In one of our earlier articles, still posted here, we took a look at the European Space Agency’s Venus Express probe, which is already in orbit around Venus.  These two projects are not redundant, nor are they in competition with each other.  The projects have been in close communication with each other since their beginning phases, and have been planned to complement each other in the construction of the most complete picture possible of the Venusian environment.  In some cases, the two Venus probes will work together on composite science projects, while in other cases, they will be doing separate work of a complementary nature.

The Venus Climate Orbiter, also called Akatsuki, will weigh 480 kg. with fuel, and will carry a science payload of 34 kg.  Basically, it will be a rectangular box with “paddle wheel” solar panels extending on either side.  There will be small thrusters at all eight of the corners for minor attitude adjustments, and a larger engine for orbital maneuvering in the rear of the unit.  There will be five instruments onboard, taking observations at different wavelengths to obtain various types of information.

Departing from Earth in May of this year, Akatsuki will first deploy all of its secondary payloads.  These include some experiments proposed by prominent Japanese universities relating to information encoding and transmission, observation of the Earth’s atmosphere for meteorological purposes, and the testing of computer technology for space use.  The last of the secondary payloads to be deployed will be the IKAROS lightsail, an exciting experiment to test the use of the pressure of sunlight to propel a spacecraft.  (See our article on lightsails at this site.)  On the journey to Venus, Akatsuki use the travel time to perform various astronomical observations and to study the interplanetary dust cloud.

Akatsuki will arrive at Venus in December 2010 and settle into a long, elliptical orbit near the planet’s equatorial plane.  This will be a 30-hour orbit in a westward direction.  The apoapsis (farthest point from the primary) will be 79,000 km., and the periapsis (nearest point to the primary) will be 300 km.  Global images of the atmosphere and the ground surface will be taken every two hours continuously.  Because of its stretched-out orbit, the probe will be making close-up observations of mid-scale features at periapsis, and more long-range observations at apoapsis.  It will take advantage of periods when it is in the planet’s shadow to make low-light studies of phenomena such as lightning and air-glow.  (Lightning has never been observed on Venus, and there is some question as to whether it even exists there at all.  Scientists will be eagerly waiting to see if Akatsuki spots any.)

Akatsuki is being called an “interplanetary meteorology” mission, because its main function is to peer deep into Venus’ murky cloud cover and obtain 3-D images of the phenomena happening there.  It is hoped that the probe will be able to see the different layers of the atmosphere, how they are moving, and how they interact with each other and with the planet’s surface.

The whole purpose is to try and understand the amazing movement of the Venusian atmosphere.  As we saw in our article on the European Space Agency’s Venus Express probe, the big mystery about this planet that has emerged in recent years is that the entire atmosphere is racing around the globe in a planet-wide gale that moves at 60 times the rate of the planet’s rotation.  If you were unlucky enough to be standing on the surface of Venus, you would literally be knocked flat by a non-stop wind of 100 meters per second.  This is called “super-rotation,” and it is a complete mystery.  There is nothing in our Terrestrial meteorology to explain such rapid motion of an entire planet’s atmosphere.  Where is all that energy coming from?  Granted, Venus is close to the sun and has an average temperature of 460 degrees C both day and night, but even that isn’t enough to explain this amazing movement of air.

In some ways, Venus and Earth are very similar.  They are small, rocky planets with roughly the same mass, and it makes sense to think that they should be fairly similar.  The weird thing is, they’re not.  These two planets have taken very different paths in their evolution, and ended up in very different states.  In contrast to our own pleasant world, Venus is a pressure-cooker with a carbon dioxide atmosphere of enormous density.  And now we learn about this super-rotation, and the mystery deepens.  We certainly don’t have anything like that here at home.  How did these two planets, which probably started out as very similar little pebbles in the beginning, end up so completely different?

And as we saw in our Venus Express article, there is another factor that makes the whole thing even more intriguing.  There now seems to be convincing evidence that there are continent-size masses of granite on Venus.  Granite only forms in the presence of water, but due to the heat and pressure, liquid water can’t even exist on Venus today.   If there’s so much granite on Venus, there must have been an awful lot of water there at one time, and that implies a different environment from what we see now.   It must have been an environment with much lower air pressure and much lower temperatures- a planet more like Earth, in fact.

Just how much like Earth?  We don’t know yet, but it is that central question, and other questions connected to it, that will dominate Venusian research in the coming years.  And this thing with the super-rotation has to do with that, because it is very unlikely that this movement of the air was happening with such energy in the earlier, more Earth-like world we’re thinking of. When did it start, and why?  Why does it continue, with no obvious source of energy?  For that matter, why did the whole environment change from a world with water and granite continents into the oven-like place we see today?

