Sci-fi inspired tractor beams are real, and could solve a major space junk problem

[Admin]

Researchers are developing a real-life tractor beam, with the goal of pulling defunct satellites out of geostationary orbit to alleviate the space junk problem.

Sci-fi inspired tractor beams are real, and could solve a major space junk problem : Read more

 

[Classical Motion]

"the defunct satellite would be pulled into a "graveyard orbit" more distant from Earth, where it could safely drift forever, Champion said."

Education has failed mankind.

 

[billslugg]

The electrostatic method takes a month to move one satellite. Replace with a laser, ablade some surface material, the junk will move in opposite direction. Done in a microsecond.

 

[Questioner]

to be precise it is not a 'beam'.
It is instilling a charge & using the opposite charge to attract something.
An interesting idea.

My thought is if we have all this otherwise useless and problematic stuff already in orbit why not stabilize it by connecting it all together and build a sun screen to combat global warming?

If it is collected together it will be relatively easier to navigate around it.

It might be possible to position it where it will be the most productive shadewise.

Goodness knows we aren't doing anything significant to reduce greenhouse gases or population numbers.

 

[billslugg]

Insufficient cross sectional area to do enough shielding to justify the cost of changing orbits.

 

[Unclear Engineer]

The electrostatic method takes a month to move one satellite. Replace with a laser, ablade some surface material, the junk will move in opposite direction. Done in a microsecond.

Considering how much fuel it takes to change orbits as much as desired, and considering the momentum transfer inefficiency of the ablated materials spraying in a hemispherical pattern from an ablated surface, I think there would be a substantial risk of creating space junk when trying to ablate enough of a satellite to be successful.

 

[Questioner]

If one had a polymer string 'gun' one could shoot at anything going in about the same orbit and draw them together.
Maybe even AI directed.
Once one had a coherent enough junk pile it would tend to sweep up ancillary stuff especially if it were magnetized. (or with gooey polymer)
(could light be manipulated to magnetize something?)
One might end up with a number of coherent orbiting junk piles.
One might steer those into useful orbits and even combine them if feasible.

The highest energy expenditure of getting stuff in orbit is already done.
Seems almost illogical not to take advantage of that.

 

[billslugg]

Considering how much fuel it takes to change orbits as much as desired, and considering the momentum transfer inefficiency of the ablated materials spraying in a hemispherical pattern from an ablated surface, I think there would be a substantial risk of creating space junk when trying to ablate enough of a satellite to be successful.

The efficiency of ablative acceleration would be about 50%. Instead of a one microsecond burst of infrared light, we might need two microseconds. Compare to a month otherwise. The laser would pulse at such a short period that only the outer few microns would ablate. No disassembly occurs.

 

[Questioner]

Better make that a reusable polymer string that uses magnetics to connect things so one doesn't need a ton of polymer.

 

[Unclear Engineer]

The efficiency of ablative acceleration would be about 50%. Instead of a one microsecond burst of infrared light, we might need two microseconds. Compare to a month otherwise. The laser would pulse at such a short period that only the outer few microns would ablate. No disassembly occurs.

Bill, However it is done, it is going to take more than microseconds. You can't raise both the apogee and perigee of the orbit with one impulse. At best, if you could raise the apogee to the desired value, you would still need to follow the piece of junk to its apogee and give it another impulse to raise its perigee. So, at best, something more than 12 hours for something starting in a circular orbit with a 24 hour period going to a higher, longer period orbit.

But, I am not even agreeing on your 50% efficiency factor for the ablated material creating the impulse in the needed direction. I don't have the time to do the integral properly right now, but considering the average over the sine function is only 0.64 in one dimension and integrating in over the 2-dimensional hemisphere gives much more area to the low tails than to the peak areas, I don't think 0.5 is even close to the effect of having it all go out in the desired direction, as if it came out of a rocket nozzle..

