A radio science subsystem (RSS) is a

subsystem A system is a group of interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its environment, is described by its boundaries, structure and purpose and expresse ...

placed on board a

spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...

for

radio science One way of outlining the subject of ''radio science'' is listing the topics associated with it by authoritative bodies. Union of Radio Science International (URSI) The International Union of Radio Science has several commissions corresponding to ...

purposes.

Function of the RSS

The RSS uses radio signals to probe a

medium Medium may refer to: Science and technology Aviation *Medium bomber, a class of war plane *Tecma Medium, a French hang glider design Communication * Media (communication), tools used to store and deliver information or data * Medium of ...

such as a planetary atmosphere. The spacecraft transmits a highly stable signal to ground stations, receives such a signal from ground stations, or both. Since the transmitted signal

parameter A parameter (), generally, is any characteristic that can help in defining or classifying a particular system (meaning an event, project, object, situation, etc.). That is, a parameter is an element of a system that is useful, or critical, when ...

s are accurately known to the receiver, any changes to these parameters are attributable to the

propagation Propagation can refer to: * Chain propagation in a chemical reaction mechanism *Crack propagation, the growth of a crack during the fracture of materials * Propaganda, non-objective information used to further an agenda * Reproduction, and other fo ...

medium or to the relative motion of the spacecraft and ground station. The RSS is usually not a separate instrument; its functions are usually "

piggyback Piggyback, piggy-back, or piggybacking may mean: Transport * Piggyback (transportation), something that is riding on the back of something else Art, entertainment, and media * Splash cymbal piggybacking, mounting a cymbal on top of an already ...

ed" on the existing

telecommunication Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...

s subsystem. More advanced systems use multiple antennas with orthogonal polarizations.

Radio science

Radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmi ...

science is commonly used to determine the

gravity field In physics, a gravitational field is a model used to explain the influences that a massive body extends into the space around itself, producing a force on another massive body. Thus, a gravitational field is used to explain gravitational phenome ...

of a

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 ...

planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...

by observing Doppler shift. This requires a highly stable oscillator on the spacecraft, or more commonly a "2-way coherent"

transponder In telecommunications, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a blend of ''transmitter'' and ''responder''. In air navigation or radio frequency identification, a flight trans ...

that phase locks the transmitted signal frequency to a rational multiple of a received

uplink In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or sha ...

signal that usually also carries spacecraft commands. Another common radio science observation is performed as a spacecraft is occulted by a planetary body. As the spacecraft moves behind the planet, its radio signals cuts through successively deeper layers of the planetary atmosphere. Measurements of signal strength and polarization vs time can yield data on the composition and temperature of the atmosphere at different altitudes. It is also common to use multiple

radio frequencies Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upper ...

coherently derived from a common source to measure the dispersion of the propagation medium. This is especially useful in determining the free

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

content of a planetary ionosphere.

Spacecraft using RSS

* Cassini–Huygens *

Mariner 2 Mariner 2 (Mariner-Venus 1962), an American space probe to Venus, was the first robotic space probe to conduct a successful planetary encounter. The first successful spacecraft in the NASA Mariner program, it was a simplified version of the B ...

, 4,5,6,7,9, and 10 * Voyager 1 and 2 * MESSENGER *

Venus Express ''Venus Express'' (VEX) was the first Venus exploration mission of the European Space Agency (ESA). Launched in November 2005, it arrived at Venus in April 2006 and began continuously sending back science data from its polar orbit around Venus. ...

Functions

* Determine composition of gas clouds such as atmospheres,

solar corona A corona ( coronas or coronae) is the outermost layer of a star's atmosphere. It consists of plasma. The Sun's corona lies above the chromosphere and extends millions of kilometres into outer space. It is most easily seen during a total solar ...

s. * Characterize gravitational fields * Estimate masses of celestial

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioi ...

s that do not have satellites of their own. * To estimate particle size of particle fields * Estimate densities of ion fields.Instruments - RSS: Radio Science Subsystem
Cassini-Huygens, ESA

Specifications

* Given a

deep space network The NASA Deep Space Network (DSN) is a worldwide network of American spacecraft communication ground segment facilities, located in the United States (California), Spain (Madrid), and Australia (Canberra), that supports NASA's interplanetary ...

(DSN) of receivers and/or transmitters. *A

Ka-band The Ka band (pronounced as either "kay-ay band" or "ka band") is a portion of the microwave part of the electromagnetic spectrum defined as frequencies in the range 26.5–40 gigahertz (GHz), i.e. wavelengths from slightly over one centime ...

traveling wave tube A traveling-wave tube (TWT, pronounced "twit") or traveling-wave tube amplifier (TWTA, pronounced "tweeta") is a specialized vacuum tube that is used in electronics to amplify radio frequency (RF) signals in the microwave range. The TWT belongs t ...

amplifier An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It may increase the power significantly, or its main effect may be to boost t ...

(K-TWTA) amplifies signals to a transmitting antenna to be received by a distal radio telescope. *Ka-band translator (KAT) receives signal from a high gain antenna and retransmits the signal back to DSN. In this way the phase and phase-shift resulting from signal modification *Ka-band exciter (KEX) it supplies

telemetry Telemetry is the in situ collection of measurements or other data at remote points and their automatic transmission to receiving equipment (telecommunication) for monitoring. The word is derived from the Greek roots ''tele'', "remote", an ...

data. *S-band transmitter is used for radio science experiments. The transmitter receives signal from the RFS, amplifies and multiplies the signal, sending a 2290 MHz signal to the antenna. *Filter microwave emitter allow only

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...

s of a given

frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

to be emitted, there is a polarizing element. There are two-bypass filters and a wave-guide. The bypass filters allow different feed polarizations, receiving and transmitting.

References

{{Satellite and spacecraft instruments Embedded systems Spacecraft instruments