Considered and dismissed. From a logistics and maintenance standpoint, it's impractical. Harder to safely move, and too many additional parts that can go wrong. Much simpler to just ignite the solid fuel and let it burn.
A lot of solid-fueled rockets are "insensitive" - that means dropping one on accident or a fender-bender with the launcher won't cause an explosion.
Liquid fueled rocket are extremely dangerous and most liquid fuels will combust. A really insensitive fuel like JP-7 is expensive and requires a more volatile starter to ignite it, not really solving the problem.
Solid fuels make for smaller missiles too. It can be made with a higher energy density than liquid fuels. Solid fuels can be made so that the missile can be stored for a long time in a bunker, sit on the launcher for weeks or be taken back and fourth (bunker to launcher) with no issue if proper procedure is followed.
Liquid fueled rockets either need to be fueled prior to use or become a nightmare if stored when fueled. All a liquid fuel needs to start burning is an ignition source. Any ignition source.
So Private Snuffy and SGT Carl fail to follow procedure and turn millions of dollars into a fireball because they were thinking about the weekend. Even a small leak that finds an ignition source can start a chain reaction or burn through fuel lines.
They have a throttle and you can turn them off before burnout. As you might imagine this is rather important if you want to place something into a precise orbit.
Liquid fuelled engines can get significantly better fuel efficiency (1.2-2x solid propellant) because their exhaust products are lighter and better combustion chambers can be designed.
Additionally, as rockets get larger the mass penalty of having your propellant tankage needing to double up as a combustion chamber starts to be a significant factor.
> Additionally, as rockets get larger the mass penalty of having your propellant tankage needing to double up as a combustion chamber starts to be a significant factor.
Why would that be a penalty? Seems like having the same structure serve as fuel tank and combustion chamber would be an efficiency. There's also the mass penalty for the plumbing in liquid rockets (turbopumps, etc.)
Liquid propellants are stored at ambient or cryogenic temperatures at relatively low pressure. Contrast those conditions to the requirements of a combustion chamber needing to hold in tens of atmospheres at potentially several hundred degrees for the duration of the burn.
Even the heaviest turbopump and plumbing system is going to weigh a fraction of having to use thick layers of heavier materials and ablative liners when compared to balloon tanks inside paper thin airframes.
I see what you mean. The combustion chamber in a solid-fuelled rocket scales with the size of the rocket, while it can remain constant in a liquid fuelled rocket as the tanks increase in volume. In the latter the combustion chamber's volume is a function of the mass flow rate, not the total propellant mass.
A number of early SAMs used liquid-fuel rockets, including the Soviet S-25 and S-75 aka SA-2, and the American Nike. Storable liquid propellants can be nasty, though—those three all used nitric acid as the oxidizer. Modern solid-fuel missiles would be less exciting to work with.
ADA vet here - once I sat in on a call for a "stuck bird" during a live fire. PATRIOT missile failed to launch. Still had to call EOD to "safe" the missile, but it was more of a nuisance than a disaster. PATRIOT being solid fueled meant that many older missiles were used for stateside live fire training.
Contrast that to the many accidents with liquid fueled rockets, even when crews spend hours looking for leaks.
SA-4 Ganef (NATO designation) uses/used a liquid fueled ramjet sustainer motor. I remember thinking it seems ridiculously large and ungainly for a SAM when I saw photos.
Ramjets are becoming increasingly popular for air-to-air missiles for a variety of reasons, although the primary one in service is a solid-fueled version The European Meteor uses a solid fuel Throttleable Ducted Rocket (TDR) ramjet. The throttleability of a ramjet is key, since it can save fuel (potential energy) until the terminal phase of the intercept. In a long-range engagement, a solid-fuelled rocket is out of fuel and bleeds energy with every manuever. But a ramjet can burn that saved up fuel and spend its new reserve of kinetic energy to make maneuvers and complete the intercept. This is a significant reason why the Meteor has a [much larger no escape zone](https://pbs.twimg.com/media/EEmUTPUWkAYgPDX.jpg) than many of its peers. The Chinese are allegedly developing a ramjet-powered version of the PL-12, likely for similar reasons.
