Old Rockets Carry Bacteria to the Stars
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Bassam Abdul-Baki wrote:
I am assuming that 1) there's no acceleration, 2) constant velocity, 3) some drag that will slow down that velocity eventually.
there is no drag. Only acceleration of gravity (or deceleration since opposite vectors) and current velocity. I must be explaining it poorly. I know I am too close to the visualization side of this type of stuff, so maybe I am being too technical, I don't know. The probes had no engines except for navigation, no acceleration of vehicles, the boosters referred to in the article provided ALL of the acceleration to reach escape velocity, therefore both probes and booster are at escape velocity. The probes turned, the boosters didn't both travelling continually out of the solar system at equal velocities. The sling-shots were navigation assists, allowing minute vectors to be increased in magnitude by the sling-shot effect around a planet. If the boosters fell back, so would the probes, because the booster provided the necessary speed and vice versa, if the boosters fell back, so would the probes. Because both achieved the right velocity much earlier, both will leave. Maybe someone else can help me here, I don't know an easier way to explain it.
_________________________ Asu no koto o ieba, tenjo de nezumi ga warau. Talk about things of tomorrow and the mice in the ceiling laugh. (Japanese Proverb)
El Corazon wrote:
I must be explaining it poorly. I know I am too close to the visualization side of this type of stuff, so maybe I am being too technical, I don't know.
No, I got it, finally. But for some reason, I always thought there is drag from solar winds, dust, and other stuff.
El Corazon wrote:
The probes had no engines except for navigation, no acceleration of vehicles, the boosters referred to in the article provided ALL of the acceleration to reach escape velocity, therefore both probes and booster are at escape velocity. The probes turned, the boosters didn't both travelling continually out of the solar system at equal velocities.
Unless there is absolutely no drag, I would expect that, but with no engines, they would eventually slow down. It would be interesting to know what there speeds where 20+ years ago, after separation, with what they are today. I guess we can't know for sure.
"It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle Web - Blog - RSS - Math - LinkedIn - BM
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If the gravitational force decreased less slowly then an inverse square that would be true. For example the constant gravitational force approximation used in basic physics for motion close to the earth has an infinite escape velocity. However because the force of gravity falls off so quickly with distance there is a finite energy needed for any object to reach infinity under that type of force. Check out this: http://en.wikipedia.org/wiki/Escape_velocity[^] Also for later spacecraft they try to follow these trajectories: http://en.wikipedia.org/wiki/Interplanetary_Superhighway[^] but they take a computer to compute. A gravitational slingshot is just a simple example of that.
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Andy Brummer wrote:
However because the force of gravity falls off so quickly with distance there is a finite energy needed for any object to reach infinity under that type of force.
That explains it.
Andy Brummer wrote:
Also for later spacecraft they try to follow these trajectories: http://en.wikipedia.org/wiki/Interplanetary\_Superhighway\[^\] but they take a computer to compute. A gravitational slingshot is just a simple example of that.
Wow! :cool:
"People who want to share their religious views with you almost never want you to share yours with them." - Anonymous Web - Blog - RSS - Math - LinkedIn - BM
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El Corazon wrote:
The sling shot is only a change in direction, nothing more.
That is incorrect. The slingshot can be modeled by a simple elastic collision with a small body and a very massive body. Imagine throwing a rock at a train heading towards you. That rock is going to bounce back traveling faster then the train. From wikipedia: http://en.wikipedia.org/wiki/Gravitational_slingshot[^] In orbital mechanics and aerospace engineering, a gravitational slingshot or gravity assist is the use of the gravity of a planet or other celestial body to alter the path and speed of an interplanetary spacecraft. It is a commonly used maneuver for visiting the outer planets, which would otherwise either take far too long or require far too much fuel using our current propulsion technologies. It was first developed in 1959 at the Department of Applied Mathematics of Steklov Institute.[1]
Using the GridView is like trying to explain to someone else how to move a third person's hands in order to tie your shoelaces for you. -Chris Maunder
Your bolded stuff cleared up Jeffrey's post from a few back that said: The bounce around slingshots entering and leaving other gravitational influences, but that increases velocity on the entry vector and decreases the velocity on the exit vector, but the net effect is nil because the probe is already too fast to be slowed. So technically, slingshots do speed up probes?
