It's awesome that they've been involving the public so much in the details of how the rover mission really works. I'd actually been wondering about this exact question, since it seems to be one of the limiting factors for the quality of images and such. From a physics standpoint, sending data is clearly a lot more complicated than I'd previously assumed.
> It's awesome that they've been involving the public so much in the details of how the rover mission really works.
It must be mission critical to spread awareness since their budget cuts are getting worse and one way to correct that is to get people excited about space exploration. They now put a considerable effort in PR, involving people in the mission, sharing most of the information and making professional videos. And i believe this is why we see twitter accounts of most astronomers, satellites, rovers and other NASA properties. The NASA's ustream has been very popular lately and they have presence on every major social network. And curiosity was named after an essay written by a student in a competition organised by NASA for school students.
In general, space travel is very risky. It's not like they can iterate. Pulling something off like landing on Mars is very impressive. Keeping this in mind, I feel it was actually quite risky that NASA streamed the landing live.
I think NASA should receive big kudos for taking that real risk.
So one wonders at what point you uplink to a satellite with ejectable flash drives which, when full, detach, make a gravity sling shot pass to leave orbit and then burn for a rendezvous with earth 9 months later. If I did the math right a 1TB drive returned from Mars in 9 months would be an effective bandwidth of 470K bits per second (or 47K bytes per second)
While we are dreaming, it would be better to have said flash drive picked up by a spacestation, refueled in orbit, and shot back to Mars.
Hmm. If storage continues to improve as fast as it has been, once the space infrastructure is there, this might be cost effective. We have a lot of data to send.
In particular, we are going to need to have a local cache of the internet on Mars. At best, the average minimum latency is 225 million kilometers / the speed of light = 12.51 minutes.
Vast data barges, roaming the solar system, keeping everyone in sync....
Building an interplanetary Internet is going to be very, very fun.
On a related note, never underestimate the bandwidth of a truck filled with...
Well I was going to say blueray disks. But the cheapest I can find bluray disks are 3 cents per gigabyte. 3 TB harddrives are easily had at 5 cents per gigabyte. If the data only needs to go 60 miles, then 120 drives ($18,000) in a truck would get 1 TB/sec, or 8,000 mbps...
Ouch. I'll go with a megabit connection. Once upon a time that sort of thing worked for bulk data ;)
Latency matters, too. Often all the data is necessary to make decisions so (for example) only immediately transmitting a limited subset of the data is not really an option.
It’s not like that rover is driving around autonomously. It has some autonomy, but it can’t decide what’s interesting and what’s not, what has to be investigated and what not.
Unfortunately, to do a gravitational slingshot, you need a body other than the one relative to which you want to accelerate. So you can use Mars to accelerate relative to the Sun, but not relative to Mars.
This means if you're already in Mars orbit you need fuel(TM) to escape. One might consider a slingshot around Deimos or Phobos but I don't think that'd be helpful enough to justify its cost (could be wrong, but I've never seen it suggested in any Mars->Earth mission plan).
I see one huge issue: if you lose the flash drive, you lose ALL of the data you collected. At least you a assured to get part of the data when it is broadcast.
Timeliness is quite important. In order to plan where to go and what to do next you need results from what you've just done. Without that you're just fumbling around blind.
So those are the lander->earth and lander->sat speeds. How fast can the satellites transmit to earth? If we somehow always had a sat in reach of the lander, how much data would we be able to send?
Apparently NASA had plans for launching an orbiter specifically as an optical communications hub for Mars but scrapped it in 2005:
"As of 2005, NASA has canceled plans to launch the Mars Telecommunications Orbiter in September 2009; it had the goal of supporting future missions to Mars and would have functioned as a possible first definitive Internet hub around another planetary body. It would use optical communications using laser beams for their lower ping rates than radiowaves."
I'm wondering how do they prevent non-NASA entities from sending commands to the rover - are they using some sort of cryptographic signatures when sending the commands?
I'm not sure about Curiosity in particular, but I work in the space industry and can say that commands are normally timestamped and encrypted. The encryption stops someone from commanding the spacecraft, the timestamp stops someone from recording a transmission and resending it later.
This kinda raises question. I for one would not use encryption just to maximize bandwith efficiency. Deep space program are no where close to being a tactical advantage over another country. I wouldn't see why someone would like to screw it up.
On the other side, there's always a moron out there to crash the party. So even if I wouldn't use encryption, I wouldn't be surprised if they use it.
I'm guessing there is a lot of data that never gets sent to earth. Do they send thumbnails of the images to determine what is interesting? Is there a software tool available that creates a thumbnail and then creates a copy of the original image that is dependent on the thumbnail to be recreated. If you can't tell I wasn't really sure how to word that last sentence. Basically, less data would be required to transmit because you are only sending the data required to reconstitute the real image. Depending on the size of the thumbnail this might result in a negligible difference.
