Orbit - not clouds...
At least not for a while.
The final plan is for aero braking and destruction in the arms of Jupiter, but that's a while after orbital insertion.
No mention of the three plucky lego figures?
By Jove! NASA's Juno prepares to slip into orbit around Jupiter
NASA's Juno spacecraft is set to enter its most critical stage as it attempts to fly into Jupiter’s orbit. At 4:18am BST, NASA’s Juno spacecraft will begin its orbital insertion burn, a move that will decelerate its velocity – slow enough to be captured by Jupiter’s gravitational field. The burn will initiate when the …
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Monday 4th July 2016 15:44 GMT Gotno iShit Wantno iShit
Pedantically speaking.....
At 4:18am BST, NASA’s Juno spacecraft will begin its orbital insertion burn, a move that will decelerate its velocity – slow enough to be captured by Jupiter’s gravitational field.
It'll all be over before 4:18AM BST, that's the time Earth should receive a tone confirming start of burn. The 48 minute transmission delay means the 35 minute burn should have ended before NASA knows it has begin.
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Tuesday 5th July 2016 07:21 GMT Anonymous Coward
Re: Delimitation
The main factors that decide the shape & size of the solar panels are (a) the maximum power consumption of the spacecraft during its nominal mission, (b) the incident solar flux (i.e. how much sunlight is actually hitting the spacecraft), and (c) the efficiency of the solar cells at the end of the nominal mission (radiation will degrade them). Normally NASA would not use solar arrays that far out, however they have a shortage of Plutonium for RTGs so that had to be ruled out early in the mission design. The spacecraft needs about 350W of power (give or take, I don't have the figures to hand right now), so they sized the overall area of the solar array so that it would give about 410W at the end of the nominal mission (490W at the start) when in orbit around Jupiter
Once you have the required solar array area it is just a case of how you split it up - you could have had two panels but they would have had to have been *huge* at at risk of being damaged during Jupiter insertion. You could have had four panels, but that would make instrument positioning very complicated. Three is a compromise that happens to work in this instance.
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Monday 4th July 2016 22:36 GMT Magani
Re: Delimitation
Isn't there an El Reg unit for unpersonned spacecraft volumes?
If not, I put forward the unit of 'VW Kombi'. Not only comprehensible to all, but apt given the number of 'gravitationally excited' events that tended to happen in them during their youth.
An icon of the best for the Jove team.
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Monday 4th July 2016 22:49 GMT Destroy All Monsters
WWH9KS
We read:
Jupiter is a giant gas ball – eleven times wider and 300 times more massive than Earth. It is unknown if the planet has a solid core so Juno will not be landing on any surface. Instead, if the spacecraft successfully enters Jovian orbit, it will be descending into its fluffy clouds.
Well, Juno will not be landing on any surface not because it is unknown whether that giant gasball has a solid core (pretty sure it does as primordial crap must accumulate somewhere) but because it would have to dive into a hydrogen ocean for several Earth diameters, then burrow through a solid "dark hydrogen" layer for a couple more Earth diameters and then worm its way through a major mass of metallic hydrogen like the angry fist of God for many additional Earth diameters to finally ding that solid, seriously hydrogenated core.
Instead, if the spacecraft successfully enters Jovian orbit, it will be descending into its fluffy clouds.
It will do what now?
What would HAL 9000 say?
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Tuesday 5th July 2016 00:27 GMT JeffyPoooh
What D.A.M wrote...
"It is unknown if the planet has a solid core so Juno will not be landing on any surface."
Otherwise it would?
"Instead, if the spacecraft successfully enters Jovian orbit, it will be descending into its fluffy clouds."
Huh? I read elsewhere it'll be thousands of km above the fluffy clouds.
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Tuesday 5th July 2016 14:23 GMT Anonymous Coward
Re: What D.A.M wrote...
Otherwise it would?
No chance; keep in mind that the Hyugens (sp?) probe was crushed after only travelling a couple of hundred kilometers into the atmosphere; it still had maybe a thousand kilometers to go plus a sea of liquid hydrogen plus another sea of metallic hydrogen.
In fact there are some doubts whether Jupiter still has a solid core left. Some of the theories suggest that the solid rocky core may be soluble in metallic hydrogen, which means it would have dissolved long ago.
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Tuesday 5th July 2016 06:23 GMT Ru'
I'm not belittling the achievements of stuff like this (and it's probably more to do with journalists and PR types than the boffins) but I'm tired of statements like "no second chance" and "no room for error" and "must work perfectly" etc.