 

[billslugg]

So pick an efficiency. You tell me how much delta V you want, name the efficiency and mass and I'll tell you how many microsecond pulses will be needed and at what power. If the desire is to cause re-entry, only about 20 m/s delta V is required and it can be done in one shot. If wanting to move to a higher orbit then two sessions are required, the second at apogee.
My point is, thermal ablation beats the time and cost of every other method by many orders of magnitude.

 

[Unclear Engineer]

Bill, I think you have the impulse requirements backwards. According to Wikipedia

"De-orbiting a geostationary satellite requires a delta-v of about 1,500 metres per second (4,900 ft/s), whereas re-orbiting it to a graveyard orbit only requires about 11 metres per second (36 ft/s).[1]" see https://en.wikipedia.org/wiki/Graveyard_orbit

"For satellites in geostationary orbit and geosynchronous orbits, the graveyard orbit is a few hundred kilometers beyond the operational orbit. The transfer to a graveyard orbit beyond geostationary orbit requires the same amount of fuel as a satellite needs for about three months of stationkeeping. It also requires a reliable attitude control during the transfer maneuver. While most satellite operators plan to perform such a maneuver at the end of their satellites' operational lives, through 2005 only about one-third succeeded.[2] Given the economic value of the positions at geosynchronous altitude, unless premature spacecraft failure precludes it, satellites are moved to a graveyard orbit prior to decommissioning."

So, Bill, if you can find the propellant requirements for station keeping for some of the bigger satellites, you can figure the propellant needs to transfer them to the graveyard orbits.

We still don't agree on how much ablated material would need to be substituted for that propellant. You seem to think it is only twice as much - I have not done the analysis, but you can if you are so inclined to prove your 0.5 efficiency.

But, to get back to the point I started with: How much of the satellite's material will need to be blasted off its surface with a laser and how likely is that to affect the integrity of the satellite. I am not thinking the ablation is only going to need to affect "a few microns" of the satellite's surface.

And, that doesn't consider the acceleration forces, either. You mentioned 20 m/s net velocity increase created by a microsecond laser pulse. That looks like 20 m/s divided by 0.000001 second of acceleration, which is equal to 20 million m/s^2. That is about 2 million Gs of acceleration. I'll give you that the ablation would last somewhat longer than the laser pulse, but it isn't going to last for a second, either, which would be needed to make it something like 2 Gs..

I don't know where you are getting your numbers, but they aren't seeming to "add up" right.

 

[billslugg]

The 20 m's I quoted is for re-entry of LEO satellite. But all delta V numbers are irrelevant to the fact that laser ablation thrusting is many orders of magnitude lower in cost than any other method.

My numbers are derived from basic principles. You want to move a satellite x amount of distance then it takes a certain amount of energy. It makes little difference if you hit it with a baseball or a laser, whether the efficiency is 100% or 1%. This merely determines the number of repetitions needed.

The duration of the g force is not limited to the duration of the pulse. The pulse will transfer its energy to the metal, the metal will vaporize and expand away, pushing against the satellite as it dissipates.

The duration of the pulse is determined by how deep into the metal you want to vaporize.
If you want to vaporize the entire satellite, about ten seconds should do it.
If you want to dig a few inches deep, one second might be good.
.
.
For one micron depth, I would start with my "pulse duration" set at about a microsecond. The entire pulse will be absorbed before more than a micron is vaporized. The amount of material is infinitesmal. Because it is so small, extremely high temperatures are generated, thus extremely high pressures. I'll choose a ten gigawatt infrared laser, providing a one microsecond pulse, the energy would be 10,000 joules, about the energy of a 22LR round.
In order to deorbit a one ton satellite in LEO, a delta V of 20 m/s is needed.

The velocity at LEO is 8,000 m/s. A one ton satellite has a kinetic energy of 1/2 * m * v^2 or 3.200e10 joules.

