Bob is an astronaut. He is in love with Alice. For his next EVA in a LEO mission, Bob knows that he will be flying above Alice's farm, located in an area without light pollution, during a moonless night.

He thinks that he can be able to send her a romantic gesture, and ask her to look up in the sky around the time he will be passing by.

He carries with him 3 cobblestones, about the size of a tennis ball. He wraps them in copper wires (leftover from some do-it-yourself electricity work in his garage) and ask his captain to inform him via the intercom when they will be flying above the coordinates of the farm.

His plan is to simply hand launch the stones toward Earth and then hopefully Alice will see 3 greenish shooting stars in her sky.

Can this plan achieve the hoped result?

Edit: As also pointed out in some of the answers, a real astronaut on a real spaceship would not jeopardize him/herself and the mission by carrying extra weight and throwing out some "garbage" for personal reason. However fictional worlds have different rules (else we would not ask if Star Wars fighter can PEW PEW when firing). In this fictional world the astronaut managed to carry something and to throw it, and thanks to some of the answers I can already correct the "target" to something smaller than cobblestones and maybe lighter, like a golf ball

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    $\begingroup$ I deleted my earlier comment since answers stating the same in a much better way exist, but I want to bring to your attention that smuggling those objects into space and then scheduling a spacewalk (I'm assuming something like that?) for some shenanigans doesn't sound like something that would actually happen. Also note that those walks are incredibly tedious and dangerous. $\endgroup$
    – Raditz_35
    Nov 17, 2017 at 9:15
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    $\begingroup$ As usual, I strongly advise playing Kerbal Space Program to get a grasp on the orbital mechanics. Burning in the direction of the planet is wasteful idea. Retrograde burn gives most deorbit from given delta V. $\endgroup$
    – Mołot
    Nov 17, 2017 at 9:33
  • $\begingroup$ You need 2 things: your cobblestones and let it falls within the meteoric zone(80 to 120km above sea level), don't be too concern with its speed if you're dropping it from orbit. $\endgroup$
    – user6760
    Nov 17, 2017 at 9:59
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    $\begingroup$ @user6760, as your comment seems to go against all other answers so far, I'd gladly see it expanded as a proper answer $\endgroup$
    – L.Dutch
    Nov 17, 2017 at 10:38
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    $\begingroup$ How is this world building? Shouldn't it be voted for closure? At the least, it should be on the Physics sight, not this one. Or is there one rule for the residents, and one for the rest of us? $\endgroup$ Nov 17, 2017 at 14:59

7 Answers 7


If he makes a giant potato-gun / slingshot / mini-rocket. Or(!)...

Our good old friend Sir Isaac is a right honorable jerk troublesome fellow in these circumstances. According to his first law, in order to de-orbit something, you need to decrease your speed in orbit (*). You need a change (normally denominated delta, $\Delta$) of velocity ($v$) of at least 150 m/s to de-orbit from Low Earth Orbit.

Space suits are bulky cumbersome things. You simply cannot perform anything with the speed and agility you normally do. And even without that hindrance a really good baseball pitcher can get no better than 50 m/s out of a good pitch.

So in order to achieve a delta-v of 150 m/s, Astronaut Bob will need to "cheat"

At first I thought that a slingshot might do it, but the draw length available, combined with the force needed to achieve 150 m/s for a tennis balls-sized object is somewhat prohibitive. He will not be able to pull that back by hand. A winch with a quick-release might do the trick.

Another way to do it might be to bring a big potato cannon.

Or he might be able to bring a little hobby rocket to attach to the stones.


All of these things are dangerous to the space craft. And they add weight to the launch. Weight is a precious commodity on space launches.

And since Astronaut Bob — albeit a very romantic guy — is also a scientist/engineer, and a sensible such (because hotshots do not get to become astronauts), he will not try to sneak this aboard. He will think up another way of displaying his affection to his beloved Alice.

...or: he can use something smaller. (Late edit)

If Astronaut Bob settles for smaller projectiles — say marble-sized copper balls, instead of the tennis ball-sized you first specified — then he might be on to something. A handheld slingshot can achieve a "muzzle" velocity of up to 500 ft per second. That is right on the mark: 150 m/s. And since objects as small as a grain of sand will make a "shooting star" that is visible to the naked eye, a ball between 1 to 3 cm in diameter will make a very good visible meteorite.

