The Large UV/Optical/Infrared (LUVOIR) surveyor: engineering design and techn...

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题名	The Large UV/Optical/Infrared (LUVOIR) surveyor: engineering design and technology overview
链接	https://doi.org/10.1117/12.2530456

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11115/2530456/The-Large-UV-Optical-Infrared-LUVOIR-surveyor--engineering-design/10.1117/12.2530456.short

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OK, LUVOIR will launch in 2039, so mark your calendars.

[LAUGHTER]

We are baselining an SLS launch vehicle, although we'll talk a little bit later about some of the other options that we've been exploring. Like most of these missions, we have a five-year prime mission. We are expecting it to be 10-year consumables. But we are actually building in the capability to service LUVOIR. That's exactly a major part of our design. So we want to be able to swap out instruments, replace spacecraft components, and so on.

Like all the other observatories, we're at L2. That's where everybody wants to be. And from there, we can observe half the sky-- nominal viewing zone. So we keep our telescope oriented in this position. Although we can tilt up to 45 degrees towards the sun for specific observations. That's a rare maneuver. Our keep-out zone is anywhere pointing towards the sun because that's bad.

We have one architecture and two concepts. This architecture is scalable. We made it scalable so that we can respond to an uncertain future. There are a lot of different launch vehicles coming online that-- some of which we don't know exactly how well they're going to perform or when they'll be available. We know that the budget of the future, of course, is unknown. And we don't know what infrastructure is going to be available in terms of both ground infrastructure for building and testing this thing as well on-orbit infrastructure for servicing.

And of course, for technology capability, I'll talk a little bit about what we're doing to develop those. So that architecture is meant to be scalable to those uncertainties. We've looked at two concepts in particular, LUVOIR-A and LUVOIR-B. [? Aki ?] spoke to these already. So LUVOIR-A is in our 8.4-meter SLS fairing here. And LUVOIR-B is in a much smaller conventional 5-meter fairing.

This is that architecture. It's a bit of an eye chart. I'm not going to go through every box on here. But basically to give you an idea of how this mission is organized. So at the mission level, we have three segments-- a ground, an observatory, and a launch segment. Each one of these is divided into elements. I'm only showing the breakdown of the observatory here. Our payload element contains the telescope and all of our instruments. And our spacecraft element has all the supporting structure. And so I'll kind of work my way through this architecture as we go forward.

First of all, I want to start with the observatory segment, the top-level summary of what this observatory is. So on the right here, you can see a deployment video of LUVOIR-A. You'll notice it looks a lot like Webb. We borrowed a lot of design cues. We had these roll-out solar arrays and a large sunshade, which you'll see. I'll talk a little bit about that later on. You can see it deploying. And then the rest looks basically like Webb deployment. Our secondary mirror unfolds out in front, our primary mirror. We have five wings as opposed to two-- sorry, four on either side.

And then the other big difference is that we can articulate the telescope relative to the sunshade. This is that pointing capability I mentioned earlier. And we can roll it about the board fight for aligning our scene. It is a 15-meter on-axis telescope. We have 120 segments. And there are four instruments, which Aki mentioned already-- our coronagraph, the LUMOS instrument, HDI, and Pollux, which is a instrument study done by our European partners led by CNES.

LUVOIR-B looks very similar. It's 8 meters. Actually, it does not look similar. You'll see that in a second. 55 segments, although very similar design cue with the same solar array, the same sunshade. The big difference is that you'll notice that LUVOIR-B is an off-axis telescope. That is, the primary mirror is unobscured.

This led to a unique, new deployment of our secondary mirror. And then the primary mirror deploys in a very similar manner. [INAUDIBLE] optic system points out. And again, we have that articulating arm for pointing the telescope relative to the sunshade. On LUVOIR-B, we are only carrying three instruments, mainly for the volume and mass constraints that we have. So only the three ECLIPS, LUMOS, and HDI instruments are on the LUVOIR-B.

Working our way down this tree, looking at the payload element in a little bit more detail, so the optical telescope assembly. Again, you've seen most of this in that video. But the main thing here is our primary mirror is very large-- 15 meters on LUVOIR-A. This backplane support frame, for example, is roughly a four-story building. So we're planning to rent some apartment space in this thing.

[CHUCKLING]

LUVOIR-B, a little bit smaller, but very similar pieces. Again, primary mirror, backplane support frame where the instruments are. And then this main difference is the secondary mirror deployment system out here.

Some of the optical specifications. So a couple I want to call your attention to-- you notice that both LUVOIR-A and LUVOIR-B have the same field of view. This is because the science instruments have the same field of view. We wanted to accomplish very similar finds with both versions of this telescope. They also both have the same focal length, the same plate scale. And this is driven largely by the microshutter array inside of LUMOS. We wanted to have the same field of view for the microshutters in the sky, which meant that the plate scale had to be the same.

Another interesting design constraint that we had was this angle of incidence constraint, which was driven by polarization aberration within the system. Tony alluded to this earlier. So in order-- the polarization aberrations degrade the contrast performance of the coronagraph. So we limited the angle of incidence to do this to less than 12 degrees. And if you want to hear more about this, Scott will talk about this later, I think this week, on the polarization modeling that he's done on LUVOIR.

