Figure 1. VPT specializes in the design and development of radiation-hardened and tolerant, space-grade DC-DC converter modules and box level power solutions. Source: VPT, Inc.

Radiation is a paramount risk factor for electronics deployed in space, accounting for early failures well within the mission life of the satellite or spacecraft. The level of screening for electronics such as power converters will directly correlate to its reliability with effects such as total ionizing dose (TID), single event effects (SEE) and neutron displacement damage (nDD).

Fully radiation-hardened (rad-hard) components have been traditionally used in space applications. However, there is an increasing trend toward the use of commercially available electronics in space due to their dramatic reduction of cost and lead-time when compared to their rad-hard counterparts.

This is where the commercialization of space with applications such as NewSpace comes into play: the combination of the shorter mission life and large scale deployments drive the necessity for cost optimization and shorter lead times. This balancing act between cost and reliability is actively being sought by space agencies and OEMs alike to better serve emerging space applications. VPT addresses this issue with an internal radiation hardness assurance (RHA) plan for the VSC line of DC-DC converters, striking a balance between the cost and time inhibiting factors of fully rad-hard components and the reliability issues of unscreened commercially available, non-rad-hard components.

How does radiation impact electronics in space?

In order to better understand what a device’s radiation tolerance is, it is important to understand how radiation can impact an electronic device in space. As shown in Figure 2, the major sources of highly energetic particles on the order of mega electron volts (MeV) are:

• Solar protons and ions
• Galactic cosmic rays
• Radiation belts (protons and electrons)

This is followed by lower energy sources such as hot plasmas and ionospheric plasmas that will have a more marginal impact on the radiation the electronics experience.

Figure 2: Sources of radiation in space and their effects. Source: VPT Rad

Test metrics such as TID, SEE and nDD are used to characterize the varying effects that radiation has on electronics. TID relates to the long-term impact of ionizing damage from protons and electrons while nDD is the long-term impact of non-ionizing damage due to protons, electrons and neutrons (typically tested with neutrons). SEE range from small transients or digital data corruption to destructive events that are caused by a single charged particle such as heavy ions and protons. These various metrics allow spacecraft designers to effectively test electronics in terms of how radiation accelerates the aging of the equipment (TID and nDD) as well as how any transient phenomena can cause changes in key components that could potentially lead to a system-wide failure from SEE. Transient SEEs are typically the result of a single, high-energy particle such as a cosmic ray that will deposit excess charge in the semiconductor material.

The radiation environment the spacecraft experiences will rely on several factors including:

1. When the spacecraft is deployed (during solar maximums or minimums)

2. Where the spacecraft will fly (LEO, MEO or GEO)

3. How long it is deployed (mission life)

4. Additional factors (mechanical shielding, spacecraft orientation in orbit, etc.)

Building all electronics subsystems to survive an absolute worst-case radiation scenario is not a practical approach for all space-based systems. Instead, system designers must be flexible to meet design deadlines by the launch date as well as any budget constraints. This might include ruggedizing SEE-sensitive parts in critical systems that must remain operational during periods of high radiation.

There is usually an acceptable degree of uncertainty based upon all these factors. Naturally, the more screening the various electronics subsystems undergo, the less uncertainties there are. However, the high reliability, fully rad-hardened part comes at a large cost and massive lead times. The problem is exacerbated with part-obsolescence where the lead time of the part must be balanced with the lifecycle of the overall system and its various subassemblies, this is a larger concern for commercial markets.

The commercialization of space and the emergence of NewSpace

The balancing act between budget, tight times to market (TTM) and potential overdesign is one that manufacturers in NewSpace are closely aware of. The modern space industry is using space in many non-traditional ways with massive constellations deployed for communications and internet, the monitoring of maritime, global forestry, space tourism, satellite or spacecraft servicing and repair, asteroid mining and more. With over 8,000 smallsats deployed since 2020, many applications within NewSpace are often defined by these more compact satellites launched into LEO with short two- to five-year life spans, making the entire project more affordable to launch and maintain.

According to Markets and Markets, $1.7 billion was spent on rad-hard electronics in 2023, a number that is meant to grow to $2.1 billion in 2029. This includes the aerospace and defense market with the influx of the relatively nascent NewSpace market. All rad-hardened electronics are expected to see a rise in demand including controllers and processors, analog/digital/mixed-signal devices, power management and memory. However, the power management devices are expected to lead this demand (Fig. 3).

Figure 3: Demand for rad-hard electronics by category. Source: Emergen Research

Procurement professionals within this industry have to balance screening and risk requirements to acceptable levels. In this commercialization of space, more companies are cropping up that do not require parts with the highest screening levels, namely the MIL-PRF-38534 Class K parts.

What is rad-hardened versus rad-tolerant?

If radiation hardness is viewed on a spectrum, a fully rad-hardened part would be the most reliable while unscreened, commercially available parts would be the least reliable. However, there is the in-between, and that would fall under “rad-tolerant.” A fully rad-hard part would follow a Defense Logistics Agency (DLA)-approved RHA plan.

