A beam(maybe multiple beams from ground crossing at, or just some very high alternating potential, something like focused haarp) on tip of rocket targeting at path of it, ionizing just the closest molecules that are about to add friction to rocket.

Rocket having same signed static electrical charge so ionized particles (cores) don't add drag because they don't come close enough before rocket passes, or at least the air pressure at all heights is decreased by a good margin.

Just like rocket traveling in a bubble of vacuum. When vacuum applied only at tip, it could pull the rocket, increasing its velocity?

In other words, could it lessen space launch fuel consumption for friction?

Doable?

Dangerous?

Trivial?

How much energy needed? More than fuel of conventional ways? But ground based ionizators would make a lighter fuel depot for rocket, would it?

closed as unclear what you're asking by CuriousOne, user36790, ACuriousMind, honeste_vivere, unsym Jun 8 '16 at 10:07

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    Hm. It's not everyday that Stack Exchange imitates SMBC. – dmckee Jun 4 '16 at 0:32
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    Wouldn't the static electric repulsion also exert an opposing force on the rocket and just be a substitution for the drag. Also ionizing air will make molecules split up in both positive and negative changed particles. So the rocket can't repel both. – fibonatic Jun 4 '16 at 1:04
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    The energy loss due to friction is of almost no importance to a rocket, it compromises only about 5% of the total energy needed for the launch. What is of importance is the aerodynamic stress on the rocket, but Max Q (max. aerodynamic pressure) occurs at an altitude of approx. 10-15km (around 90s after liftoff) and is usually countered with a slight throttling of the engines. If there was a reason to reduce it significantly, we would be launching from high elevation sites (4000m+ in altitude), but technically it's really more of an inconvenience than a real problem. – CuriousOne Jun 4 '16 at 2:37
up vote 3 down vote accepted

When you're considering hydrodynamic forces there are always two things to consider. One is the viscosity of the fluid, i.e. how much energy it takes to make it flow, and the other is the inertia of the object, i.e. how much energy it takes to make it move out of your way.

At high velocities the drag is dominated by the inertial forces. Air weighs more than you think - it's a bit over a kilogram per cubic metre. To push your way through the air you have to make it move so you have to increase its kinetic energy. It's the work you have to put in to increase the kinetic energy that causes the drag. So ionising the air isn't going to make any difference. It still has the same mass and the rocket still has to push that same mass out of the way.

In principle you could use the lasers to heat a column of air and reduce its density. That would mean there is less mass for the rocket to push out of the way, and it would indeed reduce the drag. The trouble is that it still takes energy to heat the air so all you've done is swap some of the work done by the rocket for work done by the lasers on the ground. Well, the real trouble is that it would be disastrously inefficient because the reduction in fuel needed by the rocket would be far outweighed by the massive amount of energy needed to power your lasers.

Watch a video of a rocket launch, say the space shuttle. Within a minute of the flight the launch director might make a statement about maximum dynamic pressure. The launch vehicle is producing a supersonic shock wave and the interaction of the atmosphere is at its peak. Within another $30$ seconds to a minute the dynamic pressure with the atmosphere is nearly zero. About half the atmosphere is within $4$ kilometers of sea level, and the rocket clears this within a minute and after two minutes the rocket is in the upper stratosphere with very little air pressure. While this does eat energy and fuel the rocket carries it is not a large amount.

You could heat a column of air ahead of the rocket in principle. This is not entirely easy though. First off it is clear you would want this done from the ground, rather than having the rocket carry the laser and energy source required to run it. This would take as much or more energy than energy lost by pushing through the atmosphere as is the usual case. There is still a problem in that air does not heat that much from optical radiation. The atmosphere of the Earth gains most of its temperature because solar radiation heats the ground and that in turns heat the air. In order to create a partially evacuated column of air you would need something similar to a lightning bolt. Thunder is produced by the rapid expansion of air from the current. Having a rocket fly through an ionized column of air might be problematic.

There is a similar concept used by ballistic missiles called a Drag Reducing Aerospike It is a flat disc deployed forward of the nose that...

The aerospike creates a detached shock ahead of the body. Between the shock and the forebody a zone of recirculating flow occurs which acts like a more streamlined forebody profile, reducing the drag.

Interestingly similar effects can be created with electric arcs or lasers:

Further development of this concept has resulted in the "air-spike".1 This is formed by concentrated energy, either from an electric arc torch or a pulsed laser, projected forwards from the body, which produces a region of low density hot air ahead of the body. This has the advantage over a structural aerospike that the air density is lower than that behind a shock wave providing increased drag reduction.

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