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Technical Paper for an Introduction to Mechanical Engineering class

  1. Jul 15, 2012 #1
    Hello all; I have a homework 'question' I'm hoping I can get some help with here.

    For my Introduction to Mechanical Engineering class, we have been tasked with writing a technical paper and there is a portion of the mark dedicated to using social media and the internet to enhance the paper, with regards to content as well as reaching a larger audience (ie not just the Professor and TA).

    Below I have copied out the final draft of my paper, with the figures taken out (I have also taken out sentences referencing them). Also I will leave out the sources page to save space, if you're interested in a specific one please ask either via comment or PM.

    As for my 'question' I would ask that if you're interested, give the paper a read and if you have any questions, criticism, tips/hints to please comment below.

    Thanks for your time.



    Introduction

    As interest in the scientific and economic value of real-estate outside of Low Earth Orbit (LEO) increases, the difficulties of inter-planetary travel are becoming more apparent. Conventional chemical rockets lack the capacity to economically transport material in space due to high propellant-cargo costs and inefficient propulsion technologies. The Ad Astra Rocket Company has developed a technology that –if successful- will greatly increase access to distant locations via alternative propulsion methods. Ad Astra’s Variable Specific Impulse Magnetoplasma Rocket (VASIMR®) is an electric thruster rocket that will use superheated plasma to propel a space-craft outside of LEO at a fraction of the cost of conventional methods. The VASIMR® will be useful for; drag compensation for satellites, cargo transportation to the moon and Mars, as well as resource recovery and other space missions [1]. After a successful test run of the VX-200 rocket [2], the next stage for Ad Astra will be attaching the VF-200 rocket to the International Space Station for field testing.


    Method
    In order to escape Earth’s gravity a rocket must have a thrust force greater than the forces due to Earth’s gravity. Conventional rockets used today accomplish this by burning a chemical propellant in order to create and expel exhaust gas, creating a thrust force. Velocity of a rocket is determined by the rocket equation:

    ∆v=ve 〖∙ln〗⁡〖mo/mi〗
    Where: mo= initial mass, including propellant
    mi = final total mass
    ve = effective exhaust velocity
    ∆v = max change of speed in vehicle

    Specific impulse (measured in units of seconds) represents the derivative of the impulse (the integral of force with respect to time) with respect to the amount of propellant used and is equivalent to:
    Isp= (effective exhaust velocity)/(acceleration due to gravity)

    A high specific impulse means that a lower propellant flow rate is required for a given thrust and therefore less propellant is required for a given ∆v . The fraction of propellant used to the initial mass of the system is known as the propellant mass fraction (PMF); a higher PMF suggests inefficiency since more fuel must be burned to move the same amount of payload. Current PMFs in today’s rockets remain high; the Space Shuttle had a PMF of almost 0.95 [3]. Inefficient chemical rockets leave little remaining fuel upon arrival into LEO for extracurricular activities. This is where the VASIMR® will become an asset. With a specific impulse of up to 5000s, generated by an exhaust velocity approaching 50 000 m/s, the VF-200 is a much more efficient system for in orbit transportation.
    The high specific impulse is the result of a superheated ionized plasma stream controlled by a magnetic field being ejected out of the rear of the rocket via a magnetic nozzle. The process starts at a set of radio wave antennae, or RF couplers, where a gas –such as Argon, Xenon, or Hydrogen-, is converted to plasma by ionization. This ionization is accomplished by radio frequency heating. A high frequency alternating electric field heats the gas molecules by helicon discharge; an oscillating electric field causes the dipole molecules of gas to rapidly rotate and therefore produce net kinetic energy while contained along the axis of a magnetic field [4] [5] [6]. In the next stage the plasma passes through another RF coupler. Here the magnetic field lines resonate with the ions to generate even more heat. This resonance is caused by the magnetic field generating a frequency at the resonant frequency of the plasma, which results in a driven oscillation [7]. At the end of the rocket, a magnetic nozzle converts the angular momentum of the ions to linear momentum by elongating the field lines. This linear momentum is the force behind the extremely high exhaust velocities of the VF-200 [8] [9].


    Discussion
    Due to the strong magnetic field in VASIMR®, the hot plasma does not physically come into contact with the containing structure of the rocket. This means materials last longer since they are not exposed to extreme temperatures. Another advantage of VASIMR® is its ability to control the exhaust velocity and thereby better enable it to match the required specifications of a mission.

    High Specific Impulse comes at high expense, and the VASIMR® must be able to generate its own energy in order to be functional. One of the challenges facing Ad Astra is the supply of this energy, which will likely have to be supplied by a nuclear reactor in order to generate the require energy per unit mass needed for reasonable trip times for manned missions [10].


    Conclusion
    With a working prototype planned to be launched to the ISS, Ad Astra is moving forward with their innovative ion propulsion technology. A successful trial of the VF-200 will establish the VASIMR® as a legitimate alternative to current conventional technology. The high Specific Impulse compared to chemical rockets make it is a better option with regards to in-orbit missions as well as missions beyond LEO.
    The VASIMR® presents an optimal alternative for future missions in space. Ion propulsion coupled with a variable specific impulse will allow mission planners to expand upon what current technology offers and at a more cost-effective price. While the VASIMR® has yet to prove itself in the field, plans are underway to cross this obstacle and prove the VASIMRs® place in the future of manned and robotic spaceflight.
     
    Last edited by a moderator: Jul 16, 2012
  2. jcsd
  3. Jul 16, 2012 #2
    You need to anchor this paper in time with such phrase as "at the time of writing (2012) ......", because things will develop
     
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