Hello.
I'm trying to figure out why, when comparing Galileo with GPS, there
is often a reference to GPS indicating that it's constellation is only
composed by 24 satellites...
Example:
http://www.spacedaily.com/reports/Fa...o_GPS_999.html

Galileo will consist of 30 satellites, six more than the US Global
Positioning System (GPS). The system will offer several services from
2014, becoming fully operational in 2020 when a constellation of 27
satellites, supported by three spares, is deployed.

It seems only Galileo marketing to me...
The GPS 24 satellites constellation was the original design, but I
don't even remember when there was only 24 sats!
Moreover they count the 3 spares on 30 Galileo satellites!

On 10/19/11 11:00 AM, claudegps wrote:
> Hello.
> I'm trying to figure out why, when comparing Galileo with GPS, there
> is often a reference to GPS indicating that it's constellation is only
> composed by 24 satellites...
> Example:
> http://www.spacedaily.com/reports/Fa...o_GPS_999.html
>
> Galileo will consist of 30 satellites, six more than the US Global
> Positioning System (GPS). The system will offer several services from
> 2014, becoming fully operational in 2020 when a constellation of 27
> satellites, supported by three spares, is deployed.
>
> It seems only Galileo marketing to me...
> The GPS 24 satellites constellation was the original design, but I
> don't even remember when there was only 24 sats!
> Moreover they count the 3 spares on 30 Galileo satellites!

Here's the current GPS Count: 31


GPS OPERATIONAL ADVISORY 292.OA1
SUBJ: GPS STATUS 19 OCT 2011
1. SATELLITES, PLANES, AND CLOCKS (CS=CESIUM RB=RUBIDIUM):
A. BLOCK I : NONE
B. BLOCK II: PRNS 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14
PLANE : SLOT D6, D1, C2, D4, E3, C6, A4, A3, A1, E6, D2, B4, F3, F1
CLOCK : RB, RB, CS, RB, RB, RB, RB, CS, CS, CS, RB, RB, RB, RB
BLOCK II: PRNS 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 28, 29
PLANE : SLOT F2, B1, C4, E4, C3, E1, D3, E2, F4, D5, B2, F5, B3, C1
CLOCK : RB, RB, RB, RB, RB, RB, RB, RB, RB, CS, RB, RB, RB, RB
BLOCK II: PRNS 30, 31, 32
PLANE : SLOT B5, A2, E5
CLOCK : RB, RB, RB
2. CURRENT ADVISORIES AND FORECASTS :
A. FORECASTS: FOR SEVEN DAYS AFTER EVENT CONCLUDES.
NANU MSG DATE/TIME PRN TYPE SUMMARY (JDAY/ZULU
TIME START - STOP)
B. ADVISORIES:
NANU MSG DATE/TIME PRN TYPE SUMMARY (JDAY/ZULU
TIME START - STOP)
2011083 301528Z Sep 2011 24 UNUSUFN 273/1437-/
2011085 142008Z Oct 2011 01 USABINIT 287/1953-/
C. GENERAL:
NANU MSG DATE/TIME PRN TYPE SUMMARY (JDAY/ZULU
TIME START - STOP)
2011074 042312Z Sep 2011 GENERAL /-/
3. REMARKS:
A. THE POINT OF CONTACT FOR GPS MILITARY OPERATIONAL SUPPORT IS THE GPS
OPERATIONS CENTER AT 719-567-2541 OR DSN 560-2541.
B. CIVILIAN: FOR INFORMATION, CONTACT US COAST GUARD NAVCEN AT
COMMERCIAL 719-567-2541 24 HOURS DAILY AND INTERNET
HTTPS://WWW.NAVCEN.USCG.GOV
C. MILITARY SUPPORT WEBPAGES CAN BE FOUND AT THE FOLLOWING
HTTPS://gps.afspc.af.mil/GPS OR HTTPS://gps.afspc.af.mil/GPSOC

