Question 32 2010 HSC exam. (1 Viewer)

[cook E]

Two significant problems that will affect a manned spaceflight to Mars are:
• the changes in gravitational energy
• protecting the space vehicle from high-speed electrically charged particles from

the Sun.

Use your understanding of physics to analyse each of these problems.

What do you write for the change in gravitational energy?

The sample answers wrote this:

In order to transport people to Mars the mass of them, their habitat and their spacecraft
(including fuel) must be:
1. raised from Earth’s surface into orbit around the Earth
2. raised from Earth’s orbit around the Sun to Mars’ orbit around the Sun (and placed in
orbit around Mars)
3. lowered (without crashing) from orbit around Mars to its surface
4. raised from Mars surface  Mars orbit
5. lowered from Mars orbit about Sun  Earth orbit about Sun
6. lowered (without crashing) from Earth orbit  Earth surface
Steps 1, 2 and 4 all involve positive changes in gravitational potential energy, energy that
must be supplied by the rocket engines during these stages. Steps 3, 5 and 6 involve negative
changes in gravitational potential energy and large positive changes in kinetic energy. To
prevent crash landings this kinetic energy must be lost through friction in an atmosphere or by
braking using a forward-facing rocket engine. A significant issue is that the fuel needed for
the later steps adds to the mass that must be moved in the earlier steps (unless fuel can be
made on Mars)

Is that the only thing u have to consider?

 

[nifkeh]

bump because I'm curious

 

[Fizzy_Cyst]

Find attached a sample Band 6 answer to this question, it is labelled as HSC 2012, but it is 2010..

View attachment Band_6_response_HSC_2012_Q32.pdf

 

[treebrains]

I answered it by understanding that when GPE changes, so does KE (energy is conserved blah blah)

1) And in the first half of the journey (so to speak, really meaning, "as far as the spaceflight is under the influence of Earth's grav field primarily")
- GPE is increasing as it recedes from Earth.
-> what are the implications of this on the journey? Well, a) our KE is decreasing. as a function of KE = 1/2mv^2, this means our velocity is decreasing, so we need higher acceleration/thrust to reach our desired velocity. blah blah, more fuel is needed, but this also increases our mass, posing a particularly annoying issue.

2) Second half: approaching mars
- GPE is decreasing as it approaches mars
-> what are the implications? more kinetic energy, so it is accelerating at a higher rate etc. braking procedures (fwd facing rockets) must be considered to regulate acceleration for both safe landing and regulating g-forces

there are probably more implications for both things to throw in, but that's the big picture I think