Vacuum-Rated Cable Assemblies: Development Applications and What Sets Them Apart
When it comes to temperature extremes, Death Valley and Antarctica have nothing on outer space. A typical communications satellite must be able to withstand temperature swings of more than 250°C. That requires specially made electronics, not only for the satellite but for the equipment that tests its components before it reaches the launch pad.
MilesTek is a leading maker of the cable assemblies used in thermal vacuum chamber (TVAC) research and development applications for satellites and space vehicles. We offer numerous vacuum-rated TVAC products that meet NASA’s stringent requirements. For those in the market for such products, let’s take a look at why these vacuum-rated cable assemblies differ from other cable assemblies and what characteristics to look for in the cable and connectors to find the right assembly for your application.
this post explains how vacuum-rated cable assemblies differ from other assemblies. It requires a brief explanation of the process of outgassing and how it helps determine an object’s total mass loss. We also describe some characteristics you should look for in the cable and connectors suitable for vacuum-rated TVAC cable assemblies.
Vacuum Testing to Determine Total Mass Loss
Every element of a spacecraft, down to the nuts and bolts, must have the material structure to survive the harsh conditions of space travel. A thermal vacuum chamber (TVAC) is used to simulate the temperatures and other conditions of space. After a component is placed in the chamber, all the air inside the chamber is sucked out by a vacuum pump to simulate the lack of air pressure in space. Then the temperature inside of the chamber is raised to hundreds of degrees above zero.
These harsh conditions reveal much about the component being tested. When air pressure is removed, all materials above absolute zero evaporate at a rate that increases with temperature. When impurities and gasses trapped in the material start to evaporate, the process is called outgassing. In an actual spacecraft, excessive outgassing can create problems. For instance, the evaporated material could condense on sensitive optical surfaces such as lenses and mirrors, making them less accurate or even unusable. Also, if enough outgassing takes place near high-voltage wires, unwanted electrical discharge can occur, leading to unnecessary heat being generated and causing component failure.
Both before and after this testing, the component’s mass is gauged to determine the total mass loss (TML) that occurred. NASA’s cable assemblies must be manufactured to meet its TML and outgassing requirements.
Cable and Cable Jackets
The cables commonly used in vacuum-rated TVAC applications must meet the strigent standards used in military applications. These cables feature an impedance of 78 ohms and a two-conductor twisted-pair cable known as twinaxial. Twinax has two separately insulated wires in the center of the cable, a braided wire surrounding the two, and an outside jacket.
Cable assemblies for spacecraft must be made with a jacketing material that performs under extreme heat. MilesTek uses a jacket made of perfluoroalkoxy (PFA), which can withstand temperatures of -55°C to +200°C. This cable also remains flexible at low temperatures, is UV resistant and provides outstanding resistance to chemicals.
The connectors on vacuum-rated TVAC cable assemblies must hold tight in all extreme conditions. Therefore, bayonet and threaded mounts are often employed because they can withstand severe shocks and vibrations.
Commonly seen connector designations for these applications are TRB, TRS, TTM and TCS. The TRB has a bayonet design with a center contact and an intermediate cylindrical contact. The TRS subminiature connector is a smaller alternative to the standard TRB. Threaded TTM and TCS connectors are also used for their solid contact. MilesTek cable assemblies are offered with all four connector options and in a wide variety of combinations – TRB to TRS, TTM to TRB, TCS to TCS, etc.
Vacuum-rated TVAC cable assemblies are designed for use in thermal vacuum chamber research and development applications for satellites and space vehicles. The assemblies are manufactured with materials that meet the total mass loss or outgassing requirements of NASA. These cables are made to military specifications, with jacketing that must perform under extreme heat and with connectors that can withstand severe shocks and vibrations. View MilesTek’s wide range of in-stock and ready-to-ship vacuum-rated TVAC cable assemblies.