Home | LinksRegulations | Aircraft - Rocket Technology | Photo Gallery | Accident reports

SOLID ROCKET PROPELANTS

Solid rocket propellants differ from liquid propellants in that the oxidiser and fuel are embedded or bound together in a solid compound that is cast into the rocket motor casing. They began with black powder rockets in medieval times, progressed through double base propellants in the early 1900's, and finally achieved high performance as composite propellants from the 1940's. Composite motors were developed to a high degree of perfection in the United States in the 1950's and 1960's. In Russia, due to a lack of technical leadership and rail handling problems, serious use of composite propellants did not begin until the 1960's, and then primarily for military rockets. The detailed chemistry and development of solid propellants is provided by Andre Bedard in the following separate articles:

·              Black Powder Solid Propellants

·              Double Base Solid Propellants

·              Composite Solid Propellants

·              Propellant Tables

The following summarises the development of solid rocket propellants very briefly.

Solid propellant rockets, using black powder as the propellant, were introduced by the Chinese in the early 13th century. The next significant event occurred in the late 17th and 18th centuries when the development of nitro-cellulose, nitro-glycerine, cordite, and dynamite resulted in their consideration as a rocket propellant. Immediately before World War I, the French used nitro-cellulose as a propellant for artillery rockets.

In 1936, Dr. Theodore von Karman, and his associates at Caltech began a program that resulted in the first composite propellants using an organic matrix (asphalt) and an inorganic oxidiser (potassium perchlorate). Their work also covered the beginnings of understanding the associated interior ballistics, combustion, ignition, and related structural/materials issues. This was the start of modern solid propellant rocketry. Composite propellants virtually replaced double base propellants (based on mixtures of nitro-cellulose and nitro-glycerine) in most applications.

Following World War II many companies and agencies began propellant development programs involving a wide variety of oxidisers, fuels (binders) and processing methods. In this era, improvements in performance (quantified as specific impulse) were largely achieved by increasing oxidiser loading. Most of the binders were supplied by the rapidly expanding plastics industry.

The ever increasing number of potential missile programs resulted in growing pressure to provide other propellants that had improvements in terms of: performance, structural properties (strength, stability, impact resistance) thermal characteristics (temperature range, cycling), processing, cost, safety, quality, and reliability. In the early 1950s, Atlantic Research invented the use of up to 15 percent powdered aluminium to replace a like amount of oxidiser - giving a performance gain of about 15 percent. Propellant researchers began to understand the complete chemistry of solid propellants, and the need for molecular chain extensions and cross linking of the binders became apparent. The invention of bonding agents (as part of the fuel) greatly improved not only the mechanical properties, but also the resistance to ageing, humidity, and temperature cycling.

Two mainstream composite propellant/binder families emerged (Polyurethane and Polybutadiene), but these were accompanied by a large number of variations and evolutionary products. In addition, there were numerous associated/alternative formulations and concepts tailored to specific missile program requirements. Included among them were: Nitro-polymers, Fluorine based propellants, Beryllium additives, etc. At the same time double base propellants (based on mixtures of nitro-cellulose and nitro-glycerine) continued to evolve and compete. When double base propellants were used to replace conventional binders this resulted in the highest values of specific impulse ever attained.

Aerojet initially concentrated on Polyurethane (PU), and Thiokol favoured Polybutadiene (PB). Thiokol's work included PBAA, a copolymer of Butadiene and Acrylic Acid. This was replaced by PBAN, a terpolymer including Acrylic Acid and Acrylonitrile. Aerojet also conducted considerable development effort in this area, and PBAN was used in Aerojet's 260" space booster.

Several other companies also worked in these and other related areas. For example Phillips Petroleum with Rocketdyne developed Carboxy Terminated Polybutadiene (CTPB) using both a Lithium initiated polymerisation, and a free radical type. These propellants were widely used, but were later overtaken by Hydroxyl Terminated Butadiene (HTBD). By the 1990's Aerojet favoured HTBD and formulations thereof including double base binders.

In addition to the binder evolution, there was a variety of oxidisers to choose from: ammonium and potassium nitrates, perchlorates, and picrates. Perchlorates were generally favoured, but later environmental concerns were expressed at the amount of chlorine compounds (mainly hydrochloric acid) emitted into the atmosphere. One possible solution was the use of a hybrid (liquid and solid) system with a PBAN or similar grain and liquid oxygen as the oxidiser. This also provided a substantial cost saving, and allowed thrust variation and control features that were otherwise not easily achieved.

