hckrnws
An extended family member worked on using lasers to launch payloads to orbits. [0]
Here's a quick video demonstrating the technology, using lasers to lift a small prototype several meters, back in, what I believe is the 90s: https://www.youtube.com/watch?v=i81f3LifpWY
That’s awesome, also I’m pretty sure that’s Kate Mulgrew (Captain Janeway from Star Trek: Voyager) narrating, which is also awesome.
Awesome!
...Is that ablating the ceiling as it drifts off-beam?
Another great resource for hypothetical space stuffs (with math!) is Atomic Rockets / Project Rho, here's some of their articles on laser propulsion: https://www.projectrho.com/public_html/rocket/enginelist.php
Yeah that’s a fantastically deep site. After reading the torch ship chapter I’ve come to the conclusion that we either are alone in the observable universe or we’ll be forever bound to our solar system, because we’d see fusion drive signatures on sky surveying telescopes if both are false.
Or, we're missing some corner of physics that allows for interstellar travel that doesn't leave obvious signatures (or misunderstanding a signature that is present).
https://www.eyeofmidas.com/scifi/Turtledove_RoadNotTaken.pdf
I'll always link this whenever it comes up. Highly recommended if you haven't read it.
The Fermi argument effectively puts the kibosh to scenarios where aliens are abundant and interstellar travel is easy.
we're probably alone, though: https://arxiv.org/abs/1806.02404
Electric propulsion using high power laser beaming makes way more sense outside the atmosphere for non-launch use cases, where thrust requirements to achieve desired delta-V usually aren't measured in kN and the mission longevity implied by higher Isp matters so much more and there isn't a pesky atmosphere in the way of power beaming or any concern about accidentally ablating airliners.
Numerous startups are tackling the power beaming issue with relatively short timelines and in some cases a lot of funding, but the scale of what's actually been publicly demonstrated with lasers is unimpressive...
>Electric propulsion using high power laser beaming makes way more sense outside the atmosphere for non-launch use cases
"Roundtrip Interstellar Travel Using Laser-Pushed Lightsails"
https://ia800108.us.archive.org/view_archive.php?archive=/24...
Yeah, seems like chemical rockets, or a railgun or trebuchet or something to get it up to speed first would be a lot more efficient than ground to orbit with just a laser.
It's really hard to beat chemical rockets for launch.
It's not generally understood just how remarkable rocket engines are. They're the most efficient heat engines we can make. They are orders of magnitude better than other heat engines in power/mass and power/$. Their Isp is fine for launch, particularly for the first stage where most of the propellant is consumed.
Yes, but supposedly a laser needs a medium like air to stay coherent. So a weakly powered laser has shorter range in space than (clear) air.
This is incorrect, but please expand on this because I want to understand the misunderstanding.
Can you expand on this? I thought that without the usual effects in a medium that's filled with particles lasers achieve much greater ranges.
You have that in reverse. Atmosphere distorts a laser beam. You need to pump a ton of power to have a stable self focusing beam in atmosphere.
And isn't this focusing itself unstable, leading to filamentation?
Other way round: atmosphere diffracts light away.
I think they’ll have a hard time pushing that much energy through the atmosphere without striking a plasma. Indeed, at least one of the concepts relies on striking a plasma in atmospheric gas by reflecting and focusing the incident radiation.
Multiple transmitters that constructively interfere to create plasma in the exact spot under a heat shield might work I guess? Probably impossible to track accurately and quickly enough for that even with beam forming antennas.
Laser retro-propulsion seems interesting for landing space-mined materials on earth. The obvious (to me) way to do that is to wrap the mined material in a vague lifting-body shape of metal or maybe just slag, thick enough that after it ablates away there's still enough to be economical (to be clear there's at least a couple major options: high value payload wrapped in low-value vehicle, or big aerodynamic blob of low-mid value material, with more options in between). But if you have a big laser you can shine at it to slow it down, maybe you could get away with a lot less sacrificial material.
Cool ideas. Unclear how practical any of it is (how many gigawatts is that laser producing?) but cool nonetheless. Perhaps this kind of research will be driven be the value of the space industry, which is rapidly proving itself to consumers.
