"We'd get to see a strange, new world up close," he had said. "New plants, strange animals, new scenery, excitement, adventure," he'd said. Dad had said a lot of things to get Shan to come to this godforsaken planet with him, and none of them had come true. He just wanted company... and someone to help him carry his stuff around.
Slogging through the soft sand that made up most of the small island they were assigned to catalogue – just like most of the rest of the dry land on this waterlogged world -- with a twenty kilo backpack wasn't Shan’s idea of adventure, even when Dad tried to pretend otherwise.
"I saw the tracks of an animal in the sand over that way yesterday. I should be able to get a tri-d of it tonight. From

Jerry

I think you should consider making -- "We'd get to see a strange, new world up close. New plants, strange animals, new scenery, excitement, adventure." The entire first paragraph without any indication of who’s speaking. Who said that would be obvious from the next lines which would begin the second paragraph -- Dad had said a lot of things to get Shan to come to this godforsaken planet with him, and none of them had come true.

It’s cleaner. You might even [I shudder] put that first line in italics/underline to set it off as different, as past time.

The “He” that starts the following sentence is unclear. Did Shan just want company or did Dad? It COULD be taken either way. I assume you meant Dad. So, say so. Dad just wanted company [Shan] and someone to help him carry his stuff around. Those two sentences make a nice second paragraph and – in my opinion – a great setup of the situation.

Your third paragraph needs rethinking. Why not slip us into realtime with Shan’s recounting the details of what’s making him miserable right now? Sand in his shoes, nettles pricking his ankles, and maybe this world’s version of fleas crawling up his legs.

He could ask if they’re going to finish cataloguing this island today – which would inform the reader what they’re doing. You put more interesting details in rather than the smallish info dump. Make the opening more active. Show the antagonism or whatever emotion is playing out between father and son. Since you don’t have any interesting fauna, that could be a place to start the story unfolding.

Just my opinion.

“We'll see a strange, new world up close.” “New plants, strange animals, new scenery, excitement, adventure.” “A fantastic summer vacation, exploring a new planet.”
Dad had said a lot of things to get Shan to come to this godforsaken planet with him, and none of them had come true. Dad just wanted company... and someone to help him carry his stuff around.
Shan’s calves ached as he struggled up yet another hill of the soft sand that made up most the small island Dad had been assigned to catalog. His shins itched from the coarse pseudo-grass he’d waded through on the preceding downhill. The straps of his equipment pack – heavier than usual -- dug into his shoulders. This definitely wasn’t Shan’s idea of adventure,

My opinion – make it all one quote. I know you’re trying to give the sense of many different times. Hmmmm…how to do that? Dashes?

We'll see a strange, new world up close. -- New plants, strange animals, new scenery, excitement, adventure. -- A fantastic summer vacation, exploring a new planet.

Maybe the problem is that the words here all sound like they were uttered in the same conversation not different ones.

If you want to make this work this way. Break it up. Show…yes. You could put a lot of background in subtly here. Like –

Picking me up from school on a typical cold miserable day, Dad said – If we go, it’ll be warm all the time there.

After I failed the Martian part on the big biology exam, he promised – You’ll have a chance to really experience alien plants. Feel them. Smell strange smells. You might even bring back an alien pet. Think of that.

When my friends were all packing up to go to this totally awesome gaming camp my parents couldn’t afford – Forget gaming. You’re going to have a fantastic vacation exploring a totally new planet for real. So, what do you say? Can I add you to the expedition?

Dad had said a lot of things to get me here, but Mom was right. It's really boring. Dad just wanted company... and someone to help him carry his stuff around.

Just some ideas. I don’t know how your story takes off from here, but you could really set up Shan as a surly, unhappy teen. He could be an unreliable narrator, too. That could add some spice to the story.

Hmmm… small island Dad had been assigned to catalog today