Venus is turning out to be a big box of questions, and so far, we don’t have many answers.  However, there is an ominous note in all this: while there are many things we don’t know about Venus, we do know why it is so hot.  The cause of its 460-degree heat is runaway global warming caused by carbon dioxide buildup in the air.  This probably doesn’t result from the same source as our global warming here on Earth.  Since we have absolutely no evidence that Venus ever supported an industrial society, it is far more likely that its carbon dioxide buildup is the result of some natural process.  What process, we don’t know.  Could it happen here?  Of course it could- but will it?  We don’t know, but perhaps it would be prudent to find out.  When you think of it that way, this line of research suddenly becomes more than just an academic question.

If we imagine this ancient Venus, so different from the one we see today, we are tempted to think of a place very much like Earth: balmy islands with palm trees swaying in the breeze.  In all likelihood, this view only shows our provinciality, the fact that we only know one planet.  If there is anything that our study of Venus has already taught us, it is just how different two similar planets can be.  Whatever Venus was like in that long-ago age, it probably wasn’t just like Earth.

As for what it really was like, we will have to guess for the moment.  However, someday in the not-too-distant future, landers will descend to the surface of Venus and start taking samples of the soil and rocks.  At that point, we will finally begin to unravel the evolution of this planet.  If it turns out that those ancient oceans really did exist, perhaps we will find the fossilized remains of things that swam in them.

Between now and then, smaller revelations will be coming out, some of them perhaps in the near future.  When that happens, you can read about it here.

Sources:

Akatsuki Special Site at the website of the Japan Aerospace Exploration Agency:  jaxa.jp/countdown/f17/index_e.html

“JAXA Explores the Planets of the Solar System- Anticipating Amazing Discoveries” at the website of Japan Aerospace Exploration Agency:  jaxa.jp/article/special/explore/imamura02_e.html

“Satellites and Spacecraft- Venus Climate Orbiter ‘Akatsuki’” at website of the Japan Aerospace Exploration Agency:  jaxa.jp/projects/sat/planet_c/index_e.html

“Akatsuki- Planet C” at website of the Institute of Space and Astronautical Science:  isas.jaxa.jp/e/enterp/missions/planet-c/index.shtml

In our last article, we took a look at NASA’s JEO and the main object of its observations, the intriguing moon Europa.  In this article, we will look at the ESA’s JGO, which will orbit Jupiter’s largest moon, Ganymede.

As we said above, the opening of the mission, upon arrival at Jupiter, is a collaborative overview of the entire Jovian system.  Because of its enormous gravity pull and magnetic field, the great planet has a big influence over its satellites, and the system must be viewed as a whole.  In particular, the magnetic interaction between all of these bodies is very complex, and will be studied in great detail.

In connection with this, there will be a contribution from the Japan Aerospace Exploration Agency.  JAXA is designing and building a probe called the Jupiter Magnetospheric Orbiter (JMO), which will perform some stand-alone observations of the Jovian magnetic environment, as well as collaborating with the JGO and JEO on multi-point measurements of Jupiter’s magnetic field and its interaction with its satellites.

So far, we haven’t mentioned the JMO because it will travel onboard the JGO until insertion into Jupiter orbit.  At that time, it will be deployed from the JGO and enter a separate orbit.

The Jupiter Magnetospheric Orbiter will be a spinning probe weighing about 400 kg., and it will be carrying a scientific payload of 25 kg.  When it is deployed, the spin axis will be tilted toward Earth.  This craft will employ technology borrowed from three earlier missions: the Nozomi Mars probe, the BepiColombo Mercury probe and the Solar Sail project.  (The BepiColombo and Solar Sail missions were mentioned in earlier articles at this website.  Nozomi was a Japanese unmanned Mars probe which was unfortunately lost due to technical problems, but its failure had nothing to do with the technology that will be recycled for use on the JMO.)  For its post-deployment maneuvers, it will be carrying 60 kg. of propellant.  For all of its other functions, it will be powered by electricity from two “paddle-wheel” solar panels.

(This info comes from the original mission proposal, and may change before completion.  In particular, the proposal expressed the wish to increase the payload weight.  Hopefully they will be successful in this.)

