Is rocket science really that hard? The adage, "it's not rocket science," would have you believe so. And, spoiler alert: it's true – even for aerospace engineers. Rocket science, being in space, and making satellites are very difficult endeavors. This article examines why space is an extremely challenging place for electronics systems to be. We'll look at how we have overcome some of the most challenging parts of getting to and being present in space, and highlight some of our top tried-and-true, space-ready components products.
Getting to Space
For some components, the hardest part of aerospace is actually getting there. Humans have done a fantastic job of optimizing travel speed and comfortability here on earth; i.e., Rolls Royce suspension and luxurious private jet seats. But space travel has yet to see a “comfortability” renaissance. Ultimately, the largest challenge of getting to space, is the vibrations and acceleration involved with launching a rocket. With current rocket technology, many components are tested up to 14Grms while here on earth. This is to ensure they can withstand the astonishing power, movement, vibration, and sound associated with launching a rocket. Since all satellites currently get to space via rocket launches, the satellites themselves must be designed to withstand the same extreme forces as the rocket. In essence, satellite science is equally (if not more), difficult than rocket science.
Many components, such as semiconductors, perform surprisingly well under extreme vibration and acceleration. However, special consideration must be made for the fastening of these components. Their connections can be points of failure due to strenuous vibration. On the other hand, electromechanical components are especially prone to failure during the launch event, and less prone to failure once in space. In this case, special consideration needs to be made when selecting interconnects for use in aerospace connectors. They must be able to withstand far more strenuous events than most connectors on earth. A fantastic example of cutting-edge aerospace connectors is Amphenol Aerospace’s MIL-DTL-38999 Series III, which is capable of operating under severe high-temperature vibration through 200degC. It boasts many other space-proof features, too. Luckily enough, these vibrations are not permanent design factors that engineers must worry about -- accelerating to orbital velocity can be achieved in a matter of minutes.
Another design consideration involved with traveling to space, is the thermal shock resistance of a part. Traveling from the sunny, humid coast of Florida, where many US rocket launches occur, to the frigid -100degC (-148degF) temperature of space, can be especially challenging for highly thermally conductive materials. This is because they can rapidly change temperature and create catastrophic stresses within the material.
The Environment of Space
Once a satellite is in space, however, completely different design considerations must be made for the environment in which it will remain. Much like how the ecosystem of Iceland varies from the ecosystem of French Polynesia, the space environment varies vastly, depending on its distance from earth. Depending on where in space an electronics system will reside, very different considerations must be made to accommodate the challenges presented by its inhabited environment.
Pressure in Space
Space is a vacuum. It contains relatively zero pressure compared to the atmospheric pressure on earth. Since everything in a satellite is manufactured on earth, it inherently adopts the atmospheric pressures experienced during manufacturing. However, when those components are placed in a vacuum, they can perform quite differently than when at atmospheric pressure. To ensure that components will last in space, each one must be tested in a Thermal Vacuum Chamber (TVAC) which simulates the temperature and no-pressure conditions of space. For example, if, due to a manufacturing defect, the insulative potting rubber of a connector were to have a small air bubble encapsulated within itself, that air pocket could potentially become a catastrophic explosion under vacuum conditions.
Additionally, all materials off-gas under a vacuum, whereby they release relatively substantial amounts of gaseous material, which can significantly impede adjacent components. For example, outgassed materials can coat thermal or solar arrays. This can negatively impact efficiencies, fog up sensors or optics, and even corrupt essential thermal properties of adjacent materials. Often, in order to reduce the amount of outgassed material released in space, satellite materials and electrical components are off-gassed in TVAC chambers before they are sent to space.
UV Degradation
Most low earth orbit satellites, including the International Space Station, exist within the thermosphere. In these areas, UV degradation adversely influences material properties of electronic components. UV degradation can even change the molecular composition of materials, specifically by removing oxygen atoms from oxygen-containing materials. As a result, thermal control subsystems may not properly function, optics can be degraded, and solar arrays can become less efficient. Satellites that will live in low earth orbit must utilize special UV shielding for their electronics systems. This is to ensure that no UV degradation occurs and renders components inoperable.
Particle Presence
The thermosphere is roughly 85km to 500km above earth's surface, but the entire neutral environment is 100km-1000km, and includes both the thermosphere and exosphere. In this environment, loads of oxygen, nitrogen, and helium molecules exist. However, the same UV energy from the sun that causes UV degradation on satellite materials also causes molecular degradation of oxygen, nitrogen, and helium, forming their respective atomic versions. Atomic oxygen can oxidize spacecraft, causing eventual erosion of materials. As such, special precautions must be taken when selecting components, depending on their exposure to the space environment.
Ion Presence
In two specific areas of near-earth space, called the Van Allen Radiation belts, electrons and ions are trapped in specific bands of earth's magnetic field. These belts exist at 500km to 6000km and 13000km to 60000 km from earth’s surface. These conditions create a plasma environment, which is formed by solar-charged particles interacting with atoms, creating ions and free electrons. These charged particles trapped in the earth's magnetic field can land on satellites and create a charge build-up that is similar to static energy (when you rub your feet on the carpet). If this build-up occurs in isolated areas of the satellite, an electrical gradient can develop, and the built-up energy may eventually create an arc. Many electronic components are extremely sensitive to arching, so special precautions must be made to electronic system layouts in order to prevent catastrophic arcing events.
Radiation Environment
On earth, the sun's radiation is generally absorbed by the particles in our atmosphere, and certain layers of our atmosphere absorb specific bands of radiation. However, certain satellite orbits are susceptible to very high radiation environments. This can create undesirable conditions in which a single proton or neutron -- or electrons released from the sun or galactic cosmic rays -- can pass through materials. The most common source of single event upsets are galactic cosmic rays, but other forms of exposure to these charged particles can exist, too. Satellites outside of the earth’s magnetosphere are especially prone to these free-particle radiation environments. The magnetosphere generally protects the earth from these radiation events. Satellites with lower altitude and inclination are less likely to experience the effects of solar events -- they are well protected by the magnetosphere.
Unfortunately, these free particles can cause a single event upset (switching a binary 0 to a 1), meaning that a sensor may read the exact opposite of the actual signal, which can falsely influence a program. Also, these charged particles can potentially corrupt data stored in CPU memory during the latching window of a process. This can do irreparable damage to the CPU. Since CPU speed increases for nearly every process here on earth, higher clocking speeds are rarely found in space CPUs. This is because the increased speed (i.e., more latch windows), makes the CPU more vulnerable. Scientists have mitigated this by "hardening" the semiconductor material – manufacturing it with sapphire or gallium arsenide, both of which are less susceptible to radiation than silicon. However, hardening semiconductors in this way requires a complete overhaul of a semiconductor foundry, which implies astronomical prices.
Other methodologies, such as RHBD, implement standard CMOS fabrication, and build redundancies to achieve resistance against radiation. Triple Modular Redundancy, for example, creates three identical copies of every bit within the memory. During reading, all three copies are read, and the ‘correct’ copy is chosen by majority. This reduces the ability of a single particle to corrupt the memory. Two particles would have to simultaneously interact with two different identical bit copies -- in different places on the chip -- to create a false positive during the reading phase.
Conclusion
There are a multitude of environmental factors present in various areas of space, which makes it nearly inhospitable for electronics. In order to prevent the failure of any system present on a satellite, extensive precautions must be taken. This is especially important, since aerospace engineering cannot just take a deployed satellite to a "repair shop." The extreme specialization of every satellite requires extensive tracking, design consideration, and meticulous accuracy from nearly every engineer involved.
