RUR-5 ASROC and RUM-139 VL-ASROC (VLA)

[NMaude]

Though I'm sure ruining the day of the Pakistani Navy is also on their to-do list.

I suspect that the Pakistani navy would be easier to deal with than the PLA:N.

 

[NMaude]

I've stumbled crossed this rather technical paper (There's a lot of maths in it) concerning the dynamic equations for initialising the VLA autopilot.

Dynamic Equations for Initialization of the Vertical Launch ASROC Autopilot. Revision​

 

[timmymagic]

Would be interesting to compare the US, Japanese and S.Korean versions of ther VL-ASROC.

Worth also comparing the Italian MILAS and Russian SS-N-16 Stallion, which has an interesting way of launching.

 

[NMaude]

I was thinking in regards to the RUR-5 ASROC during the late 50s/early 60s was there any thought given to a super-ASROC? By super I mean a much larger launch booster sized to launch a 21" torpedo.

 

[Josh_TN]

I was thinking in regards to the RUR-5 ASROC during the late 50s/early 60s was there any thought given to a super-ASROC? By super I mean a much larger launch booster sized to launch a 21" torpedo.

Not that I’m aware. It would involve six times the weight. What would be the goal?

 

[TomS]

Grebe (X-SUM-N-2) was actually based around a 21-inch torpedo payload (initially Mk 35, then the lightened Mk 41 or Mk 34). There were planned versions with ranges of 8,000-40,000 yards.

The main problem seems to have been that all of these outranged the detection capacity of existing sonars (less than 5000 yards), making them rather pointless. Then, when sonar performance improved and they revisited the idea with RAT and ASROC, lightweight torps were good enough to chase most sub targets.

 

[Scott Kenny]

Grebe (X-SUM-N-2) was actually based around a 21-inch torpedo payload (initially Mk 35, then the lightened Mk 41 or Mk 34). There were planned versions with ranges of 8,000-40,000 yards.

The main problem seems to have been that all of these outranged the detection capacity of existing sonars (less than 5000 yards), making them rather pointless. Then, when sonar performance improved and they revisited the idea with RAT and ASROC, lightweight torps were good enough to chase most sub targets.

Not sure I agree with that then, and we're definitely at the point now where you need a lot more range than you can get out of a 12.75" torpedo to do more than chase the submarine away.

Not that I’m aware. It would involve six times the weight. What would be the goal?

Well, a Mk37 or 2-cell DM2A4 is only twice the weight of a Mk54... 1500lbs versus ~800 (including the parachute pack, ~600 without it).

But the goal would be greater range than what you can get out of an LWT.

 

[Josh_TN]

Not sure I agree with that then, and we're definitely at the point now where you need a lot more range than you can get out of a 12.75" torpedo to do more than chase the submarine away.



Well, a Mk37 or 2-cell DM2A4 is only twice the weight of a Mk54... 1500lbs versus ~800 (including the parachute pack, ~600 without it).

But the goal would be greater range than what you can get out of an LWT.

If you need greater range, increase the size of the booster, not the torpedo. It would be better to just start out closer to the target in the air rather than increase the underwater run time. Mk54 performance is adequate, and I believe the mod 2 will adopt a lithium steam powered motor like the mk50, which will increase speed and acceleration.

 

[Scott Kenny]

If you need greater range, increase the size of the booster, not the torpedo. It would be better to just start out closer to the target in the air rather than increase the underwater run time. Mk54 performance is adequate, and I believe the mod 2 will adopt a lithium steam powered motor like the mk50, which will increase speed and acceleration.

The problem is that modern submarines like Yasen, Virginias, Astutes, etc, are capable of outrunning the LWTs even if they land practically on top of the sub.

Sub runs some 10km from where the ASROC lands, and then goes back to work.

 

[NMaude]

My idea of super VLA would be one that launches a Mk-48 ADCAP using the SM-3 Block-II version of the Mk-72 launch booster.

 

[Josh_TN]

The problem is that modern submarines like Yasen, Virginias, Astutes, etc, are capable of outrunning the LWTs even if they land practically on top of the sub.

Sub runs some 10km from where the ASROC lands, and then goes back to work.

