Space Environment: Orbital Effects and Radiation Belts

What three components primarily determine Earth's space environment?

Earth's atmosphere, solar radiation, and Earth's magnetic field.

How does Earth's space environment affect spacecraft mission design?

It influences mission altitude, duration, attitude-control requirements, and radiation-hardness requirements.

What are the dominant environmental concerns for LEO, MEO, and GEO?

LEO: atmospheric drag and reactions; MEO: Van Allen belt radiation; GEO: solar radiation.

What four external disturbances affect spacecraft attitude control?

Solar, gravity-gradient, magnetic, and aerodynamic disturbances.

What is the Kármán line, and at what altitude is it located?

The commonly used boundary between Earth's atmosphere and outer space, located at approximately 100 km (62 miles) above sea level.

How does increased solar activity affect atmospheric density and spacecraft orbital lifetime?

Increased solar activity heats and expands the upper atmosphere, increasing density and drag at a given altitude, which generally decreases orbital lifetime.

Why are advanced atmospheric models, such as the Jacchia model, useful for spacecraft mission analysis?

They account for variations in atmospheric density that simple altitude-based exponential models cannot fully represent.

Radiation vs. Plasma

Radiation: Any means of emitting energy through waves or particles.

Plasma: A collection of charged particles, including electrons and ions.

Why is Earth's magnetic field important to the space environment?

It influences charged-particle motion and helps trap energetic particles within Earth's magnetosphere.

What are the Van Allen radiation belts

Regions of energetic charged particles (protons and electrons) trapped by Earth's magnetic field, formed through the interaction of solar wind and Earth's magnetosphere.

inner belt = primarily protons; outer belt = primarily electrons.

What is the Copernican (heliocentric) model?

The Sun-centered model of the solar system, where planets orbit the Sun.

What is Kepler's First Law?

Every planet moves in an elliptical orbit with the Sun at one focus.

What is Kepler's Second Law?

A line drawn from the Sun to a planet sweeps out equal areas in equal times.

What is Kepler's Third Law?

The square of a planet's orbital period is proportional to the cube of its orbit's semi-major axis (T² ∝ a³).

What is a Hohmann transfer?

A two-burn orbital maneuver that transfers a spacecraft between two coplanar circular orbits using an elliptical transfer orbit.

What is the purpose of the first burn in a Hohmann orbit-raising transfer?

What is the purpose of the second burn in a Hohmann orbit-raising transfer?

To accelerate the spacecraft from its initial circular orbit into an elliptical transfer orbit.

To circularize the spacecraft's orbit at the higher altitude.

Why are orbital plane changes expensive?

They require a large ΔV to change the direction of the spacecraft's velocity, especially at high orbital speeds.

What is a parking orbit?

A temporary orbit used before transfer to the final orbit, for satellite checkout, storage, or end-of-life disposal.

What is a transfer orbit?

A temporary intermediate orbit used to move a satellite to its final orbit.

What is the difference between GEO and GSO?

A geosynchronous orbit (GSO) has Earth's rotation period. A geostationary orbit (GEO) is circular and equatorial, appearing stationary over one point on Earth.

What is instantaneous field of view (IFOV)?

The region of Earth's surface visible to a satellite or its instrument at a given instant.

What affects satellite coverage?

Satellite altitude, orbital inclination, latitude, and coverage swath width.

What is high-thrust propulsion?

What are the main advantages of high-thrust propulsion?

What are the main disadvantages of high-thrust propulsion?

Propulsion that produces a large force over a short period, allowing rapid velocity changes (ΔV).

Rapid maneuvers, shorter transfer times, and the ability to perform large velocity changes quickly.

Typically lower specific impulse and higher propellant consumption for a given ΔV.

What is low-thrust propulsion?

What are the main advantages of low-thrust propulsion?

What are the main disadvantages of low-thrust propulsion?

Propulsion that produces a small force continuously over a long period, gradually changing a spacecraft's orbit.

High specific impulse (Isp), greater propellant efficiency, and lower propellant mass requirements.

Longer transfer times, low acceleration, and often significant electrical power requirements.

What are examples of primary propulsion applications?

Launch, orbit changes, orbit insertion, station keeping, and interplanetary escape.

What are examples of secondary propulsion applications?

Attitude control, disturbance reduction, and formation flying.

How does electric propulsion generally compare to chemical propulsion in terms of thrust?

Electric propulsion generally produces lower thrust than chemical propulsion.

How does increasing specific impulse affect required propellant mass?