Paralleling the propellant formulation was development in the design of the propellant grain shape. In most asphalt rockets, the propellant was simply cast into the cylindrical motor chambers (or in some cases into a thin metal jacket which was then inserted into the chamber). Burning occurred only on the exposed aft end of the propellant, resulting in a constant level of thrust. The Aeroplex and other free-standing, rigid cylindrical grains (burning on the inner diameter and outer diameter.) also produced a constant thrust/time curve, because the increase in internal burning surface area just matched the decreasing external surface area.

Case-bonded propellants called for a different configuration of the burning surface. The outside of the propellant was bonded to the chamber and protected it from the hot gases. A simple cylindrical perforation down the centre of the grain would produce a steadily increasing pressure and thrust from very low at start to very high at completion of burning. The solution was to use a central star shaped perforation, which could produce an essentially flat thrust/time curve. The perforation was accomplished by casting the propellant around a core of the desired shape, which was removed after the propellant was completely cured. The tapered rays of the star provided an initial large burning surface, which decreased as the points burned away. Variations in the core geometry allowed a wide range of thrust/time characteristics, to match overall missile requirements.

Additional variations could be achieved by longitudinal variations in the core size and shape, as well as by casting layers of propellant having different characteristics. This latter concept was used for many tactical missiles requiring a boost/sustain thrust curve. For years, grain design was performed by manual geometric manipulation, but computer aided design greatly simplified the task.

The earliest production process for asphalt propellant was actually to hand-stir the ground oxidiser into the heated asphalt. Quality control and consistency were highly questionable, and the safety aspects were in hindsight, terrifying. The immediate solution was to use commercial bread dough mixers in steadily increasing size and robustness. For the more viscous propellant families, much more sturdy mixers were adapted from the tire industry. In addition, the commercially available oxidisers required grinding to achieve the desired fine grain sizes and grain size distribution.

Following fatal accidents in both propellant mixing (asphalt) and oxidiser grinding (potassium perchlorate), production processes were improved to include remote operation, modern instrumentation and control, and a host of other subsystems which significantly improved safety, versatility, and consistency.

The disadvantages of solid propellants in space applications include:

·                                 Slightly higher empty mass for the rocket stage

·                                 Slightly lower performance than storable liquid propellants

·                                 Transportability issues: Solid propellants are cast into the motor in the factory, unlike liquid fuel rockets which can be fuelled at the launch pad. This means they have to either be: 1) limited in size to be transportable (as for the Delta and Ariane strap-on motors); 2) cast in segments, with the segments assembled at the launch base (as for Titan and the Space Shuttle); or 3) cast in a factory near the launch site (actually done for large test motors intended for Saturn V upgrades).

·                                 Once ignited, they cannot be easily shut down or throttled. Thereafter they have to be pre-cast or milled out for a specific mission.

·                                 Often catastrophic results in the event of a failure

Advantages of solid rocket motors, many of which make them ideal for military applications:

·                                 High density and low volume

·                                 Nearly indefinite storage life

·                                 Instant ignition without fuelling operations

·                                 High reliability


Progressive Development of Large Solid Rocket Motors

In the United States:

·                                 Early 1950's: Hermes/ Sergeant (Army): 32 inch

·                                 March 1956: Polaris (Navy): 54 inch

·                                 Late 1950's: Minuteman (Air Force): 65 inch (Thiokol)

·                                 1960-1963: USAF space development program - 86, 96, 100, 120 inch test motors

·                                 Early 1960's: Titan 3 (DoD/NASA) - 120 inch (UTC)

·                                 1963-1965: Moon program (DoD/NASA) for Nova/Saturn vehicles

o                                                        44 inch (Aerojet), 65 (Thiokol), 120 inch (Aerojet) subscale motors

o                                                        156 inch (Lockheed and Thiokol), 260 inch (Thiokol and Aerojet) PBAN full scale motors.

·                                 Early 1970's: Shuttle - 146 inch PBAN

·                                 1990's: Titan 4B USRM - 126 inch HTPB




Fuel: Solid. Fuel Density: 1.35 g/cc.

