### EPFLx: EE585x Space Mission Design and Operations

Category: Tutorial

EPFLx: EE585x Space Mission Design and Operations
English | mp4 | H264 1280x720 | AAC 2 ch | Sub: English | 3.06 GB
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Welcome to the course Space Mission Design and Operations!
Concepts explained in this course:
C1 - Newton's laws of motion

First law: In the absence of a force, a body either is at rest or moves in a straight line with constant speed.

Second law: A body experiencing a force will be subject to an acceleration such that the force is equal to the product of the mass of the body and the acceleration.

Third law: Whenever a first body exerts a force on a second body, the second body exerts a force equal in magnitude and opposite in direction on the first body.

This concept is explained in the following video: 1.2.1.

C2 - Inertial Frame

The inertial frame is a frame with respect to which the laws of Newton are valid.

The direction of the axes of an inertial frame can be imagined as being fixed with respect to distant stars.

The center of the inertial frame, which is an orthogonal coordinate system, will depend on the application.

This concept is explained in the following video: 1.2.1.

C3 - Newton's law of gravitation

Newton's law of gravitation states that any two bodies in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

This concept is explained in the following video: 1.2.2.

C4 - Laws of motion of a solid body and in rotation

This concept is based on the Newtonâ€™s second law of motion applied for a rotation: the torque is equal to the time derivative of the angular momentum.

This concept is explained in the following video: 1.2.2.

C5 - Conservation Laws

Conservation of momentum in an isolated system (absence of forces).

Conservation of angular momentum in an isolated system (absence of torques).

Conservation of mechanical energy, potential and kinetic, in an isolated system, in a conservative force field (for instance a gravitational force field in the absence of dissipative forces).

This concept is explained in the following video: 1.2.3.

C6 - Structure and composition oF the Earth's atmosphere

Chemical composition: 78 % of nitrogen, 21 % of oxygen, 1 % of argon,

Layers: Troposphere, stratosphere, mesosphere, thermosphere. Tropopause: limit of the troposphere, 9 to 17 km altitude, depending on the latitude. Stratopause: limit of stratosphere, around 50 km altitude.

The limit of the atmosphere and the beginning of space is considered to be at 100 km altitude.

This concept is explained in the following video: 1.3.1.

C7 - Microgravity

Microgravity is the term used to characterize the very low acceleration level encountered inside a spacecraft in LEO (typically

g at 300 km altitude).

This concept is explained in the following video: 1.3.1.

C8 - Transparency of the atmosphere

The atmosphere is opaque to electromagnetic radiation except in the visible part of the spectrum and in the radio part between about 3 cm to 10 m wavelength. It has limited transparency in the infrared, between 1 and 10 microns wavelength.

This concept is explained in the following video: 1.3.2.

C9 - Light Effects

Airglow: emission of light by the atmosphere due to the photoionization of oxygen atoms and de-excitation which produces a luminescence, mainly due to the oxygen, somewhat also to nitrogen and the radical OH.

This concept is explained in the following video: 1.3.2.

C10 - Magnetic Field

Close to the Earthâ€™s surface, the geomagnetic field is essentially a bipolar field slightly offset from the center of the Earth. The expression of the amplitude of the magnetic field is a function of the distance to the center of the Earth and the magnetic latitude.

Radiation or Van Allen belts: High energy protons and electrons trapped in two regions of the magnetosphere, Protons and electrons in the inner RB, electrons only in the outer RB.

The Earth's magnetic field is significantly distorted away from the surface of Earth toward the Sun (5, up to 10 Earth radii) and in the anti-Sun direction due to solar wind, made of charged particles flowing in all directions from the Sun.

This concept is explained in the following videos: 1.4.1.

C11 - Northern/Southern lights

Northern and Southern Lights are produced from the excitation of nitrogen and oxygen atoms, by the electrons flowing from the solar wind.

This concept is explained in the following videos: 1.4.1.

