 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
| HomeDiscussion GroupsSpace ScienceAstronomyAmateur AstronomySpace FlightSpace StationShuttleSpace HistorySpace PolicySETI SpaceKB.com Contact UsLink To UsSearch & Site Map |
Space Forum / Shuttle / May 2007G-forces and fuel consumption
Assuming one has engines with unlimited thrust and no aerodynamic issues, and assuming occupants can take any G force: If, at the time of ignition, the throttles are opened to the max for an instant acceleration at high G force, would this end up saving fuel ? I am thinking that by spending the fuel at greater rate very early in flight, you would have less fuel to accelerate afterwards and hence save on the fuel. Or does it make no difference in the end because , despite the shorter time when you carry the fuel, that fuel still ends up being accelerated by the same amount ? > Assuming one has engines with unlimited thrust and no aerodynamic issues, > and assuming occupants can take any G force: [quoted text clipped - 9 lines] > time when you carry the fuel, that fuel still ends up being accelerated by > the same amount ? Nice idea, but it makes no difference. In fact the most fuel efficient rockets today are ion engines that have VERY low thrust but very high exhaust velocities/ISP. Danny Deger This of course was the premise behind all those early Sci Fi stories where the launcher was in fact a big gun! Brian  SignatureBrian Gaff....Note, this account does not accept Bcc: email. graphics are great, but the blind can't hear them Email: briang1@blueyonder.co.uk ______________________________________________________________________________________________________________ > Assuming one has engines with unlimited thrust and no aerodynamic issues, > and assuming occupants can take any G force: [quoted text clipped - 9 lines] > time when you carry the fuel, that fuel still ends up being accelerated by > the same amount ? John Doe <jdoe@doe.org> wrote: >I am thinking that by spending the fuel at greater rate very early in >flight, you would have less fuel to accelerate afterwards and hence save >on the fuel. Yes: think of the trade-offs along a line from Worst case: booster with <1G acceleration, burns all its propellant and gets nowhere to Best case: "gun" launch -- all kinetic energy delivered at once, none of it wasted on accelerating propellant to be used later, or engines that become useless when propellant is gone, or the costly large-but-light-but-strong structures to accommodate both. Of course, the downside is the extreme acceleration at the start -- mitigated but still pretty bad if the "gun" becomes a rail, ramp or tube of plausible length -- and the fact that you still need at least a small engine and some propellant to modify your trajectory into an orbit. (Any straight-line trajectory from the earth's surface that doesn't escape entirely is going to intersect the earth's surface.) related is a cargo only launcher for stuff high G wouldnt hurt, like water, fuel and durable stuff. launched by a rail gun up the side of a mountain where most of the acceleration is magnetic powered from ground based electricity. just a small rocket for final trajectory control > related is a cargo only launcher for stuff high G wouldnt hurt, like > water, fuel and durable stuff. > > launched by a rail gun up the side of a mountain where most of the > acceleration is magnetic powered from ground based electricity. just a > small rocket for final trajectory control A huge problem with this for Earth launches is you are going Mach 25 in the low atmosphere. Even the top of Everest is "low" to be going Mach 25. Current entry TPS can't handle this. They slow down before they get low. For a moon launch, a gun makes a lot of sense. Danny Deger Danny Deger "John Doe" > Or does it make no difference in the end because , despite the shorter > time when you carry the fuel, that fuel still ends up being accelerated > by the same amount ? What you are asking about is called the "specific impulse." I am not sure I follow all of your theoretical assumptions, but in general when rocket scientists have gone about designing a rocket to achieve a high specific impulse, they go the other way, as it were. The ion engine for example uses its fuel by the gram but operates for months. SignaturePosted via a free Usenet account from http://www.teranews.com |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.