Engineering Design Spotlight: Hold Down and Release Mechanisms

James Webb Space Telescope

What is a Hold Down and Release Mechanism?

A hold-down and release mechanism (HDRM) is an electromechanical system designed to securely restrain an object until a controlled release is required. HDRMs hold payloads firmly through reinforced structural components and release them via electrical signals when commanded. Environmental variations—dynamic, thermal, or atmospheric—require tailored engineering solutions to maintain consistent performance. HDRMs are considered mission-critical components, ensuring reliable release of payloads within precise timeframes.

Linear Shape Charges (LSCs)

Types of Release Mechanisms

HDRMs are generally categorized as energetic or non-energetic. Energetic mechanisms use a pyrotechnic charge for rapid release, examples include frangible joints, separation nuts, pinpullers, and linear shaped charges. Non-energetic mechanisms rely on mechanical or electromechanical triggers such as shape memory alloys (SMA), fuse-wire devices, motor-driven actuators, or magnetic force actuators. Energetic mechanisms excel where high loads and fast release are required, whereas non-energetic mechanisms are ideal for low-shock applications around sensitive components.

Non-Explosive Actuator (NEA) Hold Down and Release Mechanisms

Industries and Suppliers

HDRMs are widely used in space, aerospace, and defense industries to secure and deploy payloads, solar arrays, antennas, and military assets. Some prime customers who utilize these mechanisms include NASA, Northrop Grumman, Lockheed Martin, Amazon, SpaceX, and Boeing Space and Defense. Platforms include the James Webb Space Telescope, the Roman Space Selescope, Next Generation Interceptor, and the Europa Clipper to name a few support vehicles that utilize these mechanisms. Notable suppliers include Ensign-Bickford Aerospace & Defense (EBAD), NEA Electronics, TiNi Aerospace, Moog Inc., RUAG Space, Pacific Scientific Energetic Materials Company (PacSci EMC), Planetary Systems Corporation, and Rocket Lab, offering both energetic and non-energetic HDRM solutions for mission-critical applications.

Titanium Nickel (TiNi) Hold Down and Release Mechanisms

Spotlight: TiNi Pinpullers and Ejectors

The TiNi™ pinpuller and ejector from EBAD are non-energetic HDRMs that use Titanium-Nickel shape memory alloys (SMA) to actuate mechanical latches. When electrically heated, the SMA contracts, releasing the latch and allowing springs to retract the pin or eject a payload coupler. These devices offer low-shock, fast, and reliable actuation without pyrotechnics. They can be electrically monitored for status, are field-resettable, and ideal for spacecraft and military applications including payload, solar array, antenna, and military asset deployment.

Typical Performance Characteristics

The performance of these devices depends heavily on the environment they are exposed to. Characteristics such as power, function time, and load capability will be driven by the temperature, atmospheric pressure, and dynamic conditions.

Typical characteristics include side low and axial load, which is the load the pinpuller can take perpendicular to the output pin axis and ejector coupler can take in line with the release axis. The actuation current is the required power to warm the SMA to it's transition temperature to actuate the device. The function time is the time it takes for the device to release. The cycle life is the number of resets the device is qualified to at minimum. Operating temperature is the rated environment temperature. Typically these devices can go lower with more power applied, however there is a hot temperature limit due to the SMA transition temperature.

• Side load: Pinpullers up to 1,000 lbf

• Axial load: Ejectors up to 4,000 lbf

• Actuation current: 2.25 – 6.5 A

• Function time: 60–100 ms

• Cycles: 100 for pinpullers, 50 for ejectors

• Operating temperature: -65°C to 75°C (high-temp limit defined by SMA transition at ~90°C)

• Other Qualified Environments: Vibration, Shock, and Vacuum (Low Outgassing)

Conclusion

Dreamspace Engineering has extensive experience mechanical design engineering, performing simulation analysis, manufacturing, and testing HDRMs, including TiNi release mechanisms. Our engineering approach ensures reliable performance even in harsh environments. We provide complete solutions in product design, simulation analysis, manufacturing tooling, test equipment, documentation, and rapid prototyping.

Visit Dreamspace Engineering to request a quote for engineering service today!

Thomas A. Smith

Owner, Dreamspace Engineering Consulting

P: 661-755-9225 | E: dreamspaceconsulting@gmail.com