The Large UV Optical Infrared Surveyor (LUVOIR) is NASA's next planned flagship telescope following the James Webb Space Telescope, and a direct successor to Hubble covering the 0.1 μm (far ultraviolet) to 5 μm (mid-infrared) wavelengths. It may launch with either an 8-meter mirror or a larger 15-meter mirror. The latter would have required the Space Launch System (SLS) Block 2's large payload fairing, but now SpaceX's Big "Falcon" Rocket (BFR) is in contention:
Conceptualized to follow in the footsteps of NASA's current space telescope expertise and (hopefully) to learn from the many various mistakes made by their contractors, the LUVOIR (shorthand for Large UV/Optical/IR Surveyor) concept is currently grouped into two different categories, A and B. A is a full-scale, uncompromised telescope with an unfathomably vast 15-meter primary mirror and a sunshade with an area anywhere from 5000 to 20000 square meters (1-4 acres). B is a comparatively watered-down take on the broadband surveyor telescope, with a much smaller 8-meter primary mirror, likely accompanied by a similarly reduced sunshade (and price tag, presumably).
[...] The reason LUVOIR's conceptual design was split into two sizes is specifically tied to the question of launch, with LUVOIR B's 8m size cap dictated by the ~5 meter-diameter payload fairings prevalent and readily available in today's launch industry.
LUVOIR A's 15-meter mirror, however, would require an equally massive payload fairing. At least at the start, LUVOIR A was conceptualized with NASA's Space Launch System (SLS) Block 2 as the launch vehicle, a similarly conceptual vehicle baselined with a truly massive 8.4 or 10-meter diameter payload fairing, much larger than anything flown to this day. However, the utterly unimpressive schedule performance of the SLS Block 1 development – let alone Block 1B or 2 – has undoubtedly sown more than a little doubt over the expectation of its availability for launching LUVOIR and other huge spacecraft. As a result, NASA has reportedly funded the exploration of alternative launch vehicles for the A version of LUVOIR – SpaceX's Cargo BFR variant, in this case.
While only a maximum of 9 meters in diameter, the baselined cargo spaceship's (BFS Cargo) payload bay has been estimated to have a usable volume of approximately 1500 cubic meters, comparing favorably to SLS' 8.4 and 10-meter fairings with ~1000 to ~1700 cubic meters.
(Score: 3, Interesting) by DannyB on Tuesday July 10 2018, @09:11PM (1 child)
Launch two of the B version of the telescope. Place them at opposite sides of the same orbit such that they are just over 2 AU apart. That is, just a bit greater than Earth's orbit but at opposite sides of the sun. Now you have a really big "functional diameter" for the combined telescope and could get really good resolution.
What is the drawback to two teeny tiny 8 meter telescopes 2 AU apart? Light gathering?
Since much of what you want to look at is probably along the plane of the solar system, maybe place their 2 AU orbit at a 90 degree angle to the plane of the solar system?
The lower I set my standards the more accomplishments I have.
(Score: 3, Informative) by Anonymous Coward on Tuesday July 10 2018, @10:23PM
You only get to take advantage of their functional diameter to get better resolution if you can coherently combine their light, which for optical wavelengths has to be done real-time before it falls on a detector (radio astronomers can get away with doing it in post-processing because they can digitize and time-tag the arriving radio waves with sufficient precision at each telescope because radio waves are relatively HUGE--meters to tens of meters as compared to hundreds of nanometers for optical).
NASA and others have looked at this idea, which is basically taking some form of the two optical interferometers we've seen recently in stories here, and putting them in space. The really hard part continues to be the ability to measure and compensate for changes in optical pathlength in real-time for things that aren't sitting on really nice and stable hunks of bedrock, like the ground-based interferometers are.
(Score: 3, Interesting) by bob_super on Tuesday July 10 2018, @09:57PM (6 children)
How about sending a stack of mirrors into space, 4m each, ten per Falcon 9 launch, and then assemble them to a tiny instrument-carrying frame, and calibrate the assembly directly in space?
