More on the Pluto-Kuiper Express

addie writes "Scientific American has a great, extensive article about Pluto and the possibilities of exploring it in the near future. Neat descriptions of Kuiper Belt and what we can learn about solar system birth and growth from the tiny planet."

Comments

Don't go there

[_damnit_]

This sounds interesting, but I think there are closer subjects of interest that could be explored. Too many things could go wrong with a trip that long. I'd like to see more emphasis put on getting to Mars, developing a cheap replacement for the shuttle and whatever happened to that space elevator? I know, it was just a book. But it sounded so cool.

Too late

[Faux_Pseudo]

It's all find and nice of them to have ideas about exploring Pluto now but its too late for the fun stuff. If they had launched a craft 5 years ago we would have gotten there in time to witness the changing of the seasons.
Now its going to be another 250 years before we get to see both the summer and winter time on the planet. And what a seasonal change it is. In the summer it has a liquid nitrogen atmosphere and in the winter it freezes and falls to the ground.
If only they had gotten off their but sooner.

tech details from the article...

[bedessen]

Like most of these it was light on hardware details, but this was hidden in one of the captions:

The spacecraft has a design mass of 416 kilograms (917 pounds) and is about the size of a small lifeboat.

On the journey to Pluto, the probe will reach a top speed of about 70,000 kilometers per hour.

The craft's computers will be able to store 48 gigabits of data and transmit the information to Earth at up to 770 bits per second from Pluto (16,000 bits per second from Jupiter).

48 gigabits of radiation-hardened memory must cost a fortune...I seem to remember that Flash ram is not suited to this kind of thing since its especially susceptible to energetic particles (alpha, gamma rays) dislogding the charge trapped in the gate dielectric (which holds the information.) Anyone know how data storage is usually carried out on these things? I can't imagine using anything with moving parts, and since the craft is supposed to be powered down for most of the time while it drifts, I'd think you'd want something non-volatile. I would hate to think what would happen if there was a brief power shortage or something and all the readings from the entire mission that were queued up to be sent were lost.

As to the 770 bits/s, I'm amazed it's even that fast. Consider that the RF power decreases as 1/r^2, where r is about 7.5 billion km. They are using a directional 2.5m antenna, lets say that's 100 dBi gain. Still, even if they managed to transmit 10W at the satellite (which is a lot for radio), we'd receive about a picowatt (1e-12) of it here on earth. I've heard that number thrown around before as a typical power level that we receive from deep space, and it boggles the mind that we can detech such faint signals... guess that's why it takes arrays of gigantic dishes with supercooled LNAs to do it. And it's great example of how power and bandwidth are related in communications. The more power your signal has at the receiver, the more information you can convey (bandwidth.)

Re:tech details from the article...

[26199]

Hmm... 48 gigabits and 770 bits/s? That'd mean two years to send the whole lot... or is most of that likely to be used for processing?

Hmm, I suppose if you compress the signals, you could get the whole lot in a matter of months...

Re:tech details from the article...

[stevelinton]

Actually the received power levels are much LOWER than that.

10W at the antenna, say it's at 1cm wavelength (not sure about this, but it should be within a factor of 10). Thats a 250 wavelenth tranmitting dish, so the signal is spread over a 4 milli-radian diameter cone. At 7.5e12 m that is
9e20 m2 spot, so a 250m dish on Earth receives
125^2*pi / 9 e20 of the signal, which is about
5 e-16 W.about half a femtoWatt, ignoring any imperfections in either dish, noise, absorbtion, etc.

By radio astronomy standards this is actually quite a powerful signal. I think they work down to 10^2? W for fairly small values of ?. On the other hand, they need a 770Hx bandwidth here, which is relatively wide.

Someone else commented on the time it would take to dump 48Gb of data over this link. This fits the mision profile beautifully. They fly past Pluto/Charon in a few hours, recording frantically on all instruments, then the slowly download the results, which coasting out into interstellar space. This mission is a fly-past, not an orbiter.

Re:tech details from the article...

[Anonymous Coward]

Note: I'm a radioastronomer involved in instrumentation.

Half a femtowatt is still quite a lot of power in a 1kHz bandwidth (you want to have some redundancy in the 770 bits, so let us round it up to 1kHz).

Let us start from the noise power of a resistor at room temperature in 1kHz bandwidth, it is about -144dBm or 4e-17 W, or 40 attowatts. Now building narrowband amplifiers whose effective noise temperature is much lower than 300K is a no brainer (for people who know how to build amplifiers around discrete pseudomorphic high electron mobility transistors). I've not checked recently what the room temperature performance of the most recent transistors is but I'd believe that a noise figure of 0.5 dB (equivalent to the noise of a resistor at 40 Kelvin) is routinely guaranteed at 12 GHz on commercial transistors, like Fujitsu's FHX13. As I said better models might be available now. In a 1KHz bandwidth the equivalent input noise power of an amplfier like his ould be around 5 attowatts.

