Keep Pace with Satellite Power Demands
Satellites are evolving more quickly and launching in higher numbers, spurred by rapidly growing Low Earth Orbit (LEO) constellations and expanding satellite capabilities. With advanced RF systems and increased computing power onboard, modern satellites can direct and shape signal beams and process networking protocols and applications. Adding powerful AI processing capabilities could even enable satellites to serve as space-based data centers. These trends drive rising requirements for satellite power generation and distribution, which remain constrained by both size, weight, and power (SWaP) and the physical and economic limits of launch vehicles. As satellite power systems face increasing demands and system complexity, engineers can leverage lab-based power-emulation configurations to assess their system’s performance in scenarios that affect the performance of satellite solar arrays and battery packs.
How Do Satellite Power Demands Vary by Orbit?
To understand why satellite power is getting more complex, engineers need to consider the rising development of more satellites of various sizes, orbits, and mission capabilities. They are summarized below from lower to higher electrical power demand:
Low Earth Orbit satellites, now numbering in the tens of thousands, were among the first NewSpace technologies to lower the cost of launching missions. Many LEO satellites are CubeSats, which are small, modular platforms typically built from commercial-off-the-shelf (COTS) electronics modules. LEO platforms often operate in coordinated constellations for non-terrestrial network (NTN) services or operate individually to run experimental missions or unique exploration. The shorter distances between LEO satellites and Earth require less RF transmission power while yielding lower latency.
Medium Earth Orbit (MEO) platforms, which number in the hundreds, offer more predictable orbits. A semi-synchronous orbit, for example, passes over the same two points on the Equator each day, which is useful for navigation. Radiation at those altitudes does impact reliability, however, thereby requiring mitigation. RF transmission power is also higher for MEO satellites.
High Earth Orbit (HEO) platforms are the largest and most complex satellites, dubbed “exquisite” by planners. HEO satellites commonly use the Geosynchronous Earth Orbit (GEO). Their larger payloads enable complex missions, such as high-resolution imaging and surveillance. However, RF transmission power grows with larger distances to cover, requiring the satellite communications system to overcome more interference.
As the number of satellite platforms rises across orbits, the demand to launch and bring platforms online more quickly also increases. These trends leave less time to design and validate each unique power system design.
What Components Make Up a Satellite Power System?
Ideally, an evaluation of satellite power system requirements will include three common dynamic subsystems: a photovoltaic array for generation, power conversion and management, and energy storage, as shown in Figure 1.
Figure 1. This graphic shows a basic satellite power system. [Credit: Dr. Frankie Zhu, Hawaii Space Flight Laboratory (HSFL)].
Requirements vary with satellite size, features, payload, and mission. At the low end are modular electrical power system (EPS) cards plugged into a CubeSat backplane, providing a few common voltage rails coupled with a simpler, integral-mount photovoltaic panel and a rechargeable battery or supercapacitor pack.
Higher-end LEO, MEO, and HEO platforms with more power demand may rely on multiple photovoltaic panels, possibly with orientation capability, and a power-conditioning and distribution unit (PCDU). Often, PCDUs come fully integrated with a solar panel controller, power conversion, and a battery subsystem, with packaging ready for avionics rack mounting. Whatever the configuration, PCDUs must deliver reliable system power under all conditions, maintaining full readiness to ensure proper satellite payload and actuator operation.
How Do PCDU Designs Handle Thermal Management?
Current running through a system leads to power dissipation at points of conversion and switching. Pushing for smaller designs increases power density. If too much power dissipation concentrates in too small a space, however, overheating can occur and cause failures. Elevated temperatures over longer periods reduce reliability and mean time between failure (MTBF), thereby compromising the intended mission life. Designers must anticipate operating conditions and balance power density with thermal density. Semi-custom PCDU design is common practice among satellite avionics manufacturers, typically basing new designs on a similar unit developed for another satellite program.
Each design is unique in terms of the physical space and weight available on the satellite, the configuration of solar arrays and batteries, and the number of rails and the required wattage delivery. More complex PCDUs offer high-power switching, surge protection, and power sequencing. PCDUs, whether procured or designed in-house, become devices under test (DUTs) during the integration phase. Power supplies and passive electronic loads have served as test stimuli in many design evaluation efforts. However, today’s complex satellite power designs call for advanced testing under a broader range of realistic scenarios.
How Can You Validate Satellite Solar Array and Battery Performance?
Given the breadth of satellite orbits and the varied approaches to power system design, it can be difficult to recreate and test the exact environmental and operating conditions an orbital platform might experience. Yet accurately recreating foreseeable conditions during the power system design phase is essential, as post-launch power outages can temporarily put satellites out of service, or worse, turn them into multi-million-dollar bricks orbiting the planet uselessly. Many power design approaches adopt a min-nominal-max philosophy for testing and evaluation at a few operating points. However, the behavior of solar arrays and batteries is far more complex than simple models can capture, making the case for more sophisticated subsystem emulation shown in Figure 2.
Figure 2. This simplified graphic of a satellite design illustrates how three types of emulation units could replace subsystems for more comprehensive testing: the Keysight MP4300A Series Modular Solar Array Simulator, RP5900 Regenerative Power System, and EL4900 Regenerative Electronic Loads.
Satellite power systems should receive at least as much design and test attention as payloads and satellite control systems, as a power failure can quickly cripple an entire satellite. A setup for comprehensive satellite power emulation is reusable across multiple satellite programs, perhaps with some scaling as megawatt-ready designs appear. The time spent in lab emulation can help identify potential failures that would otherwise only appear in space, too late to fix and, in most cases, too expensive to fix by another replacement satellite launch.
Emulation gives engineers greater flexibility to design comprehensive tests that reproduce real-space conditions and ensure systems perform as expected. With growth surging in satellite development and deployment, such capabilities boost confidence in system design and performance while supporting the test and evaluation of new approaches to satellite power systems.
Learn more about satellite power challenges and solutions in the white paper, “Design Satellite Power for Dynamic Orbit Realities.”
Find out more about Keysight’s space and satellite solutions here.
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