On Oct 19, 2:00*pm, claudegps <claude...@gmail.com> wrote:
> Hello.
> I'm trying to figure out why, when comparing Galileo with GPS, there
> is often a reference to GPS indicating that it's constellation is only
> composed by 24 satellites...
> Example:http://www.spacedaily.com/reports/Fa...uropes_rival_t...
>
> Galileo will consist of 30 satellites, six more than the US Global
> Positioning System (GPS). The system will offer several services from
> 2014, becoming fully operational in 2020 when a constellation of 27
> satellites, supported by three spares, is deployed.
>
> It seems only Galileo marketing to me...
> The GPS 24 satellites constellation was the original design, but I
> don't even remember when there was only 24 sats!
> Moreover they count the 3 spares on 30 Galileo satellites!

GPS is currently limited to 31 satellites on the almanac. But that
limitation will be lifted with the OCX control segment becomes
operational latter this decade.
Plus the GPS III birds will be able to operate PRN codes higher than
the current PRN32 limit.
So its entirely conceivable that by 2020 we could have around 36
operational satellites. Right now there are 30 healthy satellites,
with PRN24 on the almanac unhealthy and PRN27 offline.
At the same time, once Galileo has 30 operational satellites, it could
be more reliable due to the lower average satellite life. But 30
operational for Galileo is far from guaranteed.
If you disregards all paired satellites, then GPS would have less than
24 satellites.
Right now only 18 Galileo satellites are funded.
Its important to realize that even if we have 36 operational GPS
satellites, at any given time we should have around dozen satellites
with single string status (some critical system have no redundancies
left, if that last critical system module fail, then the satellite is
dead).

Marcelo Pacheco

On Oct 19, 12:00*pm, claudegps <claude...@gmail.com> wrote:
> Hello.
> I'm trying to figure out why, when comparing Galileo with GPS, there
> is often a reference to GPS indicating that it's constellation is only
> composed by 24 satellites...
> Example:http://www.spacedaily.com/reports/Fa...uropes_rival_t...
>
> Galileo will consist of 30 satellites, six more than the US Global
> Positioning System (GPS). The system will offer several services from
> 2014, becoming fully operational in 2020 when a constellation of 27
> satellites, supported by three spares, is deployed.
>
> It seems only Galileo marketing to me...
> The GPS 24 satellites constellation was the original design, but I
> don't even remember when there was only 24 sats!
> Moreover they count the 3 spares on 30 Galileo satellites!


I quite often see that annoying reference to 24 GPS satellites.
That's the baseline constellation as defined in the performance
specification .. 4 satellites at the prime slots in 6 planes. But,
also defined is the expanded constellation where B1, D2 and F2
positions are expanded into satellite pairs in fore and aft
locations. That's the 24+3 configuration that's flying now. So if
you want to quantify the NAVSTAR constellation in terms of 'effective'
satellites, more accurately it consists of 27 satellites. Remaining
satellites are placed to backup weak ones in prime slots.

--- CHAS

On Oct 19, 5:51*pm, HIPAR <captc...@verizon.net> wrote:
> On Oct 19, 12:00*pm, claudegps <claude...@gmail.com> wrote:
>
> > Hello.
> > I'm trying to figure out why, when comparing Galileo with GPS, there
> > is often a reference to GPS indicating that it's constellation is only
> > composed by 24 satellites...
> > Example:http://www.spacedaily.com/reports/Fa...uropes_rival_t...
>
> > Galileo will consist of 30 satellites, six more than the US Global
> > Positioning System (GPS). The system will offer several services from
> > 2014, becoming fully operational in 2020 when a constellation of 27
> > satellites, supported by three spares, is deployed.
>
> > It seems only Galileo marketing to me...
> > The GPS 24 satellites constellation was the original design, but I
> > don't even remember when there was only 24 sats!
> > Moreover they count the 3 spares on 30 Galileo satellites!
>
> I quite often see that annoying reference to 24 GPS satellites.
> That's the baseline constellation as defined in the performance
> specification .. 4 satellites at the prime slots in 6 planes. *But,
> also defined is the expanded constellation where B1, D2 and F2
> positions are expanded into satellite pairs in fore and aft
> locations. *That's the 24+3 configuration that's flying now. *So if
> you want to quantify the NAVSTAR constellation in terms of 'effective'
> satellites, more accurately it consists of 27 satellites. *Remaining
> satellites are placed to backup weak ones in prime slots.
>
> --- *CHAS

