
Why it takes so long to get data back from New Horizons - sohkamyung
http://www.planetary.org/blogs/emily-lakdawalla/2015/01300800-talking-to-pluto-is-hard.html
======
mutagen
>The Deep Space Network has only three 70-meter dishes, and there is a lot of
competition for time on them;

It seems like I've heard this time and again, that certain data or
measurements couldn't be returned from planetary spacecraft because of
limitations in the DSN. I'd guess that a relatively modest investment could
double or tripe the DSN availability and bandwidth simply through more
antennas and the associated receivers. I'm guessing that the reasons are
political (funding), are there technical issues I'm unaware of?

Off to read up on this.

edit: They are adding antennas!

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rjaco31
Maybe it's just that building a 70-meter dish is freaking expensive?

~~~
DanBC
There are plenty of very rich people who could spend money on 70 m dishes
instead of soccer clubs or whatnot.

Adding 8 antennas and infrastructure to the VLA cost about $140m
[http://www.nrao.edu/pr/2000/evla/](http://www.nrao.edu/pr/2000/evla/)

The Green Bank telescope (largest moving land object; 100 meter dish) costs a
measly $10m per year to run. (That funding is at risk)
[http://en.wikipedia.org/wiki/Green_Bank_Telescope](http://en.wikipedia.org/wiki/Green_Bank_Telescope)

~~~
arethuza
If Roman Abramovich (or anyone else) wants to sink vast amounts of money into
football clubs that's their call.

For me a better comparison would be that $140m is slightly less than the unit
cost of an F-35B.

~~~
fapjacks
This is absolutely the best comparison. You've really gotta wonder what the
under-the-table purpose of that fighter is. As if our closer allies get told
"Hey, the ante for participating in PRISM et al is buying 26 of these totally
useless fighters that burn up on the runway." I am going to be totally
interested in whatever gets declassified about this program in the future.

~~~
lambdadmitry
Why does it need to be under-the-table? It seems pretty clear to me:

— military industry wanting more money

— deterrence

— air superiority

— hi-tech jobs, research and manufacture capabilities

Probably even in this priority order. The bottom line is that there is a lot
of good in this "useless fighters", even if it's not as sexy/obvious as DSN.
There may be a corruption element, but it doesn't mean that the program is
"useless" for general public.

After all, I'm writing this to you using the heir of DARPA's "stupid
entanglement of number-crunching machines".

~~~
fapjacks
> deterrence, air superiority

You're implying these things can actually get off the ground. For what
American taxpayers are spending on this project, you better believe there
better be some bang for that buck. And so far it's amounted to essentially
nothing but more of the same companies getting away with pillage.

~~~
lambdadmitry
According to Red Flag results, F22s are _extremely_ effective (e.g. [1]). In
fact, even if you take an article that "criticize" F22 (like [2]) and pay an
attention to what article really says, it's like "okay-okay, it's the best,
BUT YOU KNOW IT CAN SUCK SOMETIMES".

I understand the appeal of blaming govt on excessive spending. Being Russian,
I can't agree more (our govt is _way_ worse). However, I believe that blind
and self-righteous critique like "it can't get off the ground" is destructive.

[1]: [http://manglermuldoon.blogspot.ru/2012/09/red-
flag-2012-did-...](http://manglermuldoon.blogspot.ru/2012/09/red-
flag-2012-did-raptor-seriously-just.html)

[2]: [http://www.businessinsider.com/f-22-wont-win-a-dogfight-
thru...](http://www.businessinsider.com/f-22-wont-win-a-dogfight-thrust-
vectoring-raptor-typhoon-eurofighter-2013-2)

~~~
Roboprog
F22 - good; F35 - bad.

~~~
fapjacks
Precisely.

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abalone
I just love the image of a spaceship hacked to do cartwheels in space while
shunting power to its backup antenna to double the Tx rate. And that this was
developed after it was already in space.

After this and watching Apollo 13 I now have the impression "hacking" is
fundamental to space exploration.

~~~
lelandbatey
You should read the book "The Martian" by Andy Weir if you haven't already.
Doing things in space can require a lot of hacking!

~~~
car
Awesome book. And now this:
[http://www.imdb.com/title/tt3659388](http://www.imdb.com/title/tt3659388).

~~~
paulornothing
I like the cast, I hope it stays fairly true to the book.

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frik
What about the Arecibo Observatory? It has a 1,000 ft (300 m) diameter dish.
It is well know from the James Bond Golden Eye (1995) movie:
[http://en.wikipedia.org/wiki/Arecibo_Observatory](http://en.wikipedia.org/wiki/Arecibo_Observatory)
.

Are there physical limitations that would prevent a communication to Pluto?

The Parkes Observatory has _only_ a 230 ft (70 m) dish.
[http://en.wikipedia.org/wiki/Parkes_Observatory](http://en.wikipedia.org/wiki/Parkes_Observatory)
. It is well known from the first Apollo moon landing and The Dish (2000)
movie
[http://www.imdb.com/title/tt0205873/](http://www.imdb.com/title/tt0205873/)

~~~
rimantas
How long do you think communication session using Arecibo would last?

