(Download) Indian National Astronomy Olympiad (INAO) Question Papers 2014

Question paper
Exam Name : INAO Olympiad Question Papers 2014

1. (12 marks) Read the following passage and point out scientific inaccuracies. Give very brief argument for each mistake you point out.
Arrival of a spacecraft on the surface of the Moon is called a Moon landing. This includes both manned and unmanned (robotic) missions. In order to get to the Moon, a spacecraft must first cross the point, beyond which the Earth’s gravitational force is zero. The only practical way of accomplishing this currently is with a rocket. At every instant, the rocket has to produce thrust to propel itself to a velocity equal to critical velocity at that height. Jet engines can be used to propel the spacecraft to the Moon, but rockets provide greater advantage in terms of power required for given mass of the spacecraft. 
Unlike the Earth, the Moon does not have thick atmosphere to absorb most of the solar radiation and the magnetic field of the moon is too weak to deflect the UV rays. Thus, astronauts traveling to the Moon are exposed to harmful electromagnetic radiation. Spacesuits for astronauts are specially designed by keeping this in mind.
On arrival near the Moon, the spacecraft is captured by the lunar gravity in an orbit around the Moon. As the Moon is much smaller than the Earth, typically these orbits are low altitude orbits (close to the lunar surface) as compared to the polar satellites around the Earth. The spacecraft can stay in this orbit forever, however, if one needs it to land on the Moon, it has to fire its engines to change course.
Landing at the Moon can be of two types. A hard landing is equivalent to crash landing on the Moon. A soft landing is a controlled landing in which priority is to maintain all equipment and astronauts (if any) inside the spacecraft safe. Needless to say, all Apollo missions had a soft landing on the Moon. This was achieved by firing reversing rockets very close the lunar surface to slow down the spacecraft. Charring of the lunar soil, due to burning of these rockets, is one of the permanent impressions left by humankind on the Moon. 

Solution:

• Earth’s gravitational force goes to zero only at infinity. Close to the Moon, the force is small but not zero.
• Velocity needed is bigger than the critical velocity.
• For jet engines, the oxygen is taken from the air. It is not stored on-board. So they cannot be used to take spacecraft to the Moon.
• UV rays are electromagnetic waves and are not affected by the magnetic field.
• Low altitude orbits are not stable, as imperfections on the lunar surface result in change in gravitational force from point to point.

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