Al Shepard will have a rival:

Bad tee shot in space could mean disaster

Doesn't seem like the best of ideas.

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I think the danger of a hook (or slice) in space is, uh, "overblown." A shank, however, is a different danger.

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As I was going to post (but didn't) on the "empty spacesuit" thread...

Is it ever a good idea to be adding to the "space junk" that is already circling the Earth?

What I mean is that an empty spacesuit (or a golf ball) moving at orbital velocities could really ruin your day if it happened to hit your shuttle/spacecraft.

I'm sure I'm not the first to have thought of this...

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How will the ball stay on the tee ?

You know that joke of hitting the ball, seeing it flying out of view, only to hit the back of your head (preferably with stickers of all major cities )? It gets a whole new dimension .

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That was my first question... Magnets? A sticky ball? A "suction/vacuum" tee wouldn't work.

Most likely velcro, cheap, abundant in the ISS Supplies and works well in all temps.

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This bothers me, its not like a slice on the ground taking out a window. Three or four YEARS in orbit, on a similar flight path to the ISS? And the ball is small enough to be difficult to track.

I think some serious re-consideration is required here...

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well, if he hits it "down" toward the earth, i would think that it would burn up in the atmosphere relatively quickly- but if he hit it "up" it would stay in orbit longer..
and what if he loses his grip on the club, and sends it flying into a solar panel or something?
doesn't sound like the brightest thing i've ever heard of doing in LEO..

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Well, this scenario is actually somewhat complicated, analysis-wise.
First of all, I'd say it's dumb. There is a legitimate safety concern involved, certainly. Smacking a golf ball into the ISS could pose a problem, especially if it bounced off of something and came crashing back into the guy who hit it (imagine a golf ball smacking into the face plate of an astronaut at a reasonable velocity)!

There's possible damage to something, of course, but I think the idea of swinging a golf-club in free fall is at once kind of a waste of effort (it would be cumbersome and likely not too effective), and possibly dangerous, depending on how the cosmonaut is secured (all those wild forces could cause a bad day in and of themselves).

But as to the space junk argument, I don't think that's a huge consideration, really. There's alot of pieces of things orbiting this planet (pens, bolts, nuts, at least one camera I know of (I think it was Mike Collins' camera from Gemini 10)). The odds of anything hitting any of them are astronomically small, and one thing that should be remembered is that all of these orbiting tid-bits are basically going in the same direction, west to east, so a spacecfaft entering orbit isn't going to get slammed by something at 17,000 miles per hour...these things are all moving at similar velocities and directions to any orbiting craft, and their relative velocities are rather low.

Of course, the ISS is on a polar orbit (inclination of 50 degrees or so), so there's the possibility of a conflicting angle of incidence with any ISS related debris and a craft that might be moving on a more equatorial path, but again, the odds are astronomically small.

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As to what might happen to this golf ball if it is successfully "launched", that depends on the direction it's hit in. I would say that not much relative velocity will be attainable given the fact that a fully suited cosmonaut will be attempting to swing an iron at it, but several possibilities could result.

If he hit it down toward the earth, it might enter the atmosphere, depending on the velocity imparted to the ball, which would provide a really neat meteor for someone to look at, or it might just as well stabilize itself in a lower, faster orbit below the ISS.

If it was hit "up", it would establish itself in a higher orbit, and slow down as a result, and this would also happen if it was hit "back", behind the station's path of flight. The cosmonaut would actually be reducing the ball's velocity, which means it would probably stabilize itself in a higher orbit (no way he could-de-orbit the ball, I should think, and with a 6-irn, if he hit it square, he'd be hitting it up as well as back).

If it is hit along the flight path, the increase in velocity would make the ball drop into a lower orbit.

It could also be hit to one side or another, which would result in an orbital plane change for the golf ball, as well as a different orbital altitude and shape, depending on the angle relative to the fliight path of the station, and the up or down component of the golf ball's path.

Bottom line is that the golf ball will probably be knocked into a different, likely elliptical orbit, and will never be seen again, nor encountered by any other space craft...for at least another millenium or so! What precisley will happen to it is impossible to say, given the variables that are possible when hitting a golf ball.

