the story of spaceflight is the story of
energy energy lift the space vehicle
from the earth propelling it into space
energy then directs the movements of the
spacecraft in space changing its flight
path by increasing or decreasing its
speed and controlling its attitude by
forcing it to your left or right to pick
up or down to roll and also to move
sideways and energy provides the
electric power onboard a spacecraft
power needed for so many vital functions
from operating instruments and pilot
displays to transmitting radio
communications to earth
the first stage of the Apollo Saturn 5
launch vehicle is a formidable example
of energy harnessed by man then released
on his command
it's five engines generate
seven-and-a-half million pounds of
thrust to propel the Apollo space
vehicle through the first phases of a
manned lunar mission but this brief film
chapter in the story of energy and space
flight begins after the stages of the
launch vehicle and perform their tasks
our film concerns energy as it is
applied on and within the spacecraft
itself the propulsive devices which
enable it to change velocity and
maneuver and
and the electric power needed for its
operations as it travels through outer
space alone
finding and selecting the types of
energy best suited for manned spacecraft
propulsion and power is the
responsibility of the propulsion and
power division of the engineering and
development director of NASA's manned
spacecraft Center at houston texas here
scientists engineers and technicians
study and apply the principles of energy
determine spacecraft requirements and
design and develop systems subsystems
and components of propulsion and power
primarily they monitor the design
development and manufacture of such
units by private contractors throughout
the United States and subject
developmental hardware to exhaustive
tests to verify it and performance and
reliability from abstract theory to
final developmental testing the manned
spacecraft Center specialists and
propulsion and power bring to their work
a thorough knowledge of the state of the
art and the ingenuity needed to unlock
new applications of energy analyzing the
energy characteristics and capabilities
of various systems is part of their
daily work designers are bound by many
constraints and deciding which sources
of energy and which energy conversion
devices to select available funds and
the target date for a mission are
designed determinants since only those
systems can be considered which can be
developed thoroughly tested and produced
by the required date the way to the
payload which can be placed in space is
limited by the capability of the launch
vehicle each system and subsystem must
meet the test of safety and reliability
demanded for manned missions the special
requirements of a particular mission for
both propulsion and power must be
identified then analyzed
considering propulsion first there are
two categories of spacecraft systems
primary and auxiliary primary propulsion
systems are used for large increases or
decreases in spacecraft velocity
auxiliary propulsion systems are
attitude control systems some can also
achieve small velocity changes but their
main function is to Orion spacecraft in
pitch roll and yaw let us identify some
of these systems by comparing our first
three-man spacecraft mercury germany and
Apollo comparatively the propulsive
energy requirements of the mercury
spacecraft were not large only one
primary propulsion system was needed the
retro rockets fired to reduce velocity
for deorbit and re-entry into the
Earth's atmosphere there was also an
attitude control system and a launch
escape system for Germany the next
spacecraft to evolve repulsive energy
requirements were greater in addition to
AC dejection escape system
attitude control system and retrorockets
for deorbit Germany needed an additional
propulsion system to change the velocity
of the spacecraft for orbital change the
blue maneuvers in the case of the three
module Apollo spacecraft energy
requirements are immense
in addition to a more powerful launch
escape system large amount of propellant
and three primary engines are needed the
service module has a main engine to
correct the flight path on the way to
and from the moon to reduce speed to
enter lunar orbit and to thrust the
spacecraft out of lunar orbit into a
return flight path the lunar excursion
module called the LEM has a descent
engine to land on the moon and an asset
engine to lift off from the moon surface
in addition three auxiliary propulsion
systems are needed one on each module
for attitude control altogether 44
rocket engines are required for the
three auxiliary systems to better
understand the tasks of a propulsion
engineer
let us now analyze certain Apollo
spacecraft propulsion requirements by
reviewing part of an Apollo manned lunar
landing mission profile after the three
modules of the spacecraft have been
launched into Earth orbit and then into
a translunar flight path with the limbs
still attached to the third stage launch
vehicle the adapter shielding the limb
is opened by a pyrotechnic subsystem the
rocket engines of the service modules
auxiliary attitude control system then
maneuver the command and service modules
so that they pull ahead turn around and
return
to dock with the lamb the service
modules main engine is now in the clear
for firing the spacecraft is then
separated from the third stage launch
vehicle sometime later the crew prepares
for the first of three mid-course
Corrections which may have to be made in
the flight path on the way to the moon
attitude control engines orient the