C12 -Solar cycle - influence on the Earthâ€™s atmosphere

A solar cycle is a period of approximately 11 years, based on the sunspot number, which is changing over time with an increase of sunspot during 5 years until the solar maxima followed by 6 years of decrease until the solar minima.

A better determination of the phase of the solar cycle is the solar radio flux. The solar radiation flux at a wavelength of 10.7 cm varies along the solar cycle and is often used as a measure of the level of the solar activity along the cycle.

The Sun has also a significant effect on the thickness of the atmosphere; respectively on the density of the Earthâ€™s atmosphere at a given altitude.

This concept is explained in the following videos: 1.4.2.

C13 - Sun activity

The Sun is an active star. Its surface is granular with prominences: flares and coronal mass ejections.

A solar prominence is a large, bright feature extending outward from the Sunâ€™s surface, often in a loop shape. While the corona consists of extremely hot ionised gases, which do not emit much visible light, prominences contain much cooler plasma, similar in composition to that of the chromosphere.

This concept is explained in the following video: 1.4.3.

C14 - Particle flux

Following Coronal Mass Ejections or CMEs, there is an enormous amount of charged particles that flow through the Solar System all the way to the Earth and beyond.

This concept is explained in the following video: 1.5.1.

C15 - South Atlantic Anomaly

The South Atlantic Anomaly or SAA is an area where the Earthâ€™s inner Van Allen radiation belt comes closest to the Earthâ€™s surface.

This concept is explained in the following video: 1.5.1.

C16 - Solar radiation, outside the Earthâ€™s atmosphere and on the surface

Cosmic particles of galactic origin: high-energy charged particles, usually protons, electrons and fully ionized nuclei of light elements.

Radiation are expressed in RAD - Radiation Absorbed Dose - which is the amount of energy absorbed or REM (Roentgen Equivalent Man); or Sievert (Sv = 100 REM).

Astronauts have to stay way below 100 REM, or one Sievert, which is the vomiting effective threshold. Medical problems start over 100 REM and become significant above 500 REM.

This concept is explained in the following video: 1.5.1.

The total irradiance of the Sun is the total energy that it sends every unit of time or every second on a square meter surface outside of the Earth's atmosphere, in the form of electromagnetic radiation.

The solar constant is a conventional measure of the mean total solar irradiance at a distance of one Astronomical Unit.

Solar irradiance in the Solar system decreases with the distance to the Sun.

This concept is explained in the following video: 1.5.2.

C18 - Albedo

Albedo is the diffuse reflectivity or reflecting power of a surface measured from zero for no reflecting power of a perfectly black surface, to 1 for perfect reflection.

This concept is explained in the following video: 1.5.3.

C19 - Earthâ€™s energy budget

The solar constant is approximately 1368 watts per square meter. This value has been slowly decreasing over the past few years and in April 2015, the value was 1361 watts per square meter.

About 30% of this radiation is reflected back in space by the atmosphere (6%), clouds (20%) and the Earth's surface (4%). The rest is absorbed by land and oceans and re-radiated out in space in the form of infrared radiation.

From the Earth, there are two sources of radiation: the albedo, which is the solar spectrum reflected from the high layers of the Earth atmosphere, and the infrared radiation from the Earth itself.

This concept is explained in the following video: 1.5.3.

C20 - Radiation balance for a spacecraft on orbit around the Earth

If we consider a spacecraft in the vicinity of the Earth, the dominant source of radiation it receives comes from the Sun. 30% of the radiation of the Sun impacting the Earth is coming back towards space (Albedo). The other source of radiation is the Earth infrared radiation, which is a rather dim source.

The total absorbed radiation by the spacecraft is equal to the emitted radiation in a balanced situation.

The Stefan-Boltzmann law gives the value of the emitted radiation per unit surface in the case of a black body.

The spacecraft is not a black body and its emitted radiation depends of its total surface and its IR emissivity.

The equation expressing the radiation balance can be used to determine the average temperature of a spacecraft, knowing its emissivity and absorptivity.

