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Thread: Paul Allen's Stratolaunch - Viable or Gimmick?

  1. #1
    Senior Member mugaliens's Avatar
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    Default Paul Allen's Stratolaunch - Viable or Gimmick?

    I'm referencing this article: New photos reveal mammoth structure of Paul Allen’s six-engine Stratolaunch

    As we all (should) know, there are two components to a rocket launch: Altitude and Velocity.

    Altitude represents potential energy, Ep = 1/2*m*g*h, where m is the mass of the object, g is the acceleration due to gravity, and h is the object's height above the surface of the Earth. Although a more exact formula involves the distance between two bodies, U=G*M*m/r, low Earth orbit is close enough for government work, so a good approximation can be had with the simpler formula.

    Velocity represents kinetic energy, Ek = 1/2*m*v2.

    At any given time, the total energy of the system is given by ET = Ep + Ek.

    To complicate matters further, if not ridiculously, the mass of the rocket changes dramatically throughout its flight profile, not only by separating spent stages, but also by burning most of its mass in fuel.

    The question has been around for quite a while: Economically speaking, how viable is Paul Allen's Stratolaunch approach? Let's examine some data:

    Stratolaunch data:
    wingspan: 385 ft
    weight (including delivery payload): 1.2 million lbs
    range: 1,200 nm
    planform: twin-hull composite aircraft with payload between the hulls, similar to that of the "White Knight" carrier aircraft for SpaceShip One, except without any central fuselage
    engines: six 205–296 kN (46,000–66,500 lbf) thrust-range jet engines
    altitude at launch: 30,000 ft
    velocity at launch:
    development costs: $300 million

    Payload data:
    name: Pegasus II
    engines: solid (all three stages)
    delivery envelope:
    LEO: 13,500 lbs
    GTO: 4,500 lbs
    weight: 465,000 lbs

    Additional data:
    STS velocity vs altitude profile (page 3)
    Saturn V ballistics info (about 4/5 the way down the page)

    THE MISSION:
    Your mission, should you decide to accept it, will be to combine this information with additional resources, and determine the Stratolaunch/Pegasus II system's cost per pound to LEO and GTO. Include all costs, both expendables and reusables.
    My oath of office never expires. "God, who gave us life, gave us liberty. Can the liberties of a nation be secure when we have removed a conviction that these liberties are the gift of God?" - Thomas Jefferson. "I have far too long suffered fools. No longer will I tolerate the insufferable. Enjoy the vacuum." - Mugs

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  2. #2
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    Default Re: Paul Allen's Stratolaunch - Viable or Gimmick?

    Quote Originally Posted by mugaliens View Post
    I'm referencing this article: New photos reveal mammoth structure of Paul Allenís six-engine Stratolaunch

    As we all (should) know, there are two components to a rocket launch: Altitude and Velocity.

    Altitude represents potential energy, Ep = 1/2*m*g*h, where m is the mass of the object, g is the acceleration due to gravity, and h is the object's height above the surface of the Earth.
    Actually the formula is

    (Eq 1)

    Which, as you mentioned below, comes from a Taylor expansion about the point r=Re=Radius of the Earth. We also define

    (Eq 2)

    Quote Originally Posted by mugaliens View Post
    Although a more exact formula involves the distance between two bodies, U=G*M*m/r, low Earth orbit is close enough for government work, so a good approximation can be had with the simpler formula.

    Velocity represents kinetic energy, Ek = 1/2*m*v2.

    At any given time, the total energy of the system is given by ET = Ep + Ek.

    To complicate matters further, if not ridiculously, the mass of the rocket changes dramatically throughout its flight profile, not only by separating spent stages, but also by burning most of its mass in fuel.
    Fortunately, the Rocket Equation gives an answer. The NASA Web Site shows how the Rocket Equation is applied.

    Quote Originally Posted by mugaliens View Post
    The question has been around for quite a while: Economically speaking, how viable is Paul Allen's Stratolaunch approach? Let's examine some data:




    As you mention, it does look a lot like Pegasus.

    Quote Originally Posted by mugaliens View Post
    [ ... deleted ... ]
    THE MISSION:
    Your mission, should you decide to accept it, will be to combine this information with additional resources, and determine the Stratolaunch/Pegasus II system's cost per pound to LEO and GTO. Include all costs, both expendables and reusables.
    I will think about it: Iīm kind of busy these days.
    Last edited by kg4pae; 03-03-2015 at 09:53 PM. Reason: Correct Math
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