Physics Principles and Problems 2009

Chapter 17: Reflection and Mirrors

Problem of the Week

<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078807220/193800/ch18_title.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a>
Launch Logistics
The basic dilemma is this:
Can you launch a spacecraft that doesn't carry any fuel?

<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078807220/193800/lilGuy.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a>

Suppose you wish to launch a 50-kg payload into space. To launch those 50 kg you may need 50 kg of fuel. But wait, now you need to lift 100 kg, so you need to add more fuel to lift the original fuel. Adding more fuel adds more weight so you'll need to add more fuel which adds more weight... <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078807220/193800/ch18_ariane4.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (5.0K)</a>
Ariane 4 Spacecraft
As it turns out, over 90% of the weight of a rocket is fuel. You have to haul around a huge, empty gas tank once you make it into outer space. That is why many rockets are multistage.

For another solution to the fuel-weight dilemma, you could build a...

...laser-propelled airbreathing engine
The Lightcraft is a vehicle that carries no fuel. Instead, the craft gets its energy from a ground-based laser. Pulses from the laser strike a mirror at the rear of the craft and are focused into a propulsion chamber. The concentrated laser pulses superheat the air into a 54 000° F plasma which then expands explosively out the back to produce thrust. Air then reenters the chamber just in time for another laser pulse. Viola, you have power without carrying any fuel (at least while you are in the atmosphere).
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078807220/193800/ch18_lightFlight.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (5.0K)</a>
Test flight of Lightcraft
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078807220/193800/POWproblem1.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> What might be an optimal design for the rear of the craft? How might the front look? Draw a schematic of how you might design such a ship.
 
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078807220/193800/POWproblem2.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> Before the test flights, the scientists spun the craft. Why did they do this? What problem do you suppose they are trying to solve by having the craft spin?
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078807220/193800/webLinks.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (1.0K)</a> The facts of the Lightcraft can be found at http://www-aero.meche.rpi.edu/Curriculum/TAVD/. Clicking will launch a new window.
<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078807220/193800/gutter.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a><a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078807220/193800/gutter.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a><a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078807220/193800/gutter.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a><a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078807220/193800/gutter.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a><a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078807220/193800/gutter.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a>
Glencoe Online Learning CenterScience HomeProduct InfoSite MapContact Us

The McGraw-Hill CompaniesGlencoe