Space shuttle Endeavour launches in November 2008 carrying seven STS-126 crew members including Mission Specialist Don Pettit. These numbers assume ideal conditions such as no losses for atmospheric drag or combustion but are close enough for the sake of this illustration. Here the approximate cost in energy has been given in terms of velocity (kilometers per second, km/s), a common ploy engineers use to simplify the discussion. It is constructive to put a few numbers together to illustrate the grip that simple momentum balance places upon our rockets. With some clever engineering we might be able to shave a few percentage points off the fraction, but the basic result is set by the gravitational environment of our solar system (choice of where we want to go) and the chemistry of the energetic bonds of our selected chemical components (choice of propellant). There is very little we can do to alter this result. This also applies to existing rockets when new uses are contemplated. We must build our rocket within this mass fraction or it will not reach its destination. With these two variables set, the rocket mass fraction is now dictated by the rocket equation. I like to think of this selection as what you have to pay for the travel cost. Again, we simply have to accept the limit to what chemistry can offer (unless we choose other energy sources, such as nuclear). like hydrogen-oxygen combustion) and thus, the second variable is now specified. Some of the most energetic chemical reactions known are chosen for rocket propulsion (e.g. There are limits to the quantity of energy that can be extracted from chemistry and thus bounds placed outside of human control on the energy we can pack into a rocket. Currently, all our human rated rocket engines use chemical reactions (combustion of a fuel and oxidizer) to produce the energy. Next we need to choose the type of rocket propellant, thus specifying the available energy. I like to think of this as the travel cost. We simply have to accept its consequences. As humans, we are powerless to change this number. The energy expenditure against gravity is then specified by the starting and ending points of our journey. In planning an expedition into space, we first must select where we want to go. Of course there are permutations to these routes but they are the most likely ones considering our current state of technology. The most likely candidates are: from the surface of Earth to Earth orbit, Earth orbit to surface of the Moon, Earth orbit to surface of Mars, Earth orbit to cis-lunar space (the region between the Earth and the Moon, including a variety of locations such as Lagrange points, geostationary orbit, and more). For human exploration, there are only a handful places we can realistically consider at this time. The energy expenditure against gravity is specified by where you want to go. They are the energy expenditure against gravity (often called delta V or the change in rocket velocity), the energy available in your rocket propellant (often called exhaust velocity or specific impulse), and the propellant mass fraction (how much propellant you need compared to the total rocket mass). Although a momentum balance, these variables can be cast as energies. Hope, wishing, or tantrums cannot alter this result. Given any two of these, the third becomes cast in stone. The rocket equation contains three variables. All our rockets are governed by Tsiolkovsky’s rocket equation. Conservation of momentum applied to a rocket was first done by Russian visionary and scientist Konstantin Tsiolkovsky in 1903. Isaac Newton correctly defined the mathematics for this exchange of momentum in 1687. They spew gas out of a nozzle at high velocity causing the nozzle and the rocket attached to it to move in the opposite direction. If we want to expand into the solar system, this tyranny must somehow be deposed.
NASA SPACE SHUTTLE WEIGHT FREE
Such is the case when we invent machines to free us from the bounds of Earth, affecting our escape into space. This projection is a form of rationalization, perhaps a means to cope with matters that we cannot control. Tyranny is a human trait that we sometimes project onto Nature. By Expedition 30/31 Flight Engineer Don Pettit
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