If you look at the positioning of those the constellation today, there
are 18 prime slots plus pairs. Some pairs are spread a little more
than others, but beyond those 18 truly prime (3 per orbital plane) all
others are pairs (or in some cases triplets).
A constellation composed of 36 uniformly spread slots (6x6) with 9
slots empty would perform hugely better than the current 30
operational satellites, even if three birds were to fail all at once
(but not neighboring satellites). But there are many issues preventing
from moving forward with such an improvement, the primary one is the
funding uncertainty of GPS launches beyond the absolute minimum
requirement to maintain current constellation performance, second
there are always much more important issues facing the brass of
SpaceCom that would propose such an improvement to the civilian
bosses, and third, the military leadership is conservative by nature,
they always want a crazy level of fault tolerance in the system, and
having no pairs doesn't look to the military like a safe system (they
like safety in numbers). But the fact is that uniformly spreading the
available satellites would result in multiple mutual backups between
satellites, reducing the impact of all failures, except for twin
neighbor failures (in which case it would still be less of an impact
than a pair of satellites were to fail).
If you look at the contribution of PRN30 as its closer to midway
between the prime slots to the east and west and look at PDOP maps
during its westerly move, you'll see that just PRN30 moving west has
resulting in sensible improvements to PDOP where PRN30 is flying over.
During the next two months as PRN30 drifts slowly through the midway
point, PDOP improvements will be maintained, but as PRN30 gets closer
to its intended destination this PDOP improvement will be reduced.

The substantial advantage that a full Galileo constellation would have
over GPS is it will have 3 orbital slots with a total of 27 prime
slots plus 3 backups. But that's not going to happen in less than 5
years, considering that only 18 birds are funded right now.

Marcelo Pacheco (always trying to stir some healthy controversy to
make people see through the typical PR of all large organizations of
the world - always an equal opportunity offender).

On 2011-10-19 15:51 , HIPAR wrote:
> On Oct 19, 12:00 pm, claudegps<claude...@gmail.com> wrote:
>> Hello.
>> I'm trying to figure out why, when comparing Galileo with GPS, there
>> is often a reference to GPS indicating that it's constellation is only
>> composed by 24 satellites...
>> Example:http://www.spacedaily.com/reports/Fa...uropes_rival_t...
>>
>> Galileo will consist of 30 satellites, six more than the US Global
>> Positioning System (GPS). The system will offer several services from
>> 2014, becoming fully operational in 2020 when a constellation of 27
>> satellites, supported by three spares, is deployed.
>>
>> It seems only Galileo marketing to me...
>> The GPS 24 satellites constellation was the original design, but I
>> don't even remember when there was only 24 sats!
>> Moreover they count the 3 spares on 30 Galileo satellites!

I can't see your post as I filter gmail originated posts against spam,
so piggy backing on HIPAR's reply.

Extending HIPAR's reply ...

In addition to the additional coverage and spares he mentions for the
GPS' proper, WAAS gives you: 1) additional range (like a GPS satellite),
2) correction data for the coverage area and 3) satellite integrity
data. (EGNOS and MSAS do the same for Europe and Japan).

However, none of this is that important for much further into the future.

With Galileo going up over the next 4 years or so, and GLONASS in place,
not to mention the coming Compass II (China) [and to much lesser extent
the Indian system], there will be an awful lot of navigation satellites
in view at all times all over the planet. Only near the poles will
coverage be less than ideal.