The science instruments-- I'm going to go through these very briefly because you have two talks coming up later today by James [? Perfeti and ?] [? Kan ?] Yang, who will talk about the optomechanical and thermal design of these instruments. But very briefly, the high-definition imager of our wide-field camera has a UV/VIS and a near-IR channel that can operate simultaneously.

LUMOS is our UV multi-object spectrograph. It's really UV to visible. And again, for scale, here's your average six-foot mechanical designer so you can see how big these instruments are. The ECLIPS instrument is our coronagraph. And there are three channels here-- a UV channel, visible channel, and near-infrared channel. Each have a range of coronagraph masks in it. Each has its own set of deformable mirrors, its own wavefront sensing, its own spectrometers, and back end.

There will be two talks, actually. I only listed [? Roser's ?] here, but also [? Laurent ?] [INAUDIBLE], who is the instrument lead for ECLIPS. He'll be talking later this morning, I believe, to discuss ECLIPS. And then finally, that Pollux instrument is a UV spectropolarimeter, which again, is being studied by our European partners.

The next pieces of our payload is the payload articulation system. This allows us to point the telescope independently. And for some more information on this, we have talks all day on LUVOIR. Larry Dewell will talk about the wavefront performance with this vibration isolation and precision pointing system. This is a key aspect of our dynamic stability platform. And then also Lia Sacks will talk a little bit about the integrated modeling that we've done for LUVOIR on this topic.

But one of the key thing-- the two key purposes of this payload articulation system aside from the vibration isolation is, one, it allows us to point the telescope independently. This keeps the system very thermally stable. So by keeping that sunshade in the fixed orientation relative to the sun, it sees a constant thermal load if our telescope can point behind it.

The other interesting thing is we use it to actually maintain the alignment of our center of gravity with our center of pressure. This helps keep the momentum on loading at a minimum. As you point this payload, which is 20,000, 30,000 kilograms relative to this 10,000 kilogram spacecraft, you start building up a lot of momentum. So this allows us to manage that.

And then moving over to the spacecraft quickly, two pieces here-- the bus and the sunshade. The bus is shown here and how it would normally look. Here is an exploded view. So it's an octagon with eight panels. And all of our components are mounted to these external panels for easy access. So again, this is part of that serviceability argument.

The sunshade is very simpler than JWST's sunshield. There's a key distinction there. A sunshield is a precision deployment system that is very complex. Our sunshade is really not much more than a blanket. There's only three layers as opposed to five. We only really need two of those layers for our thermal requirement. And much relaxed deployment tolerances-- so as long as those layers aren't touching, we don't care how far apart they are. Whereas JWST-- there's micron and millimeter tolerances on how those sheets are aligned to each other.

Although it is much bigger, much, much bigger. So this will present new challenges that we have overcome in terms of how we're going to test and verify the system. Although I was glad to hear from Rhonda that there are some facilities in California that are big enough for their starshade, because that means it's big enough for our sunshade.

Real quickly, our launch segment-- so I mentioned that we're baselining the SLS vehicle for both of these concepts, although we have talked about SpaceX and Blue Origin about their launch vehicles that are coming online. So LUVOIR-A actually has a couple of options. We believe it could launch on a 1B once they upgrade their boosters and rocket engines, although it's baseline for the Block 2 at the moment. And it will fit in the SpaceX Starship, assuming you can modify their fairing, which they've looked at, and they believe is feasible.

LUVOIR-B fits on pretty much everything. It can fit on SLS Block 1, although we don't expect that to still be operating in the 2030s, late 2030s. Any of the other SLSs-- it'll fit in Starship easily, and it'll fit in Blue Origin New Glenn. So this is, again, building in that robustness to the uncertainty. No matter what launch vehicle comes along in the future, we believe there's a concept-- a LUVOIR concept that will fit in that vehicle.

So that was the design. Now into the technology development. And you got a great background in basically a lot of the technologies from Rhonda that have x needs, many of which are very similar to what LUVOIR needs, although not all of them. We've organized our technologies into three technology systems. And this is to emphasize the fact that these technologies have to be developed as a system. You can't just develop one widget and expect it to work with the rest of the components.

So these systems are coupled. The coronagraph and the telescope are strongly coupled. They very much depend on the performance of each other. So you have to make sure that you're developing them both parallel. The ultraviolet instrumentation is a little bit more loosely coupled. It does have impacts on the other two, although not quite as strong.

In the following slides, I'm going to use this color breakdown. I couldn't fit it on the slide, so I'm showing it up front. Blue are technology development aspects of our program. But we've also identified engineering and manufacturing development tasks. These are things, for example, which we think there's just an infrastructure problem, like we need 120 mirror segments. That means a lot of polishing stations. That's not technology. That's just facilitation. Engineering development is not so much where we need to develop something new, but it just a matter of applying the engineering expertise to get that piece to where it needs to be.

