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So while it sounds good that we've fixed the launch industry and can launch everything cheaper, that we should only have space based telescopes, space telescope

by cbanek 7y ago

So while it sounds good that we've fixed the launch industry and can launch everything cheaper, that we should only have space based telescopes, space telescopes are a very different game from ground based telescopes. First, as others have pointed out, is size. Ground based mirrors are very large, in the 10s of meters, and those mirrors are extremely heavy, like tons. You can't lift one of those mirrors up on one rocket, so you'll have to figure out some kind of in orbit construction. Not impossible, but we haven't assembled a lot of things in space, probably the biggest would be the ISS. But telescopes have tricky tolerances... Which leads me to the next issue: not only is it heavy, but telescopes are fragile. They have to be very carefully calibrated and put together. Launching something into space tends to be a very bumpy ride, and making something that can withstand that kind of vibration for launch, and then the thermal problems while in space would be certainly not trivial. But let's say you could build something and get it to work in orbit. Then it's still hard to service. Servicing the hubble to fix the optics was a very hard mission, and the hubble is relatively close to the earth. And that was when we had the shuttle, which we don't now. Cooling is very tricky for both telescopes and space. Since there's no air to radiate to, you can get big thermal gradients over the length of your craft and you have to be very careful how you point it. Same for the optics and the camera, you want to make sure they have as little thermal gradient as possible. Unlike a lot of commercial satellites, many scientific probes and telescopes are constantly refitted and reused. Ground based telescopes frequently reuse the same expensive (typically one-off) mirrors and put better cameras on them all the time. This is pretty hard to do in space. That being said, being in space does have a lot of advantages, the most obvious one being a lack of atmosphere to mess with your observations. But assembling large telescopes in space still isn't exactly easy. I think over time though, we will be heading to more space based telescopes as the cost comes down. But many slower moving telescope projects (mostly slow due to government funding) were started before Starlink was even announced.

manicdee 7y ago
The large telescope mirrors aren’t single parts even in terrestrial telescopes. We have to assemble and calibrate them on their isolated mountaintops, starting with the giant support structures intended for suspending the mirrors against the pull of gravity with minimum distortion regardless of orientation of the telescope. We then add active optics to compensate for atmospheric distortion, alter airline routes and city lighting to help improve conditions, and then pray for no clouds on the nights we want to observe. Constructing telescopes in space will become a reality within the next decade, while terrestrial telescopes currently in planning will be finding it harder and harder to navigate the mixture of light pollution, accessibility and indigenous rights. I expect there are terrestrial telescopes already in planning and even at early stages of construction which will never be finished. Between the ever-growing forest of red tape and the ever shrinking cost of building space telescopes in orbit, there will be an inflexion point where it makes sense to dedicate the remaining budget of a terrestrial telescope project to building its spaceborne replacement.
strainer 7y ago
> Ground based mirrors are very large, in the 10s of meters, and those mirrors are extremely heavy, like tons. Seemingly fantastically - SpaceX is currently constructing a system designed to launch 100 tons to LEO, for as low as $35/kg [1]. Musk says this capability is what the Starlink business is to pay for. It appears lately, more realistic than it has sounded. [1] https://caseyhandmer.wordpress.com/2019/10/29/the-spacex-starship-is-a-very-big-deal/ https://caseyhandmer.wordpress.com/2019/10/29/the-spacex-sta... ( https://news.ycombinator.com/item?id=21397285 https://news.ycombinator.com/item?id=21397285 )
- sectiondetail 7y ago
  One of the things I'm most excited about related to Starship is its landed mass capability for science purposes. Imagine being able to build radio and optical telescopes in the Daedalus crater on the central lunar far side. They'd be shielded from the optical and radio noise of the sun for 2 weeks out of 4, and permanently shielded from Earth. Or imagine infrared telescopes at the bottom of permanently shadowed polar craters, where ambient temperatures are even colder than in interplanetary space. No need to design and deploy a complex sunshield and worry about maintaining spacecraft orientation. The science potential of reusable heavy-lift rockets can't be understated.
- flashman 7y ago
  So SpaceX creates the problem and sells the solution - brilliant business strategy :P

by cbanek 7y ago

manicdee 7y ago

The large telescope mirrors aren’t single parts even in terrestrial telescopes. We have to assemble and calibrate them on their isolated mountaintops, starting with the giant support structures intended for suspending the mirrors against the pull of gravity with minimum distortion regardless of orientation of the telescope. We then add active optics to compensate for atmospheric distortion, alter airline routes and city lighting to help improve conditions, and then pray for no clouds on the nights we want to observe. Constructing telescopes in space will become a reality within the next decade, while terrestrial telescopes currently in planning will be finding it harder and harder to navigate the mixture of light pollution, accessibility and indigenous rights. I expect there are terrestrial telescopes already in planning and even at early stages of construction which will never be finished. Between the ever-growing forest of red tape and the ever shrinking cost of building space telescopes in orbit, there will be an inflexion point where it makes sense to dedicate the remaining budget of a terrestrial telescope project to building its spaceborne replacement.

strainer 7y ago

> Ground based mirrors are very large, in the 10s of meters, and those mirrors are extremely heavy, like tons. Seemingly fantastically - SpaceX is currently constructing a system designed to launch 100 tons to LEO, for as low as $35/kg [1]. Musk says this capability is what the Starlink business is to pay for. It appears lately, more realistic than it has sounded. [1] https://caseyhandmer.wordpress.com/2019/10/29/the-spacex-starship-is-a-very-big-deal/ https://caseyhandmer.wordpress.com/2019/10/29/the-spacex-sta... ( https://news.ycombinator.com/item?id=21397285 https://news.ycombinator.com/item?id=21397285 )

sectiondetail 7y ago
One of the things I'm most excited about related to Starship is its landed mass capability for science purposes. Imagine being able to build radio and optical telescopes in the Daedalus crater on the central lunar far side. They'd be shielded from the optical and radio noise of the sun for 2 weeks out of 4, and permanently shielded from Earth. Or imagine infrared telescopes at the bottom of permanently shadowed polar craters, where ambient temperatures are even colder than in interplanetary space. No need to design and deploy a complex sunshield and worry about maintaining spacecraft orientation. The science potential of reusable heavy-lift rockets can't be understated.
flashman 7y ago
So SpaceX creates the problem and sells the solution - brilliant business strategy :P