All spacecraft require propulsion methods to adjust their velocity. Most propulsion systems possess high specific impulse – that is, how quickly their speed changes per unit of propellant consumed – and are relatively energy efficient.
Earth lies deep within a gravitational well, taking 11.2 km/s to escape its gravitational pull; humans can endure much greater accelerations. There are various practical methods available for changing spacecraft’s velocity.
Launching
Launching spacecraft varies by vehicle and launch site, but generally involves powered flight through which a spacecraft ascends above Earth’s atmosphere to orbital velocity, at which point its final stage rocket separates and freefall continues into freefall.
Most satellites use simple chemical thrusters or resistojet rockets for station-keeping and attitude control, with chemical or resistojet rockets serving most orbits while Hall thrusters and ion thrusters being utilized on interplanetary missions; Hall thrusters employ positively charged molecules of unreactive fuel accelerated through an electric field to generate thrust. Ion thrusters use similar mechanisms.
Ion drives produce very low thrust but have an extremely high specific impulse (the rate at which energy consumed per unit weight on Earth). Other futuristic propulsion ideas include plasma sails and fission/fusion reactors; they may one day propel humans beyond Earth into outer space such as Mars. Though such concepts seem futuristic at first glance, NASA takes them seriously and plans on testing out several concepts such as these over the coming decades.
Orbiting
Once in orbit, spacecraft launched from rockets will remain within their designated path as long as their momentum from their rocket remains undiminished and Earth’s gravity pulls it in one direction. To alter their path, however, thrusters must be applied.
The most efficient method is firing thrusters at pericenter, or any point within the spacecraft’s orbit, which reduces Delta-V costs and allows us to easily modify its inclination with minimal amounts of propellant required.
Other methods involve firing thrusters to accelerate and decelerate a spacecraft, for instance by switching into brake mode. However, this requires significant orbital velocity changes; therefore it is more costly than simple acceleration.
Attitude control
Maintaining the attitude of a spacecraft is critical to ensure proper communications with Earth and precise onboard experiments for data collection and interpretation, heating/cooling effects from sun/shadow interactions can be utilized intelligently and short propulsive maneuvers are executed correctly.
Numerous systems exist to achieve this, such as control moment gyros, reaction wheels and spin stabilization; however, the primary method used by Voyagers since 1977 – and which consumes most of their propellant requirements – are small thrusters which continuously move back and forth within an accepted deadband of attitude error.
The control algorithm relies on feedback from multiple sensors with one or more axes, such as accelerometers, gyros and magnetic sensors with output signals converted by P controllers to rotation rate errors before being translated into motor commands by motor controllers.
High thrust
Spacecraft require propulsion subsystems for changing velocity, orbit altitude, station keeping and deorbit maneuvers. At present these needs are being fulfilled using high-tech chemical thrusters; however, electric propulsion subsystems are becoming an increasingly preferred technology option.
These systems use superconducting magnetic cells to ionize propellant gases into plasma, then expel it through a nozzle to produce high thrust, enabling velocity changes within minutes to hours rather than days using moderate-thrust chemical thrusters.
Like cars’ fuel efficiency ratings are measured in miles per gallon, spacecraft propulsion systems’ effectiveness is typically measured in specific impulse, which refers to how much their velocity changes with given amounts of propellant used. A system with high specific impulse can decrease overall mass and allow smaller rocket launches for satellite launches; currently Hall-effect thrusters – as part of Safran Aircraft Engines’s CHEOPS consortium – lead this category.
Propulsion systems on spacecrafts control its movement. This includes both rocket propulsion that propels them into orbit and thrusters for landing or reentry into Earth’s atmosphere.
Most systems require substantial power generation that adds weight and limits how much thrust can be produced, yet promising systems such as ion drives using superconducting electric accelerators could offer much more fuel-efficient propulsion for long space missions.
Spacecrafts
As spacecraft leave Earth, they must overcome Earth’s gravity to achieve their desired orbital velocity. A propulsion system provides this acceleration by propelling or decelerating according to velocity changes.
Most satellites use simple hydrazine thrusters for maneuvering and orbit adjustment, while others – like ion drives – use high speed expulsion of propellant ions from high velocity propellant ion drives to provide thrust.
Solar sailing employs sunlight’s mechanical force on large mirrors to exert mechanical pressure similar to wind pushing on a sailboat, while laser beams act as alternative light sources and exert more force; this process is known as “beam-sailing.” Both solar sailing and beam-sailing methods can accelerate spacecraft significantly faster than rocket engines while reaching other planets or star systems much quicker.
Engines
Propulsion systems of spacecraft use thrust to alter vehicle velocity. This is necessary for orbital maneuvering, interplanetary travel and landing operations. There are various propulsion methods; some can be quite efficient while others require substantial amounts of fuel.
Most vehicles utilize chemical rocket engines for launch. One notable exception is SpaceShipOne’s reentry system which utilizes an air-breathing engine. Satellites typically utilize simple reliable chemical rockets for orbital maneuvering while some geoorbiting spacecraft employ electric propulsion for stationkeeping purposes.
Few companies are exploring advanced fusion concepts that may enable faster trajectories to the inner Solar System and greater payload capacity. Such technologies generally require at least 1 gigawatt of power in order to produce enough thrust for thrust production.
Batteries
Batteries are self-contained units designed to store chemical energy and convert it to electrical power on demand. Batteries use the difference in bond energies of metals or oxides as sources for producing ions which travel from their positive electrode through electrolyte to reach their negative electrode.
Alkaline and nickel-cadmium (NiCad) batteries are inexpensive single-use disposable batteries with long lifespan. Rechargeable versions, including nickel metal hydride and lithium designs are available as secondary solutions.
Battery design demands consideration of the heat generated during cell discharge, since inadequate accommodation and dissipation could result in thermal runaway, leading to cell failure and potential thermal runaway. Battery cells may also be combined together into larger electrochemical devices like fuel cells or supercapacitors for high current at higher drain rates that is cost effective compared to individual batteries.
Fuels
Space travel captivates imagination and adventure, and watching a rocket blast off into space is nothing short of breathtaking. However, scientists work behind the scenes to solve complex equations which enable this feat – these calculations being based on Sir Isaac Newton’s laws of motion.
Propulsion methods typically entail altering a craft’s momentum by altering the velocity of some of its mass, known as its reaction mass. Unfortunately, this cannot be accomplished without fuel consumption which adds weight and costs to your vehicle.
Some systems employ electric power directly to accelerate reaction masses directly, however this limits energy efficiency and thrust/weight ratios. Ion drives have exhaust velocities significantly greater than their ideal rate resulting in excessive fuel use for very little acceleration.
Solar panels
Solar panels convert sunlight to electricity using numerous solar cells connected together and sealed in a frame. Their surfaces are protected with non-reflective glass to make sure sunlight reaches them and ensure maximum exposure to sunlight.
Solar cells generate electric current by having photons from the Sun strike them, knocking electrons off their atoms and giving the cell a negative charge, thus creating an electric current.
Solar power has quickly become one of the newest trends in space travel. We rely on it to power satellites and other spacecraft; houses and businesses also utilize it for energy purposes; trains, buses and cars using solar transit have even become popular ways of getting around our planet!