Properly designed receivers will be able to listen to as many satellites
as possible and convert each into representative pseudo ranges in ECEF
coordinates. A receiver can over determine its position to well beyond
diminishing returns - OTOH, this will help navigation in canyons
(natural or urban), mountains, forests, and so on.

Indeed I'm waiting for the etrex 30 to be available in Canada. It has a
GPS and GLONASS receiver and computes PVT based on all the sats it can
see at a time regardless of constellation.

Eventually Galileo and Compass will be available as well ... Imagine
receivers with 3 or 4 entire constellations available at all times ...
with all 4 about 120 satellites with about 40% of them in view where
there are no obstacles, that's 48 ranging sources!

I'm not sure how GLONASS and Compass will figure into commercial
aviation systems. But Galileo will definitely begin to take its place
over time.

--
gmail originated posts filtered due to spam.

On Oct 19, 7:12*pm, Alan Browne <alan.bro...@FreelunchVideotron.ca>
wrote:
> On 2011-10-19 15:51 , HIPAR wrote:
>
>
>
>
>
>
>
>
>
> > On Oct 19, 12:00 pm, claudegps<claude...@gmail.com> *wrote:
> >> Hello.
> >> I'm trying to figure out why, when comparing Galileo with GPS, there
> >> is often a reference to GPS indicating that it's constellation is only
> >> composed by 24 satellites...
> >> Example:http://www.spacedaily.com/reports/Fa...uropes_rival_t...
>
> >> Galileo will consist of 30 satellites, six more than the US Global
> >> Positioning System (GPS). The system will offer several services from
> >> 2014, becoming fully operational in 2020 when a constellation of 27
> >> satellites, supported by three spares, is deployed.
>
> >> It seems only Galileo marketing to me...
> >> The GPS 24 satellites constellation was the original design, but I
> >> don't even remember when there was only 24 sats!
> >> Moreover they count the 3 spares on 30 Galileo satellites!
>
> I can't see your post as I filter gmail originated posts against spam,
> so piggy backing on HIPAR's reply.
>
> Extending HIPAR's reply ...
>
> In addition to the additional coverage and spares he mentions for the
> GPS' proper, WAAS gives you: 1) additional range (like a GPS satellite),
> 2) correction data for the coverage area and 3) satellite integrity
> data. *(EGNOS and MSAS do the same for Europe and Japan).
>
> However, none of this is that important for much further into the future.
>
> With Galileo going up over the next 4 years or so, and GLONASS in place,
> not to mention the coming Compass II (China) [and to much lesser extent
> the Indian system], there will be an awful lot of navigation satellites
> in view at all times all over the planet. *Only near the poles will
> coverage be less than ideal.
>
> Properly designed receivers will be able to listen to as many satellites
> as possible and convert each into representative pseudo ranges in ECEF
> coordinates. *A receiver can over determine its position to well beyond
> diminishing returns - OTOH, this will help navigation in canyons
> (natural or urban), mountains, forests, and so on.
>
> Indeed I'm waiting for the etrex 30 to be available in Canada. *It has a
> GPS and GLONASS receiver and computes PVT based on all the sats it can
> see at a time regardless of constellation.
>
> Eventually Galileo and Compass will be available as well ... Imagine
> receivers with 3 or 4 entire constellations available at all times ...
> with all 4 about 120 satellites with about 40% of them in view where
> there are no obstacles, that's 48 ranging sources!
>
> I'm not sure how GLONASS and Compass will figure into commercial
> aviation systems. *But Galileo will definitely begin to take its place
> over time.
>
> --
> gmail originated posts filtered due to spam.

EGNOS already provides corrections for GLONASS. So I assume in Europe
it's legal to use GPS+GLONASS+EGNOS for safety of life, even though
I'm unaware of any GPS+GLONASS capable aviation receivers.

