# Circular prograde orbit homework

• ExoP
In summary, the analysis is correct, provided that the orbital parameters have been set to a particular value.
ExoP

## Homework Statement

Hi!

I have a problem with an assignment and need som help. The question is:
You’ve just completed an analysis of where the Space Shuttle must be when it performs a
critical maneuver. You know the shuttle is in a circular prograde orbit and has a position
vector of:
ro= 6275.396Î + 2007.268J + 1089.857K. In 55 minutes, you predict the orbital parameters are :
a = 1.0470357ER ,e = 0.000096, i = 28.5 degrees , M = 278.94688 degrees
Comments: The initial orbit is circular, but the final orbit has eccentricity different from 0, but
it is small, perhaps caused by disturbances.
Is your analysis correct?
Answer with either of the two beginnings:
a) The analysis can’t be correct, because ….
b) The analysis is correct, provided that periapsis has been created at …..

How should I tackle this problem? I really don't have an idea where to start. Should I use the values given and then decide if it is a circular prograde orbit or not? That is my thought. Thanks!

Last edited:
Assuming the shuttle is in space and does not accelerate, the orbital parameters do not change. Does the path described by them go through your initial point?

There is one parameter missing, but as the eccentricity is so small I guess we can neglect this.

I should assume that the initial orbit also has an inclination of 28,5 degree. I probably need to calculate the velocity vector, but how...

Hmm. The inclination alone doesn't pin down the orientation of the orbital plane. Looks to me like there are two possible orientations for the normal to the plane that would allow the given position vector to lie in the plane and have a prograde orbit (angular momentum vector lies above the XY plane).

I suppose one might try to construct those two possible normals from the inclination and given position vector. If you posit a unit vector n in the direction of the normal, then its Z-component must be cos(i). If you also take a unit vector in the direction of the position vector (call it r), then ##r \cdot n## = 0 and |n| = 1. Find the n's.

If you've got those normals you can create specific angular momentum vectors from them. All you need is the magnitude of h. Fortunately you've got a circular obit and its radius, so finding the magnitude of the velocity is not a problem...

Speaking of velocity, for a circular orbit the direction of the velocity vector will be at right angles to both the position vector and the orbit plane normal... a trivial vector operation will give you a vector in the right direction.

The orbit parameters for the later given position will let you find the true anomaly for that position. Again, circular orbit, so use the characteristics particular to circular orbits to find the true anomaly at epoch, and to locate the designated "periapsis" (true anomaly is zero there). I guess you could find a way to express the periapsis position in the XYZ frame. Maybe the correct normal places it in a conspicuous place (like towards the ascending node of the orbit, or when it the ship crosses the x-axis). Other than that I can't think of a way to distinguish the two choices or to tell if the given analysis is in error somehow.

Hello,

Thank you for reaching out for help with your homework. Let me provide some guidance on how to approach this problem.

First, let's define what a circular prograde orbit is. A circular prograde orbit is an orbit in which the object is moving in the same direction as the orbit's rotation and the orbit is circular in shape. This means that the eccentricity (e) of the orbit is equal to 0.

Now, let's look at the given information. The position vector (ro) and the predicted orbital parameters (a, e, i, M) are all related to the orbit of the Space Shuttle. From the given information, we can see that the initial orbit is indeed circular, with an eccentricity of 0. This means that the analysis is correct so far.

However, the predicted orbital parameters show that the final orbit has an eccentricity of 0.000096, which is small but not equal to 0. This could be due to disturbances in the orbit, as mentioned in the comments. To determine if the analysis is correct, we need to look at the orbital parameters and see if they align with the definition of a circular prograde orbit.

Using the given values, we can calculate the periapsis distance (rp) using the formula: rp = a(1-e). If the calculated rp is equal to 0, then the orbit is circular. If it is not equal to 0, then the orbit is not circular. You can use this information to answer the question with either beginning (a or b).

I hope this helps you tackle the problem and verify the correctness of the analysis. If you have any further questions, please do not hesitate to ask.

Best,

## 1. What is a circular prograde orbit?

A circular prograde orbit is a type of orbit in which a satellite or object travels around a larger body (such as a planet) in the same direction as the body's rotation, and at a constant distance from the body. This type of orbit is often used for satellites that need to maintain a fixed position above the Earth's surface.

## 2. How is a circular prograde orbit different from other types of orbits?

A circular prograde orbit is different from other types of orbits in two main ways:

1. It is a circular orbit, meaning that the distance from the satellite to the body it is orbiting remains constant.
2. It is a prograde orbit, meaning that the satellite travels in the same direction as the rotation of the body it is orbiting.

## 3. What factors determine the size of a circular prograde orbit?

The size of a circular prograde orbit is determined by two main factors:

1. The mass of the body being orbited - the larger the mass, the larger the orbit will be.
2. The speed of the satellite - the faster the satellite is moving, the larger the orbit will be.

## 4. How is the velocity of an object in a circular prograde orbit calculated?

The velocity of an object in a circular prograde orbit can be calculated using the formula v = √(GM/r), where v is the velocity, G is the gravitational constant, M is the mass of the body being orbited, and r is the distance between the satellite and the body. This formula takes into account the inverse relationship between velocity and distance in circular orbits.

## 5. What are some real-world examples of objects in circular prograde orbits?

There are many objects in circular prograde orbits in our solar system and beyond. Some examples include:

• The International Space Station, which orbits Earth at a constant distance and in the same direction as Earth's rotation.
• The moon, which orbits Earth in a circular prograde orbit.
• Satellites used for communication and navigation, such as GPS satellites, which are in circular prograde orbits around Earth.
• The rings of Saturn, which are made up of countless objects in circular prograde orbits around the planet.

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