why does a apollo rocket have to be so large whereas the lunar lander only needs a small rocket motor?

Answer 1

Earth's gravity is about 6 times greater than the Moon's.

Escape velocity on the Moon is about 5,308 mi/hr
Escape velocity on Earth is about 25,008 mi/hr

escape velocity is calculated by the formula

V = sqrt (2GM/R)
where
G is Newton's Gravitational constant
M the mass of the planet
R the radius of the planet

Answer 2

Robert is correct - the gravity force on the moon is roughly 1/6 of that on the earth. But the other issue that perhaps he didn't really clarify is that when we left the earth we had to carry all that fuel along while we were launching, which made the rocket much heavier to start with. By far the largest fraction of the Saturn rocket weight consisted of fuel that would have to be used either during the launch sequence (perhaps 95%) or during the return. Since so little fuel was needed to complete the mission once we got to the moon, the lander weighed a lot less - and then it weighed even less in the lower gravity field.

Answer 3

The Saturn V rocket used to take up Apollo had to carry its own fuel plus enough fuel to raise 3 astronauts, the command module, the lander module base and the lunar module ascent unit, plus food and oxygen for the crew for the entire trip. And it was lifting all this against Earth's gravity (by definition 1 g).

When the LEM went down to the Moon, it only carried 2 astronauts and their supplies. The third astronaut, the command module and the supplies for the return trip to Earth, remained in orbit around the Moon. A good portion of the LEM fuel got used up on the way down, making the LEM even lighter.

When the LEM took off from the Moon, it did not need its base. It was left behind, as well as some equipment (e.g., seismic experiments, Moon buggy). So, only a small mass had to be lifted up and it was against the much smaller gravity of the Moon ( 1/6 g).

Answer 4

It's all to do with what the different rockets had to do during the flight.

The ascent stage of the lunar lander had to lift itself and two men into lunar orbit. The craft is small and lightweight, the gravity is one sixth that of Earth, and the speed it has to reach to orbit the Moon is about 3,600mph. It landed with enough consumables (oxygen, food, water etc.) to support two men for a few days on the lunar surface, and by the time it lifted off about half of these had been consumed. In addition, equipment and rubbish that was not needed was thrown out of the vehicle prior to launch. This, incidentally, included those backpacks the astronauts wore on the surface.

The Saturn V has to send the fully fuelled ascent and descent stages of the lunar landing vehicle, plus the fully fuelled command/service module, plus three men, plus all the consumables needed to support them on a two-week mission, to the Moon against Earth's gravity, which required getting that whole massive spacecraft stack up to 25,000mph. So, it had to lift more, against higher gravity, and get it to a greater speed. It needed more fuel, therefore had to be bigger, and then it also had to lift that mass as well, so then more fuel had to be used... and so on. Rocket design is a balancing act between adding more fuel to get heavier payloads into space and the penalties of having to also lift that fuel.

So the Saturn V was huge, but the lander could be much smaller.

Answer 5

A normal chemical rocket must burn the *vast* majority of its mass just to get into orbit or to perform translunar injection. At launch, the engines must lift the entire mass against a gravitational acceleration of 1g.

A lunar lander motor only needs to act on a minute fraction of the mass of the fully loaded 3-stage booster - and in a gravity field roughly 1/6 that found at the Earth's surface.

Answer 6

AND--------- because the Saturn 5 had to LIFT the full weight of the Command Module and the Lander to escape velocity- 25,000 mph--------- from Earth's gravity. The Lunar Lander only had to lift off from the much less gravity of the moon and join up with the Command Module in orbit around the moon at the time.

Answer 7

The Apollo rockets had to be relatively great to hold the huge grant of gasoline mandatory to flee Earth's gravity thoroughly. The Lunar landers basically mandatory to flow from the Moon's floor to the return deliver (and vice versa), which became orbiting at relatively low altitude.

Answer 8

Because the Apollo rocket needed enough fuel to escape the earths atmosphere, whereas the lunar module needed only enough to push through an almost weightless atmosphere.

Gravity on earth is many many times greater than that on the moon!

Answer 9

the Moons gravity is about 6 times less than that of Earth,,,the Saturn 5 rockets needed to reach escape velocity,,,and needed to carry much more fuel,,,

Answer 10

well the lander does not have to leave the earth and also it is much smaller.