Talk:Juno (spacecraft)

Solar Panel Output

Since Jupiter has a perihelion and aphelion distance of 4.95 AU and 5.46 AU repectively, it receives between 1/25th and 1/30th of the sunlight levels we receive at Earth's distance from the Sun. So why then does the article state:-

"The total area of the arrays is over 60 square metres (650 sq ft). This is enough to produce over 18 kilowatts (24 hp) while in Earth orbit, and just over 400 watts (0.54 hp) while on Jupiter orbit."

Surely if the solar panels could produce 18kW of power in Earth orbit, they'd produce between 600 and 720 Watts in Jovian orbit? One of these figures must therefore be incorrect! CrackDragon (talk) 20:22, 31 July 2010 (UTC)

That assumes that you have a perfectly empty vacuum. If you have any sort of intervening material - dust, gasses, etc. - that could reduce the intensity of the light received by more than just increasing the distance would. 71.134.236.97 (talk) 08:29, 8 August 2010 (UTC)

This has nothing to do with dust, which absorbs no more than 1/10,000,000th of the light. The output drops faster because it is a non-linear function of the light intensity. Ruslik_Zero 08:37, 8 August 2010 (UTC)

With the solar panels themselves? So if they're bathed in say, half the light intensity, they produce less than 50% of the output? CrackDragon (talk) 08:40, 11 August 2010 (UTC)

Semiconductor behavior can alter with temperature. While not necessarily applicable to Juno's solar cells, an example would be the increase in electrical resistance with decreasing temperature often seen in semiconductors. More resistance = less efficient collection of electricity from the cells. And Juno's going to be colder at Jupiter than a satellite in Earth orbit. 147.160.136.10 (talk) 11:51, 13 September 2010 (UTC)

Performance specifications of Juno solar panels: At 1 A.U = 15,000 Watts. At Jupiter Orbital Insertion (Aug 2016) = 486 watts. At End-Of-Mission (Oct 2017) = 428 Watts. Factors affecting power output include some non-lineararity as light intensity falls, low temperatures, variations in Jupiters distave from Sun over mission duration, aging of cells over 7 year mission, and most importantly, deterioration of solar cells by radiation. Yale s (talk) 08:28, 5 October 2010 (UTC)

Yale s said most of it, but Just want to point out, that many semiconductors have less resistance at colder temperatures, thus the reason super cooling a CPU enables it to achieve reliable higher speeds. —Preceding unsigned comment added by Firegryphon (talk • contribs) 03:52, 20 October 2010 (UTC)

I think you're mistaken; conductors perform better at cold temperatures, but semiconductors suffer as there are fewer charge carriers, increasing resistance to the point where they all "freeze-out", turning the material into an insulator. I believe the rationale behind cooling microprocessors (besides preventing thermal heat damage) is to allow the transistors (MOSFETs) to actually shut off (have enough resistance) versus becoming uncontrollable (always on). Just my guess though. -- atropos235 ✄ (blah blah, my past) 14:47, 2 November 2010 (UTC)

Mission duration: 1 Earth year

NASA is spending $700 million on this project, and it's only lasting one year? Why not ten or more? Our weather satellites are designed to last decades. Why can't we expect similar results from Juno? Someone at NASA should get fired over this blunder.173.58.64.64 (talk) —Preceding undated comment added 16:53, 27 August 2010 (UTC).

Before firing someone at NASA, it'd probably be worthwhile to note many NASA deep space missions have a short period of performance at launch. The dramatic ones get funding extensions. For example, the Mars Exploration Rover program cost $840 million to design, build, and deliver 2 rovers to Mars and operate them for 90 days. The multi-year operational extensions beyond 90 days have, to date, cost about $140 million. http://en.wikipedia.org/wiki/Mars_Exploration_Rover Operating deep space probes is also rather more expensive than operating a weather satellite; weather satellites have lots of paying customers and need relatively simple communication hardware on the ground, while operating Juno needs time on the Deep Space Network and the support of expensive specialists. If NASA gets some dramatic wins and public interest with Juno's first year, it probably will no trouble taking your logic to Congress and saying, "We've got $700 million orbiting Jupiter that's got thousands of miles left on its tires. Give us $100 million and we can operate it for 5 more years and show the taxpayers we're getting dramatically better bang for their buck." 147.160.136.10 (talk) 12:06, 13 September 2010 (UTC)

This is not supposed to be a discussion forum, but you must understand that Earth satellites operate within the protecting envelope of the magnetosphere. In addition to the solar radiation, Juno will be exposed to large amounts of radiation emited by Jupiter.--BatteryIncluded (talk) 13:39, 15 September 2010 (UTC)

The probe will be exposed to extremely high radiation levels and would not be expected to survive for extended time. The craft will be de-orbited (as was Galileo) while it is still manageable, in order to avoid a future collision and contamination of one of Jupiter's moons. Yale s (talk) 08:35, 5 October 2010 (UTC)

This should probably be explained in the article. The article, as well as NASA's own website about the mission, only mentions that it will be deorbited after the 33rd orbit, without any explanation as to why that is. I wondered if it was to take measurements of the atmosphere directly, which would be interesting if possible to pull off. But to avoid contaminating the moons due to the spacecraft becoming uncontrollable also makes sense. Is there a reference for that, or just an educated guess? Harperska (talk) 01:19, 23 October 2012 (UTC)

A somewhat macabre joke in the flight software group was that if you were thrown out of the spacecraft in Jupiter's magnetic field without a space suit, you would die of radiation before you asphyxiated.Freakdog (talk) 08:32, 17 April 2012 (UTC)

Travel speed too low?