spacecraft precisely so that the force
vector of the main engine is aimed in
the required direction the main engine
is then fired for the first time this is
the first use of the tremendous energy
of this primary propulsion system to
change the velocity or direction of
travel of the spacecraft between
mid-course Corrections the spacecraft
coasts with the attitude control engines
stabilizing the spacecraft for
navigational sightings or scientific
measurements and controlling its role at
the rate of one or two revolutions per
hour to distribute the sun's heat evenly
after the final mid-course correction
the spacecraft approaches the moon but
its velocity and flight path if
undisturbed would carry it past the
target so the main engine is again fired
this time for approximately six minutes
during which the combustion energy of
the propellants reduces the inertial
energy of the onrushing spacecraft
thereby reducing its velocity to a
nominal 3,600 miles per hour at this
point the spacecraft's flight speed and
the moon's gravitational pull are so
balanced with the spacecraft falls into
a nearly circular orbit path around the
moon the two lunar explorers transfer
from the command module to the lamb and
the lamb is separated from the command
and service modules which will remain in
circular orbit
carrying the third crew man orbital
velocity would also keep the LEM flying
in this circular path around the moon if
no new force were applied this new force
is obtained by firing the Lambs descent
engine its retro thrust reduces the lens
velocity so that it enters a separate be
sent orbit when the lamb reaches the
point its descent orbit closest to the
moon its descent engine is again ignited
for a continuous burn to further reduce
its speed and perform the landing
maneuver a large amount of propellant
must be expended to overcome the
inertial energy of the limb to bring it
to rest on the moon surface several
other features are also essential the
attitude control system is properly
stabilized and orient the spacecraft
dataset engine must begin bold so that
the direction of its thrust can be
precisely aimed and the engine must be
throttle so that the pilot can apply a
variable amounts of thrust these
features enable the pilot to guide the
lamb along a carefully planned flight
path to let it hover over the landing
site and if necessary to change its
course before touchdown the next
propulsion requirement of the mission is
the launch from the lunar surface back
into lunar orbit the empty descent stage
serves as a launch platform for the
asset stage a large amount of propellant
and a launch engine must be carried to
the loan to supply the energy required
to return to lunar orbit the attitude
control system aims the thrust of the
ascent engine the ascent maneuver brings
the lamb into lunar orbit about five
miles from the orbiting command and
service modules the Lambs attitude
control engines are then used to
complete rendezvous
after the two explorers have rejoined
their fellow crew man in the command
module the lamb is separated to remain
in lunar orbit oriented by the service
modules attitude control system the
powerful main engine is then fired to
give the command and service module the
velocity to leave lunar orbit and enter
a flight path back toward Earth
mid-course Corrections may again be made
by firings of the main engine about 20
minutes before re-entry into Earth's
atmosphere the service module is
jettisoned the command module Falls
toward Earth reaching a speed of 25,000
miles per hour as it enters the
atmosphere a heavy and complex retro
rocket propulsion system is not needed
to slow the spacecraft to be low orbital
speed and returned from lunar missions
instead the flight path is precisely
aimed at a narrow reentry quarter which
brings the spacecraft into the
atmosphere where the tremendous kinetic
energy of the spacecraft can be
dissipated by atmospheric drag breaking
the missions final application of
propulsive energy is the use of the
command modules attitude control engines
during reentry the attitude control
system Orion the spacecraft and rolls it
to control the direction of its lift
vector this makes possible guidance of
the spacecraft through the corridor in
the atmosphere to the desired point of
parachute deployment after analyzing the
primary and auxiliary propulsion
requirements for a spacecraft to carry
out its mission spacecraft engineers
must select and develop a full
complement of propulsion systems widely
differing in specifications so as to
meet widely differing mission
requirements but the principles of
rocket thrust are the same for all
engines
large or small the propellants are
injected into a combustion chamber where
they ignite and burn in the combustion
process the inherent chemical energy of
the propellants is transformed to a
directly usable energy form the thermal
energy of the extremely hot combustion
gases which reach temperatures of 5,000
degrees Fahrenheit and higher the
purpose of the combustion is to produce
pressure within the combustion chamber
because it is the pressure which
produces the propulsive force or thrust
the pressure within the combustion
chamber acts equally on all surfaces
thus the pressure force acting to the
left is exactly counterbalanced by an
opposing pressure force acting through
the right in a similar manner if the
combustion chamber were completely
closed the pressure force acting upward
would also be exactly counterbalanced by
the pressure force acting downward in
this case all pressure forces would be
exactly balanced and there would be no
