Rocket Launch Technology-Phases in Interplanetary Mission
Phases in interplanetary mission
Rocket is a system of variable mass i.e total mass of rocket, including fuel and oxidizer gas goes on decreasing due to burning of fuel. It is based on the conservation of linear momentum.Interplanetary mission is divided in four phases; The Launch Phase, the Cruise Phase, the Encounter Phase, and the Extended Operations phase.
Launch phase The launch phase of a spacecraft comprises a period of powered flight during which the vehicle rises above Earth's atmosphere and accelerates at least to orbital velocity. Powered flight ends when the rocket's last stage burns out, and the spacecraft separates and continues in freefall. If the spacecraft has achieved escape velocity from Earth's gravitation, rather than entering Earth orbit, its flight path will then be purely a solar orbit (since the launch pad was also in solar orbit).To date, the only practical way to produced the propulsive energy needed for launching the spacecraft from the earth has been by the combustion of chemical propellants. Mass drives and Ion engine propulsion can also be used in future days for the propulsion during the launch phase. There are two groups of propellants for chemical combustion, liquids, and solids. Many spacecraft uses the both types of fuels, for example the solid boosters attached to liquid propellant. Hybrid rockets, which use the combination of both, solid and liquid also being developed. Solid rockets are generally simpler than liquid, but they can't be shut down once ignited. Liquid and hybrid engines may be shut down after ignition and again can be re ignited.
Cruise Phase Cruise phase is the time period between the launch phase and encounter phase. It may be as short as a few months up to years. It is a time during which ground system upgrades and tests may be conducted, and spacecraft flight software modifications are implemented and tested. after launch, the spacecraft is commanded to configure for cruise. Telemetry is analyzed to determine the health of the spacecraft, indicating how well it survived its launch. Any components that appear questionable might be put through test specially designed and commanded in or near real time, and their actual state determined as closely as possible by subsequent telemetry analysis. During the cruise period, additional command sequences are uplinked and loaded aboard for execution, to replace the command sequence exercised during launch. These take the spacecraft through its routine cruise operations, such as tracking Earth with its HGA and monitoring celestial references for attitude control . Flight team member begin to get the feel of their spacecraft in flight.
Encounter Phase The term encounter used here is used to indicate the high priority data gathering period of the operations for which the mission was intended. It may last a few month or weeks or even less. In some cases it may extended up to the few years. The encounter phase can be further divided into many sub-phases. The name of the sub-phases is different according to the missions. For example, during the each of the six Voyager encounter, the sub phases are called observatory phase, far encounter phase, near encounter phase, and post Encounter phase. these phases have given other name in different missions.A flyby spacecraft has a limited opportunity to gather data. Its operations are planned years in advance of the encounter, and the plans are refines and practiced in the months prior to the encounter date, sequence of the commands are prepared, tested and uplinked by the flight to carry out operations in various sub phases of the encounter phase, depending on the spacecraft distance from its target. After encounter, instrument calibrations are repeated to be sure that any changes in the instruments state.
Extended Operation Phase The primary objective of the mission's is tentatively known well during the time of launch. The efforts of the all flight team members are concentrated toward achieving those objectives. The aim of the mission is success when it gathers enough data to complete the originally stated objectives. Once a spacecraft has completed its primary objectives, it may still be in a healthy and operable state. Since, it has already undergone all the efforts involved in conception, design and construction, launch, cruise and perhaps orbit insertion, it can be very economical to redirect an existing spacecraft toward new objectives and to retrieve data over.Once a mission has ended, the flight team no longer work together and the ground hardware are sent into long term storage. Sometimes it is possible to donate excess of computer to schools.
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