Atmospheric drag

[Dracous]

Ok, I have been playing with the idea of maneuver drives produce thrust. One thing led to another and I have found myself trying to calculate atmospheric drag on a subsidised liner.

My calc was rough, I was looking at the the atmospheric drag produced when travelling at escape velocity, and I found that the drag force was greater than the force produced by the drives by a magnitude of 100.

So, my rough calculations seemed to indicate that there was a problem achieving orbit in a subsidized liner taking of from Earth.

Where did I go wrong?

 

[lastbesthope]

Well for one thing you won't accelerate to escape velocity until you're in a much thinner section of atmosphere, or even near vacuum.

Even the Space Shuttle didn't do most of it's accelerating until it was in the upper (thinner) atmosphere.

Thinner air, less drag, may solve your problems? Unless you were already taking change in altitude into account in your acceleration profile and calculations.

LBH

 

[F33D]

My calc was rough, I was looking at the the atmospheric drag produced when travelling at escape velocity, and I found that the drag force was greater than the force produced by the drives by a magnitude of 100.

Why would you be trying to reach escape velocity in atmosphere? There is no need to try that unless the G rating of the drive is LESS than the G rating of the planet you are on...

 

[GypsyComet]

Escape velocity is only important for vehicles with limited fuel supplies or atmosphere needs. A low but constant acceleration will take longer, but will get you to orbit and beyond.

 

[simonh]

The question has already been answered, but I think I can add a but more info.

The space shuttle only actually ever reaches a bit over Mach 2 in the atmosphere, but needs to reach Mach 53 or 17500 miles per hour to get into low earth orbit. As has been pointed out, most if that acceleration happens in the upper atmosphere or outside the atmosphere altogether. Your Subsidised merchant doesn't have to worry about running out of fuel, so it could happily cruise out of the upper atmosphere to orbital altitude at a steady Mach 2 or 3 and then accelerate away from the planet from there.

Escape velocity is the speed a bullet would have to be fired at, from the earths surface, in order to escape the earths gravity, assuming no atmospheric drag. It's next to irrelevant when discussing rockets which, unlike bullets, can push themselves along in flight. If your space ship doesn't care about energy efficiency, you don't even need to reach orbital velocity before getting away from earth. You could just accelerate to a comfortable cruising speed and then just use your engines to cancel out the pull of gravity and keep cruising on out into space.

Simon Hibbs

 

[Dracous]

Thanks everyone. Looks like my assumptions need some work.

 

[ShawnDriscoll]

Ok, I have been playing with the idea of maneuver drives produce thrust. One thing led to another and I have found myself trying to calculate atmospheric drag on a subsidised liner.

My calc was rough, I was looking at the the atmospheric drag produced when travelling at escape velocity, and I found that the drag force was greater than the force produced by the drives by a magnitude of 100.

So, my rough calculations seemed to indicate that there was a problem achieving orbit in a subsidized liner taking of from Earth.

Where did I go wrong?

You don't go to escape velocity until you are already in orbit. Now if you are talking about just going in orbit, you don't want to reach escape velocity.

 

[Dracous]

Yeah, a combination of late night thinking combined with too little knowledge. A little more research this morning confirms this. Still, you guys short-cutted me to the answer.

Thanks for your patience.

 

[simonh]

That's cool, "rocket science" is used as a synonym for "something that's hard to understand" for a reason.

Now, if you really want to get to grips with rocket science I highly recommend an indie game called Kerbal Space Program (just Google it). It's tons of fun, and you get to learn a huge amount about rocketry and orbital mechanics. Just bear in mind it's a game with a lot of simplifications, not reality.

Simon Hibbs