"The passengers boarded the ship in order to travel to Kronos."
Translation:Qo'noS lulengmeH raQpo'pu' Duj lutIj.
Some verbs in Klingon include a locative sense. That is, their objects are already locations. You can use -Daq on these objects if you want, but it's considered redundant.
leng is one of those verbs. The object of leng is the destination the subject is traveling to.
Qo'noS vIleng I travel to Kronos.
Qo'noSDaq vIleng I travel to Kronos (said redundantly)
Notice that if a verb has a locative sense and you use a locative that isn't its object, that locative can't mean what the object would mean.
Qo'noSDaq jIleng I travel on Kronos.
Kronos can't be my destination, because the destination of leng is its object. This sentence means that Kronos is the location that leng happens.
Some other words with a locative sense: jaH, ghoS, paw, chegh, chol.
This says, The passengers travel to Kronos, they board the ship. There's no in order to here (that's the -meH suffix).
The verb to which -meH is attached MUST come before the noun or sentence to which the purpose clause belongs. In other words, you MUST put Qo'noS lulengmeH before Duj lutIj raQpo'pu'.
However, it's usually better style to put the object and subject in the sentence in their earliest place. A better version of this sentence would be Qo'noS lulengmeH raQpo'pu', Duj lutIj. It's not wrong the way this lesson's sentence has it, but it's not as good.
(An even better version would be Qo'noS lulengmeH raQpo', Duj lutIj. The plural suffix is usually optional, and there is no question that raQpo' is being used in a plural way here, since the verb prefix lu- requires a plural subject.)
Qo'noS lulengmeH raQpo' Duj lutIj is coded as a best translation. This may have been a recent change not yet propagated to the platform, and the way it is coded gives the versions with -pu' and either placement of raQpo' equivalent status, but I agree with David that stating the subject in the first clause is preferable. The only reason not to do so here might be to avoid the possible interpretation of ambiguous boarders of a passenger ship, rather than passengers boarding a ship.