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Don't mean to alarm you – but NASA is about to pummel the planet with huge frikkin' space laser

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Joke

Management Headaches! even at NASA

You know, I have one simple request. And that is to have sharks with frickin' laser beams attached to their heads! Now evidently my cycloptic colleague informs me that that cannot be done. Ah, would you remind me what I pay you people for, honestly? Throw me a bone here! What do we have?

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Pint

Re: Management Headaches! even at NASA

You beat me by a couple of seconds to post this

Have one on me-->

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Joke

I'm not worried...

...until the frickin' lasers are attached to sharks' heads...

Mutant sea bass are a bit more scary though

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Re: I'm not worried...

What about laser breams?

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Pint

Re: I'm not worried...

"laser breams"

Brilliant! Thanks for a good laugh.

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Re: I'm not worried...

Are they ill-tempered?

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@ Adam Foxton

Only if you keep carping on about it

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Coat

Re: I'm not worried...

They are in this plaice

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Coat

Re: I'm not worried...

Mutant sea bass? wouldn't that be a bit of a fluke?

Sorry, I'll get me coat. The one with "Get Thee to a Punnery" in the pocket please

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Re: I'm not worried...

Would ye all stop, you're only codding me

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Boffin

This is the voice of the Mysterons.

We know you can hear us, Earthmen.

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Mushroom

Ah now we know who's melting the ice!

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Disquieting, the prospect of Uranus being pummelled by a huge frikkin' space laser.

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Coat

Now we know

NASA were strapped for cash but suddenly they can do this? They told the Orange one that they had lasers in space and could shoot terrorists from orbit. Then SPACE FORCE was born.

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That's no moon

It's ICESat-2

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Safe?

Aaaaarrgh!! I can't see, my eyes! My eyes!

Maybe not but your eyes are exactly 167cm above ground level.

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Re: Safe?

Actually, I was just wondering if there was some decently accurate data on when it might be scanning my house so I could pop out, look up and save a fortune on having my eyes fixed :-)

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Que alarmist news articles, 1 year after launch

New data shows ice caps at an all time low!

(Maybe, maybe not, it's the first time we'll have data this accurate. Measuring small features might tell us we've been overestimating ice mass to begin with)

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Re: Que alarmist news articles, 1 year after launch

¿Qué?

Aptly named.

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Re: Que alarmist news articles, 1 year after launch

Cue, queue, whatever.

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Pint

Err

Fantastic, triple green lasers firing 10K a second providing a mapping range as small as 70cm..... just the one question, just how accurate is this touted elevation accuracy, +- 1mm or 10Km.. unless I missed it (I’m in an liquorice and Heineken enhanced haze here), there’s perhaps absolutely no mention??

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Re: Err

Raw return accuracy is 15cm for ice, about 1m on ground and 10m on steep ground.

One of the problems/features is that the measuring spot is quite big on the ground (100m) so you average out small scale variations but end up with low overall elevation accuracy compared to terrestrial LIDAR

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Windows

Re: Err

@Atomic:

The red stuff or the black stuff?

And if the Heineken was red, I don't want to know the rest of the story yet. (There's a quart of stout upstairs somewhere I'll need to grab)

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Missing information

So, now we know that the horizontal resolution is an impressive 70cm, but not so much about the vertical resolution.

Resolving round trip time to a billionth of a second gives a theoretical accuracy of 0.1mm, but when other factors such as the accuracy with which the orbital altitude is known, atmospheric interference, etc are included, the measurement accuracy will almost certainly not be +/- 0.1mm. Its disappointing that the expected error bars on this measurement weren't quoted.

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Re: Missing information

"Resolving round trip time to a billionth of a second gives a theoretical accuracy of 0.1mm"

You sure?

Speed of light in air = 3.10^9 m/s

Divide by 1.10^9 = 3.1m

That's a round trip so can resolve to half that, so ~1.5m.

Having said that resolving to 1nS isn't much to boast about, is that correct?

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Anonymous Coward

Re: Missing information

You sure?

Speed of light in air = 3.10^9 m/s

You sure? Wikipedia says 299,792,458 metres per second, which would be approx 3 x 10^8 m/s.

Hence 1ns = 15cm round-trip.

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Anonymous Coward

Re: vertical resolution

I've always had a concern how far up it goes

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Boffin

Re: Missing information

Speed of light in air is 299,700 km/s (~3*10^8 m/s) very close to the speed of light in a vacuum so not sure where you get the 3.10^9 from (which according to my calculator is 26439.6)

Rule of thumb - light goes at about 1ft per nanosecond or more accurately 30cm/ns. Resolving to 1ns isn't too bad but better is easily achievable.

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Re: Missing information

Measuring time interval to 0.1ps is easy, measuring a laser return isn't.

You are assuming you send out a perfect square wave and get back a perfect return. At this range you send out a pulse that is a few of micro-seconds wide and get back a tiny fraction of that energy smeared over the pulse width - you have no idea where (in time) in the outgoing pulse the peak return is. It is further complicated because the same outgoing pulse will reflect off different layers in the target and give multiple return pulses.

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Pint

Re: Missing information

"You sure?" etc.

"Hence 1ns = 15cm round-trip."

Exactly.

Historical giant and computer-pioneer Grace Hopper was famous for her...

