What happens when you shoot an arrow in space?

[RainDreamer]

When we shoot a gun in microgravity, the escaping gas and the force of recoil would push the gun backward while pushing the bullet forward. But how would that work when you use a bow instead?

When you draw a bow, you are storing energy in the limbs as they compress, like a spring, and when the string is released, the limbs returns to their neutral position and pull the string with it, releasing that energy and launch the arrow nocked to the string forward. In my experience as an archer, the bow would launch itself forward too if you let your grip loose when shooting. So where does it goes in microgravity?

There is a reactive mass being launched one way, so it would make sense if the launcher get pushed to the opposite direction, though how this work with a bow confuse me.

[SargeRho]

The bow transfers energy to the arrow, by pushing on it, and as a result, the arrow pushes back with the same amount of force. Since the mass of an Arrow is pretty low, you won't accelerate by much.

[kiwi1960]

Sarge is right.... so if you braced yourself against the ISS and fired, nothing much would happen except the arrow would really whizz away....

no bracing, and some of the energy would be lost as it would be going the opposite way as well... so a slower speed for the arrow.

[Streetwind]

It's entirely possible for the bow to accelerate forwards... or backwards. It all depends on how you hold it.

When the limbs snap forwards as the string is released, they enact a force on the bow that pushes it backwards, into your hand. When the limbs stop moving in their neutral position, they enact a force that pulls the bow forwards, out of your hand.

If nothing held the bow at all, these forces would cancel each other out - it's simply a case of two identical opposing forces of acceleration acting on identical masses. The bow will lurch a small distance backwards, but otherwise return to being at rest. (Unless an arrow is fired, but we will ignore that here.) But because your hand is holding the bow as you release the string, you absord the force that pushes the bow backwards. If you do not continue holding onto the bow to [I]also[/I] absorb the opposing force, that force will pull the bow forwards out of your hand, and in microgravity it will continue drifting forwards.

When an arrow is involved, the bow works like a rocket engine, and accelerates itself backwards by accelerating the arrow forwards. This effect is independent of the one described above, but the forces will of course combine to determine the final movement of the bow, if the bow is allowed to move (not held). Edited November 22, 2015 by Streetwind

[1of6Billion]

I'm just curious... If you shot an Arrow from the ISS. Where would/could it end up?

[Shpaget]

In a slightly different orbit.
Fastest compound bows shoot at about 100 m/s. By contrast, average speed of ISS is about 7600 m/s.

[Hary R]

[quote name='1of6Billion']I'm just curious... If you shot an Arrow from the ISS. Where would/could it end up?[/QUOTE]

In orbit, up until drag reduce it apogee below dense atmosphere where it will burn from reentry.

edit : oh! got ninja'd

[softweir]

As the bow propels the arrow, it is pushed back by reaction. The elastic tension in the bow causes it to pull the string and the arrow forwards, pushing the bow backwards. The archer will experience some recoil when he looses the arrow, probably less than he would when firing a gun of any reasonable calibre. He would certainly experience much less shock because the bow imparts its energy to the arrow over a much greater interval of time, but that's the same for bows on the ground!

An arrow launched from the ISS would eventually end up on Earth - atmospheric drag at the ISS' orbit is significant, and the arrow would constantly lose velocity and end up burning up in the atmosphere. However, the difference in orbits would be very small at first because the arrow would be going at almost the same velocity, so it would zip by the ISS once every orbit (for a few orbits), passing below the ISS (possibly hitting a solar panel first time round) then missing it by increasing margins with every orbit as its orbit decays.

[Superfluous J]

[quote name='1of6Billion']I'm just curious... If you shot an Arrow from the ISS. Where would/could it end up?[/QUOTE]

Back in the ISS, an orbit later, if you fire it [s]right[/s] wrong.

[Stone Blue]

Heres one to think about:

Say you are in a 4000km Kerbin orbit, doing 876.2m/s, pointed prograde...You then fire a kerbal out of a cannon pointed retrograde, at 876.2m/s.... What orbit/velocity does the kerbal end up at? :D

[Shpaget]

This:
[url]https://www.youtube.com/watch?v=BLuI118nhzc[/url]

[Cirocco]

[quote name='Shpaget']This:
[url]https://www.youtube.com/watch?v=BLuI118nhzc[/url][/QUOTE]

if you fire the kerbal with such a force that he [I]exactly[/I] has an exit velocity of 876.2 m/s, then I believe this is pretty much what will happen.

