Notices
Results 1 to 12 of 12

Thread: What is "Speed increment at infinity" ??

  1. #1 What is "Speed increment at infinity" ?? 
    Forum Freshman
    Join Date
    Apr 2012
    Posts
    78
    How can I understand?

    "Speed increment at infinity"

    "Infinity" seems to be a speed measurement point, - by space probe trajectories, - but where is "infinity"

    http://en.wikipedia.org/wiki/Flyby_anomaly


    Reply With Quote  
     

  2.  
     

  3. #2  
    Genius Duck Moderator Dywyddyr's Avatar
    Join Date
    Jan 2013
    Location
    Scunthorpe, UK
    Posts
    11,437
    It's the term used for the speed when the probe is "no longer under the gravitational influence of the Sun".
    (Although that description too is somewhat nebulous...)


    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
    Reply With Quote  
     

  4. #3  
    Forum Freshman
    Join Date
    Apr 2012
    Posts
    78
    Quote Originally Posted by Dywyddyr View Post
    It's the term used for the speed when the probe is "no longer under the gravitational influence of the Sun".
    (Although that description too is somewhat nebulous...)
    Can you explain that further please
    Reply With Quote  
     

  5. #4  
    Genius Duck Moderator Dywyddyr's Avatar
    Join Date
    Jan 2013
    Location
    Scunthorpe, UK
    Posts
    11,437
    Quote Originally Posted by Bjarne View Post
    Can you explain that further please
    It's the speed achieved once "escape velocity" has ensured that the probe is no longer orbiting the Sun - essentially the speed that it will continue to hold until it "reaches infinity".
    (If it were orbiting then its speed would vary, unless it were in a perfectly circular orbit).
    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
    Reply With Quote  
     

  6. #5  
    Forum Freshman
    Join Date
    Apr 2012
    Posts
    78
    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by Bjarne View Post
    Can you explain that further please
    It's the speed achieved once "escape velocity" has ensured that the probe is no longer orbiting the Sun - essentially the speed that it will continue to hold until it "reaches infinity".
    (If it were orbiting then its speed would vary, unless it were in a perfectly circular orbit).
    As I understand this, - the Space probe accelerate due to it enters the strong gravity field close to the earth (by swing by).
    Due to the acceleration (towards perigee) escape velocity will be reached before the space probe isreaching perigee, - right?
    Reply With Quote  
     

  7. #6  
    Genius Duck Moderator Dywyddyr's Avatar
    Join Date
    Jan 2013
    Location
    Scunthorpe, UK
    Posts
    11,437
    Quote Originally Posted by Bjarne View Post
    As I understand this, - the Space probe accelerate due to it enters the strong gravity field close to the earth (by swing by).
    There's no necessity for swing by to achieve a speed at infinity. Granted we use it because it's practical.

    Due to the acceleration (towards perigee) escape velocity will be reached before the space probe isreaching perigee, - right?
    Not quite sure what you're getting at here.
    How about: the speed at infinity is the speed of the probe on its way "to" infinity - because the apogee is "at" infinity.
    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
    Reply With Quote  
     

  8. #7  
    Forum Freshman
    Join Date
    Apr 2012
    Posts
    78
    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by Bjarne View Post
    As I understand this, - the Space probe accelerate due to it enters the strong gravity field close to the earth (by swing by).
    There's no necessity for swing by to achieve a speed at infinity. Granted we use it because it's practical.

    Due to the acceleration (towards perigee) escape velocity will be reached before the space probe isreaching perigee, - right?

