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Juno skims the cloud tops of Jupiter

nasa.gov

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Re: Juno skims the cloud tops of Jupiter

#41

Post by ksaj »

arghwhat wrote: post #37
_Microft wrote: post #30

Earlier quoted context omitted.

Kilometer is the largest SI-prefixed variation of meter that is commonly used (among physicists that I know). I would rather suggest that you use scientific notation if you do not want to deal with large numbers of kilometers.

We don't stop at millimeters or kilowatt, so there is really no reason to stop at kilometer when megameter is more appropriate. Scientific notation is also fine, but "210 megameter" is in my opinion easier to read than "2.1 * 10^8 meters", especially for the casual reader. So while I respectfully make note of your feedback, I strongly disagree and stand by my choice of units. :)

Given how hard it is to convince most Americans to use prefixed metre measurements instead of inches, feet, yards and miles, I think it would be even harder to convince the world that a megametre, picometre, etc is the way to go.

Not that I don't agree (I fully do!), the ease of using multiples of 10 is way easier. But it is very difficult to introduce change to the masses, no matter how sensible it is.

The US is one of the only countries on the planet that still fully stick to the old system. And they're also one of the only countries that spell 'meter' instead of 'metre.' For everyone else in the world, 'meter' is a measuring gauge or tool, and so is everything that rhymes with 'thermometer' except for the American pronunciation of 'kilometre' that too many have adopted up here.

Likewise, adult Canadians still use pounds at the gym and their body weight, and feet/inches for their height. Young people are far more reasonable about measurements these days.

Change is hard, and seems to get really messy when everyone goes in different directions from the start.

Re: Juno skims the cloud tops of Jupiter

#42

Post by andrekandre »

holoduke wrote: post #4

210,000 kilometers per hour. Almost 60km/40mi per second. Amazing speed when you think about it. Wonder if there would be any time dilation noticable if the craft ever gets captured and brought back to earth.

  > 210,000 kilometers per hour.
that would get you to the moon in about one and a half hours... crazy (cool)

Re: Juno skims the cloud tops of Jupiter

#43

Post by credit_guy »

rich_sasha wrote: post #40
skohan wrote: post #32

Earlier quoted context omitted.

What's the limiting factor on bandwidth constraints for probes like this? Is it the power of the probe? Is it the distance from earth? I wonder if you could build a mesh network of satellites/probes out farther into the solar system to get better connectivity for projects like this.

The limiting factor is power/distance^2 basically, which determines the signal/noise ratio, which determines the bandwidth. A mesh network sounds fun, though you'd have to have a fair few probes, as their orbits wouldn't be in sync. Also that far from the sun, solar panela don't cut it and you need nuclear thermal generators, which have a finite lifespan.

Also the power. Juno does not have nuclear power, only solar panels. The Sun is quite dim at Jupiter’s distance.

From wikipedia:

    Power: 14 kW at Earth,435 W at Jupiter
Overall the strangth of the signal coming from a solar powered spacecraft in the outer Solar system should go down with the 4th power of the distance.

Re: Juno skims the cloud tops of Jupiter

#44

Post by wdr1 »

lifeisstillgood wrote: post #29

Basic science is the foundation stone of the past 200 years of human progress - and if anyone out there wants to put "double the science budget just because" on their manifesto they can have my vote. I am so glad we live in an age where this is possible, and that it is celebrated and respected. Fantastic.

Every year when I file my federal taxes, there's the little box to give $3 to fund presidential election campaigns.

I've never checked it.

However, if there was a box to say "Give NASA $20", I'd check it every time.

Re: Juno skims the cloud tops of Jupiter

#45

Post by wolverine876 »

lifeisstillgood wrote: post #29

Basic science is the foundation stone of the past 200 years of human progress - and if anyone out there wants to put "double the science budget just because" on their manifesto they can have my vote. I am so glad we live in an age where this is possible, and that it is celebrated and respected. Fantastic.

> Basic science is the foundation stone of the past 200 years of human progress

I agree, but to nitpick IMHO it's a foundation stone. Others are freedom and human rights (including for basic science: speech, to publish your controversial results uninhibited, religion, when your theory is heretical, etc.), rule of law (to protect your investment in your research from powerful people who want to stop or sieze it), and other basics.

