Raytheon, Northrop Grumman to build Air Force scramjet hypersonic missiles | Hacker News Reader

Raytheon, Northrop Grumman to build Air Force scramjet hypersonic missiles

militaryaerospace.com

48 pointshsnewman54 comments

Here's one way how to think about this missile.

You start from the report to Congress [1]. On page 8:

  In FY2022, the Air Force launched the Hypersonic Attack Cruise Missile (HACM) program to develop a hypersonic cruise missile that integrates Air Force and DARPA technologies. Some reports indicate that HACM is intended to be launched from both bombers and fighter aircraft, with a senior Air Force official noting that a B-52 could potentially carry 20 HACMs or more.

B-52 can carry 32 tons of munitions. So 20 of these missiles "or more" may mean that each missile is about 1500 kg. That's in line with the current AGM-86 long range air launched cruise missile [2], [3]. Of course, AGM-86 is subsonic, while HACM will be supersonic. AGM-86 has a range, depending on configuration, between 950 km and 2500 km (maybe even more, this is the non-classified range). I guess HACM will have a similar range. Being hypersonic means it's easier to carry out a saturation attack (you send more missiles than the enemy can defend against simultaneously).

That means, the US Air Force will be able to carry deterrence patrols with their B-52s in order to prevent China from sending a naval landing force to Taiwan. Without this weapon, the main deterrence was supposed to be provided by the US Navy and their carrier strike groups. With this weapon, the US Air Force may be able to provide a cost effective alternative.

[1] https://news.usni.org/2022/07/22/report-to-congress-on-hyper...

[2] https://en.wikipedia.org/wiki/AGM-86_ALCM

[3] https://www.af.mil/About-Us/Fact-Sheets/Display/Article/1046...

> B-52 can carry 32 tons of munitions. So 20 of these missiles "or more" may mean that each missile is about 1500 kg

Not necessarily. US bombers, especially old ones such as the B-52 were designed for bomb loads stored inside and dropped when the doors open. Carrying missiles was added later on, and since those have to be outside, usually on the wings, the main limitations is space, not weight. If it cannot fit more than 20 missiles due to only 10 launchers with 2 missiles each (for instance) being able to physically fit on the aircraft's fuselage/wings, it doesn't matter how many more it could carry inside.

Also, has tech advanced so much to have a similarly weighing scramjet hypersonic missile have a similar range to a supposedly more optimal subsonic one?

> Also, has tech advanced so much to have a similarly weighing scramjet hypersonic missile have a similar range to a supposedly more optimal subsonic one?

According to wikipedia [1], the Russian Kinzhal has a mass of about 2000 kg and a range of 3000 km if launched from a strategic bomber. Of course, wikipedia just repeats the Russian claims, we can't know for sure if these numbers are accurate, but if they are off, they are not off by a factor of 10.

Can the US make something similar? It's quite possible, the US military budget is more than 10 times higher.

Separately, hypersonic missiles are thought to travel at an altitude of 100km, where the air density is about one million times lower than at ground level [2]. Even if the air friction is ten 1000 times higher than for a subsonic missile (if drag is proportional to v^3 and v goes up by a factor of 10), in the end the total drag could be lower. I personally expect hypersonic missiles like this one come with increased range rather than decreased range compared to their subsonic cousins.

[1] https://en.wikipedia.org/wiki/Kh-47M2_Kinzhal

[2] http://www.braeunig.us/space/atmos.htm

The Kinzhal is basically an air-launched Iskander, a ballistic rocket, not a cruise air-breathing missile.

But the scramjet should increase, not decrease the range, no?

I've been pondering about the range thing, because my immediate kneejerk was "two balls rolling, one's 2x faster than the other, that one will go further" … but I had that "trick question" flag go off as soon as I thought that.

Things I don't know:

- It's faster … possibly huge fuel consumption to get to operating speed over comparable subsonic missile? (even if sips fuel once at operating speed/altitude)

- Will fly at higher altitude … which means lower friction (enough to counter what's added by higher speed) … but also to hit the same target, more distance must be covered (climb/descent to operating altitude + greater orbiting circumference)

- Limited "package" size … do scramjet surfaces/elements reduce the amount of space available for fuel?

- How much distance is a factor.

Here's how one can think about this, using numbers.

