Hey, I'm no Guru! :lol:
What I know is that any PC with touch screen will translate screen presses to mouse clicks.
The same goes for screencasting to Android/Apple devices.
(but no right clicks)
I also know that you have a "remote control" window in Orbiter, so you can control a spacecraft using the mouse + buttons.
But I'd say that you would have to run Orbiter in window mode, along with an onscreen keyboard. But Windows has this since 7 (and perhaps XP) so not a problem and no extra $ involved.
The best option regarding price would be to simply stream the screen from the PC, realtime, to any Droid device.
I've tried this with my low low low end phone and it works at about 1fps, so you would need a decent Pad + software. But it works
I'd say that a decent Droid Tablet might do the trick and be cheaper than a Surface PC.
On the other hand, you can simply consider that Orbiter just needs a PC and precision input methods like a keyboard + mouse to work.
In that sense then yes, it's impossible to have it on other platforms.