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Civilian Space Launch Imminent 53

Posted by timothy from the when-can-we-honeymoon-on-the-moon dept.
rossjudson writes: "Looks like the Civilian Space Exploration Team has gotten clearance from the FAA and the Bureau of Land Management to attempt the first amateur flight into space. That's pretty cool. Maybe one of you space-mathematics types out there can educate us on just what 0-Mach 5 in 15 seconds really means! Is this thing gonna just blow up?"
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Civilian Space Launch Imminent More

Civilian Space Launch Imminent

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  • about 10 Gs? (Score:3, Informative)

    by renehollan ( 138013 ) <<ten.eriwraelc> <ta> <nallohr>> on Thursday August 29, 2002 @03:27PM (#4166007) Homepage Journal
    subject says it all... speed of sound = 1100 f/s, so 5500 f/s in 15 s = 1100 f/s in 3 s = 367 f/s^2. 10 Gs would be 322 f/s^s. Close enuf. Increased accuracy is welcome.
    • At 21C (70F) altitude 0, speed of sound = 344 m/s = 1129 ft/s
      1G = 9.81m/s^2 (at the equator)
      So, the acceleration = 344 * 5 / 15 = 114.6 m/s^2 = 11.69 G.

      Wow, that's a lot. Jet fighter pilots usually blackout around 9G. I suppose the way the guinea pig is seated can make things better.

      Banging your head with a hammer is good for you. It just fells so good when you stop.
      • Slashdot Uncertainty Principle: The product of the relative error in a Slashdot post with a mathematical result, and the likelihood of it being first is a constant.
      • A fighter pilot sits fairly upright. It's a long way from the top of the head to the bottom of the feat, compared to laying down, where your head and feet are at the same level. Of course, at 11G, the blood pressure in the blood vessels at the back of your head while laying down perfectly would be about like hanging from your feet at 2G. Nevertheless, it's endurable, and greatly increases efficiency of the propulsion. You wouldn't want to perform complex tasks at even 3G, but you could easily endure it.
        The stress decreases with size of the subject anyway, so don't feel sorry for the guinea pig - envy him.
    • If you assume a constant accleration, which is not the case (this is because the atmosphere is more dense at low altitudes, and means that the drag is much higher on the rocket towards the begining of it's flight), then you can calculate the acceleration.

      You really need to take into account the fact that the speed of sound decreases with altitude. Using data from the U.S. standard atmosphere of 1976, in a non-linear shooting method and an initial guess of 98m/s/s...

      99m/s/s or 10.1G reaching mach 5.0 at an altitude of 11138 meters

      (the shooting method turned out to be linear because the speed of sound is constant to 4 significant figures between 11000 andd 20000 meters)

    • Missing the big source of error. (Score:5, Funny)

      by MarkusQ ( 450076 ) on Thursday August 29, 2002 @09:36PM (#4167956) Journal

      about 10 Gs? ... speed of sound = 1100 f/s, so 5500 f/s in 15 s = 1100 f/s in 3 s = 367 f/s^2. 10 Gs would be 322 f/s^s. Close enuf. Increased accuracy is welcome.

      I think the big source of error in our calculations here will be our uncertanty of the acceleration profile. While constant acceleration is certainly a reasonable solution, it isn't the only possibility. For example, we could have:

      • First second: no accelleration
      • Second second: no accelleration
      • Third second: still no accelleration
      • Fourth second: no accelleration continues
      • Fifth second: dito
      • Sixth second: deep rumbling sound is heard, but no accelleration
      • Seventh second: a very small amount of side-to-side accelleration, but it never amounts to anything
      • Eighth second: rumbling stops; accelleration does not start
      • Ninth second: everything is disturbingly quiet, and quite stationary
      • Tenth second: no accelleration II, the dance mix
      • Eleventh second: a very small amount of upward acceleration is detected, but it is well within the error bars for the instruments
      • Twelfth second: no accelleration, but what might be a hint of smoke
      • Thirteenth second: no accelleration, and that is definitely smoke
      • Fourteenth second: no acceleration, but the smoke is building up nicely
      • Fifteenth second: a great deal of acceleration, accompanied by a lot of smoke and a very, very loud "bang".

      I sure hope this isn't what happens, but it could fit the numbers as well as "constant accelleration at 10.5G +/- a fudge."

      -- MarkusQ

  • I do believe that Mach-1 is the speed of sound, therefore Mach-2 would be twice the speed of sound, Mach-3 is 3x the speed of sound, etc...so what they're saying is they're ship can go from 0-to-5x the speed of sound in 15 seconds.

  • X-Prize? (or was that something else?) (Score:4, Interesting)

    by dschuetz ( 10924 ) <david&dasnet,org> on Thursday August 29, 2002 @03:30PM (#4166037)
    Wasn't there a prize for the first team to loft 1 kg to 100 km? Would this qualify?

    (no, it wasn't X-prize, that was for bringing people into space and re-launching in, what, a week?)

    Been a while.

