can I miss a court ordered visitation for special circumstances?

Unless your divorce papers gives your ex the "right of first refusal", you are not necessarily obligated to give placement of your time to your ex spouse. However, they are entitled to their placement schedule, regardless of whether you are going to be gone or not; your post doesn't indicate what your plans are for who is going to take care of your child(ren) while you are gone, but whatever those arrangements might be, they will have to help in allowing your ex their every other weekend schedule while you are away. Is there a particular reason you wouldn't allow your ex to take care of your chil(ren) while you will be gone for the 3 weeks, as opposed to placing your child(ren) with some other third party, whether other family members or friends?