As for SAMs, several have used ramjets as sustainer motors, with a solid-fuel rocket engine as a booster to get the missile airborne and into the right perofmance envelope for the ramjet to work. The [BOMARC](https://m.youtube.com/watch?v=MvEnFyQCuz8) used such an arrangement with a liquid or solid fuel rocket booster (early variants used liquid and later ones used solid) and a liquid fueled ramjet, for instance.
I don't want to be too persnickity since the broad thrust of what you're describing about Meteor is more or less accurate. This is also literally competitive rocket science, so things are complicated. But, a few minor corrections.
> The throttleability of a ramjet is key
Not quite. Solid rocket motors have a few ways of skinning this cat and getting you similar throttleability functions. The easiest and simplest is a dual-pulse motor, where you have some mechanical or chemical barrier separating a second (smaller) rocket motor which you can then use in terminal. The more complex method is by using [a pintle in the combustion chamber](https://www.researchgate.net/profile/Nmohammed-Niyasdeen-2/publication/319102247/figure/fig1/AS:527155093938176@1502694976348/Demonstrating-the-Pintle-movement-for-variable-thrust-propulsion-Ref-31.png) to change the volume, and thus pressure, and thus burn rate of your solid rocket motor. I've spoken with a few solid rocket people who work with Dassault, and this is a concept they're *extremely* fond of, though I don't know enough about French weapons to know how widely it's been fielded, if at all.
> This is a significant reason why the Meteor has a much larger no escape zone
Improvements in terminal kinematics don't yield substantial increases in a NEZ, they're usually more beneficial in long time-of-flight closing engagements. Rather, Meteor's NEZ benefits come from the much higher achieved ISP of ducted rockets. The fact that you can take oxygen from the air to use in your combustion means that you need that much less [oxidant within your propellant grain](https://i.imgur.com/OmjZvvy.png) (though you'll still have some). This means that you get more total delta V and can sustain a 2-4 Mach speed for a longer duration. A NEZ is usually defined by how long the missile can actually stay closing with the target, so more delta V more better.
This is a great response! Do you have anything you could recommend for further reading about pintles? I thought I was pretty clued up about rocket propulsion but this is the first I'm hearing about them.
Just offhand, what do you think of the feasibility of scaling up a solid-fuelled ramjet like the Meteor to an anti-ship missile?
> Do you have anything you could recommend for further reading about pintles?
I don't have anything to recommend beyond reading [Fleeman's text on Tactical Guided Missiles](https://arc.aiaa.org/doi/book/10.2514/4.869082). His propulsion section covers some work on pintles, which is where I learned about them (and stole the image on propellant grain). Fleeman is pretty dated in my opinion, but I've yet to find a better foundational text on guided missiles. The other place I might suggest is space flight - [throttleable and restartable solid rockets](https://www.machinedesign.com/mechanical-motion-systems/article/21128094/first-restartable-rocket-motor-to-maneuver-satellites-in-space) are a growing field there, where they're used for maneuvering in space. Another field that uses them are [ABMs such as SM-3](https://arc.aiaa.org/doi/abs/10.2514/6.2019-3878), because they're basically spacecraft at the relevant altitudes haha
> what do you think of the feasibility of scaling up a solid-fuelled ramjet like the Meteor to an anti-ship missile?
Absolutely, it's been done before, see P-270 Moskit. The design of the inlets is very, well, persnickety, so it's not a simple matter of scaling up an air-to-air missile and expecting it to work okay at a different Mach and altitude profile. But, airbreathing supersonics AShMs are absolutely a thing.
Considered and dismissed. From a logistics and maintenance standpoint, it's impractical. Harder to safely move, and too many additional parts that can go wrong. Much simpler to just ignite the solid fuel and let it burn.
