Bury everything at least 200 ft deep in solid rock!

[NomoneyNohoney]

https://www.ausairpower.net/GBU-28.html

Technical improvisation in times of war is an artform, and a very good metric of where real capabilities lie. Those who can cobble together a vitally needed resource at short notice, with limited time and budgets, are worthy of admiration - their efforts more than often produce decisive results....This is a remarkable story of focussed technical effort, ingenuity and clever improvisation, and without doubt the shortest development cycle for any production weapon in modern military history.

[tacpot12]

Interesting story. Now Barnes Wallis' Grand Slam bombs have been beaten in size by the US's GBU-57A/B "Massive Ordenance Penetrator" or MOP. With a mass of 30,000 lbs the MOP is comfortably larger than the 22,000 lb Grand Slam bombs.

[gryffron]

It's surprising what can be achieved when you remove all budget and "Quality" (Capital Q) constraints. And probably a fair few safety considerations too.

I've actually been on the design end of projects like this.

"The army want it and they want it NOW!"
"Ok, we'll drop everything and get on with it."
...
"Will it work?"
"Dunno, we haven't tested it yet"
"No matter. We'll send it out to the field and they'll let you know the results"
...
"It worked brilliant, thanks. We'll have 100 more. Ship them individually as soon as they're ready."

Considering MOD procurement usually take 12 months to scratch their bottoms, it's amazing how fast everything moves when they just get out of the way.

Gryff

[XFool]

https://www.ausairpower.net/GBU-28.html

"The GBU-37 GAM-113 weapon employs the BLU-113 penetrator and a modified Northrop GBU-36 GAM-84 GPS inertial guided tailkit."

Anyone know what exactly "GPS inertial guided" means?

TIA.

[Gerry557]

Yes wars do lead to improvisations. The need v cost basis equation often tilts to the other side.

You only have to look back to the Falklands. The efforts to get a Vulcan bomber over Stanley. Nimrods with fuel hoses running down the walk ways for I flight refueling. Helicopters being converted for in flight refueling.Ships being adapted at short notice.

Lots wouldn't be allowed in peacetime.

[ReformedCharacter]

https://www.ausairpower.net/GBU-28.html

"The GBU-37 GAM-113 weapon employs the BLU-113 penetrator and a modified Northrop GBU-36 GAM-84 GPS inertial guided tailkit."

Anyone know what exactly "GPS inertial guided" means?

TIA.

I think it means that it uses both GPS and inertial guidance, probably using the former to update the latter to correct for inertial guidance drift.

RC

[XFool]

Anyone know what exactly "GPS inertial guided" means?

I think it means that it uses both GPS and inertial guidance, probably using the former to update the latter to correct for inertial guidance drift.

Um. Possibly.... But then, why not just rely on GPS? My three quick thoughts were:

1. It's a mistake (or BS), should just have been "GPS guided"

2. It uses a mixture of both GPS and inertial guidance continually, as you suggest. But then I don't quite understand how that would actually work

3. It uses an 'External GPS'/'Internal Inertial' handover system - to defeat GPS jamming from the ground at the target?

- Aircraft uses powerful onboard GPS system to continually update the bomb while in flight, the aircraft body helping to screen from ground based GPS jamming. At the moment of drop, the bomb's navigation switches over to internal inertial guidance (unjammable) for the short distance to the target.

[scrumpyjack]

Presumably GPS can be subject to reception interference whereas inertial guidance could not be affected by external things.

I know sometimes my golf gps distance thingummy can have great difficulty determining where it is!

Sorry, just seen Xfool's post saying the same thing!

[ReformedCharacter]

I think it means that it uses both GPS and inertial guidance, probably using the former to update the latter to correct for inertial guidance drift.

Um. Possibly.... But then, why not just rely on GPS? My three quick thoughts were:

1. It's a mistake (or BS), should just have been "GPS guided"

2. It uses a mixture of both GPS and inertial guidance continually, as you suggest. But then I don't quite understand how that would actually work

3. It uses an 'External GPS'/'Internal Inertial' handover system - to defeat GPS jamming from the ground at the target?

- Aircraft uses powerful onboard GPS system to continually update the bomb while in flight, the aircraft body helping to screen from ground based GPS jamming. At the moment of drop, the bomb's navigation switches over to internal inertial guidance (unjammable) for the short distance to the target.

The external measurement may be made by using either another inertial system or a non-inertial system. As long as the same kinematic quantity can be derived from the non-inertial data, transfer alignment can be accomplished. In-flight alignment (IFA) of a missile inertial system using GPS is an excellent example of a non-inertially derived measurement. GPS-measured position or velocity can be compared to position and velocity estimates produced from IMU measurements. Comparing these data allows a determination of the inertial-system attitude with respect to the GPS coordinate system

https://secwww.jhuapl.edu/techdigest/Content/techdigest/pdf/V28-N04/28-04-Bezick.pdf

RC

[XFool]

...OK thanks.

So, to summarise very simply (but hopefully reasonably accurately), GPS is good for moment to moment location wrt GPS coordinate system. Inertial navigation can show real time orientation, and rate change of same, of missile. Both are combined for accurately steering the missile to the target.

[servodude]

...OK thanks.

So, to summarise very simply (but hopefully reasonably accurately), GPS is good for moment to moment location wrt GPS coordinate system. Inertial navigation can show real time orientation, and rate change of same, of missile. Both are combined for accurately steering the missile to the target.

GPS updates in the order of seconds
Missiles travel really quickly.
Everything is noisy and inaccurate when you are going that fast so it's a classic use case for a Kalman filter to predict where it (probably) is