The JMO has an ambitious schedule of observations to make after being deployed from the JGO.  It will perform the first complete survey of the Jovian magnetosphere, mapping lines of magnetic force which run from Jupiter to its moons.  It will also address various questions relating to the interaction of the solar wind with the Jovian magnetosphere, as well as the effects of these interactions on the atmosphere of Jupiter.  As mentioned above, there will be some studies which will be performed in coordination with the JGO and JEO.  The presence of a third point of observation will allow the construction of three-dimensional images of the magnetosphere.

After separating from the JMO, the JGO will first take part in an elaborate series of maneuvers in coordination with the JEO, in which they will conduct a large-scale survey of Jupiter and its moon system.  The JGO’s primary goal is to study the moon Ganymede, but there will also be observations of Callisto, Io and Europa, performed either alone or in cooperation with the JEO.  After that, the JGO will go into orbit around Ganymede for prolonged observations.  (This is a greatly simplified description.  The full itinerary will include an ambitious- and confusing- array of maneuvers, a full discussion of which is far beyond the scope of this humble article.  For those who want more details, the websites of all three space agencies offer fascinating reading.)

Ganymede is Jupiter’s largest moon.  In fact, if this body orbited the sun instead of Jupiter, it would be classified as a planet.  It is larger than either Mercury or Pluto, and is three-quarters of the size of Mars.  It actually has an oxygen atmosphere, though the pressure is too low to support any kind of life known on Earth.

One interesting point about Ganymede, and the subject of some of the study on this mission, is that it is the only moon in the solar system with an active magnetic field.  Like so many other things in the Jupiter system, Ganymede’s magnetism is a result of Jupiter’s gravity.  In our last article, we saw that the big planet’s gravity causes tidal heating in the interiors of its moons, especially the closer ones.  This is the reason why Europa almost certainly has a liquid ocean beneath its surface, and it is also the reason for Io’s excessive volcanic activity.  Here we see another example, for without Jupiter’s gravity, Ganymede would not have its magnetic field.

As we saw in our article on the BepiColombo Mercury probe a couple of weeks ago, a body can only have an active magnetic field if it has a solid inner core with a molten mantle above it.  The molten mantle contains iron, and the heat which keeps it molten causes it to move in convection currents.  The solid core contains iron, too, and the movement of the molten iron mantle around the solid iron core is what makes the electrical current that forms the magnetic field.  Without this movement of iron around iron, electricity will not be generated, and the body will not have a magnetic field.  In the case of Ganymede, it is the tidal heating caused by Jupiter’s gravity that keeps the moon’s mantle liquid, allowing the convection movement that makes the whole process work.

During the time when the JGO is orbiting Ganymede, there will be times when the JEO is also passing close enough to allow coordinated observations involving both probes.  This will allow detailed study, with the JGO performing close study while the JEO observes from farther away.  In this way, it is hoped that they will be able to do precise mapping of the Ganymedan magnetic field.

We already know that Ganymede’s history has been long and complicated.  About forty percent of its surface is highly cratered, darker areas, while the other sixty percent is lighter in color, and is covered by an elaborate pattern of grooves.  The surface of Ganymede is mostly water ice, and these grooves are thought to be caused by tensional faulting of this ice, or by liquid water flowing up from below the surface.  Here, as on Europa, we have the near certainty of large amounts of liquid water beneath the surface.   The presence of liquid water always raises the possibility of life, and here again we get back to the main goal of the entire EJSM/LaPlace mission,  to search for habitable worlds.  This actually encompasses two separate questions: do these worlds have life now, and could they support human beings in the future?

The fourth moon to be examined will be Callisto, and these observations will be conducted primarily by the JGO, though the JEO will take part in some of them.  Callisto is the third largest moon in the solar system, and is almost as big as Mercury.  The unique and interesting thing about Callisto is that it seems to be a geologically dead world, with no visible seismic activity, vulcanism, or anything else to alter its surface.   Unlike the three other moons we have looked at, this one orbits much farther from Jupiter, so the kind of volcanic activity that we saw on Io, for example, is absent here.  Because of this, it is thought that Callisto has the oldest landscape in the solar system, preserving impact craters from the very early history of planetary formation.  All of the other bodies in the solar system have changed since then, but Callisto remains as a snapshot of the system’s childhood.  As you can imagine, this moon will be the subject of much study in the future, and the work that will be done by this mission will pave the way for that research by giving us our first close-up view of the body.

The EJSM/LaPlace mission is a huge undertaking which promises to yield a staggering amount of data.  Even if some of the science doesn’t come off as planned, this project will undoubtedly be one of the most productive and thorough space projects ever.  For years to come, we will be poring over the information that this project will give us.

