June 19, 2020 by Biljana Ognenova
The minutiae required in the work of satellite and space electronics engineers is unlike that of their colleagues that design terrestrial systems —the challenge is to consider environment, power generation, safety, and reliability.
Even when working on earthly design projects with stringent requirements, electrical and electronic engineers have some design guidance and best practices to help them bring the project to the end without significant harm done.
Most of these requirements and standards are based on prior experience that is gained through a sometimes painful and costly trial and error process. And many of those lessons learned from mistakes are gained on Earth’s surface before the equipment reaches outer space that has dramatically different environmental conditions.
Space has many design unknowns. The price for gaining experience can be irredeemable. For example, the reasons for the tragic Challenger tragedy were summed up to be a result of the breakage of the O-ring.
The extremely cold weather inappropriate for such a takeoff has caused the failure of the O-ring, a seal on the shuttle's right solid rocket booster that has sequentially generated hot gas leakage. Even the recent SpaceX flight into space commercialization had to wait for three more days after the initial scheduled date to find itself in an environment in which all orbital mechanics conditions are met.
Without electrical equipment for space exploration, it would be impossible to use navigation, telemetry, telecommunications, and sensor systems on spacecrafts. Without adequately designed space suits it would be out of the question for astronauts to do extravehicular activities (EVA) on lunar and planetary surfaces in microgravity.
A Soyuz satellite in space.
Weather and temperature are absolutely important for designing safe and reliable electrical and electronics equipment. Temperature standards in space design are on a completely different level than on Earth. The best example of the striking difference is in the heat transfer methods.
Space is considered very cold. However, this coldness is specific because of the diffuse gases that move in a vacuum and don’t remain the same under all circumstances. Unlike conduction, convection, and radiation, which are known as main thermal transfer methods, the only heat transfer method in space is radiation.
When astronauts work on the ISS (International Space Station) they face different temperature conditions in direct sunlight— up to 260 ℃, and in shade— down to -100 ℃. This is only one example of the harsh temperature conditions in outer space, which can exist both as a cryogenic chamber and as a microwave oven.
Humidity, on the other hand, is non-existent. The only humidity comes from astronauts and must be carefully maintained at around 60% RH so that the environment and the astronauts on the ISS stay healthy. Therefore, most of the water is recycled and reused.
The challenge for electronics engineers who design power electronics is to create robust electronics systems that endure shifts in relative humidity. One way to overcome this is by heat exchangers that transfer the fluid from one working system to another.
An example of how orbital mechanics worked to launch the SpaceX Dragon to the ISS. Image Credit: SpaceX.
If we put the environmental factors in the context of designing electronic circuits, the only secure standard for astronaut and spacecraft safety is the maximum. NASA asks for a Level 1, qualified manufacturer list Class V (QMLV) devices at the bare minimum for space level applications and will not hesitate to ask for more.
To prevent things from going wrong, engineers should take care of the following steps at the least when designing electronics for space:
Keep an eye on noise and vibration levels in the launch environment
Analyze pyroshock testing results
Consider possible outgassing (or off-gassing, as called in deep space) in a high vacuum that could cause the degraded performance of charge-coupled-device (CCD) sensors in space probes
Eliminate electrostatic discharge on satellite surfaces that shows up due to high contamination levels.
Avoid using forbidden tin-whiskers materials, such as tin, zinc, and cadmium.
As a general rule, space radiation is a major design concern. Cosmic radiation is constantly changing and can affect the variable orbiting of spaceships depending on whether they move in solar minimum or solar maximum.
As satellites grow more complex they are at a higher risk of being adversely impacted by radiation. If you ask a satellite engineer about their most sought-after improvement, radiation-tolerant electronic components would find its place high on their list of priorities.
It is not only the lack of oxygen, microgravity, and the absence of a moderate, ozone-guarded “climate” that makes the design difficult. Spaceship thrust vectoring and the friction from the atmospheric drag must be taken into consideration when working on spacecraft engines.
Even if one knows a lot about lift, weight, thrust, and drag when designing atmospheric aircraft, these insights must be examined and adjusted to design spaceships with extended chances of survival in space.
We cannot underestimate the achievements of space exploration regarding Earth telecommunications systems, including the GPS we so much rely on. Therefore, we need powerful, durable, and energy-efficient satellites.
A view of the internal components of a part of a spacecraft rocket.
Aptly put by the European Space Agency (ESA), ”without electrical power, a satellite becomes nothing more than an inert piece of space junk”. And due to the near proximity to the sun, solar energy is the most efficient way to harvest electricity for the electrical and electronic components on space vessels.
The massiveness of solar panels compared to the size of satellites and the International Space Station speaks of the amount of energy necessary to maintain satellite function and communication in space. On average, one satellite produces and spends enough solar energy to power up 40 households.
If we could disregard the space pollution created from dying satellites, we could place space equipment in the category of renewable energy systems that are designed not only in view of but also for the environment (dfE) mostly because of the solar power harvesting, hydrogen fuel, and recycling-based thermal systems.
Since space equipment must survive in space for periods as long as twenty years, longevity and frictionless functioning in lack of maintenance are also essential. Such equipment is expensive. General electrical project best practices are an extra challenge, as are the safety risks. It doesn’t help that possibilities for software risk testing in space are limited and must be dug out in innovative ways.
If we take a look at all the sundry factors that affect space electronics and electrical components, it doesn’t come as a big surprise that it takes ages to realise a mission or launch new satellites. With such immense cost of damage, circumspection must be at the forefront of EEs minds.
