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Explorer 49
Explorer 49 (also called Radio Astronomy Explorer-2, RAE-B) was a NASA satellite launched on 10 June 1973, for long wave radio astronomy research. It had four X-shaped antenna elements, which made it one of the largest spacecraft ever built. Mission The Radio Astronomy Explorer B (RAE-B) mission was the second of a pair of RAE satellites. It was placed into lunar orbit to provide radio astronomical measurements of the planets, the Sun, and the galaxy over the frequency range of 25-kHz to 13.1-MHz. The experiment complement consisted of two Ryle-Vonberg radiometers (nine channels each), three swept-frequency burst receivers (32 channels each), and an impedance probe for calibration. The experiment antenna package, made of BeCu, consisted of very long travelling wave antennas forming an X configuration: a upper V-antenna pointed away from the Moon; a lower V-antenna pointed toward the Moon; and a dipole antenna parallel to the lunar surface. There was also a boron libratio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of Australia). The Moon is a planetary-mass object with a differentiated rocky body, making it a satellite planet under the geophysical definitions of the term and larger than all known dwarf planets of the Solar System. It lacks any significant atmosphere, hydrosphere, or magnetic field. Its surface gravity is about one-sixth of Earth's at , with Jupiter's moon Io being the only satellite in the Solar System known to have a higher surface gravity and density. The Moon orbits Earth at an average distance of , or about 30 times Earth's diameter. Its gravitational influence is the main driver of Earth's tides and very slowly lengthens Earth's day. The Moon's orbit around Earth has a sidereal period of 27.3 days. During each synodic period ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nickel–cadmium Battery
The nickel–cadmium battery (Ni–Cd battery or NiCad battery) is a type of rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes. The abbreviation ''Ni-Cd'' is derived from the chemical symbols of nickel (Ni) and cadmium (Cd): the abbreviation ''NiCad'' is a registered trademark of SAFT Corporation, although this brand name is commonly used to describe all Ni–Cd batteries. Wet-cell nickel-cadmium batteries were invented in 1899. A Ni-Cd battery has a terminal voltage during discharge of around 1.2 volts which decreases little until nearly the end of discharge. The maximum electromotive force offered by a Ni-Cd cell is 1.3V. Ni-Cd batteries are made in a wide range of sizes and capacities, from portable sealed types interchangeable with carbon-zinc dry cells, to large ventilated cells used for standby power and motive power. Compared with other types of rechargeable cells they offer good cycle life and performance at low temperatures with a fai ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Decibel
The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a power ratio of 101/10 (approximately ) or root-power ratio of 10 (approximately ). The unit expresses a relative change or an absolute value. In the latter case, the numeric value expresses the ratio of a value to a fixed reference value; when used in this way, the unit symbol is often suffixed with letter codes that indicate the reference value. For example, for the reference value of 1 volt, a common suffix is " V" (e.g., "20 dBV"). Two principal types of scaling of the decibel are in common use. When expressing a power ratio, it is defined as ten times the logarithm in base 10. That is, a change in ''power'' by a factor of 10 corresponds to a 10 dB change in level. When expressing root-power quantities, a change in ''ampl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Principal Investigator
In many countries, the term principal investigator (PI) refers to the holder of an independent grant and the lead researcher for the grant project, usually in the sciences, such as a laboratory study or a clinical trial. The phrase is also often used as a synonym for "head of the laboratory" or "research group leader". While the expression is common in the sciences, it is used widely for the person or persons who make final decisions and supervise funding and expenditures on a given research project. A co-investigator (Co-I) assists the principal investigator in the management and leadership of the research project. There may be a number of co-investigators supporting a PI. Federal funding In the context of United States federal funding from agencies such as the National Institutes of Health (NIH) or the National Science Foundation (NSF), the PI is the person who takes direct responsibility for completion of a funded project, directing the research and reporting directly to the fun ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ecliptic
The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic against the background of stars. The ecliptic is an important reference plane and is the basis of the ecliptic coordinate system. Sun's apparent motion The ecliptic is the apparent path of the Sun throughout the course of a year. Because Earth takes one year to orbit the Sun, the apparent position of the Sun takes one year to make a complete circuit of the ecliptic. With slightly more than 365 days in one year, the Sun moves a little less than 1° eastward every day. This small difference in the Sun's position against the stars causes any particular spot on Earth's surface to catch up with (and stand directly north or south of) the Sun about four minutes later each day than it would if Earth did not orbit; a day on Earth is therefore 24 hours ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Revolutions Per Minute
Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionless unit equal to 1, which it refers to as a revolution, but does not define the revolution as a unit. It defines a unit of rotational frequency equal to s−1. The superseded standard ISO 80000-3:2006 did however state with reference to the unit name 'one', symbol '1', that "The special name revolution, symbol r, for this unit is widely used in specifications on rotating machines." The International System of Units (SI) does not recognize rpm as a unit, and defines the unit of frequency, Hz, as equal to s−1. :\begin 1~&\text &&=& 60~&\text \\ \frac~&\text &&=& 1~&\text \end A corresponding but distinct quantity for describing rotation is angular velocity, for which the SI unit is the ra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Apogee Kick Motor
An apogee kick motor (AKM) is a rocket motor A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propulsive jet of fluid, usually high-temperature gas. Rocket engines are reaction engines, producing thrust by ejecting mass rearward, in accordan ... that is regularly employed on artificial satellites to provide the final impulse to change the trajectory from the transfer orbit into its final (most commonly circular) orbit. For a satellite launched from the Earth, the rocket firing is done at the highest point of the transfer orbit, known as the apsis, apogee. An apogee kick motor is used, for example, for satellites launched into a geostationary orbit. As the vast majority of geostationary satellite launches are carried out from spaceports at a significant distance away from Earth's equator, the carrier rocket often only launches the satellite into an orbit with a non-zero inclination approximately equal to the latitude of the l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Command Guidance
Command guidance is a type of missile guidance in which a ground station or aircraft relay signals to a guided missile via radio control or through a wire connecting the missile to the launcher and tell the missile where to steer to intercept its target. This control may also command the missile to detonate, even if the missile has a fuze. Typically, the system giving the guidance commands is tracking both the target and the missile or missiles via radar. It determines the positions and velocities of a target and a missile, and calculates whether their paths will intersect. If not, the guidance system will relay commands to a missile, telling it to move the fins in a way that steers in the direction needed to maneuver to an intercept course with the target. If the target maneuvers, the guidance system can sense this and update the missiles' course continuously to counteract such maneuvering. If the missile passes close to the target, either its own proximity or contact fuze will ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Explorer 38
Explorer 38 (also called as Radio Astronomy Explorer A, RAE-A and RAE-1) was the first NASA satellite to study Radio astronomy. Explorer 38 was launched as part of the Explorer program, being the first of the 2 RAE-satellites. Explorer 38 was launched on 4 July 1968 from Vandenberg Air Force Base, California, with a Delta J launch vehicle. Spacecraft Explorer 38 spacecraft measured the intensity of celestial radio sources, particularly the Sun, as a function of time, direction and frequency (0.2 to 20-MHz). The spacecraft was gravity-gradient stabilized. The spacecraft weight was , and average power consumption was 25 watts. It carried two long V-antennas, one facing toward the Earth and one facing away from the Earth. A long dipole antenna was oriented tangentially with respect to the Earth's surface. The spacecraft was also equipped with one 136-MHz telemetry turnstile. The onboard experiments consisted of four step-frequency Ryle-Vonberg radiometers operating from 0. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clementine (spacecraft)
''Clementine'' (officially called the Deep Space Program Science Experiment (DSPSE)) was a joint space project between the Ballistic Missile Defense Organization (previously the Strategic Defense Initiative Organization) and NASA, launched on January 25, 1994. Its objective was to test sensors and spacecraft components in long-term exposure to space and to make scientific observations of both the Moon and the near-Earth asteroid 1620 Geographos. Results Observation of the asteroid was not made due to a malfunction in the spacecraft. The lunar observations included imaging at various wavelengths in the visible as well as in ultraviolet and infrared, laser ranging altimetry, gravimetry, and charged particle measurements. These observations were for the purposes of obtaining multi-spectral imaging of the entire lunar surface, assessing the surface mineralogy of the Moon, obtaining altimetry from 60N to 60S latitude, and obtaining gravity data for the near side. There were als ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gravity Gradient Technology Satellite
The Gravity Gradient Test Satellite was launched by the US Air Force from Cape Canaveral LC41 aboard a Titan IIIC rocket on June 16, 1966, at 14:00:01 UTC. The satellite was launched along with seven IDCSP satellites, with which it shared a bus. In contrast to the solar-powered IDCSP satellites, GGTS was battery powered. GGTS utilized the Magnetically Anchored Gravity Systems (MACS), which consisted of two identical subsystem packages, each containing an extensible rod unit and a magnetically anchored spherical viscous damper. The rod units had an extended length of , and their damper tip weights gave the satellite a symmetric dumbbell configuration. The dampers were produced by General Electric and consisted of two concentric spheres separated by a viscous damping fluid. The internal sphere contained a hollow cylindrical magnet which served to "anchor' the inner sphere to the Earth's magnetic field, stabilizing the satellite over time. It had been hoped that within 60 days of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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