The ARAIM paper starts to accept all those GNSS systems for aviation,
for future use, a proposal under discussion on ICAO for future multi
constellation/multi frequency GNSS receivers capable of APV (LPV200)
even without SBAS or GBAS. Unfortunately most countries are unwilling
to allow for WAAS/EGNOS/MSAS usage since it's not under national
control (a huge pity). With SBAS + triple constellation + dual
frequency systems, it should be feasible to move the continuity/
integrity monitoring function to the receiver allowing for zero
decision height approaches (category III), but due to the conflict of
interest with the GBAS investment and again the lack of national
control, it's not very likely to move forward.

Marcelo Pacheco

On 2011-10-19 18:55 , macpacheco wrote:
> On Oct 19, 7:12 pm, Alan Browne<alan.bro...@FreelunchVideotron.ca>
> wrote:
>> On 2011-10-19 15:51 , HIPAR wrote:
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>> On Oct 19, 12:00 pm, claudegps<claude...@gmail.com> wrote:
>>>> Hello.
>>>> I'm trying to figure out why, when comparing Galileo with GPS, there
>>>> is often a reference to GPS indicating that it's constellation is only
>>>> composed by 24 satellites...
>>>> Example:http://www.spacedaily.com/reports/Fa...uropes_rival_t...
>>
>>>> Galileo will consist of 30 satellites, six more than the US Global
>>>> Positioning System (GPS). The system will offer several services from
>>>> 2014, becoming fully operational in 2020 when a constellation of 27
>>>> satellites, supported by three spares, is deployed.
>>
>>>> It seems only Galileo marketing to me...
>>>> The GPS 24 satellites constellation was the original design, but I
>>>> don't even remember when there was only 24 sats!
>>>> Moreover they count the 3 spares on 30 Galileo satellites!
>>
>> I can't see your post as I filter gmail originated posts against spam,
>> so piggy backing on HIPAR's reply.
>>
>> Extending HIPAR's reply ...
>>
>> In addition to the additional coverage and spares he mentions for the
>> GPS' proper, WAAS gives you: 1) additional range (like a GPS satellite),
>> 2) correction data for the coverage area and 3) satellite integrity
>> data. (EGNOS and MSAS do the same for Europe and Japan).
>>
>> However, none of this is that important for much further into the future.
>>
>> With Galileo going up over the next 4 years or so, and GLONASS in place,
>> not to mention the coming Compass II (China) [and to much lesser extent
>> the Indian system], there will be an awful lot of navigation satellites
>> in view at all times all over the planet. Only near the poles will
>> coverage be less than ideal.
>>
>> Properly designed receivers will be able to listen to as many satellites
>> as possible and convert each into representative pseudo ranges in ECEF
>> coordinates. A receiver can over determine its position to well beyond
>> diminishing returns - OTOH, this will help navigation in canyons
>> (natural or urban), mountains, forests, and so on.
>>
>> Indeed I'm waiting for the etrex 30 to be available in Canada. It has a
>> GPS and GLONASS receiver and computes PVT based on all the sats it can
>> see at a time regardless of constellation.
>>
>> Eventually Galileo and Compass will be available as well ... Imagine
>> receivers with 3 or 4 entire constellations available at all times ...
>> with all 4 about 120 satellites with about 40% of them in view where
>> there are no obstacles, that's 48 ranging sources!
>>
>> I'm not sure how GLONASS and Compass will figure into commercial
>> aviation systems. But Galileo will definitely begin to take its place
>> over time.
>>
>> --
>> gmail originated posts filtered due to spam.
>
> EGNOS already provides corrections for GLONASS. So I assume in Europe
> it's legal to use GPS+GLONASS+EGNOS for safety of life, even though
> I'm unaware of any GPS+GLONASS capable aviation receivers.
>
> The ARAIM paper starts to accept all those GNSS systems for aviation,
> for future use, a proposal under discussion on ICAO for future multi
> constellation/multi frequency GNSS receivers capable of APV (LPV200)
> even without SBAS or GBAS. Unfortunately most countries are unwilling
> to allow for WAAS/EGNOS/MSAS usage since it's not under national
> control (a huge pity). With SBAS + triple constellation + dual
> frequency systems, it should be feasible to move the continuity/
> integrity monitoring function to the receiver allowing for zero
> decision height approaches (category III), but due to the conflict of
> interest with the GBAS investment and again the lack of national
> control, it's not very likely to move forward.