Edit: apparently some did not get the point I was making. Arecibo's dish is
fixed, so there is practically no way to track the object. And earth is
rotating. If you had a chance to see the stars through telescope, it rotates
FAST. With Arecibo you can only catch a blip of communication.

~~~
pp19dd
Suppose like you say, all earth-bound telescopes have a small window of
observation. How many hours a day would that be? Aside from watching Contact
or Goldeneye, my only source of knowledge about dishes is a C-band. But,
according to its wikipedia entry, Arecibo has a 40 degree range of 'motion'.

"To aim the device, the receiver is moved [by cables] to intercept signals
reflected from different directions by the spherical dish surface." ... "A
parabolic mirror would have varying astigmatism when the receiver is off the
focal point, but the error of a spherical mirror is the same in every
direction."

The limit: "This allows the Telescope to observe any region of the sky in a
forty-degree cone of visibility about the local zenith (between −1 and 38
degrees of declination)".

From universe today, "Pluto’s orbit is also highly inclined. This means that
it doesn’t orbit within the same plane as the rest of the Solar System.
Instead, Pluto orbits at an angle of 17-degrees."

Arecibo is at latitude 18.3 or so. Not at the equator, but for half a year
it's probably tilted more favorably to the middle. Does this make Arecibo even
remotely practical for the application?

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jobigoud
Argh, the idea that an autonomous spacecraft gather more interesting data than
it can possibly transmit back to Earth.

I wonder if they considered lossless _video_ compression approaches, and
combining an entire set of images into a single file.

~~~
hobbes78
Video compression (even lossless) leverages the fact that successive frames
are very similar; that's not the case here, as photos can be taken hours
apart, in various directions, and in various zoom levels. So you'll get
basically the same compression either way...

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EarthLaunch
> But how can you point stably at Earth with your guidance system shut down?

Why doesn't it stay pointed at Earth - is there something destabilizing it?
Solar wind, dust, power source, minutely inexact stabilization?

~~~
NamTaf
Any little destablisation will cause it to start to move, because there's
nothing to react it. By spinning something around its axis of maximum or
minimum moment of inertia, you stablise it - like a bullet being rifled.

The destablisation will come from any number of things - minor gravitational
inconsistencies, solar wind, dust, heat radiation from the power source, etc.

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bmaeser
"between here and pluto there is a very large number of nanoseconds"

[https://www.youtube.com/watch?v=JEpsKnWZrJ8](https://www.youtube.com/watch?v=JEpsKnWZrJ8)

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raverbashing
Funny how it's as slow as the first modems

Of course, the channel adds a lot of noise and attenuation

(I'm not sure the rate they mention is the effective ratio or before Error
Correction Codes)

~~~
kabdib
110 or 300 baud were the "first" modems. My first 1200 baud modem just
_screamed_. In comparison, of course.

An effective 2000 bits/second from Pluto is the stuff of science fiction.
(Actually, even SF from the 50s was full of situations like being out of radio
contact with Earth because of distances on the order of an AU or so. With
available technology they were probably right).

~~~
mchouza
It's mostly a question of power. The 1987 design for the TAU probe
communication system would have handled 20 kb/s from 1000 AU... by using
between 100 and 260 watts for the transmitter (and relatively big antennas):

[http://ipnpr.jpl.nasa.gov/progress_report/42-89/89L.PDF](http://ipnpr.jpl.nasa.gov/progress_report/42-89/89L.PDF)

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geuis
Very interesting overall. I like this small factoid, "They can be made even
smaller with lossy JPEG compression, but for optical navigation, precision
counts; the pictures have to be returned losslessly." I think this implies
that the most distant JPEG software is currently in route to Pluto.

~~~
mturmon
Use of lossy compression for science imagery is contentious. Because it's hard
to characterize how the compression will affect as-yet-unseen science targets,
it's hard to get scientists to accept lossy compression.

You _can_ sometimes get acceptance of prioritized downlink -- let automation
decide what is most interesting, and downlink that first. Variations on that
idea have been used for Mars rovers.

~~~
simonh
I once visited a crackpot aliens-on-the-moon conspiracy website. They were
showing zoomed-in images of lunar craters purporting to show regular,
artificial-looking features indicating alien activity.

Of course in context I'm sure you can guess what was going on. The images were
heavily compressed jpegs and I soon realised the 'regular features' were
compression artifacts.

Still, it goes to show why some scientists don't like lossy compression. When
you're looking at fine detail it's hard to be sure whether what you're seeing
is 'real' or not.

~~~
kzrdude
So we found a test to separate scientists from crackpots. Just ask what they
think about JPEG!

~~~
sp332
[https://xkcd.com/331/](https://xkcd.com/331/)

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jetskindo
All of the sudden I have no problem waiting for my town hall to finish
upgrading in 2 weeks in clash of clans.

Looks like some people use that same 2 weeks time to do far more important
things.

