The issue of person wandering around with this strategy in the sensitive areas with a mobile
device and a construction of uro I could understand the place of the new cycle, the place of the
plant, the place so I could have the same problem.
So my question is this, over the say a 20 or 30 year period that the ISK may operate,
how are you going to stop the progress of Australian civilisation impinging on that area,
or the area of the plant?
Yeah, federal legislation.
So that whole area is protected under federal legislation so that you can't actually build
or introduce any new significant radio transmitters into that area.
So it's what's called a radio quiet zone and is protected as such.
So that's exactly the, so these areas before people will spend a billion dollars building
something for radio astronomy that has to be legislative protection for that area.
So both Western Australia has that and South Africa site has that as well.
So there exist, well there's 100 people there now, they have homesteads and there are public roads.
So there is interference but we're able to define buffer zones around various bits of infrastructure.
So for example 10 kilometres either side of a road, you couldn't build an antenna.
So you can build the antennas far enough away that the interference drops off.
So we produce a mask of the area that has go and no go zones and we build the telescopes in the go zones.
Sorry, there's someone with the microphone.
I believe that confers precedence.
I have two questions. Last time on TV they had a very interesting to listen to South Africa
and really pushing the point of the fact that we are a very poor country
and we need this for our economy and that seems to be the main issue of the wonderful NISC.
I don't think that's sort of...
Yeah well that's the card they've chosen to play.
And the only reason they do that is because it has a fair chance of working.
So in Australia we're very strongly focused on building the best possible instrument on the best possible site.
So there's an evaluation process underway and whichever site comes out technically and scientifically
the best place to build the SKA is where it should be built.
Sorry?
I have to be honest and say it's difficult to say.
There are many factors that are being evaluated.
It doesn't matter how many technical and scientific factors that you consider, sometimes subjective factors come into account as well.
But I don't think it will be a big consideration.
When people are spending a billion dollars they're usually pretty rational.
Who decides?
That's a good question. So at the end of this year an international organization comes into existence called the SKA Program Office
and its job is to spend 90 million euros for the design process.
Those 90 million euros come from as it stands at the moment eight countries
and each of those countries will then have two delegates on the governing board of that organization.
Those delegates will decide.
So that's going to be the ultimate selection committee.
There'll be a number of recommendations through the evaluation process
but those documents end up with that governing board.
They've paid the money.
They've paid for the right to make that decision.
It's their money on the line.
There's no zero vacuum energy in the universe.
Does that mean that there is energy on that?
Yeah, according to my understanding of all of this and I stress again, I'm not an expert cosmologist
but yes, that vacuum energy increases.
That's about as much as I can say.
That appears to be the case that the energy is constantly created out of the vacuum.
So this is the problem.
Physics has always told us that these things are always a zero sum game.
So if nature is different, then we need to explain that and revise our physical laws.
So it is a bizarre scenario if you're used to physics.
But special relativity was bizarre.
Quantum mechanics is bizarre.
It's just the next bit of bizarre physics perhaps.
You said that there were several towns in the African area.
Have you had chance to have more of the noise before?
It's part of the evaluation process.
So a very important part of that process is to test the RFI environment.
So they built a test rig to go and measure that
and that was deployed in Australia for a number of months to make measurements.
Then exactly the same equipment was deployed in South Africa over the same number of months.
So all of the data exists.
I haven't seen it.
I've seen little bits of it.
But yes, that data will be evaluated, any differences in the interference will be discovered
and that will be taken into account when this group of people make their decision.
It will be one very strong factor.
I assume you need to minimise the amount of interference that comes with the technology that you bring in with the SAA.
It's like a modus to move the dishes.
I was wondering what is the biggest thing that brings in interference and how do you deal with it?
Really good question.
So self-generated interference from the instruments can often be the worst offender.
So you need to set stringent specifications on what interference that you are allowed to self-generate.
So I can't reel off the name of the relevant spec, but it's mill spec whatever.
It's a military specification.
It's very, very stringent and anything that goes up to be installed on the site needs to be tested in a lab
and proven to have emissions lower than the mill spec numbers.
That's actually a very, very difficult thing to do and takes a lot of time to appropriately shield all of the equipment.
So for example, some of the equipment we're sending up for the Merchants and Wide Field Array is just doing its final stages of testing in the lab.
You have to pay a lot of very careful attention to make sure that you don't spoil the site just by being there.
You said that the choice of the location of the SKIS was between Australia and Africa.
I've actually been there, but it's been quite a long time since I'm here.
It's a comfortable place, an interesting place, an adventurous place and a time of day for some reason.
