Gravity

Gravitational Field

A gravitational field is the region around a mass where its gravitational force can be felt. Gravitation is the force of attraction that a body exerts on all other bodies in the universe. This force acts between all masses and plays a key role in holding together planets, stars, and galaxies. Every mass has a gravitational field surrounding it.

Law of Universal Gravitation

The law states that the gravitational force of attraction between two masses (\( M_1 \) and \( M_2 \)) is directly proportional to the product of the masses and inversely proportional to the square of the distance (\( r \)) between them.

\[ F = G \frac{M_1 M_2}{r^2} \]

Where:

• \( M_1, M_2 \) = Masses of the two objects (kg)
• \( G \) = Gravitational constant (\( G = 6.67 \times 10^{-11} \, \text{N} \cdot \text{m}^2 \text{kg}^{-2} \))
• \( r \) = Distance between the masses (m)

Gravitational Potential (V)

Gravitational potential is the work done in bringing a unit mass from infinity to a given point. Its SI unit is J/kg.

\[ V_g = - G \frac{M}{r} \]

Where:

• \( G \) = Gravitational constant
• \( M \) = Mass generating the gravitational field
• \( r \) = Distance from the mass

Escape Velocity (\( V_e \))

Escape velocity is the minimum velocity required for an object to completely escape the gravitational pull of the Earth. The SI unit is m/s.

\[ V_e = \sqrt{2gR} \]

Where:

• \( R \) = Radius of the Earth
• \( g \) = Acceleration due to gravity (\( g = 9.8 \, \text{m/s}^2 \))

Acceleration Due to Gravity (g)

Acceleration due to gravity is the force per unit mass acting on an object at the Earth's surface.

\[ g = \frac{F}{m} \quad \text{or} \quad g = \frac{G M_e}{R_e^2} \]

Where:

• \( M_e \) = Mass of the Earth
• \( R_e \) = Radius of the Earth

Kepler’s Laws

Johannes Kepler, working with data alongside Tycho Brahe, formulated three laws that describe the motion of planets in space. These laws are:

1. The Law of Orbits

All planets move in elliptical orbits, with the Sun positioned at one of the focal points.

2. The Law of Areas

A line connecting a planet to the Sun sweeps out equal areas in equal time intervals.

3. The Law of Periods

The square of a planet’s orbital period is directly proportional to the cube of the semi-major axis of its orbit.

Although Kepler’s laws were originally derived for planetary motion around the Sun, they also apply to satellite orbits.

Rockets

Rockets are self-propelled devices that generate thrust by ejecting a high-speed stream of gases from their rear. According to Newton’s Third Law of Motion, the expulsion of gases in one direction results in the rocket moving in the opposite direction.

Rocket engines are the most powerful propulsion systems relative to their weight. Unlike jet-powered and propeller-driven engines, they produce immense thrust, making them ideal for space travel and high-speed applications.

Uses of Rockets

• Fireworks for entertainment.
• Launching missiles.
• Scientific research through sounding rockets.
• Jet-Assisted Take-Off (JATO) for heavy aircraft.
• Life-saving rockets for maritime rescue operations.
• Saturn V rockets for space exploration, including moon missions.
• Rocket-powered ejection seats for pilot safety.
• Signal rockets for distress signals at sea.

Components of a Rocket

• Propellant Tank: Stores fuel or propellant.
• Combustion Chamber: The section where fuel is burned to generate hot gases for thrust.
• Nozzle: The exhaust outlet that directs escaping gases to propel the rocket.
• Fins: Stabilizers that help maintain the rocket’s trajectory.
• Payload: Varies depending on the rocket’s mission.

Satellites

A satellite is a body that orbits a larger celestial object. Natural satellites occur in space naturally, while artificial satellites are human-made and launched into orbit for specific purposes.

Natural Satellites

Natural satellites are celestial bodies that naturally orbit a planet. For example:

• The Moon is Earth's natural satellite.
• The Earth itself is a natural satellite of the Sun.

Artificial Satellites

Artificial satellites are human-made objects placed in orbit around a celestial body. These satellites are launched by rockets to a predetermined height, where they experience minimal air resistance. After reaching this altitude, they are given a high horizontal velocity to maintain a nearly circular orbit.

Classification of Artificial Satellites

• Earth Resource Satellites: Used for environmental and resource monitoring.
• Meteorological Satellites: Provide weather and climate data.
• Satellites with Microwave Sensors: Used for communication and remote sensing.

Uses of Satellites

• Telecommunications and broadcasting.
• Geographical mapping and navigation.
• Military intelligence and surveillance.
• Meteorological studies and weather forecasting.
• Scientific exploration and research.
• Space science and planetary observations.

Components of a Satellite

• Power Generation System: Most satellites use solar panels and rechargeable batteries.
• Command and Data Handling System: Includes antennas for communication and onboard computers for data processing.
• Payload: The functional equipment, such as cameras, sensors, or communication devices, tailored to the satellite’s mission.
• Protective Shielding: Protects against extreme temperatures, radiation, and space debris.
• Rocket Thruster System: Used for repositioning and maintaining orbit.

Nigeria's Satellites

1. Niger-SAT I

Launched in 2003, Niger-SAT I was Nigeria’s first satellite in space. This micro-satellite, weighing approximately 100 kg, was primarily used for:

• Disaster monitoring and response.
• Border and security surveillance.
• Oil pipeline monitoring.
• Early detection of coastal erosion, desertification, and pollution.

The satellite was initially planned for a five-year operational period before being deorbited. It contributed significantly to mapping, meteorology, and geological studies in Nigeria. Following its success, plans were made to launch Niger-SAT II and Niger-SAT X to enhance and extend the scope of the data collection.

In 2025, Nigeria aims to launch its first satellite developed entirely by Nigerian engineers from a domestic launch site.

2. NICOM SAT I

NICOM SAT I was a communication satellite designed to improve mobile network coverage and internet services across Central Africa. However, due to the failure of its solar power system, the satellite ceased functioning prematurely.