Moving venus to a nicer spot

Korycansky et al wrote about moving Earth via 1 million
engineered asteriod near-misses, to avoid climate change
as the sun grows hotter:

http://arxiv.org/abs/astro-ph/0102126

John McCarthy (the LISP guy!) suggests moving Mars into
Earth orbit, and uses conservation of angular momentum
(which the folks in the previous paper really should have
figured out one dinner conversation after having the
original idea) to find an interesting consequence of
doing so: Venus is nearly dumped into the Sun.

http://www-formal.stanford.edu/jmc/f...mars/mars.html

It seems to me that I'd rather have Venus than Mars in
co-orbit with Earth. It's closer to the right size, which
means it can hang on to more atmosphere, which helps a
lot. But in either case, it seems like either planet is
going to do some Very Bad Things to Earth's orbit as the
orbital period approaches but does not equal Earth's.

One thing that I find exciting about this idea of orbital
engineering is the notion that low-energy perturbations
can have really large effects even a few years later.
Particularly, the notion that the delta-V required to get
very heavy objects into near-arbitrary orbits has a lower
bound determined by the precision with which one can
predict the future gravitational disturbances. You can
imagine that if total delta-V can be lowered to ~100 m/s
(admittedly a much smaller number than the first paper
suggests), a vastly scaled-up NERVA-style thruster on
an icy comet or asteroid might do the job. (1 Terawatt
reactor, 1 km/s Ve would take 30 days to impart 10 m/s
to a 10 km diameter ice ball.) Maybe moving planets is
out of our range in the forseeable future, but moving
asteroids is not.

For instance, could we get a valuable asteriod into Earth
orbit by arranging to have that asteroid have a near-miss
with the Moon, perhaps after several encounters with
other planets to dump gravitational energy?

In article .com,
wrote:
Korycansky et al wrote about moving Earth via 1 million
engineered asteriod near-misses, to avoid climate change
as the sun grows hotter:

http://arxiv.org/abs/astro-ph/0102126

John McCarthy (the LISP guy!) suggests moving Mars into
Earth orbit, and uses conservation of angular momentum
(which the folks in the previous paper really should have
figured out one dinner conversation after having the
original idea) to find an interesting consequence of
doing so: Venus is nearly dumped into the Sun.

http://www-formal.stanford.edu/jmc/f...mars/mars.html

It seems to me that I'd rather have Venus than Mars in
co-orbit with Earth. It's closer to the right size, which
means it can hang on to more atmosphere, which helps a
lot.

But Venus is very H poor, because it's at the wrong end
of billions of years of conditions that are very unlike Earth's.
Mars, OTOH, is frozen but not nearly as H poor (Which doesn't
make it H rich, of course).

--
http://www.cic.gc.ca/english/immigrate/
http://www.marryanamerican.ca
http://www.livejournal.com/users/james_nicoll

Iain It seems to me that I'd rather have Venus than Mars in
Iain co-orbit with Earth. It's closer to the right size, which
Iain means it can hang on to more atmosphere, which helps a
Iain lot.

James But Venus is very H poor, because it's at the wrong end
James of billions of years of conditions that are very unlike Earth's.
James Mars, OTOH, is frozen but not nearly as H poor (Which doesn't
James make it H rich, of course).

Suppose that, after tens of millions of years of moving the planet
into the right spot, you want to terraform it. Which is an easier
problem?

1. Fix Mars so that it can hang onto a thick atmosphere.

2. Fix Venus' biosphere to have more water.

ISTM that, so long as we're slinging around 100 km diameter asteroids,
there ought to be a way to get two big icy ones to have an unfortunate
inelastic event near Venus, such that a significant chunk of the water
ends up with less than escape velocity. Either that, or get one to
break up, spread out, and pelt the planet with icy rubble for a
thousand years.

James Nicoll wrote:

wrote:

It seems to me that I'd rather have Venus than Mars in
co-orbit with Earth. It's closer to the right size, which
means it can hang on to more atmosphere, which helps a
lot.

But Venus is very H poor, because it's at the wrong end
of billions of years of conditions that are very unlike Earth's.
Mars, OTOH, is frozen but not nearly as H poor (Which doesn't
make it H rich, of course).

So the correct way to move Venus is to form a large magnetic field and use
it to collect hydrogen and momentum from the solar wind, thus solving two
problems at once. Neat.

Perhaps better than my earlier idea (posted here some time ago) of using a
big rubber band stretched between Venus and Mars.


--
Peter Fairbrother

on Fri, 06 May 2005 00:08:55 +0100, Peter Fairbrother sez:
` James Nicoll wrote:

` wrote:
`
` It seems to me that I'd rather have Venus than Mars in
` co-orbit with Earth. It's closer to the right size, which
` means it can hang on to more atmosphere, which helps a
` lot.
`
` But Venus is very H poor, because it's at the wrong end
` of billions of years of conditions that are very unlike Earth's.
` Mars, OTOH, is frozen but not nearly as H poor (Which doesn't
` make it H rich, of course).

