TD-1A, or Thor-Delta 1A (or just TD-1), was a
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
an
astrophysical
Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. As one of the founders of the discipline said, Astrophysics "seeks to ascertain the nature of the h ...
research
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 radioisotope ...
which was launched in 1972. Operated by the
European Space Research Organisation
The European Space Research Organisation (ESRO) was an international organisation founded by 10 European nations with the intention of jointly pursuing scientific research in space. It was founded in 1964. As an organisation ESRO was based on a ...
, TD-1A made
astronomical survey
An astronomical survey is a general map or image of a region of the sky (or of the whole sky) that lacks a specific observational target. Alternatively, an astronomical survey may comprise a set of images, spectra, or other observations of obje ...
s primarily in the
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
, but also using
x-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
and
gamma ray
A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...
detectors.
Spacecraft
TD-1A was named after the
Thor-Delta
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 ...
series of rockets, a derivative of which was used to launch it. It was a satellite which measured by by . The spacecraft was
three-axis stabilised, with
sun sensor
A sun sensor is a navigational instrument used by spacecraft to detect the position of the sun. Sun sensors are used for attitude control, solar array pointing, gyro updating, and fail-safe recovery.
In addition to spacecraft, sun sensors fin ...
s used to maintain a constant attitude with respect to the
Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
.
Instruments
![TD-1A detectors diagram](https://upload.wikimedia.org/wikipedia/commons/2/25/TD-1A_detectors_diagram.gif)
Seven instruments were carried aboard TD-1A, with a combined mass of .
The
Stellar UV Radiation Experiment
Stellar means anything related to one or more stars (''stella''). The term may also refer to:
Arts, entertainment, and media
* ''Stellar'' (magazine), an Irish lifestyle and fashion magazine
* Stellar Loussier, a character from ''Mobile Suit Gun ...
, operated by
University College London
, mottoeng = Let all come who by merit deserve the most reward
, established =
, type = Public research university
, endowment = £143 million (2020)
, budget = ...
and the
University of Liège
The University of Liège (french: Université de Liège), or ULiège, is a major public university of the French Community of Belgium based in Liège, Wallonia, Belgium. Its official language is French. As of 2020, ULiège is ranked in the 301 ...
, consisted of a ultraviolet telescope, attached to a
spectrometer
A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the ...
. It was used to study
extinction
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
and to produce a
star catalogue
A star catalogue is an astronomical catalogue that lists stars. In astronomy, many stars are referred to simply by catalogue numbers. There are a great many different star catalogues which have been produced for different purposes over the years, ...
using ultraviolet observations. UV range 135 to 255 nm.
The
UV Stellar Spectrometer was operated by the Astronomical Institute of
Utrecht University
Utrecht University (UU; nl, Universiteit Utrecht, formerly ''Rijksuniversiteit Utrecht'') is a public research university in Utrecht, Netherlands. Established , it is one of the oldest universities in the Netherlands. In 2018, it had an enrollme ...
. It consisted of a grating
spectrometer
A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the ...
attached to a
Cassegrain reflector
The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas, the main characteristic being that the optical path folds back onto itself, relative to th ...
telescope. UV measurements at 216, 255 & 286 nm.
Spectrometry of Primary Charged Particles was an experiment conducted by the
Saclay Nuclear Research Centre
The CEA Paris-Saclay (formerly CEA Saclay) center is one of nine centers belonging to the French Alternative Energies and Atomic Energy Commission (CEA). The Saclay site hosts the administrative headquarters of the CEA. Historically, it was the hea ...
, which studied
cosmic ray
Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...
s, and measured their
charge spectra.
Spectrometry of Celestial X-Rays was another payload operated by the Saclay Nuclear Research Centre. It consisted of two slot
collimator
A collimator is a device which narrows a beam of particles or waves. To narrow can mean either to cause the directions of motion to become more aligned in a specific direction (i.e., make collimated light or parallel rays), or to cause the spati ...
s and a
proportional counter The proportional counter is a type of gaseous ionization detector device used to measure particles of ionizing radiation. The key feature is its ability to measure the energy of incident radiation, by producing a detector output pulse that is ''prop ...
