Pluto Mission: GROSS Nav Error

Phil Pilgrim (PhiPi)

The Pluto probe has been on its way for a mere 10 years. How could a craft the size of a grand piano possibly miss its time of closest flyby by 76 seconds?! Come on! This isn't the pre-computer age after all! Did someone at NASA do the nav calcs with a slide rule? 76 seconds is more than a freaking minute!_______________

Seriously, I'm in total awe of such precision. Just stop and ponder that for a moment. That's timing to one part in more than 4 million over a span of billions of miles! Granted, there wasn't any rush-hour traffic along the way to plan around; no speed traps in the asteroid belt to detour. But a mere millisecond difference in burn time could have produced an error of a much greater magnitude. My hat's off to the engineers and mission controllers at NASA for an incredible job! I just have to shake my head in wonder! And the photos are magnificent.
Truly, Pluto deserves to have its planetary status reinstated. I mean, it's round, it looks like a planet, it even has a moon. Why not?
-Phil

jmg

Truly, Pluto deserves to have its planetary status reinstated. I mean, it's round, it looks like a planet, it even has a moon. Why not?


Hehe, I was reading one argument for 'demotion' was that Pluto was not 'gravitationally dominant' and unable to form a proper Sphere.

Of course those who 'deduced' that from a few pixels, will be red-faced now the real photos are in....

Peter Jakacki

Such a probe built by Hollywood would always work, doesn't matter how complex it is and how impossibly short the construction time was (they always seem to know how to build it so there is never any need for R&D etc), the thing is that when they throw the switch it just works, first time.

Now we know how ridiculous that is yet the Pluto probe has done something similar (albeit the R&D and simulations etc) in that it worked first time, since no dry runs were possible anyway, and it has worked so well after so long. Hats off to the New Horizons team, it's an amazing feat of engineering.

BTW, To me, Pluto will always be a planet, the solar system just wouldn't seem complete without it. Us planets have to stick together you know.

localroger

Pluto got demoted because it doesn't gravitationally clear its orbit of trash.  In fact, Pluto is really orbital trash that Neptune tried to clear but got locked into an orbital resonance instead.

And if Pluto is accepted as a planet, then by any reasonable standard we'd also have to accept Ceres, Vesta, a couple more asteroids and half a dozen Kuiper belt objects that have been discovered in the last decade too.

But hey, ice mountains!  Nobody expected it to be geologically active.

Buck Rogers

Actually localroger, Pluto is technically a "minor planet". Its really a possible planetary fragment. Which makes the others in the two belts the same thing.
But we won't be able to prove that until we send crews to selected asteroids to collect samples and match them to the Moon stuff.
Besides, I know why she was late getting there. But I'm not going to reveal it in this forum.

Tor

Obligatory xkcd: https://xkcd.com/1532/

-Tor

Cluso99

Agreed, the results are astonishing. The initial pics are amazing. But it's going to take 16 months for Dawn to transmit all the data it recorded in a small set of hours. Impossible to imagine what else we are going to see.

IIRC the 2nd and 3rd moons are about 20 and 30 miles in diameter. There are 2 smaller moons known. And these were found by the Hubble after Dawn was launched. These are minuscule rocks/ice and again IIRC Dawn has scanned these two.

As for dwarf status, if Pluto was not demoted we would have many more than 9 planets already, and while Pluto is one of the larger ones in this group, it is not the largest. Things change, and so do definitions. Be happy it's not life threatening

Tubular

I think they found Pluto is actually the largest, for now.  Slightly bigger diameter than Eris, but much less dense.  http://phenomena.nationalgeographic.com/2015/07/13/new-horizons-science-update-pluto-is-the-biggest-one-of-all/

tritonium

Hi
I was wondering just what electronics technology they used, considering the craft is 10 years old, and even then only age proved technology would be considered. What kind of storage- already 10 years old, to reliably store data for the 16 months it will take to download at about 1 kbit per second? Apparently after lossless compression each picture is 2.5 Megabits and the transmitter can only be used for 8 hous in 24.
(16 months x 30 days x 8hrs x 60 minutes x 60 seconds x 1000 bits) / 8 bits to byte = 1,728,000,000 bytes (<2 Gbytes)
Some kind of flash memory I suppose.
In fact they developed the ability to transmit a nearly twice the speed - after launch! So in that 16 months that would require nearly 4 Gbyte.
This is an interesting link
http://www.planetary.org/blogs/emily-lakdawalla/2015/01300800-talking-to-pluto-is-hard.html
Dave

