A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Space Science » Space Shuttle
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Earth's rotation and mass calculation



 
 
Thread Tools Display Modes
  #1  
Old March 2nd 06, 10:34 PM posted to sci.space.shuttle
external usenet poster
 
Posts: n/a
Default Earth's rotation and mass calculation

As the earth rotates, it imparts a "centrifugal force" on objects which
would lessen their weight. And this varies depending on your elevation
as well as latitude. (at the pole, there would be no such "force").

And then there is the issue of the earth not being round, so I assume
that gravity is not even everywhere on earth.

When NASA calculates an object's mass for a space vehicle, must it take
the above stuff into consideration, or is that so tiny that it isn't
even worth considering even for unmanned probes that must travel a
precise path over 10 year period ?

(I realise that a true scale simply compares the weight of two objects,
but the problem is then shifted on how to manufacture the reference
object so its mass is absolutely exact)
  #2  
Old March 4th 06, 08:40 AM posted to sci.space.shuttle
external usenet poster
 
Posts: n/a
Default Earth's rotation and mass calculation

I can't address your exact question, but I have worked building
gravimeters, which can also be described as extremely sensitive vertical
accelerometers. While I was there we didn't sell any to NASA, but there
is another U.S. government outfit that was mighty interested in mapping
the gravity field. They specialized in lobbing ballistic missiles at
enemies. The warheads must fly to their targets through a lumpy gravity
field with no outside help once they leave the bus. The more that is
known about the gravity field the better the corrections and accuracy can
be.

John Doe wrote in :

As the earth rotates, it imparts a "centrifugal force" on objects which
would lessen their weight. And this varies depending on your elevation
as well as latitude. (at the pole, there would be no such "force").

And then there is the issue of the earth not being round, so I assume
that gravity is not even everywhere on earth.

When NASA calculates an object's mass for a space vehicle, must it take
the above stuff into consideration, or is that so tiny that it isn't
even worth considering even for unmanned probes that must travel a
precise path over 10 year period ?

(I realise that a true scale simply compares the weight of two objects,
but the problem is then shifted on how to manufacture the reference
object so its mass is absolutely exact)


  #3  
Old March 4th 06, 03:58 PM posted to sci.space.shuttle
external usenet poster
 
Posts: n/a
Default Earth's rotation and mass calculation

In article , John Doe wrote:
As the earth rotates, it imparts a "centrifugal force" on objects which
would lessen their weight. And this varies depending on your elevation
as well as latitude. (at the pole, there would be no such "force").


For long and involved reasons, the above factor "doesn't matter".

Starting with the fact that 'centrifugal force' exists _only_if_ your
frame of reference is rotating. Ballistic calculations assume a stationary
reference base.

Also, you're neglecting several other factors -- including the rotation
of the solar system around Betelgues, the rotation of the Milky Way, as a
whole, etc. grin


And then there is the issue of the earth not being round, so I assume
that gravity is not even everywhere on earth.


True. not only is the Earth "not perfectly round', but it is "lumpy" --
parts of it are more dense (and hence 'heavier') than other parts.

This _does_ have noticiable effect on objects in Earth orbit.

When NASA calculates an object's mass for a space vehicle, must it take
the above stuff into consideration, or is that so tiny that it isn't
even worth considering even for unmanned probes that must travel a
precise path over 10 year period ?


The varience due to the factors you cite is inisignificant _relative_ to
other sources of error. Which is why the 'long time travelling' devices
have been equipped with devices for adjusting their trajectory -- to correct
for the *inevitable* errors that creep in.


(I realise that a true scale simply compares the weight of two objects,
but the problem is then shifted on how to manufacture the reference
object so its mass is absolutely exact)


mass is mass. as long as you collect all the data in the _same_ frame
of reference, you'll have consistent values.

And, obviously, the further apart the masses are, the more nearly they
interact as true 'point' sources.


 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
[sci.astro,sci.astro.seti] Welcome! - read this first [email protected] Astronomy Misc 9 February 2nd 06 02:37 AM
[sci.astro] Astrophysics (Astronomy Frequently Asked Questions) (4/9) [email protected] Astronomy Misc 0 October 6th 05 02:36 AM
The Gravitational Instability Theory on the Formation of the Universe Br Dan Izzo Policy 6 September 7th 04 09:29 PM
Hans Moravec's Original Rotovator Paper James Bowery Policy 0 July 6th 04 07:45 AM
Ned Wright's TBBNH Page (C) Bjoern Feuerbacher Astronomy Misc 24 October 2nd 03 06:50 PM


All times are GMT +1. The time now is 02:24 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.