Laser launched rockets

[Xavier Onassiss]

Re: Laser launched rockets

 

My impression from the video (s -- I watched a couple of the related ones in English as well) is that the laser is focused by the shape of the underside of the craft to superheat the air flowing through the vents in the body, causing a rapid expansion of that air that pushes against the body of the craft and produces the thrust. This presents the practical use of the craft with two major problems:

 

1) The craft is limited to use where the density of air is great enough to provide the necessary thrust. So, no orbital lifting.

 

2) the laser must be directly underneath the craft, and lined up properly, or it will at best produce unbalanced thrust, which would drive it further, or completely, out of alignment with the laser, and back into gravity's persistent embrace. So, no flying on windy days. Or near the jet stream, if you can even fly that high.

 

It is an interesting technology, but it doesn't seem very useful.

 

1) I've seen some designs (sorry, no link handy at the moment) which use lasers to heat air at lower altitudes, then switch over to on-board reaction mass once the rocket reaches thin air/vacuum. And of course, this is exactly where reaction mass does its job best: the last thing you want to is waste reaction mass fighting air resistance.

 

2) This may be an obvious question, but haven't lasers already demonstrated precision targeting over long distances? (As in, keeping the beam trained on a rocket from ground to orbit.) This doesn't seem like an insurmountable problem. Of course, a MW laser which can reliably track a target at orbital speeds would make all the neighbors a bit nervous....

 

Don't look at me,

Xavier Onassiss

[StGrimblefig]

Re: Laser launched rockets

 

1) I've seen some designs (sorry' date=' no link handy at the moment) which use lasers to heat air at lower altitudes, then switch over to on-board reaction mass once the rocket reaches thin air/vacuum. And of course, this is exactly where reaction mass does its job best: the last thing you want to is waste reaction mass fighting air resistance. [/quote']

Sure, you could do that. Of course, you are adding to the mass that the laser system has to lift.

 

2) This may be an obvious question' date=' but haven't lasers already demonstrated precision targeting over long distances? (As in, keeping the beam trained on a rocket from ground to orbit.) This doesn't seem like an insurmountable problem. Of course, a MW laser which can reliably track a target at orbital speeds would make all the neighbors a bit nervous....[/quote']

It's not really a question of whether the laser system can track the lifting body, it is question of keeping said body lined up perfectly parallel and centered within the laser beam. It was my impression that if the lifting body either rotated very much or was pushed out of alignment with the laser (say, by a gust of wind), it would not produce balanced thrust, and would fall to the ground.

 

Now, if you could somehow confine the lifting body somehow, it could be a useful technology. Hey, maybe this could be used to power the ascent of a space elevator.

[Cancer]

Re: Laser launched rockets

 

Now' date=' if you could somehow confine the lifting body somehow, it could be a useful technology. Hey, maybe this could be used to power the ascent of a space elevator.[/quote']

 

There are concepts for the space elevator where the power is sent to the elevator car via laser from the ground. Not rocket propulsion (since it's hard to keep the elevator ribbon out of the beam), but power connection. A power reception dish can be off-axis, away from the ribbon, granting more safety space, unlike the rocket/recoil surface, which pretty much has to be on the axis of the ascent vehicle.

[ajackson]

Re: Laser launched rockets

 

There are concepts for the space elevator where the power is sent to the elevator car via laser from the ground.

Something of the sort is actually required. The energy requirement to climb a space elevator from Earth is about 95% of Earth's escape energy, or on the order of 60 megajoules per kilogram. That's around 4x the energy content of any chemical fuel that works in a non-air-breathing engine. Thus, you need a power plant for your climber that isn't air-breathing, and that pretty much limits you to beamed power and nuclear power.

[Nuclear Fridge]

Re: Laser launched rockets

 

What we're looking at here is equivalent to 1850s steam-engine tech applied to bullet-train tolerances. It's doable... as a paper exercise. Physics is pretty unforgiving.

But.

Human bloody-mindedness is a variable that we have a hard time quantifying.

[Lawnmower Boy]

Re: Laser launched rockets

 

Don't worry, we'll figure it out. Human ingenuity can overcome any difficulty and make any technology work!

 

(Well, that killed some time..)

[DusterBoy]

Re: Laser launched rockets

 

Wow. . . that must've taken you some time and effort.

 

So have rep.