First, specific impulse [1]. It's measured in seconds, and it means how many seconds an engine can provide 1 pound of thrust if it burns 1 pound of fuel. The graph [2] shows that specific impulse is a decreasing function of speed, with a profile that looks roughly like a hyperbola. The specific impulse of the engines powering Boeing 747 is listed at 6000 seconds. The specific impulse of a scramjet engine at Mach 7 is plotted at about 1000 seconds. Finally, the specific impulse of the Space Shuttle solid rocket boosters is 250 seconds (it's down in the Examples subsection).

The specific impulse of a subsonic cruise missile is not listed. However, the engine of both the AGM-86 and the Tomahawk cruise missile, the Williams F-107 [3] has a bypass ratio of 1:1, which is much much lower than the bypass ratio of commercial jets [4]. I'll make up the number to be 2500 seconds (it will make my computations below a bit easier, you can adjust them accordingly, but you'll see that it does not make a huge difference if it's 2000 or 3000 seconds; I don't think there's a chance it's above 3000 seconds).

Second thing is the lift-to-drag ratio. For hypersonic vehicles, there's the empirical observation that the max L/D ratio is 4(M+3)/M, where M is the Mach number. If M=7, we get 40/7 = 5.71. For subsonic vehicles, wikipedia lists all sorts of L/D ratios, but they roughly range from 10 to 20.

The last is the rocket equation [6] which says that delta-v is the specific impulse times the gravitational acceleration times the log of the ratio of the initial mass (i.e the fully fueled rocket) and the final mass (the "dry" rocket, after the fuel was burned).

Let's compare now a subsonic and a hypersonic missile. The subsonic one travels at Mach 0.73 (like the AGM-86) and the hypersonic 10 times faster, at Mach 7.3 (I'm making this up of course, nobody has any idea how fast the Raytheon missile will be, except that by the definition of "hypersonic" it needs to be above Mach 5). In meters per second, those speeds are around 250 m/s and 2500 m/s.

Let's also say they both have a "dry mass" of 900 kg (the mass of the warhead and the engine and the vehicle itself, but excluding any fuel).

And let's say the missile has to have a range of 2500 km.

The L/D ratio of the subsonic missile, we'll take it to be 15 (most likely it's lower than that, but I don't think it would be less than 10). The L/D ratio of the hypersonic one should be lower than 5.71, we'll take it to be 5.

The hypersonic missile will need 1000 seconds (about 17 minutes) to travel the 2500 km distance. Since it has an L/D ratio of 5 and a mass of 900, it will have a drag of 900/5 = 180 kg. The specific impulse of the hypersonic missile is 1000 seconds, so you need exactly 180 kg of fuel to push agains the 180 kg of drag for the 1000 seconds of the trip. Of course, you need some fuel to push that fuel, but this is second order things, and we can ignore.

The subsonic missile will travel for 10000 seconds (about 3 hours). It will have a drag of only 60 kg, and it has a specific impulse of 2500 seconds. You end up with a fuel need of 240 kg. That's more than for the hypersonic, but then we are not done with the hypersonic, since that one needs a rocket booster to get to its cruising altitude and speed.

Going to an altitude of 100 km is equivalent to gaining a delta-v of 1400 m/s (this comes from the kinetic energy =mv^2/2 and potential energy = mgh). We need another delta-v of Mach 7.3 = 2500 m/s, that's a total of 3900 m/s. The specific impulse of the booster is 250, and we take the gravitational acceleration to be 10, so the log of the mass ratio is 3900/2500 = 1.56, which means the initial mass is exp(1.56) = 4.76 higher than the dry mass. To push 1000 kg of hypersonic missile, the booster needs to have 3760 kg of fuel. We can ignore the dry mass of the booster itself. In any case, we need a ratio of roughly 4:1 of booster/hypersonic vehicle.

All in all, it looks like a hypersonic missile is, if anything, better in cruise mode than a subsonic missile, but since it needs the huge booster to get to cruise mode, it looks like it will carry about one fifth of the payload for the same range.

Which is not so bad. If you carry 100 kg of explosive instead of 500 kg, you can still do a lot of damage.

[1] https://en.wikipedia.org/wiki/Specific_impulse

[2] https://en.wikipedia.org/wiki/Specific_impulse#/media/File:S...