>Using a 700 Isp laser-thermal engine on the lower stage of a 50 ton rocket requires more than 2 GW of laser power to lift off the launch pad. Accounting for inefficiencies, between 5.5 and 18GW of electrical power has to be fed to the launch facility.
Oh that's all?
And you're going to avoid having to spend $600 billion on the equivalent of four Ōi Nuclear Power Plants by wishing a practically impossible flywheel proposed as an exercise in engineering optimism over 30 years ago into existence?
Sweet!
To put less than the payload of a single Falcon Heavy into space?
Why build one when you can have two at twice the price!
edit: forgot the 90s were 30 years ago.....
> Naturally, a rocket going into space cannot carry along an electrical wire to the ground to deliver energy.
I’ve been wondering about this actually. (Please keep an open mind if responding)
In theory if we used a high enough voltage. Possibly in the megavolt range we could have a very lightweight wire. And if we could turn that directly into heat on the rocket without even needed equipment to step it down.
I don’t see why we couldn’t have long wires. At least 20 miles and use it as a low speed first stage.
You underestimate how insane the power requirements of a high-g launch are. Placing one ton into orbit requires a rocket with close to 1GW peak power output (this is only a very rough figure that depends on mass ratio, thrust and exhaust velocity). Delivering this much power over 20 miles, even at 1MV, would take about a ton of aluminium wire (again, very roughly). The weight grows quadratically from there -- delivering this much power 200 mi downrange to the upper stage would take 100 tons, even setting aside all the other technical challenges. And this is where we actually want this power delivered -- we don't need to increase the ISP of the first stage, as it is mostly wasted in the exhaust anyway. An ISP above the capability of chemical propulsion is beneficial in the upper stage only.
Thanks for the feedback!
A couple notes. Running your numbers through Ai it looks like it would weigh about one ton per km of wire. And possibly much less if you’re ok with more power loss and high wire heating. Since this is a short term use that might be fine.
But on top of that the extreme amount of power is only needed because we’re trying to get up to speed as fast as possible to minimize gravity loss.
If we’re not carrying our fuel for the first stage it’s conceivable we only need enough power to hover the unit and gradually get it up to top speed.
I know it’s still a far out idea but might be workable from first principles.
Comment was deleted :(
About 20 years ago, I briefly considered what it would take to use heliostats focussed on a heat exchanger to the same effect.
The mistake I made then was thinking fuel was expensive, so I assumed similar performance to existing rockets as if I was using it to superheat cheap water to the combustion temperature of hydrogen-oxygen — the problem with this being that it's pumping the equivalent of the entire electrical power demand of the United Kingdom into an engine the size of a truck for 6 minutes without it exploding.
(Similarly, it's possible to push against Earth's magnetic field but if you use copper the resistive losses will vaporise you launch vehicle. And you can make a much stronger artificial field on the ground, but the way magnetic fields reduce with distance means the current loop on the ground has to be significantly larger than CERN's LHC).
Comment was deleted :(
> Fibre lasers, where hundreds of tiny beams are joined through optical fibres into a larger beam
I'm no laser expert, but this doesn't seem right to me.
IEEE Spectrum had their usual interesting in-depth look at this a few years ago, for military fiber lasers.
https://spectrum.ieee.org/fiber-lasers-mean-ray-guns-are-com...
The technique appears to involve multiple lasers of slightly different wavelength; this allows the beams to be combined and to not interfere with each other.
It can be done, but I don't think that's the core principle of operation of fiber lasers (which I understand to be using the fiber itself as the lasing medium, which is a powerful technique because it can be coiled up and made very long.) Maybe I misread that sentence and that isn't what's being claimed.
It is possible to create the desired wavefront using many emitters. A phased array is doing exactly that. But, yeah, tolerances for a phased array of IR lasers are much tighter. I'm not sure if it's technologically possible right now.
I'm still surprised no billionaire has latched onto this as their passion project.
This book outlined a whole space colonization effort from soup to nuts:
Comment was deleted :(
RIP Jordin Kare.
Crafted by Rajat
Source Code