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Discuss the F-35 Lightning II
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boogieman

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Unread post28 Jul 2020, 00:20

That would make more sense. Haven't been able to find a source stating it though? Most simply claim it is half the diameter of ATACMS.
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marauder2048

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Unread post28 Jul 2020, 00:48

The GMLRS tubes are 12.2 inches in diameter. So it depends on how big the PrSM tube is and if they go
for a side-by-side or staggered arrangement.
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boogieman

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Unread post28 Jul 2020, 01:08

Right, although the GMLRS missiles themselves are ~227mm/8.9in IIRC

https://asc.army.mil/web/portfolio-item ... e-warhead/

PrSM being significantly wider (and therefore having much greater volume for propellant) is the only way I can make sense of it achieving over double the max range of AARGM-ER.
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marauder2048

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Unread post28 Jul 2020, 02:56

boogieman wrote:Right, although the GMLRS missiles themselves are ~227mm/8.9in IIRC


Pretty sure the diagram is showing outer tube diameter; ER-GMLRS is larger in diameter (11 inches IIRC)
so they can get away with a pretty thin inner tube diameter.

In fact, ER-GMLRS is probably the better comparison to AARGM-ER; NG was pitching AARGM-ER in a surface
launched capacity.


boogieman wrote:PrSM being significantly wider (and therefore having much greater volume for propellant) is the only way I can make sense of it achieving over double the max range of AARGM-ER.



Could be dual pulse as well with some highly loaded grain design.

The front-end on PrSM looks to have a much better L/D so there's potentially much lower frontal drag.
The base looks to be boat-tailed as well so less base drag. I think Lockheed was only claiming 499 km with their first spiral.
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wrightwing

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Unread post28 Jul 2020, 03:47

boogieman wrote:Ok team, I’ve got one here that has me scratching my head. I was reading up on PrSM and the future roadmap for it. At ~4m long and ~30cm diameter it has similar dimensions to AARGM-ER. Here is the head scratcher:

AARGM-ER - an air to surface weapon that benefits from being launched at speed & altitude - is supposed to have a range somewhere in the order of 300km.

PrSM - a surface to surface weapon with a larger warhead - is supposed to reach twice that far (with planned growth out to 800km).

So, how is this possible?

In my reading I had thought that new propellants might be in the mix for the PrSM, but then I came across comments like this:
“'that's bunk' due to the hijacking R&D budgets for nonsensical marketing memes both the USN propulsion and warhead technology budgets for advanced compounds were effectively zeroed”

“There is NO new propellant which may provide 50% more range. The Navy's advanced energetics program was killed more than a decade ago by DoD management because of pouring the R&D money into lasers and railguns. Small money were still provided for 6.1 research in the universities, but 6.2 and 6.3 were effectively drained out. Today, after failure of the most promises made by railgun marketeers, there is an attempt to revive the energetics research in the Navy, but it's still lacking the funding”
https://breakingdefense.com/2020/06/arm ... hips-sams/

So I leave this one to the F16.net brains trust – why the massive discrepancy in range between AARGM-ER and PrSM? Why is it that the former has less range, despite the fact that it enjoys more favourable kinematic launch conditions? And finally, is it true that budgets for new propellants were slashed, or has propellant R&D continued elsewhere?

A quick google search would seem to cast at least some doubt over the claims about energetics research:
The successful Phase II Advanced Solid Rocket Motor Technology for Tactical Missiles program will serve to provide a performance enhancing capability to increase the propulsive energy of next generation envelope constrained tactical solid rocket motorsby approximately 20 percent.The technology of this program provides the rocket motor design and development community a totally new tool to be used in the design of next generation of tactical solid propellant rocket motors.

https://www.sbir.gov/node/666918

The AARGM-ER's 300km range is for a low altitude flight profile. If it flies at high altitudes, then it's more like 500+ km.
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boogieman

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Unread post28 Jul 2020, 05:20

Those are pretty eye-watering stats no matter which way you cut it. Reaching over 500km with a ~4m missile seems enormous, especially in the case of a PrSM round that must do so from a standing start at ground level. Just compare to vanilla HARM/AARGM for a sense of what a monstrous leap that is. Not saying it’s bunkum, more trying to understand how it is physically possible.
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Unread post28 Jul 2020, 06:59

boogieman wrote:Those are pretty eye-watering stats no matter which way you cut it. Reaching over 500km with a ~4m missile seems enormous, especially in the case of a PrSM round that must do so from a standing start at ground level. Just compare to vanilla HARM/AARGM for a sense of what a monstrous leap that is. Not saying it’s bunkum, more trying to understand how it is physically possible.


ATACMS unitary seems to be carrying a lot of inert mass:
1595 lbs of propellant,
500 lbs of warhead
+ inert mass
______________________

= launch weight of 3270 lbs.

