Science fiction stories have never told the entire truth about computing in space – it’s not easy to build memory and storage devices that can tolerate the harsh realities of operating off world.
Until recently, it used to be problem only organizations like NASA and its suppliers had to worry about, but with more commercial players in the space travel business and more satellites crowding the skies, there is much higher demand for computing that can handle radiation, extreme heat and cold, and vibration.
Some of the most dependable memories on Earth don’t handle the rigors of outer space all that well, while emerging memory types may go far when it comes to solving out-of-orbit computing challenges.
Radiation hardening is table stakes in space
NOR flash is a well-established parallel memory for military and aerospace applications, and Infineon Technologies’ 512 Mbit QML-qualified NOR Flash was designed with space industry applications and other extreme environments in mind, Helmut Puchner, Vice President Fellow Aerospace & Defense at Infineon Technologies, told Fierce Electronics in an interview.
The new device was funded in part by the U.S. Air Force Research Laboratory, Space Vehicles Directorate and jointly developed with Microelectronics Research Development Corporation. Based on Infineon’s SONOS (Silicon-Oxide Nitride-Oxide-Silicon) charge gate trap technology, the memory was designed for use with space-grade FPGAs and microprocessors to support boot operations, Puchner said. “If you operate in space nowadays, you have a lot of advanced processors and FPGAs, and they need memories.”
He said Infineon went the QML route because there's a lot of government programs as well as high reliability programs where the satellites need to survive all kind of nasty radiation environments. “They're not only limited to the cosmic rays and protons that are emitted from the sun, there is an ongoing threat of manmade radiation also in space.”
Those threats might include nuclear missiles being stationed in space, Puchner said, and QLM provides a framework for customers so they can expect the same components with tight process and manufacturing controls, and a memory device that can maintain data during radiation events.
Weight and size are also a factor for space-ready memory devices, which why the QMLP certification for plastic parts was developed two years ago – this NOR flash is the first plastic part Infineon has brought to market, rather than ceramic, Puchner said. “There's some advantages and disadvantages.”
While a plastic device is smaller and weighs less, it can be harder to dissipate heat out of it when compared to ceramic, he said. “If you have really high-power components, it's a little bit more tricky to get the energy out of those plastic packages.” The environment plays a role, too, depending on the temperatures the device is exposed to.
Puchner believes that in general the industry getting more comfortable with “flying plastic,” while Infineon’s proprietary SONOS technology is very stable in a radiation environment.
Different memories for different distances
Not all non-terrestrial environments are created equal, noted Puchner. Going into orbit around the Earth and going to moon have different requirements, so there’s opportunities to reduce the bill of materials depending on the levels of radiation, temperature and heat dissipation to support high volumes in a fleet for satellites. “There's a whole bunch of specific things that are you really got to get right in these use cases,” he said.
There are also many different radiation-hardened memories that can withstand harsh environments including magnetoresistive random-access memory (MRAM), ferroelectric random access memory (FRAM) and resistive random-access memory (ReRAM)
MRAM has already proven it can handle the extreme environments of automotive applications, and because it stores data as a magnetic state as opposed to a charge level, which is typical of DRAM or SRAM, the MRAM bit cell itself is immune to the effects of radiation, Joe O’Hare, senior director of marketing at MRAM maker Everspin told Fierce Electronics. “That's the beauty of MRAM.”
That makes it a good choice to support the many space missions that need memory in the past few years, he said, including low Earth orbit satellites and commercial rockets. O’Hare said Everspin doesn’t intentionally make all its products radiation tolerant or hardened, but it’s an inherent capability that makes it appealing to certain customer segments, including the military and aerospace industries, with some customers licensing its technology and layering on additional capabilities to meet requirements.
O’Hare said it’s a boon for Everspin to be able to offer its commercial grade MRAM for out-of-orbit use cases. “It is a huge advantage for these space guys. We're engaged with a range of well-known satellite launch companies.” That means the company’s MRAM could be for the space applications or the rockets that are launching satellites, which not only benefit from the radiational tolerance, but also the extended temperature range and MRAM’s high endurance – about many times data can be written to the device.
Everspin’s MRAM, including its toggle legacy MRAM and its new spin transfer torque MRAM, is being used in many satellites but also notable NASA projects, including the Mars Perseverance Program and the Lucy mission to Jupiter, O’Hare said. Typical uses are code storage or data logging for a camera system or flight controller. “It gets used in space much like it gets used in the industrial and automotive applications that we sell the product to here on Earth.”
Using its own magnetic tunnel junction MRAM technology combined with configuration bit technology, Everspin is working with QuickLogic to develop a radiation-hardened FPGA, which typically use SRAM for configuration, which is susceptible to the effects of radiation, O’Hare said. “The adoption of MRAM will continue to expand and that there will be new ways of using the technology within these applications that need the radiation tolerance.”
Ruggedness is just as important as radiation when it comes to space-bound memory, Mike Basca, vice president of embedded products and systems at Micron Technology, told Fierce Electronics in an interview. Considerations include extreme heat but also extreme cold. Even more significant: these parts can’t be easily serviced if they run into problems, he said. “We see extremely high requirements just in terms of the quality and reliability of these parts.”
Extreme reliability is where more terrestrial applications are already headed, such as industrial and automotive applications, especially with the rise of autonomous vehicles. Basca said power is also a key consideration for space applications. And just as packaging can help protect memory from radiation, it also affects power consumption by reducing the size.
Space memory volumes are gaining ground
Another bigger challenge for space memory is economics – the volume going out of orbit is not nearly as much as terrestrial applications. “Our efficiencies are in high volume opportunities,” Basca said.
However, Micron does have partnerships with integrators that are focused on space opportunities such as Mercury Systems with which it collaborates on lower volume memories, including testing environmental requirements. “It's kind of a case by case basis working together with some of these integrators to help get these products ultimately to the final destination,” Basca said.
Micron provides Mercury with NAND components for their solid-state data recorders (SSDRs) which are purpose-built for space and radiation-intense environments and are used in NASA’s Earth Surface Mineral Dust Source Investigation (EMIT) spectrometer and MethaneSAT, which is a satellite launched into orbit earlier this year and developed by a subsidiary of the non-profit Environmental Defense Fund. This NAND is manufactured in Micron’s Virginia fab dedicated to long-lifecycle products, while Mercury performs extensive upscreening on space-bound devices including electrical, environmental and radiation testing and added shielding from radiation.
Volumes for extra-orbital memory are going up for equipment such as satellites, Basca noted, and because they are relatively close to the Earth, the radiation tolerance requirements are not as stringent. “With volume also comes a lot of ingenuity from some of the players in that space that are trying to use more off the shelf parts.”
He said about half the market requires special integration, including radiation testing and special packaging, but the other half can be served by commercial off the shelf (COTS), which means the space memory market is growing year over year.
Aside from NAND, Micron also provides low power DDR DRAM (LPDDR) for space applications, which requires robust error correction schemes to ward off unwanted bit flips caused by particles and photons.
While some advanced memory technologies developed for extra-terrestrial application may eventually get adopted for more earthbound applications, what’s interesting about the space memory market is that it’s not always leading devices that solve the problem. “It's not exclusively leading edge,” Basca said.
Space also a much more dynamic market for memory, he said. “It's not such a sleepy industry by any means anymore.”