They keep saying these two words, but I don't think those words mean what they think they mean. A messy sentence if ever there was one, but the phrase the authors keep tossing around is a "Tractor Beam" and the article is about real work being done in universities to develop one.
Everyone who has watched sci-fi movies or TV shows is probably familiar with the term tractor beam. They are energy beams that one ship uses to hold onto another ship and keep it from doing what the second ship's crew wants it to do. Like here, where a Borg cube ship holds the Enterprise (from Star Trek:TNG) and keeps it from fleeing - or keeps it from doing what Captain Picard wants.
There have been scenes in these shows where one ship tows another, as if connected by physical ropes and chains. Same idea.
Instead what the researchers are working on developing is an electrostatic field generator. Their goal is to use this electrostatic field to pull (or push) satellites out of the Geostationary Orbit when they reach End of Life. Space junk and getting rid of it is becoming a big name field, with the Senate recently working on bills telling NASA to manage it better.
What's the difference? Well, the tractor beam imagined in the picture above, holds the Enterprise motionless. If the Enterprise tries to leave, the force gets stronger to keep it from leaving. I've seen shows use a tractor beam as some sort of landing assistance to get a ship into a large space station or other dock.
The system I see described is going to impart a charge on the satellite and on itself; if those charges are opposite (which they will be unless they have some fancy tricks) they will be attracted to each other. If the charges are the same, they'll repel each other. Slowly, barely perceptibly at first, but accelerating with time, unless those charges are bled off to reduce the attraction. Further, they aren't going to do this with one satellite in low Earth orbit and the other in the GEO, the satellites will be close to each other.
The electrostatic tractor would use a servicer spacecraft equipped with an electron gun that would fire negatively charged electrons at a dead target satellite, Champion told Live Science. The electrons would give the target a negative charge while leaving the servicer with a positive charge. The electrostatic attraction between the two would keep them locked together despite being separated by 65 to 100 feet (20 to 30 meters) of empty space, she said.
Once the servicer and target are "stuck together," the servicer would be able to pull the target out of orbit without touching it. Ideally, the defunct satellite would be pulled into a "graveyard orbit" more distant from Earth, where it could safely drift forever, Champion said.
The person referred to by the name Champion is project researcher Kaylee Champion, a doctoral student in the Department of Aerospace Engineering Sciences at the University of Colorado Boulder (CU Boulder).
I can't get past some gigantic holes I see in what they're saying. Maybe they think they're keeping their ideas confidential, but I don't see how they keep the target satellite from closing the distance to the servicer. They go on to say that the field would have to be weak and work over long periods of time, but eventually, there's nothing to stop the target from hitting the servicer. This is zero gravity and zero friction, after all, and there's nothing to slow or stop that target once it's moving. If they suddenly reduced the charge differential between the two, the target may stop accelerating, but it doesn't slow or stop moving unless they change it to being repelled. Perhaps they need to modulate the charge periodically back and forth between attraction and repulsion?
The electrostatic attraction between the two spacecraft would be extremely weak, due to limitations in electron gun technology and the distance by which the two would need to be separated to prevent collisions, project researcher Julian Hammerl, a doctoral student at CU Boulder, told Live Science. So the servicer would have to move very slowly, and it could take more than a month to fully move a single satellite out of GEO, he added.
Since all those "tractor beams" simply exist as a plot device nobody has ever actually put into words how they allegedly work. Using electrostatic attraction to move something is essentially the same as using a magnet. And in the real world we live in magnetism is a "weak" force when compared to other forces.
ReplyDeleteThis means using it to move satellites will be challenging and the movement will require time. Whether or not we ever develop a "tractor beam" akin to the ones in science fiction cannot be known. It may never be an actual possibility. Just like "warp" drive may never actually be possible. But you can't build something till you dream it. And SciFi dreams the dreams necessary to kick start invention in the ass.
In SciFi, most tractor beams are an extension of work on gravitics, the same handwavium that allows grav plates to impart 'gravity' and suck up momentum on said starships. Turn a grav plate on its side, make it strong in a beam format, and, et voila, a tractor or repulsor beam (ifn you can pull things, you can push things too, right?)
ReplyDeleteAs to weak electromagnetic 'beams', I'd assume that the tractor satellite would use thrusters to pull itself up, and the beam would drag the target with it. Vary the beam strength should keep the tractor ahead of the cargo.
I think a sticky clamp or a grapple or something like a fishing arrow connected to a cable would be simpler. Have the tractor snarfle by the target, fire the clamp/grapple/harpoon onto/into the target and then thrust away. Once enough thrust vector is achieved, release the clamp/grapple/harpoon or the whole line assembly and let the target drift away.
Or a tractor or tug that attaches directly to a target and then tugs or pushes.
