The Roku only has hdmi output. Does your satellite box have other than hdmi? If so, you can use hdmi to your tv from Roku and hook your sat box up using another input, possibly the yellow/red/white connections. If you can only use hdmi from both and tv has just one, you could look into an hdmi switch box, but they can be trouble. Best option is a new TV. You'll enjoy it.
"I might be moving to Montana soon..."
FZ