"I know which side I want to win regardless of how many wrongs they have to commit to achieve it." - Stan Shannon Web - Blog - RSS - Math - LinkedIn - BM
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Actually, I understand the concept that the acceleration needed to be greater than the gravitational influence, however, I did not realize that the slingshots were for direction only. I assumed a gravitational pull will increase speed, but would cancel out like you said on exit. My other issue was with:
El Corazon wrote:
Both will slow, but will not slow to 0 before leaving the influence of the sun. Once they leave, they're free.
If the booster is gone and velocity is only based upon initial velocity and momentum, then in theory, shouldn't the sun's pull bring them back in in a few hundred years? I am assuming that 1) there's no acceleration, 2) constant velocity, 3) some drag that will slow down that velocity eventually. Pull from another solar system should be negligible compared to our own.
"You can lead a horse to Vista, but it won't get in stall." - Bassam Abdul-Baki Web - Blog - RSS - Math - LinkedIn - BM
Bassam Abdul-Baki wrote:
If the booster is gone and velocity is only based upon initial velocity and momentum, then in theory, shouldn't the sun's pull bring them back in in a few hundred years?
It had enough initial speed that it is able to escape the sun's pull completely. Once it escapes, the sun is not pulling on it anymore, so it will never return, ever. That's why it is called "escape" velocity. It is the initial velocity that allows it to get far enough away that it is beyond the reach of the sun.
-------------------------------- "All that is necessary for the forces of evil to win in the world is for enough good men to do nothing" -- Edmund Burke
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You are right that the booster will slow down since the sun is constantly "pulling". But the velocity will never change direction. If the velocity (at one point) is equal to the escape velocity (for that point), that means that as the distance increases, the velocity gets lower. But the escape velocity is also lower for higher distances, so the booster still has escape velocity. As the distance to the sun approaches infinity, the velocity will approach zero, but it'll never change direction. EDIT: It's easier to understand using the formula for potential energy: Epot = G*m1*m2*(1/r1 - 1/r2) This is the energy required to bring a body from radius r1 to r2. If you set r2 = infinity, you see that you only need the finite amount of energy (G*m1*m2*(1/r1)) to shoot body infinitely far. That amount of energy is the kinetic energy of the escape velocity.
Last modified: 7mins after originally posted --
Thanks, that is easier for layman's. Andy's statement: However because the force of gravity falls off so quickly with distance there is a finite energy needed for any object to reach infinity under that type of force. also cleared it up.
"I know which side I want to win regardless of how many wrongs they have to commit to achieve it." - Stan Shannon Web - Blog - RSS - Math - LinkedIn - BM
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Your bolded stuff cleared up Jeffrey's post from a few back that said: The bounce around slingshots entering and leaving other gravitational influences, but that increases velocity on the entry vector and decreases the velocity on the exit vector, but the net effect is nil because the probe is already too fast to be slowed. So technically, slingshots do speed up probes?
"I know which side I want to win regardless of how many wrongs they have to commit to achieve it." - Stan Shannon Web - Blog - RSS - Math - LinkedIn - BM
Slingshots do speed up probes. While his argument sounds reasonable it neglects the mass and momentum differences between the two objects. This is a more earthly[^] example.
Using the GridView is like trying to explain to someone else how to move a third person's hands in order to tie your shoelaces for you. -Chris Maunder
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El Corazon wrote:
I must be explaining it poorly. I know I am too close to the visualization side of this type of stuff, so maybe I am being too technical, I don't know.
No, I got it, finally. But for some reason, I always thought there is drag from solar winds, dust, and other stuff.
El Corazon wrote:
The probes had no engines except for navigation, no acceleration of vehicles, the boosters referred to in the article provided ALL of the acceleration to reach escape velocity, therefore both probes and booster are at escape velocity. The probes turned, the boosters didn't both travelling continually out of the solar system at equal velocities.
Unless there is absolutely no drag, I would expect that, but with no engines, they would eventually slow down. It would be interesting to know what there speeds where 20+ years ago, after separation, with what they are today. I guess we can't know for sure.
