E. J. HOFFMAN AND G. H. FOUNTAIN The System Approach to Successful Space Mission Development Eric J. Hoffman and Glen H. Fountain Conceptualizing and executing space missions calls for creative thinking coupled with careful and conservative implementation. The engineers and scientists who design such missions must master a “wide dynamic range” of techniques, from brainstorming to design reviews. Operating in space has never been easy, and the “better, faster, cheaper” mandate imposed by today’s overconstrained budgets has created new complications. This article presents the Laboratory’s philosophy for meeting these challenges. (Keywords: Space history, Space mission design, Spacecraft design, System engineering.) INTRODUCTION The APL Space Department has designed, built, and Navigation System (Transit). Several important sys- launched 58 spacecraft.1 Another is in the final stages tems have been transferred to industry for production of integration and test, approaching launch, and three after being conceived and developed at APL, includ- more are in early development. Three of our space- ing Transit, the Global Positioning System Package craft—the Delta series—were developed jointly with (GPSPAC), and Geosat. More recently, APL has ex- another organization (McDonnell-Douglas), and one tended its “better, faster, cheaper” methodologies to was integrated on a standard bus purchased from Or- low-cost interplanetary missions such as the Near Earth bital Sciences (the Far Ultraviolet Spectroscopic Ex- Asteroid Rendezvous (NEAR), Advanced Composi- plorer [FUSE]). APL spacecraft have ranged from the tion Explorer (ACE), Comet Nucleus Tour (CON- 53-kg environmental research satellite 5E-3 to the TOUR), and MESSENGER. 2720-kg Midcourse Space Experiment (MSX), a 14- In the course of all this activity, APL acquired a instrument “observatory class” spacecraft comparable reputation for pragmatic and effective system engineer- in the scope of its instrumentation to the Hubble Space ing. Visitors often mention that all Space Department Telescope. APL helped pioneer quick-reaction space- engineers seem to think like system engineers, whether craft (a record possibly being the 75-days-to-launch or not they have that title. Perhaps less well known is Transit Research and Attitude Control [TRAAC]), APL’s record of innovative, yet practical, advanced invented many widely used spacecraft techniques, and technology developments. Many of the standard tech- developed entire space systems, such as the Navy niques used on today’s satellites were developed here.2 482 JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 20, NUMBER 4 (1999) SYSTEM APPROACH TO SPACE MISSION DEVELOPMENT A small but prolific advanced technology development to Earth.” It is important to remember that at the time program continues that tradition today. Kennedy set out this bold objective, the United States This article provides a top-level view of APL’s mis- had not yet orbited a single astronaut—John Glenn’s sion development process, from mission objective to first orbital flight was still 9 months away. Kennedy’s launch. Postlaunch operations and certain other as- single sentence not only stated the objective of what pects of mission development require the more detailed became the Apollo Program, it set forth the schedule as treatment given by the subsequent articles in this sec- well!) tion. A strength of the APL Space Department has The objective isolates and pinpoints what is truly been our “end-to-end” approach to mission design and important; the value of a well-crafted objective cannot execution (Fig. 1). The close working relationship be overstated. It establishes the criteria by which mis- between space scientists and engineers fosters a symbi- sion success or failure will be judged, possibly many osis that is the hallmark of APL missions. Such close- years down the road. It serves to periodically refocus the ness in a single organization is surprisingly unusual in attentions of the team on the essential purpose of the the space industry; the fact that these two groups mission, which might otherwise be forgotten in the understand and empathize with each other—not just forest of design details that accrue as time passes and tolerate each other—is even more rare. The resulting as staff and subcontractors join and leave the program. ability to provide “one-stop shopping” for government Most importantly, it helps guard against “requirements space customers has contributed greatly to APL’s record creep,” that deadly malady that has threatened more of success with better, faster, cheaper space missions.3 than one program. The objective also isolates and emphasizes the essen- tial kernel of why the mission is being done. Where does UNDERSTANDING THE PROBLEM the