Satellites in geostationary orbit (GEO) face a harsher environment due to plasma, trapped electrons, solar particles, and cosmic rays, with the environmental effect higher in magnitude compared with low Earth orbit (LEO)-Low Inclination, LEO-Polar, and International Space Station orbits. This is the primary reason why power supplies used in these satellites need to comply with stringent MIL standards for design, manufacturability, and quality.
GEO satellites circle around the earth in approximately 24 hours at about 3 km/s, at an altitude of about 35,786 km. There are only three main satellites that can cover the full globe, as these satellites are far from Earth.
In comparison, LEO satellites travel around the earth at of 7.8 km/s, at an altitude of less than 1,000 km, but they could be as low as 160 km above Earth. This is lower than GEO but still >10× higher than a commercial plane altitude at 14 km.
Total ionizing dose (TID) and single-event effects (SEEs) are two of the key radiation effects that need to be addressed by power supplies in space. Satellites placed in GEO face harsher conditions due to radiation compared with those in LEO.
GEO being farther from Earth is more susceptible to radiation; hence, the components used in GEO satellite power supplies need to be radiation-hardened (rad-hard) by design, which means all of the components must comply with TID and SEEs, as high as 100 Krad and 82 MeV cm2/mg, respectively.
In comparison, the LEO satellite components need to be radiation-tolerant with a relatively lower level of requirement of TID and SEEs. However, using no shielding from these harsh conditions may result in failure.
While individual satellites can be used for higher-resolution imaging, typically constellations of a large number of exact or similar types of relatively smaller satellites form a web or net around the earth to provide uninterrupted coverage. By working in tandem, these constellations provide simultaneous coverage for applications such as internet services and telecommunication.
The emergence of New Space has enabled the launch of multiple smaller satellites with lighter payloads for commercial purposes. Satellite internet services are slowly and steadily competing with traditional broadband and are providing more reliable connectivity for remote areas, passenger vehicles, and even aerospace.
Configurability for customization
The configurability of power supplies is an important factor for meeting a variety of space mission specifications. Voltage levels in the electrical power bus are generally standardized to certain values; however, the voltage of the solar array is not always standardized. This calls for a redesign of all the converters in the power subsystems, depending on the nature of the mission.
This redesign increases costs and development time. Thus, it is inherently important to provide DC/DC converters and low-dropout regulators (LDOs) across the power architecture that have standard specifications while providing the flexibility for customization depending on the system and load voltages. Functions such as paralleling, synchronization, and series connection are of paramount importance for power supplies when considering the specifications of different space missions.
Size, weight, power, and cost
Due to the limited volume available and the resource-intensive task of sending the objects into space against the pull of gravity, it is imperative to have smaller footprints, smaller size (volume), and lower weight while packing more power (kilowatts) in the given volume. This calls for higher power density for space optimization and higher efficiency (>80%) to get the maximum performance out of the resources available in the power system.
The load regulations need to be optimal to make sure that the output of the DC/DC converter feeds the next stage (LDOs and direct loads), matching the regulation requirements. Additionally, the tolerances of regulation against temperature variations are key in providing ruggedness and durability.
Space satellites use solar energy as the main source to power their loads. Some of the commonly used bus voltages are 28 V, 50 V, 72 V, 100 V, and 120 V. A DC/DC converter converts these voltages to secondary voltages such as 3.3 V, 5 V, 12 V, 15 V, and 28 V. Secondary bus voltages are further converted into usable voltages such as 0.8 V, 1.2 V, and 1.5 V with the help of points of load such as LDOs to feed to the microcontrollers (MCUs) and field-programable gate arrays (FPGAs) that drive the spacecraft loads.
Environmental effects in space
The space environment consists of effects such as solar plasma, protons, electrons, galactic cosmic rays, and solar flare ions. This harsh environment causes environmental effects such as displacement damage, TID, and SEEs that result in device-level effects.
The power converter considerations should be in line with the orbits in which the satellite operates, as well as the mission time. For example, GEO has more stringent radiation requirements than LEO.
The volume requirement for LEO tends to be higher due to the number of smaller satellites launched to form the constellations. The satellites’ power management faces stringent requirements and needs to comply with various MIL standards to withstand the harsh environment. The power supplies used in these satellites also need to minimize size, weight, power, and cost (SWaP-C).
Microchip provides DC/DC space converters that are suitable for these applications with the standard rad-hard SA50 series for deep space or traditional space satellites in GEO/MEO and the standard radiation-tolerant LE50 series for LEO/New Space applications. Using standard components in a non-hybrid structure (die and wire bond with hermetically sealed construction) can prevent lot jeopardy and mission schedule risk to ensure reliable and rugged solutions with faster time to market at the desired cost.
In addition to the ruggedness and SWaP-C requirements, power supply solutions also need to be scalable to cover a wide range of quality levels within the same product series. This also includes offering a range of packaging materials and qualification options to meet mission goals.
For example, Microchip’s LE50-28 isolated DC/DC power converters are available in nine variants, with single and triple outputs for optimal design configurability. The power converters have a companion EMI filter and enable engineers to design to scale and customize by choosing one to three outputs based on the voltage range needed for the end application. This series provides flexibility with up to four power converters to reach 200 W. It offers space-grade radiation tolerance with 50-Krad TID and SEE latch-up immunity of 37-MeV·cm2/mg linear energy transfer.
The space-grade LE50-28 series is based on a forward topology that offers higher efficiency and <1% output ripple. It is housed in a compact package, measuring 3.055 × 2.055 × 0.55 inches with a low weight of just 120 grams. These standard non-hybrid, radiation-tolerant devices in a surface-mount package comply with MIL-STD-461, MIL-STD-883, and MIL-STD-202.
In addition, the LE50-28 DC/DC power converters, designed for 28-V bus systems, can be integrated with Microchip’s PolarFire FPGAs, MCUs, and LX7720-RT motor control sensors for a complete electrical system solution. This enables customers to use cost-effective, standard LE50 converters to customize and configure solutions using paralleling and synchronization features to form more intricate power systems that can meet the requirements of LEO power management.
For New Space’s low- to mid-volume satellite constellations with stringent cost and schedule requirements, sub-Qualified Manufacturers List (QML) versions in plastic packages are the optimal solutions that provide the radiation tolerance of QML (space-grade) components to enable lower screening requirements for lower cost and shorter lead times. LE50 companions in this category are RTG4 FPGA plastic versions and the PIC64 high-performance spaceflight computing (PIC64-HPSC) LEO variant.
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