Learn English – Mixing present and past tense in a report or public announcement

I believe you can use either was or is but I would not use is in the sentence you wrote. This is a stylistic preference.

You state "Smith's work is always there and always thinks that the solution is feasible." Then why would you not think Smith et al. are not always present in [1]?

In [1], Smith et al. point out that the solution is feasible.

If it was some time ago, it might be better to stick with the past, and if you feel it is necessary to point out the continuing validity of the solution, you can do that.

In [1], Smith et al. pointed out that the solution was feasible, an option still in use today.

It partly depends on the (style and substance of the) rest of your paper, your preference, and the style preferences of the journal/audience to whom you will be presenting your work. I would either go with point/is or pointed/was. Pointed/is sounds a bit strange to my ear.

How to avoid it?

By Being Meticulous. There is no shortcut. You, as the author, are responsible for every word choice in your story. Every single one.

It reads fine to me to have the present tense as presented in Weir's snippet, but it could be clearer.

In first person (past tense), a thought can either be italicized and immediate (in which case it becomes present tense) or not (and remains past tense.)

You are the God of this world you have written, and you are responsible to know every detail of your creation. So go through it. Sentence by sentence. Figure out which thoughts of your creation are passing surface thoughts, and which are intimate deep thoughts.

If that passage was mine, (which it isn't; I have a different world), I'd do it like this:

I wound through the corridors toward the center of Down 15. None of the elevators were nearby, so I bounded up the stairs three at a time. The stairwells in the core were just like stairwells on Earth—short little twenty-one-centimeter-high steps. It made the tourists more comfortable. In the areas that didn’t get tourists, stairs were each a half meter high.

That’s lunar gravity for you, I thought.

Anyway, I hopped up the tourist stairs until I reached ground level. Walking up fifteen floors of stairwell probably sounds horrible, but it’s not that big a deal here. I wasn’t even winded.

Do you feel the movement into the character brain? You have this tool available to you. Don't overdo it--develop a feel for when you want a direct thought from a character. But you need to be obsessive about going through your story with a fine tooth comb and making conscious choices. There are multiple ways to write any passage.