Rocket Stage Separation | Payload Separation | Fairing Separation

Reliable rocket stage separation with PacSci EMC will occur on command, when commanded with as little impact on the attitude/rotational rate of a payload. Successful rocket stage, payload & fairing separation are critical to any aerospace and defense mission. Whether it is jettisoning components no longer needed, uncovering equipment or deploying payloads, the success of a mission is dependent upon the precise timing of the separation along with minimal changes of attitude and rotational rates to the proceeding vehicle. For over half a century we have successfully and reliably separated:

  • Missiles
    • Fin restraint release
    • Skin severance systems
    • Actuate dome covers, wings or like structures
  • Launch vehicles
  • Payloads
  • Satellites

When designing separation systems, we consider the following factors:

  • Clearance between the separating bodies
  • Weight/mass budget restrictions
  • Shock transmission to the payload or ongoing vehicle
  • Damage/contamination by debris due to separation mechanisms
  • Influences of force at the moment of separation on the separating body
  • Environmental elements of the separation (heat, vacuum, radiation etc.)

Why use pyrotechnic devices for separation? For micro-second accuracy when reliability, precision and repeatability are required, pyro is necessary.  Whether utilizing a launch vehicle or missile application energetic systems are widely used and provide high energy to weight performance.

Working on a project needing stage separation?

Precision engineered, tailor made to your specifications.

HOW STAGE SEPARATION WORKS

Multistage or step rockets are launch vehicles with more than one rocket stage, each including their own engines and propellants.  When rockets are mounted one on top of the other they are called tandem or serial stage rockets. While attached along side each other they are known as parallel stage rockets or boosters. Either way, these rockets are separated once their respective propellants have run out, creating less weight as the payload soars to its destination. With multistage rockets, there are two basic methods to stage separation.

  1. Utilizing a continuous structure to carry the payloads, a device is added to cut the structure cleanly on command (a common use of this technique is canopy transfer removal on military jets).
  2. Using separate structures which are attached by designated mating devices until separation is initiated.

These methods can be applied to either a conical shaped rocket or the cylindrical sections.

Regardless of the approach, the staging process commences when the burn out of the ongoing stage is detected and continues with the ignition of the next along with the separation of the spent stage. The latter two processes (ignition of the next stage and separation of the spent stage) may occur concurrently or with a time differential. These events may occur in any order, all dependent upon the vehicle configuration, mission requirements and whether they are programmed before lift off or real time during flight monitoring.

We have designed many successful separations using either method. The choice of one particular approach over the other will depend upon the mission, the vehicle and the engineers.

ROCKET & FLIGHT STAGE SEPARATION MECHANISMS

Release Device Performance

Separation mechanisms must be able to:

  1. Preserve their structural integrity under loads on ground and in flight
  2. On command, when commanded physically separate the structural segments
  3. Impart the necessary work between the separating bodies
  4. Not produce any forces, motions, stresses, or debris lessening the stability or structural integrity of the continuing body
  5. Protect the payload (i.e. payload fairing separation)
  6. Not impair the mission
Release Device Analysis

When considering stage separation mechanisms dynamic analysis of both the release mechanism design and the bodies to be separated is vital. The analysis is used to predict the nominal performance of the considered mechanisms and an estimation of any tip-off errors from standard tolerances on the design parameters.

For missions where there are no complex aerodynamic forces acting on the bodies to be separated, determining the worst combination of values and then confirming a satisfactory separation under these conditions provides for the design of release mechanisms with intrinsically high reliability. More complicated computer simulations of the separation are performed when the mission includes humans or complex forces, where weight is critical or the mission requirements are extremely stringent. Each force, moment, component and situation are reviewed in extreme detail with six-degrees of freedom. Analysis will also include Monte Carlo Methods and statistical studies, partial derivatives. These separation-dynamics studies include examination of both separations occurring in earth’s atmosphere (which are more complex) and those occurring in space. In the end, reliability is the goal in site no matter what depth of analysis is used. In depth studies on flight separation mechanisms by NASA and the military provide additional insights into depth of testing and analyses done on stage separation.

Some of the effects stage separations will encounter include

  • Attitude-control-system forces and torques
  • Sequencing of events
  • Nozzle-flow separation
  • Fuel sloshing
  • Mass and inertia properties of the two bodies
  • Extreme high heat & humidity
  • High structural loads
  • Aerodynamic wake
  • Inter-stage aerodynamic pressure
  • Atmospheric pressure
Release Devices

Common stage separation mechanisms and pyrotechnic fasteners on rockets and launch vehicles we produce include:

Confined linear explosives such as our flexible confined detonating cord offers all the advantages of a quick, clean release with none of the contamination associated with many line-cutting release devices.

Linear Shaped Charge – a metal sheath with the explosive energy follows the line or shape of the sheath cutting the structure in it’s path. This will produce extremely high shock and very high fragmentation.

Mild Detonating Cord is a metal clad detonating line threaded into a position on the separating body. There will be high shock and high fragmentation, but the fragmentation can be contained.

Fragmenting Explosive Bolts or Nuts – this is a notched bolt or nut with an internal explosives charge, producing high shock and high fragmentation.

Non-fragmenting Explosive Nut – a two-step release, the sealed explosive mechanism frees the bolt when initiated and is followed by piston impact ejecting the bolt. This device provides low shock and and no fragmentation or contamination.

Impact-Failure Bolt – another type of explosive bolt, this bolt drives a piston and the impact causes tension or shear failure in the necked-down section. There is no fragmentation or contamination and this device has very low shock.

Pin Pullers – a pin holds a bolt stud or connecting link in place, when gas pressure is induced by an initiator a pin is pulled releasing the connection. There is low shock and little to no fragmentation or contamination with this type of separation device.

Pin Pushers – a pin holds a bolt stud or connecting link in place, when gas pressure is induced by an initiator a pin is pushed releasing the connection. Similar to the Pin Puller above, there is low shock and little to no fragmentation or contamination.

FUNCTIONS & APPLICATIONS

Functions

Stage and payload fairing separation systems are used to separate:

  • Missile warhead release
  • Satellites
  • Space-vehicle release
  • Multi-stage rockets
Applications

Our stage severance systems have been used in multiple missile platforms, launch and space vehicles along with satellites including Delta IV, CCTS, SM, SF, X-1A and ATACMS

RELATED ARTICLES