"It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle Web - Blog - RSS - Math - LinkedIn - BM
Bassam Abdul-Baki wrote:
No, I got it, finally. But for some reason, I always thought there is drag from solar winds, dust, and other stuff.
There is, but it's low enough to be essentially irrelevant.
-- You have to explain to them [VB coders] what you mean by "typed". their first response is likely to be something like, "Of course my code is typed. Do you think i magically project it onto the screen with the power of my mind?" --- John Simmons / outlaw programmer
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El Corazon wrote:
The sling shot is only a change in direction, nothing more.
That is incorrect. The slingshot can be modeled by a simple elastic collision with a small body and a very massive body. Imagine throwing a rock at a train heading towards you. That rock is going to bounce back traveling faster then the train. From wikipedia: http://en.wikipedia.org/wiki/Gravitational_slingshot[^] In orbital mechanics and aerospace engineering, a gravitational slingshot or gravity assist is the use of the gravity of a planet or other celestial body to alter the path and speed of an interplanetary spacecraft. It is a commonly used maneuver for visiting the outer planets, which would otherwise either take far too long or require far too much fuel using our current propulsion technologies. It was first developed in 1959 at the Department of Applied Mathematics of Steklov Institute.[1]
Using the GridView is like trying to explain to someone else how to move a third person's hands in order to tie your shoelaces for you. -Chris Maunder
Andy Brummer wrote:
That is incorrect.
You are correct, I apologize. But I still thought they used the kick motors at jupiter periapsis to achieve the necessary speed for interstellar break-away, the rest of the speed was simply to accelerate the craft and reduce time to heliopause experiments while people were still around to see it, not to achieve stellar escape velocities. But I may be wrong.
_________________________ Asu no koto o ieba, tenjo de nezumi ga warau. Talk about things of tomorrow and the mice in the ceiling laugh. (Japanese Proverb)
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Slingshots do speed up probes. While his argument sounds reasonable it neglects the mass and momentum differences between the two objects. This is a more earthly[^] example.
Using the GridView is like trying to explain to someone else how to move a third person's hands in order to tie your shoelaces for you. -Chris Maunder
Andy Brummer wrote:
Slingshots do speed up probes.
I do stand corrected, sorry.
_________________________ Asu no koto o ieba, tenjo de nezumi ga warau. Talk about things of tomorrow and the mice in the ceiling laugh. (Japanese Proverb)
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I wasn't aware that Starship Troopers had a plot :-)
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The bacteria mutated into some benign strain or something along those lines; of course, not before the count down to the nuclear bomb at the bottom of the facility was initiated ... Just had a good movie plot: - Rocket booster lands on alien planet - Alien planet is populated with alien race - Bacteria infects them, killing millions - They get REAL upset, figure out where it came from - Fight ensues; human race is almost annihilated - <insert actor of choice> fights to save the Earth! Well, you get the idea. Disclaimer: All the ideas, concepts and poppycock in this posting are (c)opyright Douglas H. Troy. He'll concede to a TV mini-series if the price is right. ;P
:..::. Douglas H. Troy ::..
Bad Astronomy |VCF|wxWidgets|WTLI saw it recently, They discovered that the pathogen was very susceptible to small changes in pH. The baby crying and the drunks digestive system made both their blood acidic, making them be the only survivors of the initial outbreak and eventually leading to the connection. Great film
Philosophy: The art of never getting beyond the concept of life.
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Andy Brummer wrote:
That is incorrect.
You are correct, I apologize. But I still thought they used the kick motors at jupiter periapsis to achieve the necessary speed for interstellar break-away, the rest of the speed was simply to accelerate the craft and reduce time to heliopause experiments while people were still around to see it, not to achieve stellar escape velocities. But I may be wrong.
_________________________ Asu no koto o ieba, tenjo de nezumi ga warau. Talk about things of tomorrow and the mice in the ceiling laugh. (Japanese Proverb)
I have no idea why each of the probes did it's slingshot, some of the probes did it just to change direction. The amazing thing about it is that if you know the initial momentum, the masses and the elasticity of the collision it doesn't matter if the collision is a gravitational slingshot or a superball bouncing off the floor the equations are the same. To that model the complex interactions during collision don't matter. It's all handled by conservation of momentum. So, it can be used to slow down or speed up the probe or just change its direction. My main point was that there is momentum transfer involved.
