I'm sure that the crew from Goddard would be most interesting to talk with: they were more than several years ago (8 Years? NGT workshop), when I joined with some of them at lunch. As to outside attendance, I dopn't know - you could contact the conference organizer. I suspect you could get press credentialed by (?) ciel et cosmos (is that the right title?). Of course the NASA credentialing would take a bit longer, particularly for a foreign national. You'd want to bring a laptop and camera to snag graphics.

BWI airport is near the conference location, but transport from Dulles is available. Expect to pay about $100-$125 per night for lodging near to the conference.

Bon chance...