Radiation

Whether in the higher reaches of what is considered the Earth’s atmosphere or wholly outside of it, radiation is a much more important consideration and challenge to operation than would be faced by any Earthbound system. There are various types and sources of radiation out in space, and I will certainly not cover them all in this book as they are not particularly relevant to the cybersecurity professional. On the other hand, the fact that the electrical systems that allow a SV to operate are subject to higher amounts of radiation does affect their operation. Computers communicate in 1s and 0s at the most basic level, and those 1s and 0s are on and off switches of electricity. It is pretty straightforward to see how high doses of radiation energy could hamper or destroy electrical systems operating on finely tuned flips of an on/off switch.

SVs are subjected to radiation in two fashions and with differing degrees of severity and impact. There is the more easily planned for and understood buildup of radiation absorption by the SV simply due to the radiation emitted by our sun and other distant stars at a constant rate called total ionizing dose (TID) . Day-to-day and early on, the effects of this are negligible; however, the long-term exposure to such radiation can cause the functionality and accuracy of electrical computing actions to become degraded. The other type of radiation exposure is that from significant events, for example, proton flux, which may in a single exposure present more threat to the SV than the duration of radiation accumulated during an entire operational window. These types of events could be stellar activities such as solar flares or even originated outside the solar system in the form of gamma-ray bursts and other phenomena which may immediately damage SV components.

On Earth electrical systems are largely shielded from such events and solar radiation by the atmosphere and electromagnetic fields of Earth. In space, shielding can and often is implemented to help prevent radiation from presenting an unacceptable level of risk toward mission accomplishment. This will vary depending on the type of SV and the purpose and importance of its mission. Designers of a small satellite, with a planned operational window of only one year, may decide that the weight and space taken up by such shielding would not be worth the protection from accumulated radiation. Since the SV is not intended to operate long enough for that to become an issue, it would potentially be a waste of other resources if the risk were not simply accepted. In this type of situation, the SV would presumably be rolling the dice on a singular event hitting the unshielded system and damaging it. Other systems with longer operational windows of multiple years or decades may choose to shield from radiation some or all of their components. This would specifically be the case on systems where human life is also in the balance such as commercial space flight, government space programs, and complex systems like the space station.

Temperature

Though less prone to irregular or singular events that could impact SV operations, the extremes and swings of temperature in space can have impacts on the electrical computing systems. With radiation some aspects were largely predictable such as exposure to solar radiation and how that energy would accumulate over time in onboard components. Temperature is coped with in a similar manner to radiation where the SV has to be built to certain standards to survive normal life in space but also could receive insulating coatings and materials to prolong the SV life in the face of long-term exposure to the swings and excesses of hot and cold in space.

There is also a similar tradeoff to radiation mitigation in coping with the further ends of temperature measurements a SV may be exposed to. Weight and bulkiness of SV components will tend to grow as these types of solutions are applied and may not have adequate cost benefit in extending the SV life cycle to be worth applying. Many missions will find the line of acceptable risk for temperature exposure and work to that. This is mostly considering orbital systems around the Earth where we have good, reliable, and regular data on temperature variations and can make well-informed risk acceptance decisions. This becomes much more difficult when considering SVs that will not be on a regular orbit or orbit at all and where temperature data may be less well known and more dangerous to the spacecraft.

Space Objects and Collisions

There is a lot of junk orbiting our planet. Each time humans launch a satellite or rock or put anything high enough above the Earth, we are potentially leaving it there for years, decades, or longer. Additionally, there are several specific orbital elevations and planes that are specifically suited to the operations of different kinds of SVs with different missions. As such, these locations in the space around our planet are particularly crowded. Don’t get me wrong, space is big, really big, even in the immediate orbital vicinity of our planet. That doesn’t mean though that collisions can’t and don’t happen, they do and will increase in probability as space becomes more widely accessible.

There are essentially two types of things in outer space, those we put there and those that are naturally occurring. In our near-term future operating in space, the greater danger to SVs is posed by debris and junk as well as other operating SVs residing in the space around the planet. As with the other space challenges we have covered, space objects present another opportunity for risk acceptance and/or avoidance. If a collision is likely between space objects, those operating those objects can either accept the risk or avoid it. In accepting risk, the operator has hope that the odds of the objects actually making contact in their passing near each other are low enough to not actively deal with.