We have always had our eyes on the moons of Jupiter.  Ever since Galileo looked through his homemade telescope and drew his first crude pictures of them, we have wanted to visit them.  The more we learn about them, the more interesting they get.  These are real worlds, with atmospheres, heat and water.  They may have life, and they certainly will have it in the future, for we will visit these bodies in person someday.  While it is unlikely that hellish Io will ever be settled by humans, it certainly makes an interesting place to study, and the other three Galilean moons will almost certainly feel the tread of human feet someday.  When that happens, it will be a direct result of the knowledge we gain from this mission.

Sources:

Solar System Exploration: Moons and Planets of the Solar System at NASA website:  solarsystem.jpl.nasa.gov/planets/

OPFM: Outer Planet Flagship Mission at website of Jet Propulsion Laboratory, California Institute of Technology:  opfm.jpl.nasa.gov/europajupitersystemmissionejsm/

OPFM: Outer Planet Flagship Mission- Jupiter Ganymede Orbiter (JGO) Concept at website of Jet Propulsion Laboratory, California Institute of Technology:  opfm.jpl.nasa.gov/europajupitersystemmissionejsm/jupiterganymedeorbiterjgoconcept/

Synergy Between JMO, JGO, and JMO at ISAS/JAXA website:  sprg.isas.jaxa.jp/jupiter/pukiwiki/index.php?Synergy%20between%20JMO%2C%20JGO%2C%20and%20JEO

Scope and Purpose: The Europa Jupiter System Mission (EJSM) at ISAS/JAXA website:  sprg.isas.jaxa.jp/jupiter/pukiwiki/index.php?I.%20SCOPE%20and%20PURPOSE

III “The Spacecraft” and III.1: “Current Plan” at ISAS/JAXA website:  sprg.isas.jaxa.jp/jupiter/pukiwiki/index.php?III.%20Spacecraft

II.2.1 “Main Objectives” at ISAS/JAXA website:  sprg.isas.jaxa.jp/jupiter/pukiwiki/index.php?II.2%20Magnetospheric%20and%20Space%20Sciences

IV.1 “The Current JAXA Plan” at ISAS/JAXA website:  sprg.isas.jaxa.jp/jupiter/pukiwiki/index.php?IV.%20Orbit%20and%20Operation

As often happens in the field of space exploration, the idea was way ahead of the reality.  The mission’s unusual name is a salute to Italian astrophysicist Guiseppe “Bepi” Colombo, who originally figured out the course that such a flight should take.  In 1975, Colombo proposed a plan to NASA by which a spacecraft could swing close to Mercury three times by making gravity-assist maneuvers around Venus.  The plan would have worked, but was too ambitious for NASA at the time; it got shelved and forgotten.  Now the years have passed, and things that were once unattainable seem within reach.

Unfortunately, Bepi Colombo died in 1984.  Another sad fact about space exploration is that those who think up the great ideas often don’t live long enough to see them come of age.  The mission that he proposed years ago is going to happen at last, and it will bear his name.

BepiColombo will be launched aboard a Soyuz-Fregat rocket from Kourou, French Guiana.   The date seems to be uncertain; the JAXA website says it’s 2013, but the ESA site says 2014.  (It’s possible that the mission plans were changed in the early stages, as often happens, and that these two postings reflect different versions of the plan.)  BepiColombo’s objectives are to make precise observations of the planet’s magnetic field, magnetosphere, interior and surface.

One of the main questions that it will try to answer is why, of all the planets in the solar system, only Earth and Mercury have active magnetic fields.   Actually, we know why Earth has one, but knowing that just makes Mercury more perplexing.   Earth has an active magnetic field because it has a molten layer surrounding its solid inner core.  The innermost core is compressed into a solid by gravity, but above that, there is a viscous, molten layer called the outer mantle.  The fluid contains iron, and as it moves around the core, the entire planet becomes a giant electrical generator.  The principal is exactly the same as generators here on Earth, in which a rotor moves around a stator, creating an electrical field.  In this case, we see the basic concept expanded to a planetary scale, and the field that results is so strong, it forms lines of magnetic force that stretch around the whole planet.  The important point here is that without the molten outer layer and the solid inner layer moving past each other, you wouldn’t get the magnetic field.  It’s being constantly generated and replenished by that spinning motion inside the planet.

