A multi-purpose satellite bus is designed to accommodate several different payloads for various space missions. Thus, instead of focusing on a single mission goal like Earth observation or meteorological forecasts, a single spacecraft bus can carry out a set of different tasks, thus reducing the costs of a space mission. No doubt, there are certain peculiarities satellite bus manufacturers will have to consider when designing a multi-purpose platform, but this extra effort is well worth it considering the pace of our space exploration efforts today. So, let’s take a better look at satellite buses, their goals, designs, and objectives they can accomplish.
What is the function of a satellite bus?
Satellite buses are platforms that host all electronic equipment necessary for the spacecraft’s proper functioning. The satellite can be set to perform all sorts of tasks, from taking pictures of our planet to sending navigational data back to earth. Regardless of the actual mission objective, the main function of each and every satellite bus out there is to ensure that a satellite copes with its goals correctly. To this end, satellite buses carry payloads necessary for a spacecraft to work. This could be a rather complex structure, including computers, thrusters, and trusses to hold all of that equipment together. But why is it called a satellite bus? Mostly because all of that equipment is placed on a single, usually elongated, platform. The term is not space-technology-exclusive because you can find buses in other complex machines, for example, industrial freight cranes. But let’s take a better look at satellite bus design and structure.
Satellite Bus System Design & Main Components
Despite some minor variations that depend on the spacecraft’s purpose, a typical satellite bus structure includes a set of standard components, such as:
- Computer to ensure command and control from the ground station
- Transmitters sending signals to the ground stations
- Trusses connecting multiple payloads together
- Thermal control systems to maintain proper spacecraft temperature
- Thrusters and other necessary propulsion systems to make sure the spacecraft can adjust its position when necessary
Those systems are absolutely essential for any satellite bus, no matter which particular function the spacecraft caters to. The additional payload may include various sensors, radar, and other equipment necessary to fulfil mission goals.
The more objectives the spacecraft has to meet, the more complex the satellite bus structure can get — especially so when it comes to electronics. Often different payloads installed on a multi-purpose satellite bus require a different power supply and, consequently, voltage. So, when wondering — ‘What is satellite bus voltage?’ Always keep in mind that there is no rigid universal parameter. So far, 28 VDC is the most common figure, but the actual satellite bus voltage can be higher or lower than this widespread figure.
Any multi-purpose satellite bus (MPS) can accommodate at least two, possibly more, payloads. Often, payloads may have different configuration requirements, not only when a power supply is concerned. For example, payloads will have to be ‘matched’ in terms of axis control, altitude parameters, and even thermal requirements. Let’s consider an example when a satellite bus manufacturer intends to combine meteorological forecasts with high-frequency communication.
Traditionally, meteoritical satellites would have to be placed in sun-synchronous orbit, while communication ones — in a highly elliptical orbit. However, experiments with multi-purpose satellite buses, including studies from NASA, have proven that these two can be ‘reconciled.’ In this particular example, the spacecraft would have to use two different axes and two different altitude control systems.
Another challenge when configuring MPS is thermal control, as different payloads may have different specifications here, too. Any payload with infrared sensors, which is a common parameter for weather and EOS spacecraft, must maintain a specific temperature range to ensure its functionality. Communication spacecraft are often less picky in this regard, but generally, altitude control and thermal systems pose the greatest challenge for bus manufacturers.
The final critical parameter is the weight of the final assembly. Today, most satellite buses are roughly divided into three categories depending on how much payload they can carry. One might assume that the more a spacecraft can carry, the more versatile it is going to be. In practice, this is not always so. Often, more lightweight electronics can cope with more functions than large, heavy onboard computers and sensors.
All in all, spacecraft technology is evolving rather rapidly, and today’s buses can carry out more than just two different purposes. Besides, there is a strong tendency to tech miniaturization, which means that most spacecraft components become smaller even when their functionality increases. So, perhaps at some point in the near future, we will not have to talk about single-purpose satellites as the new generation of spacecraft will be able to cope with several tasks at once.