Drawing example from the fact that astronauts have smuggled aboard "contraband" before, something as small as a few copper balls and a slingshot does fit within the wiggle room they have for weight; the tolerances will allow it.

Also, if Astronaut Bob is really good friends with his fellow crew-mates... they can help provide the conditions for him to do this — highly unauthorized — very romantic gesture and get away with it.

From this, all Astronaut Bob needs is a ton of good luck, because margins are narrow to say the least. But you are the author... you decide if he succeeds. With a slingshot and smaller projectiles, yes, then it is physically possible for Astronaut Bob to make a shooting star for his beloved Alice.

enter image description here

The 'Fallen Astronaut', placed on the Moon by the Apollo 15 crew, was not sanctioned by NASA

(*) Being in orbit is like falling towards the planet; you are in constant free-fall. But since you have such a high sideways speed, what happens is that you keep missing the Earth. So in order to come down from space, you do not throw yourself in the direction of the Earth, because that will fail. What you do to come back to the surface is that you slow down (i.e. you "throw" yourself backwards. Once you have slowed down enough, your free-fall will then bring you into the atmosphere. From there, the atmosphere will slow you down more, and your return to Earth is guaranteed (almost).

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    $\begingroup$ @JPhi1618 It has nothing to do with size but the amount of light it emits. $\endgroup$
    – MichaelK
    Nov 17, 2017 at 15:36
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    $\begingroup$ Possibly a sling is a better launcher than a slingshot. Slingshots designed for Earth performance probably fair poorly in space, but a sling requires little more than a length of wire and room to swing. $\endgroup$
    – user25818
    Nov 17, 2017 at 18:57
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    $\begingroup$ @notstoreboughtdirt Really bad idea. A sling is difficult as it is to control properly. In a space suit(!)... no way. Also, what is to say the slingshot cannot work in space?! $\endgroup$
    – MichaelK
    Nov 17, 2017 at 22:51
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    $\begingroup$ @MichaelK I don't know that a slingshot won't work, but I know temperature cycling and sun exposure wares rubber so I guess space would be hard on it. If the characteristics of whatever material is used to make the slingshot changes significantly it would likely be less good. I do see how a sling has some serious difficulties in control and safety, but the properties that make it work are going to be effected by space. $\endgroup$
    – user25818
    Nov 17, 2017 at 23:12
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    $\begingroup$ @MichaelK I was referring to the kick of the potato gun which is usually just a rapid release of compressed air (and less about the mass of the potato). It might be the equivalent of a 5 sec burn from the spacesuit navigation unit, but that isn't necessarily trival. $\endgroup$
    – Phil M
    Nov 18, 2017 at 1:13

Baseball pitchers can throw a ball at around 100mph.

That's really quite impressive, however they train to do this and they have good footing. They're also not throwing the ball very far.

Bob is in orbit, he's throwing the ball with a starting speed of about 15,000mph perpendicular to the direction he wants it to go, and being generous, 100mph in the intended direction of travel.

He's only a few hundred miles up, doesn't that mean the rock will eventually hit the atmosphere to make his shooting star?

The Earth is only 7915 miles across, given an hour to be 100miles closer, and taking his 15,000mph orbital speed into consideration, he's going to miss the planet completely and now his rock is travelling at 100mph away from the Earth. His shooting star is now in a different, slightly more eccentric orbit than the one Bob himself is in.

That orbit may eventually decay and create the shooting star somewhere as Bob intended, or it may interact destructively with Bob's own orbit, much to the dismay of his captain.

In short, throwing his rock directly towards Earth, he could put his rocks into another orbit, but he's not able to throw them hard enough to overcome orbital speed.

