Antenna Deployment

From Satellite Wiki
Jump to: navigation, search

Why Deployment?

  • Generally frequency range for nano-satellites lies in VHF band. Therefore, the antenna length will lie in range of 10 - 150 cm (varies with frequency). In vibration, higher is the mass farther from the base (source of vibration), lesser is the natural frequency of the satellite. This means that if antennae are not deployable, but rather fixed the the satellite body (like in the case of Pratham), then they are more vulnerable to damage due to resonance during launch, since the fundamental frequency will approach the lower limit imposed by the launch vehicle. This imposes the requirement of antenna deployment so as to keep mass closer to the base (source).
  • Also if we keep antenna undeployed then we have to increase its mass to increase stiffness. It can affect the mass budget constraint.
  • Another major reason is that it covers larger space on launch vehicle.

Design Considerations

  • Side panel length is major determinant of antenna deployment. If the antenna length is larger than the side length then we have roll or wind up the antenna.
  • If power is an issue then antenna should be deployed in such way that the shadow on the solar panels should be minimized to maximize the power for charging.
  • Deployment of antenna is usually done on different sides to avoid the collision or entangling of antennae while deployment.
  • If all the antennas are to deploy on same side they should not be deployed in the same plane, else there can be collision of antennae

Deployment Mechanisms

There are several deployment mechanisms. The choice of the mechanism majorly depends on the antenna requirement and its implementation. Some mechanisms are better than the others for student satellites. We'll discuss one popular mechanism here

Burn Wire Release Mechanism

It can be implemented in many ways. Mostly burn wire mechanism is used in case of nano satellite because it is compact and more reliable and contains less number of moving parts.

The mechanism

Wind or roll flexible tape antenna around a rail and use nichrome wire to burn the dyneema wire (retention wire), this dyneema wire is the link between antenna and the nichrome. And when nichrome heats up the dyneema wire melts and the antenna deploys.

Design Takeaways

  • Burning of the securing thread for all antennas by a single burner is preferred in the interests of power and space.
  • A modular system that can be integrated easily on the satellite without disturbing the internal framework is preferred.
  • The antennas can be positioned at the top and the bottom of the satellite to incorporate the maximum number of antennas on one side without disturbing other side panel arrangements.
  • A retention film can used for stowing of antenna which is tied with Dyneema wire and goes to the burner circuit. This film is important because if we use only nylon wire then there is possibility of slippage of wire due to vibration.
  • There should be a proper interface between the dyneema wire and the resistor. Also, the heating element shouldn't be in stress condition.
  • The resistor should be properly insulated from the metallic body.
  • Heating element can be covered with some thermal insulator with only some part of heating element kept open to environment on which retention wire is tied.
  • Nuts and bolts used for attaching antenna should be taken into account when designing and analyzing the deployment mechanism.

If you are done reading this page, you can go back to Mechanical Subsystem.