James Webb Space Telescope's Smooth Launch Extended Its Life Expectancy, NASA Says (cnet.com) 45
The James Webb Space Telescope should be able to remain in orbit for more than 10 years, thanks to a fuel-efficient launch on Christmas Day, according to NASA. From a report: The telescope was carried aboard the Arianespace Ariane 5. Despite two brief midcourse corrections, its launch used less propellant than initially expected. That will allow the $10 billion observatory "science operations in orbit for significantly more than a 10-year science lifetime," the US space agency said in a release on Wednesday The first midcourse correction was a relatively minor, 65-minute post-launch burn, which bumped up the telescope's speed by approximately 45 miles per hour. Another smaller correction on Dec. 27 added an additional 6.3 mph. That added boost also allowed the JWST's solar array to unfold about a minute and a half after it separated from the Ariane 5, just 29 minutes after launch. The array was coded to automatically deploy either when the observatory reached a certain altitude or 33 minutes after launch, whichever came first.
Options for refueling? (Score:2)
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then why include visual markings (for humans)?
Re:Options for refueling? (Score:4, Informative)
then why include visual markings (for humans)?
Visual markings are not just for humans.
If anything, robots need them more than humans do. A human cashier can read a price tag, a machine needs a barcode.
A human can put gas in a car. Try to design a robot that can do the same on any vehicle. You will quickly realize that some visual alignment markings are a big help.
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I'm sure road side assistance could refuel the JWST in 10 years. They problem is no one wants to wait at L2 with the membership card. Anybody else have a better idea?
It might be cheaper to send up another one instead. All the design and development work has already been done.
A new one could also take advantage of any new tech that appears this decade.
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If we are going to build another 'scope, it makes sense to redesign to see a different part of the spectrum.
HST can see the visible spectrum. JWST sees near IR. The next-gen should be designed for deep IR, seeing further/earlier because of the redshift.
After ten years, JWST will give us so much data about near IR that launching another to look at the same wavelengths is silly.
Re: Options for refueling? (Score:1)
deep IR This would require sensors that operate close to zero Kelvin which I don't think we can do at the moment.
Re: Options for refueling? (Score:5, Interesting)
JWST main imaging system is a 2Kx2K HgCdTe sensor with a cut-off wavelength at 5.3 um from Teledyne [teledyneimaging.com]. It operates at 37K.
There's also a 1Kx1K Si:As sensor with a cut-off wavelength at 28 um, operating at 7K, from Raytheon [researchgate.net]. This is already well into the thermal infrared range.
We already have had a space instrument imaging further than 28 um: it's the Spitzer Space Telescope MIPS [psu.edu], with a 32x32 Ge:Ga sensor with a cut-off wavelength at 70 um, and a 2x20 Si:Ge sensor with cut-off wavelength at 160 nm (among others). They are mirror-scanned, so the effective resolution is higher. They were operating at 1.5K, so those temperatures were already achievable.
So deeper infrared is well possible, but the design of the next instrument will largely depends on the next scientific goals... Do we need a bigger instrument to lower the diffraction limit, a higher resolution instrument, a more precisely stabilized instrument, other wavelengths of observation ? I guess that the observations we make with JWST will allow us to better know the requirements of the next space instruments.
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"It might be cheaper to send up another one instead"
I've read that this telescope was a $500 million mission meant to fly a over decade ago?
Now I read that it's a $10 billion (yeah, with a B) mission over a decade late.
I'm very much not sure that building and launching another one is going to be cheaper than the original $500 million price tag, and I'd be mildly surprised if a second version came in cheaper and faster than the the $10 billion + 10 years overdue initial launch.
I mean, seriously, WTF??
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Designing and launching a refueling robot isn't going to be any easier.
What were you thinking? Send a guy with a gas can to L2 and bring him back afterwards?
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I was thinking get it right a decade ago and launch a $500 million mission on time and on budget.
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They actually have a fuel port. And something to attach to the main control unit.
There is no consensus on how to actually use those. But the two were left there for future mission options.
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And something to attach to the main control unit.
I hope they used something standard like USB-C. It would suck if we sent a refurb robot all the way to L2 only to find that the port needed a lightning cable.
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Slow (Score:5, Interesting)
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According to gigacalculator, 65 minutes to accelerate 45mph works out to about .000526g. I wouldn't have called a 65 minute burn minor but I guess it'd fit if it's that tiny of a push. Must've been that microwave drive.
I don't think the burn lasted 65 minutes, it just happened 65 minutes after launch. Too bad the English language can be so ambiguous.
Re:Slow (Score:5, Informative)
From NASA site:
At 7:50 pm EST, Webb’s first mid-course correction burn began. It lasted 65 minutes and is now complete. This burn is one of two milestones that are time critical — the first was the solar array deployment, which happened shortly after launch.
