7 ms·

Tianwen-1 attitude in Mars orbit

147 points by parsecs 5y ago

kerng 5y ago
Always interesting when something is on front page, but doesn't have a single comment. Anyone one know why that can happen? Is it that a title sounds interesting, so people upvote (this one had 86 votes) but noone actually reads or finds anything of interest in the article to discuss? Just curious. I, for one, find it interesting that anyone with the necessary equipment can observe spaceships and satellites, etc and what they might be doing far away. Are signals not encrypted or is this entirely via observation somehow?
- mwint 5y ago
  I may be completely wrong, but I remember reading some spacecraft have a couple “streams” of data. Control signals tend to be encrypted (don’t want a backyard idiot wrecking your spacecraft), but for most other things the limited bandwidth makes encryption overhead unappealing. Would love to hear someone who actually knows this stuff speak to it.
  - GekkePrutser 5y ago
    I don't think the backyard idiot would have this in their backyard: https://amsat-dl.org/en/20-meter-antenna/ https://amsat-dl.org/en/20-meter-antenna/ which is what they used to receive this. Sending control commands would be even harder. Mars is far. But for earth orbiting says this is more of a risk indeed. The uplink (control commands)would be encrypted for sure but the downlink (telemetry) is often not for scientific missions. For military or commercial it's a different thing obviously. Even SpaceX' launch cams (downlink) were not encrypted for a while and amateurs received them. Only when this made the news they started encrypting them. Probably because they do military launches too (the cameras for those on their web feed shut down when the payload is visible, but this would possibly show those) https://www.rtl-sdr.com/receiving-video-directly-from-a-spacex-falcon-9-rocket-scott-manley-video/ https://www.rtl-sdr.com/receiving-video-directly-from-a-spac...
    - GravitasFailure 5y ago
      Apparently the encryption has to do with needing to have a license from NOAA in order to broadcast images of Earth. https://www.theverge.com/2018/4/5/17197742/spacex-falcon-9-rocket-launch-livestream-noaa-regulation https://www.theverge.com/2018/4/5/17197742/spacex-falcon-9-r...
      - tastyfreeze 5y ago
        Thank you for sharing. NOAA requiring a license for images of Earth is infuriating. Do they require other countries to get a license as well?
        GravitasFailure 5y ago
        My understanding is it's intertwined with national security issues. NOAA doesn't have the ability to demand a license from other nations, though there may be some treaty obligations they adhere to.
        zokier 5y ago
        USG has been trying to put the satellite imagery genie back in the bottle the past 30 years with mixed results at best. I suspect they are slowly realizing that it is a losing battle. https://www.wired.com/story/how-the-government-controls-sensitive-satellite-data/ https://www.wired.com/story/how-the-government-controls-sens...
      - GekkePrutser 5y ago
        Interesting. It makes no sense at all in this case because the stated reason for the law (capturing troop movements) is impossible here. The resolution and focal length is way too low to see anything smaller than a few miles in diameter :) But it is a law... It should be repealed or specified in more detail IMO (e.g. only applying to really high detail levels). But I can imagine the US Govt has bigger fish to fry right now with a raging pandemic.
- isaacimagine 5y ago
  Sometimes, if there's a story I find interesting but am not entirely clear on, I upvote it so others more qualified have a better chance of seeing and commenting on it. I guess if enough people do this, a story'll teach the front page w/ 0 comments. Just my own 2¢.
- mendigou 5y ago
