Space
The space size continuum
New LEO satellites range in size from 10gm to 100kg
As satellites get smaller, lighter and more sophisticated, Roger Tall reviews some of the components which are helping designers to new benchmarks for performance and reliability
Integrated into Exxelia’s C series of high- power and high-frequency ceramic capacitors, the C48X dielectric combines many of the advantages of conventional NP0 and X7R dielectrics.
Roger Tall T
his year marks the 60th anniversary of the launch of the first satellite. Measuring 58cm across and weighing just under 84kg, Sputnik was launched by the Soviet Union, into a Low Earth Orbit (LEO). Since then, the space industry has come full circle: from building increasingly large and more sophisticated satellites, such as the geostationary Astra satellites of the 1980s and the International Space Station, to launching constellations of much smaller satellites. Today, there are defined classes of small satellites: Microsatellites weighing under 100kg; Nano Satellites (NanoSats) weighing between 1kg and 10kg; PicoSats at 0.1kg to 1kg and FemtoSats at 10g to 100g.
As demand for these small satellites
grows, component manufacturers are responding by extending the range of components which can help designers to meet the twin challenges of miniaturisation and reliability.
Developments in passive technologies A relatively new passive technology which has become available to satellite designers is the C48X dielectric.
40 October 2017
The key characteristics of the C48X dielectric make it a viable choice for power applications which need to minimise heat dissipation. These include a very low dissipation factor of less than 5.10–4 whilst achieving the same capacitance values under working voltage as the X7R dielectric. The C48X’s ability to withstand very high dV/dt, up to 10kV/ s, also makes it viable for pulse applications and those with fast charge/discharge cycles. Another recent addition to the list of space-grade components is the T583 polymer capacitor from Kemet which complies with ESCC Generic Specification No. 3012/00. This relatively new technology offers designers an alternative to conventional tantalum capacitors based on a Manganese Dioxide (MnO2) cathode and ceramic capacitors. The polymer cathode provides designers with a number of benefits. These start with the ability to provide the highest total capacitance alternative to MnO2-based tantalum capacitors which helps designers to meet tighter size restrictions. They also achieve enhanced capacitance retention than wet tantalum capacitors at higher frequencies whilst their very low ESR enables power to be used efficiently. A benign failure mode means that polymer capacitors also eliminate the need for the fuse which must be used to protect conventional MnO2 tantalum capacitors.
Resisting the effects of radiation The need to protect devices against the harmful effects of exposure to radiation in Low Earth Orbit (LEO) was the driver for the development of radiation-capable opto-couplers and Hall-effect sensors by TT Electronics.
The HCC100x opto-couplers integrate a LED die which demonstrates degradation of around 10 per cent after Neutron exposure. When paired with a JAN- screened silicon die, the component has
Components in Electronics
shown to be capable of passing both Total Ionizing Dose (TID) and Neutron at 100KRads and 1E12N/cm2 respectively under tests performed to 300KRADS TID and 2E12N/cm2 Neutrons. This ability to withstand radiation means that these opto- couplers can be used to provide circuit isolation between high- and low-side circuits, ensuring the integrity of insulation systems and voltage separation. By achieving virtual immunity to
environmental contaminants and TID radiation levels, the Hallogic Hall-effect sensors have earned a place on-board NASA’s mission to the planet Mars in 2020. The OMH series sensors will be used to detect magnetic fields in the motors that will control the speed and movement of the robotic arm on the Mars Rover as it collects rocks and soil samples. 30 samples, collected by a coring drill on the arm, will be deposited at selected locations ready to be retrieved and returned to Earth in a future sample-retrieval mission. Another advantage for designers is the Hallogic sensors’ ability to meet tight space constraints. The devices combine a Hall element magnetic-field sensor with integrated circuitry on a single, monolithic silicon chip. This allows the sensor to occupy less board space than conventional emitter-detector pairs. With a high level of magnetic sensitivity, the sensor also provides reliable, repetitive operations within close tolerances.
High-voltages in a vacuum The high-voltage power systems of satellites present significant fuse and fault- detection challenges to designers, particularly as they must operate reliably in a vacuum.
The use of higher voltages is a key
feature of the latest generation of satellites. Previously, designers have been able to use high-reliability fuses covered by the MIL-PRF-23419/8 standard which protects circuits operating on voltages from 28V to 50V DC. Today, however, many satellite power systems operate at voltage levels above the 135V DC limit which can be protected by a standard high-reliability solid-body fuse.
For these higher bus voltages, FM12
fuses, from AEM Inc., provide designers with minimum and maximum clear-times at overload currents regardless of vacuum conditions. Produced using a thick film technique the solid body of these QPL-listed current-limiting fuses eliminates the risk
of out-gassing. This frees designers from the de-rating factors of fuses covered by MIL-STD-975.
The solid-body construction also helps these fuses to withstand higher levels of vibration and shock which are inevitable during the launch process. For additional protection, the internal construction ensures that arc, plasma and vapour are all contained within the fuse package during a current overload. Short-circuits to the power source are also prevented by the positive temperature coefficient of the fuse element which causes resistance to increase before the fuse opens.
Sputnik was launched 60 years ago
Flexibility and future growth Designers of small satellites now have greater choice as more components are added to the Qualified Parts (QPL) and European Preferred Parts List (EPPL). There is also the option of using more readily available components which comply with the automotive AEC-Q200 standard or using additional testing. This means that the reliability options can be extended from COTS to QPL and beyond.
As the satellite industry celebrates its Diamond anniversary, the outlook for the sector is one of significant growth. But a new and more competitive market may see the pressures on designers and component manufacturers continue to get bigger as the satellites get smaller.
www.charcroft.com www.cieonline.co.uk
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60