    Not quite sure what you're getting at here.
    How about: the speed at infinity is the speed of the probe on its way "to" infinity - because the apogee is "at" infinity.
    Ok, - so the measurement point of "speed at infinity" is actuallythe "apogee speed" ?
    Reply With Quote  
     

  9. #8  
    Genius Duck Moderator Dywyddyr's Avatar
    Join Date
    Jan 2013
    Location
    Scunthorpe, UK
    Posts
    11,437
    Quote Originally Posted by Bjarne View Post
    Ok, - so the measurement point of "speed at infinity" is actuallythe "apogee speed" ?
    Essentially yes, but since the probe never reaches apogee then calling it "apogee speed" would be inaccurate.
    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
    Reply With Quote  
     

  10. #9  
    Forum Freshman
    Join Date
    Apr 2012
    Posts
    78
    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by Bjarne View Post
    Ok, - so the measurement point of "speed at infinity" is actuallythe "apogee speed" ?
    Essentially yes, but since the probe never reaches apogee then calling it "apogee speed" would be inaccurate.
    I think I begin to understand - for example the Space-probe NEAR (andmany other space-probes) was orbiting the Sun not the Earth, so these space-probes will reach aphelion (not apogee) - I understand that, - but still I am confused to where (approximately) at the orbit is then "infinity speed" ?
    Reply With Quote  
     

  11. #10  
    Genius Duck Moderator Dywyddyr's Avatar
    Join Date
    Jan 2013
    Location
    Scunthorpe, UK
    Posts
    11,437
    Quote Originally Posted by Bjarne View Post
    I think I begin to understand - for example the Space-probe NEAR (andmany other space-probes) was orbiting the Sun not the Earth, so these space-probes will reach aphelion (not apogee) - I understand that, - but still I am confused to where (approximately) at the orbit is then "infinity speed" ?
    Well, strictly speaking, they don't "reach" aphelion, since every time you check they're further away from the Sun, and will continue to increase that distance. They're never coming back. (Would that mean that it's not, by definition, an "orbit"?)
    As to "where" the speed is reached that would be, at its most basic, when the final burn (or slingshot) is complete.

    Hmm, okay, try this one:
    As any probe gets further away its speed reduces - that's basic, since, although it's moving away gravity is also "attempting" to drag it back.
    The "speed at infinity" is the final velocity achieved, the one which will never reduce (with respect to the Sun), or, to put it another way, its limiting speed.
    There's a mathematical treatment of it here.
    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
    Reply With Quote  
     

  12. #11  
    Forum Freshman
    Join Date
    Apr 2012
    Posts
    78
    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by Bjarne View Post
    I think I begin to understand - for example the Space-probe NEAR (andmany other space-probes) was orbiting the Sun not the Earth, so these space-probes will reach aphelion (not apogee) - I understand that, - but still I am confused to where (approximately) at the orbit is then "infinity speed" ?
    Well, strictly speaking, they don't "reach" aphelion, since every time you check they're further away from the Sun, and will continue to increase that distance. They're never coming back. (Would that mean that it's not, by definition, an "orbit"?)
    As to "where" the speed is reached that would be, at its most basic, when the final burn (or slingshot) is complete.

    Hmm, okay, try this one:
    As any probe gets further away its speed reduces - that's basic, since, although it's moving away gravity is also "attempting" to drag it back.
    The "speed at infinity" is the final velocity achieved, the one which will never reduce (with respect to the Sun), or, to put it another way, its limiting speed.
    There's a mathematical treatment of it here.
    OK, I think I begin to understand it, we can shortly say it is the last aphelion , right ? (I will look into the math later, thanks for the help).
    Reply With Quote  
     

  13. #12  
    Genius Duck Moderator Dywyddyr's Avatar
    Join Date
    Jan 2013
    Location
    Scunthorpe, UK
    Posts
    11,437
    For a given "definition" of aphelion yes.
    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
    Reply With Quote  
     

Similar Threads

  1. Replies: 27
    Last Post: July 1st, 2013, 08:16 AM
  2. Replies: 6
    Last Post: May 9th, 2013, 08:45 AM
  3. "Dating" posts split from "Purpose of life" thread
    By Christopher Ball in forum Pseudoscience
    Replies: 155
    Last Post: October 16th, 2011, 05:37 AM
  4. "Dating" posts split from "Purpose of life" thread
    By Christopher Ball in forum Earth Sciences
    Replies: 90
    Last Post: October 11th, 2011, 10:35 AM
  5. math on "speed of light".
    By Ghrasp in forum Mathematics
    Replies: 11
    Last Post: May 24th, 2010, 12:22 AM
Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •