Page 9 - Curriculum Visions Dynamic Book

 When the Space Shuttle (left) is on the ground, it has a huge external tank of fuel (shown brown) and booster rockets (white) attached to it. Their size is an indication of how difficult (and expensive) it is to leave the Earth’s surface (above).
The craft also needs some maneuvering capability so that it can be repointed or repositioned.
If it has people on board, there also needs to be some form of air, water, and food provided and a way to remove wastes.
The problem of gravity
GrAvity is the force that keeps us, the air, and everything else firmly on the ground.
It is the biggest obstacle to getting into orbit because a lifting force has to be developed that is bigger than the force of gravity.
The problem of overcoming gravity is
made more difficult because at the start of
a space journey, the space vehicle carries its maximum amount of fuel and is therefore at its heaviest.
To overcome the effect of gravity on a full load, enormous amounts of fuel and huge engines that develop massive amounts of tHrust are
needed simply to get off the ground.
As the spacecraft rises, fuel is used up, and the craft
becomes lighter. Thus either the same engines will be able to move the space vehicle faster (and so it will AccelerAte), or smaller engines, using less fuel, will be able to move it fast enough to counteract gravity.
Fuel efficiency is greatest if the spacecraft rises directly from the surface as fast as possible. This is the quickest way to get through the densest part of the atmosphere. That is important because the air imposes drAg on the space vehicle, using up precious fuel. On the other hand, the faster an object rises, the more the drag and the greater the stress put on the spacecraft and on any people inside it. So, a balance between these objectives has to
be struck. A gravity pull of 6 g—six times the force of gravity—at ground level is the most the human body can tolerate, and then only for short periods.
To gain speed. movement of something.
AccelerAte
drAg A force that hinders the
grAvity The force of attraction between bodies.
tHrust A very strong and continued pressure.
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