The idea of putting a telescope in space, above the blurring effects of Earth’s atmosphere, was first proposed in 1923 by Hermann Oberth, one of the pioneers of rocketry. Unfortunately, Oberth was one of those true visionaries whose imagination far outpaces the technology of his age, and the idea was ignored at the time- but in 1946, Lyman Spitzer, an American astrophysicist, wrote a paper proposing the same thing.

Spitzer became a crusader for his idea. Over the coming decades, his quiet advocacy was the main force behind a whole generation of orbital observatories, including the Copernicus Observatory and the Orbiting Astronomical Observatory. It was his authoritative voice that spurred NASA to approve the Large Space Telescope project in 1969. Unfortunately, Spitzer’s original proposal got downsized due to budget problems, and took some years to get off the ground. (Another bad pun!)

In 1974, the planning group for the project made a modification to the original idea: the satellite would carry not just one telescope, but a number of instruments which could be removed and changed. When new devices were developed, they could be added onto the existing structure, so the satellite would not become obsolete when new technology was invented.

In 1975, NASA and the European Space Agency began a collaborative effort that would eventually become the Hubble Space Telescope. Congress approved funds for the project in 1977.

NASA first planned to launch the telescope in 1983, but as often happens in space science, there were delays. The entire optical assembly was not put together until 1984, and the whole spacecraft was not assembled until 1985. However, 1983 did have one important event: that was the year when the name of the device officially became the Hubble Space Telescope, in honor of Edwin Hubble, the imminent American astronomer.

The revised launch date was in October, 1986- but then disaster struck. The space shuttle Challenger exploded just one minute into its flight, and all shuttle flights were cancelled for the indefinite future. Since Hubble was supposed to be launched from the shuttle, nobody knew when or if it would go up.

Years passed; shuttle flights were eventually continued. Planning for the Hubble telescope was resumed.

All the planning finally came to fruition in 1990. There was quite a bit of hype preceding the launch; in a world where astronomy rarely gets the front page, Hubble was as famous as a rock star. Particular attention was given to the big mirror that would focus light onto the light-sensing elements, which was praised as a masterpiece of precision workmanship.

Unfortunately, this mirror did not live up to its image (still another low-flying pun!) Due to a manufacturing error, one edge of it was off by about one-fiftieth of the width of a human hair. In astronomy, that’s enough. Some science could still be done, but the faulty mirror severely compromised the quality of the images, and parts of the mission would have to be canceled.

Somebody should write a book about the valiant and almost superhuman efforts of ground crews in correcting or compensating for problems with spacecraft. On many occasions, missions that seemed to be hopelessly doomed have been resurrected and successfully completed, because the folks on the ground just refused to give up. This was one of those occasions.

Hubble was scheduled to get its first servicing mission in 1993. Rushing to meet this deadline, engineers designed a device to fix the optical problem. The system was called the Corrective Optics Space Telescope Axial Replacement, or COSTAR.

In December of that year, COSTAR went into space. Working in two teams, the astronauts performed a record of five back-to-back spacewalks, during which COSTAR was installed and the Wide Field/Planetary Camera was replaced with an improved unit. In addition, there were routine maintenance jobs to be done, such as putting in new solar arrays and replacing four of the satellite’s gyroscopes.

The fix worked. After that, Hubble started sending back sharper images, and NASA (possibly in an attempt to salvage its damaged image) released reams of them to the press. One of the earliest and most popular was the gorgeous picture of the star-forming region in the Orion nebula, which ended up on countless calendars, posters, screen savers, etc. After that, there were many others: stars like diamond dust set against swirls and streamers of nebular gas, so detailed and delicate that it could have been painted.

Some of us had always known that space was beautiful, but now the whole world knew it.

The pictures are famous now; some of the best ones have been compiled into a gallery at the NASA website, which is certainly worth a look. But as nice as they are, pictures aren’t everything. This was supposed to be a science mission, and while the folks who make calendars, posters and screen savers must have been grateful for the new material, that really wasn’t the point of all this. 20 years on, we can now ask: just what have we learned from Hubble?

In reading over the history of Hubble at the NASA site, a few highlights stood out. Here are a few of them:

1. Observing the evolution of accretion discs around stars. The current theory of planet formation says that it all starts with the accumulation of a cloud of gas. The gas gets denser and denser, especially at its center, which finally gets so compressed that the atoms start to fuse. When that happens, light, heat and other products are emitted, and the result is a star at the center of this condensing gas cloud. Because of the increasing gravity, the rest of the gas begins to spin, just as water spins when it goes down the drain of a bathtub. The spin makes the cloud of gas get flat and disc-shaped, which causes it to be more concentrated. This concentration makes the gas molecules collide with each other and begin to form dust grains, which will eventually clump together to form planets. In observing other stars, astronomers would expect to find discs in various stages of evolution, and Hubble has done that. In January of 2005, NASA scientists announced that Hubble had found several stars with dust discs, and that some of these discs have a flared, thick edge, while others don’t. This shape was expected from computer simulations. The scientists think that the stars with the thick edges are in the early stages, and probably have not formed planets. It is thought that all of the other stars originally had flared edges, too, but the dust that was in them has already formed planets. While this theory of planet formation has been around for some time, this was the first time that “before and after” pictures have been taken of actual stars going through the process.

