I figured that this would be a good place to ask this question. I'm
in the process of reading the 1975 study by Nasa about creating a
colony at L5.
l
Here are two statements made in Chapter 2.
"L4 and L5 on the other hand represent bowl-shaped valleys, and a
body displaced in any direction returns toward the point."
"The cost of such station keeping needs to be better understood
before the usefulness of these other points for space colonies can be
evaluated."
My question is what has been done to develop a better understanding
of what the L4 and L5 limitations are? In my mind, it would be
a 'simple' task of sending a probe up to each point and gather data
about what happens to each probe over time. After enough time,
perhaps a larger probe with stationkeeping ability could be sent up.
Also, if these points have been with us for a while (duh), have any
objects like small asteroids and such gathered at the points? If
not, what has caused them to move?
Anyway, thought I might throw this out.
Chad Lupkes
chadlupkes@...
Good questions Chad!
Here are my two cents. Assumeing that we have launched a probe for the
purpose of mapping the L5 gravity gradient, my first question is how do
we measure the gravity gradient? I seem to remember that gravity
mapping of the moon used variations in the orbit of the probe to detect
variations in the density of the moon. Not much use when sitting in an
L5 location. My first design would be a tetrahedon of long spines and
use some sort of very sensative flex measurement.(I have got to get
spell checking back on this email tool.) Design of this probe would be
a good InnerTransit.org project.
www.InnerTransit.org (Homebase for collaborative engineering)
> Also, if these points have been with us for a while (duh), have any
> objects like small asteroids and such gathered at the points? If
> not, what has caused them to move?
already waiting for us? Also, how much of a collision danger might
it pose? But think of it! All the advantages of asteroids AND of
the Moon!! Has anything been done to check this out?
> Anyway, thought I might throw this out.
I'm glad you did.
> Chad Lupkes
> chadlupkes@...
Xenophile (who thinks O'Neill habitats are a good idea, even if tons
of stuff isn't waiting for us at Lagrangia)
Remember that the L-4 / L-5 points themselves are NOT stable.
>
> Good questions Chad!
> Here are my two cents. Assumeing that we have launched a probe for the
> purpose of mapping the L5 gravity gradient, my first question is how do
I am not sure why we need to do this...the orbits are well understood.
> we measure the gravity gradient? I seem to remember that gravity
> mapping of the moon used variations in the orbit of the probe to detect
> variations in the density of the moon. Not much use when sitting in an
That works in very low lunar orbits, less than 1000 km above the Moon.
Those mascons have no detectable effect out at the L-4 / l-5 region.
> L5 location. My first design would be a tetrahedon of long spines and
> use some sort of very sensative flex measurement.(I have got to get
> spell checking back on this email tool.) Design of this probe would be
> a good InnerTransit.org project.
>
Sounds rather complicated. At the L-4/5 region the gravity differences
are tiny, the spines would have to be kilometres in size to get useful
measurements.
Why not simply toss out some reflective metallic foil chaff and track
them with radar ?
There is one practical problem with that approach which will make the
collected tracking data rather difficult to analyze....
The person who figures out that problem gets 5 points :-)
> Why not simply toss out some reflective metallic foil chaff and track
> them with radar ?
>
> There is one practical problem with that approach which will make the
> collected tracking data rather difficult to analyze....
>
> The person who figures out that problem gets 5 points :-)
Could it be that to get meaningful results, you have to be able to
identify each piece of chaff individually?
??JohnWheeler
>them with radar ?
>collected tracking data rather difficult to analyze....
>The person who figures out that problem gets 5 points :-)
Hmmm, My own guess would be the effect of movement as each piece of the chaff bounces against the other pieces. I would think that a single reflective sphere at each point would be sufficient. Chad
> There is one practical problem with that approach which will make
the
> collected tracking data rather difficult to analyze....
>
> The person who figures out that problem gets 5 points :-)
>
impart energy to the foil's orbit.
>
> Could it be that to get meaningful results, you have to be able to
> identify each piece of chaff individually?
>
That is not what I had in mind. Identification is essential, however
I do not envisage it as a major problem.
>
> impart energy to the foil's orbit.
>
That is close but not what I had in mind.
There is another disturbance force which would be a lot stronger than
that.
The same force I mentioned during the discussion of mass driver pellets
returning to the point of origin (or not).
======
My own guess would be the effect of movement as each piece of the chaff
bounces against the other pieces. I would think that a single
reflective sphere at each point would be sufficient.
Chad
======
The chaff pieces would not recontact each other, they would disperse and
separate from each other. The separation increases with time. The
L-4/5 orbits are so large they would not collide.
<
There is one practical problem with that approach which will make the
collected tracking data rather difficult to analyze....>>
I know very little about astronautics so I don't mind revealing my
igonrance -- I'm a theoretical neuroscientist and I deal a lot with chaotic
dynamics. I don't know very much about orbital mechanics or the dynamics
associated with them but I'll take a guess that the small amount of momentum
imparted by the "tossing" process would swamp any effect due to
gravitational gradient at that distance, and the trajectory which was
followed by each piece of chaff would be determined far more by the
variations in initial momentum than by gravitational gradient.