So starting with our coronagraph instrument, the first two pieces are the coronagraph architecture and the deformable mirrors. These are the masks that go into that coronagraph and the DMs that do the wavefront control. Once you have them both together, you can go do a demonstration of static wavefront error. This is what's being done in the labs right now at JPL and Goddard and Princeton. Thank you.

Also, once you've had your deformable mirror, we know that there are yield issues with these mirrors. So it takes a lot of tries to get one mirror that has 100% working actuators. So we want to start doing a manufacturing development effort to improve the yields on those DMs.

Wavefront sensing is another key aspect. So here, we have an engineering development to take the low-order wavefront sensing that's been developed for W first and see how well it applies to LUVOIR, although we don't think that's going to be enough. We think we also need out-of-band wavefront sensing components as well. So that's the new technology piece here.

And then there's a series of detector developments that are necessary for the coronagraph both in the UV/VIS and in near-IR. So again, we're taking technologies that are currently being developed for W first, trying to see how well they can work on LUVOIR. So in that case, there's some engineering work to be done to package them. But then also looking at new components in terms of, for example, hole-multiplying CCDs as opposed to electron-multiplying CCDs and avalanching photodiodes.

Once you have all those pieces, now you can start doing your actual stability demonstration. This is a difficult piece. How do you actually maintain the contrast over the duration of your observation? So bringing all those pieces together into a system-level demonstration of the coronagraph instrument. And then there are two other pieces that need to be done in parallel here that are engineering-related-- one is developing a computer that can actually fly on-orbit to do all this processing on the fly, and then the coronagraph model development and validation.

A lot of LUVOIR's verification/validation program is going to be done by modeling. And so we need to have very robust models to do that. And there's a whole session on coronagraph design and modeling later this week. That'll talk a lot about those models are already in hand-- we just need to curate them relative to the LUVOIR system.

For the ultra-stable telescope system, there's thermal sensing and control development. This has been demonstrated in the lab. It's more a matter of getting the electronics into a size that can fly. Composite material development and optimization-- so again, trying to improve the yields of our composite materials, making sure that we don't have as much scrap.

The new component technology pieces here-- so our mirror substrates and our mirror actuators, so being able to have lightweight, stiff, low-CTE mirror segments, as well as picometer-resolution actuators behind them. Once you have that, you can do a full-scale mirror segment assembly. So this is building up at least one full-scale segment and showing that, as a system, that entire assembly works. And also, again, I mentioned since we need a lot of these mirrors, we need to build up the facilities to actually produce these things in a production line.

The next few pieces are part of our metrology system. So we have edge sensors and a laser metrology truss on board to do the fine alignment of all these segments, which will come together in a subsystem demonstration of our metrology and control subsystem. And then the last new technology component is our vibration isolation system. This is that VIPPS platform, the Vibration Isolation and Precision Pointing System that isolates the payload from the spacecraft.

Once you have all those pieces, now you can do your full-scale system-level demonstration for our ultra-stable segmented telescope system that combines the stiff mirrors with a vibration isolation system and a metrology system. And this would be a subscale demonstration. So again, we would need that system-level model development validation to go with this.

And there's a whole-- there's a talk coming up later this morning from Laura Coyle from one of the two industry teams on the ultra-stable telescope technology system study.

And finally, our UV instrumentation systems. So engineering development for VIS and near-IR coatings-- these are in hand. We just need to fine tune them. Freeform optic development-- the new technology is our far-UV broadband coating. So we know which coating we want to do. It's about TRL 3 right now. We need to demonstrate it and then come up with it solely to do them again on a large scale.

Next-generation microshutter array for LUMOS-- these are already currently being worked on. They're about TRL 3 now, soon to be TRL 4, with a very clear path to TRL 6 within the next few years. Microchannel plates-- much like Rhonda spoke to earlier, we're using gallium nitride and microchannel plates, which are TRL 4 right now.

And then we need a large-format high-resolution UV/VIS focal plane for our HDI and LUMOS instruments. And since these are going to work in the near UV, a part of that is also delta doping and UV enhancement those detectors. The big, overarching thing here is contamination control. So for that far UV performance, we have to be very, very careful about contamination, and so throughout this entire process, making sure that our coatings and our detectors and our architecture and our system all support contamination control.

So, we have a plan to develop all these technologies to TRL 6 prior to the start of Phase A. It's little different than you heard earlier. We believe that PDR is too late. And so we're trying to get all of our technologies to TRL 6 by Phase A start to reduce risk and control cost growth. This is a key piece of our management plan. And it's one piece.

So like any flagship-level mission, LUVOIR is very complex. It's nested system of systems. It will encounter challenges to its design and implementation, just like every flagship has. And so what we need do is learn from the past and adapt the lessons that we've learned to overcome these challenges.

And so later this afternoon, Julie Crooke will give a talk on some management strategies that are in our final report that we're proposing for how to control cost and schedule growth on these large missions that we think are applicable not just to LUVOIR, but really to any of these flagship missions.

And so that's all I have. I'll take questions now, and let you guys get a coffee.