When you look up at night and see an arcing trail of light arcing across the sky, those are spacecraft in orbit. Scientists figured out their orbits long before humans ventured into space travel.
Orbits are circular paths followed by satellites, asteroids and planets around Earth under control of gravity.
Spacecraft
Spacecraft are vehicles or robots designed to fly outside the Earth’s atmosphere and beyond its atmosphere, often for communications, weather observations, navigation and exploration of outer space. Manned spacecraft carry crew or passengers as crew or passengers while robotic spacecraft typically operate autonomously or telerobotically.
Spacecraft in orbit are equipped with payloads such as cameras to record images; cameras for recording videos; cameras to measure atmospheric and surface spectrometers, radar to investigate subsurface phenomena and landers like Cassini’s Huygens and Rosetta’s Philae, which both successfully landed on Saturn’s moon Titan and comet 67P/Churyumov-Gerasimenko respectively.
Today there are approximately 500 thousand objects orbiting Earth; these range in size from paint flecks to full-fledged satellites; however, collisions between satellites remain very unlikely.
Rockets
Rockets can be simply defined as chambers filled with pressurized gas that, when released through an opening at one end, exert force in the opposite direction. Rockets use fuel to accelerate to high speeds needed to reach space; however, most people wish for their spacecraft to achieve orbit and remain there long-term; centuries ago scientists developed ways of making this possible.
Satellites and crew must maintain an initial cosmic velocity of 28,000 km/h to remain in orbit around Earth; this allows them to escape Earth’s gravity and head toward other planets – something the International Space Station does successfully.
Mid-course corrections
Spacecraft must use mid-course corrections to stay on course toward their destination, which require firing small bursts of rocket fuel as mid-course corrections. They’re crucial in ensuring successful mission results.
Apollo 11 required one when returning from its Moon voyage; otherwise, its spacecraft would have reentered Earth’s atmosphere too quickly and risked an imminent fiery explosion.
The JWST will employ three maneuvers planned under its Mission Control Center (MCC) maneuvers to enter into an orbit near L2 in which it will orbit nearly halolike. This paper explores their design and modeling, with contingency plans prepared for their planning and monitoring, using high-order state transition tensors to characterize transfer and libration orbits, along with Monte Carlo simulations to evaluate their performance as guidance for onboard control systems.
Orbital trajectories
Satellites that orbit Earth provide communications, navigation, weather forecasting and astronomy observations. To do this, their spacecraft must follow complex set of trajectories designed with orbital mechanics as their mathematical basis.
Orbital trajectories can either be circular (round) or elliptical. An ellipse is defined as a curve with two points called foci that each have their own fixed ratio of distance from them – this ratio being called its semimajor axis and minor axis respectively.
An extra rocket burn must be used to achieve more elliptical orbits like that which hosts the International Space Station and astronauts live for months at a time; passing through a node (point of minimum eccentricity) at just the right moment requires extra thrust from this thrusting thruster rocket.
Reentry
Just as quickly rubbing two hands together can generate heat, spacecraft reentering Earth’s atmosphere create tremendous amounts of frictional heating that must be managed carefully in order to be successful in handling its loads safely. It is an exceptionally dangerous process which demands that vehicles be designed accordingly in terms of shape and engineering to avoid becoming overheated during this process.
Reentry into Earth usually follows a carefully orchestrated plan and occurs along a space corridor known as a “reentry corridor”. The goal of reentry is to safely land vehicles, cargo, and passengers at their target areas on Earth.
All objects in orbit are affected by gravity and will eventually reenter our atmosphere, with those not designed for this event reentering as debris or fragmenting when they hit. Near the time of reentry SpaceTrack issues TIP messages with more accurate predictions as to where debris may land.