Close enough for potential collision may be calculated by one SV operator as passing within a mile of another object in space. That is still a pretty wide margin, and in some situations the decision may be to maneuver the vehicle to a slightly different orbit to avoid the other object. In some situations where the SV does not have its own position or attitude adjustment capabilities, there may be no choice at all, only an ability to observe. This brings us to an interesting point. If one SV cannot maneuver and is on a potential collision course with another SV that can, does the maneuvering vehicle get to send a bill to the non-maneuvering SV for wasting part of its propulsion capabilities or mission window on maneuver? This may seem ridiculous if one cannot maneuver, but what if both can, and one operator makes a decision to accept the risk and the other to avoid it? What if the SVs are owned by different corporations or countries? There is no currently well-established legal doctrine dictating how operators of SVs should behave in such situations and where things like liability and costs should fall or be split.

Less complicated from a logical and decision-making perspective but perhaps far harder to implement is the avoidance of naturally occurring space objects. Imagine a scenario where a comet is passing close enough to the Earth that it passes through a popular orbital plan. It leaves a trail of ice and debris behind it during its pass of the Earth and now hundreds or thousands of SVs may need to attempt avoidance maneuvers. There are also natural space object considerations necessary as we look to missions that are more and more frequently going to leave the relatively well-known and friendly confines of Earth’s orbit.

Gravity

The earliest challenge presented to space operations of all shapes and sizes is gravity. You have to get your SV far enough away from Earth and travelling at the right direction and speed to economically stay within the space domain and not burn up in the atmosphere or crash to Earth. The struggle of early space programs was escaping the pull of gravity to even initially achieve space flight and eventual orbit of the Earth. Now, the SVs orbiting the planet are more concerned with maintaining the right speeds and trajectories to keep falling around the Earth and not into it.

We are now at a point in modern-day space operations where it is again a tradeoff instead of a direct challenge. If a SV needs to orbit close to Earth for the purpose of its mission, where is the acceptable tradeoff with how close it orbits because it will be falling/travelling at higher speeds and will require more energy or propulsion to maintain that orbit and not fall into Earth? On the other hand, it may be acceptable to degrade the performance of the mission slightly by orbiting higher but expending fewer resources to do so and having an extended operational life span.

Like the challenge of temperatures in space, understanding of the gravitational effects around the planet is very mature, and there is a lot of flight heritage to base risk decisions on with regard to addressing gravity during the launch and operation of a SV. The same cannot be said as we move further away from the planet. It was a lot more complicated to figure out the impacts of gravity on the long-duration missions to the moon than it was to understand how gravity affected the orbits of earthbound satellites. The complexity of the gravity problem will only increase as we move further from Earth and conduct increasingly complicated extraterrestrial or interstellar missions.

Testing

There is a whole lot of testing that goes into the validation of a SV’s ability to survive and operate as intended in outer space. A lot of testing is a check on whether or not the vehicle will survive the environmental challenges we previously discussed. At first it may be hard to accept that testing of the SV as a validation for space flight wouldn’t make a lot of sense as a challenge for operations, but it is very much so that. Let’s start with SVs are expensive, even small satellites, often known as smallsats or cubesat; the size of a loaf of bread can be multimillion-dollar programs. Components are expensive, testing is expensive, and launch is expensive.

Before you are comfortable launching your satellite into space, you want to make sure it can handle being in space and also will function after the launch itself. You have a couple options. You can build an expensive exact replica of your SV and subject it to environmental testing to see if your operationally intended unit is likely to survive. On the other hand, you can take the operationally intended SV itself, not build a copy, and subject the operational article to testing. This testing can cover many different aspects of what the SV will face in space. You will want to test it for its ability to survive temperature extremes and swings. You will want to test it in a vacuum similar to what it will operate within in outer space, you may want to test how it handles radiation exposure, and you definitely will want to test whether the vibrations it will encounter during launch will affect its deployment and operation.

To accomplish this testing, you have either spent a bunch of money, time, and resources assembling a SV article to be used solely for testing or you risk using the operational article or articles, and they could be damaged during testing to the point where you miss your assigned ride into outer space or have to scrap the program all together. Make no mistake, places that can subject SVs to such testing are also not cheap and are not prevalent so scheduling and paying for such tests are also highly impactful decisions to the overall success of a space system operation.

