HSC2005 Question (1 Viewer)

[Kukudas]

umm i was looking past paper.. and i saw this question

Question 19 (4 marks)
In 1970 NASA launched Apollo 13, their third mission planned to land humans on the Moon. Half-way to the Moon a huge explosion crippled the spacecraft. The only way home for the astronauts was to fly around the back of the Moon and then fire the rocket engine to take the craft out of lunar orbit and put it into an Earth-bound trajectory.
At the completion of the rocket engine burn, mission leader Jim Lovell was heard to say, ‘We just put Isaac Newton in the driver’s seat’.
Given that the spacecraft returned safely to Earth, justify Jim Lovell’s statement.

-_- wats the syllabus point relating to this question??? -_-

help plz

 

[davidw89]

this is a funyn question
our teacher was talking about it in class
he said that some kid got one makr for saying Issac Newton wasnt on the spacecraft roflamo

 

[venture68]

............

nice question.... ask ur teacher

 

[noobking]

it's basically jus ask u to relate newton's law to space launch

 

[airie]

:rofl: :rofl: :rofl:

Nice question. I wonder who wrote it. They think they've got some sense of humour.

Basically that Newton business is just that Newton's law of gravitation was used to transfer the spacecraft from a parking orbit around the moon to one around the Earth (the re-entry bit afterwards doesn't really relate to Newton much). So you'd basically have an elliptical path shown in the diagram attached.

If you want more connection with Newton's theory, maybe talk about how orbital velocity can be determined by equating the centripetal force on satellites to the gravitational force, as calculated by Newton's law of gravitation. Then the change in velocity of the spacecraft from the lunar orbit to an orbit around Earth can be calculated. Also, Kepler's Third Law (the whole GM/4(pi)² part is enabled by Newton's law of gravitation and thus formula for orbital velocity) can be used to calculate the time taken for the transfer.

EDIT: Forgot to attach the diagram

 

[simplistic]

yeh they had that question for our exam about both space and motors and generators , the criteria was asking for all wat was said by airie as well as mentioning somthing about the slingshot affect ...

 

[Forbidden.]

yeh they had that question for our exam about both space and motors and generators , the criteria was asking for all wat was said by airie as well as mentioning somthing about the slingshot affect ...

I would earn some marks thanks to slingshot effect ... I'll check the criteria up myself.

EDIT:

"In better responses, candidates were able to describe and relate two or more of Newton’s Laws of
Motion in words and/or equations to the return trip of Apollo 13, ie the period after leaving the
lunar orbit.
In weaker responses, candidates incorrectly applied the ‘slingshot effect’ to the motion of the rocket
around the moon."



•Presents a logical, coherent argument to support Jim Lovell’s statement,
for the period after the rocket burn including correct, relevant description
of Newton’s laws
(4 marks)

• Describes and explains the relevance of Newton’s laws to the solution of
the astronaut’s problem for the period after the rocket burn
(3 marks)

• Correctly identifies and relates one of Newton’s laws to the situation for
the periods either before or after the rocket burn
OR
• States two of Newton’s laws
(2 marks)

• Correctly states one of Newton’s laws
(1 mark)


Dammnit ... slingshot effect is not effective ... there's Newton's three laws and his law of universal gravitation.

 

[alcalder]

It is also interesting to note that should Apoloo 13 decided to stop, turn around and go back the way it came, the astronauts would have run out of oxygen.

Newton's First Law states that a body will continue on the same direction at the same speed unless a force is applied to it to change. They had two choices, use the forece of gravity from the moon to turn the ship around or use the thrust from the Apollo's engines.

To use the engines they would have to apply Newton's third law - for every action there is an equal and opposite reaction. To stop Apollo 13 they would have had to make a burn in a direction opposite to their motion and then continue to burn to start motion back towards Earth. This would involve slowing down the capsule and then accelerating again using Newton's second Law F=ma. The force applied to Apollo 13 would be proportional to the mass and acceleration of the space craft.

All this takes time.

Instead, the Apollo 13 mission used the pull of the moon to turn the ship and then the ship did not need to slow down to stop and change direction.

They would have had to enter the gravitational field of the moon at a certain velocity and at a certain height above the centre of the moon (d) in order to achieve the correct change of direction around the moon due to gravity.

F = Gm₁m₂/d²

m₁ = mass of Apollo 13
m₂ = mass of Moon

When they had done this, it was sit back and wait for Newton to take charge and spit them out the right way as they went around the back of the moon. The biggest fear was that the craft would not bend all the way around the moon but be shot out into space and be lost forever because they did not have enough air to stop the craft and turn around and come back.

In effect they chose to go the long route (one that seemed radical at the time) but it was the only way to do it. Thankyou Newton for providing them with the answer.

