Solid Rocket Engines: 1

1. Solid Rocket Engines: 1

2. Solid rocket motors Unlike liquid rocket engines, the fuel and oxidizer are premixed in solid rocket. The result is a rubbery solid that burns when heated. Solid rockets are simpler and cost less than liquid-fueled rockets have lower Isp than most liquids (~ 285 sec) are more dense -> higher “density impulse” . So packaging is easier. Cannot be throttled or shut down during the flight (unless pre-designed to do so) Thrust is limited by nozzle size – not by pump capacity. Easy to get very high thrust for boosters.

3. Applications -         Missiles (acceleration, storage)-         Booster, strap ons (high thrust per size)-         Apogee kick motors

4. Star-Grained Solid Rocket Motor http://www.nf.suite.dk/stargrain/ After 1 minute of burn

5. General configuration TE-M-364-4 is a 15,000 lb. thrust solid propellant motor developed for use as an upper stage. It is an enlarged version of the TE-M-364, one of a series of solid propellant motors that powered the workhorse USAF Burner I and Burner IIA upper stages to orbit scientific, weather, navigation, and communications satellites. The TE-M-364-4 powered the upper stages of the USAF Atlas boosters used to launch the Global Positioning System (GPS) satellites. It also was used as the second stage motor on USAF Thor vehicles that launchedsatellites of the Block 5D Defense Meteorological Satellite Program (DMSP) as well as the third stage motor on the Thor Delta launch vehicles. www.wpafb.af.mil/ museum/engines/eng62.htm

6. history.nasa.gov/ rogersrep/v1p56.htm

7. “STS SRB motors SRB motor: propellant mixture ammonium perchlorate (oxidizer, 69.6 percent by weight), aluminum (fuel, 16percent), iron oxide (a catalyst, 0.4 percent), a polymer (a binder that holds the mixture together, 12.04 percent), and an epoxy curing agent (1.96 percent). The propellant is an 11-point star- shaped perforation in the forward motor segment and a double- truncated- cone perforation in each of the aft segments and aft closure. This configuration provides high thrust at ignition and then reduces the thrust by approximately athird 50 seconds after lift-off to prevent overstressing the vehicle during maximum dynamic pressure.” liftoff.msfc.nasa.gov/ Shuttle/About/detsrb.html

8. “The SRBs are used as matched pairs and each is made up of four solid rocket motor segments. The pairs are matched by loading each of the four motor segments in pairs from the same batches of propellant ingredients to minimize any thrust imbalance. The segmented-casing design assures maximum flexibility in fabrication and ease of transportation and handling. Each segment is shipped to the launch siteon a heavy- duty rail car with a specially built cover.” liftoff.msfc.nasa.gov/ Shuttle/About/detsrb.html

9. “The forward section of each booster contains avionics, a sequencer, forward separation motors, a nose cone separation system, drogue and main parachutes, a recovery beacon, a recovery light, a parachute camera on selected flights and a range safety system. Each SRB has two integrated electronic assemblies, one forward and one aft. After burnout, the forward assembly initiates the release of the nose cap and frustum and turns on the recovery aids. The aft assembly, mounted in the external tank/SRB attach ring, connects with the forward assembly and the orbiter avionics systems for SRB ignition commands and nozzle thrust vector control. Each integrated electronic assembly has a multiplexer/ demultiplexer, which sends or receives more than one message, signal or unit of information on a single communication channel.” liftoff.msfc.nasa.gov/ Shuttle/About/detsrb.html

10. The nozzle is gimbaled for thrust vector (direction) control. Each SRB has its own redundant auxiliary power units and hydraulic pumps. The all-axis gimbaling capability is 8 degrees. Each nozzle has a carbon cloth liner that erodes and chars during firing. The nozzle is a convergent- divergent, movable design in which an aft pivot- point flexible bearing is the gimbal mechanism. The cone- shaped aft skirt reacts the aft loads between the SRB and the mobile launcher platform. The four aft separation motors are mounted on the skirt. The aft section contains avionics, a thrust vector control systemthat consists of two auxiliary power units and hydraulic pumps, hydraulic systems and a nozzle extension jettison system. Eight booster separation motors (four in the nose frustum and four in the aft skirt) of each SRB thrust for 1.02 seconds at SRB separation from the external tank. Each solid rocket separation motor is 31.1 inches long and 12.8 inches in diameter. liftoff.msfc.nasa.gov/ Shuttle/About/detsrb.html