` So the correct way to move Venus is to form a large magnetic field and use
` it to collect hydrogen and momentum from the solar wind, thus solving two
` problems at once. Neat.

` Perhaps better than my earlier idea (posted here some time ago) of using a
` big rubber band stretched between Venus and Mars.

I proposed the idea here some years ago of firing ions of opposite charge
at each planet until the electrostatic attraction trumped orbital inertia.
It was a standard excercise in high school to compute what charge would be
needed between earth and moon to keep the latter in orbit, and the number
comes out to around 6x10^13 coulomb, which means a coupla megAmps for a
year. Nudging planets would require more, but still not utterly unfeasible
numbers. The trick is just to get the ions to agree to carry the planets
along as they move to neutralize their charge...

--
================================================== ========================
Pete Vincent
Disclaimer: all I know I learned from reading Usenet.

One thing that I find exciting about this idea of orbital
engineering is the notion that low-energy perturbations
can have really large effects even a few years later.
Particularly, the notion that the delta-V required to get
very heavy objects into near-arbitrary orbits has a lower
bound determined by the precision with which one can
predict the future gravitational disturbances.

Del Cotter originally proposed this, many years ago; it's discussed in
Martyn Fogg's classic book _Terraforming: Engineering Planetary
Environments_.

You can imagine that if total delta-V can be lowered to ~100 m/s
(admittedly a much smaller number than the first paper
suggests)

Del Cotter noted that you can boostrap up, with small objects
perturbing the orbits of larger objects perturbing the orbits of larger
objects, and the quote I remember is "if you had sufficient accuracy, a
pebble tossed into the asteroid belt could move planets."
(that's a paraphrase-- too lazy to dig up my copy and post the exact
quote.)

a vastly scaled-up NERVA-style thruster on
an icy comet or asteroid might do the job. (1 Terawatt
reactor, 1 km/s Ve would take 30 days to impart 10 m/s
to a 10 km diameter ice ball.) Maybe moving planets is
out of our range in the forseeable future, but moving
asteroids is not.

--
Geoffrey A. Landis
http://www.sff.net/people/geoffrey.landis

wrote:
It seems to me that I'd rather have Venus than Mars in
co-orbit with Earth. It's closer to the right size, which
means it can hang on to more atmosphere, which helps a
lot. But in either case, it seems like either planet is
going to do some Very Bad Things to Earth's orbit as the
orbital period approaches but does not equal Earth's.

You could first modify Mars' plane. This greatly reduces the potential
for collision as there are only 2 points on each orbit where impact can
occur. However, if the orbital periods of Mars and Earth are rational
ratios to each other, then it can be set up so that no collision will
ever happen.

Step one is to change Mar's major axis so that it results in say an
orbital period of 1.25 Earth years. Once you have done that, Earth
will move 90 degrees between each time Mars passes through a danger
point. This allows you to set it up so that Mars is at least 45
degrees away from Earth when it is in the same plane. Since Mars is
slightly eccentric at this point, the other danger point is not 180
degrees away, but should be close to it, overall margin of error would
probably be better than 30 degrees anyway.

Next step is to reduce Mars' minor axis. As long as the major axis is
kept the same, this will not change the phase relationship between Mars
and Earth as period is dependant on major axis only. This might
require slight corrections to keep everything phase locked. Once Mars
is in an ellipitical orbit with minor axis below Earth's, impact is not
possible no matter what the major axis is as long as the orbital planes
are different. This step is the dangerous one as if the "safe" phase
relationship is not maintained impact can occur.

Next, the major axis of Mars is reduced to be 1 AU. This is totally
safe as long as the minor axis is kept below 1 AU. This aligns the
period of Mars' orbit to Earth's. Also, at this point the 180 degree
phase relationship would be implemented. (Though wouldn't a closer
Mars be better ? Even 180 degrees is not stable anyway)

Finally, the plane change and minor axis adjustments are made. This
puts Mars in the same plane and circular orbit.

Raph,

I really appreciate this response. I hadn't realized that the
orbital period of a planet was independent of it's minor axis.

There are a couple of points that I would be very interested in
you expanding on.

Raph [Step zero: change Mars' plane]

Raph Step one is to change Mars' major axis so that it results
Raph in say an orbital period of 1.25 Earth years. Once you
Raph have done that, Earth will move 90 degrees between each
Raph time Mars passes through a danger point. This allows you
Raph to set it up so that Mars is at least 45 degrees away
Raph from Earth when it is in the same plane.

