James Webb Space Telescope • Hacker News Board

Re: James Webb Space Telescope

#21

Post by antr » Fri, Jan 23, 2015, 4:51 PM UTC

ck2 wrote: post #20

Remember who runs congress now, prepare for it be canceled (again).

I saw this in Wikipedia:

"The JWST has a history of major cost overruns. In 2011, the United States House of Representatives voted to terminate funding, after about $3 billion had been spent and 75 percent of its hardware was in production. Funding was restored in compromise legislation with the US Senate, and spending on the program was capped at $8 billion. As of December 2014, the telescope remained on schedule and within budget, but at risk of delays."

Source: https://en.wikipedia.org/wiki/James_Webb_Space_Telescope

Re: James Webb Space Telescope

#22

Post by arrrg » Fri, Jan 23, 2015, 4:56 PM UTC

loudmax wrote: post #19

mrfusion wrote: post #7

Earlier quoted context omitted.

I never understood how we can launch something into an L2 orbit. Does the rocket just fly out there and stop? Just it get caught at that location?

If you're curious about orbital space mechanics, try Kerbal Space Program. You'll get a much better idea how NASA puts things into orbit after you've done it a few times yourself. Basically, the rocket doesn't just fire in a straight line away from the Earth all the way into orbit. It starts arcing very soon into the ascent, and the thrust is nearly parallel to the Earth's surface for much of the journey.

That’s all well and good for most of the stuff humans do in space (and it really, really helps to get a sort of general, very basic and intuitive understanding of orbital mechanics), but KSP does not do Lagrange points at all. You cannot use it to get a basic understanding of how those work with KSP.

Re: James Webb Space Telescope

#23

Post by whalesalad » Fri, Jan 23, 2015, 5:07 PM UTC

This fella is down at Northrop in Smell Segundo! My Dad always shoots me a text whenever he's had a chance to look at it. He told me a neat story once about the mirrors inside it... that when he stood in front of it, he felt really strange. It's because the mirrors we are all accustomed to have so many imperfections compared to the types used in this device. He wasn't used to seeing such a perfect mirror image.

Re: James Webb Space Telescope

#24

Post by sjburt » Fri, Jan 23, 2015, 5:08 PM UTC

mrfusion wrote: post #10

noselasd wrote: post #9

Earlier quoted context omitted.

Here's the main reasoning for placing it at L2: http://jwst.nasa.gov/orbit.html

Right I understand the reason. But as my question says, I don't understand how a rocket inserts it into that orbit.

It's easier to think of it not as "stopped", but in an orbit around the earth that takes exactly 1 year to complete. So it does have some tangential velocity.

Re: James Webb Space Telescope

#25

Post by cmsmith » Fri, Jan 23, 2015, 5:16 PM UTC

mrfusion wrote: post #7

furyofantares wrote: post #3

Earlier quoted context omitted.

Until this post I didn't realize it wasn't going to orbit Earth in roughly the same spot as Hubble -- it's going to be roughly 4 times further away from Earth than the Moon is, orbiting L2! http://jwst.nasa.gov/orbit.html

I never understood how we can launch something into an L2 orbit. Does the rocket just fly out there and stop? Just it get caught at that location?

The same way that you can push a ball just to the top of a hill. Very carefully, because if you push it too hard it will roll down the other side.

Re: James Webb Space Telescope

#26

Post by ahelwer » Fri, Jan 23, 2015, 5:28 PM UTC

whalesalad wrote: post #23

This fella is down at Northrop in Smell Segundo! My Dad always shoots me a text whenever he's had a chance to look at it. He told me a neat story once about the mirrors inside it... that when he stood in front of it, he felt really strange. It's because the mirrors we are all accustomed to have so many imperfections compared to the types used in this device. He wasn't used to seeing such a perfect mirror image.

Ever tried cracking open a hard disk drive? Same thing. The reflection clarity is pretty shocking.

Re: James Webb Space Telescope

#27

Post by bartozone » Fri, Jan 23, 2015, 6:28 PM UTC

whalesalad wrote: post #23

This fella is down at Northrop in Smell Segundo! My Dad always shoots me a text whenever he's had a chance to look at it. He told me a neat story once about the mirrors inside it... that when he stood in front of it, he felt really strange. It's because the mirrors we are all accustomed to have so many imperfections compared to the types used in this device. He wasn't used to seeing such a perfect mirror image.

I wonder if there's a market for "premium mirrors" ...

Re: James Webb Space Telescope

#28

Post by xenophonf » Fri, Jan 23, 2015, 6:54 PM UTC

arrrg wrote: post #22

loudmax wrote: post #19

Earlier quoted context omitted.

If you're curious about orbital space mechanics, try Kerbal Space Program. You'll get a much better idea how NASA puts things into orbit after you've done it a few times yourself. Basically, the rocket doesn't just fire in a straight line away from the Earth all the way into orbit. It starts arcing very soon into the ascent, and the thrust is nearly parallel to the Earth's surface for much of the journey.

That’s all well and good for most of the stuff humans do in space (and it really, really helps to get a sort of general, very basic and intuitive understanding of orbital mechanics), but KSP does not do Lagrange points at all. You cannot use it to get a basic understanding of how those work with KSP.

That's why our correspondent needs to install the Principia mod!

http://forum.kerbalspaceprogram.com/threads/68502-WIP-Princi...

Re: James Webb Space Telescope

#29

Post by Florin_Andrei » Fri, Jan 23, 2015, 6:57 PM UTC

sanxiyn wrote: post #5

freshyill wrote: post #2

As excellent has Hubble has been, the JWST is going to put it to shame. The potential risk, however is that it won't be serviceable, as Hubble famously needed to be very early in its life. If all goes as planned, we're all going to have some really nice new desktop wallpapers in a few years. And, I suppose, a better understanding of the universe will be a nice side benefit.

Interesting tidbit: JWST can't see blue. While Hubble could see entire visible light spectrum, astronomically infrared is more interesting. So JWST can see infrared, but not blue. Astronomical images always have been heavily edited and it never was "what you may see", but it is more so for JWST.

Aren't the mirrors coated with gold? If so, then they do reflect some blue, just not as much as the lower frequencies.

Perhaps the sensors are discarding that frequency.

Re: James Webb Space Telescope

#30

Post by Florin_Andrei » Fri, Jan 23, 2015, 7:04 PM UTC

whalesalad wrote: post #23

This fella is down at Northrop in Smell Segundo! My Dad always shoots me a text whenever he's had a chance to look at it. He told me a neat story once about the mirrors inside it... that when he stood in front of it, he felt really strange. It's because the mirrors we are all accustomed to have so many imperfections compared to the types used in this device. He wasn't used to seeing such a perfect mirror image.

Not to diminish the achievements of the opticians working on the JWST, but you can obtain the same level of perfection at home, using everyday tools. However, you'll be working on a much smaller surface.

Make your own telescope mirror. To pass the tests, it must follow the ideal surface with an error less than lambda/4, where lambda is the wavelength of visible light. In practice, that's 0.1 microns or less. Also, the density of scratches and pits must be very low (not detectable by usual means).

It's totally doable by hand, working in your garage, on a piece of glass the size of a dinner plate. It just takes a very, very long time, at least on first attempt. My first telescope took over a year (admittedly, I took too many breaks, and then I did a lot of experiments with the techniques).

http://florin.myip.org/blog/150-mm-f8-mirror-25-mm-pyrex-pol...