Universe Today

High-resolution view of the lunar surface (JAXA/SELENE)

Prior to the creation of JAXA, Japan, through the organizations that formed the merger, already had its own successes in its space program. For instance, as early as the 1980's until the 1990's ISAS was already deeply involved in X-ray astronomy.

The Japanese were also implementing Very Long Baseline Interferometry (VLBI), a space observation technique that enables multiple telescopes to observe a common object and thereby emulating a single telescope with a size equal to the maximum separation between them.

Last 2007, under the newly merged JAXA administration, Japan was able to launch Kaguya, a lunar orbiter. Kaguya, also known as SELENE (SELenological and ENgineering Explorer), was launched with three mission objectives: to study the origins of the Moon, obtain information about its surface, and perform radio science.

Apollo 15 halo as observed by SELENE (JAXA)

JAXA is also involved in solar sail research and even aims to send out a solar sail mission to Jupiter not later than 2010. If plans do carry out, Ikaros, the aircraft being built for this mission, will be launched aboard an H-IIA rocket together with the Akatsuki, a Venus orbiter. The launch date is tentatively scheduled some time in May this year (2010).

This is not the first time the Japanese will be undertaking research involving solar sails. In 2004, under ISAS, the Japanese were able to deploy two prototype solar sails.

In 2005, JAXA announced a 20-year vision known as JAXA 2025. It contained the following long-term objectives, all of which are found in the JAXA website:

1. To build a secure and prosperous society through the utilization of aerospace technology.

2. To prepare for the unraveling of the mysteries of the universe and for lunar utilization, in order to seek the origins of the Earth and humankind.

3. To implement world-class space transportation and Japan's indigenous space activities.

4. To develop aerospace as Japan's next key industry.

5. To establish Japan's aviation industry and develop supersonic aircraft.

Want to know more about JAXA's lunar missions? Here are some stories from Universe Today:

Japanese SELENE (Kaguya) Lunar Mission Spots Apollo 15 Landing Site (Images)
Japanese Moon Mission Returns Detailed Maps of the Lunar Surface

Of course, the most reliable source of information about JAXA would be its own website.

How about letting your ears do the work for a change? Check out this podcast at Astronomy Cast:

The Life of the Sun

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A solar sail is a thin sheet of material that is propelled by energy (or more accurately, by momentum) from electromagnetic waves. It is being considered by some scientists as a possible alternative propulsion mechanism for interstellar flight. If successful, spaceships driven by solar sails will be able to rely on a virtually unlimited source of propellant – the nearest star. In our case, the Sun.

Some of you may have seen, in your physics class before, a small device resembling a miniature windmill encased in glass. Each of the windmill's blades were colored pitch black on one side and white on the other. This device is actually called a Crookes radiometer, and it uses the same underlying principle that makes a solar sail operate the way it does.

Note: There is also the "thermal" explanation for the radiometer's dynamics, but let's just focus on the "momentum" explanation in this article as it is more attuned to the solar sail.

Alright, so how can electromagnetic waves push a solar sail? This can best be understood by trying to recall what Einstein said about these waves. According to him, electromagnetic waves possess both energy and momentum. That EM waves have momentum is subsequently best understood by trying to recall the wave-particle duality of light.

That is, that light can take the form of either a wave or a particle (or photon). If we view light in "photon form", then that means it should have momentum. Having momentum, it should be able to "collide" with other particles or (in the case of solar sails) a surface.

Now, we're all familiar with collisions. Due to the law of conservation of momentum, if the momentum possessed by the colliding particle is large enough, then the surface can move forward.

Since light from the Sun can contain high frequencies (as in ultraviolet light), they can possess high energies, and subsequently, high momenta as well. These physical quantities are directly proportional with one another according to the relationships E=hf and E=pc.

For this principle to work, the solar sail or sails should cover a vast amount of area. Speed will be increased in due time as the ship accelerates due to the constant bombardment. Maneuverability can be achieved by changing the direction of the sales much like water-based ships.

If plans carry out, Japan will launch the first ever interplanetary solar sail spacecraft named IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of theSun) this year (2010).

Japan already successfully deployed two prototype solar sails in 2004. Read about that story here by clicking on that link.
Here are some articles pertaining to space flight, of which solar sails are one of the most promising technologies.

NASA has a brief history of solar sails. From the same site, you can also find an article entitled Solar Sails Could Send Spacecraft 'Sailing' Through Space.

Check out this podcast at Astronomy Cast:

The Life of the Sun

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LightSail-1 Artists rendition of LightSail-1 by Rick Sternbach. Credit: Planetary Society

Sagan, co-founder of the Planetary Society was a long-time advocate of solar sailing.
Read more…

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Nasa Diagram of a ramjet

This engine isn't the normal workhorse jet propulsion we normally associate with the commercial airplanes – they're too slow. Ramjets operate at peak efficiency at the speed of Mach 5 or 5 times the speed of sound. This is a speed at which the forward motion of the aircraft allows it to scoop up and compress air as it flies.

The ramjet has a long history in aeronautics. The ramjet was first conceived by René Lorin in 1913. He attempted to build and test it but failed to get it working. Over the next 50 years various nations such as Russia and France developed and tested Lorin idea. The first Ramjet powered aircraft to fly was built by René Leduc and was called the Leduc 0.10. It made its first successful flight in 1949. The French owned Nord Aviation would later build on his success with the Nord 1500 Griffon which successfully achieved a flight speed of Mach 2.19 in 1958.

So what makes a ramjet operate? It works on a different application of Bernoulli's principle. Just like with other aircraft, the flow of air creates an area of high pressure and low pressure around the wings. In the case of ramjets the difference between the high air pressure in front of the ramjet engine and the low pressure behind it forces air to be sucked through the front portion of the engine called the inlet and into the combustion chamber. As I stated before this air is then heated by the burning of jet fuel to create thrust.

The ramjet engine has both advantages and weaknesses. First, a ramjet engine is quite simple in design. It consists of the inlet, the cone the diverts air into the engine, the combustion chamber, fuel injector, the flame holder, which ignites the fuel, and the nozzle which directs the heated heated exhaust to create thrust.

Second due to its simplicity it can under certain condition operate quite efficiently. This leads to a discussion of the engine's weaknesses. First there is the fact that it needs high speed forward motion to operate. Without assistance from a regular jet engine, an aircraft with a ramjet engine can not take off from a standstill. Ramjet engines can only operate with at least a speed of Mach 1. A ramjet engine also has a limited window of efficiency. The engine top level of efficiency is at Mach 5 any faster and the inlet can't properly direct airflow into the engine.

Ramjets are now being considered as a possible solution for finding new ways to propel space craft. This type of Ramjet, called a Bussard ramjet would work on the same principle as an atmospheric ramjet but would make use the interstellar cosmic winds instead.

If you enjoyed this article of Universe Today there are others you might like to read. The is an book review on solar sails that talks about the application of Bussard ramjets as interstellar propulsion. There is another great article about the unveiling of a new European space jet.

If you want to learn more about ramjets there are some great resources on the web you can check out. The NASA website has an article with more detailed information on ramjets. You might also find more information on the Purdue University engineering page.

You might also want to hear Episode 101 of Astronomy Cast. It is about advance propulsion systems.

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