Supplementary Material on Chemical Rockets for Lecture #41: Commercial Access to & Use of Lunar Resources

NEEP 533/Geology 533/Astronomy 533/EMA 601: Resources from Space

April 30, 1999

 Click here to see the PowerPoint viewgraphs shown in class.

Also see Mike Griffin's lecture 33: Heavy Lift Launch Vehicles
Next: Lecture 42: Interlune/InterMars Initiative
Previous: Lecture 40: Economics of Large Space Projects
Up: Resources from Space syllabus

Chemical rocket overview

Some rocket-history documents on the Web include A Brief History of Rocketry (from a rather American perspective), NASA's History Timeline,  and the National Space Society's Space History Hyperlinked web page.  Highlights of chemical-rocket history include:
Year Event 
300 BC Gunpowder-filled bamboo tubes used for fireworks in China 
1045 Military rockets in use in China 
1895 Konstantin Tsiolkovsky derives the fundamental rocket equation 
1926 Robert Goddard launches first liquid-fueled rocket 
1942 Wernher von Braun's team launches first successful A4 (V2) 
1957 Sputnik launch (USSR) 
1958 Explorer I launch (US)
1967 Saturn V first launch (US)
1969 Apollo 11 Moon launch 
Chemical rockets will almost certainly play a major role in space operations for the foreseeable future.  Although advanced, high-exhaust-velocity rockets will eventually take over most long-range, interplanetary missions, chemical and nuclear-thermal rockets remain the uncontested leaders in producing the high thrust-to-weight ratios required for leaving most planetary surfaces.

Specific impulse

The impulseI, given to a rocket is the thrust force integrated over the burn time. Traditionally, for the case of constant exhaust velocity (vex), the specific impulse has been used: Isp = I / (mp g0) = vex / g0, where mp is the propellant mass and g0 is Earth's surface gravity. In English units, Isp is measured in seconds and is a force per weight flow. Often today, however, specific impulse is measured in the SI units meters/second [m/s], recognizing that force per mass flow is more logically satisfying. The specific impulse is then simply equal to the exhaust velocity, Isp = vex.

Chemical rocket fuels

Two main classes of chemical-rocket fuels exist, liquid and solid. A good introductory discussion of chemical-rocket fuels can be found by clicking here. The advantages of liquid-fueled rockets are that they provide
  1. Higher exhaust velocity (specific impulse),
  2. Controllable thrust (throttle capability),
  3. Restart capability, and
  4. Termination control.
The advantages of solid-fueled rockets are that they give
  1. Reliability (fewer moving parts),
  2. Higher mass fractions (higher density implies lower tankage), and
  3. Operational simplicity.
Selected Chemical-Rocket Fuels
Liquid propellants 
Fuel Oxidizer Isp (s) 
Hydrogen(LH2) Oxygen (LOX) 450 
Kerosene LOX 260 
Monomethyl hydrazine (MMH) Nitrogen tetroxide (N2O4) 310 
Solid propellants 
Fuel Oxidizer Isp (s) 
Powdered Al Ammonium perchlorate 270 

Rocket efficiency

When the total kinetic energy of the rocket and its exhaust are taken into consideration, the highest efficiency occurs when the exhaust is equal to the instantaneous rocket velocity, as shown in the figure at right. See Sutton for a discussion.  Rocket efficiency versus ratio of rocket velocity to exhaust velocity

Ascent from planetary surfaces

Key effects that come into play during launch from planetary surfaces are shown at right. Gravity reduces the effective acceleration, and it is generally the most important force. Atmospheric drag can create significant friction, both heating and slowing a rocket. The Coriolis and centrifugal forces due to the planet's rotation are usually small effects, but the planet's rotation can often be used to give the rocket an initial velocity in a desired direction. 
Atmospheric drag 
Coriolis force 
Centrifugal force 
Wind velocity 
Planetary rotation 

Launch criteria

Various criteria are used to decide when to launch a rocket. For the Space Shuttle, these include (from Marshall Space Flight Center's Space Academy)