I believe that mk 54 uses a mk 46 propulsion setup and achieves a speed in the mid 40s. No boat is outrunning that. The mod 2 version is going to adopt the steam powered engine of the mk50, which increases top speed and acceleration. That seems like a better solution to me.

EDIT: also presumably there is an option to simply fire a second ASROC in front of the boat. A sub at flank is blind.

 

[TomS]

Not sure I agree with that then, and we're definitely at the point now where you need a lot more range than you can get out of a 12.75" torpedo to do more than chase the submarine away.

In 1957, RAT with a 10-inch Mk 43 Mod 4 torpedo could run down an 11-knot sub, going up to 16 knots for the projected Mod 6 torpedo. That would not deal with the 30-knot November SSNs just entering construction, but the vast majority of threat subs at the time would still be Zulus or Whiskeys. which would be caught. The big problem was that RAT could not reliably put the torpedo close enough to the aimpoint to leave it in a favorable geometry to engage the sub.

ASROC fixed the accuracy problem with larger fins, and simultaneously upgraded to the larger diameter Mk 44 torpedo. But by that point, the torpedo was an afterthought -- ASROC was always intended to be mainly a nuclear depth bomb delivery system. I don't care how fast a sub runs, it can't outpace a ~Mach 1 rocket with a nuke on it.

 

[sferrin]

Red Shark is very much in the same class as VLA and the Type 07 -- range somewhere between 20 and 40 km, depending on source. The Chinese Yu-8 also seems to be in the same ballpark, maybe 50 km but still nowhere close to the range of the Indian SMART. All of these missiles, aside from SMART, can be targeted from onboard sensors, at least in theory (50 km is pushing it, especially since Yu-8 has a much shorter ranged payload than the Western designs.)

I sincerely cannot figure out the use case for SMART, but I'm sure it makes sense to the Indians.

Maybe make it easier for BAMS to stay on station longer by having the weapons off-board?

 

[sferrin]

My idea of super VLA would be one that launches a Mk-48 ADCAP using the SM-3 Block-II version of the Mk-72 launch booster.

A Mk-48 weighs nearly 4,000lbs. If you want longer range just bring back Sea Lance.

 

[NMaude]

A Mk-48 weighs nearly 4,000lbs.

The Mk-72 has a thrust somewhere around 50-60,000Lb.

If you want longer range just bring back Sea Lance.

I know but what I suggested uses already existing hardware.

 

[TomS]

The Mk-72 has a thrust somewhere around 50-60,000Lb.



I know but what I suggested uses already existing hardware.

I very much doubt a current Mk 48 can survive being flung out of a launch tube by a rocket and then dropped back in the water at high speed. It was never designed for those sorts of stresses.

Now, when the Navy talked about a less expensive heavyweight torpedoes (RAPTOR) earlier this year, they hinted at alternative launch platforms, but that is almost certainly a cheap anti surface torpedo, not an ASW one.

There's also a cost issue. One Mk 48 is >$5 million. Plus $1 million for the booster, plus whatever changes are needed to allow it to survive the new environment, and suddenly we are looking a weapon costing nearly as much as an early SM-3.

 

[NMaude]

I very much doubt a current Mk 48 can survive being flung out of a launch tube by a rocketand then dropped back in the water at high speed. It was never designed for those sorts of stresses.

I don't know what the launch acceleration would be but given how heavy the Mk-48 is it's probably low, that being said some redesign of the Mk-48's internal components might be needed. As for entry into water it wouldn't be high speed due it using a parachute (Just like with the Mk-46/54 does in the VLA) but the Mk-28 torpedo stabiliser is probably too small so new, larger parachute would be needed.

There's also a cost issue. One Mk 48 is >$5 million. Plus $1 million for the booster, plus whatever changes are needed to allow it to survive the new environment

True but such a weapon would probably be used for higher value targets such as an SSBN for example.

 

[Scott Kenny]

True but such a weapon would probably be used for higher value targets such as an SSBN for example.

If you get close enough to drop a super ASROC onto an SSBN, either you got so unbelievably lucky the entire crew needs to buy lottery tickets in every port or that boomer captain needs to die because he's a danger to everyone in the ocean.

