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Thursday, November 23, 2006

Dr. Strangelove

November 13, 2006
Dr. Strangelove

My boss (Mike Fleming) and our chief engineer here at Stevens just got back from a big meeting about GOES satellites in South Carolina. Not much new on the GOES front, more of the same bureaucratic nonsense, but he did bring back another story. Seems the Navy is putting up a constellation of LEO (low earth orbit) satellites to provide broadband communications. They do not expect to fully utilize the capacity of these satellites anytime soon, so are thinking about leasing bandwidth to the commercial sector. The Navy has put up eight of these radiation hardened satellites so far. Designing radiation hardened DSP's is my boss's specialty, so he is especially interested in this. (DSP: Digital Signal Processor. Most all radio communications uses DSP these days.)

You may have heard how the space shuttle has five computers that all do the same job, and the results they produce are a result of a vote amongst these processors. They do this because of radiation. Radiation in space is higher than it is on earth, and can cause errors in computers. Radiation hardening is anything you do to a piece of equipment so that it can continue to operate when exposed to nuclear radiation. The simplest way to do it is to shield the equipment with lead or concrete or something similar. Another way is to make each component large enough that destruction of a few molecules will not impact it's performance. Both these methods mean the device is going to larger and heavier, and heavy is the enemy of space travel.

Redundant devices is another way to deal with this problem. The space shuttle uses multiple computers. Mike's method is similar to the space shuttle method, but instead of duplicating the computers, he uses multiple transistors in the processing chip at the core of the computer itself.

For the military, radiation hardening does not mean just being able to survive the normal incident radiation of outerspace, but also to survive the EMP (Electro-Magnetic Pulse) produced by a nearby nuclear explosion, such as one caused by a North Korean Missle armed with a nuclear warhead that detonates prematurely.

Anyway, with the amount of bandwidth available from these Navy satellites, we could have Sat-phones (Satellite telephone) the size of cell-phones, and we wouldn't need all these cell phone towers. The power required to reach a LEO satellite is about the same that a cell phone produces. So now we are looking at the Sat-phone business.

Since these are military satellites, privacy would be nil, on the other hand, there would be thousands of channels, and how many channels can they actually listen to? And since they are military satellites, the military could shut down the service any time they wanted, similar to their control of the GPS satellites.

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