In the book "The Moon is a Harsh Mistress" by Robert A. Heinlein, which is a fantastic science fiction book about colonizing Luna and the politics of an anarchi

In the book "The Moon is a Harsh Mistress" by Robert A. Heinlein, which is a fantastic science fiction book about colonizing Luna and the politics of an anarchistic government, he mentions the creation of a Rocket Sled (http://en.wikipedia.org/wiki/Rocket_sled_launch http://en.wikipedia.org/wiki/Rocket_sled_launch) which seems to never get mentioned when people talk about earth side technology for improving our ability to leave earth. Does anyone know if there is some reason why this technology seems to get ignored? According to wikipedia it seems like a big win. Why aren't we doing this right now?