 

[NMaude]

If you get close enough to drop a super ASROC onto an SSBN, either you got so unbelievably lucky the entire crew needs to buy lottery tickets in every port or that boomer captain needs to die because he's a danger to everyone in the ocean.

Good points however I was just using the SSBN as an example of a high-value target for use as a rocket-boosted Mk-48 could be used to destroy.

Plus $1 million for the booster

I have a hard time believing that a Mk-72 rocket-booster would cost $1 million (The most expensive part of a missile is its GCU).

 

[sferrin]

The Mk-72 has a thrust somewhere around 50-60,000Lb.

960lbs of propellant and a burn time of ~7 seconds. Thrust is probably closer to ~38k and that's with an ISP of 275. Not sure how far a Mk72 would throw a Mk48 (and the airframe to tie it together, parachute, structural mods, nosecaps, etc.), but I doubt it would be worth the hassle.

 

[TomS]

I have a hard time believing that a Mk-72 rocket-booster would cost $1 million (The most expensive part of a missile is its GCU).

Its not easy to break out, but if the price of an SM-6 is around $4.4 million and the cost of an SM-2 Block IIIC conversion kit is $2.4 million (both TWZ numbers), then the Mk 72 is easily in the ballpark of $1 million.

 

[NMaude]

(and the airframe to tie it together,

I thought about what you'd use for the airframe and it occurred to me that if you used the SM-3 Block-II version of the Mk-72 booster then a modified tail-control section from the SM-3 Block-II.

but I doubt it would be worth the hassle.

Probably not but it was an interesting idea to think about.

The problem is that modern submarines like Yasen, Virginias, Astutes, etc, are capable of outrunning the LWTs even if they land practically on top of the sub.

Maybe the USN should look at reintroducing a medium caliber torpedo, basically a homing 18" torpedo designed to be rocket-launched like with the VLA.

 

[Josh_TN]

The Mk-72 has a thrust somewhere around 50-60,000Lb.



I know but what I suggested uses already existing hardware.

That assumes the booster and mk 48 fit a Mk 41 and that a mk 48 can survive the thrust, neither of which is a given or in the first case likely.

 

[Josh_TN]

I don't know what the launch acceleration would be but given how heavy the Mk-48 is it's probably low, that being said some redesign of the Mk-48's internal components might be needed. As for entry into water it wouldn't be high speed due it using a parachute (Just like with the Mk-46/54 does in the VLA) but the Mk-28 torpedo stabiliser is probably too small so new, larger parachute would be needed.



True but such a weapon would probably be used for higher value targets such as an SSBN for example.

Why would an escort ever be near an SSBN? I am struggling to see a scenario where two or three VLAs could not do a better job than a mythical heavyweight torp on a booster.

 

[NMaude]

That assumes the booster and mk 48 fit a Mk 41

It would almost certainly need a new launcher.

and that a mk 48 can survive the thrust

It's likely that some sort of structural modifications to the design would be required but given how heavy a Mk-48/Mk-72 combination (And the weight of the airframe that would mate the Mk-72 with the Mk-48) launch acceleration may be fairly low (~5-6Gs maybe).

Why would an escort ever be near an SSBN?

I mentioned the SSBN as an example of a high-value target that would just such a weapon.

 

[Scott Kenny]

Maybe the USN should look at reintroducing a medium caliber torpedo, basically a homing 18" torpedo designed to be rocket-launched like with the VLA.

I mean, the Mk37 was basically just that. 19" weapon that had some 1" spacers around the outside to let it swim out of a 21" torpedo tube, and it's half the length and weight of a Mk48 (or a WW2 Mk14).

And modern helicopters have enough horsepower to carry a ~1500lb weapon plus all the sonar gear, so you can still use the same torpedoes between ASROC, helo, and ship launched. Just replace the Mk32 triple tube launchers with a single 21" tube like they did in the 1970s on the FRAMcans (or a single 21" tube in addition to the Mk32 triplets).

Looking at things the other way, it might be interesting to install a couple of 12.75" torp tubes to use against patrol craft etc in the littorals. Targets not big enough to use a Mk48 on if you have something smaller.

 

[Scott Kenny]

Good points however I was just using the SSBN as an example of a high-value target for use as a rocket-boosted Mk-48 could be used to destroy.

Fair enough.