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Re: Right-sizing a sat



Robert Oler wrote:
> then let me be clear.  I am proposing more satellites the size of Oscar 10
> and less the size of AO-40.
>
> Lets start with "size".  I dont think that its a fair statement that AO-40
> is a AO-10 class bird that just grew.  That doesnt fit the literature from
> both the start of the project and all points in between; particularly as
the
> project would reach one of its "end" points (ie when the ham magazines
> thought it was ready for launch).  The "size" required several new things,
> including the load bearing assembly that were not a part of earlier
Oscars.
> PUt another way AO-10 sized paylods could have been launched on other
> Arianes...this one needed V.  (you might for reference look at the
relative
> sizes of AO-40 and 10).
>
> What does size have to do with it?  Your right what "seems" to have failed
> here is the propulsion system.  Guess why the propulsion system is the
size
> that it is in terms of energy?  The mass of the spacecraft.  While
previous
> vehicles have had less then great engine performance the requirements of
the
> engine were based on teh mass.  Less mass and one can get by with less
fuel
> etc.
>
> Also we dont know that the only failure in the system will be what has
> failed right now.  While problems with the engine could be the problems
with
> the antennas there could also be other problems on board...and even had
the
> propulsion system not failed you dont know what other failures are "there"
> or why.  I think that certian transmitters were dead on orbit long before
> the "mishap".
>
> But in the end what it all boils down to is resources.  I cant imagine
that
> you believe that we could have built only 1 AO-10 class veihcle for the
time
> and resources that have gone into this bird?  AND there have been other
> launch oppurtunties which have simply been missed because no payload
exist.
> OK want a specific orbit with a specific payload and not willing to pay
then
> chances come along rare in life and this was a gold mine.  But if you are
> willing to be ready when any oppurtunity strikes then one has more
chances.
>
Hi Robert,

I just don't see how AMSAT could have significantly reduced the cost of P3D.
They would have paid a much higher cost per pound for space on an Arianne 4
flight. They had an opportunity with Arianne 5 because early flights would
not have a lot of customers. They created the SBS to provide a way to insert
AO-40 into an otherwise full flight. Because of this they got a cheap ride.

As I remember from what was published 5 years ago, AMSAT has been very
conservative in their design. The IHU, rocket engine and battery system are
the same as P3A-P3C. I believe that many of these components were in storage
so that reduced costs. I don't fault them for increasing the size of the
spacecraft as the extra space would have otherwise gone to waste and AMSAT
members did want satellites that required smaller ground station antennas.
Bigger fuel tanks and more solar panels don't affect reliability. The big
change is the use of three axis stabilization with momentum wheels. This is
a good idea as, if they work, you get twice the power from the solar panels
and three times the access time on the satellite. If they fail for some
reason, you spin stabilize the satellite and use it like AO-13.

Given that AMSAT members wanted another phase 3 satellite, AO-40 seems a
reasonable response. In the time between the AO-13 and AO-40 launches, there
were 26 LEO launches which is a much higher rate than ever before. In low
earth orbit, there are currently 3 operational linear transponders, 5
operational PACSATs and 3 operational FM transponders, plus a host of
satellites in various stages of checkout. We haven't sacrificed much to get
AO-40.

Someone at AMSAT can correct me if I am wrong, but I think that if we want
to build satellites on a production line basis to go onto any launcher we
are limited to polar orbit LEO satellites because of the launch cost. A
constellation of LEOs with ground based intersatellite links may be the best
way to go in the future but this requires a lot of new development and can't
be available for several years. Launching AO-40 to provide for the existing
users seems like it was a good decision.

73.

John
KD6OZH


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