In section Mission summary: "will travel faster ... (4.4 km/s) to reach the planet." This seems a little too low. The orbital speed of Jupiter is 13.07 km/s and the orbital speed of Earth is 29.78 km/s. I would expect the average travel speed to be above 13 km/s. If the 4.4 km/s is the minimum distance between Earth and Jupiter divided by the travel time I think it is misleading. What should it be? --Mortense (talk) 11:16, 6 August 2011 (UTC)

I suppose that is the speed required to intercept Jupiter, not chase it along. Cheers, BatteryIncluded (talk) 20:08, 6 August 2011 (UTC)

It is clear from the orbital manueavers that the slowest speed is when approaching Jupiter, chasing it. So it never travels slower than 13 km/s.— Preceding unsigned comment added by Mortense (talk • contribs)

I removed it.--Patrick (talk) 22:19, 8 August 2011 (UTC)

Other periods without sunlight?

Section Solar panels: "The solar panels will remain in sunlight continuously from launch through to the end of the mission, except for short periods during the operation of the main engine." Is that the only time it is not in sunlight? How can it avoid coming into Jupiter's shadow while in orbit around Jupiter?--Mortense (talk) 12:37, 6 August 2011 (UTC)

It is a polar orbit ~ imagine the hands of a watch circling while facing the sun and that their axel is Jupiter. Cheers, BatteryIncluded (talk) 20:14, 6 August 2011 (UTC)

Explanation for 2012 Earth Flyby

Most readers including myself will be confused as to why a spacecraft headed to Jupiter will undergo an earth flyby two full years after leaving the earth. The actual path of the Juno probe ought to be included, so as to explain the earth flyby. Also, any other details about the flight path would interest readers. Douglas.hawkes (talk) 13:17, 6 August 2011 (UTC)

I've added File:Juno's interplanetary trajectory.jpg. You can see that Juno's current orbit isn't big enough to reach Jupiter. Not sure what "DSMs" means; 'Deep Space Maneuvers'?

—WWoods (talk) 16:58, 6 August 2011 (UTC)

It took me a while to work out "EFB" = "Earth Flyby" and "JOI" = Jupiter Orbital Insertion...I think. These could do with explaining in the image comments too. NinjaKid (talk) 12:18, 9 August 2011 (UTC)

You guys are right in all accounts, and the Deep space maneuvers (DSM) are scheduled for 30/August/2011 and 3/Sept/2012. BatteryIncluded (talk) 13:39, 9 August 2011 (UTC)

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Created Cost section

I have created a "cost" section and moved the cost details out of the introduction where they interrupted the flow of the description of the subject.109.154.74.121 (talk) 08:22, 31 August 2011 (UTC)

Europa?

With a mission this size will there be any analysis of Jupiters moon Europa and it's saltwater Oceans? 69.171.160.77 (talk) 23:45, 13 October 2011 (UTC)

That question has come up in press conferences and the answer is no. This mission is specific to the planet and no moons will be targeted. There might be some imaging but no significant science will come from this mission related to the moons. The spacecraft will be sacrificed at the end of the mission specifically to prevent contamination of interesting moons such as Europa.--RadioFan (talk) 01:21, 5 February 2012 (UTC)

Billions?

The change (with summary "billions is ambiguous" from billions to millions in the article around distance measurements "1.74 billion miles (2.8 billion kilometers)" to "1,740 million miles (2,800 million kilometers)" has been reverted twice now. Before this is changed again, there should be consensus established here.

• Against given the launch date of this mission there should be no concerns that anything but the short scale definition of 1 million is being used here. All references use the billion figure. 1.74 billion is more readable that 1,740 million.--RadioFan (talk) 01:14, 5 February 2012 (UTC)

• Against. USA mission in use of North American short scale numbers. BatteryIncluded (talk) 03:05, 5 February 2012 (UTC)

Comment: An IP editor changed this to billions from the original text of millions, I merely reverted the change back to the original. Billions is ambiguous and there is no description in the article about how billions is supposed to be interpreted. Changing to Billions creates confusion. HumphreyW (talk)

Comment the change from millions to billions came in this edit by Wraithful not an IP editor (though I'm not sure why it would matter if an IP editor made the change, they are welcome to edit as well). There might be some ambiguity if this mission launched in 1911 from Europe but it didn't, it launched in 2011 by an agency that has always used the short scale. There has been global agreement on what a "billion" and beyond is for almost 30 years.--RadioFan (talk) 12:42, 5 February 2012 (UTC)

Comment: It's less important which form of numeric scale you use and far more important that a "translation" accompany it so that people from countries using the scale not used in the article understand what is meant. Please keep in mind that either way there are millions of people that use either form, so therefore being considerate to whoever's form of numeric terminology gets scrapped (by providing a clear translation note) is paramount. 98.173.62.28 (talk) 23:24, 8 June 2012 (UTC)

""Comment"": This is the English Wikipedia, and English uses short scale.101.166.150.53 (talk) 06:01, 3 January 2013 (UTC)