Building a one-time deployment system, which needs to work at 1G for testing, and needs to fit completely in one launcher, and risking the whole thing on one launch, that's pretty silly.
There is no way they'll get this thing "in the 2030s" using the same techniques that got us delayed Hubble and JWST.
Make it modular, assemble in space, and twenty years later, you can use the same assembly instructions replace any element that has failed. You can event lose a payload and have a partial telescope...
(Score: 0) by Anonymous Coward on Tuesday July 10 2018, @10:32PM (5 children)
Same problem as the response to the first question; lightweight structures are flimsy structures, which means they will flop, vibrate, etc. Whether you are using them as an interferometer (as in the first question), or as parts of a big mirror, they need to hold their positions to tens of nanometers at best to get good imagery (assuming we're talking visible wavelengths here; you need to hold them to, say a tenth of a wavelength or better to get a good image). If you're going to actively control for these errors, you need to have an active metrology system to measure these differences. By the time you work in active metrology and control systems and parts to do the correction, your lightweight mirror is now as heavy or heavier than if it was a single piece of glass. The tradeoff worked in JWST's favor because that is going to look in the IR, which have longer wavelengths and thus a little bit easier to do than in the visible.
(Score: 2) by DannyB on Wednesday July 11 2018, @01:22PM
For a vibration free environment, build a telescope on the far side of the moon, or on the dark side of Mercury.
But someone will object due to either dust storms, or moon quakes.
(It is incorrect to say you "unearthed" something on the moon. Wouldn't the term be "unmooned"? And being unmooned is the opposite of being mooned.)
The lower I set my standards the more accomplishments I have.
(Score: 0) by Anonymous Coward on Wednesday July 11 2018, @01:22PM (3 children)
For LEO access, traditional space companies said it can't be done until private guys did it.
It appears to be the business plan of these 'experts' to do a repeat for this payload as well.
This telescope plan is nuts.
There is no reason to ignore launch constraints and launch a multi-mirror scope at full working diameter.
It could either unfold or assemble in orbit.
These arguments supporting this plan are similar.
Let look at them.
"lightweight structures are flimsy structures," --- A Potato chip is a proof by existence that this is wrong. You can build stiff and light stuff with composites.
"work in active metrology and control" and your "mirror is now as heavy or heavier than if it was a single piece of glass" --- Wow, on the ground active mirror segments is a well known method for making a big scope that's not old school massive. Active compensation is a fundamental tool for making instruments that we can only dream of using old school techniques.
NASA's job used to be cheap access to space. Well, mission accomplished, just not the way you planned.
Now the new mission should be to explore based on the above. Building your grandfather's gold plated instrument is not the way to do this. You have to take risk to advance.
(Score: 0) by Anonymous Coward on Wednesday July 11 2018, @03:54PM (2 children)
You are quite confident in your ignorance. Lightweight structures are flimsy structures when you work in any kind of dynamics, whether it be simply from reaction wheels turning, or just thermal changes when the vehicle goes into or comes out of eclipse. In fact, in the structural dynamics world, there is a name for one of the modes of vibration of a plane, it is called "potato chipping".
As you say, active metrology and control works great on the ground. You see, on the ground these things are not sitting on flexible sturctures, but they are rigidly mounted on very heavy optical tables and/or secured to facilities that are either rigidly secured 20+ meters below to the bedrock, or they are on specially isolated dampeners. The problem you have in space, which Mr. Newton would readily have pointed out to you several centuries ago, is the whole action/equal-but-opposite reaction thing. You don't get the advantage of massive optical benches in space. ANYTHING you put up is dynamically very flexible. You need to put in the metrology and control systems that can measure these disturbances and correct for them at the same time that as your segmented mirror is pushing a little this way to make a correction, the structure is pushing back that way in response. Or you need to work in wavelengths where you can deal with these kind of mis-alignments and errors. It is a hell of a lot easier to put up an unfolding radar reflector telescope than it is to put up an optical telescope. JWST is hard as it is, and they have the advantage of being 2 to 10 times less tolerant because their errors can be 2 to 10 times larger since they are going to work in the infrared.