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    $\begingroup$ See this answer on sister stack, to wonderful How could a 90 m/s delta-v be enough to commit the space shuttle to landing? question. Turns out it can. Not to directly hit the ground, but to interact with atmosphere, and that's what we need here, too. 100 mph = 45 m/s is half way there. $\endgroup$
    – Mołot
    Nov 17, 2017 at 12:11
  • $\begingroup$ @Mołot Ah now that's a different calculation that MichaelK has gone into, calculating it as delta-v would require you to fire it backwards along the orbital path. Firing it perpendicular to the path as asked gives a much more complex solution which destabilises the orbit rather than necessarily causing reentry. $\endgroup$
    – Separatrix
    Nov 17, 2017 at 12:18
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    $\begingroup$ I guess OP was more interested in getting this done than in getting this done by exact direction of the throw. But I may be wrong. $\endgroup$
    – Mołot
    Nov 17, 2017 at 12:26
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    $\begingroup$ Assuming Bob is close to the atmosphere, what he can do is throw the rock retrograde (not at the planet, but "backwards" given his current velocity vector) when he is at the opposite side of the planet. This would give him the most bang for his buck in terms of lowering the rock's periapsis enough that it grazes the atmosphere (while Bob doesn't). $\endgroup$
    – Flater
    Nov 17, 2017 at 15:47
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    $\begingroup$ @Flater: Basically correct, but Bob would also have to do the throw several thousand miles before he's above Alice's farm, and at a precisely-calculated velocity. And as others note, I don't think an unaided human could throw that hard, or that precisely. $\endgroup$
    – jamesqf
    Nov 17, 2017 at 18:41

Let's assume that Bob is in an orbit similar to those that the Space Shuttle was normally operating in.

In such an orbit, a 200 ft/s retrograde burn was in some circumstances sufficient to deorbit the Shuttle. Depending on the specific orbit, the required delta-v could be as large as 550 ft/s. In civilized units, this corresponds to 61-168 m/s. The rest of the Shuttle's velocity was shedded via atmospheric drag.

MichaelK (who is not me, I promise!) has already mentioned that a good baseball pitcher can pitch 50 m/s.

Sure, as already discussed, it's hard to be a great baseball pitcher when you're wearing a spacesuit. But maybe we can handwave this away by saying that at some indeterminate point in the future, astronaut protective gear has advanced sufficiently to allow something much like that.

We can probably assume that Bob is able to use the spacecraft to prevent himself from being thrown in the other direction. (Bonus: If his tether breaks, and he's carrying these stones, he can just throw one in the direction away from the spacecraft to head back to the spacecraft. See, it's a safety system, and he's testing to see how well it works! It's official mission business!)

The difference between 50 m/s and 61 m/s is sufficiently small that this borders on plausibility. It would be hard, but perhaps not impossible.

Now, the direction he'd have to throw the stone in is counterintuitive. Throwing it downwards (technically, toward nadir) won't work. I'm fairly certain that he'd want to throw it directly retrograde, back the way he came from, possibly at a very slight angle, but Bob would need to discuss the specifics with his flight dynamics officer to be certain.

Also, unless Bob is already in the appreciable atmosphere, the right time to make the throw isn't when he's over Alice's farm, but rather, roughly on the other side of the planet. But this can be calculated relatively accurately, so is not really a problem. Again, talk to the FDO.

So, if Bob's superiors are in on the idea, and he is able to throw the stone in just the right direction at just the right time, with a speed relative to himself (and the spacecraft, hopefully) just slightly higher than that of a good baseball pitch (which places requirement on Bob's protective gear which are not currently met), then he might be able to pull this off.

Unfortunately, the odds that Bob's superiors would be in on the idea are pretty slim, given that this would incur a fair mass penalty on the spacecraft. So he probably won't get a chance to try it. Consequently, as already discussed, Bob, being a practical man, will probably think of some other way to display his affection to Alice.

But it's a nice thought, and it's the thought that counts, isn't it?

  • $\begingroup$ I was torn if I should post this as comment or answer... Turns out, it should've been an answer. $\endgroup$
    – Mołot
    Nov 17, 2017 at 12:29
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    $\begingroup$ @JustinThyme It's perfectly possible to calculate a reentry retro burn (throw) impulse that would cause reentry into the appreciable atmosphere at a fairly well-known location. If we're talking about cancelling out orbital velocity entirely Bob might just as well throw it straight down; would probably take less impulse, and give the same result in that case. I tried to stay at least within the realm of reasonable, though. :-) $\endgroup$
    – user
    Nov 17, 2017 at 18:33
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    $\begingroup$ Mechanical Counter Pressure (MCP) space suits are starting to become mainstream research. They fit like a diver's dry suit that's about 2 sizes too small. A good throw is manageable If the astronaut can anchor his feet well. You might consider a sling (as in David and Goliath). Delta V of 59m/s was measured in research cited in this link (slinging.org/forum/YaBB.pl?num=1215377301/15). Knowing that shot from slings can break bone, 65 m/s is readily achievable. $\endgroup$
    – pojo-guy
    Nov 17, 2017 at 20:41
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    $\begingroup$ Actually, he wants to throw a bit more than half an orbit before he passes over the farm. They will reach their lowest point half an orbit after being thrown but that isn't the point of maximum brilliance. Drag will slow them and take them deeper into the atmosphere where you will get much more heating. The additional distance needed depends on the mass and drag of the objects thrown, there isn't a one-size-fits-all answer and calculating it is far beyond my ability anyway. $\endgroup$ Nov 18, 2017 at 3:04
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    $\begingroup$ @pojo-guy Yes, that's something like what I had in mind. $\endgroup$
    – user
    Nov 18, 2017 at 10:19