Now if you push me, I'd tell you that by carefully selecting the transistors and operating them at cryogenic temperature, the amplifier noise will be even lower, perhaps by a factor 5 or so (over 3 guaranteed).

At this point the most difficult problem even with a high quality antenna is probably to get rid of human interference and noise is probably dominated by the scattering of the antenna beam. Note that I do millimeter radioastronomy so I don't know well the detailed technical problems of centimeter guys, but while we don't (yet) have problems of interference with other human activities, it is a severe problem at longer wavelengths.

In any case, you have a reasonable signal to noise ratio, even if the antennas are smaller than what you think (DSN antennas are 60 or 64 meters, I can't remember the exact value).

Ok, that's all, but remember that we radioastronomers use the Jansky as flux measurement unit. A Jansky is 1E-26 W/Hz/m, so it would be about 0.01 attowatt on a DSN antenna in 1 KHz BW. And 1 Jy is a strong source, even in the millimeter range, we are rather chasing the milliJansky (on wide bandwidth however).

Why exploring Pluto is worth something

[jesterzog]

There are several good reasons to study Pluto ASAP, not the least of which is the changing of the seasons. It's not really a Pluto mission as much as it's a Kuiper Belt mission. Among other things:

• The Kuiper Belt is believed to be very representative of where comets come from, so studying Kuiper objects will give a much better insight into comets and what they are. This could also help with plans for any opssible doomsday-avoiding strategy. (I'll leave it up to you whether you consider that important or not.)
• Pluto isn't just a Kuiper Belt object, it's also the one that we know most about having tracked and studied it from Earth since it was discovered in 1930. Any information returned can be correlated with existing information.
• The plan isn't just to study Pluto. It also includes flying past several other Kuiper Belt objects.
• JPL's had some high profile failures lately, and maybe that's why you think there's a lot that can go wrong. But New Horizons is a flyby mission, and by JPL standards it's easy, and it's been done heaps of times before 100% successfully. There's probably a much better chance today of this thing working than there is in the next Mars rovers working.

And anyway, how much would scuttling this mission help to explore Mars, which compared to this tiny mission already has a massive armada of effort and funding going into it? Maybe we'd get there a couple of months faster.. except we wouldn't anyway because the optimal launch window would stay where it was.

Western scientific ideals vs terrorism

[Anonymous Bullard]

And given the romance and adventure of exploring uncharted worlds, it is not surprising that so many citizens and grade school children have also become excited about this mission to new frontiers.

To me this quote represents some of the best ideals of the so-called western civilization. There's a deep-rooted sense of purpose in pushing the barriers of scientific knowledge and understanding. Despite the fact that military is also interested in any advances stemming from such exploration the ultimate aim is to have this knowledge advance the whole of humanity.

So how does terrorism - as demonstrated by the relatively recent islamic jihad against the western world - fit into this picture? Well, for a long time while "The Old World" was suffering under the Dark Ages (imposed by religion, the Church) the islamic empire had a thriving scientific culture. That fine and rather benevolent islamic culture was eventually suffocated by increasing religious dogmatism so it is highly ironic that those same forces are now attempting to destroy the West where the evolution of the State and Religion followed the opposite route.

I don't think I'm much off the mark by saying that the driving force, or motive, behind the actions of the "ultra-islamic" terrorists is simple envy and the desire to pull the West down to the same level of stagnation and religious revival that they themselves are under. If the western governments, and especially the US, decrease their scientific commitments in favour of military spending the religious terrorists have gained a victory of sorts.

PS. Would it not be ironic if scientific missions such as this one to study the Kuiper Belt would help us (the humanity) to better understand dangerous asteroids and help us learn how to repel them. Suppose just one, say 10 miles across, was on a collision course with Earth and was calculated to strike the Middle East in the 2030's. Would the Mid-East populations still support the destruction of the West? Of course, if the object was calculated to hit North America or even Europe there would probably be much rejoicing in God punishing the infidels...

The Galactic Construction Co.

[Alien54]

I remember a short SF story where some people are exploring Pluto, and they come across what is essentially a construction shack left over from the construction of the Solar System, complete with leftover diagrams.

They don't get it at first, but they figure it out because in some part, the maps they find obviously display the solar system, but some things are very different, and they come to the conclusion that the original contractor screwed up the original job.

Who knows what we'll find.