His orbit velocity will (I think) be 0 m/s (and remain there unless he gets another boost somehow), but his surface velocity will very quickly pick up as he falls straight down to his horrible, fiery and bone-crushing death, plunging through the atmosphere at a 90° angle :P

Also note that your cannon's speed will be boosted by a certain amount (how much depends on its mass) and it will end up in a slightly more elliptical orbit (assuming your orbit was circular).

[cantab]

[quote name='Stone Blue']Heres one to think about:

Say you are in a 4000km Kerbin orbit, doing 876.2m/s, pointed prograde...You then fire a kerbal out of a cannon pointed retrograde, at 876.2m/s.... What orbit/velocity does the kerbal end up at? :D[/QUOTE]Assuming the mass of the Kerbal is negligible (or that the "muzzle velocity" includes compensating for recoil) the Kerbal will be at zero speed and therefore in a degenerate orbit that's a straight line with an apoapsis where he is and a periapsis at the planet's centre. This is known as a radial elliptic trajectory.

As for the arrow, yeah, it seems to me that as the bow limbs spring forward they push the middle of the bow, and therefore you where you hold it, backwards. Edited November 23, 2015 by cantab

[Kerbart]

[quote name='Shpaget']This:
[url]https://www.youtube.com/watch?v=BLuI118nhzc[/url][/QUOTE]

But what if you put the cannon on a conveyer belt that [I]always[/I] matches the exact speed of the cannon? :p

[wumpus]

The most obvious difference is that the fletchings won't work in space (i.e. the vacuum outside a spaceship, but the would work in the ISS). Expect the arrow to tumble while maintaining the exact trajectory it launched with.
Second, the longer the range the weirder it gets:
Point blank range: no change (but don't expect it to penetrate any target due to the tumbling effect).
Normal range: Your "archery" isn't arching. No matter what the range (ignoring curvature of orbit), you are still at point blank.
Orbital range: your trajectory is supposed to be heading out to a different orbit and will return (more or less) after every orbit. The return point should move further and further behind due to the slightly longer orbit. I suspect that air resistance on something as light as an arrow would have a greater effect, but have no idea how to calculate that.

[Stone Blue]

[quote name='Shpaget']This:
[url]https://www.youtube.com/watch?v=BLuI118nhzc[/url][/QUOTE]

And we have a winner!... Saw that not long ago, thats why I posted my post... lol

[kiwi1960]

Theoretically, he would stay put.... while you moved as you were ... you would meet again at the next orbit...

theoretically...

[wumpus]

[quote name='Shpaget']This:
[URL]https://www.youtube.com/watch?v=BLuI118nhzc[/URL][/QUOTE]

Just how many pound draw do you need to fire an arrow at orbital velocity? You aren't going to hit the Earth from ISS with any bow pulled by mortal man (ignoring slow, slow air resistance).

[meve12]

[quote name='5thHorseman']Back in the ISS, an orbit later, if you fire it [s]right[/s] wrong.[/QUOTE]

I'd go with 'right'. You'd need an extremely steady hand to hit the ISS on that trajectory even if you got the timing exactly right.

[Shpaget]

[quote name='wumpus']Just how many pound draw do you need to fire an arrow at orbital velocity? You aren't going to hit the Earth from ISS with any bow pulled by mortal man (ignoring slow, slow air resistance).[/QUOTE]

If it's a physically large bow, it doesn't need to be particularly strong.
In a strong bow arrows accelerate at around 4000 m/s^2, so if your bow is big enough to have the arrow accelerate for 2 seconds, you can achieve deorbit. The displacement of the draw would be 8 km, so your mortal man would be able to pull it, but would need to walk a bit.

If you lower the mass of the arrow by a factor of 10, because why not, it will accelerate 10 times faster, so your bow can be shorter.

But I think you mistake my post to be a reply to OP. It was a reply to a previous post about a canon fired Kerbal.

[quote name='meve12']I'd go with 'right'. You'd need an extremely steady hand to hit the ISS on that trajectory even if you got the timing exactly right.[/QUOTE]

If you're onboard ISS, or just outside of it, it's not about timing, it's about the direction. You need to change velocity, without changing the speed, change direction and retain speed (and thus orbital period). Edited November 26, 2015 by Shpaget

[wumpus]

[quote name='Shpaget']If it's a physically large bow, it doesn't need to be particularly strong.
[/QUOTE]
I've never heard of a bow too long to hold, but it should work if you allow the entire thing to pivot (preferably past the point the arrow stops accelerating). I'd only expect to see such a thing in a caste (presumably permanently attached to a murder hole), but I've never heard of such a thing. Any clues to the existence of one?

[RainDreamer]

Bows are still fundamentally limited by your draw length, so you might get a really big bow, but if you can't draw it to full, you can't utilize its full potential.