Launch

Whether a space system is operated by commercial entities, academic institutions, or government agencies, they all have to compete and prioritize rides for their SVs on a launch vehicle to actually get their SV(s) into space. There are multiple considerations when a space program chooses the launch vehicle it will utilize. The launch vehicle has to be available during a window that suits the planned operation of the space system. If you get a ride too soon, you may miss it due to project issues; if it is too late, your SVs’ mission may no longer be relevant by the time it gets to space and becomes operational.

Beyond project management decisions surrounding launch are other issues that pose challenges to space systems. We covered how vibrations during the launch process may damage or impact the SV. Different types of rockets for different SVs subject their cargo to different levels of shaking and vibrations. Ruggedizing the SV to survive the vibrations of whatever launch vehicle is available or necessary to achieve appropriate positioning in space is an option. On the other hand, any increase to weight or form factor can increase costs of launch exponentially. It is not cheap to get a SV into space, on the order of hundreds of thousands of dollars for a loaf of bread-sized SV, with larger SVs having exponentially increased costs and lesser availability of launch vehicle choices and launch windows to utilize.

The big takeaway with regard to the challenge of launching a SV is that even if every other aspect of SV design, development, and operation were planned and implemented perfectly, launch constraints and issues could completely derail a space system before it gets started in its operational life span, and this challenge can fall completely outside the control of those in charge of the space system. Even then if everything else lines up, the launch vehicle can blow up on the launch pad or during its flight as well as potentially flying in a suboptimal trajectory which won’t achieve the positioning required to place the SV into an operationally suitable orbit or flight path in outer space.

Deployment

So, your launch vehicle did its job to perfection and achieved the required position in space for the deployment of your SV. There is still present a challenge in successfully deploying from the launch vehicle and into outer space. A lot of engineering goes into how SVs are deployed from their launch vehicle, but vibrations of launch and other issues can cause deployment to not go as planned. This is another reason for the testing to be as thorough as possible.

If vibrations or temperature variations or the vacuum of space negatively impact the ability for certain latches or fasteners to unhook and let the SV leave the launch vehicle, it will never begin its operational life. If the mechanism for separation, whether mechanical or via propulsion, does not operate to an expected degree of accuracy, the vehicle may be damaged or not placed into correct or recoverable positioning. There are also portions of a SV that once separate from the launch vehicle must be themselves deployed.

This could be solar panels which need to unfold or antennas that need to unwind or extend. The same environmental and operational space challenges that affect deployment from the launch vehicle can hinder or damage these components and processes and end the space system operational window before it begins or significantly impact it. Imagine the SV had two sets of solar panels but only one deployed. Now the SV must try and conduct its operational mission with half the energy production available to it. This could take away from half of the entire operational window of the space system.

Detumble

Once the SV has successfully separated from the launch vehicle and deployed any movable components like solar panels and antennas, there is a need for stabilization. At this point, whether from the deployment or the launch vehicles’ own position and rotation, the SV may be in a tumble, it may not be in exactly the right orbital plane or it may not have the necessary attitude to conduct its mission. The challenge of stabilization is present post deployment and to a certain extent is also required for position and attitude maintenance or alterations during the operation of the SV.

In some SVs and their specific missions, certain tumbles or lack of exact attitude or position may not be an issue, and stabilization need only occur to a certain extent acceptable for the operation of the SV and its mission. No matter the extent stabilization is required, it will be necessary to some degree and accomplishing stabilization involves the use of onboard resources such as electrical energy or propulsion fuel as well as time. The decision on whether to expend resources quickly to achieve stabilization or use less over a longer period to stabilize the SV falls on the operators of the SV. These decisions must be made based on the impact to the operational life span of the SV and how the expenditure of fuel or the passing of time affects the mission. In some cases, there may not be an opportunity to make such decisions; if the only option for attitude or position correction and detumbling is torque rods and momentum wheels, it may take a very long time, months even, before the SV can carry out its mission. If the operational window of the spacecraft with regard to temperature and radiation was only a year, the space system has now wasted a large percentage of its life span on stabilization. This further amplifies the need for adequate testing, well-informed decisions, and stable and expected launch and deployments.

