I go a lot further again
hey babe
welcome to this edition of NASA images
i'm lynn Bondurant during this show
we're focusing on historic NASA film
showing electric rockets and more recent
videotape showing how we may someday
explore Mars first let's go back to 1965
to see most of the film electric
propulsion though made in the mid 1960s
much of the film is still current a
concept showing how electric Rockets
could be used to fly space travelers to
Mars is included imagine for a moment
that this is the period of the 1970s and
1980s a period of amazing explorations
in space
imagine that the distant planet Jupiter
is to be investigated scientifically by
a spacecraft that will fly close by at
the correct place in its orbit it's
conventional chemical engines are fired
to accelerate it to the velocity needed
to get to Jupiter imagine also that nine
and a half months later a craft with
advanced engines is launched it slowly
accelerates until it escapes Earth's
gravity one year after the conventional
craft started of course the first craft
is well on its way since leaving Earth
it has been coasting and it's velocity
has continuously decreased but constant
thrust is applied to the second craft
for six months which continuously
increases its velocity even though it
escaped earth
a year later it reaches Jupiter about
eight months ahead of the conventional
craft and carries three times the
payload
what could make this possible electric
propulsion as used in the hypothetical
second spacecraft and it is now under
active research and development since
the advent of the Space Age the roaring
flaming spectacle of the chemically
fueled rocket has become a common
occurrence carrying space vehicles into
Earth orbit and deep space the weight of
such a payload is extremely small
compared to the liftoff weight of the
entire rocket because a chemical booster
can put only 2 to 3% of its weight into
orbit this lifting ratio cannot be
improved significantly yet today the
chemical rocket is the only means of
launching a payload from Earth once the
vehicle is in Earth orbit a chemical
engine can send only about 1/3 of its
orbital weight to the moon or the near
planets two-thirds is fuel and engines
the craft quickly burns the fuel of its
final stage to accelerate the payload to
a high velocity which then coasts the
rest of the way this coasting flight
takes considerable time to cover large
distances but many deep space missions
can be performed better by applying
small amounts of thrust during most or
all of the trip
over long distances
this continuous thrusting will
accelerate spacecraft to very high
velocities and shorten overall travel
time when perfected electric propulsion
will provide the continuous thrust
needed to reduce travel time to distant
points and will use fuel so effectively
that a larger fraction of the Earth
orbit weight will be delivered as useful
payload if the goals for electric
propulsion are achieved the entire solar
system will be open to versatile
exploration the most difficult space
mission of this decade will be the
landing of men on the moon and getting
them back safely man in space must be
transported in the shortest possible
time today only an all chemical
propulsion system can do this job of
moon exploration but what lies beyond to
establish and maintain a scientific base
on the moon will require the delivery of
large amounts of supplies and equipment
a very expensive operation to send large
manned spacecraft and unmanned probes to
Mars and Beyond will require the
propelling of very large payloads over
great distances just to lift these
heavier payloads into deep space with
all chemical systems will require either
building bigger and bigger launch
vehicles or launching several vehicles
into Earth orbit carrying engines and
fuel and then assembling them to provide
the propulsion needed both alternatives
are extremely expensive so a propulsion
system is needed that will use fuel more
economically
in a propulsion system fuel economy can
be increased by speeding up the exhaust
gases in chemical rockets the exhaust
velocity is limited by the temperatures
obtainable from combustion
so methods other than combustion have to
be used to speed up propellant gases
one way is to use the heat of a nuclear
reactor to increase the exhaust velocity
of a light gas such as hydrogen this
velocity is about 2 and 1/2 times that
of chemical engines
therefore nuclear rockets will use fuel
two and a half times as effectively as
chemical rockets another way to increase
exhaust velocity is to use electrical
energy instead of heat to accelerate the
propellant gas up to 20 times or more
than in chemical rockets these high
exhaust velocities in the electric
engine increase the effectiveness of the
fuel 20 times and more as well resulting
in much more work per pound of fuel with
this high fuel effectiveness and with
the ability to apply continuous thrust
the electric engine is a promising
candidate for true space propulsion it
cannot be used as a launch engine but
once in space it can take over after the
high thrust chemical booster has given
the space vehicle sufficient velocity to
overcome the main effects of gravity the
electric engine is started this small