  There are normally at least two radio links: telemetry and telecommand. Some spacecraft have multiple of each, with at least one channel of each being some sort of emergency channel where you can only do the most basic ops or get the most basic data. As the sibling comment mentions, command signals are normally at least signed, and many times also encrypted. Telemetry is way less sensitive, so it is usually not encrypted in scientific missions. There are well known protocols for space communications (e.g. CCSDS, PUS), so once you figure out a few fields you can make educated guesses of what each byte is. A previous post of the linked blog discusses it in detail: https://destevez.net/2020/08/tianwen-1-telemetry-framing-and-data/ https://destevez.net/2020/08/tianwen-1-telemetry-framing-and... Even without the actual telemetry, there are many things you can guess about the satellite attitude from just observing the radio signal. Many satellite and radio amateurs love doing that!
- tigerlily 5y ago
  > Always interesting when something is on front page, but doesn't have a single comment. I'm sure I've seen a name for this effect somewhere, but I don't remember it. Does anyone else know?
- deleted 5y ago
  [deleted]
- pjc50 5y ago
  > Always interesting when something is on front page, but doesn't have a single comment. Comments are for bickering. Not having comments but being on the front page is a sign of good, wholesome, undisputed content.
sharmin123 5y ago
How Does A Hacker Hack A Phone? How To Avoid Phone Hacking?: https://www.hackerslist.co/how-does-a-hacker-hack-a-phone-how-to-avoid-phone-hacking/ https://www.hackerslist.co/how-does-a-hacker-hack-a-phone-ho...
Out_of_Characte 5y ago
Its supposed to me altitude right? not attitude which is a (emotional) disposition towards something. a google search reveils no alternative meaning yet its written wrong 17 times.
- danielbarla 5y ago
  From [1] attitude, in the context of spacecraft, means: > Attitude is part of the description of how an object is placed in the space it occupies. Attitude and position fully describe how an object is placed in space. So, basically, its relative orientation and rotation. [1] https://en.wikipedia.org/wiki/Attitude_control https://en.wikipedia.org/wiki/Attitude_control
- icebadger 5y ago
  From Merriam-Webster Dictionary [0]: >5 : the position of a craft (such as an aircraft or spacecraft) determined by the relationship between its axes and a reference datum (such as the horizon or a particular star) [0] https://www.merriam-webster.com/dictionary/attitude https://www.merriam-webster.com/dictionary/attitude
- Spare_account 5y ago
  I see you've had some other answers about the meaning of 'attitude' in this context, so I thought I would address the other part of your comment: >a google search reveils no alternative meaning A Google query that worked well for me to learn more about this was 'attitude orbit'. Including another word from the knowledge area (borrowed from the article title) helped Google understand the context I was searching within: https://www.google.com/search?q=attitude+orbit https://www.google.com/search?q=attitude+orbit
- pjc50 5y ago
  https://en.wikipedia.org/wiki/Attitude_control https://en.wikipedia.org/wiki/Attitude_control > a google search reveils no alternative meaning You could file this under "yet another deterioration of google effectiveness by personalisation of search results", except it's not even true? I put "attitude" in and it gave me a dictionary expand-o-box with "3. the orientation of an aircraft or spacecraft, relative to the direction of travel."
MisterBiggs 5y ago
I was wondering how this data was gathered since to my knowledge China has been pretty secretive about their space missions (compared to NASA at least). It looks like the data came from here http://www.r00t.cz/Sats/Tianwen1 http://www.r00t.cz/Sats/Tianwen1 and I think its surprising how easy it was to break down the data. I would have assumed it would have been heavily obfuscated / encrypted.