    I'm disappointed, though, that they're being asked to keep the exact launch date a secret. If they can't protect a rocket in the middle of the Nevada desert from terrorists (or tourists), then we're all screwed.
  • In terms of car acceleration... 0 - 60 mph in 0.25 sec

  • Here's the numbers... (Score:3, Informative)

    by Spock the Baptist ( 455355 ) on Thursday August 29, 2002 @03:45PM (#4166158) Journal
    0 to Mach 5 in 15 seconds?

    That's going from 0 mph to 3700 mph, or 0 to 5400 ft/s in a quarter of a minute; assuming 740 mph = Mach 1.

    a = [v(2) - v(1)]/delta t

    a = (5400 ft/s - 0 ft/s)/15 s = 360 ft/s^2
    or about 11gees.

    9 gees is a heavy gee load in air combat maneuvering (dogfighting), so 11 gees is a very heavy gee load. At least over a protracted period.

    • Re:Here's the numbers... (Score:1, Insightful)

      by Anonymous Coward
      Mach is such a stupid point of reference. It depends on the density of air, so as your altitude increases the "Mach" number changes for the same physical speed. I wish they'd just use mph or kph or something more obvious.

      • Re:Here's the numbers... (Score:4, Interesting)

        by Louis_Wu ( 137951 ) <chris.cantrall@gmail.com> on Thursday August 29, 2002 @05:44PM (#4166948) Journal
        I'm heading under the bridge, hold this rope and pull me out if the troll gets his hands on me.

        :)

        Part of the reason for using Mach as a reference is that it is so flexible. Many aspects of fluid mechanics depend on knowing if the fluid flow is supersonic or sub-sonic. The behavior of subsonic fluid is fairly familiar to most people, but that changes radically when the flow becomes supersonic. Knowing the flow speed in relation to the shock wave speed (the speed of sound in that fluid) tells you which equations to use, and what to expect. Handy.

        The problem we have here is that we don't care about the fluid mechanics. All we care about is the speed in relation to the ground, and we can't get that easily because the reporter & the PR flack thought that spouting off Mach numbers sounded cooler or more scientific. (My idea of a scientific speed reference in this case would be two-fold: the raw speed number and the velocity vector broken down into components: vertical, North/South, & East/West. But I'm a mechanical engineer, and I want useful information.) We can get a good idea about the bounds of the acceleration involved by using speeds for Mach 1 at various altitudes (10 - 11 gravities as posted already), but a more accurate calc would account for the variation in Mach number with altitude.

        Of course, for a trully rigourous theoretical treatment, what we really want is the mass of the craft, the mass loss rate (fuel burn rate), and whatever measure of the craft's rocket power we can get (it might be the force the rocket produces [which could be a function of time], it might be the power of the rocket [which I think I could translate to a force if I had a few books in front of me], it might be the mean velocity of the rocket's exhaust stream [which I know that I could translate into a force, if I had the proper information about that flow stream]).

        With that {potential} boatload of information, we could apply the modern incarnation of Newton's Second Law, F=d(p)/dt ; force equals the derivative of momentum (p) with respect to time (t). That ends up being F=ma + v*d(m)/dt , the first part being very familiar to anyone who's ever taken physics, the second part much less so. F=ma : force (F) equals mass (m) times acceleration (a). The second term isn't very familiar, because most people don't think of mass changing over time. The classic example of this is a rocket - the topic of today's lecture. {I have no idea why I'm saying so much. Work must be more boring than normal.} F=v*d(m)/dt : force (F) equals velocity (v) times the change in mass (m) over time (t).

        [BTW, all of the "d"s are NOT variables, they are part of the notation of derivatives in calculus. (I was falling asleep during a lecture once, and I wondered why the teacher didn't cancel the extra "d"s from the top and bottom of the equation; then I woke up and almost died laughing at myself.:) ]

        Anyway, the upshot of the math is that if we knew how fast that fuel was being burned [ d(m)/dt ] how fast the craft was traveling at any time (v) and what the mass of the craft was at any time (m), we could back-calculate to get the acceleration. All that work to find out how heavy you'd feel. :)

    • 11 g is a heavy load, yes, for humans. There's nobody on board this thing. The avionics can easily withstand 11 g (and a lot more for that matter).
  • so can they utilize that anti-grav device (assuming it worked and they were able to apply enough power) to cancel out those Gs caused by this acceleration?
  • I wonder what their insurance is like? They have the rocket landing somewhere near Quebec City [civilianspace.com]. I don't think Quebec knows or ready. This could be more interesting then I thought.
  • SF authors have been suggesting for years that we let the private sector into space - competition will drive technologies forward and prices down.

    Incidentally, as a side question - anyone know if Mach 1 refers to the speed of sound in air at sea-level/standard temperature, or is it a variable depending only upon the speed of sound in whatever situation you're referring to?

    -T

  • Maybe one of you space-mathematics types out there can educate us on just what 0-Mach 5 in 15 seconds really means!

    It means, in layman's terms, "chunky salsa."

  • Don't forget that the speed of sound is a function wich, among other things, is a function of ALTITUDE.

