NASA has now selected the fourth mission in its new Discovery interplanetary space programme.
Tim Furniss/WASHINGTON DC
IN JANUARY 2006, A SMALL Discovery series spacecraft is scheduled to return to Earth after a journey across interplanetary space. The craft will contain a precious cargo of primordial material from the formation of the Solar System. The material will be contained in a re-entry capsule, which will be snared in mid-air by an aircraft over the Utah Test and Training Range in the USA.
Planetary scientists will be eager to get their hands on the "stardust", the first material from deep space to be returned to the Earth since the Luna 24 came back with a sample of Moon dust in August 1976, and the first certified interstellar material ever returned. The spacecraft, aptly called the Stardust, may have a rival in a planned Japanese Muses C craft, which may bring comet samples back to Earth in 2006.
The Stardust will be used to collect material from the coma of the comet Wild 2 and will also gather particles streaming from the direction of the constellation of Scorpio. The particles were detected by the European Space Agency (ESA) Ulysses and NASA Galileo spacecraft. "The material from the comet's coma may still contain organic material," says Mark Saunders, Discovery programme manager. Comets are the oldest representative bodies in the Solar System, but he says that the Wild 2 "...is a relatively young comet".
It is also of particular interest because the comet had been in a long, deep freeze in the outer reaches of the Solar System until 1974, when it flew close to the giant planet Jupiter and was directed into a new orbit by the planet's gravitational influence. Its new orbit will take it closer to the Sun and, during its close encounter in 2002, the Sun's radiation will cause the comet to shed the material, which is to be captured by the Stardust. The material represents well-preserved remnants of star and planetary formation.
COLLECTION PLATES
The tiny dust particles will arrive, attached to three interplanetary "flycatcher" collection plates, made of a porous, transparent silica called aerogel, the lowest bulk-density material, manufactured in the world. Aerogel is so flimsy that "...it looks like cigarette smoke", says Saunders. It weighs 0.02gm/cm3. Although it does not absorb moisture, the fluorescent substance is able to absorb large amounts of gas or particles.
The Stardust will be launched on 15 February 1999, and the craft will rendezvous with the Wild 2 at a relative speed of 6.1km/s in January 2004. "A high-resolution camera will capture images from about 100km [55nm]," Saunders says.
The Stardust was selected in November 1995 as the fourth mission in the Discovery programme, which will demonstrate NASA's new plans for "faster, better, cheaper" interplanetary exploration flights. The three other Discovery flights will be used to land a rover on Mars, to look for ice on the Moon's poles and to go into orbit around an asteroid for the first time. NASA may use other missions to fly-by one of the poles of Mercury or to deposit a fleet of rovers on the Moon (the Interlune-One project being proposed by former Apollo geologist and moonwalker Harrison "Jack" Schmitt).
Lockheed Martin, at Denver, Colorado, which is rapidly becoming NASA's favourite planetary spacecraft contractor, has been awarded an $80.4 million contract to build the Stardust, for which there is an estimated budget of $200 million, including its launch on either a yet-to-be determined, new-generation Med-Lite launcher or a Titan 2G. Compared with those of the $1 billion-class interplanetary missions of the past, the craft to be used in the programme will cost less, being smaller and more compact, and will incorporate new technologies, lightweight materials and sensors.
The craft will be built within 36 months and be launched once a year to various destinations. The project-management approach of the Discovery programme contributes to its low cost and short time-scale. The management emphasis is on a flat, team-orientated organisation, which cuts across key industry and science-team partners.
"The principal goal of the Discovery is high-quality science," says Saunders, "but also to encourage the introduction of new technology - provided that it does not affect the science. We are also working to a tighter schedule than we've ever done before."
The Stardust will be developed with Dr Donald Brownlee of the University of Washington and Ken Atkins, Stardust project manager, at NASA's Jet Propulsion Laboratory, Pasadena. "The materials we expect to capture and then study on Earth are the initial building blocks of planets in both our Solar System and other planetary systems in the Galaxy," says Brownlee.
HIGH-RESOLUTION IMAGES
The critical aerogel plates will be custom-made by the science investigators to maximise preservation of the physical state and chemical nature of the captured particles. The camera, assembled largely from spare flight components, will capture high-resolution images of a comet nucleus, predicted to be ten times sharper than the images returned of Halley's Comet by the ESA's Giotto spacecraft in March 1986.
A German particle-composition analyser of the type used on the Giotto will be used on the Stardust to obtain "real-time" data for post-mission comparison with data from the Giotto.
