Cost can be classified into various catagories

  

1) Their  management fuction

     (a) Manufacturing costs

     (b) Non manufacturing costs

2) Their ease of traceability

     (a) Direct costs

     (b) Indiect costs

3) Their timing of charges aginst sales revenue

     (a) Product costs

     (b) Period costs

4) Their behavior in accordance with changes in activity

      (a) Variable costs

      (b) Fixed costs

      (c) Semivariable costs

5) Their relevance to control and decision making

      (a) Controllable and noncontrollable costs

      (b) Standard costs

      (c) Increment costs

      (d) Sunk costs

      (e) opportunity costs

      (f) Relevant costs

 As you can see there are differant types of costs used for differant purposes. Some costs are useful for planning and budgeting and costs control. Still others are useful for short term and long term decisions,as well as inventory valuation and income determination.

     So as you can see that trying to understand the theorectical  operating concept of how a giant airplane-spaceship operates also must include how it will be constructed and operating at least in some kind of explanation and with experiance.The more experimental a design is the more you have to really put some thought behind its invention to every and through every person that it will be connected to it in some way or another. In Tinkerbells idea he found out that just getting information out about it was difficult. In goverment and lots of companies that due business with them, there is research and devolpment grants like the old airmail contracts that were political footballs these I suspect are many times just that. In understanding programs about space some programs have appeared to be built around nothing more then experimental vehicals some times being related to as a prototype,

 but not even resembling a prototype in its proper station to a production model of an airplane design. To build Tinkerbells idea of giant spsaceship airplanes that criss-cross the solar system and have a crew of 40 to 100 persons on board with gravity containers for some of the crew some of the time so they won't get sick on long space missions ( and if they can take a large asteroid out of its dangerous path with earth and perhaps use it safely to further mans path to space). Giant buildings and a giant airfeild will have to be built in the area of the missisippi valley north of St. Louis in a place known as  occcident central.