Global ADSB Tracking about to go live

[peekay4]

Interesting stuff. I assume they have a way of bringing the old Iridium satellites down to burn up ?

Yes, mostly. The plan was to de-orbit the old satellites by moving them into a low elliptical orbit (250 km at the perigee). The atmospheric drag at this altitude will eventually slow them enough that most will re-enter the atmosphere and burn up within several months.

The problem is that many of these old satellites are very nearly out of fuel -- because of delays and the need to quickly switch them to different orbital planes than originally intended.

So instead Iridium is proposing to place these satellites into an elliptical orbit with 600 km perigee. From this altitude it might take up to 10 years before the satellites will re-enter the atmosphere.

[Grumpi]

Originally Posted by peekay4

Changing the orbital plane can be done by making only a tiny, temporary change to the inclination. Changing the inclination isn't the aim -- typically the change is only a fraction of a degree -- just enough to very slowly drift the satellite towards the new plane. It can take a year before the satellite arrives at an adjacent plane.

True, switching only the plane I guess can be done with extremely small inclination changes if there is enough time to wait for the "drift".

Originally Posted by peekay4

Thanks, I hadn't read that. Looks like the next launch will go for plane 3. Do you know how many drifters will be on the next launch?

No, and for the last launch it was only published after the launch. I anyway suspect that they did not finalize that yet for the next launch, especially since they have a several month testing period before the second batch. I would assume that based on what they find, they will keep optimizing the overall slotting until very shortly before the launch, and then re-evaluate depending on how precise the orbit insertion by the rocket was.

There is a website about the configuration here:
Iridium Constellation Status

[Geosync]

In a former life I built GEO comm sats as a lead technician coming from the aviation AME world, but literally all of it was OJT mechanical and electrical work, and we were not taught any of the science-y stuff. I had to go seek it out on my time. This book is fantastic for non- math/engineering crowd-

How Spacecraft Fly: Spaceflight Without Formulae
Swinerd, Graham

Discusses rockets, orbital mechanics, satellites, space systems design, etc. A must-have for anyone interested in the space portion of "aerospace".

[ex-EGLL]

Global ADSB is a promising service, but it is only part of the system. The primary intent (I believe) is to provide surveillance over remote areas. Remote areas, and in particular oceans, have very little comm capability. If separation is to be reduced in these areas then reliable communications is going to be needed. Theoretically it may be possible to drop to 5nm over the ocean, but not with HF Voice. CPDLC is a possibility, but I can't see that working with minimum separation. Is there anything in the works fo communications systems to work in conjunction with these satellites?

[Roger Greendeck]

Between CPDLC, TCAS, and air to air VHF you'd think there are enough ways to communicate to allow safe 5nm spacing in oceanic airspace if the ADS-B coverage works. Crossing traffic would be more of an issue but aircraft on the same route should be fine if assigned a Mach number rather than allowing slight variations as happens now.

[compressor stall]

Peekay - do you have any historical data on the orbit of the parked satellites whilst they undergo checks? I ask as the other night I saw a satellite appear about 40° altitude and move downwards to about 25° altitude and disappear. Then another did the same thing about a minute or so later. Then another. We saw six do this, all the same and with similar spacing, and it's been bugging me what the hell they were!

[wiggy]

Sounds odd...I'm not sure you end up with "aged" satellites effectively clustered like that, even in some form of parking orbit (would there be any point?).

Isn't it more likely "new" satellites distributed from a single launcher/bus might appear grouped initially (genuine question for those in the know)

Roughly where were you, what was the azimuth, what sort of spacing are we talking about?

[ChickenHouse]

It'll be interesting to see how they deal with data protection issues.

[compressor stall]

Wiggy - Location S37.8E144.9 (Melbourne CBD, Myer Music Bowl)
First one noticed at 17 01 27 1057UTC (there may have been more prior)
Object appeared in the north, directly below Orion. Each about almost as bright as Betelgeuse and satellite like in appearance (i.e. just a moving star)

Just plotted it on iPad app.
All appeared at about 35° altitude and tracked directly down to about 18° altitude. Azimuth about 010°

None visible at the same time, the next one appeared about 30 seconds after the previous one had faded out. They were moving so slowly that it was hard to tell at first if they were moving. It probably took about one minute from appearing to disappearing.