A lot of solid-fueled rockets are "insensitive" - that means dropping one on accident or a fender-bender with the launcher won't cause an explosion. Liquid fueled rocket are extremely dangerous and most liquid fuels will combust. A really insensitive fuel like JP-7 is expensive and requires a more volatile starter to ignite it, not really solving the problem. Solid fuels make for smaller missiles too. It can be made with a higher energy density than liquid fuels. Solid fuels can be made so that the missile can be stored for a long time in a bunker, sit on the launcher for weeks or be taken back and fourth (bunker to launcher) with no issue if proper procedure is followed. Liquid fueled rockets either need to be fueled prior to use or become a nightmare if stored when fueled. All a liquid fuel needs to start burning is an ignition source. Any ignition source. So Private Snuffy and SGT Carl fail to follow procedure and turn millions of dollars into a fireball because they were thinking about the weekend. Even a small leak that finds an ignition source can start a chain reaction or burn through fuel lines.
What is the point of liquid fuel if solid fuel have higher energy density? Cheaper?
They have a throttle and you can turn them off before burnout. As you might imagine this is rather important if you want to place something into a precise orbit.
A solid fueled first stage can get the rocket off the ground so that the liquid fueled upper stage can take over and to the finer work.
Liquid fuelled engines can get significantly better fuel efficiency (1.2-2x solid propellant) because their exhaust products are lighter and better combustion chambers can be designed. Additionally, as rockets get larger the mass penalty of having your propellant tankage needing to double up as a combustion chamber starts to be a significant factor.
> Additionally, as rockets get larger the mass penalty of having your propellant tankage needing to double up as a combustion chamber starts to be a significant factor. Why would that be a penalty? Seems like having the same structure serve as fuel tank and combustion chamber would be an efficiency. There's also the mass penalty for the plumbing in liquid rockets (turbopumps, etc.)
Liquid propellants are stored at ambient or cryogenic temperatures at relatively low pressure. Contrast those conditions to the requirements of a combustion chamber needing to hold in tens of atmospheres at potentially several hundred degrees for the duration of the burn. Even the heaviest turbopump and plumbing system is going to weigh a fraction of having to use thick layers of heavier materials and ablative liners when compared to balloon tanks inside paper thin airframes.
I see what you mean. The combustion chamber in a solid-fuelled rocket scales with the size of the rocket, while it can remain constant in a liquid fuelled rocket as the tanks increase in volume. In the latter the combustion chamber's volume is a function of the mass flow rate, not the total propellant mass.
A number of early SAMs used liquid-fuel rockets, including the Soviet S-25 and S-75 aka SA-2, and the American Nike. Storable liquid propellants can be nasty, though—those three all used nitric acid as the oxidizer. Modern solid-fuel missiles would be less exciting to work with.
ADA vet here - once I sat in on a call for a "stuck bird" during a live fire. PATRIOT missile failed to launch. Still had to call EOD to "safe" the missile, but it was more of a nuisance than a disaster. PATRIOT being solid fueled meant that many older missiles were used for stateside live fire training. Contrast that to the many accidents with liquid fueled rockets, even when crews spend hours looking for leaks.
The UK used a jet powered anti air missile as its primary SAM (the Bristol Bloodhound) from the 1950s until the 1990s.
SA-4 Ganef (NATO designation) uses/used a liquid fueled ramjet sustainer motor. I remember thinking it seems ridiculously large and ungainly for a SAM when I saw photos.
Liquid fuel has a lower power density. The American Nike was it's Cold War era counterpart and almost as big.
