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In article <BzqBvs.J8H@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes:
>In article <1992Dec23.111923.22269@ke4zv.uucp> gary@ke4zv.UUCP (Gary Coffman) writes:
>>... A ten year life zero defects
>>GEO comsat like K2 is much cheaper than a 1 year life package
>>that costs 20 times less. That's because most of the investment is
>>not in the satellite, it's in the Earth based terminals that use it.
>
>I don't grasp this argument.  It's the same Earth-based terminals either way.
>If you're providing a service, you plan to do so over more than one satellite
>lifetime, either way.  Twenty years of service is cheaper with mass-produced
>short-life satellites, even with your (fairly unfavorable) assumptions.
>

Actually, henry.  both of you are sticking to the clarke orbit model.

Most of the effort in the Telecom industry is oriented towards
LEO comm sats.  store and forward or multiple fast relay satellittes.

in this case,  the degree of investment in the ground terminals  becomes
very small,  terminals costing under $1,000.00  and satellittes being
cheaper,  because they are smaller, lighter and need less powerful elements.
Obviously,  for a 72 sat constellation, like motorolas  or Inmarsats 21
sat config,  you want to try and keep the lifetimes up,  but if launch
costs drop significantly,  then you can deal with replacing birds
on a regular basis.


>>... Since the satellite represents a single point failure node...
>
>This is your assumption, not a self-evident fact.  Communications networks
>normally have redundancy to cover predictable single-point failures.
>Even today's gold-plated satellite networks do, despite the expense.
>

Actually,  most comm sats,  have lots of extra solar cells,  spare
gyros and thrusters  and spare transponders to handle loss of units.

now if there were some cheap way to go up and refurb these birds,  then
you would be talking some real savings.  
>>... and since for most orbits
>>the satellites aren't retrievable or repairable, and DC won't change
>>that...
>
>Again, your assumption, not a self-evident fact.  Cheap launches change
>almost everything, including the feasibility of retrieval and repair.


Oncve again,  for LEO  commsats,  rendevous is quite feasible.

you could even use the shuttle to  grab them up.



pat