Hi. Currently, the furthest man-made objects from Earth are the Voyager space probes launched in 1977. Voyager 2 is currently 17 billion kilometers from Earth. That's like going to Pluto and back and then back to Pluto again roughly and we can still contact it.

How let's find out. So what does it take to track Voyager 2 A big antenna? So in the case of this 70 meter, Deep Space Station 43. so we can track on smaller antennas, we have a couple of beam wave guys that are 34 meter. but if you want a nice signal with a lot of margin, you pick a big antenna.

So looking at it, you've got 8 000 tons four thousand below the bearing. Essentially four thousand tons of swivel. It's all hydraulic. 43 is a hydraulic antenna and it uses a unique platform called a hydrostatic bearing.

so there's no friction. So it the whole antenna that moves rides on a film of oil seven thousandth of an inch thick, pressurized 2500. PSI. It just lifts it a tiny amount and it slows round at the moment we are looking at Voyager 2.

we're tracking now. the beam width of the antenna on x-ray band 30 Milli degrees. So so we deviate any further side to side, we lose it. So in fact, it's not just the antenna pointing, that's the important thing.

It's a sub-reflector as well. The sub reflector sort of moves on all axis and we actually have calibration tables that so as the antenna goes down, we have a squint Factor That's where essentially the antenna will sag and it has to be compensated for as well. Now that's just the antenna side, so we have obviously that has to be extremely accurate. Then we also have the RF side and that's where the interesting stuff comes in.

The antenna is pointing up surface of the dish Classic parabolic classic Casa grain where it bounces off the dish surface, hits the sub reflector and then is reflected down into the cones. Now low noise amplification is important so and we certainly don't want to introduce any more noise than sort of the sky is giving us. So we we cool it and all our Lnas are cryogenically cooled about. oh, a tropical four and a half Kelvin So you get rid of the the noise effect there.

In fact, the whole system noise temperature of one of our antennas. So if you look from the cone to the the receiver itself is probably no more than 19 Kelvin. So when you're looking for very small signals in essentially a field of noise of yeah, you don't want to be introducing any any further noise if you look at what we are receiving. So strange enough, Voyager isn't the weakest signals you expect it to be because it's so far and and it's it's our weakest signal, but it doesn't really work like that.

Voyager is weak. We uh, so probably have around about negative 158 dbm. but we do have lower. Voyager has a nice big High Gain antenna.

so we all have a number of missions and I'll give you an example. So if we have Kepler which is literally just outside of our atmosphere and it's looking for exoplanets while it's looking for exoplanets, so if it's configured to talk to with on its low gain antenna and we can be receiving in the mid neg 160s so it's even lower again Maven we have around Mars again so not very far away at all relatively speaking. Uh so and you know we can pick up an egg 170 dbm on Maven and that's because it's High Gain antenna is orientated towards a towards Mars it's actually so transmitting its housekeeping, which essentially all it is. it's 20 bits per second.

It's a tiny bit rate so just to allow us to know that everything's cool, everything's operating fine, and the spacecraft health is is good. negative 158 about we receive. So what does that give us? as far as Telemetry Telemetry on Voyager is a huge 160 bits. So it's been there for quite a while and we're hoping we won't have to go any lower.

We have the margin on the 70 meter. so Voyager we actually receive 160 bits. The symbol to noise ratio on on this antenna here is around about six and a half seven. DB that's a symbol.

Noise ratios of the bit rate is 160 bits as I said. but we actually use a an encoding method called the multi-convolutional encoder. same thing you have in your ADSL modems and what that does is affect. it's A.

it's a form of forward error correction. so you transmit 320 symbols to get your 160 bits of data, but it gives you a 3db Improvement it doubles. It's a simple SNR We now have a bit SNR of double wet or just a 3db not double as in numbers. You look at a 34 meter so obviously it takes about three and a bit 34 meters to to be the equivalent 70 meter.

We're hovering around zero on the symbol to noise ratio so you can tell if we have a a little bit of rain on a 34 meter. It wipes closure out when we go below probably 30 degrees and you start getting the the ground noise coming up, it wipes out Voyager So what if we don't have a 70 meter available during that period? What we'll do. We'll array 234 meters so not the equivalent of a 70 meter, but it gets us past that hard. So I Suppose a little bit more of a margin so we can sort of ride that weather out and we can get a little bit lower on the horizon.

