Vicor Corp. has recently announced that its radiation-fault-tolerant DC-DC converter power modules will be used in Boeing-manufactured O3b mPOWER satellites. The O3b mPOWER ecosystem is a constellation of satellites in medium earth orbit (MEO) that SES will use for delivering global connectivity services to customers around the world.

A shifting focus to LEO and MEO satellites

There are basically three major types of satellites: GEO, MEO and LEO. Geostationary earth orbit (GEO) satellites require fully radiation-hardened components, and therefore are very expensive. Each satellite can cost up to $500 million, and has to last 15 – 20 years to make it worthwhile. The main advantage of GEO orbits is that at a height of 35,000 kilometers it is possible to cover a very wide geographical area with as few as three satellites.

Medium earth orbit (MEO), is between 5,000km and 12,000km in altitude, requires a constellation of 10 to 20 satellites to achieve a global coverage. Since this orbit is inside the Van Allen belt which protects the Earth, electronics providers have the leeway to use radiation-tolerant COTS solutions.

Low earth orbit (LEO) usually includes a constellation of hundreds or even thousands of satellites for stable global coverage, which makes it the growth segment of this market going forward. With LEO, there is even more leeway to use radiation-tolerant products, while mission requirements are somewhere in the 3-to-5-year range.

More satellites earmarked for New Space

“Low Earth Orbit missions are typically part of what we call New Space or Space 2.0. This market has lower cost compared to deeper space orbits, and are largely focused on increasing the internet bandwidth while at the same time reducing latency,” said Rob Russell, vice president of satellite business development at Vicor.

Low transmission latency and high throughput are essential requirements for applications like 5G, live TV, military communications and financial trading. As many of us have experienced, satellite television transmissions are subject to a delay (latency) of a few seconds compared to terrestrial or cable transmissions. While this delay can be annoying during sports events, for example, the consequences can be far worse when affecting military communications on a battlefield.

Latency issues are also very important in financial trading since even a delay of one millisecond can make the difference between a profitable operation and one with losses. In high-frequency trading, a huge number of financial transactions are performed with a profit which can be as low as few cents for each operation, and therefore reduction in latency is a big deal. The same considerations apply to the roll-out of 5G technology, where huge use of bandwidth and extremely low latency are mandatory for telecom, IoT, and other next-generation services, such as autonomous vehicles.

Besides high bandwidth and low latency, another advantage of LEO applications is the coverage, as multiple overlapping ranges can achieve total earth coverage.

“Bringing broadband to places where they can’t get it is a huge plus. One of the main goals of O3b, which stands for other three billion, is to bring broadband internet to the many people in the world for whom it is otherwise unavailable today,” said Russell.

In order to get full coverage in LEO applications, hundreds or even thousands of satellites are needed versus as few as three for GEO. That means high-volume commercial parts are needed to reduce the overall cost. Instead of using fully radiation-hardened devices, which are expensive and are always two-, three-, or even more generations behind, modern ASICs, FPGAs, and custom chips are required. Those devices need modern power solutions with high density, high current, low cost and high efficiency, while maintaining some degree of radiation tolerance

“Once a satellite is in orbit, the only power you have available is derived from solar panels. Because of the finite power available, you need high efficiency in all elements of your power chain. Vicor high-efficiency, high-density and high-current solutions really play well into this new space model,” said Russell.

Vicor rad-tolerant power solutions

Today, larger satellites use a 100V power bus, which is what the current Vicor solution handles. As shown in the figure at right, the 100V that comes out of the batteries (charged by solar panels) is split to provide the two rails (0.8V at 150A max and 3.3V at 50A max) needed to power the ASICs.

The BCM® isolated bus converter has a three-to-one conversion ratio (or K factor), since it takes 100V in input and reduces it to a voltage more suitable and efficient to be regulated. The 28V secondary bus drives the VTM™ current multipliers, which are also ratiometric devices (1/32 and 1/8, respectively) and further reduce the output voltage to the required values.

“Our basic solution is ideal for LEO and MEO satellites using 100V buses. Our modular approach offers tremendous design flexibility enabling designers to change the bus voltage or change the rail voltage relatively easily,” said Russell.

Innovative designs, careful component selection, and extensive component and system testing assure total ionizing dose (TID) radiation tolerance and single-event effect mitigation suitable for LEO and MEO missions.

Single-event effects are electronic events caused by a single highly energetic particle. For this type of testing, devices under test (DUTs) are bombarded with high-energy particles to simulate what they will find in space. Total ionizing dose effects, instead, refer to the damage caused on electronic devices by long-term radiation exposure. This is a sort of cumulative effect, and corresponds to the radiation provided by the sun. In this case, a radiation exposure over time proves that DUTs are robust enough to withstand the maximum radiation level required for that type of mission.

Looking at potential product line expansion, Russell says that, along with the 100V bus voltage, the 28V bus is one of the most prevalent solutions, while 50V and 70V buses will be required for some specific applications. Different K factors for the VTMs likely will be provided, and solutions optimized for lower power will probably be required as well. Some of the currently available technology, particularly the BCMs, might be modified to support bidirectional flow of power, improving the efficiency of the battery charge/recharge process, and reducing the amount of space taken up.

According to Vicor, the product line is well suited to serving New Space. Reliability, high current and high density are important power requirements that are instrumental in powering New Space.