net force or thrust in order to produce
thrust then an opening called a throat
is made in the combustion chamber
through which the hot combustion gases
are exhausted now the pressure forces
are no longer balanced the pressure in
the upward direction is acting against a
larger area than the pressure in the
downward direction since some of the
lower surface was removed to form the
throat a net thrust propelling the
rocket forward is the result additional
thrust is obtained by the use of a
rocket nozzle again the pressure forces
acting to the sides exactly
counterbalance one another but since the
nozzle has no rear surface the upward
and downward acting pressures are again
unbalanced resulting in additional
thrust on the rocket since the hot
combustion gases are continually being
exhausted from the rocket through the
throw
a continuous supply of propellant must
be burned to maintain the desired
pressure in the combustion chamber
although basic principles of rocket
thrust are the same and all propulsion
systems selecting the best systems to
meet mission requirements is not easy
there are many propellant combinations
pressurization systems propellant tanks
and tank arrangements engine systems and
system operating parameters from which
to choose the ideal system would give
the highest performance have the highest
reliability and way less than any other
system but it is difficult to achieve
these three factors simultaneously some
trade-offs must be made for manned
spacecraft the prime factor is high
reliability careful analyses and
vigorous discussion by preliminary
design engineers precede the selection
of propellants and propulsion systems
which account for the largest portion of
spacecraft wait
seventy-three percent for instance of
the weight of the Apollo spacecraft
chemical propellants in use today can be
classified broadly as liquids and solids
current missions generally rely on
liquid by propellants consisting of a
fuel and oxidizer liquids offer greater
flexibility and packaging and they're
more suitable for engine restarts and
throttling for example the Apollo
service module main engine must ignite
burn for a few minutes
shut down and reignite several times on
a mission while the engines of attitude
control systems must be able to fire in
pulse us lasting only a few milliseconds
and do this thousands of times during a
mission in slow motion inside this
transparent test chamber can be seen
another feature of most liquid vibe
repellents they are hypergolic that is
they ignite on contact with each other
this eliminates the need for a complex
ignition system this injector test shows
how hypergolic propellants are injected
under pressure into a combustion chamber
using water to simulate both oxidizer
and fuel the injector spray action can
be seen injecting the oxidizer at an
angle from the inside channel outward
into the chamber then injecting the fuel
from the outer channel inward into the
chamber an actual combustion the
oxidizer and fuel injected at about the
same time the two vaporized chemicals
mix ignite and learn to produce the high
pressure gases in the chamber to give
thrust from injection of propellants to
ejection of combustion gases takes three
or four milliseconds that is three or
four one thousands of a second
spacecraft retrorockets for deorbit and
escape system Rockets typically utilize
solid propellants here the launch escape
system of Apollo is being prepared for a
flight test at NASA white sands test
facility in New Mexico instant readiness
to produce high dressed in a short
period is one of the advantages of solid
propellant
others are storability and inherent
simplicity
there are no moving parts such as valves
and solid propellant rocket propellant
is back within the combustion chamber in
a predetermined shape this is called the
grain and it is ignited by a pyrotechnic
igniter the shape of the grain
determines its burned characteristics
pyrotechnic igniter Tsar packages of
solid propellants activated by either an
electric or mechanical impulse
the heat and gas produced ignite the
rocket train
but pyrotechnic devices of other kinds
are used for purposes other than solid
propellant ignition on a spacecraft
their explosive force is used to
separate stages to cut the lines of
parachutes after they have served their
purpose during re-entry to open the lamb
adapter before separation of the
spacecraft from the launch vehicle and
for other tasks on the Apollo spacecraft
alone there are more than 100
pyrotechnic devices all the
responsibility of the propulsion and
power division at the manned spacecraft
Center from spacecraft propulsion and
pyrotechnics that is now proceed to a
different but equally vital use of
energy spacecraft electric power every
instrument in the cabin of a spacecraft
is operated by electric power stored in
batteries are generated by onboard
systems for short missions storage
batteries are adequate to supply power
the mercury spacecraft relied on them
entirely without a single failure but
storage batteries cannot be recharged
when they are the sole source of to
store enough energy to meet the
requirements of extended missions such
as storage battery would be far heavier
than systems that can generate and
supply power on board the spacecraft as
it is needed for the mission
therefore energy systems engineers
investigate several different power
supply sources for long missions for
example fuel cells solar cells
and nuclear systems which are even being
developed to supply power for
instruments left on the moon to transmit
data to earth the eight-day mission of