You mean, the Earth is 90 degrees farther along its orbit each
time Mars passes through one danger point (D1). But what about
the other danger point (D2)?

When Mars' orbit is circular, Mars takes 1.25/2=0.625 years
from D1 to D2, but Earth takes 0.5 years. If Earth is late
by 0.25 years to D1, it will be late to D2 by 0.25+0.5-0.625
= 0.125 years. The total amount of margin to be had is 3/4
what you suggested, if I'm following correctly.

But it gets worse. Suppose, without loss of generality, that
D1 is while Mars' orbit is increasing in distance to the sun.
As Mars' orbit goes from e.g. circular to elliptical, the
amount of time between Mars visiting D1 to D2 goes from 0.625
years to 1.25 x 0.625 years. By arranging for Earth to
have more margin when late than when early to D1, you could
keep margin for x 1.0 (at x=1.0 there will eventually be a
crash if you stay in that configuration long enough).

So the question is, can you get the minor axis of Mars' orbit
below 1 AU, with x sufficiently below 1.0 years that close-
range gravitational effects between Earth and Mars don't
overwhelm the puny deltas that the tame Kuiper belt object
is injecting.

Raph Though wouldn't a closer Mars be better ? Even 180
Raph degrees is not stable anyway)

Do you mean, would it be better for Mars to be at L1 or L2
(60 degrees phase off Earth in Earth's orbit)? Or do you
mean less than 1 AU from the Sun, for some reason?

Raph Finally, the plane change and minor axis adjustments
Raph are made. This puts Mars in the same plane and
Raph circular orbit.

Really neat idea.

wrote:
Raph,

I really appreciate this response. I hadn't realized that the
orbital period of a planet was independent of it's minor axis.

There are a couple of points that I would be very interested in
you expanding on.

Raph [Step zero: change Mars' plane]

Raph Step one is to change Mars' major axis so that it results
Raph in say an orbital period of 1.25 Earth years. Once you
Raph have done that, Earth will move 90 degrees between each
Raph time Mars passes through a danger point. This allows you
Raph to set it up so that Mars is at least 45 degrees away
Raph from Earth when it is in the same plane.

You mean, the Earth is 90 degrees farther along its orbit each
time Mars passes through one danger point (D1). But what about
the other danger point (D2)?

Mars moves 180 degrees on its orbit between each danger point. In the
same time, Earth moves 1.25*180 = 225 degrees around its orbit. This
means that Earth's position on its orbit when Mars passes through a
danger point is:

(N = number of times Mars moves through a danger point)
(A = start angle)

Earth: A + N*225

As long as that is not 0 or 180, no collision can occur. Filling in N,
you get

0: A
1: A + 225
2: A + 90
3: A + 315
4: A + 180
5: A + 45
6: A + 270
7: A + 135
8: A (back at the start an it repeats)

Setting A to 22.5 degrees gives best safety margin (22.5 degrees or
0.75 months). Hmm, not as good as I originally thought. I just
assumed that the 2nd danger point would be an automatic miss if the
first one was.

It is possible to improve matters by using a longer period for Mars.
If Mars was set to a period of 2 years, then you could get 90 degrees
separation.



But it gets worse. Suppose, without loss of generality, that
D1 is while Mars' orbit is increasing in distance to the sun.
As Mars' orbit goes from e.g. circular to elliptical, the
amount of time between Mars visiting D1 to D2 goes from 0.625
years to 1.25 x 0.625 years. By arranging for Earth to
have more margin when late than when early to D1, you could
keep margin for x 1.0 (at x=1.0 there will eventually be a
crash if you stay in that configuration long enough).

Assuming, the period of the orbit is 1.25 years, this gives a major
axis of 1.16 AU. The minor axis would be 1 AU. This is a pretty
circular orbit, I would assume that the time between D1 and D2 is still
close to 0.625 years. Also, remember that the total time for the orbit
is still 1.25 years. Basically, as long as D1 - 0.625 is smaller than
the margin everything would be safe.


So the question is, can you get the minor axis of Mars' orbit
below 1 AU, with x sufficiently below 1.0 years that close-
range gravitational effects between Earth and Mars don't
overwhelm the puny deltas that the tame Kuiper belt object
is injecting.

Raph Though wouldn't a closer Mars be better ? Even 180
Raph degrees is not stable anyway)

Do you mean, would it be better for Mars to be at L1 or L2
(60 degrees phase off Earth in Earth's orbit)? Or do you
mean less than 1 AU from the Sun, for some reason?

The L1 and L2 would be examples of what I was thinking. It just seems
a shame to go to all that trouble and leave Mars so far away.


Raph Finally, the plane change and minor axis adjustments
Raph are made. This puts Mars in the same plane and
Raph circular orbit.

Really neat idea.