The Klingon continuous suffixes (-taH* and -lI'**) don't mean exactly what the English progressive tenses mean, even though this course makes you use one for the other.
In English, The ship is orbiting the planet uses the present progressive tense, but it might be said simply to mean The ship orbits the planet. In English, we don't colloquially use the simple present tense for simple statement of facts. Nobody, for instance, says I go to the store; one says I'm going to the store.
In Klingon, on the other hand, use of a continuous suffix means exactly what it claims to mean: the action being expressed is ongoing. If you do not specify that an action is continuous (or completed), you are expressing an idea that is explicitly not continuous (or completed).
I evade (I make the ship dodge, and the action I'm expressing is neither continuous nor completed.)
I take evasive action (I make the ship dodge continuously.)
I translated those in the present tense to make the meaning most clear, but Klingon verbs don't express tense. These could also be:
I evaded (I made the ship dodge, and the action I'm expressing is neither continuous nor completed. Notice the "nor completed": this is a statement of what kind of action I took, not a statement that I performed a dodge and finished performing it. The difference does not come across in English as it does in Klingon.)
I will evade (I will make the ship dodge; this is an expression of something not continuous and not completed.)
I took evasive action (I made the ship dodge continuously.)
I will take evasive action (I will make the ship dodge continuously.)
Now apply this to ships orbiting planets:
yuQ lubavtaH Dujmey
The ships are orbiting the planet.
This is not just a statement regarding the general disposition of the ships; it is saying specifically that the ships perform a continuous orbit around the planet.
Again, this distinction is extremely difficult to make in English. Unfortunately, the best the Duolingo course can do is require you to use English progressive tenses to equal Klingon continuous aspect. It's not exactly right.