'Dawn' asteroid probe -- highest power ever?

Alex Terrell wrote:

On 26 Feb, 15:42, "Jim Oberg" wrote:
The 'Dawn' asteroid mission (June launch) has a 10 kilowatt electrical power
system --
is that the highest power level ever for an interplanetary probe?

Cassini: 750 watts
Galileo: 500 watts
Deep Space 1: 2.4 kilowatts

SMART-1 had 2KW. (Is that interplanetary?)

10KW is a lot for a space probe.

Solar irradiance at that distance is roughly 1/10th that of Earth.

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On Feb 26, 7:42 am, "Jim Oberg" wrote:
The 'Dawn' asteroid mission (June launch) has a 10 kilowatt electrical power
system --
is that the highest power level ever for an interplanetary probe?

I suspect this spec is for 1 AU. Rosetta has similar large arrays due
to similar requirement of operating at the main belt and out to
Jupiter (~3 to 5 AU). Output of the Rosetta array is stated for 3.4
and 5.25 AU. A BOTE calculation with simple inverse square law
scaling gives about 10 KW for the Rosetta array at 1 AU.

Jim Oberg wrote:

The 'Dawn' asteroid mission (June launch) has a 10 kilowatt electrical power
system --
is that the highest power level ever for an interplanetary probe?

Cassini: 750 watts
Galileo: 500 watts
Deep Space 1: 2.4 kilowatts


Is this real power, or the equivalent when you use a very directional
antenna pointed Earth's way, to make it look like higher power?

"robert casey" wrote in message
ink.net

Is this real power, or the equivalent when you use a very directional
antenna pointed Earth's way, to make it look like higher power?

It's the entire resource or interal cash of available energy for that
spendy probe to draw upon, therefore not having anything to actually do
with the antenna gain factor.

In other words, it's little more than a very dirty bomb that we've sent
as our messenger towards other worlds. I hope ETs don't get the wrong
idea about us.
-
Brad Guth



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In article . net,
robert casey wrote:
The 'Dawn' asteroid mission (June launch) has a 10 kilowatt electrical power
system...
Cassini: 750 watts
Galileo: 500 watts
Deep Space 1: 2.4 kilowatts

Is this real power, or the equivalent when you use a very directional
antenna pointed Earth's way, to make it look like higher power?

Real power, although for solar arrays, it has to be quoted at a particular
distance from the Sun (usually 1 AU) and for beginning-of-life or
end-of-life (because the output slowly falls due to accumulated radiation
damage in the cells -- BOL is the more impressive number for the press
releases, while EOL is the number that most of the design work has to use,
usually based on the length of the primary mission). It also generally
assumes that the cells are pointed straight at the Sun, which is
reasonably accurate for spacecraft with big pointable arrays, and can
be seriously inaccurate for simple body-mounted arrays.
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"Henry Spencer" wrote in message
...

Real power, although for solar arrays, it has to be quoted at a particular
distance from the Sun (usually 1 AU) and for beginning-of-life or
end-of-life (because the output slowly falls due to accumulated radiation
damage in the cells -- BOL is the more impressive number for the press
releases, while EOL is the number that most of the design work has to use,
usually based on the length of the primary mission). It also generally
assumes that the cells are pointed straight at the Sun, which is
reasonably accurate for spacecraft with big pointable arrays, and can
be seriously inaccurate for simple body-mounted arrays.

Can they measure it in candelas instead, so that it doesn't depend on
distance but only on time?

In article om,
Mike Chan wrote:
I suspect this spec is for 1 AU. Rosetta has similar large arrays due
to similar requirement of operating at the main belt and out to
Jupiter (~3 to 5 AU). Output of the Rosetta array is stated for 3.4
and 5.25 AU. A BOTE calculation with simple inverse square law
scaling gives about 10 KW for the Rosetta array at 1 AU.

The Rosetta arrays nominally give 8.7kW at 1AU (ESA Bulletin, Nov 2002).
Solar-array output isn't quite proportional to light intensity, because
more light also means warmer solar arrays, and the cells are more
efficient cold. Rosetta's arrays in particular are optimized for the
dim/cold case, while I imagine Dawn's are more of a compromise, since it
never goes as far out as Rosetta, and will do quite a bit of its thrusting
while still fairly close in.
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In article ,
Neil Gerace wrote:
Real power, although for solar arrays, it has to be quoted at a particular
distance from the Sun (usually 1 AU)...

Can they measure it in candelas instead, so that it doesn't depend on
distance but only on time?

Alas, as I noted in another posting, the output isn't exactly proportional
to light intensity, because it also depends on temperature -- the cells
are more efficient cold -- and so trying to assign a distance-independent
number is tricky.
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spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

Is this real power, or the equivalent when you use a very directional
antenna pointed Earth's way, to make it look like higher power?


It's the entire resource or interal cash of available energy for that
spendy probe to draw upon, therefore not having anything to actually do
with the antenna gain factor.


Duh! Of course. We are talking about the probe's *power supply*, not
the power of its transmitter used to talk to Earth. Dang if I can
figure out how I read that in the original post... And it wasn't even
that late last night... :-)

"robert casey" wrote in message
ink.net

Duh! Of course. We are talking about the probe's *power supply*, not
the power of its transmitter used to talk to Earth. Dang if I can
figure out how I read that in the original post... And it wasn't even
that late last night... :-)

Good freaking Christ almighty on a stick. You're the one as having used
the antenna gain analogy. Double duh right back at you.
-
Brad Guth




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