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."

Re:Not even 0.5kilowatts..

[Anonymous Coward]

Well, yeah. Most HAMs don't have dish antennae with diameters measurable in friggin miles...

Re:450 watts?

[phorm]

I searched through the various articles trying to find that number, but no go. Maybe they're missing a zero... or perhaps 450W is actually a lot on a system that is likely drawing continuous power off a solar panel/battery.

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..

[jandrese]

On the other hand, it's not like your average HAM has the Deep Space Network [nasa.gov] at his disposal. 70m antennas [nasa.gov] are bigger that you might expect.

Re:Not even 0.5kilowatts..

[CausticPuppy]

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.

Re:Not even 0.5kilowatts..

[nyrk]

for transmitting from millions of miles away and some HAMs are using 10 kilowatts upwards just for transmitting earth-to-earth!

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?

[Fouquet]

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

[Anonymous Coward]

The rings of Saturn have puzzled astronomers ever since they were discovered by Galileo in 1610, during the first telescopic observations of the night sky. The puzzles have only increased since Voyagers 1 and 2 imaged the ring system extensively in 1980 and 1981. In addition to the images, several Voyager instruments observed occultations of the ring system with radial resolution as fine as 100 meters. The rings have been given letter names in the order of their discovery. The main rings are, working outward from the planet, known as C, B, and A. The Cassini Division is the largest gap in the rings and separates Rings B and A. In addition a number of fainter rings have been discovered more recently. The D Ring is exceedingly faint and closest to the planet. The F Ring is a narrow feature just outside the A Ring. Beyond that are two far fainter rings named G and E. The particles in Saturn's rings are composed primarily of water ice and range from microns to meters in size. The rings show a tremendous amount of structure on all scales; some of this structure is related to gravitational perturbations by Saturn's many moons, but much of it remains unexplained.
linky [yahoo.com]

Re:I hope it takes photos

[Mz6]

I can't answer for the thickness of the rings, but it was mentioned in a few of the articles that NASA is trying to stay as far away from the rings as possible. The closest approach will be from above the rings and the rest of the photographs will be taken from the top of the rings. Other than that, they consider them a collision hazard...

Re:Not even 0.5kilowatts..

[mschiller]

I should hope NO U.S. Ham is using 10 Kilowatts since we are limited to 1.5 KW output power. Now we won't talk about the Effective Radiated Power, due to the gain of the antenna's used.

1. http://web.wt.net/~w5un/mba2003.jpg

Re:Sound in space?

[lockefire]

The Huygens probe [nasa.gov] will be recording the sounds of Titan (which has an atmosphere).

Sound? What sound?

[allanj]

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.

Re:Victory of SCIENCE over ECOIDIOLOGY

[joehoya]

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) [doe.gov]. 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.

Re:450 watts?

[Rei]

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...

Choice: Saturn or Spacewalk

[CompressedAir]

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.

Re:Ah, but did it generate the 450?

[EvilTwinSkippy]

That's pretty easy to do. Look up the enthalpy of combustion for fuel oil and coal. Any good thermodynamic textbook will have both. The unit for enthalpy is KJ/g (Kilojoules per gram of fuel.) A watt is 1 joule per second. (Isn't metric lovely?)

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

[Neil Watson]

Cassini does NOT use a nuclear reactor. It uses Radioisotope Thermoelectric Generators [nasa.gov]. Please do no feed misinformation to the nuclear ignorant torch burning masses.

Re:Ah, but did it generate the 450?

[Rei]

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? :)

Re:Ah, but did it generate the 450?

[EvilTwinSkippy]

Oh yeah, and double all those amounts. That is the theoretical maximum that could be derived from the fuel. In practice, the best we can achieve is 40 percent. (In an industrial setting, small vehicle's like cars are lucky to get 10%).

So

2340 Kg / 0.40 = 5850 Kj of oil
3150 Kg / 0.40 = 7880 Kj of coal

Re:ObSpock

[Rei]

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.

Re:I hope it takes photos

[CausticPuppy]

yea but isnt the probe supposed to fly through a gap in the rings? it'd be great to get a photo taken "at level".

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

[bcrowell]

Solar power doesn't provide a lot of energy in deep space.
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

[Idarubicin]

People theorizing about asteroid mining in the past had talked about complicated ways of getting ice out of the rare ice-bearing asteroids. Now that we know Phoebe is icy, I wonder if it ends up being the most practical place in the solar system to get ice.

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?

[Vireo]

Simply reading the related article tells us that Cassini records the radio emission from the interaction between charged particles and Saturn's magnetic field (in order to measure its rotation rate). These radio waves are in the range of 50 to 500 kHz. The 100-300 kHz band was shifted to the audible 0-3 kHz band to produce the sounds.

Re:Victory of SCIENCE over ECOIDIOLOGY

[Rasta Prefect]

If it ticks like a clock, and keeps time like a clock, it's a clock. If it harnesses energy from the decay of nuclear elements, and it does so by converting heat to electricity, it's a Nuclear reactor.

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?!!

[WormholeFiend]

Actually, canada is an aboriginal word that means village.