Comments on: Heavy ATV Must Learn to Apply the Brakes Before Docking with the ISS http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/ Space and astronomy news Sun, 8 Nov 2009 10:14:11 -0600 http://wordpress.org/?v=2.8.5 hourly 1 By: jim http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/comment-page-1/#comment-15780 jim Mon, 17 Mar 2008 18:18:19 +0000 http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/#comment-15780 Autumn said: "I don't know, but if I was falling at terminal velocity in Earth's atmosphere, and a partner also falling at terminal velocity, but at a small velocity relative to me, failed to transfer the parachute to me, the results would certainly be horrific in spite of the slow relative velocities, and amplified by the Earth-centered velocities." Your example of a parachute transfer is a bad example because your downward motion will eventually end with contact with the ground. You and your partner are likely to have different terminal velocities which will tend to move you apart. Variations in air resistance will also, on average, tend to move you apart. Falling at terminal velocity through an atmosphere is NOTHING like traveling at similar velocities through a vacuum/space. To put it another way, do you have trouble parking your car in parking space because (at the equator) the earth surface is traveling at 1000 mph due to its rotation? Autumn said: "Huge velocities make everything more difficult, even between objects moving at small velocities relative to each other." Actually they don't. That is the whole point. Earth and everything in orbit around travels more than 2 million kilometer per hour as the solar system is dragged around the Milky Way. And it has absolutely no discernible effect on any of these space docking maneuvers. The only things things that count are the relative velocities of the two objects, the mass, and the physics of orbital mechanics. Autumn said:

"I don't know, but if I was falling at terminal velocity in Earth's atmosphere, and a partner also falling at terminal velocity, but at a small velocity relative to me, failed to transfer the parachute to me, the results would certainly be horrific in spite of the slow relative velocities, and amplified by the Earth-centered velocities."

Your example of a parachute transfer is a bad example because your downward motion will eventually end with contact with the ground. You and your partner are likely to have different terminal velocities which will tend to move you apart. Variations in air resistance will also, on average, tend to move you apart. Falling at terminal velocity through an atmosphere is NOTHING like traveling at similar velocities through a vacuum/space.

To put it another way, do you have trouble parking your car in parking space because (at the equator) the earth surface is traveling at 1000 mph due to its rotation?

Autumn said:
"Huge velocities make everything more difficult, even between objects moving at small velocities relative to each other."

Actually they don't. That is the whole point. Earth and everything in orbit around travels more than 2 million kilometer per hour as the solar system is dragged around the Milky Way. And it has absolutely no discernible effect on any of these space docking maneuvers. The only things things that count are the relative velocities of the two objects, the mass, and the physics of orbital mechanics.

]]> By: Jamie KItchen http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/comment-page-1/#comment-15771 Jamie KItchen Mon, 17 Mar 2008 14:49:14 +0000 http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/#comment-15771 It really struck me how this image is eerily similar the artistic work that used to adorn the pages of science fiction works such as Asimovs and other authors short stories from the 70's. Unfortunately it also reminded me of the images that were utilized in the 80's Star Wars program under Reagan. Jamie It really struck me how this image is eerily similar the artistic work that used to adorn the pages of science fiction works such as Asimovs and other authors short stories from the 70's.

Unfortunately it also reminded me of the images that were utilized in the 80's Star Wars program under Reagan.

Jamie

]]> By: Kbutler http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/comment-page-1/#comment-15765 Kbutler Mon, 17 Mar 2008 13:33:48 +0000 http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/#comment-15765 Once again, poor planning on somebody's part. What's wrong with an 'external' docking module that momics and extends the normal dock by only allowing a dock when detached from the SS? The docking module can then be positioned to the SS with the ATV attached. Once again, poor planning on somebody's part. What's wrong with an 'external' docking module that momics and extends the normal dock by only allowing a dock when detached from the SS? The docking module can then be positioned to the SS with the ATV attached.

