Designing RLVs with the Lowest Life-Cycle Cost

This was the Space Shuttle we wanted:

The Shuttle parked in the hanger.  Integration for the next mission was supposed to be comparable to Southwest Airlines loading my luggage (maybe I exaggerate a little).  This is the Space Shuttle we got:

The Shuttle requires between 200,000 and 400,000 human maintenance hours between each flight! You can barely see the shuttle in the picture above because of the scaffolding surrounding and incasing the vehicle.

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.

What I found interesting was what ratio the paper’s authors leveraged from the Space Shuttle program to include in their analysis.  The Shuttle utilizes seven support personnel for every one technician in their maintenance and integration efforts. For every one technician preparing the Space Shuttle for its next mission, there are seven individuals supporting that technician. This support staff consists of mission specialists, engineering support personnel, etc. Using this 7:1 ratio, the SpaceWorks paper estimated the need for RLV technicians and then extrapolated the number of support personnel needed.

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.”