Phil Pilgrim (PhiPi)

I always assumed that Pluto was so far from the sun that it was perpetually dark, even at high noon. But no! Here's a website that lets you experience Pluto noon from your locale:
    http://solarsystem.nasa.gov/plutotime/
Just give it your location, and it will tell you what time of day to look outdoors to experience Pluto's light levels at noon. 'Turns out, you could still read a newspaper on Pluto without a flashlight!
-Phil

LoopyByteloose

Regarding the issue of control from planet Earth, the Wikipedia entry on New Horizons mentions that the communications is X-band microwave with a baud rate of 1Kbaud for that distance.  And there is something like a 4.5 hour latency involved in the communications.

All that and traveling at huge speeds should make navigation a bit intense.

I saw some mention of relay stations - one or more of them - somewhere past Jupiter. 

We can now rephrase the Beetle's Yellow Submarine...

"We all live inside a huge Oort Cloud...."

Next we tour the Kuiper Belt.  I am wondering how much of a magnetic field the Sun provides so far and away.

Wuerfel_21

If i were them i would encode the picture in some form of interlace like this:
That way they can eat popcorn while it transforms from a blurry mess into a highres picture

Jonathan

Phil - For a second I thought you were serious! My blood pressure started to rise! Thankfully, I saw you were just kidding. Quite the feat, NASA impresses yet again. Can't wait to see the pics.
Jonathan

Tubular

Regarding the data rate, it often hits 2kbit/sec.   You can check on the DSN now page, click on a dish talking to "NHPC" then click 'more detail' https://eyes.nasa.gov/dsn/dsn.html

koehler

Pluto's demotion seems to have been more of an ego thing by some, than any sort of establishment change of view.

I can argue it does not fit the current definition of a planet, however without looking back to the 1930's criteria, it probably did back then.

The simplest thing would have been to leave it as the 9th Planet*, with an asterick next to it like for Barry Bonds, indicating it was was decided it was actually a dwarf planet.

Leave it as a historical exception, and as a useful jumping off point for the whole discussion of dwarf planets.

But no, someone's ego had to be satisfied.

Wuerfel_21

@TubularOoops, seems they have lost the signal...

Tubular

Hmm yes, better start some conspiracy theories : ) 
The other thing a bit unusual with that DSN page is the outgoing waves aren't pure - there are some harmonics built in.  I wonder that's an accurate reflection of what's actually sent.  The incoming waveforms are sometimes sinusoidal and sometimes 'harmonic'    
edit: Never mind they explain this on the 'info' page on the screen.  Its the difference between carrier only, vs carrier + data

Wuerfel_21

Maybe they use a different method of modulation, some artist was crazy or their RF circuits were built by an idiot.
Also, for a short period, the antena status was something about setup...
Also their sending at 7 Ghz...from what i know higher frequency means less range (i once tried building something that made annoying noise and it picked up long wave radio, i can recieve medium wave radio from france, while ultra short wave radio has a Smile range, and we dont talk about wifi...
Also, why send data up while there is nothing coming back(indicating the antena isn't connected to new horizons, or it pulled a BSOD)?

Tubular

NH is still conducting science readings.  I guess you need to send data 4.5 hrs in advance of knowing when it'll turn back to face earth, to receive these signals currently being sent.   

Tor

Wuerfel_21, the short range of higher frequencies on Earth is only due to the atmosphere and how radio signals bounce on the various layers of the ionosphere. 14 MHz, for example, can sometime bounce all the way around the globe and reach you from behind so to speak. While UHF will go straight through, and/or get absorbed by the ionosphere instead of bouncing. None of that applies for empty space, so a higher frequency gives you a higher modulation rate, thus more bits per second. The main problem is when going through the atmosphere when reaching Earth, and that receiving parabolic antennas have to be pointed extremely accurate (a combination of the frequency and the necessary size of the parabolic mirror).

Wuerfel_21

So then why do they only have some 1 or 2 kbaud then?

Heater.

Wuerfel_21,

"...from what i know higher frequency means less range..."

Let's think about that for a second. Light from stars in our galaxy comes to us and is visible to the naked eye form many light years away. Light from other galaxies comes to us from so far way it has taken billions of years to get here, I think the current outer limit of the Hubble telescope is 14 odd billion years. The age of the universe that is.