]]> By: Keith Norfolk http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/comment-page-1/#comment-15758 Keith Norfolk Mon, 17 Mar 2008 11:19:38 +0000 http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/#comment-15758 If the ATV applied thrust purely in the reverse direction then initially it would move away from the ISS along what was their common (roughly) circular orbit. The ATV would now however be at apogee in a new elliptical orbit and so it would start to lose height and in the process gain speed and so it would move below and ahead of the ISS. It would be the same as the first burn in a Hohmann transfer. However there is no reason why the ATV should carry out such a simple manoeuvre and so there is no reason why the collision avoidance manoeuvre should not reposition the ATV behind the ISS at a safe distance but on the same orbital path. Take a look at the ESA website for details. www.esa.int If the ATV applied thrust purely in the reverse direction then initially it would move away from the ISS along what was their common (roughly) circular orbit. The ATV would now however be at apogee in a new elliptical orbit and so it would start to lose height and in the process gain speed and so it would move below and ahead of the ISS. It would be the same as the first burn in a Hohmann transfer. However there is no reason why the ATV should carry out such a simple manoeuvre and so there is no reason why the collision avoidance manoeuvre should not reposition the ATV behind the ISS at a safe distance but on the same orbital path. Take a look at the ESA website for details. http://www.esa.int

]]> By: comprehension question http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/comment-page-1/#comment-15750 comprehension question Mon, 17 Mar 2008 07:45:38 +0000 http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/#comment-15750 I learned, that bodies fall around the earth on an elliptic path because they have the exact velocity that is linked to this path by the laws of Johannes Kepler. Now, if the ATV has to break and reverse at 5 km/h due to an incident during docking manouver, does this mean, that it does no longer fit into the path of the ISS? So, does it loose heigth and follow a lower orbit immediatelly? I learned, that bodies fall around the earth on an elliptic path because they have the exact velocity that is linked to this path by the laws of Johannes Kepler.

Now, if the ATV has to break and reverse at 5 km/h due to an incident during docking manouver, does this mean, that it does no longer fit into the path of the ISS? So, does it loose heigth and follow a lower orbit immediatelly?

]]> By: Ian O'Neill http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/comment-page-1/#comment-15746 Ian O'Neill Mon, 17 Mar 2008 06:40:40 +0000 http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/#comment-15746 Well, ok, perhaps "momentum" should be dropped into the sentence rather than the "orbital velocity": <i>Although the relative speed between the station and approaching ATV will be exceedingly slow, <b>the 20 tonne spacecraft momentum will be very high</b>, so any unforeseen collision or misalignment could be highly dangerous.</i> But as pointed out by autumn, I'm travelling at high velocity and don't have the time to correct it. Regardless, I think I emphisize the point that docking in space can be a bit risky ;-) Cheers, Ian Well, ok, perhaps "momentum" should be dropped into the sentence rather than the "orbital velocity":

Although the relative speed between the station and approaching ATV will be exceedingly slow, the 20 tonne spacecraft momentum will be very high, so any unforeseen collision or misalignment could be highly dangerous.

But as pointed out by autumn, I'm travelling at high velocity and don't have the time to correct it.

Regardless, I think I emphisize the point that docking in space can be a bit risky ;-)

Cheers, Ian

]]> By: autumn http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/comment-page-1/#comment-15742 autumn Mon, 17 Mar 2008 05:21:34 +0000 http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/#comment-15742 I don't know, but if I was falling at terminal velocity in Earth's atmosphere, and a partner also falling at terminal velocity, but at a small velocity relative to me, failed to transfer the parachute to me, the results would certainly be horrific in spite of the slow relative velocities, and amplified by the Earth-centered velocities. Huge velocities make everything more difficult, even between objects moving at small velocities relative to each other. I used the word "velocity" way too many times, but I'm pressed for time time, and have to type at a considerable velocity (yes, typing has no directional vector, and as such cannot be called a velocity). I don't know, but if I was falling at terminal velocity in Earth's atmosphere, and a partner also falling at terminal velocity, but at a small velocity relative to me, failed to transfer the parachute to me, the results would certainly be horrific in spite of the slow relative velocities, and amplified by the Earth-centered velocities.
Huge velocities make everything more difficult, even between objects moving at small velocities relative to each other.
I used the word "velocity" way too many times, but I'm pressed for time time, and have to type at a considerable velocity (yes, typing has no directional vector, and as such cannot be called a velocity).

]]> By: Jim B http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/comment-page-1/#comment-15737 Jim B Mon, 17 Mar 2008 02:19:29 +0000 http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/#comment-15737 Actually, "falling" around the Earth would be more correct. Actually, "falling" around the Earth would be more correct.

