Principles of Propulsion and its Application in Space Launchers

1. Principles of Propulsion and its Application in Space Launchers Prof. Dr.-Ing. Uwe Apel Hochschule Bremen REVA Seminar

2. Overview • How Rockets are Propelled • Thrust Generation in a Rocket Engine • Rocket Engine Performance Parameters • Classification of Space Vehicles • Application of Rocket Engines • Classification of Rocket Propulsion Systems • Physical Limits of Chemical Space Propulsion • The Rocket Equation • Staging of a Rocket REVA Seminar

3. How Rockets are Propelled • The Change of the state of motion of a rocket follows the principle of repulsion • Newton‘s law applies:ACTIO = REACTIOAny force acting on a mass creates an force of the same size in the opposite direction! • By ejection of a mass at a high velocity (usually a hot gas flow ) from the rocket engine a force is produced changing the momentum of the rocket. Important: According to Newton‘ law of momentum conservation the sum of the momentum changes of working fluid and vehicle equals 0 ! REVA Seminar

4. FunctionalPrincipleof a Rocket Thrustisgenerated exitsnozzlewithvelocity REVA Seminar

5. Thrust Generation in a Rocket Engine REVA Seminar

6. Rocket Engine Performance Parameters REVA Seminar

7. The Rocket Equation • Describes Movement of a rocket in force-free space • Calculates velocity change achievablewith a rocket geaturing a certain mass ratio and average specific Impulse • Differential form: • Integral form: REVA Seminar

8. Classification of Space Vehicles REVA Seminar

9. Classification of Rocket Propulsion Systems • Origin of propulsion energy • Chemical • Nuclear • Solar • Propellants and their aggregate state • Solid propellants • Liquid propellants • Hybrid engines • Cold gases • Thrust level • High thrust (> engine weight) • Low thrust (< engine weight) REVA Seminar

10. Application of Rocket Engines REVA Seminar

11. Typical Performances of Rocket Engines REVA Seminar

12. Rocket Engine Performance Map thrust to mass [N/kg] specificimpulse [m/s] acceleration [m/s] REVA Seminar

13. ∆V Requirement • The ∆V requirement of a space mission is dependent on: • Size and orbit of launch planet • Size and orbit of destination planet • Propulsion concept (thrust level, propulsion time) • Chosen trajectory and resulting flight time • Accuracy of orbit and attitude control system • Vehicle aerodynamics REVA Seminar

14. ∆V Calculation REVA Seminar

15. Typical ∆V Requirements REVA Seminar

16. Elements of a Space Transportation System REVA Seminar

17. Elements of a Rocket The take-off mass of a rocket consists of three major mass elements: • Structure and Engine(s) • Body and tankage • Engines and related equipment • Non-usable propellant residuals • Usable propellant reserve • Recovery equipment (parachutes, wings, landing gear, etc.) • Instrumentation and avionics • Propellants • Expected propellant consumption during flight • Propellants expended prior to lift-off • Payload REVA Seminar

18. Design Parameters • According to the rocket equation a maximisation of the ratio between the initial mass m0and the cut-off mass mc is required for a high velocity capability • Thus 80% ÷ 90% of the initial mass of a rocket is propellant mass • This requires an ultra-light structural design and small, efficient engines with a very high power density! • Key design parameters of a rocket are: • The propellant mass fraction • The propellant ratio • The payload ratio REVA Seminar

19. Technological limits for a rocket • The performance of a single-stage rocket is limited by the technologically achievable values for the mass ratio R and the exhaust velocity C and the ∆V requirements of the mission: • Limits: • useful minimum payload mass fraction of l>= 1 % • achievable propellant mass fraction of µ = 0.90 • today’s engines performance of C0 = 4300 m/s Cvac= 4600 m/s • minimum velocity increment to reach orbit ∆V = 9100 m/s • Thus, it is very difficult to design a one-stage launch vehicle! REVA Seminar

20. mpayload mpropellant mstructure High Development Risk! Technological Limits: Single-stage to Orbit (SSTO) REVA Seminar

21. Staging of a rocket • The problem can be overcome by "staging" the rocket which means distributing the total propellant mass over more than one tank for each propellant component and not further accelerating empty tankage by cutting it off • In theory a rocket with an infinite number of stages would provide a maximum payload ratio • Practically the number of stages is limited by the propellant mass fraction of each stage which increases with decreasing stage size because tanks and engines cannot be downsized linear • For transportation in orbits around Earth, 2-3 stages provide an optimum performance depending on the selected propellant combination and other design aspects REVA Seminar

22. Influence of staging on payload mass (example) One-stage design Two-stage design Assuming a launch vehicle based on following design data: Mission velocity requirement(Earth to orbit): ∆V=9200 m/s Average specific Impulse of engines: C=4400 m/s Launch mass: m0=100 Mg Propellant mass fraction: µ=0.9 REVA Seminar

23. Influence of staging on vehicle mass and payload One-stage design Two-stage design REVA Seminar

24. Optimum staging of a launch vehicle • Optimum distribution of total ∆V between the stages of a rocket depends of specific impulses of stage engines and stage propellant mass fractions • For a two-stage vehicle, the payload mass fraction l of the rocket with respect to a given mission ∆V can be obtained from the following equation REVA Seminar

25. Optimum staging of a launch vehicle • For a rocket with the same average specific impulse and propellant mass fraction in each stage, the l -Function has its maximum at U1=U2=∆V/2 • This means, that the first stage of a two-stage rocket should have a mass which is 3.6 times the mass of the second stage if the same technology is used in both stages • For a launch vehicle going from Earth‘s surface to an orbit the described theoretical optimum is additionally influenced by the ascend trajectory due to: • gravity and drag losses (changes theoretical ∆V distribution) • engine performance (C depends on ambient pressure) REVA Seminar

26. Optimum staging of a launch vehicle (Example) REVA Seminar