**General comments**

I covered part of Chapter V of the notes and Chapter VI. This included 1) Principal figures of merit for rocket performance (thrust, specific impulse and weight), 2) discussion of the general layout of rocket motor components, and 3) Given typical design parameters (nozzle throat and exit areas, and combustor chamber conditions) how to calculate the principal figures of merit. We did onr PRS questions (PRS #1)

Next lecture we will cover the last part of rockets: given the principal figures of merit, how to calculate overall vehicle performance. Please review Chapter V of the notes.

**Responses to 'Muddiest Part of the Lecture Cards'**

(14 respondents)

1)* Why for Isp=ue/g is g
= 9.8 always (even on other planets)?* (2 students) This
is just the way Isp is defined. It is the thrust one would get for a unit weight
flow rate of propellant where the weight is as measured here on earth.

2) * How do you deal with varying
combustion temps in the combustion chamber of the rocket engine in terms of
calculations?* (1 student) Do you mean varying as a function of
location or time? In terms of location, we typically assume that the gases are
well mixed (i.e. all at the same temperature). In terms of any variation with
time, this would require solving the rocket equation for small increments of
time, where the thrust was changed for each increment.

3)* Would a pressure of 300atm
inside the combustion chamber not make the Ae(po-pe) term in the thrust significant
even when compared to mdot * ue? *(1 student)
Not, not typically. Consider the space shuttle main engine: A/A* = 77.5, pc=20.5MPa.
Assuming a gamma of 1.4, then Mexit = 6.6 and pc/pe = 2855 based on isentropic
flow relations. So the exit pressure would be 0.007MPa or about 7% of standard
sea-level atmospheric pressure. The message: the flows are greatly expanded
in rocket nozzles. (And even though the temperature starts out at 3000K, the
isentropic temperature ratio is 9.7 -- so the static temperature is around room
temperature. Of course the stagnation temperature is still 3000K.)

4) * How
do types of fuels and engines affect Isp?* (1 student) In terms
of fuels we haven't yet shown how to connect Tc and Pc to Isp (but we will next
lecture). But once this connection is made, then what is required is a calculation
or measurement of the temperature and pressure changes when various reactants
are brought together and combusted. This is something we won't get to in class.
It requires thermodynamics, fluid dynamics and chemistry. Further in terms of
different types of engines (e.g. liquid propellant, solid propellant, ion engines,
nuclear engines, etc.) we will only discuss liquid propellant engines. More
details can be found in Hill and Peterson

5) * Pegasus launch?*
(1 student)You can check it out here: http://www.orbital.com/SpaceLaunch/Pegasus/index.html
Note that David W. Thompson, the Chairman and Chief Executive Officer, and Orbital
Co-Founder is a graduate from our department. And Professor Kerrebrock sits
on the Board of Directors.

6) * I will need to do a review
of thermo from last term.* (1 student) Yes you will.

7) * So max endurance gives
us maximum power required and maximum ranges gives us what?* (1
student) You are a little confused. Maximum endurance is at the minimum-power-required
point. Maximum range is at the minimum drag point.

8)
* No mud* (6 students).