[3] https://en.wikipedia.org/wiki/Williams_F107

[4] https://en.wikipedia.org/wiki/Bypass_ratio

[5] https://en.wikipedia.org/wiki/Lift-to-drag_ratio

[6] https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

EXCELLENT!! Thank you!

Please tell me you had some experience with this stuff before busting out a dissertation on of lift-to-drag calculations …

So, if we're constraining ourselves to go the same distance as a cruise missile with the same max weight/dimension, we CAN, but …

- using less fuel

- and at 10x speed

- but have a smaller warhead

So to your original question about whether a scramjet will travel further on the same amount of fuel, the answer does appear to be YES. (But with a smaller warhead, assuming same max weight/dimensions of conventional cruise missile)

So I guess the next question is: if we assume distance and dimension are constraints and we _do_ have an 80% smaller warhead … do we get 80% less damage when it impacts, given that it's traveling at 10x? Or does the speed impact the force of the warhead?

This is fun …

> Or does the speed impact the force of the warhead?

Absolutely. The energy density of TNT is 4.11 MJ/kg. An object traveling at 2.5 km/s has a kinetic energy (mv^2/2) of 3.12 MJ/kg. If we consider a simple rule of 3 for a cruise missile (1/3 the warhead, 1/3 the fuel, 1/3 the rest of the missile), then the kinetic energy of the warhead and the empty vehicle will be 50% more than the energy of the explosive (if not more). So, even if the warhead is only one fifth of the warhead of a subsonic missile, the total energy delivered on target is one half.

China and Russia are ahead of the U.S as far as hypersonic missile tech goes.

https://www.ft.com/content/c7139a23-1271-43ae-975b-9b6323301...

The Pershing II and the ASM-135 ASAT did that in the '80s, actually. The Soviet Union also had a FOBS.

China maybe, but absolutely not Russia. Let's not make jokes.

This is correct. We are substantially behind both in terms of design and infrastructure to bring those designs to life (hypersonic wind tunnels).

The U.S. believed that hypersonic tech was “not of strategic importance”.

And to us it really isn't. We use a different doctrine of attack and defense.Wwe are primarily air and information superiority concepts and are only now getting into hypersonic due to the risk of a near-peer carriers and reef air fields.

The US is ahead in terms of the populace thinking they have secret weapons nobody knows about.

Hypersonic missles aren't really new or a gamechanger. When Russia and China flaunt it, there's a reason they never point to any real use cases for it. At those speeds, you can barely even communicate with the rocket.

They're absolute gamechangers for US adversaries that makes fortress America vunerable. US military preemenence rests on assumption that US adversaries lack capability to conventially disrupt CONUS homefront. PRC's new science of military strategy specifically calls for prompt global strike program. Think port strikes to destroy major US capital power projection assets anywhere in the world. Plenty of RD reports on onboard terminal guidance as well. Don't need complex killchain/OODA loop for fixed targets. There will be massive strategic implications once US loses ability to operate out of CONUS with impunity i.e. entire US industrial bases is sustained by ~130 refineries that current missile tech has CEP to hit.

Basically high APM clicking in StarCraft becomes a transferible skill...

What platforms would they launch from? So far, they've only got land based hypersonics with nuclear warheads. In what way is that conventional?

Mate hypersonics with conventional warheads, which is within current PLA rocket force posture. On the deterrence/political layer, build nuclear deterrence to parity (see massive silo build outs) and maintain NFU while communicating that CONUS is subject to conventional strikes.

It's basically just US PGS program that US dropped decades ago because US has/had massive conventional platform lead and can project conventional fires using cheaper weapons with carriers or long range bombers so it wasn't worth increasing destability.

PGS wasn't/isn't game changer for US because they already possess cheaper capabilities for conventional fires supported by global basing. For PRC, it will take decades to build out carrier and long range bomber force that can threaten CONUS with additional difficulty of securing forward basing that makes US posture relativety economical. So short/medium term it's feasible to build out rocketry, simply because that's the only option.

Apologies, I must've gotten some wrong info because I thought the DF-17 carried only nuclear payloads until I checked it's wiki just now.

No worries, currently PLA rocket force deliberately entangles nuclear with conventional capabilities for deterrence - hard for PRC adversaries to math the cost of striking rocket force because can't know if launchers mated with nukes or not. That'll probably change once PRC builds up sufficient nuclear deterrence.