Deorbiting from LEO requires slowing it to 7980 m/s. The kinetic energy is thus 3.184e10. The delta energy is thus 160 million joules. Since each pulse needs 10,000 joules, we will need 16,000 pulses. It might take a few minutes since the pulses must be spaced out and spread around. Ratio this number by the assumed efficiency. If laser ablation is only 1% effective, it might take all night. But that beats a month by a mile.

 

[Unclear Engineer]

If we are talking Low Earth Orbit, then yes, something like 20 m/s change in velocity probably is going to work, eventually. Depends on how low "low" is. And there are some LEOs that are more than 20 m/s different from other LEOs, so we really need to talk about the resulting perigee, not the energy of one orbit compared to another.

And, now you are talking about multiple pulses "spread around" (I guess) the surface of the satellite, over some period of time. And I am not seeing the calculation of the mass of the ablated material per pulse, nor the velocity of that material away into space. I don't think you can do this with energy calculations alone, and get the right answer for the change in satellite velocity.

And, now that you mention the energy of a 22 long rifle bullet, I am wondering if it would not be cheaper to just send up a rifle and a large supply of 22 LR ammo. What does it take to power a 10 GW infrared laser for a microsecond - multiple times over a short period? Solar panels and power storage (large capacitors?) plus the laser have to weigh a bit. And, either way, you need a vehicle to contain and maneuver whatever mechanism you send up to track down multiple satellites. The ammo would be a lot cheaper than a 10 GW laser. The real question is what the impulse (momentum change) would be from one laser pulse.

And, of course we still have the question about whether it would take too many laser pulses for the satellite to hold together. Have you calculated the total mass in your few microns of satellite surface if you can hit the whole aft-facing surface? How fast does that material need to go away from the satellite? Remember, it is a spray, not a directed thrust vector as with a rocket engine. At least the 22LR could be made to put all of its momentum into achieving the delta V.

 

[billslugg]

"If we are talking Low Earth Orbit, then yes, something like 20 m/s change in velocity probably is going to work, eventually."

A 20 m/s delta V on a circular orbit of 90 minute period will lower the craft at 20 m/s, (gradually reducing) for the next quarter revolution. It will have a new perigee about 15 km lower. Repeat until the upper atmosphere is reached.
The typical deorbit burn of the Shuttle coming home from ISS 350 miles high was 90 m/s.

"I don't think you can do this with energy calculations alone, and get the right answer for the change in satellite velocity."
" And I am not seeing the calculation of the mass of the ablated material per pulse, nor the velocity of that material away into space. "

It's easy, calculate the delta energy, equate that to the laser ablation energy output, adjust for efficiency. I don't need to know how much material is blasted off, what its temperature is, how fast it goes, whatever. Energy in at a certain efficiency equals energy out.

 

[Unclear Engineer]

Bill, OK, I had some time to do the integral, and, to my surprise, the 50% efficiency looks correct if you assume that the ablated material is leaving the area distributed uniformly over a hemispherical surface.

But, I am still not agreeing with the energy derivation you are using for the orbital mechanics. It isn't just a matter of "Energy in at a certain efficiency equals energy out." It is really a matter of what the perigee is for a particular amount of orbit energy. It is necessary to get the perigee down to an altitude where the atmospheric drag causes enough deceleration to promptly deorbit the satellite.

Yes, if you start with the assumption of a circular orbit and decrease the orbital velocity by a specific value at apogee, you can calculate the perigee.

But, the decrease in orbital energy to do that depends a lot on the altitude of the initial circular orbit.

And, the momentum transfer for a certain amount of energy going into ablation depends on a lot of parameters, including the energy needed for the phase transition of the material to be ablated and the mass of the molecules/atoms of the material ablated, so that the resulting velocities of the atoms flying away can be calculated to get their momentum. That gives the impulse that is applied to the mass of the satellite to be deorbited.