And PrSM almost certainly has a smaller warhead.
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boogieman

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Unread post28 Jul 2020, 09:26

Yes I imagine miniaturizing all the non-explosive bits and maximizing the fuel fraction would have been paramount. Last I heard the warhead was 200lbs (unitary), which sounds about right. Assuming they will use a MMW or IIR terminal seeker, so 200lbs ought to be ample for destroying the emitters this thing is designed to kill. Something bigger would have been ideal for taking down larger ships, but that is why you fire them en masse.
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marauder2048

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Unread post28 Jul 2020, 17:17

boogieman wrote: Assuming they will use a MMW or IIR terminal seeker, so 200lbs ought to be ample for destroying the emitters this thing is designed to kill. Something bigger would have been ideal for taking down larger ships, but that is why you fire them en masse.


AFAIK, Cross Domain ATACMS (unitary with the JAGM seeker stack) is still moving forward.
It has Harpoon's warhead after all.
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hornetfinn

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Unread post29 Jul 2020, 07:28

boogieman wrote:Ok team, I’ve got one here that has me scratching my head. I was reading up on PrSM and the future roadmap for it. At ~4m long and ~30cm diameter it has similar dimensions to AARGM-ER. Here is the head scratcher:

AARGM-ER - an air to surface weapon that benefits from being launched at speed & altitude - is supposed to have a range somewhere in the order of 300km.

PrSM - a surface to surface weapon with a larger warhead - is supposed to reach twice that far (with planned growth out to 800km).

So, how is this possible?


There are likely several reasons for this. I can think of at least these:

- PrSM has only INS+GPS guidance which are very small nowadays while AARGM-ER has a lot more complex and larger guidance section. This very probably counters the larger warhead in PrSM.

- AARGM-ER guidance also likely takes a lot more power to function during the missile flight. INS+GPS in PrSM doesn't need much power and can do with much smaller power supply unit

- PrSM flies ballistic (or possibly quasi-ballistic) flight path which is lot more efficient than the flight path of anti-radiation missiles which likely fly a lot shallower flight path at lower altitudes to get to target. ARM needs to fly a path that allows the seeker to see the target early enough and allows maneuvering to hit it.
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boogieman

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Unread post29 Jul 2020, 08:21

hornetfinn wrote:
boogieman wrote:Ok team, I’ve got one here that has me scratching my head. I was reading up on PrSM and the future roadmap for it. At ~4m long and ~30cm diameter it has similar dimensions to AARGM-ER. Here is the head scratcher:

AARGM-ER - an air to surface weapon that benefits from being launched at speed & altitude - is supposed to have a range somewhere in the order of 300km.

PrSM - a surface to surface weapon with a larger warhead - is supposed to reach twice that far (with planned growth out to 800km).

So, how is this possible?


There are likely several reasons for this. I can think of at least these:

- PrSM has only INS+GPS guidance which are very small nowadays while AARGM-ER has a lot more complex and larger guidance section. This very probably counters the larger warhead in PrSM.

- AARGM-ER guidance also likely takes a lot more power to function during the missile flight. INS+GPS in PrSM doesn't need much power and can do with much smaller power supply unit

- PrSM flies ballistic (or possibly quasi-ballistic) flight path which is lot more efficient than the flight path of anti-radiation missiles which likely fly a lot shallower flight path at lower altitudes to get to target. ARM needs to fly a path that allows the seeker to see the target early enough and allows maneuvering to hit it.

Interesting, thanks for the input. That said it seems that the PrSM actually does use more than just GPS/INS - a dual mode RF(MMW?)/IIR seeker for terminal guidance:

https://www.janes.com/defence-news/news ... 4600d1a592

Not sure how much volume this would occupy vs the AARGM-ER setup. I certainly take your point on flight profiling though - having to push its way through thicker air at lower altitude could be very costly for the AARGM-ER in terms of range performance.
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hornetfinn

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Unread post29 Jul 2020, 08:37

Oh, you seem to be correct about that. It seems like PrSM will be upgraded with multimode seeker for improved precision and better targeting flexibility. Multimode seeker is likely quite a bit smaller than anti-radiation seeker which needs a large antenna and quite a lot of computing power. Multimode seekers are installed in very small weapons like Spear 3, StormBreaker and even JAGM.
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boogieman

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Unread post29 Jul 2020, 09:06

Yep, look the capabilities of the weapon seem pretty impressive from where I am sitting. To get that kind of range out of such a small missile is staggering and the design makes a lot of sense to me vs ATACMS. Twice as many shots to overwhelm the IADS, over twice the reach and a more versatile payload (vs bomblets/SFMs) to boot. We are on track to acquire an MLRS capability here in Australia (finally) so I am hopeful that a HIMARS + GMLRS/GMLRS-ER/PrSM combo may be in the pipeline.
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hornetfinn

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Unread post29 Jul 2020, 09:33

It's definitely very impressive system. In Finland we also have MLRS systems but cancelled the planned order for ATACMS some years ago due to cost reasons. Now we only have GMLRS for them and I'd definitely like we got PrSM also but I think there is good chance that it will not be bought due to cost reasons again. Maybe we could buy GMLR-ER though as the extra range could definitely be useful.
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