Sidenote: Entire PRC PGS talk is where PLA literature and strategic posture is trending towards - they're short/medium term future capabilties with little open source info other than PRC is doing 100s of missile tests and year and pouring massive resources into hypersonics. IMO there's a reason US reaction to PRC GFOBs demonstration was much louder than those of carrier killer missiles. The former is designed to hit fixed targets CONUS that are hard to disrupt/defend, the latter on carrier groups with difficult kill chain and many counter measures.

Doesn't MAD make all of that irrelevant anyway?

MAD game theory are recalibrated when new capabilities are introduced. Just like when survivable nuclear triad introduced second strike options from hair trigger LOW.

Consider every major US power projection platform have nuclear capable options, but US adversaries can't afford to default assume that cruise missiles from carriers air wings or subs or long range bombers are nuclear tipped. They know US wouldn't escalate to nuclear right away when there are conventional options. MAD around ICBM is based on presumption that up until recently, terminal guidance for intercontinental strikes aren't accurate or cost effective enough warrant anything but nuclear delivery. But that changes when conventional global strikes becomes technnologically and economically viable. US can claim they'll maintain launch on warning to any inbound ICBMs, but in a shooting war, when US is using forward assets to conventionally strike targets of adversaries on their homeland, but said adversaries has the capability to hit back to disrupt strategic targets on CONUS, they're absolutely going to.

IMO CONUS being vunerable to conventional strikes will open up another layer of MAD / deterrance strategies for conventional attacks. Which is to say US will lose unilateral ability to deter with conventional attacks it historically had because geographic isolation of CONUS was more or less immune to conventional rocket fires. There's already assumed MAD on cyberwarfare - Biden/US position on attack of critical infra is equivalent to conventional attack - result of network technology making US homeland vunerable. Hypersonics will be no different, but this time it will be US adversaries who can also dictate conventional attacks on their soil will be met with convetional attacks on US soil. Say US attacks mainland PRC in TW scenario or if blockade of PRC energy imports turn into shooting war to deprive PRC of 80% oil imports, why would PRC not also use cyber/hypersonics to take out 80% of US refinery capacity? Should create stability-instability paradox for conventional warfare unless huge progress in ABM/missile defense.

It seems to me that major conventional attacks between nuclear powers are already factored into MAD and won't be undertaken by the US or its rivals for this reason.

It's a huge stretch to imagine that a war where 80% of US refinery capacity was destroyed wouldn't already have gone nuclear. If the gloves come off anywhere close to this extent, both sides have to figure the war will inevitably go nuclear, in which case the incentive becomes to strike first and strike as hard as possible.

That's why in a Taiwan confrontation, US won't first-strike mainland China. China would strike US mainland in some way in response, and then it quickly escalates to nuclear war.

>already factored

I think not yet, or at least not seriously. The notion that US rivals (likely just PRC) can execute major conventional attacks on US infra is not currently accepted thinking. Only newest strategic/policy writing from Congressional Research Service and handful defense think tanks have a few lines acknowledging PRC is pursuing PGS capabilities which was only formally put on paper in PLA's 2020 Science of Military Strategy. And since it's not demonstrated capability outside of what's hinted by PRC's hypersonic glide FOBS test in late 2021, folks haven't spent too much brain cells analyzing/gaming out the potential. The renewed fixation over PGS is just getting started. Right now there's nascent acknowledgement that such capabilties are something PRC is pouring a lot of resources into pursuing. I think we'll see more serious discussion over the next few years, especially if PRC does a few more visible tests demonstrating relevant capability or rocket force adopts new hardware which at PLA speed, will shift strategic reality rapidly. Of course it could all be vaporware. In the meantime:

>US won't first-strike mainland China

PRC hawks and some warplanning/gaming currently are entertain mainland strikes. Consider that sinking PLAN invasion fleet while they mass (within PRC territorial waters) is tantamount to hitting targets within sovereign PRC territory, or that PRC considers TW literal Chinese soil. It gets messy. In general I agree hitting homeland is very far high up the escalation ladder. But until PRC has proven ability to retaliate on CONUS with proportional response, US planners still have option/incentive to plan with mainland strikes in mind, reasonably believing PRC won't escalate to nuclear due to NFU, at least not until PRC finishes current nuclear build out. We're in this latent space where it's easy for hawks to argue PRC doesn't have comprehensive conventional or nuclear deterrence against US conventional strikes on PRC mainland with acceptable costs (US homeland unscathed). Meanwhile the signs are pointing to PRC being able to close both vunerabilities/gaps sooner than later. All of which is to say, currently, US might strike mainland, or at least PLA has yet to comprehensively deterred US from doing so. Credit to RU having 6000+ nukes vs PRC racing to 1000 because ~300 (if accurate) simply wasn't sufficient.