IIIC will be LAAS (GBAS if you prefer).

IIIA -may- be SBAS - but I'd lean to LAAS.

--
gmail originated posts filtered due to spam.

On Oct 19, 10:07*pm, Alan Browne <alan.bro...@FreelunchVideotron.ca>
wrote:
> On 2011-10-19 18:55 , macpacheco wrote:
>
>
>
>
>
>
>
>
>
> > On Oct 19, 7:12 pm, Alan Browne<alan.bro...@FreelunchVideotron.ca>
> > wrote:
> >> On 2011-10-19 15:51 , HIPAR wrote:
>
> >>> On Oct 19, 12:00 pm, claudegps<claude...@gmail.com> * *wrote:
> >>>> Hello.
> >>>> I'm trying to figure out why, when comparing Galileo with GPS, there
> >>>> is often a reference to GPS indicating that it's constellation is only
> >>>> composed by 24 satellites...
> >>>> Example:http://www.spacedaily.com/reports/Fa...uropes_rival_t...
>
> >>>> Galileo will consist of 30 satellites, six more than the US Global
> >>>> Positioning System (GPS). The system will offer several services from
> >>>> 2014, becoming fully operational in 2020 when a constellation of 27
> >>>> satellites, supported by three spares, is deployed.
>
> >>>> It seems only Galileo marketing to me...
> >>>> The GPS 24 satellites constellation was the original design, but I
> >>>> don't even remember when there was only 24 sats!
> >>>> Moreover they count the 3 spares on 30 Galileo satellites!
>
> >> I can't see your post as I filter gmail originated posts against spam,
> >> so piggy backing on HIPAR's reply.
>
> >> Extending HIPAR's reply ...
>
> >> In addition to the additional coverage and spares he mentions for the
> >> GPS' proper, WAAS gives you: 1) additional range (like a GPS satellite),
> >> 2) correction data for the coverage area and 3) satellite integrity
> >> data. *(EGNOS and MSAS do the same for Europe and Japan).
>
> >> However, none of this is that important for much further into the future.
>
> >> With Galileo going up over the next 4 years or so, and GLONASS in place,
> >> not to mention the coming Compass II (China) [and to much lesser extent
> >> the Indian system], there will be an awful lot of navigation satellites
> >> in view at all times all over the planet. *Only near the poles will
> >> coverage be less than ideal.
>
> >> Properly designed receivers will be able to listen to as many satellites
> >> as possible and convert each into representative pseudo ranges in ECEF
> >> coordinates. *A receiver can over determine its position to well beyond
> >> diminishing returns - OTOH, this will help navigation in canyons
> >> (natural or urban), mountains, forests, and so on.
>
> >> Indeed I'm waiting for the etrex 30 to be available in Canada. *It has a
> >> GPS and GLONASS receiver and computes PVT based on all the sats it can
> >> see at a time regardless of constellation.
>
> >> Eventually Galileo and Compass will be available as well ... Imagine
> >> receivers with 3 or 4 entire constellations available at all times ...
> >> with all 4 about 120 satellites with about 40% of them in view where
> >> there are no obstacles, that's 48 ranging sources!
>
> >> I'm not sure how GLONASS and Compass will figure into commercial
> >> aviation systems. *But Galileo will definitely begin to take its place
> >> over time.
>
> >> --
> >> gmail originated posts filtered due to spam.
>
> > EGNOS already provides corrections for GLONASS. So I assume in Europe
> > it's legal to use GPS+GLONASS+EGNOS for safety of life, even though
> > I'm unaware of any GPS+GLONASS capable aviation receivers.
>
> > The ARAIM paper starts to accept all those GNSS systems for aviation,
> > for future use, a proposal under discussion on ICAO for future multi
> > constellation/multi frequency GNSS receivers capable of APV (LPV200)
> > even without SBAS or GBAS. Unfortunately most countries are unwilling
> > to allow for WAAS/EGNOS/MSAS usage since it's not under national
> > control (a huge pity). With SBAS + triple constellation + dual
> > frequency systems, it should be feasible to move the continuity/
> > integrity monitoring function to the receiver allowing for zero
> > decision height approaches (category III), but due to the conflict of
> > interest with the GBAS investment and again the lack of national
> > control, it's not very likely to move forward.
>
> IIIC will be LAAS (GBAS if you prefer).
>
> IIIA -may- be SBAS - but I'd lean to LAAS.
>
> --
> gmail originated posts filtered due to spam.