]]> By: Dave http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/comment-page-1/#comment-15736 Dave Mon, 17 Mar 2008 02:18:22 +0000 http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/#comment-15736 Ever heard of the term "Space Flight"? Ever heard of the term "Space Flight"?

]]> By: jim http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/comment-page-1/#comment-15730 jim Mon, 17 Mar 2008 00:40:35 +0000 http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/#comment-15730 But Ian, there is no other way to read your sentence without the implication that the orbital velocity is what makes the docking maneuver dangerous. While the 27,000 mph orbital velocity is indeed cool, it doesn't belong in that sentence. Also, these objects are not "flying" either. But Ian, there is no other way to read your sentence without the implication that the orbital velocity is what makes the docking maneuver dangerous. While the 27,000 mph orbital velocity is indeed cool, it doesn't belong in that sentence.

Also, these objects are not "flying" either.

]]> By: Ian O'Neill http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/comment-page-1/#comment-15717 Ian O'Neill Sun, 16 Mar 2008 19:13:49 +0000 http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/#comment-15717 To alastair and Ted: <i>Although the relative speed between the station and approaching ATV will be exceedingly slow, the orbital velocity of both will be approximately 27,000 km/h, so any unforeseen collision or misalignment could be highly dangerous.</i> I am fully aware that the relative speed is the important thing, and not the orbital speed. I added the orbital velocity of the station as it gives a clue as to how extreme this docking procedure will be. After all, flying 27,000 mph is a pretty cool thing to mention :-) Cheers, Ian To alastair and Ted:

Although the relative speed between the station and approaching ATV will be exceedingly slow, the orbital velocity of both will be approximately 27,000 km/h, so any unforeseen collision or misalignment could be highly dangerous.

I am fully aware that the relative speed is the important thing, and not the orbital speed. I added the orbital velocity of the station as it gives a clue as to how extreme this docking procedure will be.

After all, flying 27,000 mph is a pretty cool thing to mention :-)

Cheers, Ian

]]> By: Ted http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/comment-page-1/#comment-15707 Ted Sun, 16 Mar 2008 14:09:17 +0000 http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/#comment-15707 Agreed with the commenter above. Not sure why orbital velocity was mentioned in the post. The real threat is that something weighing 20 tons can do a lot of damage even if it hits 'you' at 2 km/h, especially if 'you' (the station) weigh a lot more. Agreed with the commenter above. Not sure why orbital velocity was mentioned in the post. The real threat is that something weighing 20 tons can do a lot of damage even if it hits 'you' at 2 km/h, especially if 'you' (the station) weigh a lot more.

]]> By: alastair http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/comment-page-1/#comment-15701 alastair Sun, 16 Mar 2008 12:40:50 +0000 http://www.universetoday.com/2008/03/16/heavy-atv-must-learn-to-apply-the-brakes-before-docking-with-the-iss/#comment-15701 The orbital velocity of the ATV and the station has *nothing* to do with how dangerous or otherwise the docking manoeuvre is. If that were true, the poking someone with your little finger would be incredibly dangerous thanks to the combined velocity of the Earth, the Sun, the local neighbourhood, the Orion Arm, the Milky Way, etcetera etcetera. It is only relative velocity that matters, and the relative velocity during docking—because the people controlling it are not insane—will be very low. The reason that the manoeuvre is dangerous is that the ATV masses 20 tonnes (according to the article), and therefore has not insignificant momentum even at low velocities. As a result, it could easily do significant damage to the station if something went wrong. The orbital velocity of the ATV and the station has *nothing* to do with how dangerous or otherwise the docking manoeuvre is. If that were true, the poking someone with your little finger would be incredibly dangerous thanks to the combined velocity of the Earth, the Sun, the local neighbourhood, the Orion Arm, the Milky Way, etcetera etcetera.

It is only relative velocity that matters, and the relative velocity during docking—because the people controlling it are not insane—will be very low.

The reason that the manoeuvre is dangerous is that the ATV masses 20 tonnes (according to the article), and therefore has not insignificant momentum even at low velocities. As a result, it could easily do significant damage to the station if something went wrong.

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