>huge stretch ... wouldn't already have gone nuclear

Yeah, IMO that's the point, viable massive conventional strikes against CONUS introduces new layer of MAD that will now ripple out to conventional actions, i.e. if US blockades PRC shipping, without ability to rapid strike CONUS, PRC relegated to run blockade and escalate to very unfavorable IndoPac naval shootout, and if situation existential, could lead to huge escalation to tactical nukes on carrier groups over international waters if things get desperate, then hard to say how things spiral. With prompt global strike, PRC will have leverage to run blockade and threaten to hit fast supply ships replenishing in Yokosuka (there are currently only 10 sustaining entire USN) without which carrier escorts and carrier group become single deployment assets with days of useful endurance. Or any carrier undergoing maintenance in drydock. Or other critical US assets, from Pinegap in AU to drilling platforms in gulf of Mexico. Lots of steps before CONUS. The purpose is to create escalation steps to bridge gap before massively disruptive homeland strikes or going nuclear.

>which case the incentive becomes to strike first and strike as hard as possible

That's already the current incentive of modern war, incredible advantage that bias towards shooting first since exquisite major assets (highend ships, subs, bombers) are difficult (if not impossible) to replace in a timely manner in ongoing war, hence anxeity over PRC preemptive attacks on regional US forces in TW scenario. IMO both sides developing PGS hypersonics is establishing credible conventional second strike that will disincentivize large scale peer war. The implication being, this massive navy we both have is really only good for bullying smaller targets because it doesn't matter who sinks whose navy first, the survivor's fleet will be scrap the second the pull into port since conventional missiles in hardened bunkers are credible second strike options that ensures nobody ends up with a blue water navy to maintain their security interests at all.

The way I see it: right now US is the big kid on the block with a fancy gun, dictating terms to everyone in the neighbourhood. Her closest big kid rivals have knives and can't get close. The big kids also have suicide vests but no one wants to use them unless on death's door. PRC plans to start a knife fight with TW who is armed with a tooth pick. US plans to step in with her fancy gun but at a distance where she's least vunerable. PGS hypersonics gives PRC a shitty gun, but it's still a gun and provides significant more deterrence and capability than the best knife. Now neither gunslingers want to fight each other, US has to reconsider whether stepping in a PRC vs TW fight is still worthwhile. A fight between gunslingers can still happen, but it's less likely than a knife vs gun fight. Eventually, both side settles with giving each other space while bullying those armed with knives and toothpicks, trying to prevent them from also acquiring guns and suicide vests. US will get a better gun, maybe start wear increasingly better bullet proof vest (ABM) while her rivals work on AP bullets, but she's not going to be as secure or have as much coercive power as when she was the only kid with the gun.

Here's a better, more researched take that shows that the perceived advantage is more misunderstandings and misplaced media hype than an advantage.

https://m.youtube.com/watch?v=ckrpVT5jS5Q

China and Russia have hypersonic glide vehicles, which work like the Space Shuttle and are 70s tech.

They don't have scramjets, which is the headline.

PRC's first scramjet test was in 2011. Lot's of development since, but no formal weapon systems adopted AFAIK.

How far away are we from making airplanes or rocket boosters with this technology?

Scramjets are not terribly useful for boosters. They are more suited to cruise missions rather than acceleration missions.

That really is the problem with scramjets - apparently the longest test flights have been only a few minutes.

https://en.m.wikipedia.org/wiki/Scramjet#Progress_in_the_201...

AFAIK, every existing hypersonic weapon out there (from any nation) uses rocket propulsion.

Thing is, if you’re able to hit your target in a few minutes, your engine, your avionics or even your software stack only needs to last a few minutes.

