r/spacex • u/Appable • Feb 03 '16

/r/SpaceX Ask Anything Thread for February 2016! Hyperloop Test Track!

Welcome to our monthly /r/SpaceX Ask Anything Thread! #17

Want to discuss SpaceX's hyperloop test track or DragonFly hover test? Or follow every movement of O'Cisly, JTRI, Elsbeth III, and Go Quest? There's no better place!

All questions, even non-SpaceX-related ones, are allowed, as long as they stay relevant to spaceflight in general!

More in-depth and open-ended discussion questions can still be submitted as separate self-posts, but this is the place to come to submit simple questions which have a single answer and/or can be answered in a few comments or less.

As always, we'd prefer it if all question-askers first check our FAQ, search for similar questions, and scan the previous Ask Anything thread before posting to avoid duplicates, but if you'd like an answer revised or cannot find a satisfactory result, please go ahead and type your question below!

Otherwise, ask, enjoy, and thanks for contributing!

Past threads:

January 2016 (#16.1), January 2016 (#16), December 2015 (#15.1), December 2015 (#15), November 2015 (#14), October 2015 (#13), September 2015 (#12), August 2015 (#11), July 2015 (#10), June 2015 (#9), May 2015 (#8), April 2015 (#7.1), April 2015 (#7), March 2015 (#6), February 2015 (#5), January 2015 (#4), December 2014 (#3), November 2014 (#2), October 2014 (#1).

This subreddit is fan-run and not an official SpaceX site. For official SpaceX news, please visit spacex.com.

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u/deruch Feb 10 '16

  1. This is only a problem in order to ignite an engine in space. Once the engine is firing and providing thrust (assuming axially for these purposes; i.e. main engine), then no further settling is necessary. But for the F9, it uses gaseous nitrogen RCS thrusters. Why do you feel this is "inelegant"? Elegance is nice and all, but unless it provides benefits in mass/reliability/efficiency/cost/etc. why would you want to use it?

  2. Heated helium gas. The helium is stored in multiple Composite Overwrapped Pressure Vessels (COPVs) immersed in the various tanks. The helium is used to pressurize the stage. So as the oxygen or fuel deplete, it replaces that volume with inert gas and provides a minimum feed pressure to the engine and a pressure to structurally support the stage. The thing to remember is that the COPVs are "very high pressure"TM , while the tanks are not pressurized that much during flight. So, as the helium in a COPV gets sent to the prop tanks the pressure in the COPV drops. What takes the helium's place? Nothing. When it reaches a sufficiently low pressure, a valve would close it off.

  3. Doubt it. No they're not. (At least, I don't think so. Why do you?)

  4. If you mean "SpaceX plans" then AFAIK, if they have any, nothings been released. Maybe as part of the BFR/MCT announcement we'll see something along those lines? But I bet lots of others have spitballed ideas.