The RHA plan is a process originally defined by NASA to ensure that the materials and electronics used within a spacecraft do not compromise system success when exposed to various levels of space radiation. This process is broken down based upon the established mission requirements (e.g., mission life), radiation hazards, assessment of a circuit’s response to radiation hazards, and finally parts categorization based upon TID, nDD and SEE performance. An RHA plan will have full characterization of the power converter and its components with worst-case analysis and will have performed the various radiation tests in accordance with numerous standards (e.g., Test Method 1019 Conditions A, C and D; Test Method 1080 per MIL-STD-750; and Test Method 1017 per MIL-STD-750 and MIL-STD-883) with much more stringent pass/fail requirements.

For a fully rad-hardened part, failure by a small .01% will result in it being positioned as “no-go.” Naturally, this level of screening will take time, drastically increasing the lead time on components. Another major factor to consider is BOM cost; rad-hard ICs that are purchased to go into another rad-hard power converter will have at least a hundredfold increase in cost. A radiation-tolerant part would not quite be an unscreened commercially available part or a full rad-hard part, but somewhere in the middle where the acceptable SEE and other radiation levels vary greatly based upon the application.

What does it mean for a DC-DC converter to be fully rad-hardened?

The MIL-PRF-38534 Class K standard for hybrid and multi-chip module (MCM) circuits, ensures that the converter and all the internal components are procured and screened to the highest reliability levels. In addition, converters that have an additional RHA rating from DLA ensure the device is of sufficient quality to meet the reliability levels required for the specific mission. Designers must often work from the ground up to ensure the converter is fully rad-hardened by either making internal circuitry resistant to damage caused by ionizing radiation, or by purchasing and integrating rad-hard parts. This approach ensures that the converter meets the space-grade component criterion.

Verification of these devices is accomplished by one of two quality programs, ultimately allowing manufacturers to land on the qualified manufacturers listing (QML). Prime military contractors and OEMs can access the QML to ensure their components meet the end-application’s reliability requirements. Many space customers will often require Class K qualified components, however, this can ratchet up the cost and lead time of the system greatly.

Using commercially available and automotive-grade components in space

The applications for more basic radiation screening have expanded even into other realms where components can remain viable with TID levels as low as 2 krad for TID and SEE at any level. Naturally, these numbers vary greatly between, for example, an academic project with limited resources launching a CubeSat in LEO and a large defense contractor with teams of researchers to analyze and assess the radiation tolerance of the satellite subsystems. It all depends upon the level of mission assurance the program requires. It is analogous to the amount of safety required in a professional racecar over a commuter vehicle; a five-point harness and roll cage might be necessary in a Formula 1 vehicle while basic safety features such as seatbelts and airbags would suffice for a consumer car.

More and more often, rad screening is performed on commercially available components, releasing radiation data without positioning the part as “go” or “no-go.” Many efforts are underway in government agencies, academia and industry to introduce commercially available or automotive-grade parts to space systems without compromising the success of the mission. Companies like VPT Rad have taken steps in this direction, releasing reports on the radiation tolerance of commercially available parts without modification, leaving it up to the customer to assess whether or not the part is rad-tolerant “enough” to integrate within their system.

Other approaches require customers to purchase specialized analog and microwave or millimeter-wave components, as well as processors or MCUs in bulk, and perform radiation testing to establish an acceptable lot for the spacecraft. Several OEMs have recognized this opportunity within the aerospace industry and are working with independent testing facilities to conduct radiation testing on their proprietary products and assign new part numbers to the radiation-screened components of an existing product line.

The compromise: A rad-tolerant converter with an RHA plan

Naturally, this obvious shift from rad-hard to rad-tolerant has called for a more nuanced understanding of the components in spacecraft, where devices that are critical to mission success may require more radiation tolerance. DC-DC converters are often seen as a key component in spacecraft, supplying a regulated DC output to main and auxiliary systems. Moreover, there is still a clear demand for power management components to be rad hardened in some capacity. And, while a full rad-hard DC-DC converter may not be entirely necessary to build and account for within a design, some type of RHA plan is often necessary.

VPT strikes this balance with an internal RHA plan that is built off the DLA-approved gold standard. The company is well aware of the DLA-approved plan as it has a legacy supplying space-grade, rad-hard Class K converters with established product lines (Table 1).

Table 1. Specifications of VPT's space-grade DC-DC converters. Data source: VPT, Inc.

The VSC Series is built and tested in accordance with the internal RHA plan. The converters also use non-rad-hard components and upscreen them, driving the cost of the VSC down significantly from its rad-hard counterparts. This series offers a distinct advantage over non-rad-hard, commercially available or automotive-grade options where the level of reliability of the component would remain questionable while also maintaining the advantages of rad-tolerant parts in terms of cost and lead time.

VPT, Inc.

Many NewSpace applications are lowering the barriers to space by creating a spectrum of acceptable radiation tolerance and risk, thereby accelerating the adoption of new technology and enabling more R&D in the space industry. VPT has specialized in space-grade power converters with a deep understanding of what it takes to make these components rad-tolerant at the device level up to finalized converter.

In order to meet the changing needs of the space industry, VPT offers rad-tolerant converters that provide a cost-optimized alternative to fully rad-hard converters while also employing a basic RHA-plan for basic quality assurance. Contact VPT today to learn more about their leading efforts in radiation assurance.