This was the Space Shuttle we wanted:
Shuttle experts can (and have) elaborated more eloquently than I could on the reasons why the Space Shuttle reusability goals fell so short. But as we prepare for suborbital RLV operations (and hopefully orbital operations) in the not so distant future, I wanted to discuss the implications of an interesting paper by SpaceWorks Engineering (Michael J. Kelly, et al) and its implications for the costs of RLV design & operations.
The paper is called, What’s Cheaper to Fly: Rocket or TBCC? Why? In it, SpaceWorks compares two hypothetical RLV designs (one rocket-based and one turbine-based) and discusses the expected operational costs of both systems. Both designs made the following RLV performance assumptions:
- Fleet of three unmanned RLV vehicles
- Fleet flies monthly (12/yr)
- Every 10 flights, RLVs spend 6-mo in offsite heavy maintenance facility
- 100 nautical mile LEO orbit
- Payload 20K lb.
Using the SpaceWorks rocket-based RLV as an example, below are the costs associated with preparing the rocket for its second flight:
Ignore the exact dollars but pay attention to the percentage. 91% of all “between flight” costs is labor using the 7:1 assumption. Stop worrying about fuel cost – start creating low-maintenance designs. Of course there are other costs that go into the price of an RLV launch: range costs, fixed cost amortization, development cost amortization, etc. But you can see how critical life-cycle costs become in RLV design discussions.
Quoting the paper, “Any program that can do better than 7:1 will probably save significant money over a program that cannot.” And “In addition to considering operational impacts when selecting engines and TPS materials, vehicle designers should strive to eliminate the need for centralized hydraulics, and for auxiliary power units.”
For example, here is what maintenance and integration costs could look like at various improvements to the Shuttle’s 7:1 support personnel to technicians ratio (all other assumptions unchanged):
I end this post with a quote from Byron Ellis, Executive Director of the Jethro Project, on life-cycle cost and Government Acquisition (just as applicable for RLV designers as Government acquisition agents):
“Executive Order 13123 requires government agencies to use life cycle cost analysis (LCCA) to minimize the government’s cost of ownership. Unfortunately, many stakeholders do not understand the concept of cost and proceed to minimize project acquisition (first) cost, rather than total project cost. However, over the life of the project, facility management cost is often two to three times higher than acquisition costs. Therefore, it is essential to design for minimum facility management cost.”