 

[helper]

When the examiners proposed the question they didn't want anything to do with the moon.

Why?
The were talking about the statement, which had occured after the travel around the moon, so it was irrelevent.

They were refusing anything to take anything to do with the moon. As everyone was going so poorly they started to accept answers with gravity of the moon to turn the craft around but you couldn't obtain full marks just talking about it.

 

[alcalder]

They didn't want an answer that had nothing to do with the moon! Hey what??

So, what did Jim Lovell mean when he said, ‘We just put Isaac Newton in the driver’s seat. ? if not something to do with the gravity of the moon because a damn lot of what made it possible for them to get back was due to the gravity of the moon (not necessarily the sling shot effect but I bet you it was due to that).

*head desk*

From Wikipedia - the Apollo 13 mission used the Free Return Trajectory to get Apollo 13 around the moon!

Free return trajectory
From Wikipedia, the free encyclopedia
Jump to: navigation, search

A free return trajectory is one of a very small sub-class of trajectories in which the trajectory of a satellite traveling away from a primary body (for example, the Earth) is modified by the presence of a secondary body (for example, the Moon) causing the satellite to return to the primary body. This method has been used by spacecraft and was somewhat popularised by its use during the Apollo 13 mission, though this trajectory was actually a hybrid, requiring some minor adjustments. If performed correctly, a true free return trajectory is completed without the assistance of any mid-course corrections or maneuvers. The free return trajectory allows a great distance to be covered relatively directly without the use of additional fuel to return the satellite to the primary body, thus the term free. It is important to note that the satellite or spacecraft will not actually be captured by the secondary body without the use of its rocket engine to slow the craft.

 

[helper]

Like it or not they weren't after the trajectory around the moon based on:

The only way home for the astronauts was to fly around the back of the Moon and then fire the rocket engine to take the craft out of lunar orbit and put it into an Earth-bound trajectory.

At the completion of the rocket engine burn, mission leader Jim Lovell was heard to
say, ‘We just put Isaac Newton in the driver’s seat’.

Since the statement was after the the rocket burn to leave lunar orbit, the lunar orbit was not what the comment was about.

Their interpretation was that after rocket burn, the astronauts could no longer pilot the capsule. So Newton was now in the Driver's seat as his laws were going to determine if they would be successful on reentry. Then using his laws to explain it.

Before that, the astronauts were in the driver's seat as they could adjust their re-entry trajectory.

If you look at the marking scheme to obtain 3 or 4 you had to talk about after the rocket burn.

 

[alcalder]

OK, fair enough. It all depends on your interpretation of "just".

Did the "just" mean, we "just now" put Newton in the driving seat, or did it mean we "have just" put Newton in the driving seat?

Certainly, after the burn and with no more fuel left to change their trajectory or speed, Newton's Laws indicated whether the acceleration they had would be enough to get through the friction of the Earth's atmosphere (but, mind you, there is also the gravitational equation to consider when approaching the Earth's gravitational influence). F=ma. First Law - cannot change velocity without a force and they had no way to do that.

 

[fwong]

It is also interesting to note that should Apoloo 13 decided to stop, turn around and go back the way it came, the astronauts would have run out of oxygen.

Newton's First Law states that a body will continue on the same direction at the same speed unless a force is applied to it to change. They had two choices, use the forece of gravity from the moon to turn the ship around or use the thrust from the Apollo's engines.

To use the engines they would have to apply Newton's third law - for every action there is an equal and opposite reaction. To stop Apollo 13 they would have had to make a burn in a direction opposite to their motion and then continue to burn to start motion back towards Earth. This would involve slowing down the capsule and then accelerating again using Newton's second Law F=ma. The force applied to Apollo 13 would be proportional to the mass and acceleration of the space craft.

All this takes time.

Instead, the Apollo 13 mission used the pull of the moon to turn the ship and then the ship did not need to slow down to stop and change direction.

They would have had to enter the gravitational field of the moon at a certain velocity and at a certain height above the centre of the moon (d) in order to achieve the correct change of direction around the moon due to gravity.

F = Gm₁m₂/d²

m₁ = mass of Apollo 13
m₂ = mass of Moon

When they had done this, it was sit back and wait for Newton to take charge and spit them out the right way as they went around the back of the moon. The biggest fear was that the craft would not bend all the way around the moon but be shot out into space and be lost forever because they did not have enough air to stop the craft and turn around and come back.

In effect they chose to go the long route (one that seemed radical at the time) but it was the only way to do it. Thankyou Newton for providing them with the answer.

This is silly. Celestrial mecahnics is UNlike driving a car where you can stop and turn around. This is impossible even in theory. The Apollo 13 essentially had no option. Period.