Space-Systems Engineering

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

Space-systems Engineering

• Space Mission Design– Designing Space

Missions– The Systems-

engineering Process– Designing Payloads

and Subsystems– The Design Process

A satellite orbits Earth

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering SECTION 9.1 3

Space Mission Design:Designing Space Missions

• Designing space missions is a process similar to any project.– Backyard BBQ platforms and an on-orbit

observation platform go through the same design process.

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

The Systems-engineering Process

• Building the International Space Station depends on careful space-systems engineering.

• This process starts with well defined requirements.

International Space Station

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

The Systems-engineering Process (cont’d)

• What is systems engineering?• All design problems begin with

a need. – NASA needed a vehicle to

launch astronauts to the Moon, so they designed the Saturn V.

– Over time, engineers have developed a well tested process for translating simply stated needs into complex systems.

• We call this process systems engineering (SE).

Saturn V Launch Vehicle

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 6

The Systems-engineering ProcessBuilding a Deck

• A simple example of how you can use systems engineering is the problem of designing and building a deck for your house.

• You would start with a general statement of your basic requirements.– Requirement: You need a flat, dry

area in your backyard, roomy enough to house your barbecue and entertain friends.

Unit 3, Chapter 9, Lesson 9: Space Systems Engineering 7

The Systems-engineering Process Building a Deck (cont’d)

• Along with this general requirement, you probably would define some constraints: – For example, you could specify your budget for the project (say, less

than $10,000).– You could specify some basic ideas about when you’d like it to be

done (in time for the summer).– You could specify its overall quality (you’d like it to last at least as long

as you’ll live in the house).• Once you’ve made this trade-off between what you want and

what you can afford, you can start specifying your deck’s characteristics (size, shape, materials, etc.).

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

The Systems-engineering Process• With these decisions made, you

finally can get down to the business of designing what it will look like and how you’ll build it. – You’ll need to make some detailed

drawings, specify the amount and type of lumber to use, choose types of nails and bolts, and state all other construction details.

– You’ll need some design tools to help you with calculations and other tasks.

• We can diagram this entire systems-engineering process.

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

The Systems-engineering Process Defining Mission Requirements and Constraints

• Yogi Berra once said:– “If you don’t know where you’re going, you’ll probably end up

someplace else!”

• We begin systems engineering by defining top-level mission requirements and constraints. – Requirements communicate what we need to others and to ourselves.– We need to ask ourselves:

• “What end result do we want to achieve?”• “What is our ultimate objective?”• In space terms, “What is the mission?”

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

The Systems-engineering Process The Mission Statement

• To define a space mission’s requirements, we begin with a mission statement that clearly and simply lays out:

– The mission objective—why we do the mission.

– The mission users—who will benefit from and use the information.

– The operations concept—how all the mission elements fit together.

• For this first systems-engineering step, we focus on the heart of the mission architecture to decide on our mission’s form and how its elements will interact.

• The architecture we define, and the systems and subsystems that underlie it, must ultimately satisfy our mission need.

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

The Systems-engineering Process Detecting Forest Fires

The FireSat mission is motivated by the need to detect and contain the damage done by forest fires.

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

The Systems-engineering Process FireSat Example

• The FireSat mission comes from the need to detect and contain forest-fire damage.

• An example mission statement:– Mission objective—detect and locate forest

fires worldwide and quickly notify users.– Users—U.S. Forest Service and other national

and international agencies who fight forest fires.

– Operations concept—several are possible for this type of mission.

• For this example, let’s pick a concept that relies on a number of spacecraft in low-Earth orbit to detect and locate the fires.

– The system will communicate this information to users through the Internet. We’ll control the entire mission using a single, dedicated ground station.

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

The Systems-engineering Process SE Constraints

• Systems-engineering constraints typically fall into three categories: – Cost—the bottom-line program cost

is an easily recognized constraint to anyone who operates on a budget.

– Schedule—often, missions must conform to a schedule to meet a launch window or simply to ensure the required spacecraft is on station in time to service paying customers.

– Performance—systems engineers must design a space-craft containing subsystems that work together reliably to accomplish the mission.

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

The Systems-engineering Process Deriving System Requirements and

Constraints• Mission requirements focus on the big-picture items (the reasons for and results of the project).

• Systems requirements focus on the system architecture’s elements to describe in more detail what we expect of each element for mission success.

• Typically, the least constrained space-mission element is the spacecraft. • We conceptually divide the spacecraft into two parts that do different

things—the payload and the spacecraft bus. – The payload consists of the sensors or other instruments that carry out the

mission. – The bus is a collection of subsystems that support the payload.

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

The Systems-engineering Process Payload Requirements

• Payload requirements usually have the most influence on the spacecraft’ design.

• We define the mission’s subject to be a natural or manufactured object or phenomena that the payload will sense or interact with. – We characterize the subject by such things as its color,

size, shape, temperature, chemical composition, or frequency.

• Only after we know the subject can we lay out clear, simple payload requirements.

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

The Systems-engineering Process FireSat Example

• The obvious subject for this mission is forest fires: what the mission objective states we should detect and locate.

• But what kind of forest fires? • How big or how hot? • What characteristics of forest fires

should the payload detect? • These questions may sound trivial, but

they can be very important to the payload designer.

• We don’t want to send out an alert when someone starts a campfire.

• On the other hand, we don’t want to ignore a multi-acre blaze that may be out of control.

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

The Systems-engineering Process Payload Requirements (cont’d)

• Once we know these payload requirements, the rest of the mission elements fall into place. – The type of payload greatly determines the

mission orbit. – Payload mass, volume, power, and other

requirements determine the spacecraft’s basic size and mass.