For some strange reason, random beams of electromagnetism firing around in orbit doesn't seem like a good idea to me.
handwavium
DeleteStolen,,
That's an old phrase for what is umpossible in current science as found in sci-fi.
DeleteKind of like 'The Rule of Cool' as spaceships swoop and maneuver like they're in atmosphere. As real space ship battles would be boring as all heck as ships fire on each other at ranges more like 100K kms or so. "Fire.... oh, we missed, reaim, fire... ha, we hit, now what just hit us?"
Star Wars runs on The Rule of Cool. Blasters that fire energy projectiles that are slower than early hande gonne bullets. Magic swords that stop or reflect everything. Swoopy space ships.
I can't watch some space battle scene without thinking not only did "fire and forget" from beyond visual range get worse, they totally forgot it even existed.
DeleteDon't try to pull a target to change the orbit, push it. To pull it the tug has to move ahead of the target, match speeds, make the towing connection then speed up the whole rig. Once done you cast off the tow and maneuver out of the way again. If you are pushing you get on the correct side, thrust until the required delta V, then pulse in the opposite direction
DeleteCombat in space that follows the rules of physics would be boring. Lethal perhaps but certainly not an entertaining spectacle for moviegoers. Which is why they always resort to the impossible to spice up such scenarios. Occasionally you will read about more realistic combat in sci fi novels... The Forever War is one of those that does a decent job of describing such relativistic encounters.
DeleteIf you're going to employ a "service satellite", why not just have it place a small, (inexpensive) propulsion system (rocket) on the "old unit" 180° away from the direction you want it to go and ignite? Or, for that matter, just have the "service satellite" give the "old unit" a slight nudge in the right direction?
ReplyDeleteNot to say that dreams and fantasies (today, anyway) aren't valuable, the new technology trying to make them work may be very useful in other areas.
Northrup Grumman has demonstrated what they call the Mission Extension System that keeps keeps a satellite on location in the GEO and can do some other stuff to help keep an older satellite useful. Seems to me the same tech could get satellites down, or push them into a more spacious orbit farther out.
DeleteThis is just a project to justify having a PhD program. Someone with common sense will just design a net to capture the (randomly-shaped) satellite and haul it off. Or perhaps just an extensible rod with sticky goo on the end of it.
ReplyDeleteThe first-year students will suggest using a vacuum suction cup...
In my first calculus class, a problem was presented as to how to variably pump out of a round tank at a constant pressure (think those old NASA ball tanks for LOX.)
DeleteI said it was a stupid question, as all you have to do is have one pump pump into another smaller tank and then use a constant pressure pump to pump from the smaller tank to the target (being a rocket, of course.)
I was told to shut up and do the problem.
As to how to deorbit, they've already determined that attaching a long ribbon will create enough 'drag' to slow a satellite down (as it gets affected by gravity, solar wind, space farts, you know, all that fun stuff) and since speed is height, a slower satellite will eventually fall into the atmosphere. About $500 in parts and labor, plus a parent satellite to attach the ribbon thingy, unless it's included on the original satellite. Been a known thing for over 30 years. So why hasn't that been used? My guess, not cool enough.
If I am not mistaken, wasn’t the basis for the SDI charged and neutral particle beams? If the beams are significant enough, it will bore holes into the satellite. I’ve seen electron beams do this to beam pipes. So this has to be a very low energy beam. How much charge could this possibly impart?
ReplyDeleteAnd electron guns are commonplace with accelerators. I’ve personally designed them to aligned pipes set in giant magnets. Let’s also not forget that electron guns were the technology that powered TVs (CRTs) up until very recently. So this is neither a new nor unproven technology.
Maybe you’re right that critical details are being left out, but I just don’t understand how this is supposed to work.
SDI was an umbrella program, looking for anything that would work. High energy lasers, particle (ion) beams, and various kinds of interceptor missiles were all on the table. Reagan probably would have at least entertained the notion of hiring space pirates.
DeleteElectron and ion beams attenuate rapidly in the atmosphere, so they had limited application.
SDI included getting ABM tech back on line after we threw away the Sprint and Spartan ABS in the 70's, even though they worked very very very well. And anti-satellite missiles, ASATs, launchable from F-15s, which worked very very well.
DeleteThe other stuff? Lasers fired from modified 747s, particle and electron beams, rail guns, possibly revamping the HARP guns for direct fire, things like that.
I have heard that many of the DE weapons were to be tasked to destroy or detect ICBM decoys, making it easier to detect/kill the actual warheads.
DeleteI once had a girlfriend with a tractor beam. Every time I strayed, sow ones oats so to speak, or out all night with the boys she would find me and tractor beam me back to her. She would always find me, day or night, miles away in different cities even. Well, I’m now married for 50 years to her, and she’s still pulling me along. NASA should give her a call.
ReplyDelete