Tianwen-1 attitude in Mars orbit

Tianwen-1 attitude in Mars orbit(destevez.net)

147 points by parsecs 4 years ago | 21 comments

kerng 4 years 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?

isaacimagine 4 years 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 4 years 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...

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!

pjc50 4 years 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.

mwint 4 years 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 4 years ago | | |

I don't think the backyard idiot would have this in their backyard: 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-spac...

tigerlily 4 years 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?

MisterBiggs 4 years 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 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.

Out_of_Characte 4 years 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.

pjc50 4 years ago | |

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."