Kepler's first law states that planetary (and satellite) orbits are ellipses. What does this mean for a satellite in a circular orbit?

A circular orbit violates Kepler's first law and is only possible with continuous engine thrust A circular orbit is a special case of an ellipse where both foci are at the same point (the centre) Circular orbits follow Newton's laws rather than Kepler's laws Kepler's first law only applies to planets orbiting the Sun, not artificial satellites

Using Kepler's third law (T² ∝ a³), if a satellite at 400 km altitude (semi-major axis ≈ 6,771 km) has a 90-minute period, what happens to the period when a satellite is placed at a much higher orbit with a larger semi-major axis?

The period decreases — satellites travel faster at higher altitudes The period stays the same — orbital speed adjusts to compensate for altitude The period increases — a larger orbit always takes longer to complete The period doubles for every 1,000 km increase in altitude

The International Space Station orbits at approximately 400 km altitude. How many times does it orbit Earth each day, and how many sunrises do astronauts see?

About 1 orbit per day and 1 sunrise per day About 8 orbits per day and 8 sunrises per day About 24 orbits per day and 24 sunrises per day About 16 orbits per day and 16 sunrises per day

GPS satellites orbit at approximately 20,200 km altitude in Medium Earth Orbit with a 12-hour period. Why is MEO preferred over LEO for GPS?

MEO has less radiation than LEO, protecting GPS satellite electronics MEO satellites travel faster, which the GPS timing system relies on for accuracy MEO satellites cover a much larger area of Earth's surface from their higher altitude, so fewer satellites are needed for global coverage MEO has no atmospheric drag, so GPS satellites never need reboosting

A geostationary satellite appears fixed above the same point on Earth's surface. What two conditions must be met for this to be possible?

The satellite must orbit at 400 km altitude and match Earth's rotation speed The satellite must be directly above the North Pole to remain stationary The satellite must orbit at 35,786 km altitude (giving a 24-hour period) AND orbit directly above the equator The satellite must orbit in the opposite direction to Earth's rotation to cancel out relative motion

A weather satellite in geostationary orbit (GEO) has a poor view of polar regions. Why?

The poles are too cold for the satellite's sensors to function properly GEO satellites orbit above the equator, so they view polar regions at a very low angle, making imagery there distorted and of limited use Radio signals cannot reach polar regions from GEO altitude due to atmospheric interference The polar ice caps reflect satellite signals, preventing accurate imaging

A spacecraft in a 400 km circular orbit needs to transfer to a 35,786 km geostationary orbit using a Hohmann transfer. How many engine burns are required?

One continuous burn that gradually spirals the spacecraft outward Three burns: one at LEO, one at mid-point, and one at GEO Two burns: one to enter the elliptical transfer orbit and one to circularise at GEO Four burns: matching speed with GEO requires additional corrective manoeuvres

The total delta-v needed to launch from Earth's surface to LEO is approximately 9.4 km/s, but Earth's orbital velocity at LEO is only 7.8 km/s. Why is the required delta-v higher than the final orbital velocity?

The rocket must also decelerate to match the ISS speed before docking, which adds extra delta-v Extra delta-v is needed to overcome gravity losses (fighting gravity during ascent) and aerodynamic drag losses through the atmosphere LEO orbital velocity is measured relative to the Sun, not Earth's surface The rocket must orbit Earth once to build up speed before ascending to LEO

What is a satellite's ground track, and how does it differ between a geostationary satellite and an ISS-like LEO satellite?

The ground track is the satellite's visible path across the night sky; both GEO and LEO trace arcs across the stars The ground track is the path traced on Earth's surface below the satellite; GEO gives a single fixed point, while LEO gives a westward-shifting sinusoidal path each orbit GEO satellites have a circular ground track around the equator; LEO satellites trace straight lines over the poles Both GEO and LEO satellites have the same ground track pattern because Earth's rotation affects them equally

The Starlink broadband internet constellation uses thousands of satellites in LEO rather than a few satellites in GEO. What is the primary advantage of using LEO for internet communications?

LEO satellites use less power because they are closer to Earth's surface LEO satellites can broadcast TV signals to standard dish antennas without special equipment LEO satellites are much closer to Earth, giving signal round-trip times (latency) of ~20 ms compared to ~600 ms for GEO LEO satellites experience less radiation, extending their operational lifetime to 30+ years

What is Kessler syndrome, and why is it considered a serious long-term threat to spaceflight?

Kessler syndrome is the accumulation of rocket exhaust gases that create a haze reducing telescope effectiveness Kessler syndrome is a cascade of collisions where each impact creates debris that causes more collisions, potentially making certain orbits unusable Kessler syndrome refers to the gradual lowering of LEO orbits due to atmospheric drag, causing satellites to re-enter prematurely Kessler syndrome is electromagnetic interference between large satellite constellations that disrupts GPS signals

There are currently over 27,000 tracked objects larger than 10 cm in Earth orbit. What method do space agencies use to protect operational satellites from collision with tracked debris?

Placing electrostatic shields around satellites that repel incoming debris electromagnetically Launching debris-sweeper spacecraft that use magnetic nets to collect and de-orbit fragments Painting satellites bright white so ground telescopes can track them and warn operators in advance Conjunction analysis — regularly computing predicted close approaches and performing avoidance manoeuvres when the collision probability exceeds a threshold