חשפו את סודות החלל: למה אנחנו בונים טלסקופים בצורה שגויה לחלוטין?

Um, hello everybody. My name is Carol. Um, I'm super excited to talk to you today about some of the research that I've been working on, um, and have you thinking a little bit differently about the way that we design our space telescopes.

Um so here is an array of some different um telescopes. On the top row we have our space-based systems. Um top left is the Nancy Grace Roman telescope that'll be launching this year. On the top right you probably recognize it as the James Web Space Telescope. Um on the bottom we have two groundbased systems. The Hail 5 meter telescope located in Palomar, California. And on the bottom right we have the KEK Observatory which is located in Hawaii. Um so as you can see like looking at all these images you probably see a lot of similarities between the different telescopes um just in form factor and that's actually not a

coincidence. Um we've been taking a lot of lessons learned from groundbased systems for a really long time um and implementing these in our space telescopes and it has worked like really well for us. You've seen like the amazing images that James Webb has put out. Um but there are a few design paradigms that I think need a little bit more questioning and one of those is the stiffness of the structure. So um in groundbased systems the stiffness of the structure is very important um because you need to uphold your weight in earth's gravitational field. Um but when you go up into space you no longer have gravity or you no longer have weight. Um so why are we still um using that design convention?

So to investigate um this question um we can look at a pretty simple spring mass damper um representation of a space telescope and it's pretty crude but you can actually get a lot of really interesting lessons learned from this. Um so here the stiffness of the system is represented by K. Um C is representing the damping. M is like the mass or the payload that we're trying to control the motion of and F is representing like onboard disturbances such as cryocoolers and reaction wheels things that are going to excite the system. um x of t is representing like the displacement of the mass. And the reason why we care about that is because the vibration of our telescope systems um directly impacts um how much science return we can get because if you have a vibrating system you're going to get wavefront error, line of sight jitter and other things that are going to degrade your performance. Um so um from this diagram we can then uh get this expression. Uh so we derive this

equation. And you can see there's three parameters that are driving uh sigma x^ squ and that is the variance of displacement which is kind of like a representation of the vibr the vibration of the system. Um in the numerator you see fot which is the forcing that I mentioned. Um and in the denominator you can see an interesting uh relationship between the vibration and the um k* c which is the product of stiffness and damping. So what this is telling us is that if we increase stiffness and damping as a product, we're going to be able to bring down the amount of vibration in the system, which is really great. Um, and in our last slide, uh, I mentioned how we've been designing our systems to be very stiff. And that's represented here. If we have K as a really high value, we're able to get, um, good performance. But now we can ask like, well, why don't we also include C in our, um, analysis, in our design. So um in order to look at this question

a little bit closer, we assigned a mass surrogate to both the stiffness and the damping. So we can see what is the mass penalty of increasing either one of those parameters. And I plotted that over on the right side of the page. You can see this plot. Um on the y-axis that's the total mass of the system. On the x-axis that's the stiffness to damping ratio. Um and you can see on the bottom of that curve we have a minimum mass solution at around 4,000 kilograms. And um for reference the damping um required for that uh minimum mass solution is around 33% damping. And for

reference of like how large this damping is um James Webb which is pictured with the orange star on the right side, James Webb is at a fraction of a percent damping. Um so traditional convent or conventional space telescopes are usually designed at that really low damping. Um, and this shows that there's potentially a really big gap between if we increase the amount of damping in the system, we could get a lot of mass um, optimization from this.

So hopefully I've convinced you that damping is like a potential way that we could improve our structures. Um, and you might be asking now like how do we actually implement damping into our structures? So one really promising way to do this is called structural impedance matching. Um, this is a method that we're looking into right now. Um, and the the concept of structural impedance matching is something that's taken from the electrical engineering field. And the idea here is that you're trying to minimally reflect vibrations and maximally absorb the vibrations in the system. Um, to show how like potentially great this could be for our systems, uh, you can see this like gray curve, um, the light gray curve with the sharpest points. That's representing the quarter of a percent damping that we typically use um, in our telescopes. And you can see really high um um response amplifications which is what we're plotting here the response amplification versus the frequency of the disturbances. Um and when we increase our damping to like 1% and 10% you see these curves starting to come down. So like the darker gray curves you see have a lot lower um amplitude. Um and the red curve is representing the impedance matched um solution. And you can see that across the entire frequency band you have um a reduction in um resonant peaks and in ouri in vibration. So this shows that impedance matching has a lot of potential um in our um to be applied as uh damping in these structures. And through this research we've also seen a lot of really um other interesting benefits to um including damping aside from mass optimization.

One of which is faster slooh time. when you have a lighter weight structure, you're able to move it more quickly. Another one is the settle time. Um, so after you move a structure and you're pointing at a new target, you're able to damp out those vibrations more quickly, which means we can get faster science return. Um, and then additionally, launch load alleviation. When you're blasting this thing off into space, you're getting a ton of vibration, and damping is a way that we could potentially bring down um the amount of loads that the structure is experiencing. So all of these different um mechanisms that are um being opened up by damping

can mean that we can get more science productivity. And the reason that I think that this um the reason I'm excited about this research and I think it's really important is I think we've mentioned it a lot today during the talks uh there's a lot of upcoming missions like the habitable habit habitable worlds observatory um which are going to be looking for um life outside of earth and I think that by optimizing our systems um considering damping as a design parameter and re rethinking the way that we um design our space telescopes we're going to be able to get to answer those questions a lot quick a lot quicker. Um, so thank you so much for listening. Um, I really appreciate it and I'd love to take questions after the talk.