11. Solid rocket Explosion: Large fragments created www.wstf.nasa.gov/.../ Explosion/HEBFTesting.htm

12. Inertial Upper Stage www.aero.org/.../crosslink/ winter2003/08.html W. Paul Dunn

13. Stinger Man-Portable S-A Missile StingerUnofficial names/slang: n/aFunction: To provide close-in, surface-to-air weapons for the defense of forward combat areas, vital areas and installations against low altitude air attacks.Date deployed: 1987Contractor: General Dynamics /RaytheonUnit cost: $38,000Length: 5' - 0"Wingspan: 3.5"Diameter: 0' - 0" (0.00m)Speed: SupersonicWeight at launch: 34.5 lbs (launcher w/ missile)Guidance: Fire-and-forget passive infrared seekerRange: approx. 1 - 8 kmEngine: Dual thrust solid fuel rocket motorWarhead: High explosive www.combatindex.com/.../ detail/mis/stinger.html

14. Solid Propellants Double Base – molecules of fuel/oxidizer are mixed (e.g., gun powder dissolved in nitroglycerine) – oxygen in both (less common, more explosive) Composite – Heterogeneous mixture of fuel, oxidizer and binder, plus some other additives – more common.

15. Fuels Powdered Aluminium STS Powdered Mg Binders most popular now The binder holds the entire formulation in a structurally sound propellant grain, under temperature and pressure variations, plus accelerations and vibration loads of flight. Binders should have low density and energy of combustion, plus structural integrity using minimal binder volume. “Solids Loading” = percentage the total propellant mass taken up by fuel + oxidizer. Usually > 90% Binders are usually long-chain polymers – keep the propellant powders and crystals in a continuous matrix through polymerizing and cross-linking.

16. Oxidizers • Ammonium Perchlorate (AP) – contains chlorine – acid rain • Ammonium Nitrate (AN) is more benign. But inherently low burning • rate and a phase change • near 30 deg. C.

17. Other Ingredients Fixers (bonding agents): improve bond between oxidizer and binder Curatives: increase rate of polymerization. Plasticizer: improve physical properties at low temperatures Darkening agents: reduce thermal radiation losses through translucent propellant HMX: increases burning rate. Can cause detonations too.

18. Propellant Burning Rate Regression Law – St. Robert’s Law regression rate proportional to pressure to some n or A “plateau” type burning rate law is more common, where n becomes close to zero over a range of pressure. Note: n has to be < 1 for stability

19. Grain cross sections to control burning • End grain: neutral • Internal Burning Tube: progressive • Internal-External Burning Tube: neutral • Rod and Tube: neutral • Internal Burning Star: neutral • Dog Bone: neutral • Slots and Tube: neutral • Slotted Tube: neutral • Wagon Wheel: neutral • Multiple Perforations: neutral • Neutral thrust history generally gives the smallest inert mass since • the maximum and average pressures on the structure are nearly • the same with this. Else use regressive thrust profiles.

20. Simple Solid Rocket Analysis In a solid rocket motor, the “chamber” pressure is related to the geometry and burn rate. Therefore we must know something about the geometry to find Pc (time) and thus thrust and Isp vs. time. Lweb pc Ab r Then from conservation of mass: (Simple end-burner design) …..(1) (mass released from surface per unit time = mass added to growing chamber volume + mass exhausted) ….(2) density of solid density of gas in bore propellant mass flow rate

21. Recall or ….(3) So where (St. Robert’s Law) …..(4)

22. Let us first assume: 1) in equilibrium 2) is small (note that is a gas density) 3) is constant (end burner type design) (and “a”, n, do not change over time) 4) (n < 1) then ..

23. ………(5) (This is a steady-state approximation) (steady-state lumped-parameter) where Pay particular attention to units in (5) if you are going to use Humble’s table of “a” in Table 6.9.  We can use equation (5) to estimate the size of an end-burner for a desired Pc and performance.

24. Example target (note for solids) in cm/s (Pc =MPa) If the desired and Find and =.0676m2

25. from (5) So and If this geometry is unacceptable, we can change Pc and resize. For example, a higher Pc will make a longer, more slender solid rocket.

26. Time varying Burn Area For a more general cross section (tube, star, wagon wheel, etc) we would expect the cross-sectional area or the total exposed burn area to change with time. Given the initial geometry and

27. Time varying Burn Area In the units we have been using for each, where typically assume and n are constant. But and Pc can change with time Let and be fixed Then

28. (at x=xf, t=tb) for most complex shapes, we will need to integrate the R.H.S. numerically, and may be a complex calculation over multiple regions. For a simple shape where L= bore length

29. So Integrating this (left to HW) gives X(t) - regression amount as a function of time and therefore Thrust (t) = And the total burn time, , can be calculated for when Pc(t)