back to article Cassini probe's death dive to send data at just 27 kilobits per second

Space is nasty and sending data across 83 light-minutes of it isn't easy, so the Cassini probe's death dive into the clouds of Saturn will be an instruments-only affair undocumented by photographs. Cassini has surveyed Saturn since 2004 but is out of fuel, so will be crashed into Saturn instead of leaving it an an orbit that …

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Good bye, Cassini

You served well, thank you for all the science and nice pictures!

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Re: Good bye, Cassini

Dear Mr Musk, if you have a spare 100 million or so a mission to Saturn would put you in the big boys club of spacefaring AND return useful science.

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"Space is nasty and sending data across 83 light-minutes of it isn't easy"

Cassini has been sending data at a good speed across 83 light-minutes of space for years.

The distance and the space has not changed.

The fact that is now descending into Saturn's atmosphere has changed.

THAT is the problem for data speeds.

NOT 83 light-minutes of space.

Can't The Register find some science writers to write science ?

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Distance... @BahBoh

Whilst I totally agree with your comment that the distance has not (drastically) changed (in the short-term) (my bracketed additions), the fact that Saturn and Earth are in different orbits, with different orbital periods, means that the distance between Earth and Saturn is constantly changing.

It reaches a maximum when Earth and Saturn are on opposite sides of the sun, and a minimum when they are on the same side.

Currently, I think that the Earth is drawing ahead of Saturn, so the distance will be increasing for the near future.

But you know this...

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Re: "Space is nasty and sending data across 83 light-minutes of it isn't easy"

The data rate is dependent on bandwidth and Cassini TX power (so SNR at Earth) both of which are ultimately ruled by power budget. I would expect telemetry data rates to be consistent throughout the mission. https://descanso.jpl.nasa.gov/DPSummary/Descanso3--Cassini2.pdf suggests a mere 10W to cover 900 million miles. Current technology would offer little improvement in power efficiency or data rates.

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Re: Distance... @BahBoh

The Earth-Saturn distance doesn't change that much. Even allowing for the eccentricity of Saturn's orbit, the range is around 8 AU (opposition when Saturn is at perihelion) to 11 AU (conjunction when Saturn is at aphelion). Given that signal strength varies as the inverse square of the distance, the signal is roughly half as strong at 11 AU than it is at 8 AU. That's not a huge dynamic range, really.

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Happy

Re: "Space is nasty and sending data across 83 light-minutes of it isn't easy"

@Bahboh - "Can't The Register find some science writers to write science ?" It did, the science fiction variety :-)

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Anonymous Coward

Re: "Space is nasty and sending data across 83 light-minutes of it isn't easy"

Am not entirely sure you know the logistics of aiming data towards a small cluster of pixels

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Re: "Space is nasty and sending data across 83 light-minutes of it isn't easy"

I think it's a bit more than what you posted. There's the issue with the high-gain antenna not pointed at earth during the final descent.

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Paris Hilton

Time is an illusion

"at 03:32Pacific Daylight Time. That data will land on Earth at 04:55 PDT"

Or, for those of us who aren't on the west coast of the mainland US... it'll be at lunchtime.

(surely sciencey articles should use something standard like UTC though, rather than some arbitrary offset that the rest of the world has to look up. Failing that, swatch internet time would do)

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Boffin

Re: Time is an illusion

Agreed, anyone with an interest can convert from UTC to their preferred timezone (of course it's super easy for us Brits for half the year). It would be great if elReg standardised on one timezone for all articles, particularly science ones, and UTC is the obvious choice.

(I can see an argument for using local time for some stories, it makes a difference if someone is going into their office at 3am or 3pm, but it doesn't make much difference to Cassini)

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Re: Time is an illusion

Or, for those of us who aren't on the west coast of the mainland US... it'll be at lunchtime.

Or after my first morning meeting, for other time zones. I'll have time to get back to my desk and misuse some employer bandwidth watching the show.

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Happy

Re: Time is an illusion

surely sciencey articles should use something standard like UTC though

Yes, they could and I also think they should, yet, I consider us lucky as it could be worse, they could use POSIX time zones ... for Mr POSIX, PDT is +7, yes, you read that right ...

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Pint

Re: Time is an illusion

I have to disagree with the use of common everyday standards.

ElReg defines the standards, just as it defines the newsworthy news, therefore I propose Beer o'clock as the universal standard.

It can be easily calculated as the time the writer thinks you should have a beer - anything interesting will be beerworthy and naturally occur at beer o'clock.

Converting between beer o'clock and local time is left as an exercise for the reader, just as it is with your fancy "scientific" measures of time...

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Re: Time is an illusion

"swatch internet time would do"

Many thanks for the SIT reference, which I didn't realize was still a thing, not heard it mentioned for about 6901000 Beats.....

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Re: Time is an illusion

The problem there is that you've invented a binary time system - it's either beer o'clock or it's not... Great for beer, not so good for planning beer related meet ups?

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Re: Time is an illusion

Agreed, anyone with an interest can convert from UTC to their preferred timezone (of course it's super easy for us Brits for half the year). It would be great if elReg standardised on one timezone for all articles, particularly science ones, and UTC is the obvious choice.

I'd say UTC-2 the obvious choice, with UTC+10.5 being second, UTC-12 being third.

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Re: Time is an illusion

Probably should be Australian Eastern Standard Time (AEST), as I understand the signal is primarily being received in Canberra?