I believe you have this backwards. Hitting the golf ball along the flight path increases its energy, thus putting it into a higher orbit (where, ironically, it will be moving more slowly), and vice versa for hitting it opposite the flight path.

I would vote for hitting it in the opposite of the direction the station is moving. That would put it in a lower orbit to start with, and as a smaller object its orbit will decay faster. So that way it should never be an issue for the space station.

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Could you hit a golf ball hard enough from the space station to make it enter the Earth's atmosphere (in a relatively short time, as opposed to a few decades or however long the space station would stay up if it had no rocket boosts from time to time)?

Wouldn't hitting the ball "down" or backwards, opposite from the space station, just result in the ball having a slightly slower orbital velocity than the space station?

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you can't have a different orbital velocity while having the same (unpowered) orbit. If that's what you're asking. Orbits are determined by their velocity.

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Honestly, I don't think a good throw or club hit could impart enough energy to the ball to make it drift far from the ISS's orbit. I may be wrong, but in space, with nothing to brace against, we'd only be talking about a few mph out of the total orbital speed.

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I wonder if some golf manufacturer is paying for this to use as advertising?

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Sounds to me like the cargo going to the ISS should be checked for contraband vodka. I know the odds of hitting another object is low, but it is another object that could hit a craft, or human.

I know I'd be quite upset if I was working in low orbit, turned around just in time to see a golfball heading towards my faceplate. And something like that happening would be so wierd that it would have to happen. Murphys laws apply here.

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If we idealize the problem (making the original orbit circular, and ignore friction and different precessional effects), the problem is interesting: once the ball is hit, and it is free, its velocity is sufficient to return it to the place (altitude) where it was hit. It may have a smaller or larger semimajor axis, depending upon which way it was hit, but the geometry allows it to return regardless, no?

*thinks*

Yes indeed I think that even with a perfectly parallel hit, you'd get an elliptical orbit that cuts the ISS orbit at the point of the hit.

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me *thinks* (or maybe rambles)

Average golf ball speed is around 200ft/sec, so lets say that they can hit it around half as hard (which I would think is phenomenal in a spacesuit).
So, we are talking somewhere around 60 mph.

If we hit the ball backwards, the ball would be in it's farthest in its orbit when it leaves (aphelion), and the next aphelion would be around 90 miles behind the station.
If we hit it forwards, then it would be in it's closest when it leaves, and the next perihelion would be around 90 miles ahead of the station.

It would take about 266 orbits for the 2 to meet again (more than 2 weeks). By that time, atmospheric drag would have some effect on both, although the space station could have been boosted in the meantime. And in the case of backwards, then the ball would have experienced more drag that the station because it dips closer to the atmosphere.

And if the 2 met, then it would hit at around 60mph.

I would be much more concerned about the activity itself than it's orbital concerns.

Yeah, the way I see it, the golf ball is not an immediate threat to the ISS. It might very well pose a hazard for other LEO satellites, meeting with them at relative velocities over 1000 km/h.

Anybody know of other operational sats at or below ISS orbit?
I thought that ISS was about as low as you can go so that the slight atmospheric drag will quickly cleans the orbit. (thus requiring occasional boosting)

That wasn't exactly what I was asking, I was replying to those that seemed to be saying that it was possible to hit a golf ball such that it would return to Earth. I was asking about that, it seemed unlikely to me since the golf ball would still retain most of the velocity of the space station.

Agree that if the velocity is slightly less then it wouldn't have an identical orbit.

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"I'm as accurate as any psychic. And I'm a cartoon!" -- Squidward

"Arrrgh, the laws of physics be a harsh mistress!" -- Bender

Since I can't do the math... I have the following questions that might show this.
1) at what altitude would atmospheric drag cause a golfball to drop within a single orbit.
2) at what speed would an orbit be where that altitude is perihelion and the ISS altitude is aphelion
3) is the difference between that speed and ISS speed hit-able?