Using the GridView is like trying to explain to someone else how to move a third person's hands in order to tie your shoelaces for you. -Chris Maunder
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Bassam Abdul-Baki wrote:
I am assuming that 1) there's no acceleration, 2) constant velocity, 3) some drag that will slow down that velocity eventually.
there is no drag. Only acceleration of gravity (or deceleration since opposite vectors) and current velocity. I must be explaining it poorly. I know I am too close to the visualization side of this type of stuff, so maybe I am being too technical, I don't know. The probes had no engines except for navigation, no acceleration of vehicles, the boosters referred to in the article provided ALL of the acceleration to reach escape velocity, therefore both probes and booster are at escape velocity. The probes turned, the boosters didn't both travelling continually out of the solar system at equal velocities. The sling-shots were navigation assists, allowing minute vectors to be increased in magnitude by the sling-shot effect around a planet. If the boosters fell back, so would the probes, because the booster provided the necessary speed and vice versa, if the boosters fell back, so would the probes. Because both achieved the right velocity much earlier, both will leave. Maybe someone else can help me here, I don't know an easier way to explain it.
_________________________ Asu no koto o ieba, tenjo de nezumi ga warau. Talk about things of tomorrow and the mice in the ceiling laugh. (Japanese Proverb)
Very good explanation. I only have a question about one thing. You stated:
El Corazon wrote:
The sling-shots were navigation assists, allowing minute vectors to be increased in magnitude by the sling-shot effect around a planet.
At least in a couple of posts, you said that the "sling-shots" did not increase the spacecraft's acceleration. However, at http://www.planetary.org/news/2007/0118_New_Horizons_to_Test_its_Mettle_during.html[^] (which was obviously written before the Jupiter flyby), the author states: "As it swings by Jupiter, the planet’s enormous gravitational pull will give the spacecraft a boost that will increase its speed by 9000 miles per hour (5600 kilometers per hour) relative to the Sun. This gravity assist will cut a full three years from New Horizons’ journey, bringing it down to a mere 9 years." Is the key phrase here "relative to the Sun"?:confused: Cheers,
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Very good explanation. I only have a question about one thing. You stated:
El Corazon wrote:
The sling-shots were navigation assists, allowing minute vectors to be increased in magnitude by the sling-shot effect around a planet.
At least in a couple of posts, you said that the "sling-shots" did not increase the spacecraft's acceleration. However, at http://www.planetary.org/news/2007/0118_New_Horizons_to_Test_its_Mettle_during.html[^] (which was obviously written before the Jupiter flyby), the author states: "As it swings by Jupiter, the planet’s enormous gravitational pull will give the spacecraft a boost that will increase its speed by 9000 miles per hour (5600 kilometers per hour) relative to the Sun. This gravity assist will cut a full three years from New Horizons’ journey, bringing it down to a mere 9 years." Is the key phrase here "relative to the Sun"?:confused: Cheers,
:doh: I should have read farther down in the posts. Someone else made my point. Sorry about that. Cheers,
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I have no idea why each of the probes did it's slingshot, some of the probes did it just to change direction. The amazing thing about it is that if you know the initial momentum, the masses and the elasticity of the collision it doesn't matter if the collision is a gravitational slingshot or a superball bouncing off the floor the equations are the same. To that model the complex interactions during collision don't matter. It's all handled by conservation of momentum. So, it can be used to slow down or speed up the probe or just change its direction. My main point was that there is momentum transfer involved.
Using the GridView is like trying to explain to someone else how to move a third person's hands in order to tie your shoelaces for you. -Chris Maunder
Andy Brummer wrote:
My main point was that there is momentum transfer involved.
So does that mean that as we keep stealing momentum from Jupiter with all our Space probes, that eventually it (Jupiter) will come down to the level of the Earth's orbit and swallow us up? :laugh: :omg: ;) Cheers,
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Andy Brummer wrote:
My main point was that there is momentum transfer involved.