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Anonymous Coward

Re: Time is an illusion

When beer o'clock becomes a binary time system, you may have a problem...

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Unhappy

Actually the problem is there is no data relay that could hoover it up and play it back slowly

Since sending any payload to Saturn is even tougher than Jupiter the idea of "wasting" payload on an infrastructure package horrifies the scientists who drive the design process.

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Re: Actually the problem is there is no data relay that could hoover it up and play it back slowly

An infrastructure package would have the same problem Cassini does, yet with far fewer instruments. Most of the mass is the bus.

There are so many moons that it has to spend a lot of fuel on station keeping. So it runs out in a scant few years, and then has to be crashed to avoid contaminating results from future missions.

Cassini itself was the infrastructure package for Huygens.

If there was a budget, we could have sent another probe before Cassini's demise to act as it's repeater - and then do More Science.

But there isn't. There's barely budget to keep listening.

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Pint

Farewell to a great probe!

This mission has brought so many awesome images, and many, many other results. I remember being spellbound by the footage of the descent of the Huygens probe on Titan. Big thumbs up to all involved in making this possible. I will be raising a glass in memory of a great mission when Cassini has performed his death dive

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"I will be raising a glass in memory of a great mission when Cassini has performed his death dive"

I'll be looking for the nearby Disaster Area concert.

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"I'll be looking for the nearby Disaster Area concert."

You really want to be in the next solar system over for the best experience.

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Pint

send data at *just* 27 kilobits per second

It's not that long since I would have been delighted if my USRobotics modem would be running at that speed from my house to the local ISP.

To be doing that from Saturn, with kit that has been up there for so long, is still a remarkable achievement.

All involved deserve a well earned beer!

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Anonymous Coward

Re: send data at *just* 27 kilobits per second

27 kb/s ... my parents-in-law used to have(*) an ADSL "broadband" connection that was only 10x faster than that!

(*) this was last Christmas! Think since then they;ve been able to switch to a new BT connection that comes from boxes in the village and isn't dependent of several kms of dodgy copper to an exchange in the nearest town!

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Re: send data at *just* 27 kilobits per second

Cassini was launched in 1997.

That's about went it was the kind of bandwidth I was getting from a modem transmitting along a wire.

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Re: send data at *just* 27 kilobits per second

Still somewhat faster than the standard Commodore 64 datasette speed, which was a mighty 300 bits per second!

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Black Helicopters

Nonsense!

They've disabled the cameras because the lock-on alert's finally gone off and they don't want us to see McDonald's factory floor before it's shot down. Once you get under the cloud cover you'll release that the Rings of Saturn are actually an ad; they just haven't finished breaking them apart.

You'll see -- they'll still be releasing pictures way after the satellite has =supposedly= gone down.

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Anonymous Coward

unless we really live on a flat earth, in which case the Dome prevents exploration. All that money was spent on creating a lie.

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Anonymous Coward

24kbps

Yeah, but all I want to know is do Houston get to listen to the dial-up handshake sounds on loudspeaker ?

;-)

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Re: 24kbps

A very distinctive sound! I get a little thrill when I hear it in a movie or commercial. Conversely, I'm glad I don't have to hear it from my computer anymore.

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Alien

"It'll have to go"

As Cassini dives through the clouds I wonder if the local inhabitants will look up to see this intruder and once they find out where it came from will they turn to singing "a number of tuneful and reflective songs on the subjects of peace, justice, morality, culture, sport, family life, and the obliteration of all other life forms."

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Happy

Just guessing but

I would assume pics are taken at a normal high speed but the data is buffered and later sent by the speed possible. In this case, as the time is up, there will be nothing to send with.The fat lady died singing.

Those guys know what they are doing, nice work.

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Re: Just guessing but

The main "camera" is just a line of pixels. It's rather interesting how it "exposes" by rotating/orbiting the target.

The post-processing required to turn this into an image is perhaps worthy of an article by itself.

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Pity. It would have been... Glorious!

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"Pity. It would have been... Glorious!"

indeed. And Commander Kor did know a thing or two about what is and isn't glorius.

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Childcatcher

Filth!

I remember when downloading pr0n at 27 kilobits per second would make my friend's day.

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Boffin

Spooky

It would be too weird if the final message received was 'Will I dream?"

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Someone check Cassini's glovebox. I think there is a can of liquid schwartz in there. I knew we should have put more than a few bucks in for fuel.

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May The Schwartz Be With You!

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Bye and thanks for all the Science

I remember even before Cassini was launched, watching Heather Couper on The Sky at Night and how excited she was about the mission, every episode she appeared in she would explain about the many things expected of Cassini. It seems that excitement was not misplaced, Cassini has done all that was promised and set the scene for so much more that we need answers to. Another explorative mission that has done so well .

Definitely Beer o Clock for the team, Congratulations!

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Too bad

If it left a cubesat type device behind it could transit images and tons more data which the cubesat could collect and store, then transmit over a period of weeks or months.

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Unhappy

""If it left a cubesat type device behind it could transit images and tons more data"

True, but cube sats had not been thought of when it was launched.

This is the problem with these once-a-career launch opportunities.

They are so rare that no one wants to "waste" a gram on a relay package that would only pay off at the end of the mission, or serve a follow on mission that may not be even planned for another decade.

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"set up to send data at just 27 kilobits per second"

Wow! That's massive speed! I had no idea space tech had progressed this far!

I didn't have more in 1994 here on earth..

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Anonymous Coward

1999 called

They want their dialup back!

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