Brainstorming a bit more about Skylon

Speculation alert:

It doesn't look like the Skylon will fit on a Stratolaunch---or Big Bird.  Can we make it smaller and lighter?

Size may be a problem because of the hydrogen tanks.  Since hydrogen is the least dense of all elements, it requires a lot of volume.  It is going to be a problem if size needs to be minimized.

Mass may be minimized more if nuclear thermal is used.  But that presents a whole new ballgame with respect to problems.  Mostly of the political variety.  However, there are technical problems-  as with shielding.

So, I wonder if there would be a way to put a couple of nuclear thermal engines on the wings, which would be next to the SABRE engines.  Perhaps extend the wing out a bit, and place them on pylons on the end of the wing.

It would be preferable to put mass between the passengers and the reactor, of course.  That's the reason for the wing placement on the outside of the SABRE engines.

Extending the wing a bit in order to accomodate an NTR would add mass, so it may not be worth it.  It may also affect how the Skylon flies, so that may not be as safe as we'd like.

Running through the rocket equation looks like a possible savings of mass.  Is it worth it?  Not enough time to tell.

Another possibility is placing the X-37C in the cargo bay.  Question: will it fit?  A quick perusal suggests that it can.  The foregoing discussion and this implies that the basic configuration of the Skylon wouldn't change too much.  But it has to get smaller, or it won't fit on the Big Bird.  Looking for a mass of about 2/3 of the original Skylon configuration.

What you may accomplish is to increase dry mass and decrease the amount of propellant needed to reach orbit.  This can reduce the size of the hydrogen tanks and allow for a smaller bird to fit under the Big Bird.  It would still use the conventional rocket mode of the SABRE engines, but for a shorter duration, thus saving reaction mass.  The NTR would do the final thrust to orbit.  The higher ISP of the NTR will use less hydrogen and no oxygen.

The downside could mean a significant redesign of the Skylon airframe.  Hopefully, not too much, though.