1 foot = 1 nanosecond

...memory aid.

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Pint

Re: Missing information

YAAC suggested, "...send out a perfect square wave..."

Hopefully they make use of a more-clever modulation technique than just square waves. And of course they'll employ repetition and signal processing techniques.

Now, excuse me... I've got to start gathering some large first-surface mirrors so that I can assemble my mediumly-huge corner reflector. Give them something to talk about...

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Alien

Keep Calm and Carry On

Me; I'm finally buying a tinfoil hat.

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Re: Keep Calm and Carry On

My tea cosy is far superior. It protects my head from frost, mind control rays and physical damage, due to being padded.

Plus I can use it to keep my tea warm.

Oh and it's the same shape as the Pope's hat, so I can blend in if I'm ever required to hide in the Vatican City.

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Big Brother

Re: Keep Calm and Carry On

My tea cosy is far superior. It protects my head from frost, Check! mind control rays Noted!* and physical damage, due to being padded. Good! Plus I can use it to keep my tea warm. All at the same time? Impressive!

* Someone will be there to chat shortly.

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Anonymous Coward

Re: Keep Calm and Carry On

"All at the same time?"

Yep plenty of room in a Pope's hat for a decent sized teapot on top of the head.

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Re: Keep Calm and Carry On

Yep plenty of room in a Pope's hat for a decent sized teapot on top of the head.

I should say so - the thing is a mitre high

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Windows

Re: Keep Calm and Carry On

--- so -- thats where the grey smoke comes from.......

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Go

Re: Keep Calm and Carry On

"Yep plenty of room in a Pope's hat for a decent sized teapot on top of the head.

I should say so - the thing is a mitre high"

His Holiness is currently visiting Ireland so I don't imagine he needed to bring his own teapot.

Cup of tea, Father? Ah go on.

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Height measurement precision

From https://www.nasa.gov/sites/default/files/thumbnails/image/icesat-2-infographic.jpg, it's equivalent to 3 cm resolution in the vertical.

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Re: Height measurement precision

I see the satellite's orbit is being measured by star-tracker and GPS. Thats fine for Lat/lon determination to about a metre, but vertical GPS resolution is a lot worse, somewhere in the 3-5m range, so either there's another scheme thats not being talked about for measuring the orbital altitude, correcting for gravitational variation etc., or the +/- 3cm height resolution calculated from photon flight time and mentioned in the referenced graphic is somewhat irrelevant.

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Anonymous Coward

Re: Height measurement precision

I always thought that the GPS height accuracy had more to do with the geoid model (which one you chose and how accurate it is for your local position) than absolute 3D positioning. Also, if you're using GPS to measure something on earth, you have the effects of the atmosphere to consider.

The other part to consider is that the absolute height of the satellite might not be critical, as long as the error is slow and predictable. If your measurements show that the ice cap dropped by 11cm and you also orbit over New York's Central Park and show that dropped by 11 cm, you can probably determine that your altitude has changed (I'm sure the orbital dynamics are more complicated, but you get the idea).

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Re: Height measurement precision

The height problem in GPS is because the satellites are much more similar in height than they are in distance to you.

Measuring the height of this satellite doesn't depend on GPS - it just depends on measuring the orbit time (easy and accurate) and knowing where the planet is and how much it weighs (trickier but we do this)

I'm guessing you can nail this to higher accuracy than the LIDAR system, so they will likely use passes over known flat fixed earth targets to calibrate the laser ranger assuming a known orbit - rather than use the LIDAR to measure the satellites' height.

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Pint

FAKE NEWS !!!! <---- ;-)!!

22 August 2018: Europeans launch the British-built Aeolus weather satellite that will "...get its data by firing a powerful laser down into the atmosphere to trace the movement of air particles." [BBC]

23 August 2018: El Reg, a British-based Tech News / Comedy website seeks to distract from their own European/British frickin' laser-wielding planet-frying death-dealing "weather" Aeolus satellite by publishing something about a future ICEsat-2 satellite: "NASA is about to pummel the planet with huge frikkin' space laser..."

It's an amusing juxtaposition of reality versus the headline. One day in the gap!!!! GEESH! :-)

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Anonymous Coward

Re. gap

I hear its photons all the way down.

(RIP Terry Pratchett)

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ESA’s Aeolus gets there first

You mention NASA, but you leave out ESA’s Aeolus with it's own big wind-measuring IR laser?

It's the same bus design as Mars Express, too.

It's designed to measure winds, but the launch was delayed by a day because of uncertain winds. Nice.

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Re: ESA’s Aeolus gets there first

"It's the same bus design as Mars Express, too."

Bloody typical. You wait ages for a bus then two come along at once!!

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Joke

Re: I'm not worried...

"the satellite's only instrument."

Canteen Worker: What's the Death Star?

Darth Vader: This is the Death Star! You're in the Death Star! I run this star!

Canteen Worker: This is a star?

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Re: I'm not worried...

"I can kill catering with a thought!"

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Let hope this climate monitoring satellite make it to orbit. Climate monitoring satellites seem to have a suspiciously high failure rate in the US.

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Turn the planet into a CD?

It's big, it's round, it spins ... we're just a big CD now. I think this explains the Nazca Lines - they are just a lead-in track for an ancient aliens CD ...

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