Photon Thermal Drive
- Thread starter Spinward Flow
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Condottiere
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1. Get a heat shielded mirror.
2. Place a laser drill behind it.
3. Fire laser drill at mirror.
4. Propulsion!
2. Place a laser drill behind it.
3. Fire laser drill at mirror.
4. Propulsion!
In nanonewtons!
Spinward Flow
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mike wightman
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Now try it in a vacuum....
the obvious flaw in both experiments is that the laser is heating the target which in turn is heating the air, the hot air is then 'pushing' - like I said, let's see the results in a vacuum.
the obvious flaw in both experiments is that the laser is heating the target which in turn is heating the air, the hot air is then 'pushing' - like I said, let's see the results in a vacuum.
QFT.
The laser lifted body tests as a takeoff mechanism has been developed for atmosphere.
The solar sail mode is, for a 31 kg spacecraft and a solar sail a bit over 15000m², 1m/s in 3.793 minutes at solar intensity at 1 AU for 0.00439m/s²... I was indeed off... millinewtons, not nanonewtons... from a 124×124m square sail. Or... 0.285µN/m² at 1 AU from a G3v yellow dwarf. so, piconewtons per m².
http://ffden-2.phys.uaf.edu/webproj...otons,a solar sailed powered spacecraft.[url]
Spinward Flow
SOC-14 5K
Hence the Photon Thermal Drive referenced in the OP which brings hydrogen "fuel" for the energy transfer beam to use as reaction mass in a vacuum.
C'mon guys ... I shouldn't have to point out the already obvious here ...
Condottiere
SOC-14 5K
If ground based giant lasers can propel a spacecraft, one closer to the target should be able to do that.
The ground based ones are not using light pressure (which is in µN/m² at about 1.3kW/m² at 1AU from a G2V); they are using the laser to ionized the air around the target point of the craft, generating pneumatic thrust well in excess of what light pressure can. It hasnt been useful for more than a small chunk of a km of altitude, and is essentially generating rolling thunder at the ends of traverse...
In theory one could trail a laser to do this, but then the mechanism is dragged through its own exhaust of superheated air. Essentially, as a takeoff device, it's worthless due to the noise impacts and the problems of dynamic output range mean that it has to be a cluster of very powerful lasers.
Oh, and the laser aunch test devices? The ones I saw reported on are single digit kg.
As for in orbit, you're better off just aiming the laser after.... the scatter and absorption of a target actually reduces the received thrust... millinewtons per megawatt level. Not accelerating very fast... were it not for the fuel issue, ion drives and other electrostatic/electromagnetic plasma drives are far more efficient.
Spinward Flow
SOC-14 5K
You have to start somewhere.
Even Von Braunn and Goddard started with "hobby" scale rockets before moving up into theater range and orbit capable ballistic missiles.
First you prove the idea WORKS at small scales before attempting the same engineering principles at larger scales.
Kind of like scale models and wind tunnel testing in aviation ... then if you've got the funding you start engineering "the real thing" at larger scales that need to work under real world conditions (not just "in the lab").
Even axial flow jet propulsion started with a kit on a bench somewhere.
Condottiere
SOC-14 5K
1. So basically, the laser acts like sunshine, in terms of mirror propulsion.
2. The ground based lasers, on the other hand, heat up gas, which act as the propulsion.
3. Which gets me thinking, since our reactionary rockets supposedly do the same, what heats up the hydrogen fuel that we feed them with from the fuel tanks?
4. Because, or at least in the MongoVerse, no power requirement is listed to heat up the reactionary rockets.
2. The ground based lasers, on the other hand, heat up gas, which act as the propulsion.
3. Which gets me thinking, since our reactionary rockets supposedly do the same, what heats up the hydrogen fuel that we feed them with from the fuel tanks?
4. Because, or at least in the MongoVerse, no power requirement is listed to heat up the reactionary rockets.
Heat from the power plant heats the reaction fuel directly or powers heating elements to do the same. The basis of TNE/T4/T5 HEPlaR is an advanced version of a Nuclear Thermal Rocket (NTR) like project NERVA which uses the heat from a fission (or fusion) plant to heat reaction mass.