    Now, the speed of sound at sea level is around 340m/s, which gives us around 11.7g's of acceleration, and an altitude of 42,000 feet in 15 seconds.

    However, the speed of sound at that altitude is significantly slower, around 290m/s-300m/s (according to my information), so our numbers for the acceleration should be a bit HIGH.

    Of course, without a nice function for me to integrate against, it is a little trickier to figure out what the acceleration really is, but we can put some bounds on it. As determined, the upper limit is 11.7g's of acceleration. The lower limit will be around 10g's. (This is found by using the slowest speed of sound number that we could possibly run across).

    So, with that range in mind, we can see that a reasonable estimate for the acceleration would be about 11g's +/- 1g.

    There, I feel more rigorous. I feel better now. :) (This is what I get for being a physicist.)

    -Jeff

    • Yes, you get the prize for being a good physicist, but not for being smart. A little internet research should reveal that these figures of mach 5 or whatever are GENERALLY quoted in sea-level sonic units where the speed of sound is 340m/s. After all, an orbital speed of mach 25 is rather slow if you are in space where the speed of sound is zero. :)
      • You are the one who looses the smarts prize. As an aerospace engineer, I can tell you that speed relative to the local speed of sound is all we care about, when it comes to Mach number. There is no point in looking at anything else! Coincidentaly 10.1Gs is the right answer. There is no need to integrate, I solved the problem in this post. [slashdot.org]


        • Hi!

          We project 18 Gs just before motor burnout.

          We've been very accurate in calculating (and then confirming) our projections in previous launches. However, I'm not the physics / aerospace guy on the project (so I don't have the wherewithal to provide the calculations). I oversee the electronics & avionics on the rocket.

          Thanks for your interest in our launch!

          Eric Knight
          Project Co-Leader & Avionics Manager
          Civilian Space eXploration Team (CSXT)
          http://www.civilianspace.com

        • I stand corrected. Still does not make any sense to quote orbital speeds in local speed of sound units though.
  • I am all for private space travel. Let companies put up their own sattelites, go mine on the moon, mars etc, open a space hotel the possibilities are endless.

    Here is a pretty cool article on the future possbility of a space elevator [howstuffworks.com]

  • Any bets on how long before NASA goes the way of the 8088 microchip?
  • Taken from NASA's Site [nasa.gov] "It takes only about eight minutes for the Space Shuttle to accelerate to a speed of more than 17,000 miles (27,358 kilometers) per hour." I'm not sure of the exact speed of sound, but it's something like 650 MPH, so that would mean the Shuttle goes from 0-Mach 26.15 (Using 650 MPH, it can vary depending on air temp, but not by much) in 8 minutes.
  • While this doesn't sound all too impressive, I'm glad to hear of it. More needs to come of space flight, and NASA surely isn't doing much on its own.

    [offtopic] Frankly, I almost with that NASA was a corporation... [/offtopic]
  • Don't people do this all the time with Sounding rockets [psu.edu]? Although maybe the point is that NASA [nasa.gov] runs that program too, and this is really independent? Still, it doesn't seem that big a deal...
    • Yes, sounding rockets push the envelope of space. However, no amateur / civilian group has yet achieved space on their own...building a rocket from scratch.

      I can tell you from first-hand experience that it is a lot harder than it looks...particularly when it is all self-funded.

      Wish us luck!

      Eric Knight
      Project Co-Leader & Avionics Manager
      Civilian Space eXploration Team (CSXT)
      http://www.civilianspace.com

  • Basic physics, assuming constant acceleration (approximately correct for a rocket): v(t) = v(0) + aT

    We know v(0) = 0 m/s, v(t) = Mach 5 = 1700 m/s, and T = 15 seconds. So let's find the acceleration. A little Algebra shows us:

    a = ( v(t) - v(0) ) / T

    a = ( 1700 m/s ) / 15 s = 113 m/s^2

    Which is about 12Gs, twelve times the force of gravity on earth. Much more than the several G's of the Space Shuttle. More than a human can stand for more than a few seconds before passing out.

    Resources:

  • I'm one of the leaders of the rocket project. (Score:3, Informative)

    by Eric Knight ( 605247 ) on Friday August 30, 2002 @04:17PM (#4173172)

    Hi, everyone. I'm glad to join your discussion here.

    I'm one of the leaders of the Civilian Space eXploration Team (CSXT). I head up all of the avionics development of the rocket project you are discussing: http://www.civilianspace.com My specialty is electronics & communications. If I can answer any questions for you, let me know.

    BTW: I see a message thread speculating on the number of g's. We expect a peak of 18 g's just before motor burnout.

    Some other numbers you might find interesting:
    * Motor burnout at 14.2 seconds
    * Mach 5.2 at motor burnout
    * Maximum dynamic pressure (Max Q): 8,500 pounds per square foot (occuring at 13.6 seconds)

    F.Y.I., Since our launch is less than a month away, I'm pretty consumed with pre-launch activities. I may only be able to stop by this forum a couple times per week. I apologize in advance for any tardy replies. ;-) Thanks for your interest in our endeavor!

    -- Eric

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