I think you don't understand the level of performance promised by
LAAS.
While WAAS today delivers 10-15 meter VPL, LAAS aims for 2-4 meter VPL/
HPL. While WAAS delivers 6.2 seconds alerting time, LAAS promisses 2
second alert time
VPL is vertical protection level, an accuracy level, but instead of
the usual 95-98%, it bounds accuracy at an impressive 99.999%
A CAT IIIB approach has no decision height level, it only requires
enough visibility for taxing, so you really can't be not even 10
meters wrong or you might be off the sides of the runway at landing.

IIIA improves the signal with a better clock, more powerful signal and
operates two clocks at once comparing both clocks. That doesn't
replace SBAS or GBAS.
IIIB with the cross link architecture reduces errors further since the
control segment will be able to upload corrections more often. This
could alleviate the need for SBAS, if all users had dual frequency
receivers, and GPS L5 were at FOC, but then there wouldn't be any
means to calculate VPL and HPL levels for the approach
IIIC adds the enhanced integrity feature, and that's the function that
could kill SBAS combined with the prior features, because GPS IIIC
ranging sources would have an inherent UDRE level associated with them
(an essential requirement to calculate VPL and HPL levels). UDRE is
the confidence bound of that specific ranging source, again, that
would require dual frequency receivers
However each of those features will only take full effect for safety
of life when there's at least 24 satellites with at least that model,
just having 24 GPS IIIA+ will take 20+ years to happen optimistically.
That's way out.
All of those features appear to be insufficient to perform CAT III
approaches, even with an all IIIC constellation, without other GNSS
constellations working together.
I speculate that 10 years from now all new aviation GNSS receivers for
transport aircraft and medium business jets will contain one or two
CSACs, and of course that size aircraft today comes with inertial
reference systems, and the combination of triple+ constellation/dual
frequency receivers with CSAC and INS as cross reference sources might
allow sub meter actual performance, allowing for VPL and HPL in the 2
meter range, and time to alert of less than 2 seconds, all
requirements for CAT III approaches. The time to alert of less than 2
seconds is the most difficult feature to achieve, again I speculate
that the detection of integrity/continuity issues will be moved to the
GNSS receiver, with 24-30 ranging sources, it would be easy to isolate
a few malfunctioning satellites automatically and abort the approach
if there's divergence in the ranging information across the board or
many simultaneous signal losses.

Just having GPS L5 FOC plus a full 30 galileo constellation along with
GLONASS replacing the older satellites will happen much sooner than
having at least 24 GPS IIIB satellites. The jury is still out on
Beidou performance without a public ICD.

Marcelo

[cut]

> The substantial advantage that a full Galileo constellation would have
> over GPS is it will have 3 orbital slots with a total of 27 prime
> slots plus 3 backups. But that's not going to happen in less than 5
> years, considering that only 18 birds are funded right now.

Interesting point