Results from the Stardust mission will be used to calibrate mission planning, for the ESA/international Rosetta project, which will place two small landers on the surface of the comet Wirtanen in 2012. The Rosetta will be launched by an Ariane 5 in January 2003 and will reach the comet in August 2011. The Japanese Muses C, is scheduled to be launched in January 2002 and it will "race" the Stardust home with samples from another comet, most likely the Nereus.
In addition to the University of Washington, JPL and Lockheed Martin, participants in the Stardust project will be Caltech, of Pasadena, California; Germany's Max Planck Institute; and two NASA organisations, the Johnson Space Center, Houston, Texas and the Ames Research Center, Moffett Field, California.
The Stardust was chosen from three finalists for the flight. The others were the Suess-Urey (a Stardust-like mission designed to capture material in the Solar wind) and the Venus Multiprobe mission to deposit 16 small capsules into the planet's "greenhouse-effect" atmosphere.
The Stardust mission was "...rated highest in terms of scientific content", says Wesley Huntress, NASA associate administrator of space science. "Combined with its low cost and high probability of success, this translates into the best return on investment," he adds.
The first Discovery mission takes off in February aboard a McDonnell Douglas Delta 2. Called the NEAR (near-Earth asteroid rendezvous), the craft will enter orbit around the sausage-shaped asteroid Eros in 1999, becoming the first to go into orbit around an asteroid, giving scientists the opportunity to monitor one at close quarters for up to two years. Asteroids are some of the most primitive bodies in the Solar System, regarded as remnants from the creation of planets in the dust cloud surrounding the Sun.
Two asteroids, Gaspra and Ida, have been inspected at close-quarters, but only during fleeting flybys by the NASA Galileo craft which began its exploration of the planet Jupiter on 7 December, 1995. The Galileo has returned the first images of these rocky bodies, which look like huge pockmarked boulders.
Eros will make an interesting sight, being 35km long but only 16km wide and 6km thick. The asteroid, which rotates on its axis every five hours, is famous for being one of the few which occasionally pass close to the Earth in their elliptical orbits around the Sun. In 1975, Eros passed the Earth at a distance of 22.5 million kilometres and could be seen as a rapidly moving, seventh magnitude "star". Eros - the second largest of the near-Earth asteroids - is thought to have a stony-iron surface.
Another near-Earth asteroid is Geographos, which was to have been explored by the Ballistic Missile Defense Organization/NASA craft, the Clementine, before that craft suffered a systems failure after its successful image-taking mission over the Moon. The Clementine served as a technological pathfinder for the Discovery missions, demonstrating the use of rapid-development and ultra-lightweight instruments (Flight International, 11-17 May, 1994).
The 805kg NEAR is being built by the Applied Physics Laboratory, in Maryland, and will be the first for a US planetary mission, to be developed outside NASA. It may also fly-by the asteroid Matilda en route to Eros.
From an orbit 13km from Eros, the craft's 55kg suite of science instruments, including a spectrometer and multi-spectral camera with a resolution of 1m, will measure the composition and structure of the asteroid.
The second Discovery spacecraft is the Mars Pathfinder, which will be launched in December, also by a Delta 2. The 870kg craft will make an unusual landing on Mars on 4 July 1997, inside a set of inflatable balloons, which will cushion its bouncy landing in the Ares Vallis, a plain at the outflow of a past, catastrophic river flood, which has left a wide variety of rocks strewn across the ruddy surface. "It's a low-cost way to get to the surface with a high-quality science package," Saunders says.
SURFACE INSTRUMENTS
On the surface, the solar panels of the Jet Propulsion Laboratory-built Mars Pathfinder will be deployed like the petals of a flower, exposing a suite of small instruments, including a stereo camera, a wind sock and an 11kg, $25 million roving vehicle the size of a microwave oven. The rover will also be equipped with a colour camera and spectrometer. It will be equipped with an artificial-intelligence system to enable it to recognise hazards and drive around them. The Pathfinder mission, which will last up to one year, will provide data on the atmosphere, weather, geology and rock composition of Mars. The rover's science programme will be crammed into the first two days, to ensure that data are returned.
The mission will cost $245 million and will be followed by several craft under a new Mars Surveyor programme (Flight International, 20 December, 1995-2 January).
The third Discovery craft, costing $59 million and weighing 233kg, will be built by Lockheed Martin. Called the Lunar Prospector, it will be launched by a Lockheed Launch Vehicle in June 1997. The Lunar Prospector will provide low-altitude mapping of the Moon, to measure elements on the surface, magnetic fields, gravity fields, gas-release elements and to search for ice on the poles. Operating from a 100km circular orbit, with a period of 118min, the Lunar Prospector will complement data collected by previous missions, including the Apollos and will contribute to understanding the origin, evolution and current state of the Moon.
Source: Flight International