germany by was the first use of fuel
cells in space to supply electricity the
germany fuel cell works like this oxygen
and hydrogen are carried in tanks in
there cryogenic extremely low
temperature state heat is applied to the
two fluids which enter separate
compartments in the fuel cell the
compartments are separated by a plastic
membrane an organic polymer with a
molecular structure having the
properties of an electrolyte the
membrane itself is sandwiched between
two poorest catalytic electrodes oxygen
is pressurized into the compartment next
to the positive electrode hydrogen into
the compartment next to the negative
electrode the electron separate from the
hydrogen atoms and travel along and
external circuit toward the positive
electrode this creates electric power
the hydrogen ions that is the nuclei of
hydrogen atoms which have lost their
electrons migrate through the
electrolytic membrane and combined with
the oxygen to form h2o old on extended
missions this water may be collected in
tanks for drinking and other onboard
purposes to independent systems composed
of several cells are carried on German
emissions each system has a maximum
output of about 1,000 watts as in the
case of rocket engines fuel cell
principles are the same although there
may be several different types of
systems depending on mission
requirements
this is a test model of the fuel cell
system for the Apollo spacecraft
the Apollo sell utilizes a liquid
electrolyte instead of an electrolytic
membrane for ion exchange still another
concept being studied as a fuel cell
with a different type of electrolytic
membrane consisting of ass bestest
saturated with the liquid electrolyte
experimental models of this type have
been used to drive tractors and other
machines more advanced engineering
models of this capillary membrane fuel
cell are being developed by NASA for
future of manned spaceflight
applications another source of electric
power is the solar cell which has been
widely used on unmanned space missions
solar cells may be adapted by power
engineers for use on manned missions
here a solar simulator radiating light
energy called photon energy comparable
to that of the sun's rays is being
beamed onto a solar cell array an
environmental test chamber simulating
the vacuum of outer space in another
area of the advanced power systems lab a
second subsystem for a possible solar
cell power system is being given a test
to determine its maximum life
this is a secondary storage battery
which can be recharged many times since
a spacecraft using solar cells may be in
the dark behind the moon or a planet
during part of its mission in these dark
phases in addition to use of the sun's
photon energy to activate solar cells
and produce electric power radioisotopes
and nuclear reactors may be used as
sources of heat energy for two other
types of power systems called
thermoelectric and thermionic
thermoelectric conversion of heat to
electric power is accomplished by
applying heat to two different materials
connected together when heat is applied
the temperature gradient across both
materials concentrates the charge
carriers
this setup a difference in the electric
potentials of the materials electrons
from the negative material flow in the
external circuit toward the positive
material thus creating usable electric
power radioactive isotopes are a
particular value in thermionic systems
experimental work on snap 13
radioisotope thermoelectric generators
is carried on in the advanced power
systems laboratory therm ionic systems
provide electric power in a manner
similar to that of a vacuum tube by
utilizing the electrons boiled off from
a heated surface and collected by a
cooler surface power systems described
so far have been static systems systems
which provide for the direct conversion
of energy of various kinds into usable
electrical energy another category of
systems understudy for spacecraft are
dynamic they utilize an indirect method
of converting energy to power one type
is similar in principle to a diesel
engine
except that its energy source is the
internal combustion of hypergolic
propellants these ignite burn and drive
a reciprocating piston which drives a
generator to produce electric power
another type of dynamic engine
understudy works on the same principle
as turbine generator plants on earth a
heat source such as propellant
combustion can be used to convert a
working fluid into a vapor such as steam
the steam causes a turban to rotate and
the turban drives a generator at the
120-acre thermal chemical test area at
the manned spacecraft Center all of the
various energy systems of electric power
as well as pyrotechnic devices and
systems for spacecraft auxiliary
repulsion are studied in developmental
stages and given additional tests in
this area captive firings are conducted
to determine engine performance
characteristics which are carefully
monitored and recorded during test
firings here to a variety of tests are
conducted on power supply systems such
as fuel cells in space environment
chambers to determine their operational
characteristics and maximum life of the
thermal chemical test branch by close of
the entire propulsion and power division
at the manned spacecraft Center are
contributing each day towards our
nation's mastery of the complex
technology of spaceflight it is a
continuing process with constantly
improving systems and techniques
the story of spacecraft energy for
propulsion pyrotechnics and power is
therefore a story whose final chapter as
yet can only be imagined
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