As far as transmit, Voyages has essentially different requirements for this transmit. We have a Blf where we transmit a series of ramps and this is to try and characterize a failed capacitor that happened years ago and we've we've handled that all the way up to today. So this is their second receiver so the first one is dead. So and if you think of Voyager 2, it's it's a very uh, 1977 and you think of the technology around at the time.

and yeah, so and it was just a failed a failed component. So unfortunately the the backup had already died. So whoever designed it came up with this clever idea of if I don't talk to it within a certain time, then obviously the spacecraft thinks there's something wrong and then it goes into a safety mode Where it's it grabs its star scanner and starts scanning around, making sure it's orientated towards Earth. So another method had to be thought of to actually get into the receiver that was failing.

So that's where we had to categorize the best lock frequency or the rest frequency of the receiver. and we'll do almost on a weekly basis of best lock frequency characterization where we just transmit a ramp and then 30 hours later we see the receiver status. So we'll get a lock status and we'll have a speed and we'll know then that when we have to transmit later on commands to it, we know exactly the the frequency that we need to transmit on. You know So you look at radios and then you look at the DSN and if we're more than a couple Hertz out over 15 billion kilometers we're doing something wrong.

So it's it's that you know to put into perspectives of our subcarrier Loop Bandwidth is half a Hertz So so they're all really tight tolerances of and and all the spacecraft that we do support, including Voyagers, are certainly well characterized as well. Uh, And also, we have a wonderful system Voyager doesn't use it where, uh, the spacecraft will turn a signal around at a fixed ratio as well. So we actually have a predicted frequency that arrives back on Earth because it's reference to our frequency of within .02 of a Hertz Again, so these things can travel billions of kilometers as well. Uh, so we we are plank.

So we have an 18 kilowatts and that allows us to send a no-op command. So every now and again we'll send a series of commands, which essentially just commands saying you're happy, just reset that timer and we'll talk to you another time. And we compensate from the failed competitor by just re-transmitting that same command. as we start ramping those frequencies.

we'll just keep on transmitting it if one gets in. That's all we need with uplinking commands. As far as a sequence where we're actually telling it to do a MAG roll or some other form of calibration, we can't We can't rely on luck. So what we'll do then is we'll characterize the best lock frequency, but we'll transmit 75 kilowatts.

We'll get that margin into the spacecraft so that receiver can hang on just a little bit further and so so far so it seems to be a successful and it has been for the last 20 years. If you look at weather, the impact of weather which is really the uh, a good way of characterizing where we drop it off and you talk about system noise temperature. So normally I say we're about 19 degrees if we get a rain shower that signal. so the the SNT the system noise temperature can raise to around about 90 Kelvin and and above and we'll see that 70 Bsnr just disappeared to zero.

So rain is a big factor here. I Should point out with Voyager as well, it has two frequencies so we receive on X but we transmit s so completely different systems. In fact of one thing you can't see is we have two separate cones and so and you'll see we have an S-band cone and then expand. You go well, hang on.

So how do we focus on both cones at the same time? Well we use a dichroic mirror think of a band pass filter so it's a piece of a hardware. So what we have is we have the Snx signals coming down and a dichroic plate. I'll try and get you on there, a dicrow plate which is has perforations which have been drilled to allow X-band through at that wavelength but reflect the big chunky Sierra bands which are reflected to a little umbrella mirror and then down into the the cone. so it follows the same path all the way to the dichroic and from there they're actually separated out.

Think of not so much signal level. think of Kelvin It probably adds two or three Kelvin So it does introduce a little bit of noise and it does attenuate ever so slightly. but it's marginal when we start looking at some of the even Mars reconnaissance Orbiter and uh, sort of Mars Odyssey and they're pumping down three megabits. They're using either a Turbo 1 6 or an Mcd-16 So essentially out of six bits, only one's good.

But we can get down to a minus six symbol SNR so you're looking so proportionally more noise than signal. So and you go okay, well, how do you pick the signal out of there? and fortunately, noise is random where hopefully the signal isn't so so we're able to from that minus six symbol SNR we can actually get a positive, five or six bit SNL So using that encoding method, so a lot of projects what they'll do is they'll sacrifice symbol SNR. So for essentially sort of knowing that they'll get the better sort of a bit SNR at the end of it after the user coding, Sierra band on 43 is 400 kilowatts. We've used it probably twice since I started here 30 years ago.

Uh, S-band is a funny frequency now. So we've the Deep Space Network has tried to move out of the Sierra band and now Sierra band is to the Moon but after that we were like X and now K K A is okay is coming into it as well about 32 gigs. So as far as weather is concerned, the care is a real pain. S-pan's really robust I mean and I suppose you look at the size of a raindrop and the you know, the size of a an X-band bandwidth.

so it's about so big. So yeah, there's obviously a fair amount of attenuation in that raindrop. You talk about S-band right? So it's far more robust. So it's a physical size of the water drop that does the damage exactly right.

