Speculative post about Spacex's RTLS concept

Elon Musk of SpaceX wants to achieve the Holy Grail of rocketry design- that is, to have a fully reusable rocket with a fast turnaround time - a Return to Launch Site rocket.  With respect to this, I've posted a number of speculative posts on how that problem might be solved.  It so happens that Trent Waddington's most recent post also deals with this very subject.  However, Trent is a bit skeptical about SpaceX's plans. As for me, I want to believe that this is possible, even if I don't really know what the heck I'm talking about.

A few ideas came to me last night, so let's take a look at some of these ideas. Trent refers to the Space Show broadcast when Gary Hudson was a guest- so I gave it a listen. Hudson says that there will be a substantial mass penalty in terms of payload in order to bring about the result that Musk seeks. I'm not so sure that he said that it was an impossible task, only that payload fraction will suffer a significant reduction. So, the question arises, is there any way to minimize this penalty? This was the question that I will explore briefly with this post.

It is useful to take a look at what has been done in the past and see what lessons there were at that time that may be useful in this context.  Let's look at the following screenshot from a video of the X-15, which was launched from a B-52, flew like a rocket and landed like a plane.  The X-15 employed a very simple device which acted as a brake, as it increased drag.   Now, this may be useful in getting something that's going too fast to slow down, or it also may be used for maneuvers, so long as there is enough atmosphere available for aerodynamic purposes.

Very simple braking system is enough to slow down rocket plane, can the technique have more potential capabilities?

In the case of the Falcon 9, it would seem that once you have first stage separation, the first task should be to slow down- a lot.   Gravity will do that, and so will drag.  Can this technique be extended by using the speed brake as a control surface that will simultaneously increase drag while steepening the trajectory?  In such a simple system, gravity and drag becomes a friend, instead of an enemy.

That's the first idea.  The next idea is to borrow a concept from the Skylon.  I realize that Musk is skeptical of air breathers, but once again, we don't have to fight drag, we can use it.  The Skylon proposition uses the air breather on the way up, but why not use it on the way down?  By the way, you don't have to use it on the way up.  Since the rocket can be used however we wish, we can simply do away with drag by using it as a rocket on the way up and an air breather on the way down.  This will save on board mass by using atmospheric oxygen.  This will save us on our mass penalty.  It may even be helpful in another way, since it may also help in slowing down while it increases drag.

If neither of these ideas can be used immediately, another idea is to use an inflatable heat shield.  That can slow down the rocket just after separation.  You may have to discard it quickly once speed is decreased sufficiently.  In such a case as that, some other techniques like those two above can be used in combination with this in order to slow down the spacecraft and get it pointed in the right direction.