Mr. Eilon Mask answered "Questions?" And asked questions about Space X's new rocket "BFR"

Reddit's special project "Ask Me Anything" (AMA: "Do you have a question?") Was held on Saturday, October 14, 2017 in the US time, Mr. Eilon Mask answered the question from the user. The question was limited to those concerning rocket and Mars exploration that Mr. Mask made at the end of September, but the huge rocket just releasedBFRThere are various questions about rocket engine etc.

I am Elon Musk, ask me anything about BFR!: Space
https://www.reddit.com/r/space/comments/76e79c/i_am_elon_musk_ask_me_anything_about_bfr/

Here's Everything Elon Musk Unveiled About Tesla & SpaceX in His AMA
https://futurism.com/elon-musk-reddit-ama-tesla-spacex/

Here's what Elon Musk revealed about the ITS and Space X's Mars ambitions in his Reddit AMA - The Verge
https://www.theverge.com/2017/10/15/16476884/elon-musk-reddit-ama-spacex-mars-interplanetary-transport-system-raptor-engines

Mr. Mask is tweeted before AMA is executed as follows. As indicated by "r / space", I announced that AMA would be implemented within the category related to space.

BFR AMA on r / space in 2 hours

- Elon Musk (@ elonmusk)October 14, 2017

About the huge rocket "BFR" and Mars exploration plan
As a matter of course, the content of the question seems to be a series of things concerning the contents announced at the International Conference on Space "International Astronautical Congress" held in Adelaide, Australia at the end of September 2017. From a user, according to the plan announced in 2016 the shape of the spacecraftSome unevennessIn contrast to the plan in 2017Simple cylindrical shapeThere was a question about what was changed to. Mr. Mask, on the other hand,To realize the mass ratio"In order to maximize the weight and strength of the tank containing the propellant, as a solution for loading more propellant, it was necessary to make the tank cylindrical and paste the insulation directly," I have answered. However, there is a sufficient possibility that this design will be reviewed in the future.

Another user said, "In the plan of 2016 Delta winged fins were on the rocket fuselage surface, but in the 2017 plan,Just with small things in the aircraft's tailWhy? Question that. Mr. Mask, on the other hand, said, "It is not a wing that produces lift," while balancing the aircraft, "to prevent rushing from the engine part when re-entering the atmosphere from the orbit", and "To make it possible to control the motion of the aircraft in the yaw direction and the movement in the pitch direction".

Mr. Mask commented on cooling the propellant tank by himself. It is not a big problem if it is an artificial satellite launch vehicle that exhausts propellant for a few minutes after injection of fuel to the tank. However, in the journey to Mars that it takes several months, the propellant tank is cooled to a low temperature It is necessary to keep it. If it receives sunlight or is overheated at the time of entering into the atmosphere, extremely low temperature methane and liquid hydrogen will evaporate, the inside of the tank will become high pressure, and valuable fuel can not be used anymore For this reason, Mr. Mask talks about "Solving the insulation directly on the tank" and "Solving the cryo cooler (CryoCooler)" on the solution.

About rocket engine "Raptor"
According to the plan as of 2017, the number of rocket engines "Raptor" mounted on rockets has decreased from 42 to 31, and the thrust per engine has also decreased from 300 tons to 170 tons about. A user asked about the reason, Mr. Mask explained that "the weight of the aircraft was lighter than the initial plan".

Mr. Mask also commented that this change is a measure to realize safe landing. By increasing the number of engines used when landing with reverse injection, it is possible to continue landing even if there is a problem in one unit. At that time, assuming that reverse injection is performed by two engines, it is necessary to increase the thrust of the other greatly when trouble occurs in one side. Mr. Mask says that the difficult part of the rocket engine with a large thrust is where the amount of change in the thrust becomes nonlinear when the throttle is greatly reduced, which means that the engine is enlarged It seems that there is an aim to be able to increase the total certainty more than using reverse engineering with a small number of engines and landing with reverse spraying using a lot of smaller engines.

And furthermore, it seems that there is operation of rocket type passenger aircraft that the aim can be reached within 1 hour in any place on the earth. In the case of a passenger aircraft that carries a lot of general passengers and does not astronauts, frequent redundancy against troubles is indispensable as well as high safety.

Mask asked, "What is the possibility of 3D printing of raptor engines?" Mr. Mask suggests that "most parts are made in the same way as before," while saying "some parts are made with 3D prints." For rocket engines that react vigorously with propellant and oxygen, it is necessary to use materials that can withstand high pressure and high temperature, but SpaceX is developing metal new materials that can withstand such a situation about.

About the environment of Mars
Questions are also being asked about Mars that SpaceX is aiming for. SpaceX produces fuels, methane and oxygen for returning from Mars by using a technology called "local resource utilization" (ISRU) that uses the resources of Mars to produce the propellant needed to propel the rocket I am planning that. About Mr. Mask asked, "Who is in charge and what is the status of progress?" About this system development "SpaceX developed, design is progressing, this technology is the key part of the whole system." Another user has been asked the question "Do you want to bring the boring machine of The Boring Company to Mars?" Established by Mr. Mask, and Mr. Mask said "more boring!" He said that he answered.

Another user gets questions such as "What kind of company is involved in this plan?" On the other hand, Mr. Mask does not disclose the name of the company etc, but the goal of SpaceX is "to deliver people and build a basic infrastructure to create fuel locally, to create a survival environment" answer. About Mr. Mask expressing it as "to make a transcontinental railroad".

Regarding this plan, Mr. Mask states that cooperation of many people and companies is indispensable. Also, although image images about "Mars city" have been released to the public, Mr. Mask is "not doing too much reading" and suggests that there are still many changes to be made from now on.