This concept is explained in the following video: 1.5.4.

C21 - Orbit decay - ballistic coefficient

The orbit decay is the reduction in the altitude of a satellite's orbit. The major cause is the drag of the Earthâ€™s atmosphere, which is more important during the solar maxima at a given altitude. Positive Feedback effect: The more the orbit decays, the lower the altitude, the faster the decay.

The drag equation expresses the force experienced by an object moving through a fluid or a gas at a velocity V.

The ballistic coefficient is the measure of the resistance to orbit decay caused by atmospheric drag and is inversely proportional to the drag coefficient and the frontal surface of the spacecraft.

This concept is explained in the following video: 1.6.1.

C22 - Space debris

Space debris is an object in space that is no longer functional and useful. There is a huge amount of space debris in LEO and GEO causing high risk of collision with active spacecraft.

Several rules have been put in place to regulate satellites allocation in certain areas and the end of missions: when a communication satellite in the geostationary orbit are is longer functional, it shall be moved to a graveyard orbit. Measures are in place to limit satellites lifetime in Low Earth Orbit to 25 years.

Two break-up: Iridium-Cosmos in 2009 and Fengyun-1C in 2007 caused a very high density of space debris around 800 km altitude.

This concept is explained in the following video: 1.6.2.

C23 - asteroid collision threat

Several asteroids collisions happened on Earth but also in other planets in the Solar System.

A major event was the Cretaceous-Paleogene extinction, 65 million years ago, large scale extinction of most of life on Earth, including dinosaurs from the impact of large meteorite Earth, probably in the region of the Yucatan peninsula, Mexico.

Different techniques to improve early detection of dangerous asteroids, and to modify their trajectories to avoid collision with earth are currently being looked at.

This concept is explained in the following video: 1.6.3.

C24 - Gravitational Profile of the Earth

Inside the Earth, considered homogeneous, the gravitational acceleration varies linearly from zero at the center to 9.81 meters per second square at the surface. From the surface on, it varies as 1/r2, r being the distance to the center of the Earth.

This concept is explained in the following video: 2.2.1.

C25 - Gravitational well, Work and Depth

A gravitational well is a conceptual model of the gravitational field surrounding a body in space.

The work necessary to lift a unit mass from the surface of a spherical object such as Earth, to infinity, is equal to the work necessary to lift the same mass from the surface of the sphere over a distance equal to the objectâ€™s radius, with a constant force equal to the force at the surface.

The objectâ€™s radius is the depth of the objectâ€™s gravitational well. The profile of the gravitational well is in 1/r

This concept is explained in the following videos: 2.2.1. and 2.2.2.

C26 - Normalized gravitational well

The depth of gravitational well of any spherical objects in the solar system or elsewhere, is always normalized to the gravitational acceleration of the Earth for comparison purposes.

This concept is explained in the following video: 2.2.2.

C27 - Escape Velocity

Escape velocity from the Earthâ€™s surface is the velocity at which a spacecraft has to leave this surface in order to go to infinity with a zero velocity. The escape velocity is independent of the direction of the initial impulse (as long as escape really takes place).

For Earth, the escape velocity from the surface is equal to 11.2 km/second. For higher altitudes, it varies as

.

This concept is explained in the following video: 2.2.3.

C28 - Circular Velocity

The circular velocity is the velocity of a spacecraft on a circular orbit around an object such as the Earth. For a spacecraft in orbit around the Earth, its circular velocity is equal to

.

This concept is explained in the following video: 2.2.3

C29 - GRavitational well in term of transfer velocity

The transfer velocity, for a given planet, is the velocity that has to be added to the planetâ€™s circular velocity for a transfer to infinity from this location in the Sunâ€™s gravitational well, i.e. as if to leave the solar system.

This concept is explained in the following video: 2.2.3.

C30 - Two-Body Problem

The two-body problem is to determine the motion of the two bodies that interact only with each other.

This concept is explained in the following video: 2.3.1.

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Tags: Mission, Design, Operations