Satellite Based ADS-B

[dans2992]

Ok, so if this is possible, why do we need to install so many ground stations? Obviously, this is good for 1090 only, but it would seem to be the "magic bullet" for global coverage at a (somewhat) reasonable price.

What's the downside I am missing? Is it not practical to use satellites to track traffic in high-density areas?

http://www.aireon.com/Home

 

[bnt83]

Ok, so if this is possible, why do we need to install so many ground stations? Obviously, this is good for 1090 only, but it would seem to be the "magic bullet" for global coverage at a (somewhat) reasonable price.

What's the downside I am missing? Is it not practical to use satellites to track traffic in high-density areas?

http://www.aireon.com/Home

Can't answer that question, but guess where all the current ADS-B out antennas are installed and where they aren't (on an airplane).

As it sits I don't think there is any airplane that has ADS-B Out that would work with a satellite tracking system unless it is some sore of data link thru a satcom transceiver.

(Currently most all ADS-B Out antennas are on the bottom of the airplane like transponder antenna) <<<--- won't cut it for satellites

 

[petrolero]

I was pondering this the other day. I suspect it has to do with the bandwidth available from satellites and also the 2-way nature of ADS-B. You might be able to put some components of the system on board satellite but that wouldn't remove the need for ground stations.

If satellite comm were better then yeah maybe it would be do-able.

 

[bnt83]

I was pondering this the other day. I suspect it has to do with the bandwidth available from satellites and also the 2-way nature of ADS-B position reporting. You might be able to put some components of the system on board satellite but that wouldn't remove the need for ground stations.

If satellite comm were better then yeah maybe it would be do-able.

ADS-B position reporting is out only, not a 2 way.

 

[petrolero]

ADS-B position reporting is out only, not a 2 way.

I know but I'm referring to the whole ADS-B solution, including the "in" portion. So that makes it 2-way. I corrected the typo.

It would be pretty hard to upload custom traffic pucks to a satellite and have them beamed back down to thousands of aircraft instantly.

Then again, maybe that customization wouldn't be required with a satellite-based solution. Maybe it just broadcasts all traffic positions all the time. But that sure seems like a bandwidth hog when combined with radar and weather output and all the rest.

 

[bnt83]

I believe for NextGen compliance eventually everyone will need ADS-B Out diversity, meaning the out antennas will be required on the top and bottom of the airplane.

If that diversity is broken up by category or type of operations hard to say.


Somewhere there is probably an FAA article about all the coming changes with an idea of what the final system will look like and what equipment will be required.

 

[petrolero]

Also ADS-B "in" currently tailors the finer resolution radar image to the tower's location. There would be no way to tailor those images from a satellite, so it would just be blasting out the full CONUS radar image all the time. That would be another likely bandwidth hog but since that radar image is not customized maybe that isn't as bad as it seems.

Also it would have to be blasting out METARs and TAFs and winds aloft and everything else for the entire country would it not? Seems pretty hard to manage all that data plus traffic through the relatively thin bandwidth of a satellite.

 

[petrolero]

I believe for NextGen compliance eventually everyone will need ADS-B Out diversity, meaning the out antennas will be required on the top and bottom of the airplane.

If that diversity is broken up by category or type of operations hard to say.


Somewhere there is probably an FAA article about all the coming changes with an idea of what the final system will look like and what equipment will be required.

What makes you believe that antenna diversity will be required for small aircraft?

Dual antennas for the system as designed now isn't needed for small airplanes because their size doesn't occlude their positions enough.

 

[bnt83]

What makes you believe that antenna diversity will be required for small aircraft?

Dual antennas for the system as designed now isn't needed for small airplanes because their size doesn't occlude their positions enough.

Just makes sense that NextGen would want to track all aircraft even in a non radar and non ground based ADS-B station environment.

 

[Bob Noel]

Ok, so if this is possible, why do we need to install so many ground stations? Obviously, this is good for 1090 only, but it would seem to be the "magic bullet" for global coverage at a (somewhat) reasonable price.

What's the downside I am missing? Is it not practical to use satellites to track traffic in high-density areas?

http://www.aireon.com/Home

Roughly speaking, the ground infrastructure is used to (1) deal with the dual frequencies (UAT and Mode S), (2) provide validation of the ADS-B out reports (without any validation it would be trivial to spoof ADS-B messages), and (3) transmit information to the aircraft.

