Controlling Rocket Fairing Separation in Zero Gravity

Vishvam
Vishvam
Altair Employee
edited December 15 in Altair Exchange
CHALLENGE 

Controlling Rocket Fairing Separation in Zero Gravity: Challenges of Cable Retraction and Trajectory Stability. Ensuring Safe Separation Without Compromising Mission Integrity

PREFACE 

Fairing separation in space requires precise control to avoid interference with a spacecraft’s trajectory. Physical testing of these events in space conditions is costly and impractical. Multibody dynamics simulation offers an efficient alternative to study and optimize the separation process in zero gravity. Software such as Altair’s MotionSolve and Inspire Motion enables engineers to model complex systems like fairing separation and evaluate the impact of various forces and constraints. Through these simulations, engineers can refine designs, ensuring the safe and controlled separation of the fairing without compromising mission success.

INTRODUCTION 

In aerospace applications, the controlled separation of components, such as rocket fairings, plays a critical role in ensuring the success of space missions. Fairings protect delicate payloads during launch and must be separated cleanly once the rocket reaches space. However, managing this separation in a zero-gravity environment presents unique challenges. Forces such as gravity, friction, and atmospheric drag, which play significant roles during launch, are absent in space. This demands careful planning and precise control mechanisms to ensure that detached components do not interfere with the rocket’s trajectory or the payload's mission.

This article explores the simulation of fairing separation in a zero-gravity environment, focusing on the dynamics of detachment. The simulation, conducted using Motionsolve, tries to replicate real-world conditions where the fairing separates cleanly but in certain cases is pulled back by cables, deviating from the intended trajectory.

SOFTWARE REQUIREMENTS

Altair MotionView (2023 or newer)

Altair MotionSolve (2023 or newer)

MODEL FILES

Fairing_Separation_Model.zip (See Attachments)

Understanding the Model Definition in MotionView

This model setup assumes a level of familiarity with Motionview/Motionsolve. A motion-ready model called Fairing_Separation_Model.mdl is available for reference in the attached zip file.

The simulation model represents half of the rocket's geometry, focusing on one of the fairings. The fairing is initially secured to the base via links and brackets held in place by bolts. In real-world scenarios, these bolts are disengaged using an explosive bolt mechanism, which is not modeled in the current simulation. Instead, the study focuses on the sequence that follows bolt disengagement: an actuator mechanism between the base and the fairing activates, pushing the fairing away from the rocket along a predefined trajectory. Additionally, cables remain attached between the fairing and the base, and their effect on the fairing’s movement is explored. The multibody simulation examines how these cables, when not detached, influence the fairing's trajectory and overall dynamics.

MODEL SETUP

Bodies:

  • The model contains a fairing, two actuation mechanisms, base of the fairing (with bolts held to the fairing) and two dummy cables.
  • The dummy cables are simple rigid link of bodies constrained with spherical/ball joints to simulate the cable-like behavior.

Joints:

  • The actuator mechanism is constrained with translational joints for simplicity
  • All the internal joints for the dummy cable bodies are spherical/ball joints, so that we can study its effects on the fairing trajectory when freely floating in space.

Motions:

  • Two motions are enabled for the translational joints for the actuator mechanisms, as s STEP function expression.

Contacts:

  • Contacts are created between the actuator mechanism and the base of the fairing. Thus, once the motion starts, the reaction from the contact force pushes the fairing away.
  • Another contact is defined near the hinge/bolt support of fairing, which pre-determines the trajectory once the separation is initiated.
image.png

Hinge/Bolt support for Fairing and Base

Sensors:

  • There is also a sensor created in the model, so that once the force in the cable joints exceeds a certain value, the joint is deactivated, and the cable is detached from the fairing/base.
  • The deactivation using sensor is achieved with the template command.
image.png
SIMULATION STEPS

The simulation initiates the actuation mechanism, causing a reaction force to push the fairing outwards. A sensor detects the force in the ball joint of the dummy cables, and once the sensor is triggered, the joint is deactivated, letting one of the cables free. Thus another cable pulls the fairing back, deviating it from its predetermined trajectory.

All the mentioned steps are achieved with a simple template script shown below.

  1. Transient simulation for 6 seconds, to initiate the motion using STEP function and begin the fairing separation.
  2. Deactivating the force sensor, once the sensor gets triggered.
  3. Deactivate one of the ball joints of dummy cables to detach it from the base.
  4. Transient simulation for further 14 seconds, to understand the trajectory of the fairing.
image-9528a310de4fa8-3201.png
RESULTS

The following animations show the effect of cable not detaching on the fairing separation trajectory

Front_view_attached.gif
Side_View_attached.gif

Another iteration is simulated as well and shown in the following animation.

Front_view_detached.gif
Side_view_detached.gif

Perfect trajectory with clean detached cables (Fairing_model_Iteration_1.zip)

CONCLUSION

The simulation of fairing separation in zero gravity using Altair MotionSolve and MotionView offers valuable insights into the challenges associated with cable retraction and trajectory stability. By replicating a real-world detachment scenario, this study demonstrates how even a small anomaly, such as an undetached cable, can significantly alter the fairing’s trajectory. The use of sensors to detect and deactivate forces at specific joints adds realism to the simulation, allowing engineers to better understand the dynamics of fairing separation in space conditions. The results show that even with precise actuation mechanisms, the presence of cables requires careful consideration to avoid interference with the spacecraft’s path.

These findings underscore the importance of simulation-driven design in aerospace engineering, particularly for events like fairing separation where physical testing is impractical. By using multibody dynamics software, engineers can optimize separation processes and reduce the risks of mission failure. Future studies can expand on this by incorporating more complex cable behaviors, including elasticity and non-linear forces, to further enhance the accuracy and robustness of fairing separation mechanisms.

AUTHOR

Vishvam Naik, Solution Engineer - Systems Integration

Fairing_Separation.zip

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