Increasing \(I_{sp}\) decreases the propellant mass needed for a given ΔV and final mass.

How can propellant mass be decreased by changing specific impulse?

Increasing \(I_{sp}\) increases effective exhaust velocity, reducing the propellant required.

Why does electric propulsion generally require less propellant than chemical propulsion?

Electric propulsion has a higher specific impulse and effective exhaust velocity.

Chemical = high thrust, shorter trips, more propellant.

Electric = low thrust, longer trips, less propellant.

How does increasing ΔV affect the required propellant-to-final-mass ratio?

Increasing ΔV increases \(m_p/m_f\) for a fixed exhaust velocity.

How does increasing specific impulse affect propellant requirements?

Increasing \(I_{sp}\) increases exhaust velocity and decreases propellant requirements.

Why are low-\(I_{sp}\) propulsion systems poorly suited for high-ΔV missions?

They require extremely large amounts of propellant to achieve high ΔV.

Chemical Propulsion advantages

disadvantages

• High thrust for launch and shorter trip times.

• No external power supply required.

• Generally more flight heritage.

• Low \(I_{sp}\) means higher propellant requirements.

• Lower precision.

• Higher disturbances due to high thrust.

Electron propulsion advantages

disadvantages

• High \(I_{sp}\) means lower propellant requirements.

• Greater ΔV margin for relatively little additional propellant.

• High precision.

• Low disturbances due to low thrust.

• Low thrust results in longer trip times.

• Higher inert mass because of the power system.

• Generally less flight heritage than chemical propulsion.

What are the four main types of chemical propulsion discussed in class?

Cold gas, liquid, solid, and hybrid propulsion.

What is the main advantage and disadvantage of chemical propulsion overall?

High thrust and shorter trip times, but relatively low specific impulse and high propellant requirements.

What is regression rate in a solid rocket motor?

The rate at which the solid propellant's burning surface recedes

What is hybrid rocket propulsion?

What is a major advantage of hybrid rockets compared with solid rockets?

A propulsion system that typically combines solid fuel with a liquid or gaseous oxidizer

Hybrid rockets can offer greater controllability, including the ability to shut down thrust.

What are the three main types of electric propulsion?

Electrothermal, electrostatic, and electromagnetic.

How does electrothermal propulsion generate thrust?

How does electrostatic propulsion generate thrust?

How does electromagnetic propulsion generate thrust?

Electricity heats propellant, which expands through a nozzle.

Electric fields accelerate charged particles (ions).

Electric currents and magnetic fields interact to accelerate ionized gas.

What is the main difference between Hall and ion thrusters?

Ion thrusters use extraction grids to accelerate ions; Hall thrusters accelerate ions through an electric field in a magnetized plasma.

Why is a higher specific impulse not always better?

Higher Isp reduces propellant mass, but can require a heavier power system.

What are three major mission applications of electric propulsion?

High-ΔV missions, low-disturbance station keeping, and precision spacecraft control.

Why is electric propulsion useful for precision spacecraft control?

Its low thrust produces small, controllable forces with minimal disturbance.

What is the main trade-off between high Isp and time of flight in electric propulsion?

Higher Isp reduces propellant requirements, but can increase maneuver time at a given power level.

What are the three main phases of an interplanetary mission?

1. Geocentric escape (hyperbolic)
2. Heliocentric transfer (typically elliptical)
3. Planetocentric encounter (hyperbolic arrival)

What is the patched conics method?

A method of analyzing interplanetary trajectories by connecting simpler two-body orbits at planetary spheres of influence (SOIs).

What is a sphere of influence (SOI)?

An approximate region around a planet where its gravity is treated as dominant for trajectory calculations.

What is the Oberth effect?

A given ΔV produces a larger change in orbital energy when the spacecraft is traveling faster. Burns are therefore especially effective near periapsis.

What is a phase angle, and why is it important?

The required angular separation between departure and destination planets at launch so the spacecraft and destination arrive at the same location simultaneously.

What is a synodic period?

The time between repeating relative alignments of two planets, which determines how frequently similar transfer opportunities occur.

What is the difference between Type I and Type II transfers?

Type I travels less than 180° around the Sun; Type II travels more than 180°.

What is Max Q?

The point of maximum dynamic pressure during ascent, when aerodynamic loading is greatest. Engines may be throttled down to reduce loads.

What is a gravity turn (pitchover maneuver)?

A maneuver that gradually redirects the rocket from a mostly vertical ascent toward the horizontal velocity needed for orbit.