Depressed Trajectory

[Forty21112]

I was reading a QA about sending a letter to New Jersey from Chicago. And I saw this term which I have never heard of before.

So, what is it and what are the possible uses for it? (if any)

PS: I'm sorry if this was in the wrong section, I don't know where to put it, and since it's a question, I thought it might be more sensible to put it here.

[Randazzo]

Per wikipedia:

"A depressed trajectory is a non-optimal, lower and flatter trajectory which takes less time between launch and impact, but with a lower throw-weight."

http://en.wikipedia.org/wiki/Throw-weight

I guess it could be useful if you didn't want to wait as long to watch your rocket crash.

Apparently it also pertains to the trajectory of space planes.

[TopGull]

I can't say I've seen that phrase before. Can you give us some context?

[RabidMonkey]

I can't say I've seen that phrase before. Can you give us some context?

The basic idea is that instead of a purely ballistic trajectory that optimizes fuel consumption, the rocket follows a shorter, more direct trajectory that optimizes speed. I've seen that term in the context of nuclear war scenarios - One of the big worries during the Cold War was a Soviet SSBN sitting a couple hundred miles off the eastern seaboard and peppering the coast with depressed-trajectory SLBM shots. From the mainland of the Soviet Union, we would have had about 30 minutes between launch and impact. A depressed-trajectory shot from close range would probably have dropped that to less than 5 minutes between launch detection and detonation.

[thadisjones]

The question is referencing XKCD What If? #107, which is about sending a letter from New Jersey to Chicago as fast as possible (BTW, buy the What If? book, its a great book and an awesome conversation piece if you are in an academic/science/engineering environment).

Normally, a surface-to-surface transatmospheric trajectory between two given points has an optimal arc which minimizes fuel consumption, the transit time of which is defined by the parameters of optimization. This is akin to how the most efficient route to orbit is a form of the gravity turn which we all know and love. However, it is possible to fly a fuel-inefficient surface-to-surface trajectory which gives a lower time in flight than the fuel-optimal arc. Since such a trajectory typically is both lower in altitude and exhibits a more platykurtic altitude distribution, it appears "squashed", "flattened", or possibly "depressed" to an observer.

[jarmund]

The question is referencing XKCD What If? #107, which is about sending a letter from New Jersey to Chicago as fast as possible (BTW, buy the What If? book, its a great book and an awesome conversation piece if you are in an academic/science/engineering environment).

Essential bathroom reading material. It's right next to my Cisco CCNP cert guide.

[thadisjones]

It's right next to my Cisco CCNP cert guide.

Nerd spotted!

…mine's sandwiched between an Eppendorf centrifuge manual and "Statistical Practices in Genetic Counseling" in my office.

[Forty21112]

It is from XKCD What If, I'm glad someone knows about it!

And, can it be used as a vehicle to get to point A to point B in the most kerbal way? Or is it limited to missiles only?