminum was acceptable for the wing spars.
I know The X-37B uses composites. The USAF and NASA brag about "expanded use of composites" in the X-37. But, given most of the work is done by Boeing and Lockheed Martin Skunkworks, you can take a guess that they're working with carbon fiber-epoxies like the 787 or carbon fiber-BMI like the F-35. And because those are the players, they'll be also be using predictable aluminum alloys in less critical areas, too.