SLS is a superheavy rocket being created by
NASA and is slated for its first launch in
2018, but that isn’t the SLS we’re talking
about today.
Instead we’re talking about the Space Launcher
System family of launch vehicles designed
by the US Air Force in the late 1950’s and
early 1960’s as part of the Air Force’s
efforts towards landing a man on the Moon
landing which was part of Project Lunex.
The family consisted of highly modular 2 or
3 stage rockets with either one or two core
stages surrounded by 4 solid boosters.
All of the SLS rockets would use segmented
solid rocket boosters for the first stage.
These boosters would come in 2 widths.
A 100 inch wide version for the smaller rockets
and a 180 inch wide version for the larger
rockets.
The length of the boosters could have also
been changed between launch vehicles by adding
or removing segments to better suit each vehicle.
The second and third stages of the rockets
all burned liquid hydrogen and liquid oxygen.
These core stages came in 3 varieties.
A, B, and C.
The A core was the smallest and would have
used a single J-2 engine.
The J-2 is the same engine that powered the
second stage of the Saturn IB and powered
stages 2 and 3 of the Saturn V. The A core
carried about 53 metric tons of fuel and had
a burn time of a little over 4 minutes.
The B core was much larger, but was a more
or less the same design.
It had 2 J-2 engines instead of one and carried
almost 150 metric tons of fuel with a burn
time of 5 minutes and 45 seconds.
The C core was the largest and would have
used 2 M-1 engines.
With a burn time similar to that of the B
core.
The C core carried over 750 metric tons of
fuel.
The smallest rocket planned for the SLS family
was the A-410.
It consisted of 4 100 inch solid boosters
around an A type core.
The solid boosters would be lit on the ground
and power the first 90 seconds of flight.
Just before the boosters ran out of fuel the
core stage would ignite its engine.
The boosters would then separate and fall
back to Earth while the core continued to
orbit.
This version would have carried about 9 metric
tons to orbit and would have been used to
test the re-entry vehicle for the Air Force’s
Lunex program.
The next size up was the AB-825.
This version used 4 180 inch wide boosters
which would power the flight for the first
100 seconds after launch.
Just like the A-410 the core would ignite
just before the boosters ran out of fuel,
but the AB-825 used a B core for the second
stage.
Once the B stage burned out an A core third
stage would light and finish the orbital insertion
or would send the payload to the Moon.
The AB-825 could send up to 39 metric tons
to low earth orbit or almost 11 metric tons
on a translunar trajectory.
This would have been enough to send the Lunex
re-entry vehicle on a flight around the Moon
in a mission similar to Apollo 8.
The largest rocket designed as part of the
SLS family was the BC-2720.
It was almost identical in concept to the
AB-825, but instead of a B core second stage
with an A core third stage it was a C core
second stage with a B core third stage.
Although the B core third stage probably would
have been modified to only use one J-2 in
order to increase payload to the Moon.
It also probably would have used solid rocket
boosters with more segments to increase thrust
and burn time for the first stage.
The BC-2720 would have been able to carry
just shy of 159 metric tons to low earth orbit
and could send over 60 metric tons to the
Moon.
Much more than the Saturn V which could only
send about 48 metric tons to the Moon.
This version of SLS would have been used to
bring humans to the surface of the Moon.
SLS was remarkably ahead of its time and had
plenty of benefits over other more conventional
rockets.
At the time liquid rockets were still very
unreliable.
It was thought by limiting the number of liquid
burning engines these rockets would have a
higher success rates.
The BC-2720 would have used only 3 liquid
engines compared to the 11 engines used by
the Saturn V.
And by limiting the number of unique components
between rockets cost would have been greatly
reduced.
Using the strap on boosters for the first
stage also allowed a reduced overall height
and eliminated the need for a interstage between
the first and second stages which reduced
weight.
It also made hot staging possible eliminating
the need for heavy ullage motor.
Some of the smaller components, such as the
A core and 100 inch solid boosters, could
have been transported via rail which would
have also reduced cost.
SLS also was designed with a pure cargo version
in mind in order to facilitate a permanent
outpost on the Moon.
So why was SLS cancelled?
It was part of Project Lunex, which faced
other problems such as complex landing vehicle
which used the direct descent method of landing
on the Moon and returned in a reuseable glider
similar to the Space Shuttle.
This would have required more extensive development
and research compared to the more conventional
Apollo program.
And when Project Lunex was killed SLS died
with it.
In 1961 president Kennedy decided it would
be NASA, not the Air Force, to bring Americans
to the Moon.
SLS hasn’t completely died, however.
Many of the concepts were brought back to
life with the Space Shuttle.
And using strap on solid rocket boosters around
a hydrolox core has become a common practice
in rocketry.
SLS influenced many rockets such as the Ariane
5, the HII-B, the Space Shuttle, the Delta
IV medium, the Titan IV, and the modern SLS.
So while the SLS rockets never themselves
flew, many of their ideas did.
