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Built-in Hold
A built-in hold is a period in a launch countdown during which no activities are scheduled and the countdown clock is stopped. The hold serves as a milestone in the countdown, an opportunity for non-launch activities (such as a shift change or meal break), and a chance to perform unanticipated activities such as equipment repair. Most importantly, a hold provides an opportunity to synchronize the pre-launch activity schedule (concluding at T−0) with the desired wall-clock time of launch (L−0). Activities might take more or less time than planned, or the launch time might be moved, e.g. due to weather. A planned hold may be of a fixed or variable duration. Criteria for exiting the hold and restarting the countdown may be based on a fixed time, the completion of a checklist of work items, or a go/no-go decision from mission management. For example, space shuttle launch countdowns begin at T−43 hours and include seven holds at T−27 hours, T−19 hours, T−11 hours, T− ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Timeframe
Time is the continuous progression of existence that occurs in an apparently irreversible succession from the past, through the present, and into the future. It is a component quantity of various measurements used to sequence events, to compare the duration of events (or the intervals between them), and to quantify rates of change of quantities in material reality or in the conscious experience. Time is often referred to as a fourth dimension, along with three spatial dimensions. Time is one of the seven fundamental physical quantities in both the International System of Units (SI) and International System of Quantities. The SI base unit of time is the second, which is defined by measuring the electronic transition frequency of caesium atoms. General relativity is the primary framework for understanding how spacetime works. Through advances in both theoretical and experimental investigations of spacetime, it has been shown that time can be distorted and dilated, par ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Launch Countdown
A countdown is a sequence of backward counting to indicate the time remaining before an event is scheduled to occur. NASA commonly employs the terms "L-minus" and "T-minus" during the preparation for and anticipation of a rocket launch, and even "E-minus" for events that involve spacecraft that are already in space, where the "T" could stand for "Test" or "Time", and the "E" stands for "Encounter", as with a comet or some other space object, like a spacecraft. Other events for which countdowns are commonly used include the detonation of an explosive, the start of a race, the start of the New Year, or any anxiously anticipated event. An early use of a countdown once signaled the start of a Cambridge University rowing race. One of the first known associations with rockets was in the 1929 German science fiction movie ''Frau im Mond'' (English: ''Woman in the Moon'') written by Thea von Harbou and directed by Fritz Lang in an attempt to increase the drama of the launch sequence o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Milestone (project Management)
Milestones are tools used in project management to mark specific points along a project timeline. These points may signal anchors such as a project start and end date, or a need for external review or input and budget checks. Some contracts for products include a "milestone fee" that may be paid out when certain points are achieved. In many instances, milestones do not impact project duration. Instead, they focus on major progress points that must be reached to achieve success. Using milestones in scheduling Milestones can add significant value to project scheduling. When combined with a scheduling methodology such as program evaluation and review technique or the critical path method, milestones allow project managers to much more accurately determine whether or not the project is on schedule. By constraining the dates associated with milestones, the critical path can be determined for major schedule intervals in addition to the entire project. Slack/float can also be cal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Go/no-go
A go/no-go test is a two-step verification process that uses two boundary conditions, or a binary classification. The test is passed only when the ''go'' condition has been met and also the ''no-go'' condition has failed. The test gives no information as to the degree of conformance to, or deviation from the boundary conditions. These tests can be used for statistical process control purposes. There are specific SPC tools that use parameter based measurements (e.g., P-charts) for determining the stability of a process. It has uses in engineering, psychology, military, and manufacturing. For example, a rocket launch status check involves a go/no-go test. Uses Engineering In engineering the test is traditionally used only to check noncritical parameters where the manufacturing process is believed to be stable and well controlled, and the tolerances are wide compared to the distribution of the parameter. For example, the preceding launch status checks before a Space Shuttle ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mission Control Center
A mission control center (MCC, sometimes called a flight control center or operations center) is a facility that manages spaceflight, space flights, usually from the point of launch until landing or the end of the mission. It is part of the ground segment of spacecraft operations. A staff of flight controllers and other support personnel monitor all aspects of the mission using telemetry, and send commands to the vehicle using ground stations. Personnel supporting the mission from an MCC can include representatives of the attitude control system, electric power, power, spacecraft propulsion, propulsion, thermal, attitude dynamics and control, attitude dynamics, orbital operations and other subsystem disciplines. The training for these missions usually falls under the responsibility of the flight controllers, typically including extensive rehearsals in the MCC. Government-operated Mission Control Centers ;America * Launch Control Center, NASA Launch Control Center controls NASA ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hour
An hour (symbol: h; also abbreviated hr) is a unit of time historically reckoned as of a day and defined contemporarily as exactly 3,600 seconds ( SI). There are 60 minutes in an hour, and 24 hours in a day. The hour was initially established in the ancient Near East as a variable measure of of the night or daytime. Such seasonal hours, also known as temporal hours or unequal hours, varied by season and latitude. Equal hours or equinoctial hours were taken as of the day as measured from noon to noon; the minor seasonal variations of this unit were eventually smoothed by making it of the mean solar day. Since this unit was not constant due to long term variations in the Earth's rotation, the hour was finally separated from the Earth's rotation and defined in terms of the atomic or physical second. It is a non-SI unit that is accepted for use with SI. In the modern metric system, one hour is defined as 3,600 atomic seconds. However, on rare occasions an hour may inc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Minute
A minute is a unit of time defined as equal to 60 seconds. It is not a unit in the International System of Units (SI), but is accepted for use with SI. The SI symbol for minutes is min (without a dot). The prime symbol is also sometimes used informally to denote minutes. In the UTC time standard, a minute on rare occasions has 61 seconds, a consequence of leap seconds; there is also a provision to insert a negative leap second, which would result in a 59-second minute, but this has never happened in more than 40 years under this system. History Al-Biruni first subdivided the hour sexagesimally into minutes, seconds, thirds and fourths in 1000 CE while discussing Jewish months. Historically, the word "minute" comes from the Latin ''pars minuta prima'', meaning "first small part". This division of the hour can be further refined with a "second small part" (Latin: ''pars minuta secunda''), and this is where the word "second" comes from. For even further refinement, the term ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States's civil list of government space agencies, space program, aeronautics research and outer space, space research. National Aeronautics and Space Act, Established in 1958, it succeeded the National Advisory Committee for Aeronautics (NACA) to give the American space development effort a distinct civilian orientation, emphasizing peaceful applications in space science. It has since led most of America's space exploration programs, including Project Mercury, Project Gemini, the 1968–1972 Apollo program missions, the Skylab space station, and the Space Shuttle. Currently, NASA supports the International Space Station (ISS) along with the Commercial Crew Program and oversees the development of the Orion (spacecraft), Orion spacecraft and the Sp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
