Avionics, or aviation electronics, is comprised of all of the electronic systems on everything from satellites to planes. The main electrical systems on an aircraft or spacecraft are the control systems used to orient and maneuver the craft, the navigation systems, and the systems that convey information to and from the people that use the craft. In addition to these main components, any other electrical systems on the craft also qualify as avionics. All components that may be placed on a spacecraft may also serve a purpose on land, so the difference between avionics and electronics is mainly the requirements the design has to meet in terms of power, radiation hardening, resistance to vibration, reliability, and the like. These lead to a system that is much more difficult to design, and the final product can often cost as much as ten times more than a terrestrial analogue.
Unfortunately, many of the constraints are interrelated, so a gain in one area may result in a loss in another area. A more robust system may weigh more or have a larger volume, for example. Surprisingly, weight savings carry almost a ten to one benefit, in that if you can drop the weight of a system by a kilogram you can carry almost ten kg more. This is due in large part to the added frame weight that is necessary to support heavier components, which in turn requires more lift, which leads to larger and more powerful engines.
Environmental factors also have a large impact on design. Components may be subjected to temperatures from -40 to 70 degrees Celsius, extreme and rapid pressure changes, large accelerations, and vibrations. This means that many components used in commercial products are not suitable for aviation applications. The standard 74LS parts I've been using in school are simply not robust enough for an aerospace environment. Military spec'd parts will fair better, but the design of the system itself will have to take into account vibration and acceleration. All of the circuit boards I've manufactured have used solder as a mechanical support, but large acceleration or too much vibration could rattle those parts off the board. Potting compound and better solder practices will be required to ensure a robust design. There are probably other things that can be done to improve resistance to vibration, which I'll be looking into later.
Lastly, robustness is a key issue in avionics equipment. A failure in your cell phone may be an annoyance, but a failure in the communications systems of a spacecraft or aircraft could be deadly or result in the loss of millions of dollars worth of equipment. Even if a problem is found before launch, it could still result in missing the launch window if it is severe enough. All avionics systems need to take this into account.
Unfortunately, many of the constraints are interrelated, so a gain in one area may result in a loss in another area. A more robust system may weigh more or have a larger volume, for example. Surprisingly, weight savings carry almost a ten to one benefit, in that if you can drop the weight of a system by a kilogram you can carry almost ten kg more. This is due in large part to the added frame weight that is necessary to support heavier components, which in turn requires more lift, which leads to larger and more powerful engines.
Environmental factors also have a large impact on design. Components may be subjected to temperatures from -40 to 70 degrees Celsius, extreme and rapid pressure changes, large accelerations, and vibrations. This means that many components used in commercial products are not suitable for aviation applications. The standard 74LS parts I've been using in school are simply not robust enough for an aerospace environment. Military spec'd parts will fair better, but the design of the system itself will have to take into account vibration and acceleration. All of the circuit boards I've manufactured have used solder as a mechanical support, but large acceleration or too much vibration could rattle those parts off the board. Potting compound and better solder practices will be required to ensure a robust design. There are probably other things that can be done to improve resistance to vibration, which I'll be looking into later.
Lastly, robustness is a key issue in avionics equipment. A failure in your cell phone may be an annoyance, but a failure in the communications systems of a spacecraft or aircraft could be deadly or result in the loss of millions of dollars worth of equipment. Even if a problem is found before launch, it could still result in missing the launch window if it is severe enough. All avionics systems need to take this into account.
For the near future, I'm going to focus on the main electronics areas of navigation, communication, human-machine interface, flight control systems, and spacecraft state sensors. Each of these covers a very large area by itself, so I've got a lot of work to do. I think what I'm going to do is make a post on each of these that outlines the basics of what each encompasses. After that I'll focus on learning about each area in turn. At this point I find flight control systems the most interesting, so I'll probably start with that after my overview posts.
For the most part, my investigation into these subsystems will probably focus on terrestrial applications for similar devices. The majority of textbooks about these subjects deal with them in the abstract, and not specifically for spaceflight or other aerospace applications. In order to take that into account, I'll have to constantly be thinking about the many restraints that avionics systems face.
For the most part, my investigation into these subsystems will probably focus on terrestrial applications for similar devices. The majority of textbooks about these subjects deal with them in the abstract, and not specifically for spaceflight or other aerospace applications. In order to take that into account, I'll have to constantly be thinking about the many restraints that avionics systems face.
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