Small satellites (smallsats) provide a cost-effective means of getting into space. In this blog, learn how solar array simulator enables ground testing for smallsats.
During 2023, 2,860 smallsats launched, constituting 97% of all spacecraft, according to Bryce Tech, an analytics and engineering firm.1 The smallsat market is expected to grow rapidly. Research firm Mordor Intelligence estimates it will grow from $166.4 billion in 2024 to $260.56 billion in 2029. Before being carried into orbit, the many smallsats launched in that period will undergo extensive ground test requiring accurate, reliable programmable power equipment, including solar-array simulators.
Launch statistics
The 97% smallsat launch percentage for 2023 mirrors that for 2022. However, smallsats made up 63% of the total upmass in 2023, up from 58% in 2022, in part because of a new definition that extends the smallsat label to satellites up to 1,200 kg. That extension allows the latest Starlink satellites to qualify for the smallsat category.
As for applications, 79% of the smallsats launched in 2023, including Starlinks, handle communications, while 13%provide remote sensing, and 7% are involved in technology development. The smallsat launches represented 267 different operators. Smallsats are a favored vehicle into space not only for governments and commercial enterprises but also academia. Bryce Tech reports that more than 200 academic institutions launched smallsats between 2014 and 2023.
The smallsats rode aboard 164 of 221 orbital launches during the year. NASA cites three launch paradigms for getting smallsats into orbit.2 Dedicated launches provide control of when to launch and where to go and enable last-minute updates. Traditional rideshare launches carry secondary smallsats in addition to a primary payload—this approach can be cost-effective, but the primary payload determines the orbit, which may not be optimal for the ridesharing smallsats. And multimission launches carry multiple smallsats only, with no primary payload. Operators also have a choice of deployment methods, ranging from CubeSat dispensers to circular-pattern or a multi-point separation system. Finally, deployment from the International Space Station is also an option.
Power-system ground test
Whatever launch options operators choose, their smallsats require extensive ground tests of equipment ranging from transceivers to instruments. Of particular importance is the electrical power system (EPS), without which none of the other equipment will work. According to NASA,2 as of 2021, more than 90% of satellites in the nanosatellite/smallsat form factor were equipped with solar panels and rechargeable batteries, and these satellites will require solar-array simulators for ground test.
Smallsats often differ from larger satellites in their approaches to solar power. Large satellites most likely employ simple and reliable shunt regulation. In contrast, smallsats must maximize the power they can extract from their comparatively small arrays. Consequently, they often rely on a more efficient maximum power-point tracking (MPPT) scheme.
MPPT options
To understand how MPPT works, consider the well-known maximum power transfer theorem from the mid-19th century. The theorem states that if you have a power source with a known output impedance, you can maximize the power transfer to a load by setting the load impedance equal to the source’s output impedance. A solar array presents a complication for applying this theorem—its output impedance varies continuously with temperature and irradiance. A satellite’s MPPT controller, therefore, must continuously monitor the array’s output I-V curve to ensure operation at the maximum power point (MPP).3
An MPPT controller can take several approaches.4 The perturb-and-observe method continually applies step changes in the operating voltage, moving up and down the I-V curve looking for the MPP (Figure 1). With this approach, a small step size increases accuracy, while a large step size speeds response to changing array conditions. The incremental conductance approach applies similar principles to locating the MPP, but it relies on the improved digital-signal-processing capabilities of modern microcontrollers to improve speed.
Figure 1. A smallsat EPS must track the MPP (within the blue oval) along an I-V curve.
Other approaches to MPPT vary in complexity. One approach is to simply measure open-circuit voltage or short-circuit current and define the MPP as a fixed percentage of either. A more complex artificial-intelligence approach applies open-circuit voltage, short-circuit current, temperature, and irradiance data to a neural network that then estimates the MPP.
Exercising the MPPT
Whatever approach is chosen, the MPPT controller requires extensive ground tests. AMETEK Programmable Power’s 840-W Elgar mini-Solar Array Simulator (m-SAS) excels at this and other smallsat tests. Specifically for MPPT test, m-SAS features low output capacitance and a high-resolution I-V curve that closely matches a solar-array I-V characteristic such as the one in Figure 1. It can also simulate dynamic conditions with a 250-Hz tracking speed.
In addition, m-SAS offers eclipse irradiance profiles that can simulate any eclipse scenario that a smallsat might encounter in low earth orbit. It also offers cost-effective protection features tailored to the requirements of the smallsat market. For more on smallsat test and the m-SAS, see our white paper, Solar-Array Simulator Enables Small Satellite Ground Test.
REFERENCES
- Smallsats by the Numbers 2024, Bryce Tech, March 2024. https://brycetech.com/reports
- State-of-the-Art of Small Spacecraft Technology, NASA, February 2024. https://www.nasa.gov/smallsat-institute/sst-soa/
- Moyo, R., et al., “The Efficacy of the Maximum Power Transfer Theorem In Improving the Efficiency of Photovoltaic Modules: A Review,” ResearchGate, April 2020. https://www.researchgate.net/publication/340449393_THE_EFFICACY_OF_THE_MAXIMUM_POWER_TRANSFER_THEOREM_IN_IMPROVING_THE_EFFICIENCY_OF_PHOTOVOLTAIC_MODULES_A_REVIEW
- Baba, A., et al., “Classification and Evaluation Review of Maximum Power Point Tracking Methods,” ScienceDirect, May 2020. https://www.sciencedirect.com/science/article/pii/S2666188820300137