objective come from? It can arise from a committee The article by Bostrom in this issue (“Defining the such as a science working group, user working group, Problem and Designing the Mission”) addressed the or study team. But some of the most impressive break- early concept and mission formulation phase. Every throughs have come from objectives set by a proverbial successful program must be able to state its objective, “wild-eyed sponsor,” one champion obsessed with solv- preferably in one concise sentence. (Possibly the best ing a particularly tough problem or performing a par- example of a concisely stated objective was President ticular mission. Kennedy’s 25 May 1961 statement to a joint session of Once the top-level objective is established, a con- Congress: “I believe that this nation should commit cept for meeting the objective is synthesized. That great itself to achieving the goal, before this decade is out, system engineer Julius Ceasar provided the key to solv- of landing a man on the moon, and returning him safely ing the really difficult, large problems: divide and con- quer. The problem is broken down into smaller pieces, and subsidiary functional requirements are estab- lished, a process known as “require- Mission concepts ments flowdown” (Fig. 2). This Fundamental process of synthesis and analysis science and Hardware technology drivers implementation represents a very creative part of Technology the mission design, with frequent synergy iterations back and forth between alternative conceptual approaches, Technology Results and transfer Launch while keeping in mind the avail- publications operations able capabilities and the numerous Education and outreach constraints (mass, schedule, cost, and a host of others). Deciding how Data to partition the system and where acquisition Mission and processing operations to establish the interfaces is almost an art form. Interface decisions made at this time can haunt (or bless) a program for its duration. Figure 1. The APL Space Department provides complete end-to-end mission design and execution capability, fostered by the symbiosis between our scientists and engineers. A “Brainstorming” is one of the basic mission concept can be taken completely through development, launch, on-orbit techniques used in this early stage of operations, and analysis of the scientific data within a single organization, at substantial searching for conceptual solutions benefit to our government customers. At the same time, we are alert for opportunities to cross-fertilize technologies to other missions or transfer them to industry, and for education (see the section on The Design and outreach opportunities. Process). Numerous books teach JOHNS HOPKINS APL TECHNICAL DIGEST, VOLUME 20, NUMBER 4 (1999) 483 E. J. HOFFMAN AND G. H. FOUNTAIN flow diagrams, specifications, interface control docu- Mission objective ments, and test plans. The Delta 180 mission provides a good example of focusing on the true objective and meeting it through “out-of-the-box thinking.” Soon after President Reagan challenged the military to develop a missile defense, the Capabilities Functional requirements Constraints newly established Strategic Defense Initiative Organi- zation (SDIO) wanted a quick and convincing demon- stration of space intercept of a thrusting target. Various aerospace organizations proposed mission concepts, but they were all too long (3–5 years) and too expensive Mission Mission ($300–500M). One reason for the high costs was design analysis that all of these concepts envisioned separate launch vehicles for the target and the interceptor. APL system engineer Michael Griffin and program manager John Dassoulas considered the essence of the problem and came up with the novel idea of carrying both target and Launch Mission interceptor on a single, low-cost Delta launch. Further- vehicle Spacecraft requirements operations more, both spacecraft could be assembled from sub- requirements requirements systems scrounged from various existing missile and launcher systems. SDIO accepted the concept, and the Delta 180 intercept was successfully carried out only 13 months from funded start, at a total program cost of Block, power-flow, Specs, interface $150M. Delta 180 received a presidential citation, two and signal-flow control documents diagrams Orbital configuration DoD distinguished public service medals, and awards (interior, exterior) from the American Institute of Aeronautics and Astro- Launch configuration (and vehicle adapter) nautics (AIAA), the American Defense Preparedness Association, and Aviation Week & Space Technology Figure 2. Starting with the all-important mission objective, top magazine. It was even popularized in Reader’s Digest.6 functional requirements are established, taking into