Q: Everyone here had a hand in building Hayabusa, but what were your individual roles?

Oshima: I was the system manager. We also had a project manager, just like at JAXA. For Hayabusa, Mr. Hagino, who was introduced in Tale 2, handled this job. The main role of the project manager is to manage the staff, budget, and schedule, as well as to determine the overall direction of the project.
Basically, the project manager is responsible for setting up the overall plan based on an understanding of technical issues so that development can proceed smoothly.
The system manager, on the other hand, is the technical manager responsible for the probe as a whole. You can imagine that some problems will occur when developing a probe. For example, although the total probe weight and power are limited, each on-board piece of equipment has minimum weight and power requirements. It was my job as the system manager to determine which parts to change to improve the overall probe design and how to change parts to ensure probe balance. I also had to provide instructions to engineers.

Q: So, what you mean is that you look at the probe as a whole, instead of individual pieces of equipment, to distribute resources in a balanced way?

Oshima: That's right. The parts of a probe, which we call components, include various pieces of on-board equipment. The system manager finds a way to connect these pieces of equipment so as to satisfy the requirements of the probe as a whole. There are many constraints, such as on the weight, power, temperature, attitude, sensor field of vision, positional relationships between pieces of equipment and the center of gravity. There are also constraints on the internal plumbing and wiring. Let’s say, some parts cannot exceed certain lengths, and some wiring cannot exceed certain temperatures. My job is to optimize the probe as a whole to satisfy all the constraint requirements.

Q: So, it's obviously not enough just to fill up the probe with all the individual pieces of equipment?

Oshima: Yeah, just optimizing the individual components does not optimize the probe as a whole. That's why I'm there to oversee the probe as a whole and make sure that the necessary adjustments are made.

Okudaira: And the ones who actually responded to Mr. Oshima's impossible demands for Hayabusa were Mr. Shouji and I .

Oshima: What, did I really make impossible demands? I sure don't remember anything like that…

Shouji: Yeah, it's a lot easier for the person who makes the demands to forget about them. (Laughs)

Okudaira: I was in charge of the structural design. Simply put, I guess you could say I determined Hayabusa's shape. The technical term for this is configuration. My job was to determine how to arrange Hayabusa’s on-board equipment?including the antennas, ion engines, sampler, and collection capsule?into one probe.

Q: Was that specific to Hayabusa?

Okudaira: Structural design is required for any satellite, but, because Hayabusa's mission was to return a sample from an asteroid, the probe had many specialized pieces of equipment and was difficult to design. Take, for example, the sampler, an especially distinctive feature of Hayabusa. First, since there was no precedent for collecting an asteroid sample, we had to start with sampler research. We had various ideas, including using a sticky substance to collect a sample or wrapping the sample in cloth, but after long discussion, we finally decided to fire a pellet and collect the particles that flew up.
The collected sample also had to be moved to the collection capsule, so we needed to design a transportation route from the sampler to the collection capsule inside Hayabusa. And, the best place for the sampler was definitely on the bottom surface of the probe at the center, where it passed through the center of gravity. This is because, at this position, the sampler would not cause the probe to lose its balance when it touched down on Itokawa.

Oshima: However, this is still only partial optimization, because the collection capsule had to separate from Hayabusa when the probe returned to Earth, which means the capsule had to be attached to the outside of the probe. But, if the sampler was attached to the center of the bottom surface and the capsule was attached to the outside of the probe, the transportation route inside the probe would be too long. So, from the standpoint of designing a system that was optimized as a whole, attaching the sampler horn to the center was not acceptable.

Okudaira: To address this issue, after considering many possibilities, we decided to attach the sampler to the edge of the bottom probe surface so as to minimize the length of the transportation route, as close to the collection capsule as possible. Unfortunately, this meant that there was a risk of the probe losing its balance on touchdown. Therefore, we designed the sampler so that it could expand and contract like a car suspension system, absorbing any shock.

Shouji: After the mechanical system engineers, including Mr. Okudaira and me, and the system engineers determined the shape and arrangement of the probe, the next step was to draw up a detailed design. We, the mechanical system engineers, were also responsible for this task. I was in charge of designing the probe and actually drew up the blueprints.

Okudaira: Building Hayabusa was truly hard work. When the work started, we didn't even know what kind of equipment or how many pieces of equipment had to be installed. And we would have run out of time if we had waited until all this information was collected. We had to do whatever we could with our limited resources.