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No, the burn actually did last for 65 minutes. It occurred about 12.5 hours after launch. NASA blog post [nasa.gov]. The second mid-course burn was about 9-1/2 minutes, 60 hours after launch. The main thruster is rather puny, and the spacecraft is a bit over 6 tons.
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The "burn" lasted 65 minutes because it was a xenon ion thruster, not a rocket.
Ion thrusters are extremely mass efficient but require plenty of energy, so they can only be used after the solar panels deploy.
The 65-minute "burn" used about 12 grams of xenon fuel. Of course, nothing was burned.
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Your information is faulty. The primary thruster for these maneuvers is a fairly conventional hyperbolic bi-propellant (hydrazine and dinitrogen tetroxide). It is fair to say that the stuff really burns, and is really a rocket. It’s just a relatively small one. Here is one reference [slashdot.org].
This kind of propulsion is pretty common for spacecraft, because it is 1) highly reliable, 2) mechanically simple (no pumps - it
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No, the burn actually did last for 65 minutes. It occurred about 12.5 hours after launch. NASA blog post [nasa.gov]. The second mid-course burn was about 9-1/2 minutes, 60 hours after launch. The main thruster is rather puny, and the spacecraft is a bit over 6 tons.
Also, the engine controller was advanced enough to be told to imagine it was a Floridian accelerating on an interstate on-ramp.
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Re:Slow (Score:5, Informative)
From what I have read, they want to 'sneak' up on the final velocity. They cannot decelerate if they exceed the intended velocity since that would entail turning the spacecraft around (apparently no reverse thrusters). They can't turn the spacecraft around since that would present the wrong side to the sun and cause unintended heating of components that must remain super cooled in order to detect the low infrared.
Their statement seems to indicate that they calculated fairly accurately what the thrust required would be for their velocity/trajectory and hence will not need planned contingency burns.
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Re:Slow (Score:5, Informative)
Correct. No thrusters on the observatory side since they would potentially contaminate the telescope mirrors/optics/sensors.
Can't turn around to use the ones on the other side because pointing the instruments towards the Sun/Earth would damage them - they can't handle that light and heat environment.
Launch vehicle intentionally launched short of velocity to reach L2.
First correction was intentionally a bit short as well to make sure they didn't overshoot.
Second correction let them trim it.
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The spacecraft has 16 hydrazine thrusters that each provide about one pound of thrust. So its maximum acceleration is 0.001g or so. Sounds like they used about half power for this burn.
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Yeah, you don't add those numbers together....
Those point in a bunch of different directions for attitude control and unloading the momentum wheels, so if you fire them all, you don't net much of anything.
There are two pairs of bi-propellant thrusters for velocity changes like these corrections. One pair (prime/backup) for the early burns they've completed while it's folded up, and another pair (prime/backup) for the ones once the get to L2 for the rest of the mission when it's fully deployed. Center Mass
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You are correct, I misread which thrusters are used for major course correction vs minor ones. Anyway, it just so happens that the two primary thrusters also have a combined thrust of 16 pounds so the numbers are the same.
aye capt'ain (Score:4, Funny)
Better Link (Score:5, Informative)
https://blogs.nasa.gov/webb/ [nasa.gov]
Specifically, this post [nasa.gov] discusses the fuel consumption of the first two burns, coming well under target, thus extending the mission life.
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What are you talking about, this is Slashdot. Be happy you got CNN and not some subscription paywalled article talking about a science paper Elsevier will sue should you try and even track down a copy.
"attitude" not "altitude" (Score:1)
The article quoted said "The array was coded to automatically deploy either when the observatory reached a certain altitude or 33 minutes after launch, whichever came first". That should be "attitude" (facing the Sun) not "altitude" (distance from Earth).
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From an official NASA tweet: "That deployment was executed automatically after rocket separation, based on a stored command to deploy either when Webb reached a certain attitude toward the Sun or automatically at 33 min. after launch."
Anyone know how many (Score:2)
Re:Anyone know how many (Score:4, Informative)
https://webb.nasa.gov/content/... [nasa.gov]
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The "Deployment explorer" shows about 25 steps after separation, the 7th of which completed today https://webb.nasa.gov/content/webbLaunch/deploymentExplorer.html [nasa.gov]
Not a rocket scientist (Score:2)
65-minute post-launch burn, which bumped up the telescope's speed by approximately 45 miles per hour
I'm presuming it took that long to get an extra few mph because it was a slow burn, right? It wasn't treated like a launch burn.
To me, taking 65 minutes to get an extra 45 mph seems like it was creeping along.
Re:Not a rocket scientist (Score:5, Insightful)
As pointed out above, it is intentionally creeping along. They can't overshoot the velocity because there is no way to slow down. So they make very slow changes.
It did not get married (Score:2)
Of course it has increased life expectancy. When we send a Mrs. Webb up there let me know what happens.
Pathetic (Score:2)
They cannot even calculate how much fuel it needs. Not even close.