67

A bore in the solid propellant grain increases exposed surface area and allows for a higher burn rate to increase thrust. There might be several grain geometries used, to meet launch vehicle's ascent profile needs through grain regression and with it control flow rate as the solid propellant core burns. From Wikipedia on Solid-fuel rocket - Grain geometry: ...


30

It depends on the particular engine. Thrust from a solid rocket is approximately proportional to the burning surface area of the fuel (also called the grain). A long solid rocket motor with a channel along its length is burning more surface area than an "end-burning" motor, so produces more thrust. Typically solid rocket boosters are used to provide very ...


29

The shuttle stack broke up at ~73 seconds after launch of STS-51L. The Solid Rocket Boosters separated from the other elements and continued flying in a more or less stable manner (surprisingly). Air Force range safety personnel detonated the boosters at ~110 seconds after launch using the self-destruct system built into the boosters. (timeline reference) ...


26

SRB Ignition SRB ignition can occur only when a manual lock pin from each SRB safe and arm device has been removed. The ground crew removes the pin during prelaunch activities. At T minus five minutes, the SRB safe and arm device is rotated to the arm position. The solid rocket motor ignition commands are issued when the three SSMEs are at or ...


21

Solid rockets have advantages, but also drawbacks: they have low Isp. Especially on upper stages, this means the stage has to be large. they generate more vibration than a liquid stage. they're not as simple to scale as you think. Casting the solid fuel is a difficult process that has to be tightly controlled to get repeatable results. because the ...


20

The Delta II first stage thrust structure is designed with attach points for up to nine strap-on boosters, of which either three, four, or all nine are used. If we number the attach points sequentially around the circumference of the first stage (they aren't, but let's pretend anyway), three boosters might use attach points 1, 4, and 7, leaving two empty ...


19

A solid stage can have a very low dry mass fraction, and can be spin stabilized avoiding the need for heavy guidance systems in the final stage. Both add mass directly to what is available for the payload. The Isp of solids is competitive with liquids other than LOX/LH2. A little bit of inaccuracy due to uncertainty in the total impulse of the motor can be ...


19

The NASA Spaceflight article Japanese sounding rocket claims record-breaking orbital launch describes JAXA's use of its SS-520-4 sounding rocket to put the Tricom-1R cubesat (43201, 2018-016A) into orbit. While there was an issue related to communications during the ascent, the satellite is currently in a 1572 x 189 km orbit. This is probably the smallest ...


18

The solid propellant is stored in the engine, so it doesn't have to be moved. The engine consists of a large cylinder that contains the propellant (indicated as 'grain' in the image, but it's a solid block with a grainy structure), with the nozzle at one end of the cylinder. Here's one segment of a Space Shuttle solid booster, with the void down the ...


16

Try looking at research done at The Aerospace Corporation, Penn State and Utah State. It turns out that there are very good reasons to print the fuel for hybrids. Adding a third dimension, beyond the images, above, of standard grain shapes can cause increased mixing of oxidizer and fuel, raising Isp. Regression rate was significantly increased in tests at ...


16

Solid fuel motors aren't unknown for upper stage use (e.g IUS, Star-48, among others). While solids generally have the drawbacks of poor Isp and controllability, their simplicity keeps cost and stage dry mass down on small upper stages. Note that in early launchers such as Vanguard, the specific impulse of the solid stage wasn't much less than that of the ...


15

The SRBs are pretty close to burnout when they separate: SRB separation is initiated when the three solid rocket motor chamber pressure transducers are processed in the redundancy management middle value select and the head- end chamber pressure of both SRBs is less than or equal to 50 psi. A backup cue is the time elapsed from booster ignition. ...


15

Offered as a supplement to the other answers, here are some data about SRBs thrust profiles and operation. Thrust of a SRB is function of the area of the solid fuel burning, as shown below: You can find here how the space shuttle SRBs are filled: The propellant had an 11-point star-shaped perforation in the forward motor segment and a double-truncated-...


15

Solid fuel ramjets exist The problem for a launch system is you would need a lot of oxidiser anyway — ramjets only start to produce thrust from Mach 1.5–2. They also start to lose thrust above Mach 4–5. Add onto this the huge amount of intake air that would be needed for a system with a high thrust/weight ratio and the complexity of ...