thrust applied intermittently or
continuously for months or years will
result in a very high velocity
the effect of a very small thrust
applied over a long time is the same as
a very large thrust applied for a very
short time thrust multiplied by the time
it is applied is called total impulse a
million pounds of thrust applied for 30
seconds will deliver 30 million pound
seconds of total impulse the same as a
pound of thrust applied for 30 million
seconds which is roughly a year each
flight in space requires a certain total
impulse the goal of deep space
propulsion is to use the least amount of
fuel for a given total impulse in space
propulsion fuel economy of a rocket
engine is discussed in terms of specific
impulse which is defined as the total
impulse generated per pound of fuel used
the higher the specific impulse the
longer in seconds one pound of fuel will
deliver one pound of thrust for
convenience specific impulse is
expressed in seconds chemical rockets
are limited to specific impulses of
about 450 seconds and relatively little
improvement can be expected solid fuel
nuclear rockets are expected to deliver
up to about 1000 seconds of specific
impulse electric engines however are now
operating at specific impulses from
around 800 to 10,000 seconds and higher
in laboratory vacuum chambers
the higher the specific impulse
the higher the fuel economy but
unfortunately as specific impulse
increases for the same thrust the
electric power needs increase and
powerplant
weight goes up even more so an optimum
value must be bound for each mission but
even with this compromise for many
manned and unmanned interplanetary
missions the electric engine appears to
be the propulsion system to deliver
significant payloads within a reasonable
time for missions to Pluto for example
the electric engine is the only device
that can deliver any payload at all the
power source for electric engines will
be either a nuclear reactor or solar
cells or heat concentrators depending
upon how much power is needed waste heat
is rejected to space by a radiator heat
from the power source drives an
electrical generator the electrical
power is conditioned and controlled to
provide the necessary voltages and
currents the typical propulsion system
also includes propellant storage and
feed devices which lead to the engine
itself three types of electric engines
are under development they differ
primarily in the way the propellant is
accelerated the electro thermal engine
uses an electric arc or resistance
element to heat a propellant gas to a
very high temperature which produces a
high exhaust velocity specific impulses
from 802 in excess of 2,500 seconds are
possible with these engines the electro
thermal engines have demonstrated good
performance in vacuum chamber tests
however laboratory work must continue in
order
to improve performance in
electromagnetic engines a fast-moving
ionized gas is generated and used as the
propellant this gas is a plasma of ions
and electrons electric and magnetic
fields then speed up the charged
particles to much higher exhaust
velocities a specific impulse range of
800 to an excess of 10,000 seconds
appears to be possible these
electromagnetic devices are the least
developed at this time however there are
many promising designs under laboratory
investigation in the third type the
electrostatic or ion engine cesium or
mercury fuel is ionized and the
resulting electrons removed the ions
being positively charged are accelerated
to very high velocities by a high
negative voltage electrode these engines
will operate at specific impulses from
3500 to 10,000 seconds or more
electrostatic ion engines are the most
advanced electric type but much work
remains to develop larger more efficient
and reliable engine systems
though work on electric engines has been
underway only since 1959 great progress
has been made in government and
contractor laboratories thrust levels
approaching a pound have already been
obtained yet enormous strides must still
be taken before larger reliable engines
are available goals for electric systems
include achieving power supply weights
of less than 40 and an ultimate goal of
20 pounds per kilowatt with lifetimes of
more than 10,000 hours development of
the engines themselves strives for
smaller weight and size per unit thrust
and higher overall effectiveness
eventually the entire engine system must
operate continuously for up to four
years by grouping engines together as
building blocks power levels up to 40
megawatts and total thrusts of over 450
pounds may be obtained in addition to
this laboratory work electric engines
must be flight tested space conditions
cannot be totally simulated even in
these advanced vacuum chambers and there
may be influential environmental factors
in space unknown at this time small
electric engines already being developed
may perform early missions the first
application may be to control a
synchronous communication satellite
these engines can deliver small accurate
bits of thrust for months or years using
only small amounts of fuel solar cells
will furnish the power another solar
powered application could be the raising
of an advanced communication satellite
from a low Earth orbit to its final
22,000 300 mile orbit
