Greetings,
i am game mastering a small Adventures Group. We play the Shackelton Campaign.
My Question: Is the Second Edition backwards compatible? Can we switch or should we continue in the first Edition.
FYI: We are playing with some exotic Species as Player Characters. Orion, Catian, Denobulan, Soong Android,
Thanks in Advance
Its tremendously backwards compatible. Everything just runs simpler.
There are a lot of changes that you just need to apply, e.g. a new calculation for Stress, fixed weapon damage, etc.
The only change that’s not as smoothly backwards compatible is that every species not has a built-in ability. This may require some work for species outside the new Core Rulebook, like Caitian and Soong-type Android you mentioned. I just took one of their species talents and converted it to a species ability. So if PCs already have that talent, I let them pick a new one.
What is your take on the lack of rolling challenge dice?
In my opinion this takes a lot of fun out of the game (rpg and the “thrill” dice-rolling are just bound together imho)…
I don’t hope that they do the same thing with A!C…
In my experience, rolling CD was largely pointless. You rolled so many dice and had a very cheap way to reroll undesired results, you nearly always ended up rolling basically the same amount of damage anyway.
I agree that rolling dice is fun, but not in the way it was done previously. If you want to retain the dice rolling aspect, I think you are better off rolling just 1 or 2 CD.
Is it possible to play 2e and simultaneously use this old CD-based rule? Or does this break too many other aspects of 2e?
Well, no longer rolling CD/d6 is a (if not the) major aspect of 2e, so it fundamentally depends on your understanding of “breaking” aspects. 
If you want to retain CD/d6, I, personally, would recommend to use 1e rules and just back-port the aspects of 2e you like (e.g. species-talents, pasttimes, etc.).
Not out of the box, this would have to be house-ruled. I think you would be OK when you reduce the damage of all weapons by 1 and roll 1 CD when attacking. You just need some cool effect when you roll the Delta symbol, maybe 1 bonus Momentum.
This sounds simple… But do I understand it right? So you would recommend to use a combination of a fixed but amount of damage (when using a weapon according to 2e ruleset) and the use of one damage die?
Actually I would recommend to first use and understand the 2e rules as-is. Because it’s not just CD vs. fixed damage that has changed. Now if you hit someone, you always deal at least 1 damage to them. Also, this magical “deal 5+ damage and cause an Injury” threshold doesn’t exist anymore. So personally, I don’t see the point in rolling CD since you can just use Momentum to boost damage.
If you want to preserve an element of randomness, I would use a combination of fixed damage plus 1 CD. So yeah, you understood this right. In my opinion this makes it easier to use the 2e rules as a baseline.
Thx for the explanation! 
Okay so I have a question how would I apply this talent (Sturdy Construction: When the station suffers damage, it suffers a Breach if 8 or more damage is inflicted, instead of the normal 5 or more.) in Star Trek 2E?
I would say it either ignores the first breach, or the first shaken. Or maybe it just gets extra stress points? I do wonder if there’s an analog talent in the 2E book… I’ll check later.
Yeah I noticed that the Berengarian Dragon has a similar ability in 1st Edition and in 2nd Edition it gets two extra Injuries before being defeated. So I figure I will give the Station TWO extra Breaches and call it good.