Reusable Launch System Operational Concept - Attributes of the "Vision"
The top level strategic plan, noted by the Space Propulsion Strategic Planning Support Working Panel , is intended to provide direction for propulsion technology and system development so the United States can achieve reliable and affordable access to space. The President's National Space Transportation Policy directs NASA and the industry to concentrate on developing technologies and system capabilities from which a resilient and cost effective space transportation infrastructure can be forged. RLV is a potential keystone of that infrastructure. It has the opportunity to be the first truly affordable space transportation system through its potential for greatly simplified ground processing and increased launch rate enabled by innovative vehicle architecture.
1.0 Mission Requirements
Mission requirements and relative capability for launch vehicles are usually stated in terms of pound of payload to low Earth orbit. For ground operations purposes (and overall program planning) the life cycle cost is of paramount interest. This approach requires a look not just at payload size and cost to orbit a pound of payload, but the cost to orbit pounds of payload per year. Launch rate, and the resultant cost per launch, is thereby factored into the data and "levels the playing field" among different vehicle concepts.
2.0 Attributes
The attributes are goals for vehicle/system characteristics desired by the customer. In the case of launch vehicles, two customers are defined. The first is the payload owner who wants the payload delivered to a specific Earth orbit. Several types of payload owners are considered. They are military, civil (NASA/scientific), and commercial. They all want the same attributes, however, each one stresses attributes somewhat differently. The military emphasizes launch on demand, while the civilian agency stresses safety, reliability, and environmental acceptability . The commercial owner stresses operating cost because of competition from foreign launchers. The second "customer" is the system operator engaged in checking out, maintaining, and launching the vehicle. This customer stresses system operability to maintain a viable and robust launch program and to keep the operating costs under control.
The RLV program is a promise to integrate Operations concerns into the initial and developmental design activities.
Summarizing in more detail:
Commercial stressed:
Civilian agency stressed:
System operator (launch site):
A set of launch vehicle and systems attributes (Table 1) was developed during 1992 by the Space Propulsion Strategic Planning Support Working Panel. Scope of the documented results of their deliberations have operational impacts far greater than "mere propulsion".
Once the attributes were established, they were ranked in priority of need for improvement and assigned weighting factors. The factors were based on the working panel attendee's estimate of the importance of each attribute, and on present status and planned improvement as envisioned by the supplier.
As can be seen from the above discussion, transportation system requirements vary widely and can be satisfied by different technological approaches. The common threads that run through all space transportation system requirements are affordability, reliability, and operability. They can be more precisely expressed by a series of system attributes described in the following section.
Table 1
What do these mean?
2.2 Environmental Compatibility
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Edgar Zapata, NASA Kennedy Space Center
Shuttle Process Engineering Directorate, Fluid Systems Division