I was in the middle of a crowd at an outdoor concert so more accurate observations were not possible. My wife saw them as well, independently of me and remarked about them, unprompted.

Yes - was thinking that they were the new ones waiting in line to be boosted up. I can't find any data on them in Heavens-above or similar.

[SATCOS WHIPPING BOY]

Have I misunderstood the capacity of the Aireon system? It says 10,000 aircraft globally; a quick check just now on flightradar has 9000+ and this excludes most of Africa, China, Russia.

[peekay4]

Hi compressor stall, it is possible that you indeed saw the Iridium Next satellites.

According to (approximate) calculations for that date from your location, Iridium 114 would have been at 36° elevation, 14° azimuth at 10:57 UTC and dropping to 22° elevation, 11° azimuth a minute later -- matching your observations. Many of the other Iridium Next satellites would have been nearby.

You can compute past or predicted positions by using an app or online calculator tool that accept "Two Line Element" (TLE) observation data published by the US Space Surveillance Network. Here's an example TLE for Iridium 114:

IRIDIUM 114 [+]
1 41923U 17003G 17030.22607686 .00000357 00000-0 39151-4 0 9996
2 41923 86.6609 79.6394 0011490 177.2547 182.8728 14.84387795 2297

This particular observation was made at Jan 30 00:25 UTC so calculations beyond a several days from this date wouldn't be too accurate.

Link: Iridium NEXT TLEs from Celestrak.

[compressor stall]

Thanks peekay. Great data, and good to know my obs were pretty accurate given I was in the middle of a concert crowd!

I'd been looking for historical data, and will folllow up on the links you provided. Cheers.

[Ian W]

Originally Posted by Roger Greendeck

Between CPDLC, TCAS, and air to air VHF you'd think there are enough ways to communicate to allow safe 5nm spacing in oceanic airspace if the ADS-B coverage works. Crossing traffic would be more of an issue but aircraft on the same route should be fine if assigned a Mach number rather than allowing slight variations as happens now.

The ADS-B capability is in a hosted payload on Iridium Next satellites which are primarily a fully global communications network. So every aircraft that can be seen by Iridium hosted payload could have one or more broadband comms links including voice comms.

Welcome to the brave new world of ubiquitous communications

[Max Angle]

Unless the new satellites have the same antenna design, unlikely I suspect, it will be the end of "iridium flares". The antennas of the current units have a highly polished surface that produces a bright flash of light when the sun shines on it, this can be seen at night as a brief very bright star shining in the night sky. Seen quite a few over the years and there are various websites that offer a prediction of where and when.

[wiggy]

Thanks peekay.

Max-

there are various websites that offer a prediction of where and when.

Indeed the previously mentioned "Heavens above" is a good 'un.

Heavens-Above

For the unitiated I'd say if you're looking for the bright iridium flashes using that software (and no doubt all the others) it's worth making the effort to put a really accurate position in, rather than a generic "nearest town" or even village. it is interesting to see how narrow the iridium flash ground tracks are and a handful of Kms of position error can make a big difference between a predicted event being a "wow" or a "what, that's it? but you told me.....".

[ve3id]

Malaysian goes with satellite ADSB worldwide tracking

And some said it was not possible:

https://flightaware.com/news/article...t-tracking/278

[wiggy]

Did they? I know there were lots of arguments about the feasibility of continuous downloading of FDR data via satellite, but this is ADS-B and whilst it offers an improvement in coverage as the report says:

No new avionics or modifications are needed for aircraft to take advantage of this service.

[ve3id]

Yes they did! It was assumed that the data would be decoded only by land stations, and therefore only over and LOS from land. I engaged in a discussion with someone who said it would be useless in Northern Canada since there would be too many ground stations needed!

Of course, satellites can pick up and process position squints quite nicely since they have a small payload.

[DaveReidUK]

That strikes me as a somewhat circular argument.

[Airbubba]

I believe several carriers are already doing satellite based ADS-B tracking using existing platforms.

For example, on Inmarsat (at the bottom of the Other Tracking Info tab):

http://sat-global.adsbexchange.com/V...r/desktop.html