Obviously I may be wrong, but I would think that you would include room for errors, and would allow for things not working absolutely perfectly, i.e. you'd design for the real world where there are tolerances.
Depending how close you look, I would argue that nothing is perfect to start with, so nothing at all can work completely perfectly, with zero error.
But grumpiness aside, top work Juno boffins!
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Tuesday 5th July 2016 07:36 GMT Anonymous Coward
It's like a Japanese sword duel
Well, once you commit, you better be sure you have chosen the right manoeuver to commit to. You will also find out exceedingly quickly. You can't go back. You have to stay on track.
To avoid nasty surprises, we have
* Duplicated/Triplicated system
* Fail-safe systems
* Watchdog circuits
* Autonomous systems
* Software rejuvenation (aka. hit the reset button when something smells)
* Test, test, test
* Formal verification
* Physical devices (like thrusters) that are as simple as possible in design and are known to work well
etc.
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Tuesday 5th July 2016 15:37 GMT cray74
Obviously I may be wrong, but I would think that you would include room for errors, and would allow for things not working absolutely perfectly, i.e. you'd design for the real world where there are tolerances.
Juno probably used an approach like the ill-fated Mars Climate Orbiter, which had a number of pre-planned, optional trajectory correction maneuvers. In Lockheed-built MCO's case, the navigation team was noticing errors in the spacecraft's course up to a week in advance but decided not to use a 5th correction burn. Or decided to, but never bothered.
Anyway, Juno probably had several pre-planned opportunities to tweak its course before it performed the main, fuel-draining braking maneuver. NASA would probably like the final opportunities to find out if Lockheed-built Juno was exhibiting metric conversion problems. ;)
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Tuesday 5th July 2016 09:32 GMT Chris 239
Gobsmacked that El Reg published an article with crap like "Instead, if the spacecraft successfully enters Jovian orbit, it will be descending into its fluffy clouds."! Really!
(For those as ignorant as Katyanna Quach, orbiting requires quite carefully avoiding the fluffy clouds or anything but the thinnest remnant of atmosphere. Hittting the atmophere at orbital speed turns you into metor and kills you unless yo have an intact heat shield. Slowing down from orbital speed would require a rocket almost as big as the one that got you there)
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Tuesday 5th July 2016 11:40 GMT TheWeenie
ElReg needs to have a new unit of disinformation/bollocks. I propose the "Gove". So "Instead, if the spacecraft successfully enters Jovian orbit, it will be descending into its fluffy clouds." would qualify as about 0.2 Goves.
Surely 1.0 Goves would be a constant, like 0K or e. So to deal with mundane stuff like this you'd need to have smaller units, such as the milligove or the microgove.
A minor sexing-up of the editorial pales into insignificance next to the Reference Unit himself. Maybe a couple of milligoves at most.
I'd like to propse the use of the Bojo too - a bit like the Becquerel - but instead of one radioactive decay per second, one Bojo would reflect the number of words spoken by an individual that would generate one lie per second. Obviously that's a tiny, weeny little unit, so we'd need to go the other way with the sequence - the kilobojo, megabojo, gigabojo and terabojo respectively.
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Tuesday 5th July 2016 16:09 GMT cray74
Re: Home significant a speed change?
According to Wikipedia it was approaching Jupiter at 74,000 m/s so less than a 1% change which seems remarkable!
With a mass as big as Jupiter's, the Oberth Effect applied near the cloud tops can be a mighty thing.
Juno actually approached Jupiter from a near standstill. Its orbit around the sun was slowing to crawl relative to Jupiter when Jupiter overtook the probe. Juno then began a fall toward Jupiter that peaked at 74,000m/s over Jupiter's cloud tops, so that 74,000m/s is almost entirely the result of Jupiter's own gravity. Had Juno not fired its engine, it would've swung away toward deep space on a hyperbolic path and gradually slowed back to Si as Jupiter's gravity reluctantly let it go.
By firing its engine deep in the gravity well, Juno spent more time climbing away from Jupiter than it spent falling in. That use of gravity gives a potent multiplication of braking delta-V. Let the giant planet and it's gravity do the grunt work of capturing the probe.
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Wednesday 6th July 2016 19:37 GMT cray74
Obligatory XKCD
Juno's great Satur-...er...Jupiter success!
Biting the hand that feeds IT