You are talking about nanometers of depth of the surface of the satellite being ablated. Assuming that the surface is aluminum, with a density of about 2.7 grams/cm^3, a nanometer of ablation is only going to get 10^-9 m x 100 cm/m x 2.7 grams/cm^3 x (100 cm/m)^2 = 2.7 x 10^-3 grams off a 1 meter square surface hit by the laser. I am not going to calculate whether a 10 Gigawatt laser could even reach ablative conditions when spreading the watts over 1 square meter for a microsecond, but that needs to be looked at, too.

For now, just consider that the 2.7 x 10-3 grams of aluminum would need to be going 20 m/s x 2000 kg x 1000 gm/kg /2.7 x 10^-3 grams = 1.48 x10^10 m/sec to change the velocity of a one metric ton satellite by 20 m/sec. That is 49 times the speed of light. Not going to happen!

Check my math, but I think that there would need to be a lot more material ablated than you are thinking, and that it would need to be done over a longer period of time than you are thinking.

Do you have any URL links to some engineering analysis that describes this ablative deorbiting process in enough detail that some of these guestimates can be checked?

 

[billslugg]

I would refer you to Reagan's Star War program, also many current weapon systems that use infrared lasers. We do it all the time down on the ground. Space would be easier due to no air turbulence or absorption. The technology is well developed. We can bore a hole in the side of a missile, I am sure we can ablade the skin off one in space. Pick whatever depth you want, dial it in on the "pulse duration" knob on the control panel. Dial in the desired thrust by controlling repetitions. If the skin is getting too hot, move it around. Plenty of options here. We've done this. Google Boeing Airborne Laser YAL-1, also the Israeli Iron Beam.

Your analysis of grams and velocities is not neccessary. We know for a fact that the enegy we impart to something has to "go" somewhere. It goes into the acceleration of ablated material. There is no other significant output. By the laws of physics the rebound must be exactly the same as the energy we imparted.

The expelled vaporized material will assume whatever velocity is needed to account for the energy it possesses. There is a limit to velocity of a particle but that limit is approached asymptotically . There is no limit to how much energy can be imparted into the atoms. You just keep getting closer to c.

 

[Unclear Engineer]

I am aware that there are laser weapons that can vaporize holes into things like aircraft. But, for the issue of deorbiting a satellite, it is mainly the resulting impulse, not the total energy transfer, if you want to calculate the change in satellite trajectory. I don't think that is an issue with the weapons development programs - they just want to make the target inoperable.

What I did with my calculation was an easily scalable example that shows a very large mismatch between your expectations for very short blasts of a laser removing very thin layers of surface material compared to the amount of impulse you are expecting from that in order to get the stated change in velocity of the target.

Where the energy goes is not something that you can just assume. There is energy needed to change the phase of the solid material to gaseous material. There is energy that probably goes to ionizing that gaseous material - certainly if it is going to relativistic velocities. There is probably re-radiated energy in the form of photons at higher frequencies due to incandescence. There is some sort of efficiency factor with respect to how much energy is absorbed into the structure without creating ablation. There may be some surface reflection of the incident energy. All of that needs to be deducted from the assumed kinetic energy of the ablate materials moving away from the satellite, which is what creates the impulse to slow the satellite.

Your calculation in post #13 simply makes the assumptions that the energy added to the satellite in the form of a laser shining on it will decrease the total energy of the remaining satellite by all of that energy somehow going into the kinetic energy of the ablated material, so that it acts like a rocket slowing the forward motion of the satellite. Yes, you did admit to a possibility of an efficiency factor, and said that it would still work if that was only 1%.

I will agree that it is theoretically possible to do what you say. But, I don't think you have any quantitative basis for saying how efficient it would be. So, I don't see any support for saying that it is clearly the cheapest approach.

And, I don't see any quantitative analysis that says that it could be done without the potential for substantial structural damage to the target that might create additional pieces of space junk. And, that was my entry issue to this whole discussion. I think you are going to need to ablate a lot more material over a much longer period of time than you indicated with your initial "done in a microsecond" post.

