7 thoughts on “Hawthorne News”

  1. Harriet may not teach SpaceX anything about tunneling faster since it will probably require a different technology than a cheese grater bit.

    Going faster might require a water jet cutter o something else which Harriet would have little in common with.

    This also goes against Elon’s whole philosophy of looking at projects from first principles. It could indicate his lack of interest (which would still be more interest than most would spend.) Just because Elon invests in an idea doesn’t mean it’s a core issue to him. He just doesn’t let go of ideas as quickly as most would.

  2. “We’re going to get this machine, take it apart, figure out how to make it go much faster while still being safe and not affecting people on the surface,” Musk said in January. “We’ll see how much progress we can make, but I’m optimistic tunneling can be improved by at least five-fold, maybe 10-fold. That’s really key to a lot of technologies — road tunnels, train tunnels, Hyperloop tunnels.”

    Hot-rod Harriet. I can hardly wait.

  3. While I understand Musk’s sentiments, that’s quite an arrogant statement and does a disservice to the engineers who designed these tunnel boring machines. It really lowers my opinion of Musk and SpaceX in general.

    1. Hubris is the risk you take when you challenge the status quo so often and so successfully. Is he getting ready for a fall?

    2. Aren’t you the touchy little snowflake.

      I’d say Musk’s statement is more an acknowledgement of the reality that quite a number of high-profile projects involving large tunnel boring machines have come a cropper in recent years. That suggests that conventional tunnel boring technology is no more a settled field of engineering than launch vehicle technology turned out to be.

      To anyone currently active in the field of tunnel boring engineering who feels insulted by Mr. Musk’s statement, let them do a better job their own damned selves instead of whining like little girls.

      1. I’m certainly not a snowflake when I point out arrogance.

        Would you like it if I told you that you’re incompetent at your job even though I know nothing of the expertise that goes into your work?

        Musk uses people that are skilled in the areas that he wants to develop and improve. Unless he hires people involved in tunnel boring machines, he is as arrogant as a hollywood actress pontificating on politics.

        1. Arrogance, sir, is assuming Elon Musk knows nothing about tunnel boring technology.

          He didn’t start out knowing anything about rocket engine technology either. But Musk has proven to be a quick study. He went to autodidact school on the subject before ever starting SpaceX after deciding extant suppliers weren’t taking him – and wouldn’t take him – seriously.

          One of his very early brilliant moves was getting Tom Mueller on-board at SpaceX. Mueller, it turns out, was the best liquid propellant rocket engine designer in the United States, but had never worked anywhere his designs got beyond the prototype shop and the test stand.

          Mueller designed the Merlin, which has turned out to have the highest thrust-to-weight ratio of any rocket engine ever built and flown. Then he turned his hand to the Raptor, which has the highest combustion chamber pressure of any rocket engine ever built and seems likely to beat its older, smaller sibling in the thrust-to-weight metric as well.

          Both the Merlin and the Raptor stand as working rebukes to those who scoffed at the SpaceX parvenus because they allegedly knew nothing about “how these things are done.”

          For all we know, Elon may already have the tunnel boring equivalent of Tom Mueller on his payroll.

          Just as Mueller didn’t invent anything that was completely novel for the Merlin and Raptor – just combined existing art in ways that fundamentally advanced the state of practice – so too may Elon’s tunnel boring efforts yield comparable fruit.

          Let’s examine Elon’s “at least five-fold, maybe 10-fold” stated improvement goal in terms of what we’ve already been told about Harriet.

          A number of media stories have quoted L.A. Metro Transit Authority sources as saying that Harriet averaged 60 feet of tunnel per day and traveled at 3 inches per minute when tunneling.

          A little quick math reveals that these two numbers are not congruent. 1/4 foot per minute times 60 minutes per hour times 24 hours per day comes to 360 feet per day. Another source I found reports that tunneling was a 24-hour-per-day effort, but only for five days each week.

          I couldn’t find any derivation for the 60 feet per day number so I didn’t know if the average included only tunneling days or all days between start and finish of tunneling operations. If the latter, I didn’t know whether the total number of days included the days of work to initially position Harriet and to reposition her for the second of the two parallel tunnels dug.

          What seems to be agreed is that it took roughly a year to dig two parallel tunnels that are each roughly a mile long. That means it took roughly six months to dig each tunnel. For arithmetic simplicity, and to deliberately put our thumb a bit on the scale in favor of the L.A. MTA and its contractors, let’s define a half year as 180 days and a mile as 5,400 feet. That’s a tunneling rate – overall – of 30 feet per day.

          Based on this calculation, it seems most likely that the 60 feet per day figure in press reports is based only on actual tunneling days. We already know the tunneling was halted for two days every week. It seems the time needed to initially dig Harriet in and to turn her around accounted for the equivalent of another day and a half per week.

          So, Harriet, when she digs, goes at 3 inches a minute, but only makes 60 feet of progress per day. That pretty straightforwardly translates into a 16-2/3% duty cycle. In other words, Harriet is only digging for one hour in six even on the days she is operating.

          If Elon and his associates can figure out a way to flip these numbers – get Harriet able to tunnel for five hours of every six, he will have achieved the lower end of his stated 5-to-10-times-improvement range. This can probably be accomplihed with no changes to the cutter head mechanism, just improvements to the mechanical components to its rear and/or to the procedures used in operating the machine.

          Further advances would likely require some mods to the cutter head as well. I could speculate about what such changes might include, but this comment is already fairly lengthy – especially for this forum – and I believe the case that radical improvements to current tunnel boring practice are possible has already been adequately made.

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