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Cassini-Huygens Saturn Orbit Insertion Imminent
Anonymous Explorer writes "Fresh
off of its fly-by with the Saturnian satellite Phoebe, the
Cassini-Huygens
craft is set for Saturn
Orbit Insertion on June 30, 2004.
Cassini-Huygens has a planned four year mission ahead for Saturn
and its many moons. With 450 watts of power for the electronics, this
mission has plenty enough horses to run the stretch with plenty-o-pep
to spare. Thanks to all that power, and the plethora of electronics on Cassini
and the Huygens
probe, we
can now hear sounds from Saturn. Pretty cool stuff! Festivities are
scheduled to begin on June 29th with a broadcast of Cassini Saturn
Orbit Insertion Press Conference on Nasa TV. SOI [PDF link] will occur after Cassini
fires its main engine for 96 minutes, in order
to slow down and be grabbed by the pull of Saturn. As always we extend
an invitation to everyone to join
#cassini on irc.freenode.net and
help us celebrate this historic mission."
On the other hand, it's not like your average HAM has the Deep Space Network at his disposal. 70m antennas are bigger that you might expect.
I read the internet for the articles.
Yeah but it's directional signal coming from the probe. 0.5 kilowatts of narrow-beam signal goes a lot farther than 10 kilowatts broadcasted from an omnidirectional antenna. But you need dishes at both ends, and they have to be aligned correctly.
I'm sure I'm not using the correct terminology (in case HAM radio experts are reading this) but that is the gist of it.
-CausticPuppy "Of all the people I know, you're certainly one of them." -Somebody I don't know
That's a bit low, but not too far off. Cassini uses 3 RTG power sources to generate the ~700-800 W necessary for the science instruments. Solar cells are not practical at that distance.
This PDF file details the power supply situation on the spacecraft.
It's pretty remarkable how little power spacecraft like this consume (and I'm pretty sure that Cassini is the most power hungry of the 'outer-solarsystem' probes NASA has launched).
The sound they refer to is a frequency-shifted and time-compressed recording of emissions from charged particles in the magnetic field around Saturn. There is no actual "sound" there, as sound requires an athmosphere(sp?) of some sort. There's athmosphere a-plenty on Saturn (most of it IS probably gas, after all), but none near or around the probe.
Black holes are where God divided by zero
Lots of people are saying that Cassini uses a nuclear reactor... this is not the case as Cassini actually uses 3 Radioisotope Thermoelectric Generators (RTG). RTGs are different from reactors in that they are much simpler devices which produce electricity directly from the decay of radioactive material, in this case PU-238. Reactors on the other hand produce power from heat generated by a controlled nuclear chain-reaction.
RTGs decrease in power production over time (since we're dealing with half lifes here). It has three RTGs which, initially, produced 285 watts of power each. With a half life of 87 years for Pu238, they should be somewhere around 250 watts each currently, so that sounds reasonable...
I'm an owl exterminator!
Today marks an interesting first (at least as far as I have been able to tell): the NASA channel has had to choose which current space activity to put on TV.
On Wednesday there will be an EVA on the ISS right around the time the Cassini stuff will be happening. Thus, NASA TV had to choose, for the first time, which thing happening in space was more exciting.
How cool is that? There's actually enough going on up there that one TV channel is not enough!
Whadya know, the revolution IS televised.
I googled around and found some stats from the power industry as "energy density of fossil fuel"
Energy density of Fuel Oil: 42.5 MJ/Kg
Energy density of Anthracite Coal: 31.4 MJ/Kg
MJ/Kg is Mega (million) joules per Kilogram. Our power unit provides 450 watts, thus uses 0.00045 MJ/s. A day's worth of power is 0.00045 MJ/s 3600 s/hour * 24 hours/day = 38.9 MJ. (Remember your signifigant digits!)
To convert that back to weight:
38.9 MJ/Kg / 42.5 MJ = 0.915 Kg/day of Oil
38.9 MJ/Kg / 31.4 MJ = 1.23 Kg/day of Coal
We are in the 7th year of the flight, so:
0.915 Kg/day * 365.26 days/year * 7 years = 2340 Kg of Oil
1.23 Kg/day * 365.26 * 7 = 3150 Kg of Coal.
Plus or minus.
"Learning is not compulsory... neither is survival."
--Dr.W.Edwards Deming
Cassini does NOT use a nuclear reactor. It uses Radioisotope Thermoelectric Generators. Please do no feed misinformation to the nuclear ignorant torch burning masses.
UNIX/Linux Consulting
I'll do it for gasoline. :)
:)
Let's assume that Cassini averages needing 700 watts over the course of its lifetime, and lets assume a lifetime of 18 years. That's about 80 MWh of power. Assuming a 40% efficiency diesel engine burning gasoline and oxygen (have to take the O2 with you!)...
Gasoline has an energy density of 45.8 MJ/kg. Since 2 molecule of gasoline requires about 25 molecules oxygen (O2) to react, you have a molar ratio of 1 mole gasoline to 12.5 moles oxygen. 1 mole of gasoline mass about 114 grams; 12.5 moles of o2 mass about 400 grams. So, your overall energy density is about 10.2 MJ/kg.
Since we're burning at 40% efficiency, that's about 4.1MJ of energy per kg fuel/oxidizer. 1 joule = 0.0002778 Wh. 4.1MJ/kg = 1.1kWh/kg. 80MWh / 1.1kWh/kg = ~73 metric tons.
33 kilograms of plutonium suddenly sounds quite appealing, ne?
I'm an owl exterminator!
So
2340 Kg / 0.40 = 5850 Kj of oil
3150 Kg / 0.40 = 7880 Kj of coal
"Learning is not compulsory... neither is survival."
--Dr.W.Edwards Deming
You know, though... when people complain about there being sound in the middle of a big space battle, it always kind of bothers me a bit. Because if you were in space with space ships and missiles blowing up all around you, you *would* hear the sound of explosions as the pressurized gasses and debris from the ship expand in a shock wave travelling at speeds probably quite similar to what we're used to for sound. Sure, it would be all sudden bursts as your spacecraft was hit by the shockwaves, with no prolonged rumbles, but there *would be sound* to a viewer in a spacecraft somewhere.
And then there's the other things that could possibly cause sound - some of these futurisitic engines are supposed to be powerful ion drives or plasma thrusters, which means that there are very powerful magnetic fields being used and streams of high-velocity charged particles, both of which could possibly have an impact on certain parts of your spacecraft when you get close and make noise. If a beam weapon starts cutting at your ship's hull, your hull is definitely going to make some noise, especially when mechanical components are damaged or gasses start to leak. Etc. There would be lots of sound in a space battle.
I'm an owl exterminator!