# Fundamentals Of Astrodynamics

## Question:

1.Compare Qualitative Low Earth and Geostationary Orbits.

2. Account for satellite orbital decay.

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3.Identify data sources, collect, analyze, and present information regarding the contribution of one or more of the following to space exploration development: Oberth (Tsiolkovsky), Oberth (Goddard), Esnault-Pelterie. O’Neill.

4. Recognize why the term g-forces is used to describe forces acting upon an astronaut during launch.

5.Discuss safety-related issues for safe reentry into Earth’s atmosphere, landing on Earth’s surface.

6. Recognize that there is an optimal angle for safe entry of a manned spacecraft into Earth’s atmosphere. This angle can be compared to the consequences of failing to attain it.

7.Discuss Newton’s law of universal gravity in understanding and calculating the motions of satellites.

1. A low Earth orbit technically refers any satellite less than 1500km above the Earth’s surface.

The orbital period of low earth orbits lasts approximately 960 minutes and each orbital velocity is 8km/s.

Geostationary orbits have an orbital period that lasts 24 hours and they are more likely to remain in a fixed spot on the Earth’s surface.

They are much higher than Low Earth Orbits at altitude, reaching 36000km. However, their orbital velocity is lower at about 3km/s.

Geostationary orbits are a special geosynchronous orbit type.

Any orbit that has an orbital duration of 24 hours is a geosynchronous orbit.

Not all geo-synchronous orbits have to be geo-stationary.

You will be traveling directly above and below the equator.

The simplest explanation is that low Earth orbits have lower altitudes and longer orbital periods than geostationary orbits.

2.A satellite that orbits the Earth in a stable orbit is known to contain some amount mechanical energy. This is a combination its gravitational energy and its kinetic energy due to its high speed, as well as its energy from gravity.

This means that a satellite orbiting at a lower altitude will contain less mechanical energy.

Satellites encounter frictional forces when they are moving.

This friction leads to the loss in energy and makes satellites impossible to operate. The satellite then drops to an altitude equal to the amount of energy after energy losses from friction.

At this new level, satellites tend to move faster than before, even though they have more kinetic energy from the potential energy lost.

Remember that the orbits are lower, so the orbits move at higher speeds [2].

Orbital decay occurs in a cycle. The new lower orbits of satellites are found within a denser atmosphere, which leads to more friction and energy loss.

The speed of the process increases as time passes.

Russian scientist Konstantin Tsiolkovsky was the one who came up many ideas that were considered to be prophetic and important for space travel.

His key ideas and principles included rocket propulsion, liquid fuels and multi-stage rockets.

Konstantin Tsiolkovsky illustrated how Newton’s third law of motion would apply to rocket[3].

This principle underlies rockets’ operation and is important for understanding them.

Konstantin Tsiolkovsky proposed that liquid oxygen and/or liquid hydrogen could both be used as rocket fuels so that the rocket’s thrust could be varied.

These same fuels were used to power the Saturn V rocket’s Apollo missions to the Moon. It was also demonstrated that liquid fuels can be used to control the g forces experienced by astronauts.

4. “G-Forces” are forces experienced by an astronaut in terms of gravityal strength of Earth at the surface.

The equivalent force that an astronaut feels while walking on the Earth’s surface is 1G: w=mg, where g=9.8N/kg.

An astronaut who is traveling at 9.8m/s2 would experience 2Gs net force. This is twice the force that it experienced due the Earth’s gravity.

Free-fall would give astronauts 0Gs.

The term gforces is used because it is easy to remember and simplifies calculations regarding the forces that can easily be handled by the human body during launch.

5.Re-entry can be complicated because of the high temperatures experienced and the high velocities. It also requires a precise balance in the trajectory required to safely land.

The first step to successfully land a satellite vehicle is to slow down and then travel down via the atmosphere. This process must occur simultaneously with the drag caused by the atmosphere.

Friction is caused by the vehicle’s high speed, which in turn heats it up to 3000?C.

This makes it necessary to use a shielding material that can resist very high temperatures. Most commonly, this is carbon or ceramic. These materials are strong enough to withstand these temperatures and protect the vehicle during the descent process.

6. Between 5.2? and 7.2.2? is the optimal angle to allow safe reentry into the atmosphere.

Between 5.2? und 7.2? is the optimal angle required for safe re-entry to the atmosphere.

Any angle that is beyond this range will cause the upward friction to become very strong and the craft would accelerate very fast, causing it melt.

The aircraft would bounce off the atmosphere if it entered at a lower angle than the range.

In this situation, the craft may not have enough fuel for a second attempt and could burn up[5].

7.To launch a satellite, it is necessary to know the velocity of its orbit.

For a satellite to be launched, it must know the orbit velocity.

Newton’s Law of Universal Gravitation plays an important role in understanding and calculating the motion of satellites, since it is required to determine the value of Fg that is used in calculating the velocity of the orbits.

Newton’s Law can also be used in the derivation of Kepler’s Law of Periods. It is an important tool for the thorough understanding of orbital motion.

Refer to

Roger R. Bate. Fundamentals of Astrodynamics.

Curtis Howard D. Orbital Mechanics – For Engineering Students.

Why Beliefs Matter: Reflections about the Nature of Science.

Chicago: Oxford University Press. 2010.

Leondes C. T. Advances in Control Systems – Theory and Applications.

Fundamental Planetary Science: Chemistry, Physics, and Habitability

Paris: Cambridge University Press. 2013.

Geophysics: Fundamentals.

Paris: Cambridge University Press 2015

Three Body Dynamics, and Its Applications to Exoplanets.

Rainey Larry B.

Space Modeling, Simulation: Roles of the System Lifecycle.

Stevens Brian L. Aircraft Control and Simulation.

Manchester: John Wiley & Sons.

New York: Pascal Press.

Roger R. Bate. Fundamentals of Astrodynamics.

New York, Courier Corporation, 2010Curtis Howard D. Orbital Mechanics For Engineering Students.

Why beliefs matter: Reflections about the Nature of Science.

Chicago: Oxford University Press. 2010.

Leondes C. T. Advances in Control Systems – Theory and Applications.

Fundamental Planetary Science: Chemistry, Physics, and Habitability

Paris: Cambridge University Press. 2013.

Geophysics: Fundamentals.

Paris: Cambridge University Press 2015, Quarles, Billy.

Three Body Dynamics, and Its Applications to Exoplanets.

Rainey Larry B.

Space Modeling, Simulation: Roles of the System Lifecycle.

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