As for the question, the largest bow type ever is the Japanese Yumi, specifically the Daikyu (literally means large bow), which is as tall as 2 meters or more. The draw weight of a war yumi is estimated to be about 80-90 lbs - less than the English long bow which can have like 100+ lbs draw weight. I am not good enough with physics to actually calculate the acceleration of an arrow firing from one of those bows though, so I won't touch on that.

Though you can try to be a little crazier in micro grav and use your feet as anchor against the bow and pull the strings using all your upper muscles, which can let you draw real far and essentially turning you to a human crossbow. I have no idea what would happen if you pull such a stunt though in space, but lots of things flying off at several directions, I assume.

[Plusck]

The ISS has an orbital speed of just over 7600 m/s and an orbital period of just under 93 minutes, meaning that its orbital path is almost exactly 42,600 km long.

Fire your arrow at exactly 90° to prograde, and it'll whizz back past you every 41,5 minutes in the opposite direction. Any other angle and it will do the same - but coming in above and below you and/or side to side in front or behind you - at a slightly slower frequency depending on how close to pro/retrograde you shoot.

With a perfect normal or anti-normal shot, this means that the speed of the arrow relative to the ISS will start at 100m/s (say) and drop to 0m/s after 21.25 minutes, a quarter of the way around the orbit. I'm not sure of my maths here but I think that suggests the maximum distance from the ISS it can reach is 79.2 km.
A perfect radial / anti-radial shot will end up being below and ahead, or above and behind, after a quarter orbit, but again a maximum distance of 79.2 km.
Which suggests that you'd need to get your arrow firing at around 1000m/s to have a hope of getting it below LEO.

Also, an exact prograde or retrograde shot will be 1/76th slower or faster than you, so that suggests you'll have to wait 76 orbits for it to be back on a collision course - by which time it'll have travelled over 30 million km...

[wumpus]

[quote name='RainDreamer']Bows are still fundamentally limited by your draw length, so you might get a really big bow, but if you can't draw it to full, you can't utilize its full potential.
[/QUOTE]
That's what I assumed until I thought about it a bit more. You could presumably take a few steps back with a sufficiently big bow and then brace yourself for the last bit. Presumably the bow would also include two "kissers": one for the drawpoint on the string, the other as a reference sticking out from the end of the bow (you need some means of making sure the angle and length of those are the same). I was just wondering if anybody ever made one. Considering that castle archery points were essentially carved out of stone, you could easily mount something huge there and have an even greater advantage (you are already higher) over the attackers.

[looks at google images]Pull *behind* the head? I wonder how you maintain your drawpoint? Although all I know about kyudo is that it each step is even more spelled out than the routine for firing a smoothbore musket in a musket square. Think archery moves taken to tea ceremony type obsession and you have my impression of kyudo.

[RainDreamer]

[quote name='wumpus']That's what I assumed until I thought about it a bit more. You could presumably take a few steps back with a sufficiently big bow and then brace yourself for the last bit.[/QUOTE]

I am not sure I can picture what you have in mind... Though, if you have to hold the bow with one hand, then your draw will only goes as far as your drawing arm's shoulder, the furthest anchor point I ever tried. If you want to go further, you probably will have to do something like spread your arms and draw the bow like you are pulling the bow and the string apart in front of you so you can use both of your arms' length, but that makes for horrible aim and release, and no one sane ever tried it as far as I know.

[quote name='wumpus']
Presumably the bow would also include two "kissers": one for the drawpoint on the string, the other as a reference sticking out from the end of the bow (you need some means of making sure the angle and length of those are the same). I was just wondering if anybody ever made one. Considering that castle archery points were essentially carved out of stone, you could easily mount something huge there and have an even greater advantage (you are already higher) over the attackers.[/QUOTE]

Kissers are usually for allowing compound shooters to have an anchor point on their face even if they draw past it, while they aim down their sight, so only one is needed on the string. As for the castle arrowslits, they usually use siege crossbows or a whole ballista behind those, so yeah, huge.

[quote name='wumpus']
[looks at google images]Pull *behind* the head? I wonder how you maintain your drawpoint? Although all I know about kyudo is that it each step is even more spelled out than the routine for firing a smoothbore musket in a musket square. Think archery moves taken to tea ceremony type obsession and you have my impression of kyudo.[/QUOTE]

You maintain your anchor point by practice it enough until it is muscle memory, though it is helpful to have a place on your body your drawing hand can touch, like the corner of the lips, chin, or shoulder so you can pull it to the same point every time. While I don't practice kyudo (mongolian draw style here), from what I have seen, all the steps are to ensure that their movement is the same every time they draw, so that they can shoot consistently.