If Earth’s molten outer core were to cool down and become solid- which will happen eventually, in our planet’s old age- the magnetic field would no longer be generated.  Of course, this does not mean that the earth’s magnetic field would suddenly disappear.  We all know that when you place a piece of iron in a magnetic field for a while, it becomes magnetized, too.  If you cut off the magnetism, the iron will still retain some of that energy, but it will be weaker than the original source, and it will fade with time.  If the iron is all mixed up with a bunch of rocks and other stuff, and the mixture is of a very uneven consistency, then the magnetism will fade at an uneven rate.  If there’s more iron in one spot than another, then of course, that spot will hold the magnetism longer.  Eventually you will end up with a glob of iron and rock and stuff which has a very weak, uneven magnetic field around it.  If you had the instruments to measure it, it would be immediately obvious that this was an old, fading field rather than an active one that is being constantly replenished from within.

Let’s leave Mercury for a moment and look at Mars.  This planet has a weak, spotty magnetic field, which tells us that it once had a molten outer core like Earth’s, but that core has now become solid and is no longer generating magnetism.  This is not surprising, because Mars is smaller than Earth, and must have lost the initial heat of its birth faster than Earth has.  Mars is said to have a “fossil” magnetic field.

So here we have the two extremes: Earth with its active field, and poor old Mars with its weak, faded one.  In the old days, when we were looking at Mercury from afar, the popular thought was that it would probably have no magnetic field at all, or if it did, the field would only be a fossil field.   The reasoning was that since Mercury is considerably smaller than either Earth or Mars, it should have long since lost all of the original heat from its formation.  And despite the fact that Mercury is the closest planet to the sun, it still isn’t hot enough to melt rock.  After all, the planet’s surface is still quite solid.  Since the inner region of the planet should have lost all of its original heat, and is insulated by all the rock that lies above it, it must be cooler than the sun-baked surface.  So, if the surface is solid, the core should be, too.  Looking at it logically, you get a picture of a small planet with a relatively cool and very solid interior.

Or so we thought, back in the olden days.  When Mariner 10 made its flyby of Mercury in March of 1974, it revealed what nobody had expected to find: an active magnetic field.  Amazingly, this little planet seems to have a molten portion in its interior, just as Earth does.  Either that, or the current theory about how planetary magnetic fields are generated is completely wrong.  If that’s the case, it means we’ll have to throw away all the textbooks and start over at square one- and since this would be a scandalous waste of paper, we can only hope that it won’t be necessary.  A less revolutionary explanation is that Mercury may have large amounts of radioactive material in its interior, which generates enough heat to melt iron and form a molten mantle- but at the moment, this is pure speculation.

In any case, the planetary scientists certainly want to have a closer look.  The part of BepiColombo’s instrumentation which was contributed by JAXA is the Mercury Magnetospheric Orbiter (MMO) which will observe the planet’s magnetic field with unprecedented accuracy in an effort to better understand its configuration and how it is being created.  It is hoped that the probe can also reveal how Mercury’s magnetosphere differs from Earth’s.  Since these are the only bodies known to have magnetospheres, it is possible that comparing the two will help us understand  something about both of them.

Another job of the MMO is to observe the tenuous exosphere of Mercury.  Rather than a gaseous atmosphere like Earth’s, Mercury is surrounded by a very thin layer of atoms, mainly sodium, that have been blasted off the surface by the fierce solar radiation and the impacts of micrometeorites.  These atoms quickly heat up and escape into space, so Mercury never builds up as much pressure as Earth’s atmosphere has.  This exosphere has never been studied in detail before, and the MMO will observe its structure and the process of formation and escape into space.

The other component of the BepiColombo mission is the Mercury Planetary Orbiter (MPO), contributed by the European Space Agency.  The function of this probe is to study Mercury as a planet: its form, interior, structure, geology, composition and craters.  This will result in a more accurate and detailed map of Mercury than we have ever had before, as well as a better understanding of just what the planet is made of.

One specific question that will be addressed by the MPO is whether there is frozen water at Mercury’s poles.  In the flyby of Mariner 10 back in 1974, the satellite received radar reflections from the polar regions, so we know that there’s something highly reflective there.  Nature doesn’t produce many things that are that reflective; frozen water is the most common.  And it makes sense, because there are areas at Mercury’s poles that are permanently shaded, and probably have been been since the planet was formed.  As strange as it seems, the closest planet to the sun has places that have never felt sunlight, and may be the coldest piece of ground in the solar system.  The MPO will subject these areas to closer scrutiny, looking for ice.