 

[dans2992]

Also ADS-B "in" currently tailors the finer resolution radar image to the tower's location. There would be no way to tailor those images from a satellite, so it would just be blasting out the full CONUS radar image all the time. That would be another likely bandwidth hog but since that radar image is not customized maybe that isn't as bad as it seems.

Also it would have to be blasting out METARs and TAFs and winds aloft and everything else for the entire country would it not? Seems pretty hard to manage all that data plus traffic through the relatively thin bandwidth of a satellite.

XM does all of this (except traffic) so, clearly it's possible. Probably not on 1090mhz though...


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[petrolero]

XM does all of this (except traffic) so, clearly it's possible. Probably not on 1090mhz though...


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Yeah and I was thinking about that as well but I forgot to mention it. That's a good point.

Should be doable.

 

[Indiana_Pilot]

I would say it has to do with the latency of the data transmissions.. there can be a few second delay or more.. The groundstations provide a more "realtime" traffic picture

Also, cost.. ease of mainenance... I would also say the ground stations would be more reliable.. (often in range of more than one) One satellite goes out and it could be an entire region... one groundstation goes out.. well there are usually others within in range... Just my random thoughts anyway!

 

[Jim_R]

Launching and maintaining satellite infrastructure is waaaay more costly than ground infrastructure. Even remote ground infrastructure in jillions of locations. FAA's not interested in solving global air traffic issues...just domestic.

The website doesn't have a price list, but it's clearly a paid service marketed to turbine operators who can get some operational efficiency from the system and potentially reap savings greater than the cost of the service.

No piston-engined aircraft will ever find such a deal cost-effective.

 

[bullwinkle]

Ground stations are far cheaper and easier to repair than satellites in orbit.

 

[JohnSBA]

Ground stations can also broadcast with lots of power, directed antenna, and are much closer to your aircraft (inverse square of distance) = less susceptible to interference. Alas, ground station signals can probably still can be spoofed but that's not a disadvantage to satellite and those are easier to jam due to their weaker signal.

 

[John Collins]

Just makes sense that NextGen would want to track all aircraft even in a non radar and non ground based ADS-B station environment.

The diversity requirement is mostly for larger aircraft and for surface ADS-B operation. Surface ADS-B is available at the 35 largest airports and provides both surface tracking and runway approach/departure awareness. There is interest in tracking in the oceanic areas using LEO satellites. This is an airline thing, no more MH370's going missing. See http://www.aireon.com/AboutAireon/AnIridiumInnovation

But this is not needed in the US airspace because we already have radar and ADS-B that is ground based.

 

[dans2992]

Couldn't it eliminate areas of no radar/ADS-B coverage in mountainous areas?


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[Clark1961]

Couldn't it eliminate areas of no radar/ADS-B coverage in mountainous areas?

WAM is much cheaper for continental US. Probably cheaper anywhere but dunno fer sure.

 

[dans2992]

WAM?


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[denverpilot]

Wide area multilateralization.

It's a technology with fixed locations that listen for transponder returns and a central transmitter site that transmits the "query" via an omnidirectional antenna. In fact all of the antennas are ommi.

No moving parts, it calculates aircraft location precisely without a need for a spinning radar or the "trailing" mode c interrogation antenna offset from the primary radar antenna.

Currently certified and in use in the Aspen valley for IFR ops. Been there a number of years. System feeds into ZDV and is treated as accurate as other radar sources. Of course no primary targets, only transponder equipped aircraft show up.

But it's cheap, work every well, and could easily have met the aircraft location requirements that they claim ADS-B was meant to accomplish. With ZERO change to on board equipment.

Two problems:

Not invented here. You buy it from the Germans. No pork to sell to Congress.

It doesn't IDENTIFY the aircraft and frankly, much as they'll say that isn't the reason for ADS-B it is. They don't care about the location of aircraft for traffic purposes. They want to know who is in the airspace and when.

That data will be fed to the kids in New Mexico and their nifty gov'mint jobs, data mining for possible illegal activities in multiple databases.

The same retarded database that tagged a leased airplane John and Martha King were flying as a possible drug runner.

The database weenies want to get to know and love you with their algorithms. They'll know when your airplane goes places it usually doesn't. And they'll be happy little database campers.

And my first software writing college instructor's predictions, who was a female Ada coder for DoD for two decades, will be correct... "Don't willingly allow information that isn't necessary to be put into a database, into a database. They can be used for very inappropriate things with a simple table join."