For example, a very naive implementation might create a thumbnail from every pixel where x or y is odd and then when/if you want the original image you can get the data required to put the image back together (it would be a similar sized thumbnail but with the even pixels) For this naive approach the thumbnail would likely be much larger than you want and would not help at all :)
This may be a silly question, but I don't understand why the bandwidth is so low. I understand the latency will be high, since you're limited by the speed of light; but wouldn't you be able to get more bandwidth just by increasing the spectrum of light used, as well as the baud of the transmitter/receiver?
Very cool concept. Unfortunately, this only proxies the starting hostname and doesn't rewrite absolute URLs, so on most modern websites, image/CSS/JS resources (being served from subdomains or S3 etc.) will load unproxied and not get slowed down.
Does anyone know more about the architecture of this space radio network? For example does it use tcp/ip on top over radio or is it packet switched as with amateur packet radio?
Generally they use the CCSDS specifications, CCSDS is an international body with the space agencies of each major country contributing. Google for CCSDS, they have a bunch of open standards. Space networks really aren't quite at the level of fully mature, layered, multi-hop packetized networks... It's a Hard Problem.
Basically, TCP/IP doesn't scale to meet the constraints of deep-space networks (high latency, asymmetric data rates, intermittent connectivity). It just breaks down. That's why there's a lot of active research in DTN (delay/disruption tolerant networking and ad-hoc networking protocols). ION (Interplanetary Overlay Network) is the JPL implementation of the DTN protocols, and has been flown in a demonstration capacity on some extended-mission/end-of-life Deep Space missions. Much of it has been open sourced at this point.
Round-trip latency is the time it takes a signal to travel from Earth to Mars and back.
As Mars and Earth orbit around the sun, their distance relative to each other is constantly changing. The minimum distance from Earth to Mars is 35,000,000 miles, and the maximum is 249,375,000 miles.
Since light travels at 670,000,000 miles per hour in a vaccuum, we can calculate the minimum and maximum round-trip latency:
Minimum round-trip latency
= (2 * 35,000,000 miles) / (670,000,000 miles per hour)
= (0.167164 hours) * (60 hours per minute
= 10.0299 minutes
Maximum round-trip latency
= (2 * 249,375,000 miles) / (670,000,000 miles per hour)
= (0.744402 hours) * (60 hours per minute
= 44.6642 minutes
It varies. As others have said, it's currently just under 14 minutes.
But it can be as low as 3 minutes or as high as 21 minutes, depending on the distance from Earth to Mars. Which of course varies as they orbit the sun.
There must be some amateur radio people out there able to receive these signals, no? With the protocol stacks mentioned in the other comments, I wonder if they're able to extract the encrypted data. Which leads me to think there have got to be people/governments trying to figure those out.
I love this statement (from the Preventing Busy Signals page): "The Deep Space Network (DSN) communicates with nearly all spacecraft flying throughout our solar system."
[+] [-] ryusage|13 years ago|reply
[+] [-] Achshar|13 years ago|reply
It must be mission critical to spread awareness since their budget cuts are getting worse and one way to correct that is to get people excited about space exploration. They now put a considerable effort in PR, involving people in the mission, sharing most of the information and making professional videos. And i believe this is why we see twitter accounts of most astronomers, satellites, rovers and other NASA properties. The NASA's ustream has been very popular lately and they have presence on every major social network. And curiosity was named after an essay written by a student in a competition organised by NASA for school students.
[+] [-] keithpeter|13 years ago|reply
I'm impressed with the reception technology that allows 'direct to home' communication at all given the power levels available.
[+] [-] ericHosick|13 years ago|reply
I think NASA should receive big kudos for taking that real risk.
[+] [-] ChuckMcM|13 years ago|reply
[+] [-] eupharis|13 years ago|reply
Hmm. If storage continues to improve as fast as it has been, once the space infrastructure is there, this might be cost effective. We have a lot of data to send.
In particular, we are going to need to have a local cache of the internet on Mars. At best, the average minimum latency is 225 million kilometers / the speed of light = 12.51 minutes.
Vast data barges, roaming the solar system, keeping everyone in sync....
Building an interplanetary Internet is going to be very, very fun.
On a related note, never underestimate the bandwidth of a truck filled with...
Well I was going to say blueray disks. But the cheapest I can find bluray disks are 3 cents per gigabyte. 3 TB harddrives are easily had at 5 cents per gigabyte. If the data only needs to go 60 miles, then 120 drives ($18,000) in a truck would get 1 TB/sec, or 8,000 mbps...
Ouch. I'll go with a megabit connection. Once upon a time that sort of thing worked for bulk data ;)
[+] [-] arrrg|13 years ago|reply
It’s not like that rover is driving around autonomously. It has some autonomy, but it can’t decide what’s interesting and what’s not, what has to be investigated and what not.