Like some other places in the solar system, Mercury is interesting because it can tell us something about the system’s early times.  On Earth, any substances that we find have been crushed, melted, reformed, eroded and then reformed again, possibly many times over.  There really isn’t much pristine matter from the solar system’s birth for us to study here.   On some of the other bodies in the system, there may be more unchanged matter that can give us a better picture of the original accretion disc which gave birth to all of this.  In particular, if there is ice at the Mercurian poles, it may be a sample of the water vapor that was present in that disc around the sun, which froze in those early times and has remained frozen ever since.  As you can imagine, the planetary scientists are itching to get a peek at it.

The questions are there, just waiting to be answered- and BepiColombo will bring us some of those answers.  By the time it arrives in 2020, we should already have a lot of new information on Mercury from NASA’s MESSENGER probe, which will have been in orbit around the planet for nine years.  BepiColombo will fill in more of the gaps in our knowledge, providing us with our most complete picture yet of the sun’s first planet.    The projected mission is only supposed to last for one Earth year, but there is the possibility of an extension beyond that.

BepiColombo is a big, ambitious mission with huge potential.  It is a remarkable technical achievement, and in the coming years it will bring us some fascinating science about one of the last unexplored bodies in our system.

The fun is just beginning!  As the news comes in, you get always get it here.

Sources:
Mercury Exploration Mission “BepiColombo” at website of Japan Aerospace Exploration Agency:  jaxa.jp/projects/sat/bepi/index_e.html

BepiColombo page at website of the European Space Agency:  sci.esa.int/science-e/www/area/index.cfm?fareaid=30

BepiColombo Overview on the Science and Technology page at website of the European Space Agency:  esa.int/esaSC/120391_index_0_m.html

World Book at NASA- Mercury:  nasa.gov/worldbook/mercury_worldbook.html

Mercury: Closest Planet to the Sun at website of National Geographic:  science.nationalgeographic.com/science/space/solar-system/mercury-article.html

BepiColombo: Mercury Interior at website of the European Space Agency:  sci.esa.int/science-e/www/object/index.cfm?fobjectid=31272

For space kids who grew up reading science fiction, this idea requires no explanation.  For those unfortunate readers who did not have this experience, we offer this quick summary:

The warm, gentle sunlight that we feel here on Earth is really only a tiny fraction of the sun’s full output.  Even the hottest places on Earth- say, Death Valley or the Sahara Desert- are only receiving a small percentage of the solar radiation that hits the atmosphere above them.  Luckily for us, we are protected from most of it by that thick blanket of air.  Outside of that protection, the wind from the sun is a blasting torrent, a constant tsunami of radiation and particles.

And of course, sunlight exerts a certain amount of pressure.  The pressure is very weak down here on Earth, but if you get off the Earth and move into the full blast of the solar wind, everything changes.  Suddenly you’re in the full tsunami, and the pressure exerted by it is much greater.

Consider what you’ve got here.  It’s a stream of propulsive force which, in human terms, is inexhaustible- and unlike the intermittent thrust of rockets, this is constant propulsion, which allows you to build up enormous speed over time.  In the world of space exploration, this is the Holy Grail.  It is the thing that can finally free us from that necessary evil of space flight: fuel.  The sad fact is that when you’re using conventional rockets, the fuel is the biggest part of the weight.

Now, we’ll always need a big push to get out of the atmosphere and attain orbital velocity, and chemical rockets are still the only way to get that (though other ideas have been discussed- more on this in future articles).  However, once you get into orbit and you’ve got all that sunlight,  why not use it?  Throw out a kite and ride!

That’s the definition of a lightsail: a kite that uses the solar wind to move a spacecraft.  In the old days, this was pure sci-fi, because we didn’t have any materials that were strong and light enough to do the job, but recent advances in materials science have provided lightweight plastics that are bringing the goal within reach.   Not only that, but we now have a couple of possible embellishments that build on the basic concept and use the power of light in different ways.

As mentioned above, there are actual prototypes being readied for launch this year.  The Japan Aerospace Exploration Agency, a rising power in the field of space exploration, is planning to send up a craft called IKAROS in May.  In an effort to cut costs, the craft will be launched aboard the same rocket with Japan’s Venus Climate Orbiter, the partner to the European Space Agency’s Venus Express which we discussed a few weeks ago.

IKAROS takes the idea of a lightsail a step or two further.  Here, the plastic membrane is not only used for propulsion, but also contains three other systems: a thin-film electrical power generation system, a set of steering devices and a dust-counter.  They do all this on a layer of polyimide that is only .0075 mm thick.  When fully deployed, IKAROS will be a square with a diagonal length of 20 m.  Its mission will be in two stages.  In the first stage, the sail will be deployed and used to generate electricity.  This will be the first time a lightsail has been used for this purpose, and if the mission ended right there, it would have already started a revolution in the field of space electronics.