Engine design

F-1 engine
Chemical-rocket engines are technological marvels, combining knowledge of physics, chemistry, materials, heat transfer, and many other fields in a complicated, integrated system. The F-1 engine used in the first stage of the Saturn V rockets that launched the Apollo missions appears at right.  Saturn V engine, the F-1

Heat transfer

Heat transfer presents a critical problem for rocket engine designers. Various approaches have been considered, including


Rocket nozzles are usually of an expansion-deflection design. This allows better handling of the transition from subsonic flow within the combustion chamber to supersonic flow as the propellant expands out the end of the nozzle and produces thrust. Many nozzle variations exist. The governing equation for the magnitude of the thrust, in its simplest form, is

F = vex dm/dt + (pex - pa) Aex = veq dm/dt,

where vex is the exhaust velocity, dm/dt is the propellant mass flow rate, pex is the pressure of the exhaust gases, pa is the pressure of the atmosphere, Aex is the area of the nozzle at the exit, and veq is the equivalent exhaust velocity (that is, corrected for the pressure terms). If the pressure inside the chamber is too low, the flow will stagnate, while too high a pressure will give a turbulent exhaust--resulting in power wasted to transverse flow.

Saturn V

Saturn V launch
Wernher von Braun's team at Marshall Space Flight Center developed the three-stage Saturn V rocket, shown at right. The Saturn V served as the workhorse of the Apollo Moon launches. Its first stage developed over 30 MN (7.5 million lbs) of thrust and burned about 14 tonnes of propellant per second for 2.5 minutes. 

Space Shuttle

Space Shuttle on launch pad 
Approximate parameters for the Space Shuttle (officially, the Space Transportation System or STS) are listed in the table below. A good Worldwide Web link for further information is NASA's Space Shuttle home page.  Space Shuttle on pad
Space Shuttle Parameters
Total length 56 m 
Total height 23 m 
Wingspan 24 m 
Mass at liftoff 2x106 kg 
Orbiter dry mass 79,000--82,000 kg 
Solid-rocket booster thrust, each of 2 15,000,000 N 
SSME (main engine), each of 3 1,750,000 N 

Single-stage to orbit (SSTO)

The Delta Clipper is a key candidate single-stage-to-orbit vehicle. The experimental version DC-X appears at right. Goals for the research program include complete reusability and minimal cost. Driving the concept of a single-stage-to-orbit vehicle is the premise that Earth launch will become affordable only when operations become similar to those of commercial airlines.  The DC-X program has evolved into the X-33 program.  DC-X launch

Useful references


George P. Sutton, Rocket Propulsion Elements (Wiley-Interscience, New York, 1992).
Michael D. Griffin and James R. French, Space Vehicle Design (AIAA, Washington, DC, 1991).

Worldwide Web

The Jet Propulsion Laboratory (JPL) maintains a Web site, Basics of Space Flight, which gives a good tutorial introduction to many of the topics covered here.

The Cambridge University Press's Handbook of Space Astronomy and Astrophysics contains an excellent chapter on Aeronautics and Astronautics, with parameters for many current launch vehicles.

Space-related, government, and other potentially useful Web sites

Potential Questions

  1. Discuss the relative advantages of liquid propellants and solid propellants.
  2. Assuming that a rocket nozzle is designed to be most efficient part way along the rocket's flight path, explain the effects reducing efficiency before and after this point.
  3. Consider the problem of routine access to space from Earth's surface, and discuss the relative advantages and disadvantages of
    1. Heavy-lift launch vehicles, as epitomized by the Saturn V
    2. Space Shuttles
    3. Single-Stage to Orbit (X-33) vehicles

Also see Mike Griffin's lecture 33: Heavy Lift Launch Vehicles
Next: Lecture 42: Interlune/InterMars Initiative
Previous: Lecture 40: Economics of Large Space Projects
Up: Resources from Space syllabus

Dr. John F Santarius

Fusion Technology Institute,
University of Wisconsin-Madison
1500 Engineering Dr.
Madison, WI 53706

415 Engineering Research Building
e-mail:; ph: 608/263-1694; fax: 608/263-4499
Last modified: April 27, 1999