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Posted: |
Jul 4, 2016 - 10:01 AM
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By: |
Grecchus
(Member)
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A very interesting mission. Juno, apparently, won't last as long as other probes because the radiation emanating from Jupiter is highly energetic and it's instrumentation is going to get cooked very quickly. I wonder who has placed bets on how long the hardware will last?
I didn't think a probe could orbit the giant planet at such close range because the fuel required to do so would be prohibitive. To get to Jupiter, Juno had to fly past the earth a second time to capitalize on the slingshot effect, so I guess one of the reasons it has taken a while to get there was due to the fuel constraints on the mission - that is to say, a high proportion needed to be reserved just to slow down enough right at the end.
If anyone didn't already know, in Arthur C. Clarke's sequel to 2001 - 2010: Odyssey Two, the alien race looking out for humanity decides to turn Jupiter into another star, which in the book was renamed "Lucifer." To do this, the Monolith somehow compressed the hydrogen/helium volume normally occupied by Jupiter to fit into a much smaller size, thereby allowing it to shine as a star via the nuclear fusion process. The aim in the story was to give life on Europa a chance. Some people, in fact, view Jupiter as a "failed" star. It's almost as though Jupiter itself is made from residual gas which somehow cleaved off from the mass which formed the Sun. The ratio between large gaseous and small rocky planets, and their formation locations within a given solar system is currently a hot topic.
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This is really cool stuff and i hope it all goes as well as it can and we learn some really interesting things from the data they collect. 99% of it is beyond the capabilities of my tiny mind but its good stuff.
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Posted: |
Jul 6, 2016 - 10:36 AM
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By: |
Grecchus
(Member)
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Warlock's question about the entry point in the ellipse is a discerning one. The reason for a polar orbit is obvious - all the weather bands parallel to the planetary equator are traversed. The hemispherical "sparking" is monitored both ends, so to speak. Don't quote me, but the ellipse could be entered at any point, just so long as the spacecraft rocket engine can fire with sufficient thrust and duration to place it with the required velocity. But you can enter either at the point of closest or furthest approach. When making course corrections, it is best to do so while further away from a gravitational source because that force peters out with greater radial distance due to the inverse square law. The closer you get to the planet the faster you fall to the centre, and the more fuel you need to counter that greater stranglehold. So I think Juno might have entered the orbit around Jupiter at the point furthest away from the planetary periphery, where the altitude is highest. Theoretically, that way the probe should need a slightly lesser amount of fuel to jockey for position. The hard part was braking - changing the shape of the orbit then requires less energy, though, with something the size of Jupiter, all evolutions would require highly energetic impulses to be put into effect, I should think.
Edit: My guess was out. Looks like Juno fired it's rocket engine at closest approach. The orbit is much more elliptical than I could have imagined. If you care to look there's an animation which gives a little more insight how things worked:
http://spaceflight101.com/juno/juno-mission-trajectory-design/
https://www.youtube.com/watch?v=kMdcTRE8uR8
https://www.youtube.com/watch?v=ka6OERznXh4
https://www.youtube.com/watch?v=NNHfoNIiZ8Y
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