Simplifying total energy equation orbital mechanics

In summary, the conversation discusses the attempt to prove an equation involving the velocity and radius of circular orbits and the Hohmann ellipse transfer. The conversation suggests using the expressions for velocity and the relationship between the semi-major axis and radius to simplify the equation.
  • #1
Dustinsfl
2,281
5
I am trying to show that
$$
\frac{\Delta v}{v_{c_1}} = \frac{1}{\sqrt{R}} - \frac{\sqrt{2}(1 - R)}{\sqrt{R(1+R)}} - 1
$$
where ##R=r_2/r_1##.

##r_1## is the radius of the circular orbit 1 and ##r_2## is the radius of the circular orbit 2. Similarly, ##v_{c_1}## is the velcotiy of the circular orbit 1 and so on for ##v_{c_2}##.
The velocity of a circular orbit is
$$
v_{c_k} = \sqrt{\frac{\mu}{r_k}}
$$
where ##k = 1,2##.
By the Law of Cosine,
$$
(\Delta v)^2 = v_{c_2}^2 + v^2 - 2v_{c_2}vv_{\theta}
$$
where ##v## is the velocity from the Hohmann ellipse transfer and ##v_{\theta} = \frac{h}{r} = \frac{\sqrt{\mu p}}{r}##.
The velocity of the ellipse is ##v = \sqrt{\mu\left(\frac{2}{r} - \frac{1}{a}\right)}##.
$$
a = \frac{1 + R}{2},\quad r = r_2 - r_1,\quad p = a(1 - e^2),\quad e = \frac{r_2 - r_1}{r_2 + r_1} = \frac{R - 1}{R + 1}
$$

So I took ##\frac{(\Delta v)^2}{v_{c_1}^2}##.
$$
\frac{(\Delta v)^2}{v_{c_1}^2} = \frac{1}{R} + \frac{2}{R - 1} - \frac{4r_1}{R + 1} - 2r_1\sqrt{\frac{2}{r_2r} - \frac{1}{r_2a}}\frac{\sqrt{a\mu(1 - e^2)}}{r}
$$
At this point, I can't seem to make any useful head way towards the result.
 
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  • #2


Hello,

Thank you for sharing your progress so far! It looks like you have made some good initial steps towards proving the given equation.

One suggestion I have is to try using the expression for ##v_{c_k}## in terms of ##r_k##, which is given by ##v_{c_k} = \sqrt{\frac{\mu}{r_k}}##. This may help simplify some of the expressions involving r1 and r2.

Additionally, you may want to consider using the relationship between the semi-major axis ##a## and the radius of the circular orbit ##r_c##, which is given by ##a = \frac{r_c}{2}##. This may also help simplify some of the expressions.

I hope these suggestions are helpful and good luck with your further analysis!
 

What is the total energy equation in orbital mechanics?

The total energy equation in orbital mechanics is a mathematical representation of the total energy of an object in orbit around another object. It takes into account both the kinetic energy and potential energy of the object in orbit.

Why is it important to simplify the total energy equation in orbital mechanics?

Simplifying the total energy equation in orbital mechanics allows for a better understanding of the factors that affect the motion of objects in orbit. It also makes it easier to calculate and analyze orbital trajectories.

What are the variables involved in the total energy equation in orbital mechanics?

The variables involved in the total energy equation in orbital mechanics include the mass of the two objects, the distance between them, and the velocities of the objects.

How does the total energy equation change for different types of orbits?

The total energy equation changes depending on the type of orbit. For circular orbits, the kinetic energy and potential energy are equal, resulting in a simplified equation. For elliptical orbits, the equation includes the eccentricity of the orbit.

What is the significance of the total energy equation in understanding orbital mechanics?

The total energy equation is crucial in understanding orbital mechanics because it helps scientists determine the stability of an orbit and predict the behavior of objects in orbit. It also allows for the calculation of important orbital parameters, such as the orbital period and velocity.

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