How to deploy a meteorite

In order for Bob's cobblestones to be visible above Alice's house, he's going to need to brush up on orbital decay, drag and gravity. Or crib off the work of ALE’s “Sky Canvas” project, which I am sort of doing right now.

ALE would like to release colored meteorites into the atmosphere for a show. As you can see by the handy info-graphic, some planning has to happen to use gravity, friction, drag into account for proper deployment.

Bob is in orbit moving around 15,000 mph. In order for his cobblestones to hit the sky above Alice's house, he's going to have to figure a way to de-orbit them, or slow them down so they drop exactly(ish) where he wants them. If he releases them and lets them fend for themselves, it could take several years before their orbit decays enough to fall to earth.

For a more precise entry, he's going to need a device like a rocket to slow down the cobblestones for a more precise de-orbit. This means during his EVA, he may have to start the de-orbiting process hours or days in advance of being over Alice's house. The exact timing depends on how fast Bob wants to de-orbit them.

If I could make a suggestion, it would be to use strontium and magnesium instead of plain old cobblestones. The strontium will burn bright red and illuminate the sky. The magnesium will create a whitish blue that will be extremely visible.

Good luck.

Colored meteorites

  • $\begingroup$ If Bob is a professional astronaut, I should hope those matters are not something he'll need to brush up on. $\endgroup$ Nov 18, 2017 at 19:02
  • $\begingroup$ @Henning Makholm If Bob is a professional astronaut, he wouldn't even be considering this. It would be the end of his career. $\endgroup$ Nov 19, 2017 at 15:58
  • $\begingroup$ @JustinThyme, - Oh the things men do for a pretty face like Alice. $\endgroup$
    – gwally
    Nov 20, 2017 at 18:49

Orbit isn't far away. Orbit is closer than a nearby city. Orbit is fast away.

Things in orbit are going at a ridiculous speed so that they miss the Earth in the time it would take them to fall to the ground, and instead end up on the other side.

The small amount of impulse a throwing arm could give would result in a slightly different orbit, missing the Earth differently, unless the orbit was already extremely low.

If the orbit was extremely low, then an impulse could result in the stones being slowed down slightly more by the atmosphere. This would reduce its orbit even more, and eventually it would fall to the planet. Of course, the same was true of the original "orbit", it would just happen faster here.

Accuracy would be next to impossible, as the tumble and air resistance properties of the stone would be difficult to predict, and the rentry point would be sensitive to relatively small changes in the speed and direction the rocks where thrown at. The stone could easily take more than one orbit to fall, with the shape of second (and later) orbits a function of how much speed it bled off in the earlier close approaches.

It would definitely not involve throwing the stones "at" the location in question.


No, because he is moving far too fast for the rock to either slow down enough to freefall or travel far enough to reach the thicker atmosphere where it will burn up before it has traveled too far to long to be seen by his love. He could throw it toward earth LONG before he is above her, so the rock has enough time to reach the atmosphere above her.But even then i think it would miss the earth(though i don't know)

