Radioprotective design under the space information system COTS technology
Foreword
The space information processing system, as the key part on the small satellite, it is used mainly in control of satellite, affair management of the star, data processing,etc., the information processing system work of space is in the rugged environment on a relative ground, have proposed more high requirement for researchers.
A natural method is shielding and strengthening, the correlated data shows: The thicker the aluminium sheet is, the less the radiation effect is, and one grade of abilities to resist radiation of CMOS device strengthened of space flight is stronger than regular CMOS greatly. One grade of radioprotective microprocessors and other computer devices that strengthens lag behind the most advanced commercial product for several years in space flight at present, .
COTS(Commercial Off-The-Shelf) Technical leading-in, the instant using commercial device replaces the radioprotective reinforcement device of grade of space flight, it is a trend of the present design space information processing system. What reliability of security system, how to adopt the lower priced commercial device, utilize the intersection of operation and fast soft assorted programming its fully platform improve and application software make up flexible while the characteristic more, systematically, take measures to make it have function against radiation to space environment to the commercial stock device, it is a challenging subject.
A space radiation environment and effect analysis
1.1 Space radiation effect
The effect on the electronic device of radiation environment of space is fallen into two categories.
Radiation total dose TID (Total Ionizing Dbse) : The one that was described is a series of characteristics under the environment of radiation of electronic device, mean the great change (permanent fault) is taking place in the device Energy level of total absorption that can bear ago. Its unit is Rad, namely stockpile the energy in a gram of silicons.
Primary particle effect SEE (Single-Event Effect) : Mean the single energetic particle strikes the momentary disturbance of the electronic device state caused, whether or permanent damage. The energetic particle in the space includes heavy particle, proton, alpha particle, neutron,etc.. The primary particle effect is divided into two kinds again.
The primary particle turns over SEU (Single-Event Upset) : Cause the turning over of flip-flop in the circuit and memory cell, logic error, memorizer mistake or missed synchronization,etc. have appeared. SEU is often considered as soft error (softerror) .
The primary particle is occluded SEL (Single-Evcnt Latchup) : The door caused under the radiation environment hits, burns or occludes (1atch up) ,Shown as CMOS circuit and shorted out, occluded in thermal stress year,etc.. SEL is often considered as the hard error (harderror) .
1.2 The countermeasure is studied and summarized
Because locus and service life of the small satellite are different, and the radiating total dose and primary particle effect and is up to different space environments (orbit altitude, dip angle) of space information processing system And different tasks time differs significantly (even there are the changes of several pieces of order of magnitude in the environmental parameter of radiation) ,So, its intensity and measure against radiation are not the same.
At present, totally shield and prevent radiation from being very difficult to realize and unnecessary on the hardware. In COTS technical application, after taking appropriate shielding and reinforcement measure, still can't at all up to the system and resist spokes and avoid permitting the system to present the radiation effect under the situation by mistake; But it is redundant to pass (such as the strong machine system) It makes the system work normally that it is calculated and fault-tolerant, and design and use some protective circuit to deal with radiation effect, become and understand the problem method.
CMOS technology is developing constantly, typical CMOS technology makes TID that the apparatus can be born before physics is being damaged is probably 5 KRad at present; And according to National Aeronautics and Space Administration (NAsA) The radiation model analysis that offers reveals, computer application message processing module C&DH (Command and Data Handling) of its small representative satellite ION-F TID of the subsystem is 25 Rad. Therefore can draw the conclusion: Only in terms of space information processing system in the small satellite, under the environment of typical task cycle sum, the influence of TID can be neglected. China " Practise size five " The satellite analyzes that has drawn the similar conclusion too. Consider task service life and environment of small satellite are polytropical, it should be enough to meet the requirement which disturb TID that general reinforcement and aluminium of the appropriate thickness are shielded.
With the development of technology. Accompanied by the reducing of the device voltage and increase of bit density, sending oxen frequency and is on the rise of SEE, and it is very definite to shield the function on the energetic particle. So, in quite a long time, SEE is comparatively speaking a more high problem of more noteworthy and latent danger in the design. SEU exerts a largest influence on storage device, COTS technology makes usable redundancy (such as the duplex machine system) within the processor And adopt the appropriate architecture to organize, the memorizer is measured and corrected the mistake by oneself with ECC or other check-up yard, in addition can also use watchdogs (watch dog) Technology.
Do not shield and strengthen technology within the range of research herein; More mature double machine system architecture, check-up yard and watchdog's technology have solved the problem of SEU radiation effect.
2 SEL solves conceptual design
SEL is bulk effect technological CMOS (Bulk CMOS technologies) (non- insulating silicon) Bipolar transistors parasitic touching off and causing a short circuit among Piower supply and earthing. The preparation method of CMOS has prevented the appearance of this kind of situation in case of normal operation. But in the universe, some electric charge caused by passing through the energetic particle may still touch off this kind of effect to deposit. SEL may be confined to a very small local area. It would influence it to the majority of the chip also may spread. If does not take the protection measure, the heavy current caused by shorting out may make the device cause and damage permanently.