In Japan a project little known in the US is successfully following a step-by-step development route to a fully reusable launch vehicle (RLV). Since 1999 the RVT (Reusable Vehicle Testing) project has flown to low altitudes a vertical take-off and landing vehicle powered by a liquid hydrogen/liquid oxygen engine. The vehicle has undergone three major modifications in which each new version involved tests of additional components, systems and techniques needed for practical RLVs. The third configuration completed a series of test flights in October 2003. To find out more about this fascinating project, I contacted its leader Yoshifumi Inatani. He is a professor of the space system engineering division at ISAS (the Institute of Space and Astronautical Science). ISAS is a university organization

Test flight of the RVT#2 on June 25, 2002. (Video)

Prof. Inatani generously agreed to answer a set of questions I sent to him by email. (A second set of follow-up questions and answers are shown indented.)

Mark Oakley of Rocket Man Blog contributed some questions on the vehicle design.

Prof. Yoshifumi Inatani

HS: Many space advocates in the US look back on the DC-X project as a huge success and lament the fact that it was not followed with an incremental, step-by-step development of a series of vehicles that eventually reached orbit. Instead, NASA jumped to the X-33 and the failure of that project has discredited SSTO, and RLVs in general, in the eyes of many here. It is great to see that you are in fact following the step-by-step approach and actually flying single stage rocket VTVL vehicles. Could you briefly review the three RVT vehicles flown so far and what you have learned from each? Inatani: : The background idea of our activity is as follows. ISAS Reusable Vehicle Testing (RVT) team has been continuously

Since 1999, the test vehicle was built and flight-tested, gradually increasing [the] test and demonstration items and flight articles. The first test campaign was conducted for qualifying landing operation making use of engine throttling in 1999. Primarily improving engine durability and landing guidance, the second flight test was made in 2001. Many parts of the vehicle were replaced by newly developed articles such as combustion chamber by electroforming technique, RTK-GPS for landing navigation and optimized flight guidance for minimum use of fuel and oxidizer for landing, aero-shell installation for managing aerodynamics, and so on. As a result, flight envelope was extended and these new articles were qualified. Since then new challenges; e.g. fuel and oxidizer injector using electroforming for reducing number of parts and increasing durability, and composite cryogenic tank for liquid hydrogen, further improvement in onboard failure detection and safe-landing architecture, were conducted. Taking these new articles accommodated into the vehicle, the third flight test campaign (RVT#3) was carried out in October 2003 and completed three flights as they were planned.

The RVT campaign is [...] for making maximum use of repeated flight environment, and various new technical items and challenges presented above have been studied, developed and flight demonstrated through these study and flight-test environments. The team realizes that the way of doing things is totally different from that in the expendable vehicle studies and testing, because it comes back and does it again. The team has experienced already eight [flights] altogether, and [a] wide range of design knowledge and exercises in repeated flight operation have been accumulated from test to test. The campaign will be continued with conducting more new studies of integrated propulsion system, more composite articles onboard, refinement in safe abort in flight and in ground operation for turnaround, and flight envelope extension. The next goal is to build the vehicle [for] exo-atmospheric ballistic flight and safe return to the place it is launched. For the readiness of the target vehicle, the RVT campaign will be a good opportunity for keeping the team highly motivated. Moreover, [a] better understanding [of] how to design and build the future vehicle is in progress. (Is the answer too much in detail?)

HS: As I understand it, the next version (I will refer to it as RVT#4) will be a high altitude vehicle. Can you describe this vehicle and what you hope to accomplish with it? How high do you plan for it to go? Inatani: As stated in [the previous answer], our next goal is to build a ballistic flight vehicle, and we are doing system analysis on it. This could not be RVT#4, because we still live with the progress on the present vehicle. Both studies are underway. Keep in mind that our study is still in the frame of BASIC STUDY, using very small amount of funding [so] in [this] environment we are free from "NATIONAL POLICY". [It is very difficult to convince decision makers to determine how the investment for the future should be.] How about you in the US?

The three variations of the RVT. (RVT#3 actually flew in 2003.).

HS: As I understand from your response, the RVT#1-3 names refer to different versions of the same vehicle. The exo-atmospheric ballistic vehicle would not be called RVT#4 but would have a new name to reflect that it is a whole new vehicle. Other than being larger, how will the ballistic vehicle design differ from the RVT? Will it involve any important technology that you have not tested in RVT#1-3 such as a composite LOX tank?

Inatani: System studies are underway. It should have continuous intact safe abort capability. Since the necessary performance of the 100km-plus vehicle is low, we can allocate much [of the] weight budget to this abort capability. Safe return and landing in one-engine-out situation is one of the typical cases we assume. Though high reliability is of course one of the important things, it is not all. We are thinking about making difference between contained and uncontained failure, which means it is important to detect the signal of failure such as engine-out.

On the subsystem level, we are studying [an] integrated propulsion and power system which eliminates toxic fuels, and which make it possible to use only LOX and LH2 for primary and auxiliary propulsion and power generation. It will be one of the keys to safe and quick turnaround. I do not know to what extent [the] integrated system [will be] employed to the next ballistic vehicle. It depends on the funding and time we have.

These two new things will be very important for the "reusable system architecture" studies to our understanding. Our goal is to do the flight as [in] aircraft operations. Some other things such as more composite to tanks and vehicle structures are also in our scope.

HS: Do you have funding for [the exo-atmospheric vehicle]? Assuming you do, when would it begin flying?

