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Juno spacecraft question
Since Juno has three very large solar arrays on it to give sufficient
electrical power via sunlight (rather than RTGs) at Jupiter's distance from the Sun, why wasn't it equipped with an ion engine to cut its trip time down some? The arrays would generate lots of power while it's in the inner solar system, as it will be for a lot of time till the Earth encounter in October of 2013 slingshots it out to Jupiter: http://www.youtube.com/watch?v=sYp5p2oL51g Also, what's the purpose of the fabric cover over the transceiver dish? They expecting to encounter a lot of micrometeors on the way? Pat |
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Juno spacecraft question
In sci.space.history Pat Flannery wrote:
Since Juno has three very large solar arrays on it to give sufficient electrical power via sunlight (rather than RTGs) at Jupiter's distance from the Sun, why wasn't it equipped with an ion engine to cut its trip time down some? The arrays would generate lots of power while it's in the inner solar system, as it will be for a lot of time till the Earth encounter in October of 2013 slingshots it out to Jupiter: Concerns about added complexity? How close was Juno to an Atlas V 551 configuration's mass limits? rick jones -- firebug n, the idiot who tosses a lit cigarette out his car window these opinions are mine, all mine; HP might not want them anyway... feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH... |
#3
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Juno spacecraft question
On Aug 10, 11:01*am, Pat Flannery wrote:
Since Juno has three very large solar arrays on it to give sufficient electrical power via sunlight (rather than RTGs) at Jupiter's distance from the Sun, why wasn't it equipped with an ion engine to cut its trip time down some? One obvious answer would be that while, as you note, the spacecraft had a lot of extra energy available for that, this would have required extra reaction mass to be added to the craft. Since the goal was to put a specific scientific payload into orbit around Jupiter, but _when_ that payload arrived didn't really matter much, what point would there be in cutting down the trip time at the cost of increasing the size of the booster needed to launch the craft in the first place? Instead, they launched Juno into a 2-year orbit - as if it was just going to Mars, but needed a fast free-return trajectory - thus reducing the required delta-V - and when it gets back to Earth, it will do a gravity-assist maneuver which will finally give its orbit the aphelion required to actually reach Jupiter. So that shows where the emphasis is he on getting the thing to Jupiter with the smallest booster they can get away with. Not getting it there quickly. Mind you, I'm surprised they didn't save even more fuel, and launch it into a 1.5 year orbit, so that it would do the gravity-assist maneuver *three* years later. It's not like they have any astronauts on it that need life-support. But perhaps the relative speed of the spaceship and the Earth wouldn't have been high enough for the required gravity assist while still staying outside the atmosphere. And doing more than one gravity assist involved diminishing returns and wasn't necessary. John Savard |
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Juno spacecraft question
On Wed, 10 Aug 2011 09:01:36 -0800, Pat Flannery
wrote: Since Juno has three very large solar arrays on it to give sufficient electrical power via sunlight (rather than RTGs) at Jupiter's distance from the Sun, why wasn't it equipped with an ion engine to cut its trip time down some? Cost. It had to fit within the New Frontiers program budget. The ion-powered Dawn busted that budget and had to beg to be reinstated. Lesson learned. Brian |
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