Question: Information:  - A sounding rocket, sometimes called a research rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The rockets are used to carry instruments from above the surface of the Earth; the altitude generally between weather balloons and satellites (the maximum altitude for balloons is about and the minimum for satellites is approximately ). Certain sounding rockets, such as the Black Brant X and XII, have an apogee between ; the maximum apogee of their class. Sounding rockets often use military surplus rocket motors. NASA routinely flies the Terrier Mk 70 boosted Improved Orion lifting payloads into the exoatmospheric region between .  - Physics (from , from "phúsis" "nature") is the natural science that involves the study of matter and its motion and behavior through space and time, along with related concepts such as energy and force. One of the most fundamental scientific disciplines, the main goal of physics is to understand how the universe behaves.  - A rocket (from Italian "rocchetto" "bobbin") is a missile, spacecraft, aircraft or other vehicle that obtains thrust from a rocket engine. Rocket engine exhaust is formed entirely from propellant carried within the rocket before use. Rocket engines work by action and reaction and push rockets forward simply by expelling their exhaust in the opposite direction at high speed, and can therefore work in the vacuum of space.  - In astronomy, Kepler's laws of planetary motion are three scientific laws describing the motion of planets around the Sun.  - In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet about a star or a natural satellite around a planet. Normally, orbit refers to a regularly repeating path around a body, although it may occasionally be used for a non recurring trajectory or a path around a point in space. To a close approximation, planets and satellites follow elliptical orbits, with the central mass being orbited at a focal point of the ellipse, as described by Kepler's laws of planetary motion.  - In mathematics, an ellipse is a curve in a plane surrounding two focal points such that the sum of the distances to the two focal points is constant for every point on the curve. As such, it is a generalization of a circle, which is a special type of an ellipse having both focal points at the same location. The shape of an ellipse (how "elongated" it is) is represented by its eccentricity, which for an ellipse can be any number from 0 (the limiting case of a circle) to arbitrarily close to but less than 1.  - In the context of spaceflight, a satellite is an artificial object which has been intentionally placed into orbit. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as Earth's Moon.  - A planet is an astronomical body orbiting a star or stellar remnant that The term "planet" is ancient, with ties to history, astrology, science, mythology, and religion. Several planets in the Solar System can be seen with the naked eye. These were regarded by many early cultures as divine, or as emissaries of deities. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. In 2006, the International Astronomical Union (IAU) officially adopted a resolution defining planets within the Solar System. This definition is controversial because it excludes many objects of planetary mass based on where or what they orbit. Although eight of the planetary bodies discovered before 1950 remain "planets" under the modern definition, some celestial bodies, such as Ceres, Pallas, Juno and Vesta (each an object in the solar asteroid belt), and Pluto (the first trans-Neptunian object discovered), that were once considered planets by the scientific community, are no longer viewed as such.  - The Thor - Delta , also known as Delta DM - 19 or just Delta was an early American expendable launch system used for 12 orbital launches in the early 1960s . A derivative of the Thor - Able , it was a member of the Thor family of rockets , and the first member of the Delta family . The first stage was a Thor missile in the DM - 19 configuration . The second stage was the Delta , which had been derived from the earlier Able stage . An Altair solid rocket motor was used as a third stage . The Thor - Delta was the first rocket to use the combination of a Thor missile and a Delta upper stage . This configuration was reused for a large number of later rockets , and a derivative , the Delta II , remained in service into 2011 . The Thor - Delta launched a number of significant payloads , including the first communications satellite , Echo 1A ; the first British satellite , Ariel 1 ; and the first active direct - relay communications satellite , Telstar 1 . All 12 launches occurred from Cape Canaveral Air Force Station Launch Complex 17 . The launch of Telstar 1 used pad B , while all other launches were from pad A. All launches were successful except the maiden flight , which failed to place Echo 1 into orbit due a problem with the second stage .  - A natural satellite or moon is, in the most common usage, an astronomical body that orbits a planet or minor planet (or sometimes another Small Solar System Body).  - An expendable launch system is a launch system that uses an expendable launch vehicle (ELV) to carry a payload into space. The vehicles used in expendable launch systems are designed to be used only once (i.e. they are "expended" during a single flight), and their components are not recovered for re-use after launch. The vehicle typically consists of several rocket stages, discarded one by one as the vehicle gains altitude and speed.  - In physics, mass is a property of a physical body. It is the measure of an object's resistance to acceleration (a change in its state of motion) when a net force is applied. It also determines the strength of its mutual gravitational attraction to other bodies. The basic SI unit of mass is the kilogram (kg).  - The Thor-Able was an American expendable launch system and sounding rocket used for a series of re-entry vehicle tests and satellite launches between 1958 and 1960. It was a two stage rocket, consisting of a Thor IRBM as a first stage, and a Vanguard-derived Able second stage. On some flights, an Altair solid rocket motor was added as a third stage. It was a member of the Thor family, and an early predecessor of the Delta.  - A star is a luminous sphere of plasma held together by its own gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, the brightest of which gained proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the stars in the Universe, including all stars outside our galaxy, the Milky Way, are invisible to the naked eye from Earth. Indeed, most are invisible from Earth even through the most powerful telescopes.    After reading the paragraphs above, choose the best answer for the entity that related to 'thor-delta' with the relationship of 'subclass of'.  Choices: - aircraft  - astronomy  - behavior  - being  - class  - curve  - delta  - energy  - expendable launch system  - eye  - flight  - forward  - generalization  - human  - launch vehicle  - mass  - mathematics  - measurements  - member  - military  - minor planet  - missile  - motion  - natural  - natural satellite  - natural science  - object  - orbit  - path  - physics  - plane  - planet  - plasma  - point  - propellant  - property  - resolution  - rocket  - satellite  - science  - scientific knowledge  - series  - small solar system body  - solid  - sounding rocket  - spacecraft  - spaceflight  - sphere  - star  - study  - sum  - surface  - system  - term  - third  - thor  - trajectory  - vehicle  - work
Answer:
launch vehicle