
TAU (Thousand Astronomical Units) was a proposed
uncrewed
An uncrewed vehicle or unmanned vehicle is a vehicle without a person on board. Uncrewed vehicles can either be under telerobotic control—remote controlled or remote guided vehicles—or they can be autonomously controlled—autonomous vehicl ...
interstellar probe
An interstellar probe is a space probe that has left—or is expected to leave—the Solar System and enter interstellar medium, interstellar space, which is typically defined as the region beyond the Heliopause (astronomy), heliopause. It also r ...
that would go to a distance of one thousand
astronomical units
The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its mode ...
(1000 AU) from the Earth and Sun by the
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
Jet Propulsion Laboratory
The Jet Propulsion Laboratory (JPL) is a Federally funded research and development centers, federally funded research and development center (FFRDC) in La Cañada Flintridge, California, Crescenta Valley, United States. Founded in 1936 by Cali ...
in 1987 using tested technology. One scientific purpose would be to measure the distance to other stars via
stellar parallax
Stellar parallax is the apparent shift of position (''parallax'') of any nearby star (or other object) against the background of distant stars. By extension, it is a method for determining the distance to the star through trigonometry, the stel ...
. Studies continued into 1990, working with a launch in the 2005–2010 timeframe.
Overview
TAU was a proposed
nuclear electric rocket
A nuclear electric rocket (more properly nuclear electric propulsion) is a type of spacecraft propulsion system where thermal energy from a nuclear reactor is converted to electrical energy, which is used to drive an ion thruster or other electrica ...
spacecraft that used a 1
MW fission reactor and an
ion drive
An ion thruster, ion drive, or ion engine is a form of electrically powered spacecraft propulsion, electric propulsion used for spacecraft propulsion. An ion thruster creates a cloud of cation, positive ions from a neutral gas by ionizing i ...
(with a burn time of about 10 years) to reach a distance of 1000 AU in 50 years. The primary goal of the mission was to improve parallax measurements of the distances to stars inside and outside the
Milky Way
The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...
, with secondary goals being the study of the
heliopause, measurements of conditions in the
interstellar medium
The interstellar medium (ISM) is the matter and radiation that exists in the outer space, space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as cosmic dust, dust and cosmic rays. It f ...
, and (via communications with Earth) tests of
general relativity
General relativity, also known as the general theory of relativity, and as Einstein's theory of gravity, is the differential geometry, geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of grav ...
.
One of the tasks envisioned for TAU would be a flyby of
Pluto
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of Trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Su ...
. A Pluto flyby was achieved in 2015 by the
New Frontiers program
The New Frontiers program is a series of space exploration missions being conducted by NASA
The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the ...
mission ''
New Horizons
''New Horizons'' is an Interplanetary spaceflight, interplanetary space probe launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research Institut ...
''.
Some of the instruments proposed for the design included a 1.5-meter telescope for observations and a 1-meter telescope for laser communication with Earth.
After launch it would accelerate to about 106 km/s (about 22.4 AU/year, or ~0.04% the speed of light) over 10 years, using
xenon
Xenon is a chemical element; it has symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
as propellant and a nuclear fission reactor for power.
At a distance of 1000 AU parallax measurement will have a baseline 500 times longer than on Earth. With such a long baseline the parallax of the nearest stars will be in the order of arcminutes, making those parallaxes visible even to the naked eye.
Description and mission profile
Source:
*Payload module (5,000 kg mass including a 10-watt laser transponder+1-meter-
aperture
In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...
laser communications telescope capable of transmitting data at 20 kilobits/second at 1000 AU, and a 1.5 meter astrometric telescope plus other experiments)
*Propulsion module (4,000 kg dry mass including ten 4.45
newton
Newton most commonly refers to:
* Isaac Newton (1642–1726/1727), English scientist
* Newton (unit), SI unit of force named after Isaac Newton
Newton may also refer to:
People
* Newton (surname), including a list of people with the surname
* ...
thrust ion propulsion clustered in groups of five and fired paired for two years each. The total specific mass of ion thrusters, power processor units, etc. would be 4 kg/kWe (kilograms per kilowatt electrical power))
*1-MWe nuclear reactor+shield+radiator (6,000 kg mass or 12.5 kg/kWe specific mass)
The 25,000 kg (gross launch mass including 10,000 kg of
xenon
Xenon is a chemical element; it has symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
propellant) ''TAU'' spacecraft would have been launched into a low Earth orbit by the
Space Shuttle
The Space Shuttle is a retired, partially reusable launch system, reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. ...
in 2005–2010. Once deployed, a central boom would have telescoped the three main units listed above to a total 40 meter length to separate the payload from the nuclear reactor. The ion propulsion/xenon propellant module would have been positioned close to the
center of gravity
In physics, the center of mass of a distribution of mass in space (sometimes referred to as the barycenter or balance point) is the unique point at any given time where the weighted relative position of the distributed mass sums to zero. For ...
