1. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 1 The Systems-engineering Process Trading Requirements We use the requirements loopa necessary and continuous process within a process to re-evaluate requirements based on new information. The requirements loop is a continuous process within a process.

2. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 2 Designing Payloads and Subsystems The Payload The payloadestablishes spin-off requirements for the spacecraft bus: – Where and how precisely the spacecraft must point – The amount of data the bus must process and transmit – How much electrical power the payload needs – The acceptable range of operating temperatures – The payloads volume and mass

3. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering3 Designing Payload and Subsystems The Spacecraft Bus The Spacecraft Bus exists solely to support the payload, with all the necessary housekeeping to keep it healthy and safe. The best way to visualize the relationship between the payload and bus is to picture a common, everyday, school bus.

4. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 4 Designing Payloads and Subsystems The Spacecraft Bus (contd) In designing a school bus you need to know: – How far and how fast the students need to go, so we have a big enough engine and plenty of gas. – How many students the bus must carry, so we know how large to make it. – How warm to keep the bus, so the students dont freeze or overheat. – Other requirements that support the overall mission, so we know how to design important subsystems such as a steering system, a horn, and a radio.

5. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering5 Designing Payloads and Subsystems The Magellan Spacecraft This exploded view of the Magellan spacecraft shows where many of its subsystems are, as well as the primary payload. (Courtesy of Lockheed Martin)

6. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 6 Designing Payloads and Subsystems Steering - Spacecraft Control School bus drivers must know what route to take, where they are, and how to steer their buses to get where they need to go. This is all part of controlling their vehicles. On a spacecraft, a similar subsystem steers the vehicle to control its attitude and orbit.

7. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 7 Designing Payloads and Subsystems Attitude and Orbit Control Systems Tracking and Data Relay Satellite Systems (TDRSS) On spacecraft, the subsystem that steers the vehicle is the attitude and orbit control subsystem (AOCS).

8. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering8 Designing Payloads and Subsystems Communications and Data Handling We can easily identify the driver on the school bus. Its the person in front, behind the steering wheel. On a spacecraft, the driver is less easy to pick out, but its role is just as important. The driver of the spacecraft bus is called the communication and data- handling subsystem (CDHS).

9. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 9 Designing Payloads and Subsystems Electrical Power Just like the school bus, spacecraft depend on electrical power to keep components running. The electrical power on a spacecraft is no different from that used to run your television. Unfortunately, in space, theres no outlet to plug into, and an extension cord to Earth would have to be very long! Therefore, a spacecraft must produce its own electrical power from some energy source, usually the Sun.

10. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering10 Designing Payloads and Subsystems Environmental Control and life-support Subsystem (ECLSS) To keep the payload healthy and happy, the Environmental Control and Life- Support Subsystem (ECLSS) must keep the temperature within an acceptable operating range.

11. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 11 Designing Payloads and Subsystems ECLSS (contd) A school bus engine would overheat without a radiator to keep it cool. Similarly, a spacecraft must regulate the temperature of its components to keep them from getting too cold or too hot. In addition, on the Space Shuttle and the International Space Station, something must protect astronauts from the harsh space environment. The spacecrafts environmental control and life-support subsystem (ECLSS) maintains the required temperature, atmosphere, and other conditions needed to keep the payload (including astronauts!) healthy and happy.

12. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering12 Designing Payloads and Subsystems Structures and Mechanisms A school buss structure holds it together. A spacecrafts structure must be sturdy enough to handle all the stresses in space while holding all other subsystems in place. Courtesy Ball Aerospace & Technologies Corp.

13. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering13 Designing Payloads and Subsystems Propulsion Subsystem A school bus has an engine and drive train that supply torque to the wheels, moving the bus where the driver wants it to go. In space we use rockets to expel mass in one direction, which causes the spacecraft to move in the other. – Large rockets on launch vehicles produce the thrust needed to get the spacecraft into orbit. – Once there, smaller rockets in its propulsion subsystem produce thrust to maneuver it between orbits and control its attitude. Courtesy of NASA/Johnson Space Center

14. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering14 The Design Process The spacecraft design process shows how a spacecrafts subsystems depend on each other. When we adjust the design of one subsystem, were likely to have to adjust some, or all, of the others.

15. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 15 The Design Process Design and Analysis Tools To help make complex design decisions, mission planners and systems engineers have many design and analysis tools in their toolkit. These range from: – simple back-of-the-envelope calculations using a pencil, paper, and calculator (or spreadsheet) to – complex computer simulations requiring hours of run time.

16. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering16 The Design Process Validating the Design Too often, people responsible for specific subsystems get so involved in designing their own small piece of the mission that they lose sight of how their decisions affect other sub- systems and the missions overall performance. Figure 9-25 offers a humorous look at how subsystem designers often view the spacecraft.

17. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering17 The Design Process The Space Systems- engineering Process By following this process, systems engineers design spacecraft that meet mission requirements while staying within the budget and on schedule.

18. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 18 Summary Space Mission Design – Designing Space Missions – The Systems-engineering Process – Designing Payloads and Subsystems – The Design Process

19. Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 19 Next In the next lesson well look in more detail at space-vehicle control systems.