 

[Meteoric Marmot]

to be precise it is not a 'beam'.
It is instilling a charge & using the opposite charge to attract something.
An interesting idea.

It is a beam for half of the process. The electron beam used to transfer charge to the target will need to run for "a while" which will depend on the intensity of the beam. So call it a beamtractor ( BEAM + atTRACTOR)

 

[Meteoric Marmot]

I would refer you to Reagan's Star War program, also many current weapon systems that use infrared lasers. We do it all the time down on the ground. Space would be easier due to no air turbulence or absorption. The technology is well developed. We can bore a hole in the side of a missile, I am sure we can ablade the skin off one in space. Pick whatever depth you want, dial it in on the "pulse duration" knob on the control panel. Dial in the desired thrust by controlling repetitions. If the skin is getting too hot, move it around. Plenty of options here. We've done this. Google Boeing Airborne Laser YAL-1, also the Israeli Iron Beam.

Your analysis of grams and velocities is not neccessary. We know for a fact that the enegy we impart to something has to "go" somewhere. It goes into the acceleration of ablated material. There is no other significant output. By the laws of physics the rebound must be exactly the same as the energy we imparted.

The expelled vaporized material will assume whatever velocity is needed to account for the energy it possesses. There is a limit to velocity of a particle but that limit is approached asymptotically . There is no limit to how much energy can be imparted into the atoms. You just keep getting closer to c.

Any time a commenter comes up with a "why don't they just do this?" question, especially when it is an obvious possibility like laser ablation, they are making the assumption that the people doing the project are idiots and haven't evaluated the other obvious solutions. Since that is highly unlikely, what you should be asking yourself is, "What's wrong with this obvious solution that kept them from choosing it?"

My first instinct would be to find out what the consequences of hitting a piece of aluminum with a laser when it might be very cold. Will it ablate or will it fracture and release particles big enough to be an issue themselves? The Star Wars program didn't worry about creating orbital debris so that wouldn't have been a consideration. I don't pretend to know the answer to this kind of question, but something kept them from choosing this idea.

 

[billslugg]

They have not been stopped from using this idea. They are not yet at the stage of selecting a process. It is still a long ways off.

The laser beam heats only the outer few microns, the underlying metal is unaware of what happened.

 

[Unclear Engineer]

Bill, The idea that a laser is going to heat the metallic surface hot enough and fast enough to cause enough material to ablate and fly away to give a substantial momentum impulse to an entire satellite is just highly inconsistent with the idea that "the underlying metal is unaware of what happened".

If nothing else, there is stress to transmit the localized force into the entire structure so as to change its speed.

All I am seeing from you on this is assertions without analytical support. I asked before if you can provide a URL to a description of this process that we can read to see more about how it has been analyzed. Is this just your idea, or is there some literature that provides quantitative evaluation?

 

[billslugg]

I already told you there are no references, that my ideas are generated from first principles. What you have seen is "best I can do" in explaining it. If you don't believe it, that's OK.

 

[Classical Motion]

Maybe ejection from the target's surface is not necessary. I recall seeing pulsed lasers accelerate reflective disks, up a thread......over twenty years ago. I recall close ups of that disk and indications and mention of surface deformation or ejection was not shown.

I'll bet, one could paint that disk black and get the same response.

I don't think we need to change the speed of the target......just steer it in the right direction, and let nature take it's course.

One would think we could put "english" on a laser beam by now.

My opinions and comments are based on what I read.

The superposition of EM flux can become much more dense and solid than any mass object could become. Mass is not needed for momentum.....only density is.

A sufficient blast(flux) of EM should be able to sweep an area of all mass objects. A real vacuum......but still not 0 temp. There would still be static.

 

[billslugg]

Yes, all EM waves have momentum. If you bounce one off an object you get a twofer. That is one impulse when landing and the second when reflecting off. The problem with EM is the force is small for your money. A gigawatt produces one Newton. That's only 110 grams.