Vibration Testing of Small Satellites (VTSS)

This 2-day course provides a tutorial, practical guidance, examples, and recommendations for testing a small satellite on an electrodynamic shaker. Addressed are sine-burst testing, random vibration testing, and low-level diagnostic sine sweeps. Notching, response limiting, and force limiting are addressed in detail, with examples. There is also a section on strategies for designing a SmallSat to withstand the vibration tests. The course is primarily aimed at satellites in the 50 – 500 lb (23 – 230 kg) range, but it also applies to CubeSats. Most of the guidance applies to larger satellites as well if they will be tested on a shaker, as well as to spacecraft components.

The one-day computer workshop, Notching and Force Limiting Workshop (NFLW), is an optional supplement to the VTSS course.  

• Establish an effective vibration test program
• Identify and clearly state test objectives
• Design (or recognize) a test that satisfies the identified objectives while minimizing risk of an over test
• Establish pass/fail criteria and interpret test data
• Write effective test plans and reports
• Design a SmallSat to withstand the vibration tests

All engineers & managers involved in ensuring small spacecraft can withstand launch environments.

Overview

• Shaker basics
• Test Objectives
• Review: Mechanics of Vibration; transmissibility
• Common types of vibration tests
• Pass/fail criteria
• Limitations of testing on a shaker
• Dry running the test

Test Configuration, Fixtures, and Instrumentation

• Test article configuration
• Test fixture design
• Providing a flight-like interface
• Mass simulator design
• Accelerometers
• Strategies for determining base force and moment

Low-level Sine Sweep Testing

• Objectives and test parameters
• Examples of response data
• Deriving damping from test data
• Criteria for pre- and post-test comparisons
• Common reasons for differences between pre and post-test data
• Limitations of sine-sweep comparisons in detecting failure

Sine Burst Testing

• Introduction and objectives
• Applicable standards
• Limitations of sine-burst test effectiveness
• Pass/fail criteria
• Designing the sine-burst test environment
• Establishing the test axes and deriving the target accelerations
• Selecting the sine-burst frequency
• Accounting for dynamic amplification
• Potential problem and recommendations

Random Vibration Testing

• Introduction and objectives
• Acceleration (or power) spectral density: understanding g²/Hz
• Root-mean-square acceleration
• Peak acceleration for random vibration
• Decibels
• How test environments are derived
• Government standards
• Use of GEVS environments and a related common problem
• Data resolution
• Interpreting test data

Notching and Force Limiting

• What is notching, and why do we do it?
• Methods of notching: force limiting, response limiting, and manual notching
• Case history: how notching without technical rationale led to mission failure
• Using force gages to measure base force
• Force limiting: references, the semi-empirical method of deriving force limits, examples modification during test
• Response limiting
• Manual notching

Test Documentation and Reviews

• Managing the process
• Test plans and procedures
• Getting buy-in before the test
• Test-readiness review
• Pre-teardown review
• Flash report
• Test report

Designing a SmallSat to Pass the Vibration Test

• Avoiding weight criticality
• Making load paths direct
• Separating modal frequencies
• Panels used to mount components and mounting strategies
• Understanding how the primary structure carries loads
• Attachments and joints
• Design loads
• Case study:  FalconSat-2

Tom Sarafin is President and Chief Engineer of Instar Engineering and Consulting, Inc. He has worked full time in the space industry since 1979 as a structural engineer, a mechanical systems engineer, a project manager, and a consultant. Since founding Instar in 1993, he’s consulted for NASA, DARPA, the DOD Space Test Program, Lockheed Martin, DigitalGlobe (Maxar), Sierra Nevada Corp, Spaceflight Industries, Millennium Space Systems (Boeing), and other organizations. He was a key member of the team that developed NASA-STD-5020, “Requirements for Threaded Fastening Systems in Spaceflight Hardware” (March 2012). He is the editor and principal author of Spacecraft Structures and Mechanisms: From Concept to Launch and is a contributing author to Space Mission Analysis and Design. He’s also the principal author of a series of papers titled “Vibration Testing of Small Satellites.” Since 1995, he has taught over 300 courses to more than 6000 engineers and managers in the aerospace industry.