By John McHale
MANASSAS, Va. 1 June 2009 – Storage technology for future NASA space missions to the deepest parts of the solar system will require not only enhanced non-volatile memory capacity for video and other data but improved radiation immunity that current technologies do not provide.
Engineers at BAE Systems in Manassas, Va., partnered with Ovonyx in Rochester Hills, Mich., to develop C-RAM – or chalcogenide random-access memory – for spacecraft. The C-RAM hard drive is designed for applications requiring large amounts of radiation-hardened, non-volatile memory such as spacecraft avionics systems.
There was a need to upgrade the current standards for non-volatile memory in space applications, says Vic Scuderi, manager of satellite electronics at BAE Systems. The older standards such as FLASH and EEPROM do have the performance capability nor necessary radiation immunity – EEPROM only has an immunity of 100,000 rads, he continues.
According to the BAE Systems release C-RAM "provides 20 times the tolerance to total-dose radiation over current EEPROM designs and four to 16 times the density of competing non-volatile memory technologies." C-RAM also only uses a single 3.3-volt power supply for programming and operation where EEPROM needs two power supplies.
For upcoming NASA missions toward Jupiter and its moon, Europa, the spacecraft will see radiation-levels of 4 to 10 megarads, so a replacement was needed, Scuderi says. CRAM offers the necessary megarad immunity and performance capability needed for the solid state recorders to efficiently record and download data from these missions, he adds.
The Space Vehicles Directorate of Air Force Research Laboratory at Kirtland Air Force Base, N.M., and other agencies funded this effort, BAE Systems officials say.
C-RAM will be offered in two total-dose immune levels, 500-kilorad and 1-meagrad. According to BAE Systems release it is also 1,000 times more single event upset (SEU) immune than EEPROM.
BAE Systems' C-RAM offers 70-nanosecond read-cycle times and 500-nanosecond write-cycle times (100 times faster than EEPROM), requires low operating and standby power, and is latchup-immune.
Ovonyx experts provided the C-RAM technology and BAE Systems performed the radiation-hardening of the devices. Ovonyx officials call their technology Ovonic Unified Memory or OUM.
The technology is similar to how read-write CD and DVD technology users a laser to record data, Scuderi says. "However, in space it is not yet feasible to use a laser," so another method is needed. Ovonyx writes to the drive with small transistors that electrically charge the phase-changing Chalcogenide material, he explains.
According to the Ovonyx website "optical memory disks use laser light to write small spots by converting the thin film back and forth from amorphous (disordered atomic structure) to crystalline (regular, highly repetitive, and ordered atomic structure). The digital data of 1s and 0s are stored as amorphous (high resistance and non-reflective) or crystalline (low resistance and reflective) structures."
The small transistors "electronically convert the material to crystalline or to amorphous" – a 1 or a 0, according to the website.
The C-RAM devices are currently undergoing qualification, with Q-level qualification expected to be complete this fall and QML-V qualification early next year, company officials say. The monolithic 2-megabit and 4-megabit devices will be available in 40-pin flat packs. C-RAM product offerings also will include 16-megabit and 20-megabit multi-chip modules.
