Fundamental of Rocket Science

1. LIQUID
MONOPROPELLANTS

2.  Monopropellant used in propellant feed
system enhances the system’s efficiency for
certain applications.
 Let us try to understand it by few examples:

3.  Hydrazine as a monopropellant is used as
small attitude and trajectory central
corrections for satellites & spacecrafts.
 Ethylene oxide OR nitro-methane were used
for experimental purposes but are not used
today.

4.  Concentrated hydrogen peroxide was used
for monopropellant gas generations is USA,
Russia & Germany in engines before 1955.
 Ignition of a monopropellant can be
produced by:
a. Electricity
b. Flame heat
c. Catalyst

5.  A monopropellant must be chemically and
thermally stable to ensure good liquid
storage properties.
 Liquid monopropellants should be easily
decomposed to give good combustion
properties.

6.  Tendency of a material to resist change or
decomposition due to internal reaction, or
due to the action of air, heat, light, pressure,
etc is called chemical stability.
 Tendency of a material to resist change
caused solely(only) by heat is called thermal
stability.

7. Hydrazine (N2H4)
 Excellent fuel and monopropellant when
decomposed by a suitable solid or liquid
catalyst.
 As a monopropellant used in gas generators
or in space craft attitude control engines.
 It can be stored for long ( as long as 15 years)

8.  Hydrazine is decomposed in two steps:
i. Hydrazine (N2H4) decomposes into gaseous
ammonia and nitrogen (N2)
(this reaction is exothermic and releases
heat)
ii. Ammonia further decomposes into
nitrogen and hydrogen gas
(this reaction is endothermic and heat is
absorbed)

9.  Hydrazine is manufactured in many grades
of quite purity.
 Monopropellant hydrazine has grades:
i. less than 1% H2O
ii. less than 0.5% aniline(is an organic compound
with the formula C6H5NH2. Consisting of a phenyl
group attached to an amino group)
iii. traces of ammonia, carbondioxide,
chlorides & UDMH/MMH)

10.  The highly purified grade of hydrazine has:
i. Less water
ii. Less than 0.005 % aniline.
iii. Less than 0.003 % carbon materials.
 They do not contaminate the catalyst.

11. Hydroxyl Ammonium Nitrate
(NH2OH+NO3)
 This monopropellant is rich in oxygen but also
contains hydrogen & nitrogen (HAN).
 It is opaque hygroscopic solid when it is pure.
 It is colorless & odorless liquid in aqueous
solution.
 Specific gravity of solid HAN= 1.84
 The specific gravity of a material is defined as the
ratio of its density to the density of some standard
material, such as water at a specified temperature.

12.  Both solid & liquid HAN burn smoothly and
can be decomposed with any catalyst.
 Their boiling point = (110-145°C) & freezing
point (-15 to - 44°C) .
 It varies with the water content.

13.  HAN is more viscous as percentage of water
is reduced.
 Liquid HAN is more corrosive, toxic and
dense than hydrazine monopropellant.
 Specific impulse of monopropellants = (206-
265) secs. depending upon water content and
mixing of aqueous HAN with any organic
fuel liquids.