Page 87 - Intro to Space Sciences Spacecraft Applications

Zntroduction to Space Sciences and Spacecraft Applications
14
have to maintain the tanks and lines within acceptable temperatures so the
fuel does not freeze and burst its containers. The loss of the $1 billion
Mars Observer as it was approaching its destination in August 1993 was
attributed to burst propulsion system pipes.
Also, since the exhaust gases may remain in the Vicinity of the space-
craft, the propellant must not become a source of contamination to the
spacecraft systems or the operation of the payload. Pressurized gases such
as nitrogen, which are less of a source of contamination than many other
propellants, are often used for attitude control; however, their perfor-
mance (specific impulse) is less than that of liquid propellants and may
not be acceptable for higher thrust purposes. A commonly used liquid
mono-propellant for station-keeping and attitude control is hydrazine
(N2H4), of which there are several variations (monomethylhydrazine
[MMH] and unsymmetrical dimethylhydrazine [UDMH] are common
examples). Hydrazine has many desirable characteristics in terms of stor-
age and contamination, and delivers a very acceptable specific impulse of
over 200 seconds.

REFERENCES/ADDITIONAL READING

Anderson, J., Zntroduction to Flight, 2nd ed. New York: McGraw-Hill,
Inc., 1985.
Sutton, G., Rocket Propulsion Elements, 5th ed. New York: John Wiley &
Sons, Inc., 1986.
C. Cochran, D. Gorman, and J. Dumoulin (Eds.), Space Handbook.
Alabama: Air University Press, 1985.

EXERCISES

1. Determine the theoretical exhaust velocity for the liquid hydrogedliq-
uid oxygen fueVoxidizer combination given in the reading. Consider
the ratio of exhaust pressure to combustion chamber pressure (pJp,)
and the ratio of specific heats (y) to be 0.001 and 1.4, respectively.
2. Recompute the above exhaust velocity with an increase and then a
decrease in the pressure ratio of a factor of ten (Le., p$po = 0.01 and
pJp, = 0.0001).