| 词条 | Space vehicle | |||
| 释义 |
A space vehicle or spaceship is a rocket-powered vehicle used to transport unmanned satellites or humans between the Earth's surface and outer space. The earliest space vehicles were expendable launch systems, consisting of rocket launch vehicles carrying spacecraft payloads (satellites or human-bearing space capsules) which were relatively small portions of the total vehicle size and mass.[1] The single or multistage rocket without the payload is referred to as a launch vehicle. Most space vehicles in production use are expendable systems, although reusable launch systems have been envisioned since the late 1960s.[2] Visionary space shipsThe "space ship" (or "rocket ship") was first envisioned in twentieth century science fiction, such as Flash Gordon, as a self-contained, presumably rocket-powered, unitized vehicle capable of reaching an extraterrestrial destination keeping its structure intact, and requiring only refueling, like an airplane. Real-world rocket technology did not make this possible; while the airplane requires an amount of fuel occupying a relatively small fraction of the total size and mass, the rocket requires an oxidizer in order to operate in the vacuum of space.[3] It also cannot use atmospheric air as its propellant; this function is served by the high-volume and high-mass fuel and oxidizer. Also, the high amount of energy required to reach at least low Earth orbital speed requires an extremely high proportion of propellant to dry vehicle mass. Also, mid-twentieth century structural technologies made it impossible to construct a single set of propellant tanks capable of holding enough mass to reach the required velocity. Thus, expendable multi-stage launch vehicles were the necessary design choice when spaceflight began in the late 1950s. Expendable space vehicles{{Main|Expendable launch system}}A majority of launch systems currently in use are expendable, designed to carry a single payload into space but not for recovery and reuse. They typically consist of several stages which detach in sequence as the vehicle gains speed and altitude and booster propellant is exhausted. Reusable space vehicles{{Main|Reusable launch system}}Reusable launch systems are capable of launching multiple payloads and can be recovered after each use. No entirely reusable system is currently employed by any space program, however, reusable systems are in active development by private space enterprises such as SpaceX and Blue Origin.{{Specify|date=September 2017}}GalleryReferences1. ^{{Cite web|title = Expendable Launch Vehicle Investigations - Space Flight Systems|url = https://spaceflightsystems.grc.nasa.gov/sopo/ihho/psrp/expendable/|website = Space Flight Systems|access-date = 2016-02-09|language = en-US}} 2. ^{{Cite web|title = Reusable Launch Vehicles and Lunar Return|url = http://www.airspacemag.com/daily-planet/reusable-launch-vehicles-and-lunar-return-180957849/?no-ist|website = Air & Space Magazine|access-date = 2016-02-09|first = Paul D.|last = Spudis}} 3. ^{{Cite web|title = PROPELLANTS|url = https://history.nasa.gov/conghand/propelnt.htm|website = history.nasa.gov|access-date = 2016-02-09}} 1 : Spaceflight |
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