One of the things that being a Service Member offer is the ability to travel using military vehicles. Known as the Space Available program, or Space A, eligible Service members, dependents, and other eligible people can travel on Department of Defense vehicles (mostly aircraft) after all the service needs are filled. Unused or open seats are then made available to those passengers who are eligible.
In the years following September 11, 2001, the Space Available program has undergone many changes, not the least of which has been the elimination of many sources of schedule information. In the past, schedules of flights and mission schedules were available, even on the Internet, and you could literally book a Space Available flight online.  Following the Twin Towers and other tragedies from 9/11, the military has removed those sources of schedule information. Accessing Space Available is still possible, but more difficult.
But if you are willing to be patient, and to be diligent, it is possible to travel long distances for free or practically free. In many ways the system is disjointed, and it can be very confusing, but it is still a benefit available to those Service Members willing to be a bit long suffering.
Traveling with Space A is something that takes flexibility and a little bit of time, but the rewards can be great.
Understanding Space Available travel is half of the battle. When you travel using Space Available Travel you are assigned a category of travel. This category of travel then becomes your priority for travel. The two terms are one in the same for our purposes. Each Category of travel moves before the next category. There are six categories. You are assigned to your category (priority) based on two issues, your Service Status (Uniformed Service, Reservist, Department of Defense employee, or whomever) and your situation/need (example, ordinary leave, service related travel, emergency leave).
Categories for Space Available travel are:
Category One
Emergency round trip travel concerning serious illness, impending death, or death of a immediate family of any Service member or Department of Defense Employee.
Category Two
Environmental Morale Leave.
Category Three
Regular or normal ordinary Leave.
Category Four
Dependents traveling Unaccompanied.
Category Five
Temporary Duty of a permissive nature, and also students.
Category Six
Retirees.
Traveling Space Available is only possible after all passengers and duty cargo has been taken care of and accommodated. There is no guarantee of movement within a certain time frame, so patience is very important, if you are determined you likely will travel eventually, but it may take a while.
