Know the systems-engineering process.

Apply systems engineering to design space missions

Understanding the Systems Engineering Process

Space-Systems Engineering

Space Mission DesignDesigning Space MissionsThe Systems-Engineering

Process

The Systems-Engineering Process: Why?Building the International

Space Station for example depends on careful space-systems engineering.

This process starts with well defined requirements…..

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).

The Systems-Engineering Process: What?

“If you don’t know where you’re going, you’ll probably end up someplace else!” -Yogi Berra

The Systems-Engineering Process

The Systems-Engineering Process: Defining Mission Requirements and Constraints 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?”

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.

The Systems-Engineering Process: Example: Detecting Forest Fires

The Department of Forestry and firefighters need a reliable and fast way to detect forest fires. From this comes….

The Systems-Engineering Process: FireSatThe 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.

The Systems-Engineering Process: Constraints

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

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

The Systems-engineering Process Deriving System Requirements and ConstraintsMission 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.

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.

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

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.

The Systems-Engineering Process Payload Requirements

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.

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.”

The Systems-engineering Process Trading Requirements

Tomorrow we look at the next step in the process…

System requirements and constraints

Subsystem designs

Know the systems-engineering process.

Apply systems engineering to design space missions

Understanding the Systems Engineering Process