I discovered that an effectively endless loop of vocabularly, units, carbon and potentially other resources can be gained during communication with aliens. I'm sure this can be done with any species, but the particular species used in this example is the Korvax.

1 Korvax Alien
Carbon Required: 80 Carbon
Carbon Recommended: 200 Carbon
Standing Required: Point of Interest
Standing Recommended: Traveler of the Atlas

Step 1: Gather the required Carbon and get the required standing. Easiest way to do this is to find a Korvax planet and run around and find Plaques and Monoliths.

Step 2: Find an alien. Again, easiest way is to find a transmitter and follow it to an advanced alien species.

Step 3: Communicate with that alien. Before you can start the loop, you have to talk to that alien. You get one communication for free. This is the hard part. Since alien encounters are randomly generated, you'll have to figure this one out on your own.

Step 4: Start the loop. After you've done the random alien encounter, it costs 20 Carbon to communicate with the alien again. Once you pay your 20, you get a randomly chosen choice from the list below. Once you have paid the 20 carbon, the type of choice doesn't change until you pick one of the three options. If you exit the choice without choosing an option, you must pay 20 Carbon again to speak to the alien, but the options do not regenerate until you pick one.

Possible options for Korvax
Choice type A - Gift/Healing/Shield Recharge (Cube OR Casing/TS/PoI)
Choice type B - Silicate/Healing/Word (Thesis/TS/PoI)
Choice type C - Fuel/Healing/Shield Recharge (Thesis/TS/PoI)
Choice type D - Isotope/Healing/Shield (Thesis/TS/PoI)
Choice type E - Oxide/Healing/Word (Thesis/TS/PoI)
Choice type F - Units/Healing/Word (Thesis/TS/PoI)
Choice type G - Repair/Healing/Word (Cube OR Casing/TS/PoI)
[For Choices A and G, the Gift and Repair requires either a Korvax Casing or a Convergence Cube. Which one is required appears to be randomly chosen. I've run into every possible permutation of this one.]

Step 5 - The Loop.
To get the loop going, you'll need a certain amount of Carbon. The most important choices in the loop are Choices C and D. Choosing Fuel and Isotopes gives you a certain amount of Carbon back. For me, at the hightest level of reputation, I was paying 20 and getting 67 back, for a net gain of 47. This makes the loop more or less neverending. At lower reputation levels, it's possible that it is less efficient, but based on the relative abundance of carbon, the loop is still worth it.

Occasionally I find myself short, but most of the time I'm actually gaining carbon. I started with 150 carbon and after doing this for several hours working on the Korvax language, I've never run and even managed to turn a tidy profit. I found a Korvax next to a Sales Terminal and I've been racking up units as well as vocab at quite a rate.

Appendex

Korvax Reputation Levels (Drawn from the NMS Gamepedia Wiki)

Reputation ranks with the Korvax include, from low to high:

Korvax Thesis
Korvax Test Subject
Korvax Point of Interest
Korvax Research Focus
Traveler of the Atlas

This is my first guide, so I welcome any comments and suggestions.

If anyone wants to add anything to this, please don.

-Housellama