Power

Power on a SV is an extremely constraining factor for its operation and its survival. Even after successful stabilization, and stabilization that did not require unexpected expenditures of energy or propulsion, the energy budget for a SV is deterministic in its ability to conduct its mission, stay in correct position and attitude, as well as communicate down to ground stations. We have already also discussed how unsuspected maneuvers to avoid collisions may impact the power budget of the SV. Stabilization and maneuvering may take so much of the SV’s initial or stored power budget that it must spend the next orbit or two doing nothing but charging its batteries with its solar panels and not conducting mission activities or even communicating with the ground.

The operational window of a spacecraft is planned out in regard to power generation via solar panels or potentially other means, power storage via batteries, and power consumption from the bus and payload of the SV. Everything centers on the survival of the SV, which is why if the power consumption of maneuvers, stabilization, or even conducting mission activities endangers the ability of the SV to continue to fly, it must prioritize maintenance of its power budget via increased charging. The long story short of power and SVs is that there is a finite amount that can be generated and stored. Just because a SV is in orbital position to take a picture of with its payload doesn’t mean that it is within the power budget to do so and maintain optimal operability. Power impacts the operational window of the SV in its totality as well as intermittently during the course of the operational life span as the SV must maintain power budget for flight even at the expense of payload operation and mission tasking.

Emanations

Wouldn’t it be a shame if once the SV made it to its proper position and orbit in space, the mission conducting payload, intent on listening for certain signals, was unable to distinguish those signals from the emanations radiating from the SV itself as a result of its communications and day-to-day functions? Worse yet, emanations from a payload emitter could impact the ability of the ground station to communicate with the SV itself.

Emanation challenges are complex but can be tested for and designed around. The difficulty with emanation testing compared to some of the other testing we have discussed is that it is very difficult to replicate the quiet of space here on Earth where there are millions of radio, cell, GPS, and other signals being emitted from devices everywhere. To test whether emanations from one part of the SV will impact the functioning of other onboard components, you have to get the SV into a place where no other signals would impact the results. These types of places, known as anechoic chambers, are not very common, and testing emanations can be more expensive and hard to come by than other tests. Depending on the payload mission and bus communication methods designed for in the space system, such chambers may be required beyond nominal self-compatibility testing of emitters and sensors to address the risk of finding out in space that emanations are an insurmountable problem.

Frequency

Even beyond the emanations of the SV, there is the concept of signal pollution which may not be hugely impactful in space, but to the ground station trying to talk to the SV through all the signal noise on Earth, it can be a serious problem. Choosing the right wave frequency with which to carry out radio communications between SV and ground station is an important design decision. Frequency can impact the type of antennas, the directionality of signals possible, as well as the reliability and bandwidth available across that signal frequency.

Unfortunately, frequency is not just a challenge in regard to choosing the right type of communication signal for the SV and ground station to utilize, but it also must be available and legal. Unlike other aspects of space operations such as collision avoidance maneuvering, frequency use is an enforced aspect of space system functionality. In fact, space systems must apply and register for the frequency they would like to utilize, and it must not conflict with other frequencies of signals already in use and registered or set aside for specific emergency or military use. Similar to launch windows, this is a third-party controlled constraint where another organization is determining whether or not the frequency you say you need is OK for you to utilize. This means that frequency determination must be made early on and registration complete and successful before design and development get too far down the road. On the plus, registration of signal frequencies means there should be less impactful noise to compete with when trying to talk between the ground station and the SV. You wouldn’t want to try communicating over the same frequency as cell phones as the noise level present would be extreme and may make successful communications to or from the ground station impossible.

De-orbit

Space junk and debris are a growing problem and will only exponentially increase with the accessibility of space operations. To address this, there are certain de-orbit requirements depending on where in relation to Earth your SV will operate. Whether via orbital positioning, position adjustment, or propulsion reserves, you have to be able to prove that even after the operational window of your SV has concluded, the SV will burn up in the Earth’s atmosphere within a predetermined time span. This is done to declutter the popular orbital positions and planes around the planet.

Though not required of every SV, this type of requirement is something I imagine will be levied against more and more space systems moving forward to try and tamp down on the space junk problem. Thus, it must be added to the challenges of space system operation since carrying onboard propulsion for de-orbit or maintaining power creation, storage, and utilization by torque rods to enter a de-orbit trajectory far beyond the operational window of the spacecraft must be proven. This means potentially added weight, components, or other constraining attributes to an already complex operation.