So we also have uh, physical issues of water on. We actually use a Capcom window so which is uh, so essentially a film, a plastic film that goes over the cones nitrogen pumped to keep it moist, keep the moisture out. it blows them out. uh, and RF as transparent.

So if we get water beading on that, we actually have attenuation as well. So so we've got a retrofitted vacuum cleaner set to reverse so that's continuously blowing that, blowing that water off, and or stopping it from settling as well. We try to use uh, essentially commercial power as much as possible. obviously it's cheaper.

We have recently gone to a three megawatt uh Op system, which can take us to three minutes so it can deliver three megawatts for three minutes. But in in that three minutes, hopefully our diesels have started kicking in. so we have Uh four, three quarter of a megawatt s of Caterpillars in there and one station and four in another so we can provide Oodles of power. Uh, but but yeah, we tried to use commercial uh on that three minute ups and uh, but we always had the backup with the diesel.

In fact, so when we go to level ones and for us, a level one is anything that involves Uh encounters, uh Landings uh For instance, when MSL hit Mars well gently and not like beagle that hit Mars So so uh, then then the site would have been on on on diesel power sort of. And so so regardless of what the commercial power does, we've got a guaranteed power supply. If you look at the DSN you know we're here to essentially to to establish that connection between the project and and their spacecraft. Voyager was launched in 1977.

the Deep Space Network has supported it sort of from launch so you know it's on I Still have colleagues who can remember that launch now. So I'm a relative newcomer at 30 years. so we actually have a a guy who's 15 years and he's said to be here dog watch so and who who was the last recruit. So so uh, Voyage is a special spacecraft for the entire DSN The fact that Canberra has the only visibility makes it even more special.

We do have site of Voyager 1 and every time we go down on Voyager one, it's like it feels they were poaching. So because nobody can see our Voyager too. So Voyager 2 is definitely a southern hemisphere spacecraft that's a really sort of belongs to Canberra so we have a vested interest to make sure that it lasts. And whereas Voyager one has has exited into Interstellar space, Voyager 2 has isn't there yet.

so we're still waiting for that Milestone as well. So so there's with Voyage to this little element of anticipation. So and you know you think of a spacecraft just going out and out and out doing nothing. It's not, It's still an active spacecraft, you know.

So on a regular basis it's doing calibrations that we're monitoring on Earth So you know when it it calibrates its magnetometer in what they refer to as a MAG roll where they spin the Gyros up a couple of days before and they rotate the entire magnet spheric antenna around and then they'll do it again and we actually see that variation on the downlink as well. So and here we are 15 billion kilometers away and you really do feel a part of it. So even though you're separated by an awful lot of space, uh, what we have for the future, Voyager was launched with an RTG and as far as a power source which means it has little pellets of plutonium that have a half-life of a fairway I Think that's 70 odd years. I think for plutonium.

Unfortunately, the RTG themselves are starting to break down, so it's not the plutonium that's the issue. it's essentially the uh, the transducers so we can't see us tracking. Voyager Beyond say 2025 which is still a fair number of years and we're still hoping that it will hit Interstellar Space sometime within that I'd hate it to lose it. and then so suddenly it found it and 160 bits, we can still go further down, right? We can still go down to 40 bits 40 bits per second.

so in fact, it does that now. So when it does, uh, sort of changes on board. So and it does equipment swaps, it will go down to an engineering 40 bits. and we're talking about the pain drying.

Uh, so 160 bits takes probably about three or four minutes to lock. So 40 40 bits, you know you're pushing it out a little bit further. actually talking about Maven the 20 bits. It could be anything up to 14 minutes to lock.

After 13 minutes, you find there's some some issue with configuration. it's a it's a long wait to get to that second frame so so that can be an issue as well. So so Now Voyager is quite special for the deep space. Network And also you know other other spacecraft will come and go, but that's the one that's going to endure.

special. They design it to last that long did they think it would? I Suppose by its nature, the fact that it had the RTG meant it could I Honestly don't believe they thought it would. You know you look at the primary missions that they had, you know sat in Jupiter. After that it was all.

it was like Woohoo! Yeah, so it was. And the fact that they actually got one shooting out to the South and one shooting out to the north of the ecliptic so gave a little bit of diversity as well. And sort of, you know, not so much of a Voyager one, but Voyage who had the secondary encounters and they just kept on going. Sad thing, we went in the wrong right part of this space to do Pluto right? But uh, you know the Uranus Neptune sort of encounters were quite special as well.

Foreign.