I can’t find a Google reference right now on my mobile, but there’s a relatively well known example of a mission having some sort of loop related overflow in the guidance software that wasn’t fixed because by the time it could possibly happen, the rocket has burned out and the missile has done its job, it’s either exploded or is falling out of the sky and the software bug was irrelevant.

Well when you are moving at about a mile per second, a few minutes is a long flight.

The issue with scramjets is they operate under extreme conditions which are both unforgiving (small errors are catastrophic) and difficult to model (experimental data is limited and expensive to gain). The only path to development is to produce lots of full scale, fully functional prototypes with the understanding most will be destroyed in seconds and there will be little if anything recoverable afterwards to study to determine what went wrong.

Tl;dr:

- deal is for just a hair short of US$1bn

- jobs are in Tucson

- proposed delivery starts 2027

- proposed launch platform is f-15

- tech is undescribed, this is a from-scratch development, not an existing propulsion platform

Seems like a project to inject cash to relatively remotely areas to help deal with the housing crisis indirectly.

That wouldn’t be atypical, but Tucson isn’t especially remote or underfunded.

Well, you cannot throw money into the middle of nowhere, but Tucson definitely won't be most people's first choice for places to live.

Might also help create jobs for the people at the border aswell. Hitting multiple bird's with a single stone.

Tucson is the headquarters of Raytheon's Missile and Defense division. Been located there for 70 years. It started out as a Hughes Aircraft Company facility relocated away from the west coast during WW2 to avoid the threat of Japanese attack.

Cool tidbit! Makes a lot more sense now!

SLAM!!!

I mean I don't think anybody outside of Siberia is going to try to do nuclear powered ramjets https://en.wikipedia.org/wiki/Supersonic_Low_Altitude_Missil... (I hope)

never happening. I don't think the US can do it anymore.

I love the phrasing used in this press release.

> hypersonic weapon designed to hold high-value targets at risk

We don't destroy targets anymore. We hold our targets at risk.

What's wrong with the wording?

ICBM missile solo, not something you really want to blow up, but it would be cool if you could eliminate it within minutes should it start to pose a risk.

How would the Russians react? Would they launch extra nukes just to be "safe"? Maybe we should build a weapon that ~enhances the yield of their nukes, so that they figure sending one is enough!

Your username suggests that, had you been born 10 years earlier, you would have already been thinking about things like that for several years when the Berlin wall came down. But instead, you were 9 and the world has rarely been at risk of full-scale nuclear war for you.

The questions that you seem to be posing sarcastically were really, truly discussed seriously from 1959 through 1989.

Holding targets at risk is fundamentally different from destroying targets.

Hypersonic anti-ship weapons allow China to hold US carriers off the coast of Taiwan "at risk", but it doesn't mean they have to destroy them to be effective.

I know you're trying to dunk on this press release, but it's actually a specific phrase that has real meaning in the defense world.

Exactly. Words, when used precisely, can carry be used to infer a significant amount of intentions behind the text.

In this case, holding targets at risk implies a strategy of deterrence, a desire for peace and the de-escalatition of conflicts, as opposed to initiating the first strike with the intention of destruction.

I understand deterrence. I am commenting on the doublespeak. "Holding a target at risk" here exactly means wielding a credible way to destroy said target.

I would argue that replacing the phrase:

> ...weapon designed to hold high-value targets at risk in contested environments from standoff distances

with:

> ...weapon designed to destroy high-value targets in contested environments from standoff distances

leaves the meaning of the quote and overall press release completely unchanged.

There's some truth to it. These missiles won't be used for bombing the Middle East. They'll be used for things like demonstrating to China that an invasion fleet in the Taiwan Strait is vulnerable. If they ever have to destroy a target it will be because that primary strategy failed.

> These missiles won't be used for bombing the Middle East.

Maybe not out of any kind of tactical necessity. But quite possibly just to show off the new missile, depending on the commander in chief.

Basically that means it is for deterrence.

This is a logical and normal term in strategic military planning, the concept of knowing that your own important thing will almost assuredly be destroyed in a retaliatory strike, should you be the one to initiate the war. See also the last 70 years of cold war era mutually assured destruction calculus.

This is one of the reasons why highly advanced anti ballistic missile systems are seen as very dangerous because they upset the parity of two nuclear ICBM armed states being in approximate equal capability with each other.

The cold war never really ended.

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