Strange Increase in the Total Energy of a Rocket in the 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 it's 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

On Apr 18, 9:07 am, 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 it's 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

Just a speculation.. do you need to include Chemical Potential along
with the other two energies?
Kinetic + Grav. Pot + Chem. Pot.

Just a speculation.. do you need to include Chemical Potential along
with the other two energies?
Kinetic + Grav. Pot + Chem. Pot.

I hadn't thought about that. I'm not too worried about what happens to
the total energy when the boost is applied, the bigger concern is why
the value rises as it approaches the Moon.

I've also noticed that the absolute value of the rocket's total energy
is around -3 x 10^10 J. Why is this value negative? The mass of the
rocket is set at 30332 kg.

Kind Regards,

Matt

"Matt" wrote in message
ups.com...
Just a speculation.. do you need to include Chemical Potential along
with the other two energies?
Kinetic + Grav. Pot + Chem. Pot.

I hadn't thought about that. I'm not too worried about what happens to
the total energy when the boost is applied, the bigger concern is why
the value rises as it approaches the Moon.

I've also noticed that the absolute value of the rocket's total energy
is around -3 x 10^10 J. Why is this value negative? The mass of the
rocket is set at 30332 kg.

I think you mean that the total mechanical energy is
negative, rather than its absolute value. Absolute
values are always positive (or zero).

A negative energy means that the object is gravitationally
bound to the system. If it were positive it would be on
an escape trajectory away from the Earth-Moon system.

I think you mean that the total mechanical energy is
negative, rather than its absolute value. Absolute
values are always positive (or zero).

Yes you're right, sorry to type something misleading :s

A negative energy means that the object is gravitationally
bound to the system. If it were positive it would be on
an escape trajectory away from the Earth-Moon system.

I don't know why I didn't realise that sooner! That expains it
perfectly

Kind Regards,

Matt

In article . com,
Matt wrote:

Just a speculation.. do you need to include Chemical Potential along
with the other two energies?
Kinetic + Grav. Pot + Chem. Pot.

I hadn't thought about that. I'm not too worried about what happens to
the total energy when the boost is applied, the bigger concern is why
the value rises as it approaches the Moon.

I've also noticed that the absolute value of the rocket's total energy
is around -3 x 10^10 J. Why is this value negative? The mass of the
rocket is set at 30332 kg.


Its gaining energy from the gravitational potential of the moon. Once you're
past the point where the forces of gravity balance...

Negative energy = bound.

--
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 . com,
Matt wrote:

Just a speculation.. do you need to include Chemical Potential along
with the other two energies?
Kinetic + Grav. Pot + Chem. Pot.

I hadn't thought about that. I'm not too worried about what happens to
the total energy when the boost is applied, the bigger concern is why
the value rises as it approaches the Moon.

I've also noticed that the absolute value of the rocket's total energy
is around -3 x 10^10 J. Why is this value negative? The mass of the
rocket is set at 30332 kg.


Its gaining energy from the gravitational potential of the moon. Once
you're past the point where the forces of gravity balance...

Negative energy = bound.

it's like a ****ing flashback to 7th grade.

don't forget about the van allen belt radiation in your calculations or else
you'll be to blame when this kid gets a red mark on his homework.

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

In article ,
Artimus Q Dufflebag wrote:

Phineas T Puddleduck wrote:

In article . com,
Matt wrote:

Just a speculation.. do you need to include Chemical Potential along
with the other two energies?
Kinetic + Grav. Pot + Chem. Pot.

I hadn't thought about that. I'm not too worried about what happens to
the total energy when the boost is applied, the bigger concern is why
the value rises as it approaches the Moon.

I've also noticed that the absolute value of the rocket's total energy
is around -3 x 10^10 J. Why is this value negative? The mass of the
rocket is set at 30332 kg.


Its gaining energy from the gravitational potential of the moon. Once
you're past the point where the forces of gravity balance...

Negative energy = bound.

it's like a ****ing flashback to 7th grade.

don't forget about the van allen belt radiation in your calculations or else
you'll be to blame when this kid gets a red mark on his homework.


I apologise Matt, as it seems I have something stuck to my shoe.

--
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).

Matt wrote:
I'm not too worried about what happens to
the total energy when the boost is applied, the bigger concern is why
the value rises as it approaches the Moon.

My first thought was the same as others: the Moon's potential energy.
From a later post, though, you appear to have that right. Could the
problem be numerical inaccuracy? How are you doing the orbit
integration?

I've also noticed that the absolute value of the rocket's total energy
is around -3 x 10^10 J. Why is this value negative?

Think about what energy=0 would mean. Can the rocket escape the Earth-
Moon system?

problem be numerical inaccuracy? How are you doing the orbit
integration?

Using a Fourth Order Runge-Kutta Method