Solid propellants have the fuel and oxidiser embedded in a rubbery matrix. They were developed to a high degree of perfection in the United States in the 1950's and 1960's. In Russia, development was slower, due to a lack of technical leadership in the area and rail handling problems. The disadvantages of solid propellants include:

·                                 Slightly higher empty mass for the rocket stage

·                                 Slightly lower performance than storable liquid propellants

·                                 Transportability issues: Solid propellants are cast into the motor in the factory, unlike liquid fuel rockets which can be fueled at the launch pad. This means they have to either be: 1) limited in size to be transportable (as for the Delta and Ariane strap-on motors); 2) cast in segments, with the segments assembled at the launch base (as for Titan and the Space Shuttle); or 3) cast in a factory at the launch site (actually done for large test motors intended for Saturn V upgrades).

·                                 Once ignited, they cannot be easily shut down or throttled. Thereafter they have to be pre-cast or milled out for a specific mission.

·                                 Nearly always catastrophic results in the event of a failure

Advantages of solid rocket motors, many of which make them ideal for military applications:

·                                High density and low volume

                      Nearly indefinite storage life

·                                 Instant ignition without fuelling operations

·                                 High reliability

 

Eng-engineslink

Thrust

(vac)-kgf

Thrust(vac)-kN

Isp-sec

Isp (sealevel)-sec

Designed for

Status

15D305

1

0.01

 

 

First Stages

Out of Production

Star 5A

17

 

250

 

Upper Stages

In Production

NOTS-4

72

0.70

250

204

Upper Stages

Out of Production

Star 5C/CB

199

 

266

 

Upper Stages

In Production

Star 5CB

203

2.00

 

 

Upper Stages

In Production

Star 5C

208

 

 

 

Upper Stages

Out of Production

NOTS-3

231

2.26

250

204

Upper Stages

Out of Production

Star 6B

256

 

273

 

Upper Stages

In Production

Star 10

342

 

251

 

Upper Stages

In Production

Star 13

387

3.80

273

 

Upper Stages

Out of Production

PRD-22

400

3.92

 

 

First Stages

Out of Production

Martlet 4-3

550

5.39

300

210

Upper Stages

Study 1962

Star 12

567

 

252

 

Upper Stages

In Production

Star 13A

599

 

287

 

Upper Stages

In Production

Sergeant

680

6.66

235

214

Upper Stages

Out of Production

Star 12A

739

 

270

 

Upper Stages

In Production

Star 13B

775

 

286

 

Upper Stages

Out of Production

MIHT-4

1,000

9.80

295

 

Upper Stages

In Production

Star 17

1,116

19.60

286

220

Upper Stages

In Production

GCRC

1,179

11.60

230

210

Upper Stages

Out of Production

X-248

1,270

12.40

256

233

Upper Stages

Out of Production

X-248A

1,406

13.80

255

232

Upper Stages

Out of Production

Kartukov LL

1,500

14.70

 

 

First Stages

Developed 1946-48

Star 17A

1,633

 

287

 

Upper Stages

In Production

Star 24

1,891

20.00

283

 

Upper Stages

In Production

Mage 1

1,978

19.40

295

220

Upper Stages

Out of Production

Martlet 4-2

2,100

20.60

300

210

Upper Stages

Study 1962

Star 24C

2,189

 

282

 

Upper Stages

In Production

X-258

2,268

22.20

266

242

Upper Stages

Out of Production

Star 20B

2,495

 

289

 

Upper Stages

In Production

SPRD-99

2,500

24.50

 

 

First Stages

Out of Production

FW4-D

2,549

25.00

287

250

Upper Stages

Out of Production

Star 27

2,726

27.00

288

 

Upper Stages

In Production

SLV-4

2,736

26.80

283

60

Upper Stages

In Production

Star 30BP

2,753

27.00

292

 

Upper Stages

In Production

Star 20

2,767

 

287

 

Upper Stages

In Production

FW-4S,TEM640

2,800

27.40

280

255

Upper Stages

Out of Production

GF-02

2,957

29.00

230

200

Upper Stages

Out of Production

P6

3,000

29.40

211

211

Upper Stages

Out of Production

Iris

3,000

29.40

291

115

Upper Stages

Out of Production

Black Arrow-3

3,000

29.40

278

245

Upper Stages

Out of Production

Star 30C

3,329

1,647.00

287

 

Upper Stages

In Production

Star 26

3,402

39.10

271

220

Upper Stages

In Production

Pegasus-3

3,525

34.60

287

 

Upper Stages

In Production

Star 26B

3,531

 

272

 

