The SM-6 (particularly Block 1B) is way bigger than the PAC-3 MSE, though?
Besides, the HQ-29's missile tubes (and its TEL) looks to be quite longer than those of the S-500. The cancelled KEI seems to be closer in dimension to the HQ-29.
In the meantime, hopefully China will field SM-3 (and better yet, GPI) equivalent(s) soon.
The PAC-3 MSE is a way better missile than the SM-6 in anti-BM work. The important characteristics for ABM are acceleration, top speed, low drag and high-altitude agility. The PAC-3 MSE is better than the SM-6 in all of these. The SM-6 has a higher sectional density and a much higher lift. Which mean a good energy retention while maneuvering and a very long glide (hence range).
There is an insider comment here:
https://www.reddit.com/r/CredibleDefense/comments/1dsytpz/_/lb7r4tg
SM-6, however is optimized for air defense. It is substantially slower, both in terms of terminal velocity and acceleration. As a result, the BMD footprint of SM-6 and MSE (when MSE is able to make use of a more capable sensor, such as the TPY-2) is very similar. The long range claims for SM-6 are about engaging slow, non-maneuverable targets, but as target complexity increases its range decreases rapidly. This is really just a symptom of SM-6 being an improved version of a 1960s missile design; we can replace the motor, the warhead, the electronics, and the seeker, but at a conceptual level SM-6 is ultimately just an extremely improved RIM-2C. Whereas MSE is a design leveraging design philosophies several decades newer.
The TLDR here is that while MSE has less range in absolute terms, it loses range more slowly as threat complexity increases—to the point where they are very close. Meanwhile MSE has substantially greater lethality against most targets and reentry vehicles in particular thanks to both its hit to kill approach and much more advanced seeker.
Also, I am kinda annoyed by the comparison of Chinese missiles to S-something, and the use of the names HQ-2x. Russian systems are a black box at this point, and dare I say, I think the Russians are being convoluted deliberately. What is the A-235 for example? It seems it is just modernized A-135 elements. 9M82M? S-500? They were lately talking about S-550 too which nobody knows what exact capability it refers to. Their missile categories appear different from the Israeli, American and Chinese categories and there is an excess variety. Looking at the said three countries, I see this categories in ABM:
- Low-to-mid atmosphere and the range is low. Below 100 km (targeted point) against not-so-fast BMs.
- High-atmosphere. Some of these missiles also have some exo-atmospheric capability. This is the first tier that has a useful range against an ICBM RV. The range is in hundreds of kilometers against MRBM types.
- True exo-atmospheric. These missiles aren't even designed to resist heat and dynamic pressure. They are for use above the atmosphere. The range can exceed 500 km against ICBM warheads. These are also capable of ASAT.
- ICBM mid-course interceptor. Like the previous category but even bigger. ASAT capability of these would be better. More shooting opportunities and higher orbits could be targeted.
- Hypersonic glider midcourse interceptor. No such missile exists yet. It would need to have aerodynamic maneuverability and heat resistance while being as fast as the third category if not more.
China currently fills the first category with the HQ-9B and C. These are suboptimal but I guess they would work against what China faces. I see no urgency from the PLA. They would likely introduce a PAC-3 MSE-like missile in the future to fill this. Smaller is better for this category. Gives magazine depth which is very important in ABM. Double or quad-packing in UVLS would be very nice.
The second category is filled by the HQ-19. I assume it has exoatmospheric capability too as it is usually referred as the Sino-THAAD.
The third one was rumored for long. I assume they have something in service. The new TEL is a good evidence.
The fourth one is spicy. I believe that big single tube thing is this. Such a missile would be heavy.
