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Comment by dogma1138 | Hacker News Reader

The final command for this part of the mission as no further communications would be possible until the flyby has been complete and the probe can reorient itself to call back home, it would take 18 months to get the data back from New Horizons as its current data rate is 1kbp/s or 2 with induced spin.

This isn’t the end of the mission for NH.

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I’m currently reading this book about the history of the DSN.

https://www.amazon.com/Uplink-Downlink-History-Space-Network...

Fascinating stuff. I wonder how they will manage the priority of getting that data back over the next two years? Timeshareing on the DSN has been a problem since the early 60’s.

I’m not sure they can even get all of the data back.

The probe has limited data storage capacity and even more limited bandwidth to send it back to earth.

I’m guessing they have a protocol to prioritize data from different instruments as well as prioritize data purging if there is an opportunity to look at something more interesting before everything could be sent back home.

It can be a heartbreaking process for some of the teams for sure.

My best bet is that they get some initial indication of what data was collected then prioritize based on what they think is the most interesting or valuable from what was collected.

They were still retrieving data form the original Pluto flyby as this one was planned I’m not sure if they even got all the data from pluto yet.

> purging if there is an opportunity to look at something more interesting before everything could be sent back home.

This is not a risk as, with high probability, there is nothing else on their trajectory they will be able to look at for the 18-month downlink time.

> I’m not sure if they even got all the data from pluto yet.

They did. It's true that they have limited data storage space, but they have had plenty of time to download the entire data set from Pluto.

https://futurism.com/it-took-15-months-but-all-of-new-horizo...

I believe the major constraint is how much data they can take during the short flyby time, not storage space or downlink time.

Well it sorta both yes the flybys at this point are so short that the amount of data they collect is limited but they still collect GB’s of data and the up line data rate will likely drop even further as the probe goes further.

It’s still astonishing to me that they can get 1kbp/s with s 1.5m dish antenna pointed at a target 0.29281 arc minutes in size.

This is the equivalent of pissing into your toilet form orbit.

But heck now the FCC can claim that broadband coverage has been expanded up to the Kuiper Belt.

Even if they cannot get all the data back, I suppose they could do a preliminary analysis onboard and decide what to send back.

It is, in a very broad sense, the same problem we have at the LHC. There is just too much data taken for the available storage and bandwidth.

Re: I'm guessing they have a protocol to prioritize data from different instruments as well as prioritize data purging if there is an opportunity to look at something more interesting before everything could be sent back home.

I suspect if a new nearby target were discovered, they may have to send back just thumbnails and summarized/compressed data, review the summaries back on Earth, and only request the more promising full images and data snippets.

I just hope they already have such compression/summarizing software onboard because sending significant new software that far can be a bear. I wonder if they planned for such a "rush job" scenario?

It’s main CPU is a 12mhz MIPS processor I don’t think they do any complex software analysis on board.

Summarizing doesn't necessarily require complex algorithms. For example, a 64x64 pixel image can be averaged into a 16x16 image, and/or a highly compressed JPEG. And data streams can maybe average 1-second intervals into 30-second intervals. You can get a little fancier by only averaging intervals that don't vary much, using standard statistical algorithms (including "cheap" approximations to save CPU). A lot of times cameras and instruments will be pointing at empty space because they error on the side of capturing unknown petributions/objects. If you are not looking for faint moons etc., you can mostly ignore those "dark areas", at least in a "data emergency".

And remember, the summarized versions are used to narrow down the set of full data sets returned. Thus, if something looks unusual in the summaries, the full set of that segment is requested from the probe. If there is a need to rush, it's a matter of narrowing down which parts of the data you want to send back in full.

The instruments are turned off until they are needed they cannot be used when the space craft is spinning which is required for it to transmit data to earth which is what it does most of the time the flyby lasts minutes at the most, the data takes over a year to transmit.

Also even if it didn’t need to be spun the instruments would be turned off to save power, the probe has no instruments that could detect any objects without a preplanned flyby.

I don't see how this is related to the above. It seems there's context confusion. I meant data processing (summarizing) of existing STORED data so that humans can review and decide on what to keep (fully download) and what to discard/delete so that there's enough storage for an upcoming new target.

After passing a target, there's boatloads of data to send back. If a new target means there's not enough time to download it ALL before storage is needed for the new target, then decisions have to be made about what to fully send back and what to skip and/or only send summarized/compressed versions of. This has very little to do with instrument activation; it's a "between targets" process.

>This isn’t the end of the mission for NH.

At ~1:30 in the video interview with Alan Stern he says they have ~20 years of power in the RTG and 'plenty of fuel' to get around. Sounds like there could be a lot of science yet to come!!

Sounds like there could be a lot of science yet to come!!

From Wiki: at Pluto's distance, a rate of approximately 1 kbit/s per transmitter is expected. Besides the low data rate, Pluto's distance also causes a latency of about 4.5 hours (one-way).

Scientists have a lot more patience than I do!

In a lot of ways, science and patience are the same thing.

Not in all ways. But a lot of them.

I wonder if they watch their planet porn arrive one scan line at a time.

There's a lovely photo of scientists manually painting the scan lines coming in from Mariner 4, like a paint by numbers picture

https://www.nasa.gov/multimedia/imagegallery/image_feature_1...

I can tell you stories about the days of 300 baud dial-up modems.

And 110 baud before that (Model 33 Teletype).

When 256 colors was good enough...

For high res displays. The rest of us got by on 16 colors.

