European spacecraft to put cold eyes on the Universe
BY STEPHEN CLARK
Posted: May 13, 2009
The largest space telescope ever launched is set to begin its journey into deep space Thursday, penning the first chapter of a three-year mission that will peer deep into unseen cold and distant parts of the universe.
It all begins Thursday with a scheduled launch at 1312 GMT (9:12 a.m. EDT) aboard a commercial Ariane 5 rocket based at Kourou, French Guiana, along the northeast coast of South America.
The 7,500-pound spacecraft will ride into space with Planck, another ESA observatory designed to map the primordial universe.
Herschel will be deployed first, separating from the Ariane 5's upper stage 26 minutes after liftoff. Planck will follow about two-and-a-half minutes later.
The observatory is shaped like a tube, standing nearly 25 feet tall and stretching almost 15 feet across. Thales Alenia Space of France led a team of industrial contractors from 17 countries that built the spacecraft.
The spacecraft is named for William Herschel, the German-born British astronomer that discovered Uranus and infrared radiation.
The telescope's three instruments will look into far infrared light wavelengths never before studied, allowing the sensors to see through dust clouds and deep into star-forming regions across the Milky Way and other galaxies.
"I like to say that if you want to understand the life of a star you make a comparison with the lives of people," said Goran Pilbratt, Herschel's project scientist at the European Space Agency.
Observatories like the Hubble Space Telescope that detect visible light can see "adult" stars and most infrared instruments can take pictures of "child" stars, Pilbratt said.
But Herschel will be able to see much more, thanks to a suite of high-tech detectors and a perfectly-crafted primary mirror spanning three-and-a-half meters, or about 11.5 feet, in diameter.
"We're going to see the embryos, the ones that are not born yet. We're going to see right into the wombs where stars are born," Pilbratt said.
Stars form inside relatively cool clouds of dust and gas that hide stellar incubation from normal telescopes designed to magnify what could be seen by the human eye.
"The birth of new stars takes place in these very optically opaque clouds of dust and gas," said Paul Goldsmith, NASA's Herschel project scientist.
Infrared telescopes like Herschel can see through the enshrouding clouds to see condensing gas and dust before stars can flicker to life.
"That's what I think is going to be most exciting, to really be able to get this almost unblocked, highly detailed view of what's going on inside these clouds," Goldsmith said.
Herschel is sensitive enough to even see star formation in other galaxies.
Another objective of the mission is to take a census of forming stars in our galactic neighborhood.
The observatory will look far back in time to study how galaxies formed and evolved up to 10 billion years ago, during the first three billion years after the Big Bang.
"Galaxies evolve by the formation of new stars, especially massive stars that then die and explode as supernovae and enrich galaxies with heavy elements. They put so much energy out that they really dominate the structures of these galaxies," Goldsmith said.
Scientists will also focus Herschel's telescope on debris clouds around other stars to learn more about how planetary systems form.
Closer to home, Herschel will help astronomers create highly-detailed chemical maps of objects in the solar system. The observatory will use spectrometers to probe the composition of comets, which scientists believe harbor the frozen building blocks of the solar system.
NASA contributed critical detecting equipment, electronics and other key technologies to two of Herschel's three instruments, boosting their observing capability.
A NASA Herschel Science Center has also been established at the California Institute of Technology's Infrared Processing and Analysis Center, which also oversees data gathered by the agency's Spitzer Space Telescope.
NASA's contributions are valued at $272 million, including spacecraft hardware and operational costs, according to an agency spokesperson.
The total cost of the Herschel mission is quoted at 1 billion euros, or nearly $1.3 billion in current exchange rates. That number equates to about 1 million euros for each day of Herschel's primary mission, Pilbratt said.
The cost also includes figures for the construction of the spacecraft, science instruments, the launch vehicle and projected operations.
Scientists began studying a mission like Herschel in the early 1980s, but it has taken nearly three decades to go from white papers to the launch pad.
Industrial production of the observatory, then called the Far Infrared Space Telescope, began in 2001.
"I know people who have been dreaming about this since the 1970s and I have myself been working full time on Herschel since 1991, which is much longer than industry has been on the job," Pilbratt said.
NASA later joined the mission to add technical expertise and broaden the base of researchers that will use the telescope.
Herschel's 11.5-foot-wide primary mirror, the largest ever flown in space, is made of silicon carbide, a ceramic material with properties similar to glass.
Engineers at Astrium in Toulouse, France, assembled the mirror from 12 segments after machining, polishing and coating the pieces.
Herschel's mirror has a collecting area of about 100 square feet, around 15 times larger than NASA's Spitzer observatory. Herschel's mirror is nearly four feet wider than the mirror on Hubble.
"Our mirror is much larger, which will enable us to not only collect more energy but to see much sharper at these wavelengths," Pilbratt said.
The primary mirror and a secondary mirror will focus incoming light into a focal plane inside the cryostat, an insulated vacuum flask that provides cooling to ultra-sensitive detectors to a fraction of a degree above the coldest temperature possible.
The telescope design is relatively simple, but it relies on exotic technologies that must withstand a wide range of temperatures and the intense vibrations of launch, according to Pilbratt.
