Stuart Shaklanÿ
SAG 24: Exploring the Complementary Science Value of Starshade Observations

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Thank you.
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Yeah, my computer's like that sometimes. I'll just.

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I'll get in close, OK.
Great. Thank you, first of all.
Hi everyone and very sorry not to be there but circumstances require me to kind of remain close to home.
I am one of the lucky ones.
Still have a house, even though it's only a quarter mile from where the big fire started, and certainly my heart goes out to those colleagues and friends who.
Have lost pretty much everything.
Next slide please.
It's coming. Sorry.

OK.
So just briefly, I'll, I'll, I'll just cover the participants the I'll review what is a star shade and why we wanna do it.
What are its advantages?
I'll cover very briefly where we are with technology Starship technology.
I'll cover the SAG goals and then if there's any time left, I'll actually talk about what we've actually been doing.
So next slide please.
So this is the the group of participants that has been with us through more or less monthly telecoms and discussions, which can be quite enthusiastic. They represent you know our our major NASA labs universities, graduate students, senior researchers, engineers and scientists.
So it's a very good cross section and as I said, very enthusiastic.
Next slide please.
So So what is a star shade and why are we interested in it and enthusiastic about it?
First of all, it's a. It's a giant screen shaped.
It's kind of like a flower that flies in front of a telescope, and it's far enough away that it allows you to see very close to the stars.
So of course you can directly image the planet while at the same time it's blocking the planet and it's shaped like a flower.
For the purpose of controlling the diffraction of the star, it eliminates that spot of Irago or Poisson's pot that you would get on axis if if it if it had. If it was shaped, if it was, if it was circular for example.
It is it.
It has to move in the sky from target to target.
It typically takes one to two weeks. The chart at lower left shows a path that might it might follow across the sky. It's capable without refuelling of up to something like 200 observations over over 10 years.
And the science project didn't get out of it is a direct image.
It is an imaging system along with.
You know, a low to medium resolution spectroscopy.
Of the planets.
It has high throughput.
There's nothing blocking the planet light once it's seen out beyond the tips of the petals, so it's got 100% throughput.
It has a very broad bandwidth, very deep contrast.
It works great in the ultraviolet as well as throughout the rest of the spectrum, but it's even easier as you go into the ultraviolet.
It has small working angle and it's telescope agnostic.
It doesn't matter if the telescope is segmented or on axis or off axis or whatever next slide please.
So where are we with technology? And Nick touched on this a little bit earlier. There are three major gaps that we started working on actually before S5 or sorry before the Starship technology program was formed in 2018, we were working toward.
Toward these through SAT proposals.
The first is an optical gap, which is can we form deep contrast and can we reduce solar glint to an acceptable level?
The second is formation flying, which is mainly a.
Sensing gap can we sense with enough accuracy to keep ourselves aligned?
And the third is can we build A star shade?
Accurately enough to give it the right shape such that it will control the diffraction.
So with regards to optics, Nick showed a curve which was the the measured contrast curve getting down to below 10 to -10 contrast and that's in in broadband light. We also did experimentation with where we purposely perturb the star shade and did model validation where the model.
Just matches very beautifully the.
The the diffraction that comes from those perturbations formation flying we we did hardware in the loop demonstrations using outer band light where the star acts as its own natural kind of GuideStar that worked fantastically well. And in terms of hardware and building A star shade we have.
6 metre long pedals that were built with with high accuracy we have.
Seen in the upper right A4 meter pedal that was used for thermal testing to show that the thermal behavior is going to.
Easily meet specifications.
We built A10 meter diameter disk.
Maybe you saw it on the cover of National Geographic.
Maybe you're almost two years ago now, I guess and.
We've deployed that multiple times and and all these things related to the mechanics of the star shade all easily meet or exceed our requirements. They all use standard machine tolerance. Seeing there's there's nothing exceedingly hard about it at all, actually.
Not that it's not complex, but it's it's very doable.
Next slide please.
So our goals and this is back to the saga.
Our overarching goal is to study how the star shaped with its throughput and bandwidth, and at the same time it's limited mobility, can improve on the science case of of the corona graph.
We're studying the detection and characterization yield.
We're identifying how the broader spectral range, particularly in the UV and its higher SNR, can improve planet classification, and we're doing realistic.
Modeling of the star shape to evaluate on, in particular the.
The visible performance. Next slide please.
So I'm I'm I'm surely seeing the choir here, but it's worth stating that broadband measurements are essential to characterizing exoplanets first at at low SNR and at low spectral resolution.
We can, and we have misidentified molecules.
For example, methane is is confused with water, so you need to have multiple bands to measure multiple bands to. To truly distinguish the the different gases.
2nd we need to measure.
The bio signatures of gases in the context of other of other gases to understand really what we're seeing.
And when we look at how the the atmosphere of a planet can evolve, as you can see, we're going from an archaean earth to a protozoic earth.
