"*experimental*"?

[Frostiken]

I've noticed a couple parts show up with that on their info card sometime. Does this have any effect in-game?

[FleetAdmiralJ]

are they highlighted blue? If so they're probably loaner parts that you need to test to fulfill a contract.

[KasperVld]

These are parts that you get when you accept a contract to test that part, but you haven't unlocked it in the tech tree yet. If I recall correctly you'll get a limited supply of them, and only for the time that such a contract is valid (unless you unlock them in the tech tree of course)

[cpast]

It means you've accepted a part test contract for them, but have not researched them in R&D. HarvesteR had said that those parts have a limited supply, so you can fail the test contract if you lose them without completing it; not sure if this is still the case, but if it is, it means any use of them that does *not* fulfill the contract you have them for must end in their recovery.

[guitarxe]

A bit off-topic, but did I imagine things or are the experimental versions slightly worse than the researched ones? For example the thrust of an experimental engine is 10 lower than the thrust of the fully researched one.

[Frostiken]

A bit off-topic, but did I imagine things or are the experimental versions slightly worse than the researched ones? For example the thrust of an experimental engine is 10 lower than the thrust of the fully researched one.

That would be kind of a neat idea for making science a little less mundane, having to do R&D to perfect your parts.

[kujuman]

Does this have any effect in-game?

Aside from what FleetAdmiralJ said, there may be some differences in how the part is activated. I had to test a nuclear engine in orbit and pressing spacebar would not activate it, right click on it revealed "Run Test" which started the engine up as if I had staged it.

[Geschosskopf]

I've noticed a couple parts show up with that on their info card sometime. Does this have any effect in-game?

The main in-game effect is that any ship you build with experimental parts will get tagged as having experimental parts aboard, which you'll see in the list of saved ships in the VAB and at the Launchpad from the KSC screen. As long as the contract for the part hasn't been completed, you can still launch the ship. However, once you complete the contract, if you still haven't unlocked the part in the tech tree, the ship can no longer be launched. You can, however, open the ship in the VAB to remove the experimental part.