PLANET-C (Courtesy of Akihiro Ikeshita)
Image of Venus taken by U.S. Magellan (Courtesy of NASA/JPL)
Q. What will we learn form the study of the Venusian atmosphere? And, how will we benefit from it?
On Earth, we are very familiar with weather forecasting, which relies on meteorological data accumulated over time. But this does not mean that we have full comprehension of the principles of meteorology. By studying the Venusian atmosphere and establishing the principles of Venusian meteorology, we hope to fill in some gaps in our current understanding of meteorology on Earth. Earth and Venus have very different climates, but from the point of view of geophysics, the two are almost identical - they have the same size, mass, and density. The fact that they have the same density suggests that they have the same gravity to keep their atmospheres. In other words, the surface gravity of Venus is the same as the Earth's - 1G. In addition, the Venusian and Earth atmospheres both circulate according to the laws of fluid dynamics, so I expect that we will discover more common characteristics between them. By comparing their differences and similarities, we'll be able to better understand the principles of meteorology on Earth. Ultimately, I'd like to contribute to the establishment of planetary meteorology by studying all the solar planets. If we can acquire a deeper understanding of the meteorology of different planets, I think that it will help us respond to the consequences of future climate change on Earth.
Global warming is a critical problem, and the volume of CO2 in Earth's atmosphere seems to have a lot to do with it. Ninety-six percent of the Venusian atmosphere is CO2, and the ground surface temperature reaches 460°C due to the greenhouse effect caused by the CO2. Global warming on Earth is likely to get worse in the future, but we may be able to find a solution by studying the atmosphere of Venus.
Earth (Courtesy of NASA)
I think planetary exploration forces us to see ourselves in a much broader context, to shake up our self-awareness. As long as you're looking only at the modern Earth, you'll know nothing but a world where life and relative security are taken for granted. But imagine Earth 3 billion years ago, when the oceans and Mother Nature already existed, long before humans arrived. Understanding the nature of things now and in the past, which planetary exploration helps us to do, will give us an opportunity to think deeply about what we humans really are. Planetary exploration is similar to searching for our origins by studying the ancient oceans. I think that the universe can help us remember to be humble again. Each solar planet is unique, and by exploring them all, we will further recognize the diversity that surrounds us. I think it is time for us to bring ourselves to ponder our existence among such diversity.
Q. How would you like to advance Japan's planetary exploration in the future?
I'd like to make Japan's planetary sciences world class. I'd like to execute planetary exploration missions that make scientists around the world eager to get our data. Just following in the path of other nations is out of the question. We need missions that are unique and original. In order to achieve this, Japan must stimulate the development of its own planetary exploration technology. Many people are under the impression that Japan is always capable of doing something cutting edge, but this is not true.
For example, Japan needs to enhance its technology to measure the distance from Earth to spacecraft in order to determine its position. Japan has a 64-meter antenna at JAXA's Usuda Deep Space Center, which was established in 1984. This is sufficient for a single, straight-line measurement from Earth to spacecraft, but it doesn't allow you to use the triangulation method, which gives a more precise measurement. On the other hand, the United Sates, for example, has successfully advanced its orbit determination technology by deploying three ground stations in the northern and southern hemispheres to track spacecraft. For Japan to establish the same technology, we need a ground station in the southern hemisphere, in order to be able to track the position of spacecraft from two different directions.
In addition, we need more than one ground station to track spacecraft continuously. Europe and the United States have their own deep-space networks. NASA's Deep Space Network (DSN) has three antennae - in the U.S., Spain, and Australia - to communicate with their spacecraft 24 hours a day. Because Japan has only one ground station, however, our planetary exploration missions have always had to rely on NASA's antennae, which become available only when the U.S. is not using them. The asteroid explorer Hayabusa used the U.S. antennae, and so will PLANET-C for its data operation. In such circumstances, I'd hesitate to call our mission truly our own. I really believe that Japan needs a deep-space ground station overseas, especially in the southern hemisphere.
It's also essential to develop electric propulsion engines with high thrust. Hayabusa successfully touched down on an asteroid using ion engines, which are a kind of electric propulsion engine. Compared to conventional chemical propulsion engines, electric propulsion engines have less instantaneous thrust, but have better energy efficiency, which makes them ideal for delivering a large volume of materials to a distant destination. JAXA is now developing high-performance ion engines with the technology passed on from Hayabusa. The establishment of this technology will enable us to send spacecraft farther at a faster speed.
Another necessary development is an advanced rocket for planetary exploration. The H-IIA rockets are the world's best two-stage liquid-fuel rockets, specifically designed for inserting satellites into geostationary orbit. However, because they do not have a third stage, the second stage of the H-IIA rocket will have to make the flight to Venus with the 500-kilogram PLANET-C probe - which is much heavier than the second stage itself - as its payload. I'm truly appreciative of the H-IIA staff for their work to actualize the launch. But if an upper stage for the H-IIA rocket is developed one day, that rocket will be incomparable. The M-V rocket, which was retired in 2006, was a solid-fuel rocket developed for launching large-scale scientific satellites that orbit around the Earth and for planetary probes. The three stages of the rocket accelerated in turn, and they had great efficiency (a fourth stage was added for outer space flights). JAXA is currently developing the next-generation solid rocket.
Japan has these areas to improve in its planetary exploration technology. I'd like to contribute to planetary sciences as we clear these issues one by one, collaborating with researchers overseas. I also have great expectations for younger researchers who will be leading the future.
Dr. Masato Nakamura
Professor, Research Division for Basic Space Science, Institute of Space and Astronautical Science, JAXA
Dr. Nakamura received a B.Sc. from the Department of Earth and Planetary Science in 1982, and a Ph.D. from the Graduate School of Science in 1987, both from the University of Tokyo. He was a physicist at the Max-Planck-Institut in Germany, a research assistant at the Institute of Space and Astronautical Science (ISAS), and an associate professor at the Graduate School of Science at the University of Tokyo. He has been in his current position since 2002. He specializes in planetary atmospheric plasma physics.
