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The Forefront of Space Science

“The Next Goal for Rockets” or “The World of the Swindler?”
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With current-launcher safety-ratio levels, however, a reusable vehicle would crash once every day or two if tens of flights were performed per day. By contrast, the ratio of aircraft lost in accidents in the present-day air transportation industry is under one-millionth. Fig. 2 is an excerpt from a paper on the safety of reusable engines. The left of the figure shows flights without any failures. The center shows cases where: (1) if any engine anomaly occurs, the engine is safely stopped; (2) if an engine fails to fire, or breaks up, the damage spread is successfully limited. Even in this case, air-worthiness is maintained and a safe landing is possible. The worst case is shown at right, i.e., vehicle loss. The increase in reliability for expendable rockets means an increase in the no-failure ratio, i.e., “mission success” at left in the figure. The center of the figure shows what is required for reusable vehicles. The bottom line is that we must create a system with a scheme to permit malfunctions and yet achieve a safe landing. We board modern airplanes without concern. In fact, however, while there are quite a few malfunctions on aircrafts, there are few accidents. This is because aircraft incorporate technologies to cope with failures in their systems. Some people simply compare the safety ratio of rockets with the 10-6 ratio of aircraft and say that rockets are dangerous. This remark has no meaning outside the above discussion. Let’s think how we can design such a rocket. What I would like to stress here is that the significant points for a reusable rocket are thousands of repeat flights and the creation of a system that allows failures without causing accidents.

Figure 2
Figure 2. Safety is remarkably increased by fault-tolerance system in re-use

“Launcher men” are always overdoing it. When filling liquid-hydrogen fuel, they say “Up to 1km radius is off-limits.” Today, the development of the “hydrogen society” is under way to supply all energy requirements with hydrogen and clean-energy sources in response to environmental concerns. When I talk to auto- or energy-industry people, I notice that their ways of thinking are different from us. It is a difference between people who focus on a separate world – space – and people who try to create systems acceptable by society. No one evacuates the area when they fill up with gasoline at a gas station or as they drive cars. There is a big contrast between those who plan to treat hydrogen in the same way as gasoline and invest in the hydrogen business, versus those who urge us all to evacuate. In other words, it is the difference between those who face society and those who do not. At this stage, auto-industry people still come to us to ask, “How are you handling hydrogen?” As their technology will exceed ours in the future, however, we old-fashioned rocket men must not remain distant from them. As long as we stay inside our closed world of space, there can be no real progress.

To experience real repeated flight, we are now launching a toy-like rocket. Our staff is excited by the project: “our rocket has a mechanism to perform an emergency landing when failure is detected,” “repeat flights carrying liquid hydrogen” and “one flight a day, successive flights for three days.” Actually our rocket is inferior to an airplane: it ascends to an altitude of only tens of meters, hovers and lands. Present-day rockets are produced based on the idea that it is acceptable to make a single launch. However, I have learned that we have to design a reusable vehicle in a different way to enable it to launch again tomorrow after a launch today. This is called (rather pretentiously) “system architecture for re-use.” Our current experiments have received responses from the public that differ from regular rockets. The main picture shows one of them, “Will space travel be like this?” Travelers are seen carrying souvenir bags and putting on slippers. I doubt that we will be able to board the vehicle in such an easy and relaxed way. The body of the vehicle is also somewhat strange. The feel of space travel is well expressed, however. We never receive such responses to M-V or H-IIA rockets. I interpret this positively: such responses show that the public is interested in and supports our rocket and that they see a promising future in it.

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