News for hackers. Stuff that matters.

A comment on Why it takes so long to get data back from New Horizons.

Re:Why it takes so long to get data back from New Horizons by mrb on Sunday July 19, 2015 @03:06AM (#9910291)
I dislike that the article doesn't even clearly answer its own question. The probe only records 8GB of data to one of two 8GB memory bank (one primary, one backup). Then the data is compressed and sent at either 2 kbit/s or 4 kbit/s (if they manage to get the higher speed working). By this math it should take either 12 or 6 months. Actually even less since the data is compressed. So why will it take 16 months?? Gizmodo needs better writers.
[ Parent | on HN ]
Re:Why it takes so long to get data back from New Horizons by rootbear on Sunday July 19, 2015 @09:28AM (#9911120)
The downlink is actually 1kbps, with 2kbps optional, by using both amplifiers with opposite circular polarizations. But they can't use that trick all the time. A nice article with more technical details is at http://www.planetary.org/blogs/emily-lakdawalla/2015/0130080...
[ Parent | on HN ]
Re:Why it takes so long to get data back from New Horizons by dang on Sunday July 19, 2015 @01:54PM (#9912098)
Ok, since the consensus in the thread is that the submitted article (http://gizmodo.com/why-itll-take-new-horizons-16-months-to-s...) wasn't very good, let's try switching to that one.
[ Parent | on HN ]
Re:Why it takes so long to get data back from New Horizons by mikeash on Sunday July 19, 2015 @04:17PM (#9912669)
Great article. And for anyone who didn't see it, to call this mode "optional" is putting it extremely mildly: to get enough power to run both amplifiers at once, they have to shut down the spacecraft's guidance system (!) and keep it pointed at Earth by using the thrusters to spin it up like a top. And this whole crazy scheme was developed after launch.
[ Parent | on HN ]
Re:Why it takes so long to get data back from New Horizons by aleph_naught on Sunday July 19, 2015 @03:34AM (#9910353)
the DSN (deep space network) is a shared resource under high contention---it is effectively used by every deep space mission from Voyager to MSL(via MRO relay). missions generally have a dsn rep that negotiates dsn tracks based on need. high priority events like MSL's EDL or spacecraft safing events generally take priority. i haven't looked into the specifics but it is unlikely that new horizons gets 24hr coverage for 12 months straight.
[ Parent | on HN ]
Re:Why it takes so long to get data back from New Horizons by waterlesscloud on Sunday July 19, 2015 @02:37PM (#9912290)
You can see what DSN is up to right now here- http://eyes.nasa.gov/dsn/dsn.html
[ Parent | on HN ]
Re:Why it takes so long to get data back from New Horizons by logicallee on Sunday July 19, 2015 @04:32AM (#9910475)
this totally makes sense - you should work for comcast!
[ Parent | on HN ]
Re:Why it takes so long to get data back from New Horizons by simoncion on Sunday July 19, 2015 @09:07AM (#9911070)
Given Comcast's reputation, it sounds like you're being insulting. Was this your intention?

If it was, you should actually read about the DSN. It (like most things pertaining to extraterrestrial operation) is pretty damn cool.

[ Parent | on HN ]
Re:Why it takes so long to get data back from New Horizons by jjtheblunt on Sunday July 19, 2015 @12:02PM (#9911601)
I thought not meant to be insulting but hopeful comcast would then improve.
[ Parent | on HN ]
Re:Why it takes so long to get data back from New Horizons by logicallee on Sunday July 19, 2015 @12:33PM (#9911692)
neither, it was just a joke :) I mean that this is a great way to explain 2 kbit/s or 4 kbit/s (makes sense in context) and I was just joking that that's about as bad as Comcast's service sometimes... :) (And so with explanations that great he should be their PR guy...)

I guess it didn't go over too well, but no worries! You miss 100% of shots you don't take...

[ Parent | on HN ]
Re:Why it takes so long to get data back from New Horizons by ArikBe on Sunday July 19, 2015 @09:15AM (#9911090)
In the press conference shortly after the flyby, one of the staff (I can't remember her name) said that the speed depends on the position of the probe relative to the ground antenna. So not only is transmission not 24 hrs, but when the probe appears to be on the horizon, transmission speeds are slower.
[ Parent | on HN ]
Re:Why it takes so long to get data back from New Horizons by hga on Sunday July 19, 2015 @11:07AM (#9911396)
Lately I've been checking out the real time reporting page for the DSN (http://eyes.nasa.gov/dsn/dsn.html), and frequently one of the three big dishes at Goldstone, Arizona, USA, Madrid, or Canberra is allocated to a satellite, but is not right then doing any communicating, presumably because it's waiting for the earth to turn enough to get line of sight.

Right now New Horizons is downloading at 2.11 kbs to Canberra, the max with both amplifiers transmitting with opposite circular polarizations. For a bit of comparison, Rosetta is talking to Goldstone right now at 104.86 kbs, with a received power 3 orders of magnitude stronger. And Voyager 2, which doesn't have much to say, is still plugging away with a smaller Canberra antenna at 159 b/s, and a received power about that of New Horizons.

[ Parent | on HN ]
Re:Why it takes so long to get data back from New Horizons by CamperBob2 on Sunday July 19, 2015 @03:21AM (#9910327)
One possibility might be DSN receiver availability. There are only three sites in the network, and they have several other missions to support.
[ Parent | on HN ]
Re:Why it takes so long to get data back from New Horizons by icw on Sunday July 19, 2015 @02:17PM (#9912199)
Forward error correction can add significant overhead. From the specification of the RF subsystem posted earlier (http://www.boulder.swri.edu/~tcase/NH%20RF%20Telecom%20Sys%2...), 5/6 of the data returned is redundant.
[ Parent | on HN ]
Re:Why it takes so long to get data back from New Horizons by maaku on Sunday July 19, 2015 @03:08AM (#9910297)
Because redundancy in transmission? Also I would be very surprised if the the data is not already compressed.
[ Parent | on HN ]
Re:Why it takes so long to get data back from New Horizons by mgkimsal on Sunday July 19, 2015 @01:03PM (#9911827)
isn't the fact that the transmitter is going further away during those 6 or 12 months adding to the time as well? or do the distances travelled not have much of an impact over that time frame?
[ Parent | on HN ]