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Hey Vsauce, I'm Jake and if I wanted to get from here to there, the
most sensible thing to do would be to run, point a rocket launcher at the ground, jump
in the air, and fire a missile below me, using the explosion to propel me into the sky...
or that is what Team Fortress 2, Halo, Quake 3 and many other video games have lead me
to believe. Or who could forget Freddie Wong's awesome video of a rocket jump in real life?
Only thing is, how possible would a rocket jump really be ... without special effects?
... or most importantly.... dying?
Well let's take the most common carry-able rocket launcher, the RPG-7 with over 9 million
produced. And it's most recognizable warhead, the PG-7VL
Now the deadly blast radius for this is 4 meters with lethal fragments from the warhead
flying as far as 150 meters from the impact.
An average person can do a high jump of around 1.68 meters and the world record is 2.45 meters,
which means you'd still be in the deadly blast radius.
But what would actually happen to your body if a rocket exploded that close to you?
First there would be a blast wave of highly compressed air particles that fly at you faster
than the speed of sound. Because of the drastic change in pressure your eardrums would most
likely pop...forever.
Immediately following the blast wave is the shock wave which passes through your whole
body, rupturing organs and tissue.
Mixed in with these waves of energy is all the debris from the rocket itself and whatever
the rocket was aimed at.
Let's say you could wear strong enough body armor to protect you from a warhead that can
penetrate 400mm of steel.
Is the force of the RPG-7's rocket's explosion enough to lift you? Not enough to make it
worth your while and definitely not enough to propel you to the heights that video games
depict.
Since the launcher is recoilless, blowback from the rocket would actually push you down
into the explosion.
However, the one big problem you'll run into is that the warhead isn't live right after
launch. It needs about 5 meters of inertia for it to be fully armed. So if you were to
point a RPG-7 at the ground and fire...the rocket would shoot out, and nothing would happen.
But even if you were protected by magic armor and had a powerful enough weapon to technically
launch your body into an ideal rocket jump.... acceleration would be the problem.
xkcd has a brilliant What If? post about the possibility of using a bunch of constantly
firing machine guns as a jet pack. It's worth reading, but points out that constant thrust
is incredibly important. A single shot fired down -- if strong enough to propel you up
like you see in video games -- would induce a lethal g-force. Instead of one giant boom,
a slow and steady burn, like a jet pack, is much smarter. But giant explosions are more
fun ... we just need to have enough of them. Enter: Project Orion
Project Orion was a concept space craft that used thousands of nuclear bombs detonated
gradually behind the craft to push it forward, a technique called Nuclear Pulse Propulsion.
At it's maximum speed, it could theoretically go 10,000km/s which is around 3% the speed
of light.
To put that into perspective, it would take about 47 hours to fly around the world in
a commercial airplane. If Orion flew at it's peak speed the whole way, it would take about
4 seconds.
Of course it takes time to achieve that level of acceleration and time to slow down, so
if I were to go to...say... Saturn, it would take more like 2.5 years...which isn't that
bad considering it's 1.2 billion kilometers away.
George Dyson has an amazing TED Talk about Orion, you can find the link in the description
to watch it but now that you're at Saturn, why not try another classic video game move,
the double jump.
Titan, the largest of Saturn's 62 moons, has an incredibly dense atmosphere and lower
gravity than Earth so, hypothetically, you could jump and while in the air, jump again
using the thick atmosphere to launch yourself. Thus successfully pulling off a double jump
and reaching an elusive weapon upgrade or giant gold coin.