Cassini-Huygens Saturn Orbit Insertion Imminent 205
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."
Re:Not even 0.5kilowatts.. (Score:2, Informative)
Re:450 watts? (Score:4, Informative)
Considering the computer power needed to go to the moon, it's not likely that this thing needs an 3.2Ghz processor and GeForce
My Epia-M is plugged in taking about less than 30W of power (including HDD and DVD-ROM)... so really the equivilent of an efficient 1Ghz processor wouldn't need anything near your desktop machine's draw.
Re:Not even 0.5kilowatts.. (Score:5, Informative)
Re:Not even 0.5kilowatts.. (Score:5, Informative)
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.
Re:Not even 0.5kilowatts.. (Score:2, Informative)
Some, but it is considered very bad form to use more power than necessary. Transmitting across the ground is very different than transmitting through the space. Line of sight drastically reduces the ammount of power you need, as well as using directional antenas.
Re:450 watts? (Score:5, Informative)
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 [nasa.gov] 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).
This is from NASA's page (Score:3, Informative)
linky [yahoo.com]
Re:I hope it takes photos (Score:4, Informative)
Re:Not even 0.5kilowatts.. (Score:2, Informative)
Re:Sound in space? (Score:3, Informative)
Sound? What sound? (Score:5, Informative)
Re:Victory of SCIENCE over ECOIDIOLOGY (Score:5, Informative)
Re:450 watts? (Score:5, Informative)
Choice: Saturn or Spacewalk (Score:4, Informative)
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.
Re:Ah, but did it generate the 450? (Score:5, Informative)
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.
Re:Pheobe as a source of ice (Score:5, Informative)
Re:Ah, but did it generate the 450? (Score:5, Informative)
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?
Re:Ah, but did it generate the 450? (Score:5, Informative)
So
2340 Kg / 0.40 = 5850 Kj of oil
3150 Kg / 0.40 = 7880 Kj of coal
Re:ObSpock (Score:5, Informative)
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.
Re:I hope it takes photos (Score:3, Informative)
It is flying through a visible gap, and it's an area that seems to be clear of debris according to all the analysis done so far. But it could just be that the debris is so sparse that it's not visible.
The entry point is actually well outside the visible rings, but there is another very faint ring (G ring) even farther out.
NASA realized this during the design phase, which is why they are rotating the spacecraft around so that the dish of its high gain antenna will provide some protection against small rocks while it passes through the ring plane. Seems like if the high gain antenna is damaged, then they have other problems though! I'm thinking it was designed with this purpose in mind, at least for protection against particles under a certain size.
Re:Pheobe as a source of ice (Score:3, Informative)
Solar-powered ion drives don't require a lot of power; they use low thrust over long periods of time. Check out this link [nasa.gov] for an example. Note that the name of the craft is "Deep Space 1." It went to the asteroid belt, but even if it went out as far as the orbit of Saturn, it would just have to operate at lower thrust.
That why Cassini needed a nuclear reactor.
Cassini doesn't have a nuclear reactor, it has a radioactive source that provides energy by passive heating. (A reactor uses a chain reaction.)
Re:Pheobe as a source of ice (Score:4, Informative)
A variant of this idea was explored by Isaac Asimov way back in the novella, The Martian Way (Galaxy Science Fiction, November 1952; subsequently republished in several collections).
The characters in the novel propose capturing chunks of ice from Saturn's ring system. We don't need to grab a whole moon--there are cubic-mile-sized chunks of ice in the rings. They might be a bit more manageable to manoeuvre. There are lots to choose from, too.
Re:Sound in space? (Score:3, Informative)
Re:Victory of SCIENCE over ECOIDIOLOGY (Score:4, Informative)
There are some very significant differences. A Nuclear reactor involves an induced chain reaction. This is just harnessing energy from passive decay. RTG's last a lot longer, but produce less power.
Re:Sounds of Martian Life?!! (Score:3, Informative)