Re: Juno skims the cloud tops of Jupiter

#46

Post by [deleted] »

lifeisstillgood wrote: post #29

Basic science is the foundation stone of the past 200 years of human progress - and if anyone out there wants to put "double the science budget just because" on their manifesto they can have my vote. I am so glad we live in an age where this is possible, and that it is celebrated and respected. Fantastic.

[deleted]

Re: Juno skims the cloud tops of Jupiter

#47

Post by abrichr »

sgt wrote: post #5
pjscott wrote: post #3

In case anybody was wondering "Why is the frame rate so lousy?" the answer is that the probe only has about 325 bits per second of downlink on average. https://en.wikipedia.org/wiki/Juno_(spacecraft)

Would it be possible to extrapolate frames in between to give one smooth flyover?

Here's an attempt: https://youtu.be/RgvxLEYeb3g

Re: Juno skims the cloud tops of Jupiter

#48

Post by ncmncm »

Crontab wrote: post #28
holoduke wrote: post #4

210,000 kilometers per hour. Almost 60km/40mi per second. Amazing speed when you think about it. Wonder if there would be any time dilation noticable if the craft ever gets captured and brought back to earth.

I've read that time moves a tiny bit slower on Earth than it does in space and that it affects satellites. I wonder how much difference there is for something like the Voyagers, which has been in space since the 70's, and us on the ground.

You could calculate it yourself. It would be a good exercise.

Wolfram Alpha could be helpful.

Re: Juno skims the cloud tops of Jupiter

#49

Post by ncmncm »

wdr1 wrote: post #44
lifeisstillgood wrote: post #29

Basic science is the foundation stone of the past 200 years of human progress - and if anyone out there wants to put "double the science budget just because" on their manifesto they can have my vote. I am so glad we live in an age where this is possible, and that it is celebrated and respected. Fantastic.

Every year when I file my federal taxes, there's the little box to give $3 to fund presidential election campaigns. I've never checked it. However, if there was a box to say "Give NASA $20", I'd check it every time.

Those check boxes never have any practical effect, but pols like them because they seem like they might.

Re: Juno skims the cloud tops of Jupiter

#50

Post by raattgift »

_Microft wrote: post #30
arghwhat wrote: post #22

Earlier quoted context omitted.

As a point of reference, our solar system orbits our galaxy at approximately 4 times that speed at 828 megameters per hour, so 210 megameters per second isn't that big a deal in the grand scheme of things...

Kilometer is the largest SI-prefixed variation of meter that is commonly used (among physicists that I know). I would rather suggest that you use scientific notation if you do not want to deal with large numbers of kilometers.

I think you're right, but with a tiny handful of notable exceptions in astrophysics, where gigametres can be a characteristic or upper length scale.

LISA is practically always described as a gigametre-scale observatory.

One example: "LISA, a gigameter-scale space-based gravitational wave observatory, will explore the gravitational wave universe in the band from below 0.1 mHz to above 0.1 Hz." https://about.cern/news/announcement/physics/cern-colloquium...>, and a trawl through arxiv will show a common association of Gm and LISA.

Assuming LISA is successfully deployed, gigametre may be seen more commonly.

The only other place I've seen Gm scales in common use is in galactic physics, particularly with respect to turbulence and star and planetary nebula formation (stars have ~ Gm diameters; very large stars like VY Canis Majoris have ~ Tm diameters; star systems like ours have gravitationally bound rocky and icy objects at ~ Tm diameters).

1 petameter ~ 0.1 lightyear; 30 petameter ~ 1 parsec, so those are obvious cutoffs for the SI unit of length in astronomy and astrophysics.

Gigaparsecs and (less frequently) gigalightyears are commonly used in physical cosmology (e.g. https://duckduckgo.com/?q=gigaparsec+site%3Aarxiv.org&ia=web>).

Penultimately, truly long lengths are typically measured in cosmological redshift z, which is unitless (being a ratio \frac{\delta\lambda}{\lambda}, or 1+z = \frac{a_{now}}{a_{then}} where a is the scale factor), leading to such things as a comoving volume (1 + z)^3. For z > 0.2 one would be using Gpc lengths, or in SI units Ym; or when working in these sorts of comological volumes in 2023's Britain, trevigintillions of acre-feet.

Finally, cf. the excellent printable table at https://arxiv.org/abs/1303.5961>, the leftmost column (redshift) and the r_comov column (megaparsecs) being the most directly relevant.

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