Light is a very high frequency EM wave. Clearly higher frequencies is not a limit on range.

As for the 2 kbaud thing. Despite the fact that a signal is in the Ghz range and can get here over such vast distances it will be very weak. Think inverse square law and all that. That means it it is very hard to separate the signal from all the noise you will be receiving or inherent in your receiver hardware.Turns out the maximum data rate you can send over a channel is related to the noise on that channel. See here : https://en.wikipedia.org/wiki/Shannon–Hartley_theorem

People have been thinking about this for a long time.

LoopyByteloose

Well, the Wiki on the New Horizons mentioned something about a 12watt transceiver.  That seems a bit amazing.

 I believe there is a relay somewhere past Jupiter, but it might be that there is a bit of wobble involved in the dishes and as they get further apart, slower data rates are required to compensate for such motion.

As far as Pluto being demoted, it was personally disheartening.  My astrological horoscope has Pluto conjunct Midheaven -- which personally makes it define my destiny in this lifetime.

But being recently discovered and then demoted means that astrologers have never developed a consensus as to what that should mean.  So it dead-ended my astrological studies.  LOL

Heater.

Loopy,
Wait a minute, Pluto was not discovered until 1930 or so. 
Astrology has been around since forever.  
What about all those people born before that, what signs and "conjunctions" were they born under?
What a load of bull astrology is.
 

Wuerfel_21

Well, learned another thing!

Dave Hein

There are a few problems with calling Pluto a planet.  If Pluto is reinstated as a planet we would need to add Eris as a planet as well.  Eris is about the same size as Pluto, but has more mass than Pluto.  There are also 7 moons in the solar system that are larger than Pluto.  Should they be called planets also?  Pluto and Eris orbit around the sun in the region known as the Kuiper Belt, where there are many large celestial objects.  Should all of those objects be called planets?

mindrobots

How about

"Pluto, the celestial body formerly know as a planet"  - use its symbol instead:








It kind of worked for Prince......

Peter Jakacki

Prince who? AFAIK it's AFKAP

Love that symbol, how do you pronounce it?

koehler

There are a few problems with calling Pluto a planet.  If Pluto is reinstated as a planet we would need to add Eris as a planet as well.  Eris is about the same size as Pluto, but has more mass than Pluto.  There are also 7 moons in the solar system that are larger than Pluto.  Should they be called planets also?  Pluto and Eris orbit around the sun in the region known as the Kuiper Belt, where there are many large celestial objects.  Should all of those objects be called planets?

Dave,
 
   Pluto is larger than Eris, however less massive.
As the 7 moons, are, moons, then that sort of disqualifies them as being planets also.
There are probably going to be larger bodies than either Pluto or Eris found, true.

However, since it was a planet for almost a century, they probably could have resolved it as easily by say it was the last 'planet' in the Solar System, and a dwarf Planet at that.

Of course, it would be funny if there were to be found a real planet-sized body further out......

Viva Pluto!

LoopyByteloose

For horoscopes, one can always revert to the ancient astrological scheme where Saturn was the last planet in the solar system -- no Uranus, no Neptune, and no Pluto. In my case, the alternative horoscope interpretation is rather disappointing and a bit less interesting.  So I am stuck hoping that Pluto will someday cause me a change in fortune.

I was watching TV last night about the Apollo 8 mission and someone referred to Earth's moon as a planet.  Seems to me that it is all very unclear what should be a planet or not.  Even NASA has different opinions.

localroger

On the bit rate -- microwaves are used so that a relatively modest dish on the probe can focus a tight beam back to Earth.  The higher the frequency, the tighter the focus can be for a given dish.

The low bit rate is due to the signal strength.  There is no relay; all comms are directly from New Horizons to one of the 70 meter dishes, which are the only dishes sensitive enough to receive from NH.  The weaker the signal, the longer it takes to establish that a bit is 1 or 0 and thus the lower the transmission rate.

They sometime get to 2 kbps because there are two transmitters.  However, at current RTG power output levels the two transmitters can only be used at the same time if the science instruments are powered off and the craft is spin stabilized.  So there is a bit of a juggling act between doing science, doing comms while being ready for science or navigation maneuvers, and focusing on the best transmission rate back to Earth.