Are inertial navigating devices being improved ?

[stilton]

Most jet transports still use inertial units as a source for navigation and their inputs provide data for aircraft instrumentation



Of course inertial position data is updated by GPS but, especially in light of recent events those signals can’t always be depended on



INS by itself is still an outstanding technology, independent, self contained with no need for any outside signals, so good it allowed us to go to the moon


My question is, are today’s inertial navigators being improved on to refine their performance and improve their accuracy, or have their parameters remained static for some time ?

[tdracer]

Most jet transports still use inertial units as a source for navigation and their inputs provide data for aircraft instrumentation



Of course inertial position data is updated by GPS but, especially in light of recent events those signals can’t always be depended on

INS by itself is still an outstanding technology, independent, self contained with no need for any outside signals, so good it allowed us to go to the moon

My question is, are today’s inertial navigators being improved on to refine their performance and improve their accuracy, or have their parameters remained static for some time ?
I believe that last major improvement in stand alone INS was the introduction of the ring laser gyros - a huge improvement over the old spinning gyros.
I suspect there have been subtle improvements in the ring laser gyros due to the incremental improvements in the associated electronics. But I don't think the basic technology has changed aside from being able to use GPS updates.

[MechEngr]

I think that's an overestimation of the capacity of the Apollo INU. They used star sighting for updating the orientation and location of the spacecraft as well as ground based tracking. The INU was used as a controls input but was not left standalone and uncorrected for the entire flight.

In the intervening time the main change has been to replace mechanical gyros with lasers, particularly fiber-optic systems, and with MEMS devices to drop the size, power, and cost. It's likely that precision could go up, but unless there is some system need for it the other drivers are more important. GPS has removed much of the need for long term stability and it's possible to build detailed terrain maps to manage a flight path over land that doesn't require an inertial reference. I can also imagine a system based on passive reception from cell towers to manage position and orientation information within a few meters. From my understanding a street mapping effort also mapped Wi-Fi as well - that could also be used for location. I'm sure some 3 letter agencies already have tech to do that.

[Specaircrew]

[QUOTE=stilton;11188944]


Of course inertial position data is updated by GPS but, especially in light of recent events those signals can’t always be depended on


To be pedantic, the inertial position is never updated once you've aligned it and selected Nav. GPS updates the FMS position which is the PPOS that your aircraft is using. As the FMS calculates PPOS from the inputs of up to 3 x IRS, Radio aids and GPS the loss of GPS will cause the FMS posn to shift slightly as it's got one less input in the mix. RLG's and solid state accelerometers will always suffer from some small inaccuracies, so integrated over time you're still going to get some IRS drift.

I think the biggest advance in IRS technology in recent years is the ability to realign in the air for some recent equipment, something that used to be impossible.......and still is if you're taking ATPL exams ;-)

[stilton]

[QUOTE=stilton;11188944]


Of course inertial position data is updated by GPS but, especially in light of recent events those signals can’t always be depended on


To be pedantic, the inertial position is never updated once you've aligned it and selected Nav. GPS updates the FMS position which is the PPOS that your aircraft is using. As the FMS calculates PPOS from the inputs of up to 3 x IRS, Radio aids and GPS the loss of GPS will cause the FMS posn to shift slightly as it's got one less input in the mix. RLG's and solid state accelerometers will always suffer from some small inaccuracies, so integrated over time you're still going to get some IRS drift.

I think the biggest advance in IRS technology in recent years is the ability to realign in the air for some recent equipment, something that used to be impossible.......and still is if you're taking ATPL exams ;-)



That’s correct but it doesn’t answer my question

[Alpine Flyer]

A bit OT but Honeywell is testing star tracking and magnetic field anomaly as an alternative to GPS. I'd also suppose that general improvements in electronics will allow RLG INS to gain accuracy (e.g. by being able to detect smaller differences in frequency). What's almost equally amazing is the improvement in Piezo gyros for GA applications.

[FlightDetent]

My question is, are today’s inertial navigators being improved on to refine their performance and improve their accuracy, or have their parameters remained static for some time ?
Research done on this one: https://www.researchgate.net/publication/332220773_Analysis_of_ring_laser_gyroscopes_including_laser_ dynamics

https://www.caltech.edu/about/news/new-chip-based-laser-gyroscope-measures-earths-rotation

While the rotation seems mastered, what about SoA acceleration measurement?