147 points by parsecs 5y ago

Always interesting when something is on front page, but doesn't have a single comment. Anyone one know why that can happen? Is it that a title sounds interesting, so people upvote (this one had 86 votes) but noone actually reads or finds anything of interest in the article to discuss? Just curious. I, for one, find it interesting that anyone with the necessary equipment can observe spaceships and satellites, etc and what they might be doing far away. Are signals not encrypted or is this entirely via observation somehow?

mwint 5y ago
I may be completely wrong, but I remember reading some spacecraft have a couple “streams” of data. Control signals tend to be encrypted (don’t want a backyard idiot wrecking your spacecraft), but for most other things the limited bandwidth makes encryption overhead unappealing. Would love to hear someone who actually knows this stuff speak to it.
- GekkePrutser 5y ago
  I don't think the backyard idiot would have this in their backyard: https://amsat-dl.org/en/20-meter-antenna/ https://amsat-dl.org/en/20-meter-antenna/ which is what they used to receive this. Sending control commands would be even harder. Mars is far. But for earth orbiting says this is more of a risk indeed. The uplink (control commands)would be encrypted for sure but the downlink (telemetry) is often not for scientific missions. For military or commercial it's a different thing obviously. Even SpaceX' launch cams (downlink) were not encrypted for a while and amateurs received them. Only when this made the news they started encrypting them. Probably because they do military launches too (the cameras for those on their web feed shut down when the payload is visible, but this would possibly show those) https://www.rtl-sdr.com/receiving-video-directly-from-a-spacex-falcon-9-rocket-scott-manley-video/ https://www.rtl-sdr.com/receiving-video-directly-from-a-spac...
  - GravitasFailure 5y ago
    Apparently the encryption has to do with needing to have a license from NOAA in order to broadcast images of Earth. https://www.theverge.com/2018/4/5/17197742/spacex-falcon-9-rocket-launch-livestream-noaa-regulation https://www.theverge.com/2018/4/5/17197742/spacex-falcon-9-r...
    - tastyfreeze 5y ago
      Thank you for sharing. NOAA requiring a license for images of Earth is infuriating. Do they require other countries to get a license as well?
      - GravitasFailure 5y ago
        My understanding is it's intertwined with national security issues. NOAA doesn't have the ability to demand a license from other nations, though there may be some treaty obligations they adhere to.
        zokier 5y ago
        USG has been trying to put the satellite imagery genie back in the bottle the past 30 years with mixed results at best. I suspect they are slowly realizing that it is a losing battle. https://www.wired.com/story/how-the-government-controls-sensitive-satellite-data/ https://www.wired.com/story/how-the-government-controls-sens...
    - GekkePrutser 5y ago
      Interesting. It makes no sense at all in this case because the stated reason for the law (capturing troop movements) is impossible here. The resolution and focal length is way too low to see anything smaller than a few miles in diameter :) But it is a law... It should be repealed or specified in more detail IMO (e.g. only applying to really high detail levels). But I can imagine the US Govt has bigger fish to fry right now with a raging pandemic.
isaacimagine 5y ago
Sometimes, if there's a story I find interesting but am not entirely clear on, I upvote it so others more qualified have a better chance of seeing and commenting on it. I guess if enough people do this, a story'll teach the front page w/ 0 comments. Just my own 2¢.
mendigou 5y ago
There are normally at least two radio links: telemetry and telecommand. Some spacecraft have multiple of each, with at least one channel of each being some sort of emergency channel where you can only do the most basic ops or get the most basic data. As the sibling comment mentions, command signals are normally at least signed, and many times also encrypted. Telemetry is way less sensitive, so it is usually not encrypted in scientific missions. There are well known protocols for space communications (e.g. CCSDS, PUS), so once you figure out a few fields you can make educated guesses of what each byte is. A previous post of the linked blog discusses it in detail: https://destevez.net/2020/08/tianwen-1-telemetry-framing-and-data/ https://destevez.net/2020/08/tianwen-1-telemetry-framing-and... Even without the actual telemetry, there are many things you can guess about the satellite attitude from just observing the radio signal. Many satellite and radio amateurs love doing that!
tigerlily 5y ago
> Always interesting when something is on front page, but doesn't have a single comment. I'm sure I've seen a name for this effect somewhere, but I don't remember it. Does anyone else know?
deleted 5y ago
[deleted]
pjc50 5y ago
> Always interesting when something is on front page, but doesn't have a single comment. Comments are for bickering. Not having comments but being on the front page is a sign of good, wholesome, undisputed content.

sharmin123 5y ago

How Does A Hacker Hack A Phone? How To Avoid Phone Hacking?: https://www.hackerslist.co/how-does-a-hacker-hack-a-phone-how-to-avoid-phone-hacking/ https://www.hackerslist.co/how-does-a-hacker-hack-a-phone-ho...

Out_of_Characte 5y ago

Its supposed to me altitude right? not attitude which is a (emotional) disposition towards something. a google search reveils no alternative meaning yet its written wrong 17 times.

danielbarla 5y ago
From [1] attitude, in the context of spacecraft, means: > Attitude is part of the description of how an object is placed in the space it occupies. Attitude and position fully describe how an object is placed in space. So, basically, its relative orientation and rotation. [1] https://en.wikipedia.org/wiki/Attitude_control https://en.wikipedia.org/wiki/Attitude_control
icebadger 5y ago
From Merriam-Webster Dictionary [0]: >5 : the position of a craft (such as an aircraft or spacecraft) determined by the relationship between its axes and a reference datum (such as the horizon or a particular star) [0] https://www.merriam-webster.com/dictionary/attitude https://www.merriam-webster.com/dictionary/attitude
Spare_account 5y ago
I see you've had some other answers about the meaning of 'attitude' in this context, so I thought I would address the other part of your comment: >a google search reveils no alternative meaning A Google query that worked well for me to learn more about this was 'attitude orbit'. Including another word from the knowledge area (borrowed from the article title) helped Google understand the context I was searching within: https://www.google.com/search?q=attitude+orbit https://www.google.com/search?q=attitude+orbit
pjc50 5y ago
https://en.wikipedia.org/wiki/Attitude_control https://en.wikipedia.org/wiki/Attitude_control > a google search reveils no alternative meaning You could file this under "yet another deterioration of google effectiveness by personalisation of search results", except it's not even true? I put "attitude" in and it gave me a dictionary expand-o-box with "3. the orientation of an aircraft or spacecraft, relative to the direction of travel."

MisterBiggs 5y ago

I was wondering how this data was gathered since to my knowledge China has been pretty secretive about their space missions (compared to NASA at least). It looks like the data came from here http://www.r00t.cz/Sats/Tianwen1 http://www.r00t.cz/Sats/Tianwen1 and I think its surprising how easy it was to break down the data. I would have assumed it would have been heavily obfuscated / encrypted.