Constellations of small satellites (smallsats) promise to bring tangible benefits to national security space (NSS) programs, where there is a critical need to minimize construction and deployment costs. Multiple smallsats, defined as satellites with launch mass of 500 Kg or less, can be built quickly and cheaply and then deployed rapidly and responsively to implement a network of NSS assets that address today's ever-changing threat landscape.

Until now, smallsat system developers have had only two component options. On the one hand, commercial off-the-shelf (COTS) components reduce cost and lead times but often must be adapted for space requirements; the alternative is more expensive components with longer lead times that are radiation-hardened by design and screened and qualified to QML Class Q and V standards. Now a third “sub-QML” option bridges the gap with a new class of components that combine the radiation tolerance of QML devices with a spaceflight heritage that permits lower screening requirements and associated shorter lead times.

Demand grows for NSS smallsats

Two enabling factors have converged over recent years to permit the emergence of multiple smallsat programs for NSS applications.

One factor is the reduction of launch costs: Competition in the launch-services market combined with the growth of commercial providers has exerted downward pricing pressure, to the advantage of all types of satellite operators worldwide. With their low volume and mass, multiple smallsats can be launched simultaneously, often with a larger satellite as the primary launch payload. The cost of launch services can be shared, reducing overall program costs.

The second factor favoring smallsat development is the ever-increasing capability of modern electronic components. This reality enables smallsats to pack more functionality in less volume and mass.

The availability of lower launch-service costs and the increasing functionality afforded by smallsats has given rise to some new and emerging mission models. With a constellation of multiple smallsats, reconnaissance missions can achieve much higher revisit rates over an area of interest. For tactical reconnaissance purposes, the rapid availability of current surveillance imagery can be a matter of life or death for the warfighter.

The appeal of smallsats is not constrained to surveillance and reconnaissance, however. Following the success of the Iridium, Globalstar, and O3B commercial communications constellations, additional smallsat communications programs have been proposed. Several are in advanced stages of development. These programs seek to provide high-bandwidth data-communications access to areas of the world that are underserved by today’s fixed terrestrial infrastructure. Smallsat communications constellations can also bring significant advantages to tactical military communications, where dedicated secure channels may otherwise be unavailable.

While most traditional satellite programs require the use of electronics components qualified and screened to very high levels, this approach poses cost and delivery challenges for NSS smallsat programs where the emphasis is on low acquisition costs and faster service entry. Switching to COTS components can introduce other costs – and trade-offs.

The COTS versus QML dilemma

By far the most common screening and qualification standards used for monolithic electronic integrated circuits (ICs) are defined in MIL-PRF-38535, which is published by the Defense Logistics Agency, part of the U. S. Department of Defense (DoD). Similar standards exist for hybrids and discrete semiconductors. Components qualified and screened in compliance with MIL-PRF-38535 are granted a Qualified Manufacturers Listing, or QML qualification. This requirement assures that mission objectives will be met but does add to cost and lengthens lead times as compared to COTS components.

Many have tried to trim smallsat cost and construction time by replacing QML components with COTS options that eliminate this screening. However, spaceflight hardware developers who select COTS components may still need to invest in proving they will meet all necessary quality, reliability, and radiation requirements. This assurance can be expensive and, too often, the choice of a low-cost COTS part can result in much higher cost of ownership.

As an example, while generic plastic-packaged COTS components offer intrinsically high levels of quality and reliability, they are not designed with the space-radiation environment in mind, nor are they built to withstand the shock and vibration of launch into space. Additional engineering work is necessary to characterize their radiation behavior and mechanical characteristics and to evaluate workarounds for any weaknesses.

The systems-engineering work required to mitigate radiation effects in radiation-soft COTS components can be extensive, time-consuming, and expensive. Further, given the relatively small quantities of components that constellation programs will purchase (hundreds of parts per year, which is very low compared to the millions or tens of millions of parts sold into consumer or automotive applications), many commercial COTS component suppliers will not be willing to spend time performing failure analysis, extended-temperature screening, radiation characterization, or other technical support activities for constellation programs. High-volume suppliers often do not provide traceability or change notifications for changes in foundry or packaging subcontractors. All of these are important factors for space systems developers, as consistency of supply is important when building spaceflight systems.

Further, while the high production volumes of plastic packaged COTS components bring a high degree of reliability assurance, space programs will likely run into situations where accidental damage may happen to components that are intended for, or already integrated into, flight hardware. As the contractor base for NSS programs migrates to providing lower-cost systems using COTS components, the need for technical support from component suppliers to support mission assurance objectives should be kept in mind.

The sub-QML option solves these challenges, offering a critically important combination of cost-reduction and space-flight reliability benefits that neither COTS or QML components can deliver.

Bridging the gap

The satellite industry has been served for many decades by a modest number of component manufacturers that have decades of history successfully supporting space missions and lengthy accumulated flight heritage on many programs. Some of these component suppliers offer products for low-cost satellite constellations where there is a need to deploy large quantities of satellites requiring large quantities of components. Radiation-tolerant but absent QML screening, these sub-QML products meet very high standards for reliability and radiation protection (Figure 1). The same parts can also be offered in plastic packages, which, although they are not compliant with QML, are well suited to certain smallsat applications.

Sub-QML components may not be the right choice for many traditional space programs that require the highest screening possible because of their strategic nature, or because the cost of the electronics content is minor compared to other development or construction costs. They are, however, ideal for smallsat constellations where it is critical to minimize the cost of construction and deployment of the satellites. Adopting a sub-QML approach to component selection can significantly improve cost without sacrificing the reliability or radiation tolerance that is necessary for deployment of space systems.

Several component suppliers today already offer sub-QML components for space applications. As an example, Microsemi together with its new parent Microchip Technology offers a total system solution with sub-QML FPGAs [field-programmable gate arrays], mixed-signal ICs, microprocessors and microcontrollers, discrete MOSFETs [metal-oxide semiconductor field-effect transistors], bipolar transistors and diodes, chip-scale atomic clocks, and precision oscillators.

For systems intended for national security missions, the use of radiation-tolerant sub-QML devices with lower costs and shorter lead times relieves smallsat system designers from the burden of qualifying COTS components for space applications, while reducing bill-of-materials cost. Further, the experience, dedication, responsiveness, and expertise in radiation tolerance that established suppliers of these space components bring to system developers can substantially reduce any risks associated with using generic COTS components. Working with these suppliers, developers can meet cost targets with the confidence that they are not putting mission objectives at risk.

Ken O’Neill is Director of Marketing, Space and Aviation, at Microsemi (A Microchip Technology Company). He has supported FPGA applications in space, aviation, and other high-reliability markets for 25 years. Before joining Microsemi, O’Neill served as a Design Engineer with Hewlett-Packard’s Computer Peripherals Group. Prior to that, he was a Design Engineer with Racal-Comsec Ltd. O’Neill holds a bachelor’s degree in electronics engineering from the University of Reading, England. Readers may reach Ken at [email protected].

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