Depressing Note

I was just looking back to see when was the last time that I had posted original technical material here (before last week’s post on xGRF). Has it really been since mid-February? That’s depressing.

Anyhow, I have a provisional patent app I really need to get in this week, but once that’s over, I’m going to try to get back into my groove. The sad thing is, it’s been so long since I’ve done the sort of innovative technical blogging that got most of you people here, that I no longer get a lot of comments, even when I think I have something important to talk about… As I said, that’s somewhat depressing.

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Jonathan Goff

Jonathan Goff

President/CEO at Altius Space Machines
Jonathan Goff is a space technologist, inventor, and serial space entrepreneur who created the Selenian Boondocks blog. Jon was a co-founder of Masten Space Systems, and is the founder and CEO of Altius Space Machines, a space robotics startup in Broomfield, CO. His family includes his wife, Tiffany, and five boys: Jarom (deceased), Jonathan, James, Peter, and Andrew. Jon has a BS in Manufacturing Engineering (1999) and an MS in Mechanical Engineering (2007) from Brigham Young University, and served an LDS proselytizing mission in Olongapo, Philippines from 2000-2002.
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20 Responses to Depressing Note

  1. If it makes you feel any better, I have definitely noticed a strong inverse correlation between how much you blog and how much you’re doing in your technical area.

  2. I think it’s more a matter of how unsettled life has been for most of this year. Ever since I found out Ian was leaving Masten, it’s been kind of crazy. 13000 miles worth of driving since this summer, sleeping on different beds almost every week, it adds up. I’m really looking forward to getting things back to some semblance of order. Its hard to express creativity on a blog when you have that much stress everywhere else.

    But yeah, getting stuff done does tend to interfere with flapping ones gums about theoreticals, huh?

    How goes the LFTR stuff?


  3. Perhaps you should post some depressing note about how depressing it is, that should get the users bouncing back 🙂

  4. Mike Garceau says:

    Dude! You are starting an innovative business in a location in which you have no prior history. OF COURSE you will be both stressed, busy with the necessities of life / business, and therefore lacking the postiness that we all enjoyed when you had a more structured life. Don’t sweat it. Blog commenters are like ants — once good stuff is found, we leave little trails to encourage others to find it.

    Then we overwhelm the place, and the exterminators come…

  5. redneck says:

    I’ve also had an unsettled year. Picking up on a discussion on ARocket that blogging technical rocket stuff could possibly cause ITAR problems was an early damper. Business survival, income cuts, and another unexpected move just cut it back even more. Ideas don’t flow so well when concern about making a living is foremost on your mind.

  6. john hare says:

    I sometimes post as redneck and didn’t check the sig on the last comment. John Hare

  7. PrairieKirk says:

    Well Jon, I’m glad to see you back with a major technical post. I enjoyed xGRF greatly!

    And as for your users, I think the wisdom of Field of Dreams works here: If you blog it, they will come.

  8. John, those threads happen monthly on arocket.

  9. Seer says:

    Jon, I have a some quasi-technical questions for you.
    Can you explain why the mass fraction of propellant tanks drops as much as it does for increasing tank size? I thought that tank mass is proportional to propellant mass.
    E.g Centaur (20 tonnes) is about 8%, the upper stage of Direct’s proposed Jupiter launcher (180 tonnes) has 5.5% mass fraction but the shuttle ET (750 tonnes) is 3.7%.
    Which leads me on to some thoughts on building an rlv.
    Many ssto designs of the past, e.g delta clipper, millenium express, seemed to assume tanks would be only ~ 2% of GLOW, even though these rockets were about 500 tonnes. Some of the smaller ssto’s, such as BETA (120 tonnes GLOW) only budget 3% for the propellant tanks. These numbers seem shockingly low.

    Even for a two stage rlv, small vehicles might be impossible to build.
    I know you think that a small rlv can be made with payload of a couple tonnes. I would assume GLOW would then be about 100 tonnes. How much mass have you budgeted for your tanks?
    Thanks, hope this drums up some interest from your commentators!

  10. john hare says:

    Trent, the monthly threads do critisize ITAR, but I never read that blogging space ideas wasn’t first amendment protected until last December.

  11. David says:

    I still check in regularly to read the posts. I look forward to more posts from yourself and the others as life settles.

  12. Paul says:

    Seer, if you think of the tank-mass as roughly proportional to the surface area of a spherical volume of fuel, it makes more sense. Area increases with the square of radius, volume with the cube. (Ie, 8 times the volume (fuel mass) = 4 times the surface area (tank mass.))

  13. Seer,
    A couple of things…first off your numbers for the Centaur tank mass are off. The Centaur dry mass (tanks, engines, RCS, batteries, structure, etc) is only 10% of the stage GLOW (approximately). I have exact numbers, just can’t give them. But suffice it to say, the tank mass is less than half of the stage dry mass.

    I think a lot of the SSTO designs with very low tank mass were counting on denser propellants than LOX/LH2. For instance, the tank mass for LOX is usually something in the 1% or so of propellant mass range.

    Of course, there are scaling issues (flanges, baffles, mounting scale down poorly), pressure matters (the membrane mass of the tanks tends to scale with pressure x volume), and materials considerations (various materials and manufacturing options have various strength/weight ratios), design considerations (isogrid vs balloon vs balloon with some stringers/ribs), etc….

    …lots of details.


  14. John, oh right. I’ve wondered about that. For example, if you were to offer a print version of your blog and say “this is an online version of the print edition” would that solve this nonsense “the Internet isn’t publishing” argument?

    Most ITAR fear seems to be completely irrational anyway. Ultimately, the law is written such that *anything* can be illegal if the jackboots want it to be.. and with that kind of law the only sensible thing to do is fight it.

  15. Stephen Langford says:

    Your site is linked by several alt-space bloggers. If you start posting again in the reasonably near future, your readers will come back. We are a patient crew.

  16. Nels Anderson says:

    Seer, to amplify on Jon’s reply to your question regarding mass fractions, there’s a nice little 1996 paper by John Whitehead that breaks launch-vehicle masses down and provides some scaling laws for components:

    There’s also an ancient usenet post in which Mitchell Burnside-Clapp calculated weights of various rocket stages w/o engines:*+author:Burnside-Clapp+PFSMF#0945baea33c95a22

  17. Seer says:

    Thanks for those links Nels. One factor I ignored was whether the stage needs to be strengthened because of the weight of the payload above it. This would apply to the Direct upper stage. SSTO’s on the other hand have insignificant payload weights as a fraction of the stage.

  18. Geoffrey says:

    You might have seen this already but on since you posted that survey about risk tolerance on a trip to mars I thought I would point to the poll currently on Slashdot.
    (Hopefully that link works)

    It has a large response(20000) and while slashdot readers are probably still space geeks they are probably less biased then the readers of a space blog. I would say the results are positive with about 40% willing to at least accept some risk of death for a chance to go.

  19. Jon, if we readers all selected the (RSS) Feed option offered at the top right of each page, we would know immediately when you had posted again.

    Apparently I’m not the only one who depends on a mention at Clark Lindsay’s to send me here rather than the automated RSS Feed. Good to hear that your real job is consuming time, and good to read you again!
    -Paradox Olbers in Second Life
    President of the International Spaceflight Museum in SL

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