Dunno about the first one, but in our previous example, the ISS orbit is assumed circular so everywhere is perihelion/aphelion. The perihelion point is where the object is going fastest, and the velocity is perpendicular to the radius--so hitting the golf ball forward at any speed would produce that. Does that answer 2) and 3)?

I don't think that's what he asked.

but 1 and 2 do not ask for the same, as flying at an altitude all the time has more drag effects than flying that low only at perigee (I don't think Helios is a relevant center object here ).

On 3: I don't think that speed difference is attainable with a golf stick, but I might be wrong.

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Ack. Right. Apogee/perigee.

Interestingly, most dictionaries allow apogee/perigee for orbits around any body. But not aphelion/perihelion.

As I had indicated, orbital mechanics is a complicated thing. Alot of variables come into play. It's somewhat counter-intuitive, actually, like flying an airplane.

People tend to think that pulling the stick back means "up", and pushing the nose down means "down". Also, it is common to think of increasing the throttle as "faster" and decreasing the throttle as "slower". Initially, this is true, but the final effects of these maneuvers are counter intuitive.

The throttle is actually the up and down control in an aircraft, and the stick is the fast and slow control. If pilots aren't trained that way, and intuitively feel this, they will die. It's a rather long and confusing explanation, but in orbital mechanics a similar wierdness occurs.

Two spacecraft executing rendezvous have a similarly counter-intuitive situation occurring. The chase craft is approaching from the rear, at a faster speed, and a lower orbit (an eliptical orbit, with changing speeds all the way through its path). If the chase craft gets a visual on its target up ahead and above it, and decides to point the nose at it and thrust toward it, everything looks fine for a time, and then, things go wacky. The chase craft begins to drop and overtake the other craft. This is because a faster craft will eventually stabilize itself in an orbit that corresponds to its speed. In order to attain equilibrium, the falling object (which all orbiting spacecraft are) finds its proper orbit based on its velocity. something going fast will tend to drop into a lower stable orbit, and , strangely enough, something going slow will tend to climb eventually...so long as it hasn't slowed enough to de-orbit itself. Odds are they will both go into a rather eccentric eliptical orbit.

It's a very wierd set of circumstances and complex mathematics.

However, the bottom line is, without specific data regarding the velocity and vector imparted to a golf ball, it would be impossible to predict the exact results of the golf-ball orbit.

Hitting straight back, the golf ball would drop, enter an elliptical orbit, and climb. Hitting ahead, without any upward moment, the golf ball would accellerate andneventually stabilize into a lower orbit. With an upward moment to the velocity, the golf ball would climb, then enter an ellipse of somewhat different character than the decellerated balls ellipse.

Kinda wacky, no?

For 1), I would say that any orbit below around 350,000 feet (70 or so miles) would result in a rather quick drag down.

For 2), I can't say, as earth orbits are not generally designed to be anywhere close to the earth's atmosphere at perigee, and in elliptical orbits, there is a constant increase and decrease in velocity. In other words, there's no constant speed. However, I can approximate that the velocity of an orbit that cut down to about 70 miles (if it lasted at all ) would be about 18400 miles per hour, and at the apogee of the ISS altitude (about 250 miles), would be about 17300 miles per hour.

As to 3) probably not. The difference in velocity is about 1600 feet per second (around 1000-1100 miles per hour), and it's not really as simple as cutting 1600 feet per second from the orbital velocity of the ISS to attain this orbital eccentric.


As another poster has said, if they could get 60 mph (retrograde or posigrade) from hitting a golf ball of of the ISS, that would probably be pretty good, but that's no where near the difference between the perigee velocity close to the upper fringes of the tenable atmosphere.


I also don't think de-orbiting would be possible with a golf stick. Youd need between 250-300 miles per hour of delta V to de-orbit from the ISS altitude (about 400 FPS). So, the golf ball, hit in a retrograde direction, would enter an elliptical orbit of some undetermined and undeterminable parameters without tracking data (and I cannot imagine anyone attempting to track this thing...as I cannot imagine anyone actually doing this thing!).