2. Observing the seasons of Pluto. In February 2010, NASA released pictures of Pluto taken by Hubble. These are our most detailed pictures of that body ever taken, and they show Pluto changing colors over a period of time. During the period of observation (2000 to 2002), Pluto became significantly redder, while the northern hemisphere got brighter. It is thought that the color change is the result of surface ices evaporating over one pole and then refreezing over the other pole, as Pluto starts the next phase of its year, which lasts for 248 Earth years. Just taking these shots was a challenge, since the resolution necessary is comparable to that needed to read the brand name on a soccer ball 40 miles away.

3. Imaging of cross-shaped “comet-like object”. This one has both scientific value and visual appeal. It is a picture of a structure shaped like a cross, with trails swept back by the solar wind. NASA scientists think this is the remnant of a recent collision between two asteroids. The lines of the cross are trails left by the two objects, and the long trails behind the object are particles of debris from the impact. It was an amazing stroke of luck to catch the object right after such an impact, and we may never see another one. The picture is stunning. It’s a safe bet that this one will end up hanging on a few walls, too.

4. First detection of organic molecules on a planet orbiting another star. Last but not least, this one has enormous implications for future space exploration. If nature is going to create life, it has to have the right ingredients. While it is possible to imagine exotic forms of life with bizarre chemistries, the only kinds of life that we know are made from what we call organic molecules. If we can find planets with organic molecules, there is a chance we may be able to find lifeforms there. Until recently this was just theoretical, but in March of 2008, Hubble detected the organic molecule methane in the atmosphere of a Jupiter-size planet in the constellation Vulpecula, some 63 lightyears from here. While this planet is too hot for the kind of chemical reactions that would create life, just finding an organic molecule on another planet is a big step.

The list goes on, and Hubble isn’t done yet. In May of 2009, astronauts made a repair mission to Hubble, refurbishing it for further duty. Now it’s sending back lots of wonderful pictures again, and hopefully will continue to do so for years to come. At 20 years and counting, it is certainly one of the most successful missions in the history of space exploration- and we haven’t seen the last from it yet.

Sources:

“Hubble Space Telescope History” at aerospaceguide.net: aerospaceguide.net/spacehistory/hubble-history.html

“Hubblesite: Hubble Discoveries” at the NASA website: hubblesite.org/hubble_discoveries/

Feature: “Hubble Finds MIssing Link in Planet Formation” at NASA website: nasa.gov/vision/universe/newworlds/0112_missing_link.html

“20 Years of Hubble: Hubble Finds First Organic Molecule on an Exoplanet” at NASA website: nasa.gov/mission_pages/hubble/science/hst_img_20080319.html

“20 Years of Hubble: New Hubble Maps of Pluto Show Surface Changes” at NASA website: nasa.gov/mission_pages/hubble/science/pluto-20100204.html

“20 Years of Hubble: Suspected Asteroid Collision Leaves Odd X-Pattern of Trailing Debris” at NASA website: nasa.gov/mission_pages/hubble/science/asteroid-20100202.html

The New Frontiers program came about following a study in 2001 which was conducted to look at the state of solar system exploration at that time and identify priorities for continued exploration during the 10 year period 2003 to 2013. The study identified five medium class missions that were considered of importance and the New Frontiers program was set up to examine and implement these.

The first mission launched was named New Horizons and its goal is to visit and explore Pluto. It will also visit one or more Kuiper Belt objects during the mission. New Horizons was launched in January 2006 and is scheduled to reach its destination by July 2015. The second New Frontiers mission is named Juno and has been designed to conduct an in-depth study of Jupiter. It is currently scheduled for launch in August 2011. At the end of December 2009 NASA announced that three candidates had been chosen for the third New Frontiers program and these include some exciting possibilities for solar system exploration.

The first potential candidate is named the Sunrise and Atmosphere Geochemical Explorer (SAGE) and would comprise a mission to Venus. On arrival it would release a probe into the atmosphere of the planet which would undertake extensive measurements as it descended to the surface of Venus. Upon landing the probe would conduct studies to assess the composition and mineralogy of the surface material.

The second candidate is called the Origins Spectral Interpretation Resource Identification Security Regolith Explorer or Osiris-Rex for short. This mission would be designed to travel to and orbit an asteroid. Extensive measurements of the asteroid would be taken while the spacecraft was in orbit around it. Samples would then be collected from the surface of the asteroid and these would be returned to Earth. These samples would be used to assist in the study of the formation of the solar system and the origins of the molecules necessary for life.

The third candidate would send a spacecraft to land in an area near the south pole of the moon which would collect lunar material and return it to Earth. This mission is known as Moonrise: Lunar South Pole – Aitken Basin Sample Return Mission. The returned lunar sample would be used to help gain an insight into the early history of the Earth-moon system.