[stilton]

A bit OT but Honeywell is testing star tracking and magnetic field anomaly as an alternative to GPS. I'd also suppose that general improvements in electronics will allow RLG INS to gain accuracy (e.g. by being able to detect smaller differences in frequency). What's almost equally amazing is the improvement in Piezo gyros for GA applications.


Very interesting, star tracking was used by the SR71 for navigation, it’s good to see alternatives to GPS being developed that can’t be jammed

[gums]

Salute!

Ahem.....

1) Star tracking was used by the most accurate ICBM kniown as well as the submarine Trident INS. Worked on that one and was amazed. As long as initial position of launch was within a few miles (SECRETNOFORN). the INS rotated all the gimbal shells to align a hole on the star of interest. So that sucker could launch from a few thousand miles away and hit inside of a football stadium with a big bomb.

2) The advent of super clocks made the RLG INS and GPS possible, as well as optics that used the interference patterns of the laser beam for the RLG systems. Add in fairly cheap digital accelerometers for the short term and you have very good systems. The RLG's and similar are super, as virtually zero mechanical drift as we had in the 60's INS that used spinning gyro's. The strapdown INS systems for new missiles are super for short time-of-flight navigation if they have a good positional update at launch. For a minute or so, their posiitonal accuracy is scary. Body rates and attitude are easy peasy within a second of pressing the launch button..

3) Over dependence upon GPS, IMHO, is not very viable for the military due to somebody mesing around or actually destroying much of the system. Best bet for updates is using a star or landmark visible with optical sensors or radar. We did this in late 60's to great effect.

4) As far back as 1970, the A-7D could do airborne alignments of the INS and overall nav system by using the doppler system we had. Had to wait about 2 minutes or so to get "platform" level. Refinement and pointing north could be done after launch. A decent intial position helped, but you could take off and flyover a point that was on out projected map and get a decent position - say within 1000 feet or so.

Gums sends...

[EEngr]

Probably improvements in MEMS accelerometer precision due to process improvements in chip manufacturing. What used to be very small and fiddly dimensions are now huge compared to current microprocessor component sizes.

[Alpine Flyer]

Very interesting, star tracking was used by the SR71 for navigation, it’s good to see alternatives to GPS being developed that can’t be jammed
I read about the SR-71 and was baffled how that was achieved with 1960s technologgy,

[gums]

Salute!

What seems to be missing here is the advancement in clocks The folks working the "longitude problem" back then would have cut off part of their body to have the accuracy of a fairly modest wristwatch you can buy now at the drugstore.

Our clocks got so much better in later 60's and onward, that we could do things the old navigators could not even dream of. Further, the GPS sats give a time synch with the nav message, so your unit can back in the time the message was transmitted, and then do it for three or more sats. Easy peasy with three or more positions and nanosecond times, to plot the time of arrival arcs and such - think the MA370 problem, huh? For stationary receivers like surveyors use, you can track the carrier wave itself and resolve the phase of the wave to a few millimeters.

The advances in MEMS and super sftwe algorithms have made small GPS and GPS-aided inertial systems orders of magnitude better than what I flew back in the 70's and 80's.

Gums sends...

[aek]

If the thing is flying fast then no problem because the mission does not take a long time. In a more useful application (e.g. a ship) it's difficult to reach true autonomy, because of number of factors. Periodic correction seems more practical approach. That again brings us to a global navigation system. GNSS works fine but it can't be the only option because who's said the nature will always be on the our side? Everyone knows that but little is achieved so far because of no commercial interest. AFAIK in the Trump era, the government program to develop a backup navigation system was announced and the three companies were asked for proposals. No idea about any real outcome from that. Anyway it's not about new technology. Such systems were in use well before satellites. They all were using low frequencies so the antennas were bulky. But it's not inevitable. Seen a nice tiny part that combines GPS patch antenna and H-field e-LORAN antenna. Designed specifically for mobile phones. So the only problem is commercialization. No enemy no funding. Seems not any more.