But hopefully, IKAROS will keep on going.  The second phase of its mission is to actually use solar power to navigate the craft.   The destination of IKAROS is uncertain, but it will be steered toward Venus.  As mentioned above, it will be sent into orbit on the same rocket with the Venus Climate Orbiter, and hopefully both craft will eventually arrive at that planet.

IKAROS is the first of two proposed Japanese missions.  The second one will take place in the late 2010′s, and will consist of a hybrid craft which combines all of the technology of IKAROS with an ion propulsion system.

The ion drive uses electricity generated by solar power to excite xenon fuel.  The excited fuel is focused into a jet by passing it between two powerful magnetic fields, and leaves the engine at high velocity.  The advantage of an ion engine is that the xenon fuel is capable of delivering a large amount of thrust in proportion to its weight, which means that a spacecraft can carry enough fuel to keep going for years.

When you combine this system with the lightsail idea, you get a hybrid craft that can use both systems to maximum advantage.   For instance, such a craft might use its lightsail while it’s near the sun, riding the solar wind and storing up electricity.  Later, when it gets farther out where the sunlight is weaker, it might fold up its sail and use the stored electricity to run the ion drive.

Here in the US, the Planetary Society is making its second attempt at testing a lightsail.  Their first one, Cosmos I, was tragically lost when its launch rocket crashed, but now the Society has embarked on an ambitious project to deploy three sails over the next few years.   While the Japanese project is focused on broad technologies that will be used for multiple projects in the future, the Planetary Society is focusing more on practical and specific jobs, such as monitoring the sun for solar storms and providing stable Earth observation platforms.

Their first sail, Lightsail I, will be launched this year and will demonstrate the deployment of the sail and its use for propulsion.  The second sail will do the same, but will move to a much higher Earth orbit.  The third sail in the Planetary Society’s program will leave Earth orbit and navigate to the Earth-Sun libration point, L1.  This will be an ideal location for weather-sensing satellites and other devices, which in the future will hopefully be propelled into their positions by lightsails.

The Planetary Society’s ambitions are set on greater goals someday.  Louis Friedman, the Society’s executive director, recently posted an article on their website about the glowing possibilities offered by this line of research.  One possibility that he brought up is the idea of using a lightsail with an Earth-based laser for propulsion instead of sunlight.  With something like that, you could send a beam of coherent light at another star and ride it all the way there.  When you arrived, you could set up another laser and point it back at Earth, then ride the beam back home.  Whereas the basic solar sail idea only allows travel within the solar system, the laser idea could give us access to the stars.

It’s a long way off, but someday it could happen.  In the meantime, we need to do the basic groundwork, and that’s what’s about to happen.  Both the JAXA craft and Lightsail 1 will go up this year, and the results of those projects will show the way to the future.

In 1964, Arthur C. Clarke wrote a short story called “The Sunjammer,” which was about a race between solar-propelled spacecraft.  It was published in a popular boys’ magazine, and was read by a whole generation of kids in love with space.  Some of those kids are probably working on these projects today- and some of them are also reading and writing about them.

Stick with us, and you won’t miss a thing.

Sources:
Satellites and Spacecraft: Small Solar Power Sail Demonstrator “IKAROS” at JAXA website:  jaxa.jp/projects/sat/ikaros/index_e.html

IKAROS Project page at JAXA website: jspec.jaxa.jp/e/activity/ikaros.html

Let’s Set Sail for the Solar System by a Solar Yacht!  at JSPEC website: jspec.jaxa.jp/ikaros_cam/e/03.html

Lightsail- the Future of Solar Sailing at the Planetary Society website:  planetary.org/programs/projects/solar_sailing/

Friedman, Louis D.: Lightsail: A New Way and a New Chance to Fly on Light at the Planetary Society website:  planetary.org/programs/projects/solar_sailing/tpr_lightsail.html

HAYABUSA was launched on May 9, 2003 on an M-V-5 launch vehicle from Uchinoura Space Center on Kyushu Island, Japan. About a year later, the probe modified its orbit by performing a flyby of Earth, and was sent on a trajectory for its destination. It arrived at Itokawa on September 12, 2005.

It was a perilous journey. Along the way, HAYABUSA had to endure two solar flares, one of which damaged its solar panels, resulting in a delay in arrival. Despite the problems, the mission was a technological success, premiering an array of new devices that will also be used on future space missions. The craft is a beautiful piece of equipment, featuring four ion drive propulsion units and an autonomous guidance system allowing the probe to guide itself without directions from Earth. Its flyby of Earth was the first such maneuver to be achieved using only ion drive as the propulsion.

