Total Energy of Rocket Increasing in Earth-Moon System

Hey guys. I am currently working on a project to model the trajectory
of a rocket traversing the Earth-Moon system. Basically it moves from
a circular orbit about the Earth to an intercept course with the Moon
by applying an impulse or boost to its tangential velocity.

Basically, my problem is that the total energy of the rocket in this
system (i.e. Kinetic + Gravitational Potential) is not constant.
Naturally, there is an increase when the boost is applied, but there
is also an increase as the rocket approaches the Moon, which seems
bizarre because surely the gravitational potential should become more
negative as the rocket's velocity (and thus its kinetic energy)
increases, leading to no net increase in total energy.

Does anyone have any ideas why this is happening?

Kind Regards,

Matt

In article .com,
Matt wrote:

Hey guys. I am currently working on a project to model the trajectory
of a rocket traversing the Earth-Moon system. Basically it moves from
a circular orbit about the Earth to an intercept course with the Moon
by applying an impulse or boost to its tangential velocity.

Basically, my problem is that the total energy of the rocket in this
system (i.e. Kinetic + Gravitational Potential) is not constant.
Naturally, there is an increase when the boost is applied, but there
is also an increase as the rocket approaches the Moon, which seems
bizarre because surely the gravitational potential should become more
negative as the rocket's velocity (and thus its kinetic energy)
increases, leading to no net increase in total energy.

Does anyone have any ideas why this is happening?


Your system is the Earth and moon and rocket. Are you accurately modelling the
potential to include both for r? Don't forget that the rocket is gaining ke
from the decrease in pe from the moon.

--
Sacred keeper of the Hollow Sphere, and the space within. Coffee boy to the
rich and famous

COOSN-174-07-82116: alt.astronomy's favourite poster (from a survey taken
of the saucerhead high command).

Phineas T Puddleduck wrote:

In article .com,
Matt wrote:

Hey guys. I am currently working on a project to model the trajectory
of a rocket traversing the Earth-Moon system. Basically it moves from
a circular orbit about the Earth to an intercept course with the Moon
by applying an impulse or boost to its tangential velocity.

Basically, my problem is that the total energy of the rocket in this
system (i.e. Kinetic + Gravitational Potential) is not constant.
Naturally, there is an increase when the boost is applied, but there
is also an increase as the rocket approaches the Moon, which seems
bizarre because surely the gravitational potential should become more
negative as the rocket's velocity (and thus its kinetic energy)
increases, leading to no net increase in total energy.

Does anyone have any ideas why this is happening?


Your system is the Earth and moon and rocket. Are you accurately modelling
the potential to include both for r? Don't forget that the rocket is
gaining ke from the decrease in pe from the moon.


wow, you teach 6th grade physics too?

impressive.

--
Posted via a free Usenet account from http://www.teranews.com

In article ,
Artimus Q Dufflebag wrote:

Your system is the Earth and moon and rocket. Are you accurately modelling
the potential to include both for r? Don't forget that the rocket is
gaining ke from the decrease in pe from the moon.


wow, you teach 6th grade physics too?

impressive.


Wow. You really are obsessed.


--
Sacred keeper of the Hollow Sphere, and the space within. Coffee boy to the
rich and famous. Proud owner of the Mop Jockey.

COOSN-174-07-82116: alt.astronomy's favourite poster (from a survey taken
of the saucerhead high command).

Phineas T Puddleduck wrote:

In article ,
Artimus Q Dufflebag wrote:

Your system is the Earth and moon and rocket. Are you accurately
modelling the potential to include both for r? Don't forget that the
rocket is gaining ke from the decrease in pe from the moon.


wow, you teach 6th grade physics too?

impressive.


Wow. You really are obsessed.

yeah. i perch way up above in the clouds and swoop down on alt.astronomy to
pounce on unsuspecting tards... oh wait... that's you.


--
Posted via a free Usenet account from http://www.teranews.com

"Phineas T Puddleduck" wrote in message
news
In article ,
Artimus Q Dufflebag wrote:

Your system is the Earth and moon and rocket. Are you accurately
modelling
the potential to include both for r? Don't forget that the rocket is
gaining ke from the decrease in pe from the moon.


wow, you teach 6th grade physics too?

impressive.


Wow. You really are obsessed.

Wow. You really are Gay.

HJ

Your system is the Earth and moon and rocket. Are you accurately modelling the
potential to include both for r? Don't forget that the rocket is gaining ke
from the decrease in pe from the moon.

My gravitiational potential term includes both the Earth and Moon.
It's given as follows:

U = - G(M1)m/(Re) - G(M2)m/(Rm)

Where U is the gravtiational potential of the rocket at that location,
M1 is the mass of the Earth, M2 is the mass of the Moon, Re is the
rocket-Earth distance and Rm is the rocket-Moon distance.

Does this seem correct?

Kind Regards,

Matt

"Matt" wrote in message
oups.com...
My gravitiational potential term includes both the Earth and Moon.
It's given as follows:

U = - G(M1)m/(Re) - G(M2)m/(Rm)

Where U is the gravtiational potential of the rocket at that location,
M1 is the mass of the Earth, M2 is the mass of the Moon, Re is the
rocket-Earth distance and Rm is the rocket-Moon distance.

Does this seem correct?

I'm no expert but... What happens when Re is zero? U becomes very large so
it looks like somethings wrong.

Try the equation after this paragraph..

"With this simplifying assumption, integrating force over distance leads to
the following general expression for the gravitational potential energy, Ug,
of a system of two masses"

on this page...

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

Regarding h1....(h1 is the reference level the separation at which potential
energy is considered to be zero) ...

When working out the contribution due to the earth use h1 = radius of the
earth.
Then working out the contribution due to the moon h1 = (earth moon
seperation - radus of the earth)

or something like that.

"CWatters" wrote in message
...

"Matt" wrote in message
oups.com...
My gravitiational potential term includes both the Earth and Moon.
It's given as follows:

U = - G(M1)m/(Re) - G(M2)m/(Rm)

Where U is the gravtiational potential of the rocket at that location,
M1 is the mass of the Earth, M2 is the mass of the Moon, Re is the
rocket-Earth distance and Rm is the rocket-Moon distance.

Does this seem correct?

I'm no expert but... What happens when Re is zero? U becomes very large so
it looks like somethings wrong.

No, it's fine. In the real world the Earth and Moon are not
point masses, so the distances between mass m and either of
M1 or M2 can never be less than their respective radii. If
somehow m were to be able to burrow into either one, then
progressively less mass would be between it and the center,
so you'd end up with a situation where you'd need to start
considering limits (mass approaches zero as radius approaches
zero).

Matt might want to inform us what kind of model he's
using to perform his calculations. Perhaps he's performing
a simple integration of the trajectory and something's
amiss with his implementation.

Matt might want to inform us what kind of model he's
using to perform his calculations. Perhaps he's performing
a simple integration of the trajectory and something's
amiss with his implementation.

That is essentially all I'm doing. I was thinking the problem may be
due to the finite nature of numerical integration accuracy, however
the increase in total energy is from -3 x 10^8 J to -2.5 x 10^8 J, so
it's an appreciable difference and I don't think my Fourth Order
Method could cause that alone.

Kind Regards,

Matt