So wouldn't the Australian site have a huge car that they can buy with respect to security
for the equipment and the technology and the installation itself?
Wouldn't that be a major factor that we would just basically choose to try?
The formal evaluation follows scientific parameters, technical parameters and geopolitical parameters.
So those sorts of things are factored in, so the evaluation will consider all sorts of things,
the cost of labour in the two countries, the availability of skilled workforce, security,
all of these sorts of things will be factored into the decision.
There's about five pages of factors and each factor has its own weight assigned to it.
So yes, the short answer is yes, that all of these things will be looked at.
Are there any arrangements putting place for the sharing of data?
Sorry, where are we?
Radio astronomy has traditionally followed what's called the open skies policy,
which is regardless of who's paid for the instrument, the resultant data or the access to the instrument
is open to absolutely anyone.
So regardless of who pays for it, typically it's been the case that all they've asked in return
is for people to do the best science, regardless of whether they paid for it or not.
And so it's a sort of reciprocal thing amongst the countries in the world
where we use facilities in the US for free and US people use facilities in Australia for free.
That paradigm has shifted a little bit in recent years.
I don't think it's fully decided how it will work for the SKA,
but I suspect given the countries and many of the individuals involved,
there will be a very strong push to keep that open skies policy.
Are there any advantages over a north-south access,
I would say at least west access over north-south access?
Yeah, that's a really good question and the short answer is yes.
So one of the things that I've been involved in is designing the remote station configuration
and it's definitely the case that an east-west configuration has advantages over a north-south configuration
and that's because if you make an observation over a number of hours,
the rotation of the earth gives you a better result for an east-west array than a north-south array.
It's a pretty technical consideration, but it's true that east-west is better.
Yeah, I've gone back to the noise question again,
particularly the noise generated by the mission itself.
To what extent can that be made not noise by having a deterministic signal
so that you can now subtract it from?
Yeah, there's a number of different ways that you can deal with interference.
So of course the best way is not to produce any interference at all.
But when the data is being processed, whether the signals are deterministic or not,
there are certain signal processing techniques that you can use to remove the interference from the data.
As long as the interference is not so strong that it overloads the RF analog front-end components
of the telescope like the amplifiers.
As soon as you drive the system nonlinear, there's nothing you can do.
If the instrument's working within its sort of linear dynamic range,
then there's a lot of things you can do in the signal processing afterwards.
So first thing is, minimize the interference to generate.
Second thing is, put into place the signal processing algorithms
that allow you to remove the interference from the data before you make an image.
Stephen, I'm interested in the sensitivity of the antenna,
but what's the difference between the antenna and down to the horizon
and what is the area that it won't go?
Yeah, so that's also a good question.
So the dishes can point in any direction.
So the dishes to within about 10 degrees elevation can maintain full sensitivity all over the sky.
The aperture arrays that sit on the ground in a non-steerable suffer from a projection effect.
So if your object is at zenith, you get full sensitivity,
and as you're looking at objects closer and closer to the horizon, you're flat.
At the zenith, you know, you're getting a full collecting area.
At 45 degrees, you're getting the projected part of that area,
and at horizon, you're getting nothing.
So your sensitivity varies as a function of the elevation of the object that you're looking at.
But it varies predictably, and you can always design sequences of observations
that keep you close to the zenith to maintain full sensitivity.
I have a question that follows on from that. If the arrays built in Australia,
what proportion of the celestial sphere will it be able to see?
Yeah, it'll see, let's see.
It'll see to about plus 30 declination with some sensitivity.
So that's most of the sky.
The really important thing about being in the southern hemisphere is that
the centre of the Milky Way galaxy passes overhead.
So initially, there were four sites considered.
China, Brazil, Argentina, South Africa, Australia.
And a big point in favour of South Africa and Australia is that
they're at latitude around about minus 30, so the galaxy goes straight overhead.
Obviously, the biggest telescope in the world should be able to see our galaxy.
So the northern hemisphere is not much good.
Pretty technical questions.
Yeah?
Yeah, well, to do some of these cosmology experiments,
it doesn't matter because every direction you look, you see the universe.
Probably the very, very first observations will be looking at some part of the sky
that's very well known, so we can first of all make sure that we're getting the right answer out.
And having gone through that acceptance phase,
the telescope will be scheduled to do lots of different things
and can possibly do many different experiments simultaneously.
So you might be searching for pulsars at the same time that you're mapping the hydrogen in the galaxy
and the same time that you're doing cosmological observations for dark energy.
So it's one of the really nice things about the instrument is that
you can probably simultaneously run quite different experiments.
Does it make it a shee?
Does it make it a shee?
Yeah, why not?
