MaxQ on Mars

[smartcooky]

I have a question which I would like one of the rocket scientists/experts here to answer. I am pretty sure I understand MaxQ but here is a quick recap in case I have anything wrong.

As a rocket accelerates upwards, the dynamic pressure on the rocket's structure increases due to air resistance. All the while, the air is getting thinner but the rate of acceleration is greater than the rate at which the air density is falling so the dynamic pressure continues climbing. However, a point is reached where the air density has fallen, and continues to fall so quickly that the dynamic pressure starts to fall even though the rocket is still accelerating. That point where the air resistance and the air density "cross"  is MaxQ, and usually occurs 1 - 2 min after launch at about 10km altitude +- depending on the rocket.

My question is, what happens to MaxQ with a rocket launched on Mars?

Mars has a very thin atmosphere and far lower gravity than Earth (36%?).  So, will MaxQ be earlier at a lower altitude due to the thinner atmosphere, or will that be compensated for to a degree by the higher rate rate of acceleration allowed by the lower gravity? My intuition is that MaxQ would take place much quicker and at a lower altitude than on Earth, but as we all know, intuition doesn't always match what happens in the real world.   

[gwiz]

Your understanding is basically correct, you've just left out that q depends on the product of the density and the square of the speed.

Not sure about Mars.  The lower gravity would mean the density dropping more slowly with altitude, so that would compensate for a higher rocket acceleration.  In any case, a Mars ascent rocket could be designed for lower acceleration to limit g-loading.  I'm inclined to think that max-q could well be higher on Mars.

[Count Zero]

Just as an example the altitude at which the Space Shuttle reached maxQ was around 35,000 feet.  The air pressure at the surface of Mars is roughly the same as it is at 70,000 feet on Earth.

[smartcooky]

Your understanding is basically correct, you've just left out that q depends on the product of the density and the square of the speed.

Not sure about Mars.  The lower gravity would mean the density dropping more slowly with altitude, so that would compensate for a higher rocket acceleration.  In any case, a Mars ascent rocket could be designed for lower acceleration to limit g-loading.  I'm inclined to think that max-q could well be higher on Mars.

OK, so a related question. I'm assuming that it is more desirable for Max Q to take place at a lower velocity (less stress on the structure?). So, when a rocket lifts off, does the G force from its acceleration take account of the gravitational field strength of the body it is lifting off from i.e. would an object accelerating off the Earth at, say, 20m/s² be pulling the same "g" as one taking off from the Moon or Mars at the same acceleration?

[gwiz]

The net acceleration is proportional to thrust less weight, but the structural loads are just proportional to thrust.
 
The gravitational force of the parent body acts equally on every component so causes no relative loads, but the thrust of the engines has to spread itself through the structure to accelerate parts remote from the engines.
Thus there are relative loads proportional to thrust between the components of the vehicle. Similarly, loads due to aerodynamic forces proportional to q also act between components.