Re: IRAN posts video from captured drone.

Message posted by greatguess on February 09, 2013 at 18:09:47 PST:

Keep in mind one thing before I start - you don't know if your drone will return to you. You hope it does, but it doesn't always come home. That "unknown" effects everything when looking at data handling on a drone.

I will try to answer your question based on my knowledge of flight test data vs drone data. These two types of data applications are quite similar but in some ways quite different.

How much data is stored? In the old days (good old days?) data storage was an significant issue; data needed to be stored in an analog format (voltage levels) instead of digital (1's and 0's). (Photographic data used film for storage) Analog data recording required a magnetic medium such as magnetic tape which had serious bandwidth limitations. Magnetic tape was also heavy as was the equipment used to spool it and record the information. Data recording methods were revised with the advent of digital sensors and digital storage. Early digital equipment was not a lot smaller and lighter than the mag tape recorders but the bandwidth was usually greater so more data could be stored; often a combination of analog and digital recording was used. Currently digital data storage is VERY inexpensive and SMALL so recording massive amounts of data onboard is very simple and efficient. You can store HUGE amounts of data compared to what you might transmit to the ground (or satellites) so you will typically find more data stored onboard than is transmitted; data stored onboard is analyzed when (and if) the drone returns to you from the mission.

In an world of limited data storage (good old days) you would only record critical parts of the mission; data on-data off, data on-data off, etc. With virtually unlimited storage you can now do "data on" once and then "data off" once when you arrive at and then leave the area of interest. You can also simplify that approach by having data recording "on" all the time the system is powered up. How much of the mission is recorded is a tradeoff that is made by the designers and operators and it depends on the mission and hardware capabilities. There is no "one answer" to that question.

Transmission vs onboard recording The onboard recorded data is pristine (clean) because it simply flows over circuits to its digital storage location - perfect data. When you transmit anything you get losses - those losses are called "dropouts". Dropouts have a magic quality that is not understood to this day - dropouts ALWAYS occur right when the most important and interesting data is being transmitted. The analysts need to wait for the onboard data to look at that critical information gathered during a dropout after the drone returns to their location.

Back to encryption Data that is encrypted (recorded onboard or transmitted) has an overhead cost that can be a real pain - the keys to decrypt it. When you transmit, you may need to encrypt if the data is sensitive and you don't want anybody to intercept it and see what you collected. This is probably not so big a deal in the drone spy world. The fact you are collecting the information is the real secret; the bad guys know what you are looking for. In the world of flight testing the situation is completely different - the data is often very classified and compromise must be avoided at all costs.

In flight test, you almost always encrypt - there is even a DOD rule that says you must encrypt even if the data is unclassified. The data onboard is usually not encrypted for reasons i stated in my first post. To me, the biggest benefit of not encrypting the onboard data is that there are no keys that need to be managed once you have the data in hand. Remember - you must keep the keys as long as you keep the data; this is a security and key management effort that is nice to avoid. It is much easier to store a classified disk/tape than to track keys forever. If you keep encrypted data you must also keep the equipment necessary to decrypt it in addition to the keys. Spell that PITA.

Did that add anything for you?

In Reply to: Re: IRAN posts video from captured drone. posted by Desert Watchdog on February 09, 2013 at 0:30:06 PST:


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