She knew where we were heading, now more than 20 years ago. And tried to tell a generation of coders to beware.

 

[dans2992]

I have a Raspberry Pi on my roof that does MLAT. I wouldn't use it to control IFR traffic, but it does work...


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[denverpilot]

I have a Raspberry Pi on my roof that does MLAT. I wouldn't use it to control IFR traffic, but it does work...


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That's nifty. What software? Using an SDR I assume and a known location of the transmitter site for the radar?

The certified systems are surveyed and they know exactly where the antennas are located and have very high accuracy. Measuring the time from interrogation to reception by multiple receivers at fixed, well known, accurately surveyed locations, gives a very good "solution" on where the target is.

It took about six months as I recall for FAA to certify the Aspen valley one enough that they'd allow the data to become a primary (not to be confused with primary radar) data source at ZDV and allow simultaneous approaches into the valley, where traditional radar simply never reached.

Cheap, effective, pretty easy to scale up, required nothing new in the panel of any transponder equipped aircraft, didn't create multi-billion dollar boondoggle.

Of COURSE it wasn't used instead of ADS-B.

Imagine the $$$ the entire world would have saved if someone had just applied two or three brain cells.

Or, pop on the tin foil hat and come to the realization that ADS-B was never about locations of aircraft and was all about IDENTIFICATION of aircraft.

Just sayin'...

 

[dans2992]

I imagine there's some additional benefits to ADS-B, however. You only need a single ground station in range of the aircraft instead of 3-4.

Also, can you apply multilateration to multiple Mode C aircraft squawking the same code (ie 1200)?


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[dans2992]

I am using FlightAware's PiAware image. MLAT was an add on to 1090 ADS-B reception. They actually use ADS-B signals from known aircraft in range of all the participating stations to do the time coordination instead of trying to do it with NTP/GPS, etc. works surprisingly well.

I have another raspberry Pi grabbing the 978 transmissions. Can't wait until all aircraft are equipped.


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[denverpilot]

I imagine there's some additional benefits to ADS-B, however. You only need a single ground station in range of the aircraft instead of 3-4.

Also, can you apply multilateration to multiple Mode C aircraft squawking the same code (ie 1200)?

Yes.

I am using FlightAware's PiAware image. MLAT was an add on to 1090 ADS-B reception. They actually use ADS-B signals from known aircraft in range of all the participating stations to do the time coordination instead of trying to do it with NTP/GPS, etc. works surprisingly well.

I have another raspberry Pi grabbing the 978 transmissions. Can't wait until all aircraft are equipped.

2020 isn't that far away. You can buy me a transponder and a GPS if you like to speed up the process.

I'm so glad I'll be entertaining hobbyist SWLs with that $8K.

 

[kontiki]

Ok, so if this is possible, why do we need to install so many ground stations? Obviously, this is good for 1090 only, but it would seem to be the "magic bullet" for global coverage at a (somewhat) reasonable price.

What's the downside I am missing? Is it not practical to use satellites to track traffic in high-density areas?

Satcom is in very widespread use, but it's not cheap. In general, airline equipment defers to cheaper ground based network service providers for ACARS support when it can establish a decent link, before cutting over to a satellite service providers.

1090ES ADS-B pumps out position (along with possibly 200 other pieces of data) at a pseudo randomized interval generally less than 1/2 sec.

There is a huge quantity of data continuously pumped out of airliners via ACARS. ACARS with ground and satellite network coverage routinely provides position updates about every 15 minutes. Depending on the installation. That's not sufficient for ATC to provide separation service, so they may use oceanic rules (50-80 nm).

I help support some of the equipment, but don't know all the uses.

There are 100s of data transmissions, some from the crew, some automated like engine performance monitoring (fuel, temps, vibrations), event triggered transmissions like annunciations, accelerometer exceedences (abnormal G loads) etc.

Aircraft health monitoring is to the point on modern jets (if you pay for the service) where you can log into a provider and request that the system generate an email to you to let you know if the #2 engine oil temp on a specific airplane has exceeded a certain value while it's en route.

None of that is free though. ACARS used to charge by the byte. Everything is transmitted, received, stored in a huge data warehouses where it can be retrieved by ICAO address and flight leg. It's a huge expensive business, with a lot of logistics involved.

Not to digress, but the only reason MH370 is missing is because the airline didn't write the check for services and equipment that would have allowed tracking. It's not mandatory.