For a while I was able to dispatch a ship to planet surfaces, but currently the game isn't letting me. What are the requirements for dispatching to the planet surface?
There are 4 requirements to be able to land on the planet surface:
It must NOT be a planet covered by Ur-Quan Slave Shield. E.g. you can't land on Earth, or Chmmmr's planet; or Syreen's planet. You won't even be able to scan them.
You have to have at least one planetary lander (you start out with one; but it is possible to sell it for 500RU during your stay on Earth Starbase; or have it be destroyed by the hostile environment or hostile life-forms on the planet).
You can see if you have any landers in 2 ways:
At the starbase, when outfitting modules:
When looking at your ship diagram, any landers you own will be displayed as small squiggles above fuel counter, right below the ship's name:
You must have crewmembers on your Precursor vessel.
It's quite possible to have your vessel with zero crew: You either sell them all at the starbase; or transfer 100% of the crewmembers to other ships.
You must have sufficient fuel for landing.
The amount of fuel required for landing depends on the planet
It usually varies between 0.2 and 1 fuel units
The exact fuel needed will be displayed when you're scanning the planet, after you hit "DISPATCH" option in the menu.