The Hubble scope had to spend many hours to find this target, basically taking "before" and "after" images to find changes: dots moving against the background stars seen via subtracting the pixels values of before and after. Once they find rough candidates, they take more pics to narrow down their orbits. Any new targets will be further away and thus probably dimmer to Hubble than Thule. Also, New Horizons only has so much fuel to change direction. Its room to operate is a very narrow cone, kind of like a long lopsided straw. It will be challenging finding new objects to visit. I wish they didn't have to depend on Hubble so much.

Interestingly, we'll solve this problem just about when it won't matter anymore for New Horizons. In the 2020s the Large Synoptic Survey Telescope will come online, which will (among other things) catalog tens of thousands of KBOs/TNOs.

Isn't TESS kind of built to do the same thing? Wide field analysis? Presumably it's looking for dimming rather than relative motion, but that seems more like a software issue than a hardware one?

Not exactly. TESS monitors bright objects. It uses actually quite small telescopes (only 10cm aperture or so), but the it has 4 such telescopes and uses very wide fields of view to monitor a large number of stars continuously. To see KBOs/TNOs requires more light gathering power.

Ah! OK, makes sense. Thank you!

Time to send a telescope into distant orbit?

Considering the size of the Kuiper belt it wouldn’t make much difference if you observe if form earth orbit or from within an orbit in the belt.

There would be no reason to do that. Putting telescope into distant orbit will not make it easier to observe anything except for the thing you are orbiting.

The problem with kuiper belt objects is not that they are far away but that there is not much light reflected from them. The belt is huge, and if you put say Hubble in there you have no guarantee you would see anything.

Putting space observatory is costly project, money are better spent by putting it in Earth orbit as it is much cheaper to put it there and possible to service while in orbit. If history teaches us anything it is that being able to service the telescope in orbit is very important for getting as much bang for the buck as possible.

Re: There would be no reason to do that.

In general, probably; BUT I'd qualify that to say it depends on the mission. As I mentioned nearby, visiting the bigger known Kuiper objects seems a bigger priority than finding new smaller ones (and finding them is better done near Earth).

However, if something unusual were found at Thule such that a mission to study lots of smaller Kuiper objects were deemed warranted (like being made of gold or clear signs of life), then a probe with a relatively big telescope could be sent into the Kuiper Belt to hunt such objects in its approximate vicinity. That may still be cheaper than building larger-than-Hubble scopes near Earth to guide New-Horizons-like probes. But the math on that may depend how sparse smaller Kuiper objects are.

That probe would be worse than a Hubble like telescope at an earth or near SOL orbit.

Firstly due to their relative small size their angular size wouldn’t make much difference at those distances.

Secondly you essentially limiting your search envelope to a small section of the belt as most of it would be further away form the telescope in the belt than from earth.

And lastly you can launch a much bigger telescope to a near earth orbit than to the belt and you can also get the data much more rapidly so you can actually search for candidates in hours not in months and readjust the telescope as you see fit.

Is there any reason to think of an array of telescopes, like the VLA? Like, multiple smaller telescopes scattered at large distances? Or is that too difficult to coordinate?

This has a lot of sense and shouldn't be too difficult to coordinate. This has already been tested by LISA Pathfinder (https://en.wikipedia.org/wiki/LISA_Pathfinder) and proven to be feasible. Still, the reson here to get something far away from Earth as a general is not to have closer observation point but to have large distance between array nodes.

You mean send a Telescope to the Kuiper Belt? I believe resources would be better spent sending a probe to one or few of the bigger Kuiper Belt objects, such as Eris and Sedna. New Horizon's "target problem" is rather specific to that probe. Pluto was its primary mission. Other bodies were considered a bonus, and the probe doesn't have enough fuel to target the bigger (known) objects. Perhaps that was a mistake; but many of these were discovered after the probe was budgeted.

Their biggest problem atm isn’t time but speed, they have fuel but they can only do limited course correction as they don’t have that much specific impulse available to them.

So they need to find interesting things on their way bwfore they fly off.

“Plenty of fuel” is a PR spin. They have enough fuel for an additional flyby, but it has to be an object that is pretty much along their path anyway, or far enough out that a little tiny nudge will correct their course over a good portion of that 20 years. Hopefully such an object will be discovered once they start looking.

Is that the effective payload data rate after error correction has been applied or the actual transmitted bit rate meaning that the payload rate is much less? I've read that NH uses a 1/6 Turbo code for forward error correction. If true, that would imply that the transmitted data rate is actually 5 to 10 kbps or the payload rate (after e.c.) is 200-400 bps.

That’s the data rate afaik

http://pluto.jhuapl.edu/Mission/Spacecraft/Data-Collection.p...

https://en.m.wikipedia.org/wiki/New_Horizons#Telecommunicati...

Pluto encounter data rate was 2000 bp/s but that is with the spin, I’m guessing it’s lower now since it’s well past Pluto.

I can’t find the link to the interview which had a bit more information about it now, but I don’t think they refer to the payload data rate.

New Horizons can't use many of its scientific instruments and cameras in spin mode. Spin mode gyroscopically stabilizes it so that its main antenna can be pointed more precisely, allowing a higher data rate. Thus, I suspect they won't want to enter spin mode until it's no longer doing any photographic or scientific observations of Thule. Therefore, data packets will be slow in the days before and after encounter because they want to still aim instruments; but this makes antenna pointing less precise. New Horizons can't chew gum and talk at the same time :-)

Again they won’t plan missions in this manner, in the rare event that they’ll need to override data they’ll have a clear protocol sending a summary in this case would be a waste of bandwidth.

Both your statements are not clear to me. There still seems to be some unstated assumption that is confusing one or both of us.

Thanks for clarifying that. The velocity of this probe is really astounding!

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