orbital effects of Earth satellites

[canadave]

Hey folks,

OK, so I'm brushing up on my orbital mechanics, reading about gravity assists at Jupiter.  When Voyager 2 swung
around it, the planet lost some momentum (obviously very little, due to the small mass of the spacecraft compared to
Jupiter's size).

But it got me thinking.  Earth's a lot smaller than Jupiter.  And we've got a ton of satellites flying around us.  Is it
possible that the net sum effect of all these satellites will make a noticeable effect on Earth's orbit?

Inquiring minds want to know

[McBrain]

tons of satellites - billions of billions of tons "earth material"


maybe the mass ratio is about 0.000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000489763876

[Krytom]

Mmmmmmmmmmmmm

Maybe.

If Canadave's theory is correct then hanging around in a spacecraft next to the ISS would have an effect,
no?

[McBrain]

well, calculate the gravity of an satellite would be funny!

[Atom]

How do you calculate the gravitaional pull of an object? That would be really cool to know.

[freespace2dotcom]

You shouldn't have asked that, atom.

Soon someone's going to come up with a big, evil formula.

the only serious effect I can think of from all of those satelites are miniscule.  it would be far more notable if they were
ejected to another planet. For the most part, each of them are pulling at earth at one angle, but then they move (as
all objects in orbit do) and pull from another angle, and eventually a 360 degree circle completes and any permanent
effect would be negated. In the case of gravity assists, you take some momentum at one point and there's never a
chance to complete a circle and negate it.

So that's my attempt at a layman's version of the thing. but you got to admit. a lot more people should understand
it.

[reekchaa]

canadave wrote:
Inquiring minds want to know

The Master Has Returned!  

I believe waaaaay back when a Mars-sized planet slammed Earth and resulted in the creation of the Moon, they both
were spinning much faster.  The MOON now has Zero rotation, or is in sync with the Earth (hence 'The Dark Side' of
the moon).  I also recall that A big ol' scientist confirmed geologic proof that the Earth had 23 hour days some
Millions of years ago.

So by the time the Sun exhausts it's fuel and scorches the inner planets, the Earth might have ZERO rotation!  
AHHH!!  Get Rutan on it!!!   Only 5 billion years to go!

.. so who can confirm all my wonderfully precise data?  

[StarLost]

No big mean formula, just the usual mass, distance ratios of the two objects modified by the gravitational constant.

The effect is measurable, though, and noted by the changing orbital parameters.  There was some discussion of this in (I
think) SpaceDaily, a while back.  An effect on the orbital parameters was also noticed when the astronauts went EVA and
pushed off from the ISS while working or inadvertently kicking it.

Again, no big mean formulas.  Action and reaction.

The actual obtaining of the formulas and their application is left as an exercise for the class.

Cheers, all

[Simonpro]

F=(Gc*m1*m2)/r^2

Normal inverse square law.
Gc is the gravitational constant, something like 6.654e-11 (i think, but am probably wrong).
effect of satellite is small.
If EVERY satellite in EO was on one side of the planet (lets say they were all over 1deg E Lattitude) then there would
be a small effect upon the earth - however satellites are spread out over a large distance and so there is equal
chance of a satellite being in any place, meaning the net effect is zero.

[DocHoliday]

hehe, I was waiting for Simonpro to appear

Otherwise, I mostly agree with Freespace and Simonpro:
- there are so many satellites they mostly cancel eachother out in terms of the effect they have on Earth. The number
is growing and no reason why it will stop doing so in the future.
- the total mass of satellites is still zilch comparred to Earth, something like 6*10^23kg (no idea how many lbs that
makes).

hehe, back in high school we had a neat homework. We all had to pick a person whom we liked and then calculate
the attraction force between us, using the formula Simon posted. hehe, you might try doing that. A few months ago, I
wasn't sure if Orbiter simulated vessel mass gravity effects, so I calculated the gravitational force fot the Death Star
addon. Don't remember the numbers, but that thing ought to produce quite an acceleration if you were like 5 km
away from the surface. Sadly though, in Orbiter nothing happened


I have a counter question for you guys. Ignoring the costs for a minute. Is there any reason why we shouldn't
dump really dangerous waste, like nuclear waste and the like to the Sun? What would happen? Can it be done?
Would the cost really be ridiculous?