Spectra signatures can disappear.
No ones can, can reappear and.
If you're looking at a protozoic earth, for example, those spectral signatures become quite weak, except for the very pronouncement which has appeared, which is the ozone signature.
Due to the presence of oxygen.
Which is appearing there in the ultraviolet.
So this is a signal that's easily detectable with the right instrument. You know, that's what the rest of this talk will mainly about.
And it's a it's of course a proxy for hard to detect oxygen. Next slide, please.
On.
And so, so here's a way to look at Planet classification, which really, which really caught our attention. And this tree highlights the different bands that are used for for classification with four bands shown shown in the rectangular boxes.
Going from Uvald to 1.8 microns.
So our thinking is that it would be very interesting to look at this chart in a different way and to formulate it by putting ozone at the top, because once you've done that in in a short period of time and maybe a one to three day measurement.
You can detect the ozone and determine whether or not oxygen is present, so that that would then really help to, I guess, prioritize the next set of measurements you want to make to to further characterize the plan.
So that's something that we'd like to go back and look at and and and see how interesting that would be our next slide please.
So all right.
So why do I say that?
That it's, you know, this is a making these measurements is is something that's within the grasp of * shape.
Well, first of all, what does star shade look like? That that can make these measurements?
For have worlds.
A6 meter have worlds telescope.
We've designed a 35m star shade that gets us to 65,000,000 working angle and it does it in a in a broadband covering 250 to 500 nanometers.
It's quite similar, as you can see on the right.
We call our baseline star shade, which we studied for many years.
That's the star shade that was intended for a rendezvous mission with, with the Roman space, with with the Roman telescope, and all of the pictures I showed you earlier of the hardware that that was all intended for for Roman.
So we're close in scale.
To that.
But what's really interesting is that once you go into the UV, the the resolution of the telescope and the the the the easier ability of that is of the star shaped to form a shadow.
Relax the requirements so so it's actually easier to make this 35m and make it perform than it would be for the for that 26 metre.
So we're quite confident that that this star shade would work at least as well as what we've been studying up to now.
To go into visible. That's that's. Now that the longer wavelength it's a larger star shade that's a 60 meter diameter star shade. Next slide please.
So we are modeling observations of the UV absorption feature of a modern earth, and this is led by Zara Ahmed at Stanford.
So we have a realistic model, the star shade.
We have a so-called worst case X azoot which is based on Chris Dark's dust map code with models provided to us by Miles Curry, and as you can see in the chart, a range of.
Earth, you know phases and inclinations and exosod densities.
Next chart please.
So here's an example of simulations broken down into different components that we're adding in.
On the left we have a diffraction related to a the leakage of the Starlight that is related to a highly perturbed star shade. It's very conservative.
Model of of Starship that's been deformed by up to centimeters, or up to 8 centimeter.
We had solar glint related to the the sharp edges and the coatings that we can put on the edges.
There's micrometeoroid leakage holes will get penetrated in starshade that will allow Starlight to leak to leak through, and sunlight to leak through.
That's included in the model.
As is other sources of solar scatter and there's Commission flying errors in here as well.
And even when we include all of these together and you can see how they contribute in three different bands across that chart, they still pale in comparison to to the exo zodi, which is the dominant source of of background force. And on the right you can see what.
The full scene looks like again dominated by Exo, zodi.
Next slide please.
Here's an example of post process.
Of a result that we would get.
This is what the spectrum looks like.
This is using very simple parametric model of of XS OD which is leads to the systematic error that you see in the visible.
It's not so prominent, and if you go to the next slide, you see now as we go from a 30ø inclination or 60ø inclination, the X axis contribution comes more important, but we still easily can pull out that UV signal.
So we'll be, we're preparing a paper on this, which will go into special issue of Jatis next.
Wait, it'll be submitted next Monday, right? OK. Next slide please.
So Rhonda Morgan and Mario Damiano have been studying the capability to move the star shape from target to target. And I guess without going into detail here, they found that for a reason.
Fuel capacity of.
Something like 4500 kilograms.
We don't run out of fuel even after 10 years and 180 maneuvers.
Next slide please.
This gets back to a 60 meter * shape.
A study simply of what is the yield of the star shade as a function of telescope diameter, both for the star shade and for the coronagraph, and the Takata requirement of 20 fiveverse characterize across the broadband is shown there as well.
We have different diameter star shades that work with different diameter telescopes and and this shows that and what's really critical in this chart though is that.
There's a priori knowledge assumed for these planets, and if you don't have that, if you don't know where the planets are and what their orbits are, neither the Starship nor the corona graph are going to are going to meet that decay requirement.
I guess that's that's I'm going to run out of time. So let me.
I guess just put up my conclusion slides and.
If there's any time, take any questions. Thank you.
Next slide, please. Thanks.

Thank you, Stuart.