(For the rest of this article, you must bear in mind that there was a 30-minute signal delay, so the events that are related here in a few paragraphs actually took place over many worried hours, with much nail-biting by the mission control crew.)

So far, so good. HAYABUSA had arrived a little battered, but still capable of performing its mission. It made observations of the asteroid from a few kilometers out. (Itokawa looks a bit like a cucumber: elongated and slightly bent, with little lumps here and there on its surface.) The next part of the mission was to deploy a small hopping robot to rove over the asteroid’s surface. On rough terrain, hopping is sometimes a better way to get around than rolling. It was hoped that this little device would be able to get to places that the larger unit couldn’t.

Unfortunately, this part of the mission was a failure. A technical malfunction caused the hopper to fire in the wrong direction, missing the asteroid completely. It’s still out there somewhere, whizzing around the sun: an artificial asteroid. That was a disappointment, but the main part of the mission was still to come. HAYABUSA prepared for its landing on the surface of Itokawa.

At this point, there was a malfunction that almost ended the mission prematurely. HAYABUSA made two landing attempts, and on the second one, a leak developed in a fluid line within the probe, causing a cascade of damage. After that, there was a period of confusion.

The probe continued to approach the asteroid. The moment of landing came and went, and the probe kept signaling that it was descending. Why was it still descending? Had it missed the asteroid completely, or was the signal simply incorrect? The mission control team decided to give the probe instructions for an emergency ascent in the direction of Earth. It was a gamble, since they were not sure of the status of their probe and were not even certain if it could respond, but it was their only chance.

To their enormous relief, it worked. Communication was reestablished with the probe, which sent an update relating the exact sequence of events:

The first landing attempt was aborted by the probe itself, because it detected an obstacle during the descent and recognized it as a danger. On the second landing attempt, apparently the signal indicating that the probe was still descending after the expected landing time was incorrect. The landing was successful, and the probe remained on the surface of the asteroid for about half an hour. The probe then lifted off from the asteroid.

It was at this point that the leak in the fluid line had developed, resulting in a period of signal loss. During this time, the probe’s onboard computer had rebooted once, causing the loss of all data that was stored at that time. This left the central question unanswered: did HAYABUSA successfully collect its sample of asteroid dust? The team members pored over their data, and there were conflicting press reports which first indicated that the sample had been taken, then that it had not.

The plan had been for HAYABUSA to fire one or two pellets into the ground, throwing up a plume of dust which would be captured and stored in the probe’s sample container. In examining the data from the probe, the scientists were unable to determine if this had been carried out. However, it was ascertained that during the 30 minutes that HAYABUSA was on Itokawa, its sample collector was open and in contact with the ground. It is hoped that even if the pellets were not fired as planned, some dust from the surface may have been disturbed by the landing and drifted into the container. Even a microscopic amount would be of enormous scientific importance.

The problems were not over for HAYABUSA. A malfunction developed in the craft’s ion drive, raising the possibility that it might not be able to put itself into orbit for return to Earth. (We can guess that this may be related to the original fluid leak.) In a heroic save, the team managed to link parts of two of the craft’s four ion engines, thus achieving the thrust of one engine. The reduction in thrust would delay the probe’s return to Earth, originally planned for 2007, until June of 2010.

That day is coming in just a few months now, and provided that the probe’s return to Earth is successful, we will finally learn if it contains the dust of an asteroid. Even if it doesn’t, the Japan Aeronautical Exploration Agency has earned praise from the scientific community for their heroic and ingenious efforts in overcoming the many obstacles that this mission faced. Regardless of the result of the HAYABUSA mission, Japan has suddenly moved into the forefront of space exploration.

Watch for an update at this site when HAYABUSA returns to Earth in June.

Sources:

Website of the Japan Aerospace Exploration Agency (JAXA): jaxa.jp/projects/sat/muses_c/index_e.html

Current Status of the Asteroid Explorer HAYABUSA in Space Daily: Your Portal to Space, February 6, 2009: spacedaily.com/reports/Current_Status_Of_The_Asteroid_Explorer_Hayabusa_999.html

Space Topics: HAYABUSA (Muses-C) at website of the Planetary Society: planetary.org/explore/topics/hayabusa/

Cain, Fraser: HAYABUSA Successfully Collects an Asteroid Sample in Universe Today: universetoday.com/2005/11/29/hayabusa-successfully-collects-an-asteroid-sample/