It may come as a great shock to you, but these kind of issues have been worked on for decades. However, you are well positioned to make a great name for yourself in the opto-mechanical-thermodynamical engineering community if you shared your obvious and apparently overlooked solutions to all of these problems.
(Score: 0) by Anonymous Coward on Wednesday July 11 2018, @11:54PM (1 child)
My optical bench isn't massive and tied to the earth. It's a metal plate for random attachments backed by a composite honeycomb which is both nicely stiff and damped. It sits on air bags to isolate it from unpredictable building vibrations. Admittedly it's light by concrete and steel standards, but probably massive by flight standards.
https://www.thorlabs.com/navigation.cfm?guide_id=41 [thorlabs.com]
With regards to do I have a better idea.
Given that it's my tax money being spent, let me give it a try and you tell me.
Here's a theory for a dynamics control architecture.
First, lightweight structures can be very stiff relative to their mass, but I'm not sure stiffness is your friend because stiff raises the resonance of the structure.
Over short periods of time, mass is the natural way to keep things in place.
Stiffness works against this and so it would make any active control servo have to work faster.
On the ground, I can't use this trick because I don't know the forces from external things like the AC air handler and folks walking around.
In an unmanned space vehicle, I should be in control of everything that moves.
So the servo system should be able to predict and choose what to do with the servos.
(This seems a fundamental advantage for an instrument in space?)
The actual heirarchy I have in mind is
A predictable but somewhat springy backbone
Separate servo systems connecting each critical component to the backbone (mirrors, sensors, relay lenses, and measurement?)
Perhaps also some servos connecting various parts of the backbone together.
Measurement reflector stations on each critical component
A common optical position measurement system looking at the stations
A servo loop watching the measurements and controlling the servos at a loop bandwidth faster than unpredictabilities in the loose, springy backbone can mess things up.
I can see 2 things which are necessary for success.
Getting a good complexity balance between the structure design and the control loop. Today's availability of crazy amounts of CPU cycles help this, but there might be a temptation to go too far in this direction. (Obviously, I think the design you propose is too far in the other direction.)
Apriori knowledge that some things are built right on the ground with known error bands. IE the relationship between each critical component and it's measurement stations. Perhaps go so far as grinding the stations into the blank of each mirror and use them in the mirror surface grinding..
Given sub wavelength relative position sensors for the mirrors and sensors, and suitable servos in the right place, it seems like it should be possible to make a big gadget that self aligns in space.
(Score: 0) by Anonymous Coward on Thursday July 12 2018, @01:17AM
Still quite confident in my ignorance, let's talk about those servos.
Since old school space has torquers, for fun lets call them forcers.
A critical component like a mirror would have three between it and the vehicle backbone.
When not operating, they capture the component to the vehicle backbone.
But when operating, if you really believe that mass is your friend to keep things still, then a forcer should only apply force.
That means after releasing capture and there should be no contact between the component and vehicle.
In other words, when operating, this makes the instrument a set of random objects free floating in space with servo system forces to keep them friends.
Once said, why would you want anything else?
How to make such a forcer?
Perhaps a few permanent magnets on the component side and on the vehicle backbone side a local servo positioning coils to good positions to apply force.
How far these servos can move is the compliance range of the forcer.
The assemble in space part and vehicle dynamics only have to be good enough to stay in the compliance range.
If you have good control of the magnetic gaps, you can use induction to send power to the component.
A short free space optical path can provide data.
(Not sure how to handle cooling.)
You can't try these on the ground, but ISS could.
Seems like a great way to embrace space to make a truly great instrument.
If the compliance range is sufficient, it might work on a manned vehicle like ISS.
A telescope with free floating pieces needs a great name, that part and actually making it work is yours.
Definitely not your grandfather's telescope.