The jet test vehicle is kinda lame in my opinion. The Chinese can use an upper stage engine with a different nozzle and make something similar to the DC-X or the Lunar Lander quite easily. For example they could have used the YF-20 gas generator engine or the YF-75D expander cycle engine. Much like the DC-X used the RL-10 expander cycle engine.
China's Space Program News Thread
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BeiDou-3 GEO-1 - the first geostationary BeiDou-3 satellite
A Long March-3B rocket launched the first geostationary BeiDou-3 navigation satellite from the Xichang Satellite Launch Center, Sichuan Province, southwest China, on 1 November 2018, at 15:57 UTC (23:57 local time).
I can see one really good reason for using jet engines. They have much less downtime between tests, and you can probably conduct tests for longer. If your interest is in collecting enough data for your stability algorithm this is a huge upside.
The mass flow out of rocket engine is much much higher than that of a jet engine. Rocket engine uses concentrated oxidizer while jet engine uses regular air (20% oxygen) and it allows it to burn very efficiently but also very violently. Thus, rocket engines are incredibly difficult to control.
Rocket re-usability requires unprecedented ability to control (especially in real time) the throttling of the engine.
In comparison, a jet engine is much more well behaved.
You have two problems you want to solve. So you eliminate one problem as best you can (using a much more well behaved jet engine) so you can concentrate to generate a control law algorithm.
After that, you have a baseline software. As you change to rocket engine, you can evolve your baseline software.
That was the approach used by Blue Origin. By the way, Blue Origin is the very first company to successful performed a vertical landing of a functioning reusable rocket (New Shepherd Rocket), beating SpaceX by several months. In many aerospace circles, Blue Origin is considered the 2nd best entities (even ahead of NASA), right after SpaceX, as the future of space travel. I don't share that sentiment. But Blue Origin is certainly highly respected.
Rocket re-usability requires unprecedented ability to control (especially in real time) the throttling of the engine.
In comparison, a jet engine is much more well behaved.
You have two problems you want to solve. So you eliminate one problem as best you can (using a much more well behaved jet engine) so you can concentrate to generate a control law algorithm.
After that, you have a baseline software. As you change to rocket engine, you can evolve your baseline software.
That was the approach used by Blue Origin. By the way, Blue Origin is the very first company to successful performed a vertical landing of a functioning reusable rocket (New Shepherd Rocket), beating SpaceX by several months. In many aerospace circles, Blue Origin is considered the 2nd best entities (even ahead of NASA), right after SpaceX, as the future of space travel. I don't share that sentiment. But Blue Origin is certainly highly respected.
The DC-X predates both efforts and it used RL-10 derived rocket engines. Expander cycle engines, like the RL-10, are typically deeply throttleable and capable of multiple restarts. Like I said the Chinese have the YF-75D which is a similar engine. IMHO Blue Origin keeps spending money and time in futile demo designs which serve little purpose and ignore a lot of fundamental technologies like those that SpaceX developed in terms of modeling combustion flow via computer software. This allowed SpaceX to develop an extremely complex engine like the Raptor with minimal fuss while Blue Origin was exploding engines on the test stand.
Yes, DC-X is a good experience to use. But your criticism about Blue Origin is completely unfounded.
Blue Origin is highly respected in the aerospace community is not because it has a famous founder, but because of the engineers who work there. Many engineers who worked on DC-X are currently working in Blue Origin.
William Gaubatz, the former director of DC-X, called Blue Origin's Goddard test vehicle as ingenious.
There is a huge gape between a lunar lander and a reusable rocket. The same guys who designed DC-X, and are currently working in Blue Origin, decided they need two separate projects to tackle two separate problems. Thus, they created "Charon" to tackle flight control software and "Goddard" to tackle rockets. After that, they combine the results and created "New Shepard".
New Shepard reusable rocket is world's first successful reusable rocket to space. It is not just a success, it is a historical success. (Note, SpaceX is world's first reusable rocket to orbit).
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