Glossary - H
Half transponder mode
the technique of transmitting two TV channels on a single transponder by allocating each channel half of the bandwidth
(satellite communication, broadcasting)
Hand off
the transferring of a subscriber call from one satellite to another
(satellite communications)
Headend
the electronic control centre of a CATV system, usually including antennas, preamplifiers, frequency converters and demodulators
(broadcasting)
Heat pipe
a passive heat transfer device generally consisting of a pipe partially filled with a volatile liquid which uses a phase transition in the liquid to transfer heat
(spacecraft technology)
Heat shield
1: a thermal protection system used to protect a spacecraft from aerodynamic heating during high speed entry into a planet’s atmosphere
(spacecraft technology)
Heat shield
1: a thermal protection system used to protect temperature sensitive equipment such as fuel tanks and electronics from the heat generated by rocket engines
(launcher technology)
Heliocentric
Sun centred
(orbital geometry)
Heliopause
the boundary between the heliosphere and the surrounding interstellar medium
(solar physics)
Heliosphere
the vast volume of space around the sun in which the solar wind and sun’s magnetic field are dominant, rather than the plasma and magnetic field in the surrounding interstellar medium
(astrophysics)
Hohmann transfer orbit
an orbit linking the orbits of two objects in the Solar System allowing for movement between the two object with the minimum expenditure of energy
(orbital dynamics)
Horizon to horizon mount
a compact polar mount allowing a wide range of movement and accurate tracking
(earth station technology)
Hot staging
the firing of the rocket engines on an upper stage of a launch vehicle just prior to separation from the previous stage to give it the push to cleanly move away from the previous stage
(satellite communications)
Hour angle
the angle measured westwards along the celestial equator between the meridian plane (which contains the Earth’s axis and the zenith) and the hour circle (the plane containing the Earth’s axis and the celestial object of interest)
(astronomy)
Hub
large central earth station in a satellite network with a star topology
(satellite communications)
Hydrazine
a highly reactive, toxic compound (formula N2H4) used as a rocket fuel
(spacecraft technology, launcher technology)
Hydrometeors
rain, snow and hailstones
(communications)
Hypergolic propellant
a bipropellant rocket fuel in which the two components (fuel and oxidiser) ignite spontaneously on contact; the most common hypergolic propellant is dinitrogen tetroxide and hydrazine
(spacecraft technology, launcher technology)
