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To: Jeff Vayda who wrote (3928)	4/16/1999 4:30:00 PM
From: DoctorEvil	Read Replies (2) \| Respond to of 29987

If I may interject for a moment . . . While propellant use is key in determining the useful life of the satellites, solar array performance is equally, if not more, important. At the beginning of life [BOL], the solar arrays can generate far more power than at end of life [EOL]. This is due to the fact that over time in orbit, the satellite is constantly bombarded by tiny bits of space dust. These micrometeorites slowly pit the solar cells, reducing their overall efficiency. Eventually, the efficiency will be reduced enough that the satellite will be unable to collect enough solar power to balance the power consumed by the payload (or at least sustain full-power operations). It is this effect, coupled with propellant usage, that determines when the satellite is retired. Taking both solar array degradation and propellant usage into account, a 7.5 - 10 year satellite lifespan is a pretty good estimate. - Dr. Evil

To: Jeff Vayda who wrote (3928)	4/17/1999 10:32:00 AM
From: Mr. Adrenaline	Read Replies (1) \| Respond to of 29987

A couple of items: Re: Seems to be quite the difference, (20 yrs ) in a propellant lives for a Delta vs Soyuz launch. Kinda flies in the way of your optimization arguments from the earlier post (life span of propellant vs system, to get to a 7.5 yr 'average' life span for all systems and operations) Not really. You have the benefit of hindsight here. Not too long ago the constellation was to be established almost exclusively with Soyuz & Zenit. Designing to the shortest life out of all (and most from the designers perspective) launch vehicles was 7 1/2 years. Re: solar arrays degradation. Solar arrays certainly do degrade over life. I lump this into mechanical wear out. The rate that power output drops off is well defined. It is also logarithmic, meaning most of the degradation occurs up front, and tapers off. It is also due almost entirely to radiation and not mechanical pitting from micrometeorites. (At least for satellites with any real altitude, unlike, say the shuttle or space station -- I'm not sure at those low altitudes.) Re: Maurice's random orbits. Well, Maurice, you get a point for trying, at least. Perhaps it would work with your anti-gravity device. But wherever there is gravity, orbits can't be random. But, if you meant just don't spend the fuel to keep 'em where you want 'em, well that's another story. Not a very good one, but another story. There are lots of reasons why you want to keep 'em in place - collision avoidance come to mind. As does being efficient with your resources. Licensing agency wouldn't stand for it. On and on. And, while I'm at it, almost no fuel is spent for attitude control (trivial amounts). This is true for almost any satellite. Satellites that do spend significant amounts fuel for attitude control are the low life types. One last thing. "LORLURKER", the post from another board -- the guy knows what he is talking about. Regards, Mr A