Cheers,
Janez

[David Fox]

Gc=6.67259e-11

[David Fox]

P.S. - that's in units N*m^2/kg^2, so it requires that m1, m2 are in kg and r is in m

[canadave]

Doc: Sure, it could be done....if you ignored the cost  Which would be--pardon the pun--astronomical  Not to
mention the risk involved...what happens if the rocket the waste is on blows up on the launchpad? 8o

[Simonpro]

Lol, i got the internet back just in time
Cheers for the correct Gc, dave, nice to see someone remembers it (and uses nice units)
Doc: Yeah, the cost would be stupidly high for the amount of waste you are sending, but it is entirely possible.
Wouldn't be worth doing though :p

[tony]

accereration due to gravity:
a = GM * (1/d)^2
not too mean of a formula.

G is the gravitational constant (there are many different values for G, depending on what units you're using for Mass
and distance, and what units you'd like your acceleration to be in.)

M is the mass of the central object (units dependent of the value of G used)
d is the distance from the center of the 2 objects. (units dependent of the value of G used)

Notice that M2 is not part of this formula.  That's because this is not a force formula.  It's an acceleration formula.  A
speck of dust accelerates just as much as a boulder.

For satellites to make a difference in Earth's orbit, they would have to leave Earth orbit and enter interplanetary
space.   Otherwise, they're still part of a closed system.

[reekchaa]

Tony, is there an easy way to explain the syncronization of the moon to earth's orbit?  (the dark side always away)

Is it Friction created by Tidal forces ?

[DocHoliday]

I think that Moon's center of gravity is not in the direct center of the Moon, so the moon tends to wobble into position
where the CoG is closest to the Earth. Sort of like when you put a not-totally-round ball into watter and it will turn
and position itself so that the heavier part of the ball (where the CoG is) points towards the bottom.

The CoG is where it is (off-center) because Moon formed in the presence of Earth, hence Earth influenced the actual
shapping process of the Moon from the start. It's really NOT an uncommon site in the Solar System. Mercury is the
same way and quite a lot of Jovian and Saturn moons too if memory serves.

I guess that's a rather simplistic explanation, but I am too ignorant to give you a more educated one. But that's what
I read and it seems to make sense. So basically in some way we ARE talking about tidal forces, Earth influencing
Moon.

Cheers,

[Simonpro]

yep, the earth creates a "bulge" on the near side of the moon, which leads to the center of gravity being closer to
the earth than the center of the planet. Now when the moon tries to rotate its near side away from the earth the fact
that it has a larger mass (and hence larger gravitational attraction) always makes it rotate backso the near side is
facing us. In other words, it is "tidally locked" to the earth. This is exactly the same as the seas on earth rising up
when the moon passes by, but up there on the moon we replaces seas with rock!

An interesting point, though, is that the lunar "seas" are actually caused by tides! The light coloured rock that makes
up the seas is actually denser than the dark rock, and hence it breaks through to the surface of the planet due to the
earths gravitational pull.
I always like that fact

[canadave]

Great discussion guys.

I've always wondered about that too, though--why wouldn't Earth's huge gravitational pull on the Moon have caused
it to form into an "egg-shape" rather than an oblate spheroid?

[canadave]

Duh...in thinking about my question for two seconds, I realized that when you rotate an egg shape sideways
enough, it becomes an oblate spheroid

[Simonpro]

Lol

[DocHoliday]

heh, imagine the tidal forces if the moon were closer and orbiter faster.. Rising seas, sand storm trail in the deserts, I
don't wanna know what, if it passed over an urban area

[freespace2dotcom]

Thankfully, because of tides, the mass of all that raised water is enough to pull at the moon at another angle, raising
it into a slightly higher orbit constantly;

a few inches every year!!

[Simonpro]

sigh

[DocHoliday]

Really, where'd you get this from?