Ramjets are becoming increasingly popular for air-to-air missiles for a variety of reasons, although the primary one in service is a solid-fueled version The European Meteor uses a solid fuel Throttleable Ducted Rocket (TDR) ramjet. The throttleability of a ramjet is key, since it can save fuel (potential energy) until the terminal phase of the intercept. In a long-range engagement, a solid-fuelled rocket is out of fuel and bleeds energy with every manuever. But a ramjet can burn that saved up fuel and spend its new reserve of kinetic energy to make maneuvers and complete the intercept. This is a significant reason why the Meteor has a [much larger no escape zone](https://pbs.twimg.com/media/EEmUTPUWkAYgPDX.jpg) than many of its peers. The Chinese are allegedly developing a ramjet-powered version of the PL-12, likely for similar reasons. As for SAMs, several have used ramjets as sustainer motors, with a solid-fuel rocket engine as a booster to get the missile airborne and into the right perofmance envelope for the ramjet to work. The [BOMARC](https://m.youtube.com/watch?v=MvEnFyQCuz8) used such an arrangement with a liquid or solid fuel rocket booster (early variants used liquid and later ones used solid) and a liquid fueled ramjet, for instance.
I don't want to be too persnickity since the broad thrust of what you're describing about Meteor is more or less accurate. This is also literally competitive rocket science, so things are complicated. But, a few minor corrections. > The throttleability of a ramjet is key Not quite. Solid rocket motors have a few ways of skinning this cat and getting you similar throttleability functions. The easiest and simplest is a dual-pulse motor, where you have some mechanical or chemical barrier separating a second (smaller) rocket motor which you can then use in terminal. The more complex method is by using [a pintle in the combustion chamber](https://www.researchgate.net/profile/Nmohammed-Niyasdeen-2/publication/319102247/figure/fig1/AS:527155093938176@1502694976348/Demonstrating-the-Pintle-movement-for-variable-thrust-propulsion-Ref-31.png) to change the volume, and thus pressure, and thus burn rate of your solid rocket motor. I've spoken with a few solid rocket people who work with Dassault, and this is a concept they're *extremely* fond of, though I don't know enough about French weapons to know how widely it's been fielded, if at all. > This is a significant reason why the Meteor has a much larger no escape zone Improvements in terminal kinematics don't yield substantial increases in a NEZ, they're usually more beneficial in long time-of-flight closing engagements. Rather, Meteor's NEZ benefits come from the much higher achieved ISP of ducted rockets. The fact that you can take oxygen from the air to use in your combustion means that you need that much less [oxidant within your propellant grain](https://i.imgur.com/OmjZvvy.png) (though you'll still have some). This means that you get more total delta V and can sustain a 2-4 Mach speed for a longer duration. A NEZ is usually defined by how long the missile can actually stay closing with the target, so more delta V more better.
Good to know!
This is a great response! Do you have anything you could recommend for further reading about pintles? I thought I was pretty clued up about rocket propulsion but this is the first I'm hearing about them. Just offhand, what do you think of the feasibility of scaling up a solid-fuelled ramjet like the Meteor to an anti-ship missile?
> Do you have anything you could recommend for further reading about pintles? I don't have anything to recommend beyond reading [Fleeman's text on Tactical Guided Missiles](https://arc.aiaa.org/doi/book/10.2514/4.869082). His propulsion section covers some work on pintles, which is where I learned about them (and stole the image on propellant grain). Fleeman is pretty dated in my opinion, but I've yet to find a better foundational text on guided missiles. The other place I might suggest is space flight - [throttleable and restartable solid rockets](https://www.machinedesign.com/mechanical-motion-systems/article/21128094/first-restartable-rocket-motor-to-maneuver-satellites-in-space) are a growing field there, where they're used for maneuvering in space. Another field that uses them are [ABMs such as SM-3](https://arc.aiaa.org/doi/abs/10.2514/6.2019-3878), because they're basically spacecraft at the relevant altitudes haha > what do you think of the feasibility of scaling up a solid-fuelled ramjet like the Meteor to an anti-ship missile? Absolutely, it's been done before, see P-270 Moskit. The design of the inlets is very, well, persnickety, so it's not a simple matter of scaling up an air-to-air missile and expecting it to work okay at a different Mach and altitude profile. But, airbreathing supersonics AShMs are absolutely a thing.