solar-powered electric engines may also
be used to slowly spiral out a
scientific satellite to make a detailed
study of the Van Allen belt flight tests
and early missions will provide data
that will help perfect the larger
electric engines needed for more
ambitious projects large electric
propulsion systems
when perfected they take large amounts
of supplies and equipment to the moon
and do it much cheaper than all chemical
systems chemically propelled boosters
will place the freight into Earth orbit
the spacecraft may incorporate a small
chemical engine and electrically
propelled lunar freighter will
rendezvous with the craft take it to the
vicinity of the moon and place it in a
lunar orbit
the chemical stage will lower the
freight loaded craft to the lunar
surface
while the electrically driven freighter
returns to Earth orbit for another load
it will continue to shuttle back and
forth with periodic fuel replacement as
long as its power supply lasts of course
the electric freighter will take longer
to get to the moon but for most Freight
the longer travel time is not an
important consideration for the same
amount of freight this system will need
far fewer expensive earth launch
boosters than all chemical system would
require
on small vehicle missions to the near
planets Mars and Venus electric engines
can deliver much more payload by taking
a slightly longer time a three-stage
chemical rocket now being studied could
get a 2,500 pound payload into an orbit
around Mars in about 210 days and
electrically propel spacecraft
substituted for the third stage could do
as well in the same time but by using a
higher specific impulse engine and
taking only 40 more days it can deliver
twice the payload to those planets
beyond Mars and Venus electric
propulsion gives both the payload and
time advantage it appears to be the most
promising means of sending scientific
probes from Earth orbit into the
asteroid belt beyond Mars to Jupiter and
farther a greater the distance the
greater the advantages of electric
propulsion looking toward the day when
large power supplies from 20 to 40
megawatts and large engines of proven
reliability are available scientists
have developed a concept for a manned
Mars expedition with electrically
propelled vehicles the concept suggests
the expedition will consist of five
spaceships which will be assembled in a
low Earth orbit before departure
the completed ships will each weigh 360
tons and will carry a payload of 40 tons
at one end of the vehicle
there will be a 40 megawatt nuclear
power supply next will be power
converter equipment there also will be
radiators to give off waste heat and
cesium fuel tanks at the other end will
be a three-man crew compartment there
will be a total of 15 men to perform all
the mission objectives three of the
ships will carry piggyback Mars landing
vehicles while the other two will carry
extra fuel for the return to earth five
vehicles will be used for safety
purposes if one or more failed the men
would be transferred to the other ships
to continue the flight or return to
Earth after checkout and placing the
flight crew aboard the electric engines
would spiral them continuously for 56
days until they escape the Earth's
gravity then they would enter a transfer
orbit around the Sun traveling toward
Mars the ships would take 148 days to
make the trip to the vicinity of the
planet
once near Mars they would spiral into a
low orbit this would take an additional
21 days once in this orbit one of the
piggyback chemical vehicles would go
down to the surface without men to land
equipment then one manned craft would
land to explore the surface after 29
days the party would board the landing
craft and rejoin the ships then the
landing craft would be abandoned and the
fuel equalized between ships for the
return trip they would reverse their
original flight path and head back to a
low Earth orbit this would take another
318 days making a total of five hundred
seventy-two days for the round-trip by
applying thrust continuously over vast
distances travel time will be greatly
reduced
he will will be used so effectively that
a much bigger weight fraction of the
space vehicle will be devoted to useful
payload reduce travel time to the
distant planets larger useful payloads
these are the goals of electric
propulsion which will allow numerous
missions to be carried out that would
otherwise be impractical or impossible
our next film is more recent from 1987
it's also about exploring Mars Mars
commonly referred to as the red planet
is one of our closest neighbors beyond
the moon it has qualities that make it a
potentially habitable outpost before all
Martian exploration ended in November
1982 a handful of probes had made the
year-long journey Viking ones orbiter
completed nearly 1500 picture-taking
trips around the planet
while it's Lander studied samples and
returned to views from the surface as a
result Mars is well met but many
questions remain so researchers are
designing systems to explore the varied
Martian geography in anticipation of a
return mission on calm sunny mornings
Jim Burke can often be found flying this
lightweight solar balloon in the
courtyard at NASA's Jet Propulsion
Laboratory in Pasadena California mr.
