The secret moon mission isnt really a secret. It only got there because NASA has refused to believe the possibility of an alternative design to their Ares rocket. The newer design could be cheaper, safer and easier to build according to sources. But NASA aint buying any of that. This means that the scientists who still do believe in this alternate design are being forced to do so in their own personal time.

And unlike Google which pays its engineers to dream up new concepts by giving them paid time especially for that, NASA has no such extravagances. To be fair, NASA does say that the new design was reviewed last fall and that the design was flawed . The design is called as Jupiter.

So why would some scientists still continue to back Jupiter. Well, for one the Jupiter rockets would save NASA $19 billion in development costs and another $16 billion in operating costs over two decades. There are even accusations of NASA suppresing information on Jupiter so as to make sure that support for Ares does not waver.

More details about Ares can be found on Wikipedia

More details about Jupiter and a comparison with Ares can be found here