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Comment by Someone1234 | Hacker News Reader

Older cruise missiles with less sophisticated guidance systems flew at higher altitudes, but that made them susceptible to anti-missile defences (from lasers to David's Sling).

Modern ones "skim" along the terrain, this massively reduces their radar detection range (due to the horizon) and allows them to navigate around known defensive measures.

This is also why both the US and Russia has spent millions of dollars on extremely sensitive microphones to literally "hear" an incoming cruise missile.

A system like this, combined with a system to combat high altitude cruise missile attacks, could theoretically work. Or certainly limit/disrupt the ability for very low altitude weapons to enter your territory uncontested.

Plus low altitude drones definitely have a future, particularly against a technologically advanced nation.

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> A system like this ... could theoretically work.

Sorry, but no. You know how modern ones skim along terrain? Terrain maps. If you are using terrain maps to navigate, then you don't need GPS - so this system has no hopes of working against low altitude cruise missiles. Also, the cruise missiles would need to be flying lower than the cell towers - which would only be a problem if the directional antenna was sensitive to 180 degrees. Beamforming tech is so common now that it has found its way into wifi routers.

> You know how modern ones skim along terrain? Terrain maps.

Terrain maps require active radar. Active radar increases your detectability.

> If you are using terrain maps to navigate, then you don't need GPS - so this system has no hopes of working against low altitude cruise missiles.

Some currently deployed US Navy Cruise Missiles already utilise GPS. Including the Block III TLAM[0].

They support INS (inaccurate), TERCOM (which has a radar signature), and DSMAC (which relies on TERCOM or GPS, and only increases final target accuracy).

You'd definitely use GPS if you could use GPS, it is the most reliable and quietest system. This system proposes to neuter your ability to use GPS in Russian territory.

> Also, the cruise missiles would need to be flying lower than the cell towers

That isn't how radio signals work.

[0] http://www.navy.mil/navydata/fact_display.asp?cid=2200&tid=1...

> Active radar increases your detectability.

An active radar pointed at the ground, so you'd need a pretty extensive detection network. Also, I don't think stealth is much of a concern once the cruise missiles are over the target's territory. BTW, TERCOM doesn't need to be continuously radiating when in use, it only needs to get a fix frequently enough to keep INS within acceptable accuracy bounds.

> That isn't how radio signals work.

It is when you're talking about trying to interfere with a weapons grade radio, by transmitting to the sidelobe instead of mainlobe.

> An active radar pointed at the ground, so you'd need a pretty extensive detection network.

So they can't navigate a sudden cliff in the way?

If the cliff materialized between the time the path was plotted and uploaded to the missile prior to launch, then no. The missile has an internal map, the radar measurements are like mile markers on the highway - used to find your position on the map, not used to tell you what is ahead (that is what the map is for).

You're underestimating the mind-blowing awesomeness of high-end inertial navigation in general, and the awesomeness of inertial navigation inputs mixed in with other sensor systems in particular. It should be possible to build a system that can handle some sophisticated jamming and still keep flying with a high degree of precision...

...but the spectacle of Iran downing one of our drones a few years back using GPS spoofing makes me wonder if maybe defense contractors are hiring engineers who couldn't get jobs working at the phone company, or something. So yeah. Bleh.

(the maker of the laser ring gyros used in the F-15 used to brag that the plane could go up, patrol, and land and the indicated coordinates were in the same hangar. I'm sure the tech has only gotten better.)

I think it's just that they weren't designed with spoofing in the threat model.

That's the point of filtering inputs from multiple navigation sources, though. One of them should be able to go wrong, it should be apparent, and the rest of the system should just be able to continue to function. There's ample experience integrating GPS, inertial, stellar (!), and so on.

Mostly I was responding the parent's comment about inertial, which is way off base. Inertial navigation is amazing.

I don't buy it. First: just because you're close to the cell tower doesn't mean you're below it. Directional antennae work really well, it's trivial to shield yourself against jamming from below. Also, note that cruise missiles have inertial backup too. As long as they get a decent GPS fix in the non urban area outside the city where there are no jamming towers, they can still hit their target.

Add that to the "duh, who's interested in bombing Russia?" angle and I agree: 100% propaganda for internal consumption.

My memory might be hazy, but I thought it was the other way around. INS as the primary navigation with periodic corrections from GPS.

Obligatory: https://www.youtube.com/watch?v=bZe5J8SVCYQ

Well, the method of fire-and-forget has long been the holy grail of arms manufacturers for many decades now. What that has done, has create levels of precision and the acceptability of precision upper/lower bounds is relative to what optically, thermal imaging, and radar provide beyond the low altitude signature and physical characteristics of that projectile going down range (aka stealth, etc). I CAN say with some conviction that audio disruption has already been thought of and implemented as a counter jamming measure and counter counter jamming measure to increase effectiveness of projectiles fired at a target. The "tools" of the trade to hit a target are much more sophisticated than even stated here ... but the conceptual point of the jamming method ... is effective, but not impossible to defeat based on current tech Im aware of.

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