Each of the candidates will now have around a year to complete a detailed concept study which is required to consider the feasibility of implementation, the costs involved and technical plans for carrying out and completing the mission. The teams will receive approximately $3.3 million to undertake the concept study and it is currently proposed that selection of the winning candidate will be made in mid 2011. Planning and preparation for the chosen mission would then take around seven years and the spacecraft has to be ready for launch by no later than the end of December 2018.

Each of the missions represents an opportunity for further study of a celestial body and the winning candidate is sure to advance our knowledge of the solar system. All three are potentially exciting opportunities to learn something new and any one of them would provide scientists with a rich source of data. Only time will tell which of the candidates will be successful and for now the three teams have a year of hard work ahead of them.

The Jupiter flyby was a huge success, allowing observations of the giant planet and its moons in unprecedented detail.  Among other things, information was gathered about the atmosphere and weather of Jupiter.  Data on cloud composition was collected by the visible light, infrared and ultraviolet remote sensing devices, and ammonia was observed welling up from the lower atmosphere to form clouds.  Lightning strikes were observed at the poles, the first polar lightning ever seen off Earth, and from this it was learned that heat moves evenly through water clouds at all latitudes across Jupiter.  New Horizons also made size and speed measurements of waves in the Jovian atmosphere, indicating strong storm activity beneath, and obtained close-up images of the Little Red Spot, a smaller version of the Great Red Spot.  The smaller feature is about half the size of the bigger one, or about 70 per cent of Earth’s diameter.

New Horizons obtained the clearest images yet of the tenuous Jovian rings.  Here clumps of material were observed that may be from a recent impact within the ring system.  The probe got a detailed view of the ring dynamics involved here, with moons Metis and Adrastea shepherding the materials around the rings.  A search for small moons within the rings yielded negative results.

The probe performed observations of Jupiter’s four largest moons, focusing especially on Io, closest to Jupiter and volcanically active.  Eleven volcanic plumes of varying size were seen, three for the first time.  One of these, a 200-mile-high eruption from the volcano Tvashtar, offered a chance to see the structure and motion of the plume as it condensed and fell back to the surface.  Instruments picked up infrared radiation from at least 36 volcanoes on Io with lava temperatures about 1900 degrees Fahrenheit, which is comparable to volcanoes on Earth.  Io is the most active body in the solar system, and more than 20 geological changes had occurred since the Galileo Jupiter orbiter was there in 2001.  Observations of Io while in Jupiter’s shadow showed glowing clouds over many of the volcanoes, a possible source of gas for Io’s atmosphere.

The probe passed down Jupiter’s magnetotail and got the closest-ever look at this region.  Particle detectors indicated that volcanic material from Io moves down the tail in slow-moving blobs.  Scientists are hoping to learn how these gases are ionized, trapped and energized by Jupiter’s magnetic field, and then finally ejected from the system.

New Horizons left Cape Canaveral in January, 2006.  It is the fastest spacecraft ever built, reaching Jupiter in only 13 months.  It is now about halfway between the orbits of Jupiter and Saturn, more than 743 million miles from Earth, and it will fly past Pluto and its moons Charon, Nix and Hydra in July 2015 before going deeper into the Kuiper Belt.

At present, the mission continues to go well.  In November of 2009, the probe was brought out of hibernation to repoint the communications dish antenna in order to keep up with the changing position of Earth around the sun.  This wake-up also provided an opportunity to download several months of stored data, correct a minor bug in the fault protection system software, perform adjustments to refine the craft’s trajectory, and upload instructions for the running of the craft from now until its next scheduled wake up in January 2010.

While New Horizons will not reach its destination until 2015, it will be able to perform some observations of Pluto and its largest moon, Charon, about a year earlier.  It will be taking pictures of the two at that point, and a few months later, it will be able to generate a map of Pluto.

The long approach will give an opportunity to watch seasonal changes in Pluto’s atmosphere.    Since 1989, Pluto has been heading away from the sun.  In 1999, it crossed the orbit of Neptune, once again becoming the outermost of the nine traditional planets.  It is now heading into its 200-year winter, when its atmosphere is expected to freeze and fall to the surface as snow, and because of this, the New Horizons mission will be the last chance to study the atmosphere of Pluto.  The probe will obtain information about its chemical composition, and also allow observations of cloud formation.  Clouds, probably composed of nitrogen or carbon monoxide, have already been observed in the thin atmosphere of Pluto.

Once New Horizons has passed Pluto, it will head out into the Kuiper Belt to find and study some of the mysterious bodies that exist there, which are thought to be icy and comet-like.  The probe will conduct a search for Kuiper Belt bodies, and when it finds them, will modify its own course to approach and observe them.  It is hoped that New Horizons will find six to ten of these bodies to study.

The outermost region of the solar system is a vast, dark area that is only beginning to reveal its secrets.   What else is out there?  Over the next few years, we will begin to find out.