Dear Max,

I think that the use of photonic laser thrust to put an object into orbit is quite impossible. We are speaking of direct momentum exchange from photons. The requirement in terms of power should be excessive and the infrastructure requirement too large. In gereral we are speaking of an in-space propulsion system. Moreover, generator and spacecraft are separate one from the other.

The linked paper discusses such technology and drafts different types of mission, from launch to interstellar travels. It appears that such propulsion is a good candidate for interstellar missions, not for payload launch.

http://www.sciencedirect.com/science/article/pii/S187538921202514X

Max,

It's an excellent idea.

I remember reading about this in the 'Continuum' section of OMNI back in the 80s.

Problems are legion, but if you've a spare MW of power, your spacecraft can be 90% reaction mass (big block of plastic in a tough steel cylinder, open at the base, springs to mind). Illuminate it vigorously from below, tighten your seatbelt, and ride it to orbit.

Circularization is left as an exercise for the student.

Dear Max,

I think that the use of photonic laser thrust to put an object into orbit is quite impossible. We are speaking of direct momentum exchange from photons. The requirement in terms of power should be excessive and the infrastructure requirement too large. In gereral we are speaking of an in-space propulsion system. Moreover, generator and spacecraft are separate one from the other.

The linked paper discusses such technology and drafts different types of mission, from launch to interstellar travels. It appears that such propulsion is a good candidate for interstellar missions, not for payload launch.

http://www.sciencedirect.com/science/article/pii/S187538921202514X

They did some of this at White Sands in the early 2000's, sent a little light-craft up a 100 meters or so. To send a 1 kg craft to space requires a MW class laser and on-board propellant (to supplement when the atmosphere is too rarefied). CO2 laser is your best bet. Or use the idea of the laser+super sonic nozzle(Rezunkov, 2014) Russians seem to really love this idea. :-)

This video is cool! https://www.youtube.com/watch?v=XhUasBcoj-Q

Reminds me of the project ORION (https://www.youtube.com/watch?v=uQCrPNEsQaY)

For a photon, momentum p is the energy divided by the speed of light. The rate of change of montume is the force so

F=P/c

where F is the force and P is the beam power.

To overcome gravity plus give an upward acceleration of ~1g for a 1kg load needs 6GW of continuous power. The problem that creates is that some is absorbed by pollution in the atmosphere. It's only a small fraction but it heats the air making it expand and become less dense. That makes it a lens which spreads the light, that's why your link talks only of its use in space. Overall, it is completely impractical to use the light pressure itself.

George, 

There's a factor of two to be gained if the photon is reflected, which still makes a pure photon momentum rocket utterly impractical.

Heating reaction mass is the only 'sane' way to ride a laser.

James, you sound like one of those Escape Dynamics kids from Caltech! ;-)

Too bad they just folded. :-(

http://spacenews.com/advanced-space-propulsion-startup-shuts-down/

Kirk,

Back in the late 90s I chatted with Greg Bedford about microwaves - but I still like optical photons for heating reaction mass. Admittedly, you can't just point it up the tail-pipe, reaction products (smoke, soot) don't help, so one might need a trio of lasers a Good Distance away to direct energy into the expansion chamber without obscuration.

See, I'd spent a few years working on European TSTO/SSTO and wasn't overly enamored of things with wings as a result. I recall a FESTIP launcher for MBB-Erno that took half an Earth's circumference to accelerate to orbit.

Use it in space, conventional launch much better than photonic launch when all the issues are factored in.  I'll add one...how do you keep the sail pointed?

Don't forget the EM thruster!  Seems it might actually produce thrust?!?!

http://www.sciencealert.com/the-em-drive-still-producing-mysterious-thrust-after-another-round-of-nasa-tests

George,

the link suggests that if we can permit a thousand bounces of an individual light packet we can cut the power consumption by 1000. So instead of 6GW we shall need 6MW for lift off.

That's right, but to get a thousand bounces, (a) you need a reflectivity better than 99.95% which is impractical at a large size and (b) you need to stop the beam spreading out. As I said, power in the GW range (1000 times the MW input) will heat the air so it looks like the air above a road on a hot day. I'm sure you seen how it makes the distance shimmer and move. That will spread your beam rapidly so most of the power will spill out of the sides after even a single round trip. This is a well known practical problem for high power lasers in general, even at kW power levels.

Hello,

Since you are very interested in non-chemical propulsion schemes, I would like to suggest the following book to you, if you are not already aware of it,

Eugene Mallove, Gregory Matloff; The Starflight Handbook; John Wiley & Sons, Inc.; 1989; ISBN 0-471-61912-4.

For example, Chapter 5 - Beamed Energy Propulsion, discusses a laser sail propulsion system proposed by the physicist Robert L. Forward and a Lorentz force turning system, again by Forward, similar to one you suggested in a different question about charging a spacecraft and then using interaction between the Earth's magnetic field and the moving charged spacecraft.

Anyway, Robert L. Forward envisioned and theoretically analyzed many of these schemes, and you should look him up.  This book is a good starting point since its bibliography contains citations to many of Forward's papers in the AIAA Journal, JBIS, Journal of Astronautical Sciences, etc.  I believe Forward also patented some of his ideas.  Your ideas are so similar to his, that for a while, I thought you were Forward, except that he died in 2002, I believe.  From what I remember, he also worked with Joseph Weber on the first gravity wave telescope at the University of Maryland.

Regards,

Tom Cuff

Thank you Thomas, for the information.