14

The Rutherford engines produce much less vibration than SRB's. This is actually a major selling point for Rocket Lab, as pointed out by Peter Beck here after 31:03: In essence, the low vibration spectrum enables the customer to put more useful payload onboard the Electron, because they need less/lighter mechanical structure....


13

It's always easier to create a new launcher by making a small modification to a reliable existing launcher. Small solid rocket stages are relatively simple and reliable, so building up a launcher from solids is less risky than the stage count might indicate. Small solid stages are also extremely cheap. The Peacekeeper ICBM is a three-stage suborbital ...


13

Orbital Sciences likes solid rockets. They've produced the Taurus/Minotaur all-solid booster. And, in its three-stage configuration the Pegasus is all-solid. Ignoring that kerosene-fueled launch platform of course.


12

It's not hypergolics per se that are super-desirable for ICBMs, but room-temperature-storable fuels. ICBMs have to stay ready for long periods of time and be launched on short notice, so that means they have to stay fueled up more or less constantly. In practice, that means solid fuels or something in the UDMH/NTO family. A cryogenic fuel ICBM would need ...


12

In addition to SS-520-4, I would also point to Chinese CZ-11 rocket, Israeli Shavit and many others


11

The reason is refurbishment cost and turnaround: For a liquid booster, you can more or less pump more fuel and you are ready to go. With a SRB, it isn't so easy: You need to dismantle everything, check it and build it again. Space Shuttle's SRB refurbishment has been quoted as a marginal improvement over building them again from scratch, altho I couldn't ...


11

Solid Rocket Motors are inexpensive to manufacture if you have the knowledge and experience already. For space use they are commonly made by weapons makers, sharing many production assets with weapon manufacturing. Minus the military infrastructure, they are not as easy or economical. A private company like Rocket Lab would likely have to buy solid rocket ...


10

According to the Aerojet wiki, they were considered. Aerojet solid fuel technology was under consideration for use in Saturn first stages. In the 1963, the U.S. Air Force gave Aerojet General $3 million to start construction of a manufacturing and testing site several miles southwest of Homestead, Florida. . . . .Between Sept. 25, 1965 and June 17, 1967, ...


10

Hill and Peterson "Mechanics and Thermodynamics of Propulsion", third printing, November 1970, page 385, has a diagram that agrees with your intuition. (sorry for poor scan quality) You are correct - as the surface area increases, so does the mass flow rate. There must be other factors in play in the graph from Wikipedia.


10

From Russian wiki on RS-82: RS-82 and RS-132 are unguided air-to-air, air-to-ground rockets developed during 1929-1937. Further developed into М-8, М-13 "Katyusha" rockets. It seems the final propellant was a solid fuel N developed by a group lead by A. Bakaev in mid 30s: nitrocellulose (collodion cotton) - 57% nitroglycerine - 28% dinitrotoluene - 11% ...


10

The Soyuz descent module has SRMs that are fired just before touchdown. Does that count?


9

This is the tail end of the thrust graph given in Hobbes' answer: I've added guidelines showing the point where thrust falls below the 60,000 lbf point, about 2.7 seconds before it hits zero. The area under the curve there has units of lbf × seconds, which is impulse. The pic is a little fuzzy, so it's hard to tell if the arc continues smoothly all the ...


9

Problem with separating SRB during burn, be it to use SRB to accelerate or decelerate for reentry, is that you'd have big problems designing their mounts so they detach while they still accelerate in the direction relative to the main vehicle for which they would be designed to have the strongest grip to it. Once they're depleted, it's the vehicle itself ...


9

A solid rocket can stop early, and typically in a situation where they rely on it, they will have extra fuel, and just cut off the rocket early. This is very commonly done for missile systems, which have to be very flexible, and be able to fire with little time, and near other people. In addition, they can correct for other wrongness by moving the thrust ...


9

Basing on two papers I had managed to find: Electrical Solid Propellants: A Safe, Micro to Macro Propulsion Technology and Plasma Plume Characterization of Electric Solid Propellant Pulsed Microthrusters. First, the concept isn't new; it's an incremental research on Pulsed Plasma Thrusters which were used first on soviet Zond 2 and Zond 3, starting in ...


9

Underneath the diagrams in the Wikipedia article you link, there's a mention of the BATES grain geometry: Circular bore: if in BATES configuration, produces progressive-regressive thrust curve https://en.wikipedia.org/wiki/BATES In which there is combustion occurring on both ends of a cylindrical segment as well as the central bore. In such a case, ...


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