Ok I did say I was only guessing. It's back to you serious guys now.
Kathryn
>
><
>
> There is one practical problem with that approach which will make the
> collected tracking data rather difficult to analyze....>>
Is it the solar wind? I imagine that might have a non-negligible effect
on thin metallic foil, compared to such a weak gravitational effect.
--Chris
>
> I know very little about astronautics so I don't mind revealing my
> igonrance -- I'm a theoretical neuroscientist and I deal a lot with chaotic
> dynamics. I don't know very much about orbital mechanics or the dynamics
> associated with them but I'll take a guess that the small amount of momentum
> imparted by the "tossing" process would swamp any effect due to
> gravitational gradient at that distance, and the trajectory which was
> followed by each piece of chaff would be determined far more by the
> variations in initial momentum than by gravitational gradient.
>
Yes, these are known as "tip-off" forces and could certainly be
significant.
Designing a deployment system to deliver pieces of chaff to precise
positions with zero residual velocity relative to the desired orbit
would be a challenge indeed.
Your answer is worth 3 points IMHO :-)
>
> Is it the solar wind? I imagine that might have a non-negligible effect
> on thin metallic foil, compared to such a weak gravitational effect.
>
Probably worth three points :-)
The solar wind is a stream of subatomic particles and exerts a
negligible force.
However, radiation pressure from sunlight exerts a substantial force
hundreds of times stronger than the solar wind.
Each of the bits of chaff would also be a mini-solar sail. Figuring
out how much of the motion is caused by gravity and how much caused by
radiation pressure would be practically impossible.
Radar bounces would also cause some pressure, but a lot less than
sunlight, that would also be worth about another 3 points :-)
>> Is it the solar wind? I imagine that might have a non-negligible
>> effect on thin metallic foil, compared to such a weak
>> gravitational effect.
>
> Probably worth three points :-)
>
> The solar wind is a stream of subatomic particles and exerts a
> negligible force.
>
> However, radiation pressure from sunlight exerts a substantial force
> hundreds of times stronger than the solar wind.
>
> Each of the bits of chaff would also be a mini-solar sail. Figuring
> out how much of the motion is caused by gravity and how much caused
> by radiation pressure would be practically impossible.
>
> Radar bounces would also cause some pressure, but a lot less than
> sunlight, that would also be worth about another 3 points :-)
Oh, I knew that.
Shyau, right!
So is there stuff already there that can be used? Is it worth trying
to find out, or would we already know if it were there? Could there
be only a collection of things smaller than rice grains, in which
case it may not be worth it to track it down, much less recover it,
even if it all adds up to hundreds of thousands of tons? Or could
there be 10,000 ton chunks of metal and silicates and volatiles?
Would Earth's magnetosphere have any effect? I read an article recently
by Robert Zubrin where he proposed a magsail concept using the
magnetoshere to accelerate a spacecraft out of LEO. Whould there be
similar forces at the lagrange points?
> > Is it the solar wind? I imagine that might have a non-negligible effect
> > on thin metallic foil, compared to such a weak gravitational effect.
> >
> Almost correct, but not quite.
>
> Probably worth three points :-)
>
> The solar wind is a stream of subatomic particles and exerts a
> negligible force.
>
> However, radiation pressure from sunlight exerts a substantial force
> hundreds of times stronger than the solar wind.
>
> Each of the bits of chaff would also be a mini-solar sail. Figuring
> out how much of the motion is caused by gravity and how much caused by
> radiation pressure would be practically impossible.
>
> Radar bounces would also cause some pressure, but a lot less than
> sunlight, that would also be worth about another 3 points :-)
>
Robin Chew
proU.net, Inc. - http://www.proU.net
Lucidcafe Interactive Cafe - http://www.lucidcafe.com
>
> Would Earth's magnetosphere have any effect? I read an article recently
> by Robert Zubrin where he proposed a magsail concept using the
> magnetoshere to accelerate a spacecraft out of LEO. Whould there be
> similar forces at the lagrange points?
>
Out at L-4/5 there would not be any useful force,
or even detectable force using simple instruments.
> However, radiation pressure from sunlight exerts a substantial force
> hundreds of times stronger than the solar wind.
>
> Each of the bits of chaff would also be a mini-solar sail.
Figuring
> out how much of the motion is caused by gravity and how much caused
by
> radiation pressure would be practically impossible.
>
> Radar bounces would also cause some pressure, but a lot less than
> sunlight, that would also be worth about another 3 points :-)
Think ball bearings instead of foil. Increases mass = higher costs
though. Another benefit, initial imparted release velocity could be
quantified early in the experiment (ie, a few seconds upon release,
measured over a specific time) and would become a known constant.
king_rodent (putting the eek in geek)
> king_rodent (putting the eek in geek)
acts, such as biting the head off a live chicken.
Bill
>
> > king_rodent (putting the eek in geek)
>
> Geek (slang) : A carnival performer whose show consists of bizarre
> acts, such as biting the head off a live chicken.
(or was it some other performer who bit the head off a bat?)