You are most likely aware of the European Union’s “Galileo” system (a version of GPS) and the Russian Global Navigation Satellite System (GLONASS). But did you know that in early October, Japan launched the fourth of a series of geo-positioning satellites in their Quasi-Zenith Satellite System (QZSS), Figure 1, which will allow them to start operating its own GPS-like system? I’d bet the answer is “probably not.”
Japan’s Quasi-Zenith Satellite System (QZSS) will be a localized version of the world-wide GPS, and is scheduled for basic operation in 2018; the present array of four satellites (eventually seven by 2023) allows for basic operation. (Image source: Government of Japan)
A recent article in The Wall Street Journal (of all places) reported on the Japan launch, news of which was otherwise buried in the onrushing torrent of daily items ranging from the Kardashians to North Korean nuclear events. The article, “Japan’s New Satellite to Help Keep Self-Driving Cars—and North Korea—In Line,” (sorry, it may be behind a paywall) also had a useful summary Table 1 of the various GPS-like systems in operation or coming online, with brief details on their public accuracy, operational status, and satellite complement (a more-detailed table is available here). Franky, I had not realized there were so many systems in place or soon to be operating.
(Sources: U.S. National Coordination Office for Space-Based Positioning, Navigation, and Timing; European Global Navigation Satellite Systems Agency; Russian Information and Analysis Center for Positioning, Navigation and Timing; BeiDou Navigation Satellite System; India Space Research Organization; Japan Cabinet Office)
Regardless of the rationale or real need for these multiple systems, their existence is good news for the analog-circuit world, for several reasons. First, no matter how “digital” the signal stream is, a satellite by its very nature is a very analog system, with preamps, LNA, sensors, signal conditioning, power subsystems, propellant control…it’s a long list.
Second, the existence of all these multi-satellite systems is transforming the satellite “business” from a one-off, custom-design world to a mass-production, standardized design environment. Of course, “mass production” here refers to unit volumes of under a hundred units, but that is still very different than having each satellite being a unique design. That changes everything about planning, schedule, design, simulation, validation, procurement, assembly, test, launch, and operation, all of which helps analog design and manufacture make the transition from “art form and magic” to consistency.
This “mass production” trend began with the roughly simultaneous deployment of GPS (see “Pinpoint: How GPS is Changing Technology, Culture, and Our Minds”) and the Iridium global wireless voice system (see “Iridium: The Audacious SatComm Network That (Almost) Couldn't”). It’s now moved down to the CubeSat approach, where standardized form factors and modules are used to extent possible to reduce cost, risk, and completion time, Figure 2.
The Atlas V launch in 2015 from Vandenburg AFB put 13 CubeSats in orbit from a wide range of designers and with diverse missions. (Image source: CubeSat)
Satellite-system designers have a difficult dilemma. On one hand, they would like to use the latest components to take advantage of their improvements in performance, power, size, and other factors. On the other hand, they need to rely on components with a substantial history – even if they meet specs “on paper” – because of the rigors of space and unforeseen component issues which only appear after many hours of use, and across hundreds and more of fielded units. A lot depends on the vendor’s track record, commitment, and credibility, beyond what’s on that data sheet.
For example, look at the just-introduced SKY65623-682LF from Skyworks Solutions, Inc. Not only is this low-noise amplifier (LNA) for 1559 to 1608 MHz, a low-power, single-supply device (1 mA with a 1.8 V supply), but it’s diminutive size is truly impressive: it’s a five-lead device in a 0.8 × 0.8 mm package. Sounds like an innovative device worth considering, but would you use it in your satellite? I’m certainly not the person evaluate and decide on that.
At the transmit side, there’s also the trend away from traveling wave tubes (TWTs), long the standard power amplifier for satellites (and other applications). These specialized vacuum tubes can deliver significant power over a broad band, have matured to the point where they are very well understood, are highly reliable, and there are even efforts to standardize among vendors to some extent (see here), all of which have virtuous attributes.
Still, they are vacuum tubes, and require relatively high voltages and special design-in considerations which adds to satellite complexity. They are being replaced In many designs by solid-state devices based on GaN process technologies, such as discussed here and with these 6-GHz GaN products from Analog Devices which can produce the needed power ratings in many cases, but this brings new challenges including a more limited bandwidth in some cases and less historical experience. The momentum is clearly with the alternatives to TWTs, but there’s a risk associated with these disruptive changes.
What’s your view on how relatively high volumes of similar or even identical satellites, coupled with standardized small-satellite form factors, is affecting the analog world ranging from LNAs through PAs, as well as power supplies and other analog-laden functions?
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