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    $\begingroup$ Welcome to Worldbuilding! Would you be able to explain your reasoning here? Especially the bit where you talk about missing the Earth, which is quite big and tends to attract things (especially small ones) towards it... Also, do you know it'll burn up when thrown from a LEO orbit? $\endgroup$ Nov 17, 2017 at 8:41
  • $\begingroup$ I don't know if you knew this, but the fact that the bob is ORBITING means that he is falling towards earth but then missing it. If he threw the rock it would probably end up in a more eratic orbit, but since he is moving so fast it doesn't matter that the earth is attracting the rock and it doesn't matter that the earth is huge the rock would still miss. $\endgroup$
    – Georgios
    Nov 18, 2017 at 1:57
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    $\begingroup$ That's true in an ideal scenario, but in Low Earth Orbit (LEO), objects tend to experience atmospheric drag to a large enough extent that the object will slow down and spiral in towards the Earth. That is, it may very well burn up in the atmosphere, but it won't miss the Earth $\endgroup$ Nov 18, 2017 at 8:47
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    $\begingroup$ ... The point is that the scenario isn't ideal and so the object will de-orbit by itself. For future notice, it might be worth thinking about how guessing an answer makes it a good answer and how constructive statements like "Be gone." are for getting good answers $\endgroup$ Nov 18, 2017 at 10:07
  • $\begingroup$ Mithrandir you have simply been provoking me, and i did not apreciate it. THat is why i wanted you to leave me alone. $\endgroup$
    – Georgios
    Nov 20, 2017 at 6:00

There is just so much that is wrong about this.

First, he is an astronaut. He would have taken extensive courses in orbital dynamics. He would understand the math and the physics. There would be no speculation. He would KNOW.

Second, the orbs would already have a forward velocity. Dropping them does not destroy it. Should he drop them over his sweetheart's house they would continue their forward velocity, and certainly not enter atmosphere above her house. Perhaps they might re-enter in a few years or so. Lost in Space: 8 Weird Pieces of Space Junk He would not need to sway her into going outside when he released them. He could wait until he got back home and was with her. They could watch it together. Somewhere. But probably not over her house.

Third, meteors 'burn up' because of the tremendous speed (roughly 20 km./sec.) at which they they hit the earth. The slower speed of these orbs (approx. 6 km./sec.) would not produce nearly the fireworks. The copper wire would be naught but fluff floating in the wind. It may glow, but certainly no naked eyesight observable effects. And it would never stay wrapped around the orb. The cobblestones would probably get hot enough to cause the surrounding air to glow, and one might get enough light from them to be seen by a good telescope that was aimed directly at them. Cobblestone balls, however, because of their high melting point and round shape, are more likely to actually survive and hit ground then burn up. SPACECRAFT REENTRY There is a greater chance of his love being hit by the orbs than of her seeing them.

Fourth, it is strictly against regulations, and would not be tolerated. Doing so would get the astronaut evicted from the space program. Debris release from spacecraft is strictly regulated. Given that it WOULD be tracked, there is no possible way it could be covered up.

See the following guidelines Debris Assessment Software User’s Guide Version 2.1 if you are at all interested in a NASA software tool for calculating the orbits and time frame for debris in LEO, as well as regulations regarding space debris.

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    $\begingroup$ There is so much wrong with your answer: 1) Yes, Bob would know. OP does not know, and is trying to figure out. 2) Bob would — of course — throw (that is what OP said, not "drop") at the appropriate window in space and time. 3a) Nothing in that article say that the orbital speed of something in LEO is not enough to make it glow. 3b) The object can be modified to better suit Bob's needs. Nothing says it must be that which OP suggested and absolutely nothing else. 4) Yes, it is a stunt. However since this is fiction we can allow Bob to get away with it, either by stealth or leniency. $\endgroup$
    – MichaelK
    Nov 17, 2017 at 16:55
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    $\begingroup$ Down-vote because you are more focused on shooting down the concept than trying to find a solution, and for bringing forth unnecessary and querulous points into the post in order to achieve this. $\endgroup$
    – MichaelK
    Nov 17, 2017 at 16:57
  • $\begingroup$ @MichaelK The OP question was 'Can this plan achieve the hoped result?' My answer is, for good and sound reasons, 'No, it can not'. It is neither realistic nor feasible. It is neither scientifically valid nor logistically valid. Just because you do not like the implications of the answer, does not make it a bad one. $\endgroup$ Nov 19, 2017 at 14:57
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    $\begingroup$ Maintaining my down-vote because "No, that exact plan cannot work" is a bad answer while "It could work, if you make the following reasonable changes" is a much better one. You even go as far to stick the strikt meaning of individual words ("drop" instead of "throw") just to be able to shoot down the answer. $\endgroup$
    – MichaelK
    Nov 19, 2017 at 15:21
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    $\begingroup$ You apparently did not read any other answers in this thread. $\endgroup$
    – MichaelK
    Nov 19, 2017 at 21:21

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