Upper Stages

In Production

Star 26C

3,570

 

272

 

Upper Stages

In Production

Star 30E

3,608

1,780.00

291

 

Upper Stages

In Production

Star 37XFP

3,878

31.50

290

 

Upper Stages

In Production

Star 37

4,441

43.50

260

220

Upper Stages

Out of Production

Mage 2

4,638

45.50

293

 

Upper Stages

Out of Production

Star 37FM

4,819

47.90

290

 

Upper Stages

In Production

Star 37X

5,216

51.10

296

230

Upper Stages

Out of Production

M-V-4

5,300

52.00

298

 

Upper Stages

In Production

RSA-3-3

5,300

51.00

292

 

Upper Stages

Out of Production

NOTS-1

5,441

53.40

204

204

First Stages

Out of Production

X-254

6,169

60.50

256

233

Upper Stages

Out of Production

Star 48

6,848

67.20

287

 

Upper Stages

Out of Production

Martlet 4-1

6,900

67.70

300

210

First Stages

Study 1962

Star 48A s

7,863

 

283

 

Upper Stages

In Production

Star 48B s

7,863

 

286

 

Upper Stages

In Production

UM-129A

7,900

77.50

291

220

Upper Stages

In Production

H-1-3

7,900

77.00

291

220

Upper Stages

Out of Production

SRM-2

7,996

78.40

304

200

Upper Stages

In Production

Star 48B

8,044

66.00

286

 

Upper Stages

In Production

X-259A

8,239

80.80

295

 

Upper Stages

Out of Production

Star 31

8,391

80.00

294

 

Upper Stages

In Production

Star 63D

8,641

 

283

 

Upper Stages

In Production

SLV-3

9,249

90.70

277

190

Upper Stages

In Production

X-259

9,493

93.10

293

233

Upper Stages

Out of Production

Star 63F

10,669

 

297

 

Upper Stages

In Production

Star 63

10,931

107.20

282

 

Upper Stages

In Production

Pegasus-2

12,053

118.20

290

 

Upper Stages

In Production

M-3B-J

13,469

132.10

294

 

Upper Stages

Developed 1995-

M-3B-Mu

13,472

132.10

294

 

Upper Stages

In Production

Pegasus XL-2

15,653

153.50

290

240

Upper Stages

In Production

Kartukov Soyuz T - TM SAS 17k

17,500

171.00

 

 

First Stages

In Production

EPKM

18,000

 

292

 

Upper Stages

Hardware

P4

18,000

176.50

273

240

Upper Stages

Out of Production

Kartukov P-5

18,300

179.00

 

 

First Stages

Out of Production

SRM-1

18,508

181.50

296

115

Upper Stages

In Production

Star 75

20,511

242.80

288

 

Upper Stages

In Production

M56A-1

23,300

228.50

297

270

Upper Stages

Out of Production

MIHT-3

25,000

245.20

280

220

Upper Stages

In Production

TX-354-3

26,402

258.90

262

232

First Stages

In Production

SLV-2

27,227

267.00

267

216

Upper Stages

In Production

M33-20-4

29,164

286.00

247

232

First Stages

Out of Production

SPRD-30

30,000

294.00

 

 

First Stages

Out of Production

Kartukov P-35

30,000

294.00

 

 

First Stages

Out of Production

M34

30,000

294.20

301

 

Upper Stages

In Production

SB-735

33,430

327.80

263

238

First Stages

In Production

PSLV-3

33,519

328.70

291

160

Upper Stages

In Production

S-44

33,900

332.40

282

 

Upper Stages

In Production

PRD-15

40,000

392.00

 

 

First Stages

Out of Production

SPRD-15

41,000

402.00

 

 

First Stages

Out of Production

Castor 4

41,524

407.20

261

228

First Stages

Out of Production

Castor 4BXL

43,746

429.00

267

 

Upper Stages

In Production

Castor 4B

43,910

430.60

281

220

Upper Stages

In Production

Algol 3A

47,387

464.70

259

226

First Stages

In Production

Algol 1

48,022

470.90

236

214

First Stages

Out of Production

Algol 3

48,121

471.90

284

238

First Stages

In Production

Castor 4A

48,774

478.30

266

237

First Stages

In Production

Pegasus-1

49,447

484.90

285

180

First Stages

In Production

MIHT-2

50,000

490.30

280

220

Upper Stages

In Production

GEM 40

50,905

499.20

274

245

First Stages

In Production

RSA-3-1

51,000

500.00

273

230

First Stages

Out of Production

SLV-1

51,251

502.60

253

229

First Stages

In Production

RSA-3-2

53,000

519.00

284

220

Upper Stages

Developed -1995

M-23-Mu

53,433

524.00

285

220

Upper Stages

In Production

M-23-J

53,515

524.80

282

 