RVT#3 in Oct. 2003 flies by the sea in a low altitude test. (Video)

Inatani: As stated in [an earlier answer], we are on the year-by-year-funded basis as basic study. Nothing is determined yet. Again, "decision maker" problem. We believe we are ready to build ballistic flight vehicle. RVT campaign will help it greatly. HS: Most development of RLVs in the US is happening in the private sector. There are about a dozen small companies with significant amounts of talent and money who are making serious efforts at developing manned suborbital rocket vehicles. Also, SpaceX in the spring will launch a satellite on a partially reusable unmanned orbital vehicle that is completely funded by a private investor.

Have you seen any interest from private companies in Japan in developing RLVs or in collaborating with your project?

Inatani: There [is] some interest but just showing their interest, and nothing happens for the moment. In Japan it is very difficult for private people to do space or to do flight tests. Big heavy-industry companies are only looking at the government's money. Rather than these companies, a company like Toyota or Honda might be a potential mind sharer to our thoughts and goal.

HS: One area where there has been some US government interest is with the use of suborbital RLVs as observation platforms for remote sensing and reconnaissance. The company "TGV Rockets", for example, has begun development of a vehicle aimed primarily at this market. I was wondering if there has been any interest by Japanese "decision makers" for such applications of a suborbital vehicle?

For example, the main target of the satellites lost on the recent H-2A flight could be monitored also by a suborbital rocket flying routinely to +100km above southern Japan.

Inatani: I understand your question, but space and military activities in Japan are strictly separated.

HS: Will RVT#4 have any significant payload capability such as for carrying small scientific experiments? Inatani: Our ballistic vehicle as a next goal should have payload capability. In our system study, we assume 100kg to 130km in altitude, which will make science and micro-G experiment possible. To convince the community outside rocketry [to] recognize the benefit of reusable vehicle is one of the key issues, otherwise nobody needs it or reusable is a sort of selfishness of space community. In order to do so stepwise, even a small vehicle can stimulate this trait. It is what we should do NOW. That is why we work with [...] people outside rocketry.

RVT#1 executes a short hop in 1999.

In what ways do you think that suborbital RLV development can contribute to the development of robust, lower cost orbital RLVs?

Inatani: I do not know Mockingbird. I answer in a different way. Is the rocket SSTO a dream? madness? When we assume daily flight or very quick turnaround, the vehicles other than SSTO does not make sense. As far as I know, [only a] vehicle [capable of] frequent flights [...] can take care of the future demand [such] as tourism for general public or SPS [Solar Power System] construction. Only technical guys or those in space community are quarreling on Single-stager vs. Two-stager issue and rocket vs. air-breathing issues. From viewpoint of those who invest, it is a childish way of doing thing. Again, technically viable things must be realized when people need it. We still have many years before these demands are maturing, and we can expect light-weight and thermally durable material's progress much more. .

HS: Many of the people I know in the private RLV development community point to the 1950's and 60's not for the technology, but for the X project development style such as with the X-15. The DC-X project, in fact, was a direct emulation of that style. One study showed that the cost of the DC-X would have been about 10 times higher if it had been done with the usual aerospace industry organizational structure.

From here it looks like the RVT project has also followed an X vehicle approach by using a small, tightly focused group that worked step-by-step on a small budget. Do you see advantages with this kind of project structure? Or is it simply a necessity that you must live with and you could make much faster progress with lots of money and a big organization?

Inatani: It is difficult to answer. You pointed out the difference between a small program and a big one. Following is my understanding. In the highly matured society and community like US, strict regulation in safety and in the way of qualification are established already, particularly in the government program. The "formal" safety and reliability are required, however what really happens is out of this scope. Substantial thoughts about these things are essential. This comes from highly motivated and well-experienced team, and from time to time it is difficult to establish this kind of GOOD team in [a] big program.

HS: With respect to the propulsion system, Mark had a couple questions: a) The RVT uses what you call "free venting" for the LOX and LH2 tanks. You say that you have not had any problems with this system, but what precautions are you taking to keep the gaseous hydrogen from entering into your airframe??

Inatani: It was our concern, too. Free venting means both venting of tanks and [to keep] out the gases for chilling down engine freely to the outside. These are guided to the outside by tubing through fuselage. As long as we did both in the ground firing tests with flight configuration and flight tests, nothing happened. More than 25 engine firings with free venting were made. We are monitoring gaseous hydrogen inside the airframe on the ground before and after the flight and in flight, too. We also have had to be careful about ground wind. Outside the vehicle, when the hydrogen damped and engine fired, it slowly burns in a few cases, but no influence to the vehicle and its flight. No burning occurs in most cases.

HS: Your fluid schematics show both the LOX and LH2 tanks as using a dip tube. If the tanks had an outlet at the bottom, you would be able to use a larger portion of the fuel in the tanks. Why did you choose to use dip tubes as opposed to an outlet at the bottom of the tanks?

Inatani: One of the reasons is to avoid unexpected leakage from valves when it is in the bottom of each tank. For quick turnaround it is difficult to check valves in detail on every flight. We took safer location of valves.

HS: To build a reliable, low cost fully reusable orbital vehicle requires a robust high ISP engine. How is your current testing plan advancing the development of such an engine?

Inatani: Orbital vehicle is not within our scope for the moment. I admit both higher performance and higher reliability [are] essential as you point out. Our current study is aiming at establishing a system architecture which allows failure [without loss of vehicle] as I stated.

HS: Thanks very much this interview and the best of luck with your future projects.