[+] [-] DavidSJ|13 years ago|reply
This means if you're already in Mars orbit you need fuel(TM) to escape. One might consider a slingshot around Deimos or Phobos but I don't think that'd be helpful enough to justify its cost (could be wrong, but I've never seen it suggested in any Mars->Earth mission plan).
[+] [-] zandor|13 years ago|reply
http://en.wikipedia.org/wiki/Corona_(satellite)
[+] [-] kleim|13 years ago|reply
[+] [-] InclinedPlane|13 years ago|reply
[+] [-] eric-hu|13 years ago|reply
[+] [-] rodion_89|13 years ago|reply
(assuming 8-bit bytes)
[+] [-] Dylan16807|13 years ago|reply
Edit: Did the research. MRO's antenna can handle .5 to 4 megabits depending on the distance between planets. Wow, having to wait for flybys is a huge bottleneck. http://mars.jpl.nasa.gov/mro/mission/communications/commxban...
[+] [-] zhoutong|13 years ago|reply
[+] [-] rwhitman|13 years ago|reply
Apparently NASA had plans for launching an orbiter specifically as an optical communications hub for Mars but scrapped it in 2005:
"As of 2005, NASA has canceled plans to launch the Mars Telecommunications Orbiter in September 2009; it had the goal of supporting future missions to Mars and would have functioned as a possible first definitive Internet hub around another planetary body. It would use optical communications using laser beams for their lower ping rates than radiowaves."
[+] [-] jk4930|13 years ago|reply
(OT: Note the picture at the bottom, the astronaut is one of ours: Austrian Space Forum, a private space R&D org.)
[+] [-] vladd|13 years ago|reply
[+] [-] lavezza|13 years ago|reply
[+] [-] iwwr|13 years ago|reply
[+] [-] pothibo|13 years ago|reply
On the other side, there's always a moron out there to crash the party. So even if I wouldn't use encryption, I wouldn't be surprised if they use it.
[+] [-] bwr|13 years ago|reply
For example, a very naive implementation might create a thumbnail from every pixel where x or y is odd and then when/if you want the original image you can get the data required to put the image back together (it would be a similar sized thumbnail but with the even pixels) For this naive approach the thumbnail would likely be much larger than you want and would not help at all :)
[+] [-] nemilar|13 years ago|reply
[+] [-] accountoftheday|13 years ago|reply
[+] [-] DanBC|13 years ago|reply
(http://www.dallaway.com/sloppy/)
[+] [-] graue|13 years ago|reply
[+] [-] ck2|13 years ago|reply
The orbiter can talk to earth at up to 6Mbps depending on how far away we are at that time.
6Mbps at that distance is a staggering feat of engineering.
[+] [-] fsiefken|13 years ago|reply
[+] [-] vbtemp|13 years ago|reply
Basically, TCP/IP doesn't scale to meet the constraints of deep-space networks (high latency, asymmetric data rates, intermittent connectivity). It just breaks down. That's why there's a lot of active research in DTN (delay/disruption tolerant networking and ad-hoc networking protocols). ION (Interplanetary Overlay Network) is the JPL implementation of the DTN protocols, and has been flown in a demonstration capacity on some extended-mission/end-of-life Deep Space missions. Much of it has been open sourced at this point.
[+] [-] noselasd|13 years ago|reply
[+] [-] gchang|13 years ago|reply
[+] [-] drumdance|13 years ago|reply
Anyway, he compared the energy used to transmit from the probe to that of a flower petal falling from a height of six feet.
[+] [-] darkstalker|13 years ago|reply
[+] [-] ntkachov|13 years ago|reply
http://www.quora.com/Curiosity-Mars-Rover-1/What-is-the-bit-...
[+] [-] sillysaurus|13 years ago|reply
As Mars and Earth orbit around the sun, their distance relative to each other is constantly changing. The minimum distance from Earth to Mars is 35,000,000 miles, and the maximum is 249,375,000 miles.
Since light travels at 670,000,000 miles per hour in a vaccuum, we can calculate the minimum and maximum round-trip latency:
[+] [-] sp332|13 years ago|reply
[+] [-] waterlesscloud|13 years ago|reply
But it can be as low as 3 minutes or as high as 21 minutes, depending on the distance from Earth to Mars. Which of course varies as they orbit the sun.
[+] [-] dantotheman|13 years ago|reply
[+] [-] Achshar|13 years ago|reply
[+] [-] 205guy|13 years ago|reply
[+] [-] kayoone|13 years ago|reply
[+] [-] mistercow|13 years ago|reply
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[+] [-] oleyb|13 years ago|reply
[+] [-] barking|13 years ago|reply
[+] [-] Florin_Andrei|13 years ago|reply
[+] [-] diminish|13 years ago|reply