Why the Rocket Equation is Holding Us Back
Thanks to rocket technology we’ve been around the globe, to the moon, sent probes to explore
the inner planets, ventured through the asteroid belt, passed by and photographed the outer
planets, and even travelled beyond our own solar system and into the depths of interstellar
space.
And yet, the same science that has given us that success also places severe limitations
on how much further we can go.
This is Unveiled, and today we’re answering the extraordinary question; Is the rocket
equation holding us back?
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Development of the rocket equation really dates all the way back to the mid-17th century,
when Isaac Newton and Gottfried Leibniz developed calculus - and, with it, a better understanding
of momentum.
Fast forward to 1903, and the Russian scientist Konstantin Tsiolkovsky applies Newton’s
ideas to the building of rockets, and the age of space flight was set into motion.
A rocket is essentially an object achieving lift-off by focusing and channelling a precise
spray of energy out of its opposite end.
Rockets are objects of momentum, and they depend on that force to even escape our atmosphere.
The general idea isn’t a new one, though; the Chinese were using rocket technology around
100 A.D. for fireworks - for example.
For centuries, rocket technology has been in some way used in various armies and militaries
too, providing the fundamental basics for many a devastating weapon.
Of course, those weapons became even bigger and more destructive throughout the twentieth
century… but this was also when we began to build even larger rockets not with the
intent to kill, but to explore.
And explore we have; we’ve placed a flag on the moon, built a space station in orbit,
and have in some way seen all the known planets in our solar system.
So, how could the Rocket Equation possibly be limiting us?
The equation itself consists of three main variables: Delta V, which is the energy expenditure
against gravity (or the velocity it can possibly achieve); Exhaust Velocity, which is the power
of the rocket fuel (or how much energy it can possibly create); and the Propellant Mass
Fraction, which tells you how much of a ship’s mass should be dedicated to fuel.
Simplified, the rocket equation focuses on 1) How much speed your vehicle needs to beat
gravity, 2) how much speed your fuel can possibly produce, and 3) how much fuel you’ll need
to carry to reach your destination.
All things considered, we’re mostly limited by the amount of rocket fuel needed - which
tends to weigh a lot.
As an example, say we wanted to lift a one-pound rocket off of the ground, but needed one pound
of fuel to overcome gravity and achieve it.
Before we’ve even started, we now have a two-pound rocket, which requires more fuel
to lift off…
making it even heavier, meaning we’d need even more fuel, and so on.
Of all vehicles that rely on fuel, none are restricted by this fact as severely as the
rocket is.
While cars are about 4% fuel by their mass, and fighter jets are up to 40%, a rocket ship
has to be constructed with 85% of its total mass devoted to the fuel needed to get it
off the ground.
Which leaves a meagre 15% to account for the crew, various complex life support systems,
food storage, oxygen tanks, on-board plumbing, computers, communication devices... anything
and everything else that’s needed for a mission.
And some rockets feel that space limitation more extremely than others… the Saturn Five
was reportedly left with only 4% of its own mass after fuel!
But, surely this all stems from the fuel we use?
Couldn’t we just find something more efficient?
It’s a question that NASA, the ESA, Roscosmos and all other space agencies have pondered
plenty of times.
And we have continually experimented with different fuel types, but not yet without
significantly sidestepping the rocket equation’s parameters.
Across various iterations, seemingly “lighter” fuel tends to expend energy quicker or it’s
less powerful in the first place.
The fuel that NASA most often uses is a mixture of liquid hydrogen and liquid oxygen.
It burns the best and gives the most energy of the different fuel types available to us,
but it’s also the most complex option out there - and it’s still guided by the same
limitations.
In many ways, it’s simply a question of chemistry; and we can’t force any more energy
out of the fuel we’ve so far developed than we already do.
But what if we could work around other external factors?
Perhaps we could use the same fuel but achieve better results.
One of the most significant hurdles is that all of our resources come from earth, and
it takes a massive amount of energy to escape earth’s orbit.
Rockets need to be travelling at around 25,000 miles per hour just to break free of our planet’s
gravity.
All of which means, on a trip to mars, around half of the fuel required for the entire journey
would actually be used just getting the shuttle off of earth and into orbit.
So, if we could build a launch base elsewhere - say, the moon, which is 1/6th of earth’s
gravity - it’d take much less energy to get a rocket going.
We already know the moon has ice, and with sufficient resources we could theoretically
turn that ice into hydrogen-oxygen fuel for a lunar rocket launch.
There’s an obvious catch, though… because, while this would help solve our fuel problems,
the difficulties in getting supplies to the moon to accomplish such a feat remain - and
are arguably even more complex.
Some scientists have proposed using nuclear power to fuel the engines instead.
And some early, experimental nuclear energy options have indeed enabled us to achieve
up to double the energy output that our current fuel can.
Should a nuclear alternative be widely used in the future, perhaps we could explore farther
than ever before… but the move would bring about all new, inherent risks.
As proven by disasters like Chernobyl or Fukushima, nuclear power has the potential to be extremely
dangerous.
So, for many, the prospect of combining it with the literal life-or-death intricacies
of space flight is a major concern.
With rockets, even the smallest of glitches can create the biggest and most devastating
of problems.
Take the Space Shuttle Challenger, which exploded shortly after take-off reportedly because
of a single faulty O-ring and weather that was slightly colder than expected.
Now imagine a nuclear rocket in danger of exploding for similar, seemingly small reasons…
the results could be catastrophic.
It’s not all bad news, though.
NASA has also experimented with ion engines, which have so far yielded promising results.
Ion engines work by using the only energy source common among the stars - the stars
themselves.
An ion rocket has solar panels that channel the light energy into its engine, energizing
the electrons and causing them to smash into xenon in the core, which then releases a stream
of ion jets.
These ion jets have a much slower acceleration than traditional fuel, but also weigh about
1/10th as much as liquid fuel does for the same energy output.
NASA has already used an ion engine multiple times - notably in the 2007 DAWN mission,
which reached the asteroid Vesta.
So, there is hope for the future!
We have the rocket equation to thank for most of all the space travel we’ve achieved so
far.
But scientists are beginning to look beyond it.
If we could one day workaround it, lengthy interstellar voyages would seem much more
possible; space missions could be cheaper without the price of weighty fuel to drive
up the costs; and every rocket vehicle would have more room for supplies, thereby theoretically
reducing the overall number of trips needed.
We’d move one step closer to becoming a space-faring, interplanetary society.
Our shuttles would be faster, significantly more comfortable given all the extra space,
and hopefully safer as well.
But, until such time as we find another way to traverse the stars, the so-called “tyranny
of the rocket equation” holds firm, capping our ideas for future space travel.
And that’s why the rocket equation is holding us back.
What do you think?
Is there anything we missed?
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