Burke views his study as an important
stepping stone to a larger goal in
gathering more precise information about
the red planet NOW the Martian
atmosphere is carbon dioxide and if you
put a black balloon that's light enough
with a light enough payload into that
atmosphere the sun shining on the black
balloon will warm it up like the heat
inside a parked car with the windows
shut and it gets hot enough inside to
become a hot air balloon scientists
students and engineers from JPL and the
California Institute of Technology have
taken the concept a step further by
testing the feasibility of this 30 foot
diameter solar balloon that might be
used to study Mars in theory the device
could be blown around by local Martian
winds during the day to collect data and
take pictures at night it would cool
down lose buoyancy and lower itself to
the ground to survey the planet's
surface the small clear balloon holds
the larger one off the ground at night
so it won't get damaged
there are many regions of Mars that
could be explored this way
to Gymboree one very interesting
possibility is to put the balloon in the
atmosphere get it inflated operating up
in the polar regions and let the
circumpolar winds drift it down across
the polar cap over the layered terrain
which is in the canyons that spiral out
from the polar cap then across the
immense dune fields that surround the
polar caps and on downward into
temperate latitudes on Mars to remotely
explore the surface of Mars a number of
devices have been investigated they
include early roving vehicle prototypes
designed to crawl or wheel their way
across alien terrain Rovers continue to
be designed today based on some of these
models University of Arizona's lunar and
planetary labs graduate students and
faculty have recently built this
gigantic two-wheeled prototype Mars
rover
another vehicle being developed as this
robotic six wheeled version which is
JPL's latest testbed for understanding
the control and vision systems needed
for a Mars mission according to Brian
Wilcox of the robotics and tella
operators Research Group at JPL sending
commands to a rover on Mars would be
difficult because of the 10 to 40 minute
round-trip delay you can't just sit
there and steer in your armchair from a
TV monitor and make the vehicle do
useful things because of this long speed
of light delay so we've identified
several techniques to maneuver a vehicle
on Mars in such a way that you can go
useful distances in a day in spite of
the fact that the humans are this long
speed of light delay remove from the
action
the rugged vehicle has two TV cameras
for eyes and is capable of climbing
objects 1/3 taller than its wheel height
the proposed mission vehicle would have
robotic arms to make measurements and
collect rock and soil samples
using Rovers onboard vision system
scientists can freeze three-dimensional
images from its pair of television
cameras they can then designate the
pathway to follow continually updating
commands from Earth so that the rover is
able to avoid obstacles and hazards as
more sophisticated visual systems are
developed greater artificial
intelligence can help the rover find its
own way if given high-resolution imagery
of the Martian surface and a list of
targeted regions designated by
earthbound scientists the hope is to
someday send a manned mission to Mars
but a more detailed study of the planet
is necessary first and these pioneering
steps can be made by roving vehicles and
balloons again Brian Wilcox if you
imagine an expedition Lewis and Clark
trying to survey the Louisiana Purchase
they've basically made one track across
a very small fraction of the land
surface of the earth took them years to
do it and yet they found incredible
things all along the way we could
certainly have a dozen Rover missions
which yielded equally interesting
results the exploration of Mars sending
unmanned vehicles as pathfinders for the
future
that's all we have for this edition of
NASA images but before we go let me
remind you that you're cordially invited
to see the displays here at the Visitor
Center at the NASA Lewis Research Center
we're located near Hopkins International
Airport in Cleveland until next time
this is Lynn Bondurant saying goodbye