Select a result to preview

Space System Engineering

Against Space Mission Engineering, Space System Engineering is concerned primarily with the formal requirements definition process and how to validate that all the requirements will be met.

The System Engineer's Dilemma

Space System Engineering-3.png
Source: NASA System Engineering Handbook ed. 2016

Life-Cycle Cost

In the early phase there will not be a lot of money expended, but a lot of money will be allocated. This means changing the system in later stages is far more expensive than in the beginning.
Space System Engineering-2.png

System Engineering Tasks

The System Engineering can be split up into different tasks. There are 10 tasks defined on the JPL system, and the 14 Steps of Space Mission Engineering out of the SMAD covers the first two tasks.

10 System Engineering Tasks

  1. Architecting - Develop the system architecture
  2. Requirements- Develop and maintain requirements
  3. System Design - Document, analyze and characterize the system design
  4. Technical Resources - manage and allocate technical resources
  5. Interfaces - Develop and maintain interfaces
  6. V&V - Verify and validate the system requirements and design
  7. Reviews - Organize technical peer reviews
  8. Risk Management - Identify, manage and mitigate risks
  9. manage the Design Process - Manage/control requirements and design (configuration control)
  10. Task Management - Manage the system engineering task

Space System Engineering-5.png

1. Architecting

This includes the first 12 steps from Space Mission Engineering.

2. Requirements

This includes step 13 and 14 from Space Mission Engineering.

3. System Design

The Design has to be documented, analyzed and characterized. This can be done with for example:

Single-Point Failures and Fault Protection has to be studied.

4. Technical Resources

This is mainly budget management. Typical budgets are:

Warning

Mass and Power will grow over the development cycle.

The tricky part here is to balance margins, to little margin, and they are maybe not enough, too much margin and the system is overbuilt. Allocation and Margin can be divided:

Margins

For example, the required mass margin decreases over time, so a typical holding margin in the beginning is 30% that can be reduced over the different Mission Phases.

5. Interfaces

A point of interaction between two system elements (hardware, software, humans, or organizations). It enables functional integration and exchange of energy, data, or forces.

So everyone is on the same page, there are Operational Interface Agreements (OIAs) and Software Interface Specifications (SISs). There is a formal agreement on how elements interact, the Interface Control Documents (ICDs)

Problems with interfaces could be:

Causes of these could be:

6. Verify and Validate

Verification:

Validation:

Types of verification methods
Requirement Closure

All requirements have to be tested and validated, now there are two ways how a requirement can be closed out

Roll-up: The requirement at Level n is closed when all its children at Level n+1 are closed

Glue Logic: The requirement at Level n is closed when all its children at Level n+1 are closed and an overarching summary analysis (or test) at Level n is completed.

Testing mindset

"Test like you fly, fly like you test"

7. Reviews

Technical Peer Reviews are when you show the current project to a peer, and he hopefully tells you all the things you did wrong. It's better to be critiqued among your colleagues ahead of a formal project review than in the formal review itself.

8. Risk Management

A risk is an uncertainty with consequences. There is the Risk Triplet:

The process of risk management is:

  1. Identify: What can go wrong?
  2. Analyze: Estimate probability and consequence
  3. Plan (Mitigate): Define strategies
  4. Track: Monitor risk evolution over time
  5. Control: Apply corrective actions, update baseline
  6. Communicate: Share risks across teams and partners
Risk Assessment

The risk matrix is a good tool to assess different risks. The probability (Likelihood) and the Severity (Consequence) are found/estimated, and then the risk is classified into categories based on the location in the risk matrix.

A-standard-risk-matrix.png

Risk Mitigations

Design Mitigations:

Mitigation is about balancing risk vs cost/complexity, not every risk can be eliminated.
The analysis can be done in a Failure Modes & Criticality Analysis (FMECA)

9. Configuration Control

During the all the Mission Phases, some parts have to be set, so the next things can be built upon it. There are set under configuration control and then can not easily be changed, except though an Engineering Change Request or a Waiver.

Space System Engineering-6.png

10. Task Management

All Tasks of the process have to be managed and organized, there are a lot of Reviews over all Mission Phases. The technology used has to be on a certain Technology Readiness Levels.

Component Qualification and Acceptance Testing

Qualification Testing:
If a representative article passes a sequence of qualification tests, all other articles built to the same engineering data should also pass. In other words, the design in qualified.

Acceptance Testing:
Once the design is qualified, subsequent articles built from the same data and controlled manufacturing processes are then subject to less severe acceptance tests that certify the workmanship of these articles.

Types of Hardware

Types of Tests

Integration & Functional Tests
These test the different systems or subsystems, alone or in combination

Environmental Tests
These test the system on different environmental impacts.