No, I disagree. A faster craft will accelerate away from the Earth, losing speed in the process, until it's in a higher orbit and going even more slowly than it was. The contradiction in rendezvous is that if you speed up to try to catch the target, you fall behind, and if you initially slow down to let the target catch you, pretty soon you're moving even faster. Note that when the shuttle (or any orbiting spacecraft) wants to return to Earth, it fires its engines in the direction of motion to slow itself down and lower its orbit into the atmosphere.

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I think you're presenting the dependence of speed on flight path angle and the dependence of lift on airspeed in an overly black&white manner, where these effects become more important than the primary effects. Of course it all depends on the flight regime. In a long cruise, the dependency of lift on speed (hence thrust) is important. During climbs, it depends whether you're doing a sustained or an energy exchanging climb. In sailplanes, it's a whole other situation. You control speed with the stick, but if you forget about altitude that will end up very bad and vice versa.

As for rendez-vous: rendez-vous is counterintiutive indeed. But the principles apply from the start of firing the engines, when you deform your orbit into an elliptical orbit with different roundtime than the one of the other plane. This way, you do the initial rendez-vous. The actual docking (the final steps) can be done with multiple thrusters, and in this phase one can more or less "forget" about orbital mechanics as multiple thrusters make the craft omve Newton-wise against the trusters. Of course this is not an efficient way, and therefore it is not usable for the initial rendez-vous. That phase takes long anyway, and to counteract orbital particulars over a long period of time would require a lot of thrust.

The easiest way to understand the paradox of rendez-vous is looking at the simple case of one burn per orbit:

*leader and chaser are in a circular orbit.
*chaser brakes and falls into an elliptical orbit.
*that orbit has apogee at the circular orbit.
*one orbit after the burn, the chaser will have moved in on the leader (or even overtaken it) due to the shorter elliptical orbit of the chaser.
*an accelerating burn at apogee brings chaser back into the circular orbit.

This simple D/A scheme takes a whole orbit (say 90 minutes) for 1 adaptation, but does not require orbits to settle into circular ones. In reality, the rendez-vous software continuously calculates accelerations and decelerations, sending chaser over a whole collection of elliptical orbits, such that it does not take 90 minutes per change anymore. But the principle of the paradox gets lost that way, so a simple D/A of the chaser is more clearly to explain it.


The shuttle fires against the direction of flight (so decelerating) so the orbital height becomes apogee and the perigee is somewhere low in the atmosphere. This way, the shuttle gets into an elliptical orbit sending it into the atmosphere, which does not require the orbit to resettle into a circular one. Of course there is some ambiguous wording in firing engines. The shuttle flies engines first during the de-orbit burn. It burns into the direction of flight, but the force is against the direction of flight, decelerating the craft. With "firing against the direction of flight" I mean "generating thrust against the direction of flight". In fact a de-orbit burn is not counter-intuitive, as you brake to descend. Moving towards any different altitude (circular) orbit on a 2burn scheme is only counter-intuitive when looking at the net delta-V. But the first burn is intuitive: decelerate to get lower; accelerate to get faster. To get lower you decelerate first, but at perigee you must accelerate more than you decelerated. To get higher, you accelerate first, but at apogee you must decelerate more than you acelerated.

The shuttle deorbit only requires the first deceleration step to get lower, after all we don't want to settle into a lower orbit but go down all the way, so there's no need to accelerate ourselves to settle into a lower circular orbit.

A spacecraft does not settle into another circular orbit fast. If you do a delta-V, you go into an elliptical orbit and tend to stay there. It's only disturbances that round the orbit, or deliberate burns.

So changing altitude is no that counterintuitive when looking at the primary action: decelerate to get lower. But in rendez-vous, it is the orbital period that is of importance. By decelerating, you get into an elliptical orbit with lower period than your initial orbit, hence traveling shorter paths than the leader and catching up on him! Be it in a different orbit, with only 1 crossing point (apogee of your deceleration ellipse). Here the primary action is counte-intuitive: deccelerate to close in on the leader.

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