First off, I’m going to do something bad: I’m going to respond to myself. Yes, I know, how gauche, how unapologetically declasse. Get over it. 
I talked about how movies can contain ideas; I feel I should follow that up with a clarification. The ideas that movies best address are those regarding human behavior: how we get into wars, or how we fall in love, or how we can engage in self-denial, that sort of thing. Movies are notably poor at exploring abstract ideas – things like squaring the circle, or the distribution of load-bearing members in a tall building, or the relative ethics of cloning. They can be covered in documentaries and training films, but for the genre we’re talking about – fiction, specifically the adaptation of Heinlein’s fiction – those sorts of concepts are notoriously difficult to cover. When Heinlein talks about an individual’s debt and responsibility to society, that can form the foundation of a movie, by setting up various characters as examples and counterexamples and letting the system run. But when he’s just creating a loopy timeline, or exploring the impact of technology on macroeconomic systems… well, I wouldn’t want to be the screenwriter who tackles that one. Human-oriented ideas are easy; abstract or external ideas are not. (Compare Dune: The Messiah-complex material translated easily to film; the ecosystem stuff did not.)
Now, other questions:
dhanson:
This idea isn’t unique to Heinlein. There are several theories of story construction; most come up with eight or ten basic storylines. Robert McKee, in his very influential writing guide Story, lists about twenty.
sdimbert:
Maybe she just didn’t care. Tom Wolfe, for example, is famous for selling off the rights to his books, and never looking back. He knows the movie will be vastly different, and will probably stink; he doesn’t feel he needs to waste his time worrying about it. Partly this is because movies in general don’t impact his worldview all that much: He just signs the contract and cashes the check, and he might, maybe, find out the movie actually was made and released if a friend tells him. Sort of like me and, oh, say, UK rugby standings. Really important to some people; not even a flicker on my radar.
Surgoshan:
I think this is true of good science fiction in general, not just Heinlein. Asimov and others have said over and over again that the whole point of doing what they do is to take the human experience and extrapolate it into a new setting or social dynamic. Anything else is just engineering. Movies, unfortunately, tend to forget this, and get seduced by the special effects. There’s a really good movie bouncing around inside James Cameron’s The Abyss, for example, but he unfortunately gets sidetracked a bit too much by the hardware, I think. Compare Blade Runner, and its examination of what really makes people human. We don’t need to know how Replicants are made; we just accept that this is a future in which they exist, and let the thematic exploration proceed.
sdimbert again:
Copyright law on this point is fairly clear. You can write whatever you want for your own personal use; you can adapt Heinlein’s TEFL or Bradbury’s R is for Rocket or, though I’d question your sanity for wanting to do so, Grisham’s Runaway Jury if you really wanted to, as long as the script stayed in your desk drawer and was solely for your personal enjoyment. The minute you want to actually represent that script to another reader whether for sale or for any other purpose, though, you’d better have permission from the copyright holder (i.e. the original author, or whoever bought the rights, or in Heinlein’s case the administrator of his estate) or you get in big, big trouble. You could certainly pen a script, and then have a literary agent or lawyer contact Virginia with a formal proposal: “I’d like to do this; here’s a brief description of my take on the material. If you’re interested, let’s discuss financial terms, an option agreement, etc.” Once the agreement is in place, you can then have your agent begin representing the script in the marketplace, but not before.
But again, if you want to write the script yourself, and not do anything else with it, you’re free to do so. I’ve been toying with the idea of writing up Timothy Zahn’s Deadman Switch purely as an exercise; it’s got a great hook, and a great third-act twist, and I think with some condensing and shuffling a truly crackerjack sci-fi adventure could come out of it. I don’t hold out hopes of actually being able to sell it; I’d just do it as an exercise, to see how good I am at taking 300 pages and 80,000 words and condensing them down to 120 pages and 12,000 words.
By the way, if you look at those numbers again, you see another major problem with adapting Heinlein: He’s just so damn prolific. Most of his books (that I’ve read, anyway) tend to the long side, and defy easy compression. More than one screenwriter has stated that the best source material for a movie is actually a short story, rather than a novel: Look at Stand By Me and Shawshank Redemption, both rather elegantly reworked from Stephen King’s shorter-than-average originals. There’s a lot of potential material out there, from the stories in Ben Bova’s Challenges to the stuff by Benford and Brin and the “Future On…” books edited by Card; but because short stories don’t land on best-seller lists, they don’t automatically come with “heat,” i.e. awareness and buzz that makes for an easy sale.
That’s just marketing, though. The original point – and yes, I did have one – is still valid: The length and structure of shorter stories (e.g. Greg Bear’s Heads) is more conducive to screen adaptation than from longer novels (e.g. Moving Mars by the same author).
Movie Geek Central – Reviews, news, analysis, and more! http://moviegeek.homestead.com