Herschel will launch with 2,300 liters, or about 607 gallons, of cryogenic liquid helium to chill the telescope's coldest detector to a temperature of 0.3 Kelvin, or below -459 degrees Fahrenheit.
The detectors must be subjected to such frigid conditions to see faint emissions of cold objects scattered in the distant universe. Herschel will detect light from material as cold as -441 degrees Fahrenheit.
Herschel's instruments come from scientists in 18 countries, including European states, the United States, Russia, China, Canada, and Taiwan.
The Photodetector Array Camera and Spectrometer and the Spectral and Photometric Imaging Receiver, respectively called PACS and SPIRE, will capture images in a wide swath of the electromagnetic spectrum ranging from infrared to submillimeter wavelengths.
Both instruments can take pictures and slice infrared light into its spectral components, like the colors of a rainbow. This capability will help scientists remotely determine what chemicals are present in Herschel's celestial targets.
A third instrument, called the Heterodyne Instrument for the Far Infrared, will obtain revolutionary new information about the composition and motion of star-forming regions, galactic nuclei and interstellar gas.
Scientists measure infrared light wavelengths in microns, a unit equal to one-millionth of a meter.
Herschel will observe light in wavelengths from about 55 microns to nearly 700 microns, according to Pilbratt.
Spitzer, today's standard-bearer in infrared astronomy, can resolve wavelengths from 3 microns to about 160 microns.
"Where Spitzer leaves off, that's where Herschel is just getting going," Goldsmith said. "We're looking at even longer wavelengths, which means we can see even better into these opaque clouds of dust."
Herschel overlaps Spitzer in longer infrared wavelengths and the joint NASA and ESA James Webb Space Telescope will supplant Spitzer's coverage of shorter wavelengths in even finer detail.
"There are not only orders of magnitude improvements for being able to do the same observations, but there are capabilities on Herschel and Webb that Spitzer never had even on its best day," said Mike Werner, NASA's Spitzer project scientist.
JWST is also billed as a replacement for Hubble because it is sensitive to optical and near infrared light. The next-generation telescope will launch in late 2013 or 2014.
Spitzer was preceded by the Infrared Astronomical Satellite and the Infrared Space Observatory. Japan's Akari telescope joined the effort in 2006.
NASA is also developing an airborne infrared observatory called SOFIA to complement the Spitzer and Herschel telescopes.
The Earth's atmosphere blocks most infrared emissions from reaching the surface, so astronomers seeking to detect these wavelengths must use telescopes in the upper atmosphere or in space.
"When I first started working in infrared, there was a lot of mystic, jargon and stange things that people did in the infrared, limited by either the atmosphere or by the properties of our instruments," Werner said.
Scientists have cleared those hurdles by launching satellites and building more advanced sensors.
Goldsmith said it is difficult to predict what Herschel will find because it is studying an unexplored part of the spectrum.
"We haven't had ready access to the wavelengths between infrared and microwaves before, in part because Earth's atmosphere blocks them from reaching the ground," Goldsmith said. "Because our views were so limited before, we can expect a vast range of serendipitous discoveries, from new molecules in interstellar space to new types of objects."
Herschel will spend at least three years watching the cosmos from a post at the second Lagrange point nearly 1 million miles from the night side of Earth.
The L2 point is the location where the gravitational pull from the sun balances with the tug from Earth.
It is a popular destination for deep space observatories because it is positioned away from natural interference from the Earth, but still close enough to allow high bandwidth communications between spacecraft and ground stations.
The Ariane 5 rocket will boost Herschel into an unusually high trajectory stretching beyond the orbit of the moon.
It will take Herschel about two months to drift away from Earth and be captured by L2, where it will enter a looping halo orbit with an average diameter of about 1 million miles.
Officials plan to start activating Herschel and testing its systems immediately after launch. Early science observations can begin as soon as testing ends and Herschel opens the door covering the telescope's cryostat, allowing the instruments to cool down.
"When we first open the cryostat cover, we still have a lot of things to do before we really start doing science," Pilbratt said. "We will be able to at least start making some nice pictures at that point, so that we have something to show."
Routine observations should begin about six months after launch, after commissioning and performance verifications, according to Pilbratt.
Officials have already allocated observing time for the first 18 months of the mission for scientists to study the solar system, star-forming regions and other galaxies.
Herschel will also take a deep field image of a dark part of the sky to see galaxies in the early universe. These observations, similar to pictures taken by Hubble, will reveal important information about the evolution of galaxies.
NASA scientists have received about one-third of the observing time released so far, officials said.
Officials will grant researchers more access to the telescope throughout its mission. Scientists from Herschel's instrument team are guaranteed about one-third of the total observing time, and the rest will be released to the worldwide scientific community.
Plans call for Herschel to offer about 7,000 hours of science time per year.
Herschel's observations program is managed by officials at the mission's science center in Spain. Mission operations will be conducted from the European Space Operations Center in Darmstadt, Germany.
Although Herschel's primary mission is approved for three years, the spacecract carries enough liquid helium to cool its instruments for up to four years.
Scientists envision operating Herschel until the helium runs out to maximize the mission's scientific return.
"We have an observatory whose lifetime is limited by something that is boiling away constantly, so we will endeavor to waste as little time as possible," Pilbratt said.