(On a side note, an Antimatter Thermal Rocket (ATR) can use very small quantities of antimatter injected into reaction mass to super-heat it for propulsion purposes).
Condottiere
SOC-14 5K
Yeah, but our spaceships, and I think the ecks boat, don't need reactors.
That's the thing: They've shown that laser-thermal atmospheric launch does NOT scale. The more power you use, the less air can replenish to be expanded for more thrust. Couple that with the inverse square law, and it's a boondoggle.
Once you're in orbit, a laser is a highly inefficient continuous thruster. And a navigation hazard. A tightly collimated non-laser light is just about as efficient and less dangerous.
Still µN thrusts do add up. And can cut the trip time a lot... but the needed power source is a lot of mass....
Generally, they do when you have a maneuver drive.
Condottiere
SOC-14 5K
Batteries, and apparently solar panelling.
However, since it's whatever advanced variant of rockets that's under the scope, and as far as I know the fuel is hydrogen that needs heating up, I suspect you'd need some form of energy to ignite that to an efficient form, which I assume is plasma.
However, since it's whatever advanced variant of rockets that's under the scope, and as far as I know the fuel is hydrogen that needs heating up, I suspect you'd need some form of energy to ignite that to an efficient form, which I assume is plasma.
Spinward Flow
SOC-14 5K
You only need energy.
The energy for a Photon Thermal Drive is external to the craft being propelled.
The energy is photons/EM radiation sent from a ground station or satellite and "beamed" to the craft (probably by laser or equivalent) ... hence photons.
Onboard the craft, that energy is received and converted into thermal heating of the H2 fuel supply onboard. It's not chemical combustion, it's simple/plain thermal heating of the H2 using the energy input from the ground station/satellite. The heated H2 is exhausted as rocket propulsion after being heated.
Because there is no need for an oxidizer to combust the fuel, you need a LOT LESS mass onboard the craft in order to make this setup work. You essentially "offshore" the energy source needed to make the whole thing work (and go) from the craft allowing the craft to be small and low mass, vastly improving the Rocket Equation relative to a conventional chemical rocket.
If it helps, think of it as being the high tech equivalent of a crystal radio set ... except done for rocket propulsion instead of communications.
- The crystal set makes the sounds you hear, but the power to make it "go" comes from the radio tower broadcasting signal.
- The H2 onboard creates thrust in a vacuum, but the power to make it "go" comes from the ground station/satellite beaming photons out to the craft.
This shouldn't be that difficult to figure out.
In space, even small accelerations can have very important implications to orbit/course/trajectory over longer time frames. It's only when you're "in a hurry" (and combat counts as one of those times) when you're going to want to have a LOT of acceleration over a short time frame, rather than a teeny tiny acceleration over a long time frame.
Condottiere
SOC-14 5K
To be fair, I was referring to our Traveller reactionary rockets, however they are defined in each edition.
Probably every little bit helps in the Mars Express, and if Elon, Dick and Jeff are that anxious to go, we should help speed them along.
Probably every little bit helps in the Mars Express, and if Elon, Dick and Jeff are that anxious to go, we should help speed them along.
Saw a good interview (by a bad interviewer) about what's being proposed for NASA...
it's a thermal rocket, powered in space only by using the laser and a mirror to heat a working fluid to a plasma for thrust. This is how it's getting NERVA level thrust without nukes aboard...
The scientists working on it avoided all mention of the inverse square law as far as I could tolerate Angry Astronaut's ignorance about the meaning of ISP, delta-v, and acceleration.
Angry doesn't grok that ISP is fuel efficiency, delta-V is total ability to change vector (delta = change, v = velocity).
So, it's not a great drive solution. It can, however burn-turn-burn...on an asymmetric if using a single laser.
it's a thermal rocket, powered in space only by using the laser and a mirror to heat a working fluid to a plasma for thrust. This is how it's getting NERVA level thrust without nukes aboard...
The scientists working on it avoided all mention of the inverse square law as far as I could tolerate Angry Astronaut's ignorance about the meaning of ISP, delta-v, and acceleration.
Angry doesn't grok that ISP is fuel efficiency, delta-V is total ability to change vector (delta = change, v = velocity).
So, it's not a great drive solution. It can, however burn-turn-burn...on an asymmetric if using a single laser.