So does that mean that as we keep stealing momentum from Jupiter with all our Space probes, that eventually it (Jupiter) will come down to the level of the Earth's orbit and swallow us up? :laugh: :omg: ;) Cheers,
Yes, and some of our probes slingshot off the Earth slowing us down and eventually plunging us into the sun. :doh:
Using the GridView is like trying to explain to someone else how to move a third person's hands in order to tie your shoelaces for you. -Chris Maunder
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Andy Brummer wrote:
My main point was that there is momentum transfer involved.
So does that mean that as we keep stealing momentum from Jupiter with all our Space probes, that eventually it (Jupiter) will come down to the level of the Earth's orbit and swallow us up? :laugh: :omg: ;) Cheers,
afaik no, we're stealing rotational momentum not orbital momentum in the flybys. That said it is possible to xfer orbital momentum instead, and humanity ever gets serious about its long term (over >10MY) future, fitting an large asteroid/kupier belt object with solar powered engines to make a close flyby of each planet approx every 10k years would be sufficient to keep us inside the habital zone of the sun as it keeps heating for about 5bn years until it reaches the red giant phase. If we don't act in the next 500m-1bn years we'll find ourselves too close to the hotter sun and will spend a billion years boiling the oceans off and pumping water vapor high enough into the atmosphere to decompose it. The hydrogen will then escape the Earths gravity and we'll end up as Venus2.
-- You have to explain to them [VB coders] what you mean by "typed". their first response is likely to be something like, "Of course my code is typed. Do you think i magically project it onto the screen with the power of my mind?" --- John Simmons / outlaw programmer
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afaik no, we're stealing rotational momentum not orbital momentum in the flybys. That said it is possible to xfer orbital momentum instead, and humanity ever gets serious about its long term (over >10MY) future, fitting an large asteroid/kupier belt object with solar powered engines to make a close flyby of each planet approx every 10k years would be sufficient to keep us inside the habital zone of the sun as it keeps heating for about 5bn years until it reaches the red giant phase. If we don't act in the next 500m-1bn years we'll find ourselves too close to the hotter sun and will spend a billion years boiling the oceans off and pumping water vapor high enough into the atmosphere to decompose it. The hydrogen will then escape the Earths gravity and we'll end up as Venus2.
-- You have to explain to them [VB coders] what you mean by "typed". their first response is likely to be something like, "Of course my code is typed. Do you think i magically project it onto the screen with the power of my mind?" --- John Simmons / outlaw programmer
dan neely wrote:
afaik no, we're stealing rotational momentum not orbital momentum in the flybys.
:doh: No wonder we need all those dang leap seconds! ;)
dan neely wrote:
fitting an large asteroid/kupier belt object with solar powered engines to make a close flyby of each planet approx every 10k years would be sufficient to keep us inside the habital zone of the sun
I just hope whoever is piloting this Pluto-sized object does not miss! Future "Space Command" conversation: "You idiot! We said close FLYBY! Now we have a new asteroid belt where Mars used to be!" :laugh: Cheers,
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afaik no, we're stealing rotational momentum not orbital momentum in the flybys. That said it is possible to xfer orbital momentum instead, and humanity ever gets serious about its long term (over >10MY) future, fitting an large asteroid/kupier belt object with solar powered engines to make a close flyby of each planet approx every 10k years would be sufficient to keep us inside the habital zone of the sun as it keeps heating for about 5bn years until it reaches the red giant phase. If we don't act in the next 500m-1bn years we'll find ourselves too close to the hotter sun and will spend a billion years boiling the oceans off and pumping water vapor high enough into the atmosphere to decompose it. The hydrogen will then escape the Earths gravity and we'll end up as Venus2.
-- You have to explain to them [VB coders] what you mean by "typed". their first response is likely to be something like, "Of course my code is typed. Do you think i magically project it onto the screen with the power of my mind?" --- John Simmons / outlaw programmer
dan neely wrote:
we're stealing rotational momentum
Actually, I had another thought. Every time we launch a satellite from Earth, are we not stealing a wee bit of rotational momentum from the Earth to help propel it into orbit (which is why virtually all [if not all] satellites are launched on an eastward trajectory)? :~ Cheers,