, its 250 km/s exhaust velocity ion engines providing an acceleration of 0.35 mm/s
2. ''TAU'' would have attained
Earth escape velocity in 250 days in a spiraling orbit, followed by Solar System escape speed 700 days later.
The ''TAU'' payload module would have separated from the rest of the spacecraft after ten years of constant thruster firing at a distance of 12 billion km (80 AU)
[Solar System Log by Andrew Wilson (page 125), Jane's Publishing Company Limited, 1987, ] as the xenon propellant tanks would have been depleted. ''TAU'' would have reached 200 AU in 15 years after launch, 400 AU in 23 years, 600 AU in 32 years, 800 AU in 41 years and the full 1000 AU in half a century. Even so, it would have traversed less than 0.4% of the 4.3 light years to
Alpha Centauri
Alpha Centauri (, α Cen, or Alpha Cen) is a star system in the southern constellation of Centaurus (constellation), Centaurus. It consists of three stars: Rigil Kentaurus (), Toliman (), and Proxima Centauri (). Proxima Centauri ...
, the nearest star.
See also
*
Innovative Interstellar Explorer
Innovative Interstellar Explorer was a NASA "Vision Mission" study funded by NASA following a proposal under NRA-03-OSS-01 on 11 September 2003. This study focused on measuring the interstellar medium, the region outside the influence of the ...
(NASA 2003)
*
Interstellar Probe
An interstellar probe is a space probe that has left—or is expected to leave—the Solar System and enter interstellar medium, interstellar space, which is typically defined as the region beyond the Heliopause (astronomy), heliopause. It also r ...
(NASA 1999)
*
Interstellar probe
An interstellar probe is a space probe that has left—or is expected to leave—the Solar System and enter interstellar medium, interstellar space, which is typically defined as the region beyond the Heliopause (astronomy), heliopause. It also r ...
(Generic)
*
Cosmic distance ladder
The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A ''direct'' distance measurement of an astronomical object is possible ...
* (has an aphelion over 1000+ AU and orbits the Sun)
*Related to Solar System departure:
**
Interstellar travel
Interstellar travel is the hypothetical travel of spacecraft between star systems. Due to the vast distances between the Solar System and nearby stars, interstellar travel is not practicable with current propulsion technologies.
To travel between ...
**
Spacecraft escaping the Solar System
A spacecraft is a vehicle that is designed to fly and operate in outer space. Spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, planetary exploration, ...
(Category)
**
Artificial objects escaping the Solar System
*
Nuclear power in space
Nuclear power in space is the use of nuclear power in outer space, typically either small nuclear fission, fission systems or radioactive decay for electricity or heat. Another use is for scientific observation, as in a Mössbauer spectrometer. T ...
References
External links
Tau (Thousand Astronomical Unit) Missionin ''The Encyclopedia of Astrobiology, Astronomy, and Spaceflight''.
Abstract of "TAU -- A MISSION TO A THOUSAND ASTRONOMICAL UNITS"by
K. T. Nock of the
Jet Propulsion Laboratory
The Jet Propulsion Laboratory (JPL) is a Federally funded research and development centers, federally funded research and development center (FFRDC) in La Cañada Flintridge, California, Crescenta Valley, United States. Founded in 1936 by Cali ...
.
Abstract of "Preliminary scientific rationale for a voyage to a thousand astronomical units"by
M. I. Etchegaray of the
Jet Propulsion Laboratory
The Jet Propulsion Laboratory (JPL) is a Federally funded research and development centers, federally funded research and development center (FFRDC) in La Cañada Flintridge, California, Crescenta Valley, United States. Founded in 1936 by Cali ...
and the
California Institute of Technology
The California Institute of Technology (branded as Caltech) is a private research university in Pasadena, California, United States. The university is responsible for many modern scientific advancements and is among a small group of institutes ...
.
{{Pluto
Cancelled space probes
Interstellar travel
Space astrometry missions