Tuesday, October 25, 2016

Elon Musk Answers Questions About SpaceX’s Mars Plans in Surprise Reddit AMA

A rendering of what SpaceX expects the Interplanetary Transport System to look like. The rocket will launch from historic Launch Complex 39A, which sent the first humans to the Moon in 1969. Image Credit: SpaceX

In stark contrast to questions SpaceX founder and CEO Elon Musk encountered following his Mars architecture announcement at the 2016 International Astronautical Congress (IAC) earlier this year, the NewSpace entrepreneur entertained questions from a more informed group in a surprise Reddit AMA (Ask Me Anything) on Oct. 23, 2016.

The AMA took place in the website’s r/spacex forum and shed some light on SpaceX’s future plans. Participants were asked to refrain from asking questions about Tesla or Solar City. If fact, Musk spent little time discussing much beyond the company’s Mars-centric hardware. He did, however, talk about the company’s upcoming upgrade for the Falcon 9 rocket.

In response to redditor FoxhoundBat, Musk said the Falcon 9 was undergoing a redesign meant to improve performance and reusability:

"Final Falcon 9 has a lot of minor refinements that collectively are important, but uprated thrust and improved legs are the most significant.

Actually, I think the F9 boosters could be used almost indefinitely, so long as there is scheduled maintenance and careful inspections. Falcon 9 Block 5 – the final version in the series – is the one that has the most performance and is designed for easy reuse, so it just makes sense to focus on that long term and retire the earlier versions. Block 5 starts production in about 3 months and initial flight is in 6 to 8 months, so there isn’t much point in ground testing Block 3 or 4 much beyond a few reflights."

With the change to the Falcon 9 allowing for practically indefinite reuses, the company has the potential to focus more than 5 percent of its resources toward getting its Mars plans off the ground.

Interestingly, Musk noted the upcoming iteration of the company’s workhorse launcher will be the Block 5. This marks a change to the company’s tradition of christening the successive modifications to the rocket with a version number.

However, if one were to ascribe a “block number” to the preceding iterations of the Falcon 9, it’s not readily apparent how the latest design is the “Block 5”. There seems to be a generation missing in this naming scheme, although Musk did not elaborate. That did not discourage some redditors from attempting to work it out.

It was also not discussed what impact, if any, this change to the Falcon 9 may have on the vehicle’s certification to launch payloads for the United States Air Force.

The greatest interest from the AMA participants was definitely centered on SpaceX’s Mars architecture. Musk spent time answering a wide range of questions about the topic. Notably, he is not a fan of the ITS moniker:

"I think we need a new name. ITS just isn’t working. I’m using BFR and BFS for the rocket and spaceship, which is fine internally, but…"

While the SpaceX CEO may not like the ITS name so much, he has already settled on a name for the first ship of the line that will visit the Red Planet: Heart of Gold. A nod to the vessel of the same name from The Hitchhiker’s Guide to the Galaxy, SpaceX’s ship will precede any crewed mission and will be laden with equipment meant for constructing a propellant manufacturing plant.

Before any ITS-class ship ever makes a journey to Mars, the company plans to send several Dragon-class missions to gather as much entry, descent, and landing data as possible to mitigate the chances of adding to the collection of craters on Mars’ surface, as well as to better understand the best process for extracting water for making the propellant.

Ever the science fiction fan, Musk seems to take pleasure any time he can integrate something from the genre into SpaceX’s operations. ITS is no different. When asked about the number of engines in the ITS’s first stage, Musk had a quick and very Musk-esque answer:

“It had to be 42 for important scientific and fictional reasons! The dense packing is just to max out thrust to weight, but it would be cool if there was a virtual nozzle side effect.”

The number “42” plays a notable role in The Hitchhiker’s Guide to the Galaxy as the “Answer to the Ultimate Question of Life, The Universe, and Everything”.

However, not all of Elon’s interactions were steeped in science fiction lore. Redditor TheVehicleDestroyer wanted to know some specifics on the performance of the sea-level Raptor engine when used in vacuum. Musk said the Raptors meant for atmospheric operation would still have quite a bit of power, pushing 290 metric tons of thrust and operating with a specific impulse of approximately 360 seconds.

Although there is a preponderance of evidence that Mars may have been habitable in the past, it certainly is not welcoming to humans at present. Redditor Ulysius questioned Musk on plans for permanent human habitation on the Red Planet, to which the SpaceX founder replied:

"Initially, glass panes with carbon fiber frames to build geodesic domes on the surface, plus a lot of miner/tunneling droids. With the latter, you can build out a huge amount of pressurized space for industrial operations and leave the glass domes for green living space."

One of the key announcements in Musk’s address at the IAC conference was the revealing of a large composite fuel tank. Long the goal of many in the spaceflight industry with their mass savings translating into greater payload capabilities, composite propellant tanks have proven problematic at best, and catastrophic at worst.

Elon, however, feels SpaceX has a good handle on the manufacture of large composite tanks. Responding to redditor nalyd8991, Musk fairly gushed over the composite structure:

"Yeah, for those that know their stuff, that was really the big news. The flight tank will actually be slightly longer than the development tank shown, but the same diameter. That was built with latest and greatest carbon fiber prepreg. In theory, it should hold cryogenic propellant without leaking and without a sealing linker. Early tests are promising. Will take it up to 2/3 of burst pressure on an ocean barge in the coming weeks."

Testing the tank at sea, away from personnel and structures, will help to ensure the maximum level of safety should a failure occur.

SpaceX, however, has some challenges relating to not only the propellant tanks but also to the alloys used in the Raptor’s turbopumps.

Operating at pressures much higher than any other engine, the turbopumps will be subjected to oxygen-rich conditions which may lead to erosion in the pump, though early test firings didn’t indicate that would be a likely problem.

However, according to Musk, “…there is still room for optimization.”

Written by: Curt Godwin
Original source: spaceflightinsider.com

1 comment:

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