And here it is!

http://stuffin.space/?intldes=1970-008B

Wow, that’s a cool site! I’ve never seen orbiting satellites visualized like that. (But of course, also haven’t sought any out.)

Yes, this is really interesting. There are all sorts of interesting things up there. This one is particularly ironic:

http://stuffin.space/?intldes=1998-067NT

I'd never heard of the West Ford Needles:

https://space.skyrocket.de/doc_sdat/westford.htm

I wonder how the Lemur 2 satellites are named:

http://stuffin.space/?intldes=2018-111N&search=lemur%202

wow, there seem to be a lot more blue dots around - these are all junk; the red one are fewers - these are active sats. Also if there is a longer sequence of red dots on the same orbit then these are all spacelink satelites. Amazing site, thanks!

what kind of black magic is that ?

There should be also stuffin.ocean and stuffin.atmosphere

CO2 / plastic.

When the society is mature enough to clean the mess created ?

P.S. Sorry for offtopic rant

Your father's satellite is very high (1400km, 1000km above the ISS) at the edge of what is classified as low earth orbit. It will be up there for a long while but the chance of it ever hitting anything is infinitesimal.

That makes the very big assumption that the density of other things to hit doesn’t massively increase.

That makes a big assumption we can't remove the junk before the density is high enough

It is worthy of note that SpaceX is pitching Starship for active debris removal in space.

It is worthy of note from https://spacenews.com/upper-stages-top-list-of-most-dangerou... that in a list of the 50 most concerning objects in orbit, 78% are rocket bodies, and 80% were launched before 2000 when various mitigation strategies for space junk began to be improved.

There is therefore a Pareto principle at work here. We are tracking over 25,000 objects, but only a few of them contribute most of the risk, and we aren't adding as much to the risk as the number of launches would make you think.

Infinitesimal over 100,000 years? I'm not losing any sleep over it personally, but that's a long time.

The surface area of the sphere at 1400km is far greater than the earth's surface area. And satellites at that altitude are traveling much slower. Put together, the probabilities would akin to a handful of birds flying on earth, at random altitudes/places/directions, and two of them colliding.

> The surface area of the sphere at 1400km is far greater than the earth's surface area

It's only about 50% larger (1+1400/6371)^2 = 1.49

This! How likely would collisions be on a sphere the size of the earth? How do the probabilities change from low earth orbit to higher orbits?

"much slower" is still >7000 m/s

Yes but at that altitude their orbital period is about 1/2 that of low orbits, meaning that even if two orbits do cross paths, there would be fewer potential collisions in a given time. They are 'slower' in relation to size of the sphere they occupy.

90 mins at 400km vs 110 mins at 1400km

I guess that makes sense since the Earth’s radius is around 6400km so from 400 to 1400km is really a change from 6800 to 7800km which is proportionally similar to a change from 90 to 110 minutes.

Edit: I just looked up the formula for orbital period and it turns out period is proportional to radius^(3/2) (See: https://en.m.wikipedia.org/wiki/Orbital_period)

Yeah, that statement makes a lot of assumptions about the next 99,950 years.

That's true, but the chances of quite a lot of things happening over 100,000 years are fairly big.

Almost everything we do carries a small but non-zero risk of something which, if you stretched it over a hundred thousand years, would almost certainly be realized.

On the other hand, the average damage from a collision in space within 100,000 years is also pretty small.

I wonder how the odds stack up against the odds of a human being hit by a meteorite? Those kind of odd's/statistics I can get my head around.

Suppose there are just two satellites orbiting at the same altitude, a bit higher, let's say 5 orbits a day (ISS orbits 18 times a day, roughly). The two satellites cross each other's path twice per orbit. Over the course of a year, that's 3650 potential collisions. Given the length of their orbit might be 50,000 km, then the average distance between these two crossings is 13 km. Over 10 years, that reduces down to 1.3 km. Over 100, 130m. Over 100000, it's 0.130m. They are gonna collide.

Of course, I am assuming a few things, like their orbits don't decay, they aren't exactly synchronized (i.e. they drift, and will eventually cross every point on the other's), but also that the uneven gravity of Earth doesn't corral them into narrower orbital paths (which it absolutely will, increasing the chances of collision).

That's for only two satellites. There are literally thousands. And when they smash apart, they can each generate hundreds more killer-sized fragments.

Kessler syndrome is a very real possibility on a long timescale.

We should be more careful the junk we put in space.

> Launch date: 23 January 1970

Phew, 23 days earlier your father would have had to code all timestamps in negative.

Joke apart, which OS did such satellites run? Unix? Probably not, since timestamps only started in 1970. Just "C"? Even today, how do you register time on satellites? With Unix timestamps (a long since 1970-01-01)? Can they synchronize based on objective points (stars or Earth position to the sun) or are satellites always resynchronized from Earth signals?

I have to say that the assumption of a hobbyist satellite in 1970 to be able to run UNIX is pretty amusing, considering (Wikipedia):

> In a 1970 survey, The New York Times suggested a consensus definition of a minicomputer as a machine costing less than US$25,000 (equivalent to $165,000 in 2019), with an input-output device such as a teleprinter and at least four thousand words of memory, that is capable of running programs in a higher level language, such as Fortran or BASIC.

I think it’s safe to say that the biggest issue with launching computers running UNIX into space in 1970 probably was not the lack of a standardized time stamp :-)

I have no knowledge of old-style satellites, but have worked on cubesats (low earth orbit) reasonably recently.

Star trackers give you location in orbit and orientation of your satellite. I don't believe you can get absolute time from them, especially given that Earth time is somewhat decoupled from Earth's orbital dynamics.

What you can do is get time using GPS, like you would on the ground. Not sure if that's possible for higher orbits, but definitely for low orbits. There have also been some experiments with laser-based synchronization (a PPS-style signal, I believe?) and you could get a coarse sync with a regular old radio uplink.

Back then most satellites were likely just hardwired electronics, possibly with some limited remote command support. Sure, there were exceptions for high profile missions such as space probes and spy satellites.

IIRC there have been some proposals to use Pulsar signals on satellites/probes not just for time synchronization but more importantly navigation. Not sure if it's actually in production use yet.

> "Passive magnetic attitude stabilization was performed by carrying two bar magnets to align with the Earth's magnetic field in order to provide a favorable antenna footprint."

Wow! I heard of this technique recently but I didn't realize it had already been deployed so long ago.

Dad is credited with developing that part of it!

Small world. I got to know the A05 guys really well when I put together a new team at UniMelb to do the same thing a few years ago. Even got some cringeworthy lines in this documentary with them.

https://vimeo.com/191605076

We'll figure out how to clean it up when or if it's ever a problem. He shouldn't worry about it.