Photonic Drive / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Photonic Drive

1 2 next

Move Thread

LAN_403

Conundrum

Sat Mar 14 2015, 07:14AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Hi all.

Some interesting analysis presented on another thread got me thinking about this.

Given that very high power (100W+) pulsed semiconductor lasers now exist, it would be feasible
to build a "Photonic Drive" by simply focusing the beam(s) onto a plate in a vacuum and using action-reaction caused by the material ablating into the vacuum then simply accelerate the particles using electrostatics for extra thrust.
Something like sodium (Na) alloyed with other metals such as aluminum would be ideal for this and easy enough to make.

The impulse would be quite large and if a multiple diode array was used then steering could be accomplished easily.
As for consumables simply heating up the sodium plate(s) would reform the surface although it would use a lot of energy, maybe have a drive plate cover that retracts after this is done?

Am I overlooking something really obvious or could this actually work?

-A

Dr. Slack

Sat Mar 14 2015, 08:14AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Are you ejecting the sodium as a consumable? If yes, then you have a limited amount of reaction medium. I don't see how simply heating the surface scavenges space for all the stuff you've ejected. It is a nice idea though for a tiny solid state micro-thruster.

The benefit of ejecting photons or Shawyerons if that you have unlimited reaction medium.

Conundrum

Sat Mar 14 2015, 10:10AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

No, the idea of heating the surface is to re-form it in order to avoid burn through.
Sodium alloy would be relatively easy to use as it strongly absorbs some wavelengths of light.

Sulaiman

Sat Mar 14 2015, 12:29PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

design it so that there is enough sodium to get to a significant fraction of c
then when consumed the laser shines backwards for continued acceleration.

If this is feasible then use telescopes to look for emissions from alien craft using light propulsion,
none spotted yet, oh well, probably not viable.

hen918

Sat Mar 14 2015, 01:00PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

Conundrum wrote ...

No, the idea of heating the surface is to re-form it in order to avoid burn through.
Sodium alloy would be relatively easy to use as it strongly absorbs some wavelengths of light.

You could use the laser, unfocused, with a lower power to heat the sodium. It could do a heating cycle every now and again to reform the surface.

Patric

Sat Mar 14 2015, 03:50PM

Registered Member #2899 Joined: Wed Jun 02 2010, 06:31PM
Location: Deinze, Belgium
Posts: 255

Photonic drive...

BigBad

Sat Mar 14 2015, 07:11PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

It's not particularly difficult to design a thruster with very high exhaust velocities, the difficult bit is getting a power supply that can support the drive to give useful thrust (or more important, useful acceleration, since power supplies have a fixed power/weight ratio).

Everything else being equal (for any given power supply), from conservation of energy, thrust and exhaust velocity are inversely proportional and for very high exhaust velocities you take longer to reach your destination, and use more energy.

Ash Small

Sat Mar 14 2015, 09:00PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

BigBad wrote ...

It's not particularly difficult to design a thruster with very high exhaust velocities, the difficult bit is getting a power supply that can support the drive to give useful thrust (or more important, useful acceleration, since power supplies have a fixed power/weight ratio).

Everything else being equal (for any given power supply), from conservation of energy, thrust and exhaust velocity are inversely proportional and for very high exhaust velocities you take longer to reach your destination, and use more energy.

Isn't the idea to use the natural photon (EM) radiation in space to heat the sodium, or whatever, and then get re-emmited directionally as thrust?

Doesn't it just 'harvest' the available energy in space?

Conundrum

Sun Mar 15 2015, 08:32AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

That approach could actually work, wonder if NASA have considered it?
ie use an easily vaporized metal and a hybrid system powered by solar cells to accelerate the generated
particles further for an efficiency boost.
Sort of like a juiced up solar sail.

EDIT: Even better, the maximum possible thrust would be obtained close to the star so if it was aimed right (ie compensating for stellar drift) you could accelerate to a fair fraction of c and lose power around the orbit of Mars.
using Jupiter for a slingshot effect would hurl you out of the Solar System and then once near the destination star (ie Epsilon Eridani) use the reverse effect to slow down.

-A

BigBad

Mon Mar 16 2015, 02:42AM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

Solar thermal drives? Sure, they've been investigated. They work best with hydrogen fuel; water/steam is OK. Heavy metals give poor performance.

You want low molecular mass for high exhaust velocity.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob