Spoke with the folks this morning and was provided the following info.
The annual fee of $15.00 can be paid at the visitor center as well as being mailed in. For the senior citizen (us old folks ) the fee is $10.00 and is the world pass good at all U.S. national parks, forrest, wild life refuge, etc. and is good for life.
For those of us who are veterans the fee is $10.00 and is good for life at all the above places.
For those of us who are disabled veterans the pass is free and good for life at the above. To get the free pass proof of disability is required. The VA notice of disability is all the proof needed. As a side note the same applies at the Fl. state parks such as Sebastain Inlet. I was issued a free family pass , however, that pass must be renewed annually. If you keep the original receipt that is stamped as disability confirmed there is no need to bring the disability paper work with you when it's time to renew.
Hours of operation for the visitors center is 8-5 6 days a week until Nov when it is open 7 days a week.
Hope this is of some help especially to you other disabled vets.