Tianwen-1 attitude in Mars orbit | Hacker News Reader

Tianwen-1 attitude in Mars orbit

destevez.net

147 pointsparsecs21 comments

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?

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.

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...

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-r...

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?

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.

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-sens...

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.

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¢.

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!

> 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?

> 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.

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.

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.

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

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

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://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."

Could still be due to search personalisation.

I get programming results even for non programming terms. I am pretty confident that's not the case for my mom.

It stands to reason that people's search results could be wholly uninformative if Google thinks the subject matter is unlike what you usually read.

The other day I was looking for official website of Moldovan government to find out their covid rules.It took me an hour to find, it was below UK and US gov pages about Moldova and below random media articles and blogposts.

There are also many times when you search an official UK government service, like applying for a driving lisence or filing taxes, and the first page is just full of scams. This has been goung on for years, they should pin the official resources to the top for cases like this.

Googling tip: if what you're looking for is the definition of a word, try typing:

  define:attitude

You'll see that the third definition which comes up is: "the orientation of an aircraft or spacecraft, relative to the direction of travel."

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