hopdavid

hopdavid

  • Commented on Lunch with the Astronaut
    Some thought tethers were discredited when electric current fried a tether in February 1996. http://www-istp.gsfc.nasa.gov/Education/wtether.html However, they learned from that experience. A number of tethers have been launched, some of them successful. http://en.wikipedia.org/wiki/Space_tether_missions Kirk Sorensen has a number of tether...
  • Commented on You probably already saw this, but ...
    (Reading your post 108...) I don't see that you have a clue that the constraints and requirements of ascent from earth's surface is quite different from an orbital burn. Ascending through a thick atmosphere up the slopes of a steep...
  • Commented on You probably already saw this, but ...
    I was saying re-entry abuse is one the factors that make reusable earth to orbit vehicles difficult (if not impossible). The 10 km/sec to LEO delta V budget likely mandates multi-stage expendables even without thermal protection. Add in re-entry abuse,...
  • Commented on You probably already saw this, but ...
    Please see my post 112. Launching from earth's surface you want a dense, high thrust propellent to minimize drag and gravity loss. In orbit, gravity loss is not an issue. It makes more sense for an upper stage to use...
  • Commented on You probably already saw this, but ...
    Besides being easier to handle, kerosene has a better thrust to weight ratio. In general, better ISP means worse thrust. The initial part of the trip to orbit must be a vertical ascent. Gravity loss is incurred during vertical ascent....
  • Commented on You probably already saw this, but ...
    Any power source generates heat. Whether nuclear, fossil fuels, what have you. The human generated power is a minute amount compared to what the sun gives the earth. Power generation may contribute noticeably to warming if it generates green house...
  • Commented on You probably already saw this, but ...
    Please see my post 47 above. A mirror with perfect optics at Molniya apogee would project an image of the sun about 370 km in diameter. About the size of state of Massachusetts. You would need a photovoltaic array of...
  • Commented on You probably already saw this, but ...
    Yes, it would likely be difficult mining lunar propellant. How difficult? Some factors to consider: The elevated CPR found by Chandrayaan-1's mini Sar radar seems to indicate sheets of ice at least two meters thick. Lunar light lag is only...
  • Commented on You probably already saw this, but ...
    Given perfect optics, the diameter of the image projected by the mirror will be ((distance from mirror to image)/(distance to sun)) * diameter sun. A Molniya's orbit apogee has an altitude of about 40,000 km. The projected image of the...
  • Commented on You probably already saw this, but ...
    Propellant depots could drastically decrease the complexity. As delta V budget climbs, you rapidly reach an undoable mass fraction. At this point you start discarding mass in the form of expendable stages. More stages mean more mass, complexity and failure...
  • Commented on You probably already saw this, but ...
    Both moon and Mars are inhospitable vacuum. The chief selling point for Mars has been CHON. But LRO and Chandrayaan-1 have found CHON at the lunar poles. Not only is water useful for life support and radiation shielding but it...
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