Upper Stages

Developed 1995-

Algol 2

57,537

564.20

255

232

First Stages

Out of Production

Pegasus XL-1

60,062

589.00

293

180

First Stages

In Production

Castor 4AXL

61,164

599.80

269

 

Upper Stages

In Production

GEM 46

62,000

608.10

274

242

First Stages

In Production

RSA-4-2

69,000

676.00

275

220

Upper Stages

Out of Production

SPB 7.35

70,360

690.00

263

240

First Stages

Out of Production

P9.5

70,360

690.00

263

240

First Stages

In Production

Kartukov Soyuz T - TM SAS 73k

73,000

715.00

 

 

First Stages

In Production

LK-1

79,000

 

272

250

Lower Stages

Development

PRD-52

80,000

784.00

 

 

First Stages

Out of Production

Kartukov Soyuz SAS

80,100

785.00

 

 

First Stages

Out of Production

M55/TX-55/Tu-122

80,700

792.00

262

237

First Stages

Out of Production

GEM 60

86,830

851.50

275

245

First Stages

In Production

MIHT-1

100,000

980.60

263

238

First Stages

In Production

M24

126,984

1,245.30

288

203

Upper Stages

In Production

M-13

128,731

1,262.40

263

238

First Stages

In Production

RSA-4-1

155,000

1,520.00

263

238

First Stages

Out of Production

H-2-0

157,036

1,540.00

273

237

First Stages

In Production

H-2/J-1-1

158,730

1,556.60

273

248

First Stages

In Production

Castor 120

168,000

1,650.00

280

229

First Stages

In Production

S-40TM

212,500

2,083.90

272

204

Upper Stages

In Production

Peackeeper-1

224,796

2,204.40

282

250

First Stages

In Production

Peacekeeper 1

224,796

2,204.50

282

250

First Stages

In Production

SRB-A

230,000

 

280

 

First Stages

In Development

S-43

309,000

3,030.20

265

225

First Stages

In Production

S-43TM

327,000

3,206.70

276

170

Upper Stages

In Production

M14

385,488

3,780.30

276

246

First Stages

In Production

PSLV-1

495,590

4,860.00

264

237

First Stages

In Production

UA1205

596,474

5,849.30

263

238

First Stages

Out of Production

UA1206

634,977

6,226.90

265

240

First Stages

Out of Production

P230

660,000

6,472.30

286

259

First Stages

In Production

UA1207

725,732

7,116.90

272

245

First Stages

In Production

USRM

770,975

7,560.50

286

259

First Stages

In Production

UA-156

910,044

8,924.30

263

238

First Stages

Developed to 1966

AJ-260-1/3

1,030,455

10,105.00

275

 

First Stages

Design concept 1960's

200 inch solid, segment x 4

1,134,000

11,120.00

285

 

Upper Stages

Study, NASA, 1960

AJ-260X 1/3

1,136,300

11,143.00

263

238

First Stages

Design concept 1960's

SRB

1,174,713

11,519.80

269

237

First Stages

In Production

Redesigned SRM

1,174,736

11,520.00

269

 

First Stages

In Production

Thiokol 156

1,503,716

14,746.10

263

238

First Stages

Developed to 1966

Hercules

1,587,302

15,565.80

286

259

First Stages

Developed 1995-

AJ-260-2

1,804,460

17,695.30

263

238

First Stages

Developed to 1966

200 inch solid, segment x 6

2,857,000

28,017.00

263

238

First Stages

Out of Production

AJ-260X

3,608,918

35,390.70

263

238

First Stages

Developed to 1966

280 inch solid

4,712,000

46,208.00

265

238

First Stages

Study 1963

300 inch solid

6,485,000

63,595.00

263

234

First Stages

Study 1963

325 in solid

7,041,000

69,047.00

263

238

First Stages

Study General Dynamics 1963

credit © Mark Wade   http://www.astronautix.com/ 

Back to Top

 

Home | LinksRegulations | Aircraft - Rocket Technology | Photo Gallery | Accident reports