, which were used to study the spectra of incident
x-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
s. Due to an encoder malfunction, the experiment was not operational for most of the first survey; it was deactivated a few months after launch and remained inactive until 1 July 1973; at the start of the second survey.
Solar Gamma-Rays in the 50 to 500 MeV Energy Range was an experiment operated by the
University of Milan
The University of Milan ( it, Università degli Studi di Milano; la, Universitas Studiorum Mediolanensis), known colloquially as UniMi or Statale, is a public research university in Milan, Italy. It is one of the largest universities in Europe ...
which was used to measure the
flux
Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ph ...
of solar gamma ray emissions. It consisted of
scintillator
A scintillator is a material that exhibits scintillation, the property of luminescence, when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate (i.e. re-emit the absorbed ...
s and
photomultiplier A photomultiplier is a device that converts incident photons into an electrical signal.
Kinds of photomultiplier include:
* Photomultiplier tube, a vacuum tube converting incident photons into an electric signal. Photomultiplier tubes (PMTs for sho ...
s, which measured the radiation. The
Solar X-Ray Monitor was operated by the Utrecht University. It used a scintillation counter to detect hard x-rays emitted by the Sun. The Saclay Nuclear Research Centre's
Gamma-Ray Measurement experiment used a
spark chamber {{short description, Charged particle detector
A spark chamber is a particle detector: a device used in particle physics for detecting electrically charged particles. They were most widely used as research tools from the 1930s to the 1960s and have ...
to detect gamma rays during the sky survey.
Launch
A
Delta N
The Delta N or Thor-Delta N was an American expendable launch system used for nine orbital launches between 1968 and 1972. It was a member of the Delta family of rockets, and the last Delta to be given an alphabetical designation - subsequent roc ...
, also known as the Thor-Delta N, was used to place it into orbit. The launch occurred at 01:55:08 UTC, from
Space Launch Complex 2E at
Vandenberg Air Force Base Vandenberg may refer to:
* Vandenberg (surname), including a list of people with the name
* USS General Harry Taylor (AP-145), USNS ''General Hoyt S. Vandenberg'' (T-AGM-10), transport ship in the United States Navy, sank as an artificial reef in K ...
.
The launch of TD-1A marked the final flight of the Delta N, and the last launch from Space Launch Complex 2E.
TD-1A was placed into a
low Earth orbit
A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never mor ...
; on 11 April 1974 it was tracked in an orbit with a
perigee
An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion.
General description
There are two apsides in any ellip ...
of , an
apogee
An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion.
General description
There are two apsides in any ellip ...
of , 97.5 degrees of
inclination
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...
, and a
period
Period may refer to:
Common uses
* Era, a length or span of time
* Full stop (or period), a punctuation mark
Arts, entertainment, and media
* Period (music), a concept in musical composition
* Periodic sentence (or rhetorical period), a concept ...
of 95.32 minutes.
Operation
TD-1A operated for twenty six months, conducting two complete sky surveys, and completing approximately half of a third scan, in all mapping 95 percent of the sky. By maintaining a constant orientation to the sun, TD-1A was able to scan a thin band of the sky on each orbit, and Earth's movement around the sun enabled it to scan the entire sky over a period of six months.
TD-1A was affected by reliability issues with an onboard tape recorder, used to store experimental data for transmission to Earth, however the fault was intermittent, and still enabled the completion of the spacecraft's mission.
An encoder problem led to the Spectrometry of Celestial X-rays experiment not being run during the first survey, however this was activated in time for the second survey, and was still completed successfully.
In May 1974, TD-1A ceased operations when its attitude control system depleted its last remaining propellant, leaving it unable to maintain its orientation. It
decayed from orbit and
reentered the atmosphere on 9 January 1980.
References
{{Orbital launches in 1972
Ultraviolet telescopes
Spacecraft launched in 1972
Spacecraft which reentered in 1980
History of University College London