Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 1 The Systems-engineering Process Trading Requirements We use the requirements loopa necessary and.

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 1

The Systems-engineering Process Trading Requirements

• We use the “requirements loop”—a 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.”

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 2

Designing Payloads and SubsystemsThe Payload

• The payload—establishes “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 payload’s volume and mass

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 3

Designing Payload and SubsystemsThe 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.

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 4

Designing Payloads and SubsystemsThe Spacecraft Bus (cont’d)

• 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 don’t 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.

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 5

Designing Payloads and SubsystemsThe 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)

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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.

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).

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 8

Designing Payloads and Subsystems Communications and Data Handling

• We can easily identify the driver on the school bus. It’s 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).

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, there’s 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.

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 10

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.

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 11

Designing Payloads and Subsystems ECLSS (cont’d)

• 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 spacecraft’s 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.

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 12

Designing Payloads and Subsystems Structures and Mechanisms

• A school bus’s structure holds it together.

• A spacecraft’s structure must be sturdy enough to handle all the stresses in space while holding all other subsystems in place.

Courtesy Ball Aerospace & Technologies Corp.

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 13

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

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 14

The Design Process

• The spacecraft design process shows how a spacecraft’s subsystems depend on each other. When we adjust the design of one subsystem, we’re likely to have to adjust some, or all, of the others.

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 15

The Design ProcessDesign 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.

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 16

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 mission’s overall performance.

• Figure 9-25 offers a humorous look at how subsystem designers often view the spacecraft.

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 17

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.

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

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 19

Next• In the next lesson we’ll look in more detail at

space-vehicle control systems.