An Orbiting Atmospheric Gatherer

[vogon13]

Glad to see some math finally being done in this thread.<br /><br />* For atmospheric gathering, you will need to burn fuel to make your orbit intersect the atmosphere.<br /><br />* You will need to burn fuel to accelerate captured atmosphere<br /><br />* You will need to burn fuel to make up for atmospheric drag during gathering<br /><br />* you will need to burn fuel to recircularize your orbit following the gathering<br /><br />* you will need to burn fuel for 78% of the atmospheric nitrogen and 1% argon which is useless to you<br /><br />* you will need to expend energy, somehow, to compress and liquify and store the atmospheric gases<br /><br /><br /><br />It seemed to me about halfway thru that it would just be easier to have carried more LOX up in the first place instead of all that extra fuel . . .<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[vogon13]

Oh, almost forgot the picture.<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[kelvinzero]

I think the razor sharp critique of the electrodynamic tether approach implicit in vogon13's message stands by itself. <img src="/images/icons/laugh.gif" /><br /><br />Reading certain people's replies, I seriously wonder sometimes if the sysops are playing a practical joke on them. Maybe they actually arnt reading the same text?

 

[gunsandrockets]

None of your objections are even relevant. You did read the post you are responding to, didn't you? The 'Gatherer' doesn't 'dip' out of orbit, nor does it's stationkeeping or orbital adjustment rely upon rocket propulsion.<br /><br /><For atmospheric gathering, you will need to burn fuel to make your orbit intersect the atmosphere...You will need to burn fuel to make up for atmospheric drag during gathering /> <br /><br />Nope, because Paul said, "Anywhere above 100 km, we must use a molecular pump to gather atmosphere. This gathering can be done."<br /><br />< You will need to burn fuel to accelerate captured atmosphere...you will need to burn fuel to recircularize your orbit following the gathering /><br /><br />Nope, because Paul said, "Recovery of momentum is important. We use an electrodynamic tether. Our device operates at altitudes where an electrodynamic tether is functional."<br /><br /><br /><you will need to burn fuel for 78% of the atmospheric nitrogen and 1% argon which is useless to you /><br /><br />Nope, because Paul said, "We may pump our low value/waste gases such as liquid nitrogen into ion propulsion engines to boost payloads to geostationary orbit."<br /><br /><you will need to expend energy, somehow, to compress and liquify and store the atmospheric gases /><br /><br />Well of course. If there is a power system adequate for the 'Gatherer' to use electrodynamic tether propulsion, the extra power for the molecular pump and the active cooling of stored propellant is small beans in comparison.<br /><br />If there is any weakness in Paul's concept it lies in the physics of the molecular pump or the power requirements of the electrodynamic tether. What Paul is suggesting amounts to a self-filling orbital refuelling depot, a concept with huge potential should it work as advertised.<br /><br />The idea of using the depot to give fuel to a suborbital spacecraft is a little hairbrained. But the depot could still be an invaluable waystation for delivering

 

[kelvinzero]

One addition to gunsandrockets message is that Paul's scheme is really two independent projects. Responsibility for proving the tether approach does not really rest on Paul's shoulders. Technology for compensating for degrading orbits is of general interest and will proceed regardless.<br /><br />Furthermore, even without a proven station-keeping technique the atmosphere gatherer could begin to pay for itself: not by making money, but by mitigating the cost that has to be spent anyway on keeping the ISS in orbit. If you placed some atmosphere gathering surfaces in positions where the atmosphere would just have impacted on the station anyway, then you havent lost anything you hadnt bugeted on losing anyway.<br /><br />In fact merely by stopping a particle instead of letting it bounce off forwards again, you could up to halve the momentum loss of each particle impact, reducing the propellent cost you eventually need to spend to remain in orbit.<br /><br />(that rings a bell.. was there a plan for paint that did this?)<br /><br />Admittedly it is nowhere near as interesting until it both projects are combined, and the savings might be pretty meaningless, my point is just that the pump technology can be proven totally independently of other requirements.

 

[JonClarke]

One early concept for atmospheric harvesting was the PROFAC http://www.bisbos.com/rocketscience/spacecraft/profac/profac.html<br /><br />Not sure how the concept stands up now in the light of nearly 50 years of actual space experience.<br /><br />Jon<br /><br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[paul_klinkman]

"* For atmospheric gathering, you will need to burn fuel to make your orbit intersect the atmosphere. "<br /><br />Which part of the atmosphere? Technically, the atmosphere never ends. "Atmosphere" in the form of a very few hydrogen ions exists in interstellar space. We have already wrestled with the question of where the atmosphere ends. <br /><br />We're not too far from earth, 300-400 km up, where the atmosphere is not really empty, so we can do far better than a gatherer in interstellar space. Also, at this altitude we collect more than one type of gas atom. Still, we have to gather cubic miles of fairly empty "atmosphere" in the exosphere to come up with kilograms of gases. Fortunately, a gatherer one square foot in diameter can gather a volume of one square foot times 17,500 miles every hour, so gathering cubic miles of nearly empty atmosphere isn't a problem for us. So, we've got our oxygen mine in a fairly nice high, useful orbit and we have no intention of ever collecting gases at a lower altitude.<br /><br />"* You will need to burn fuel to accelerate captured atmosphere"<br /><br />We need to accelerate with something. One more time: we have an electrodynamic tether attached to the gatherer. If the tether generates a steady 0.2 Newtons of force for us, that translates to the acceleration of one ton of gases per year to orbital velocity.<br /><br />The rest of the message is moot because we haven't gone anywhere in the first place. <br /><br />By the way, at 400 km we expect to pick up 87% oxygen, 7% nitrogen by mass, 5% helium by mass and 1% hydrogen by mass. The chemistry is different in orbit.

 

[paul_klinkman]

"The idea of using the depot to give fuel to a suborbital spacecraft is a little hairbrained."<br /><br />Given a 10 ton device in orbit gathering and refining 1000 tons of propellants over its 10 year lifespan, I don't know if boosting suborbital spacecraft is completely harebrained. I hear plenty of "can't be done" on this website, but the reasons so far boil down to "no one has wanted to try it". Is that who you want to be?

 

[kelvinzero]

ah.. they're ok.<br /><br />We are really going around in circles waiting for actual details. I guess after you have presented it at those symposiums or whatnot we'll start hearing scientific opinions.<br /><br />In the mean time, is there a way of getting some idea what the design would look like? eg, a flat square panel attached to a spherical tank? what relative sizes? The reason im asking is that I have reasonable 3ds max skills and want to start modeling some plausible near future visons. Possibly I could come up with something that would also be useful for promotion.

 

[gunsandrockets]

<One early concept for atmospheric harvesting was the PROFAC http://www.bisbos.com/rocketscience/spacecraft/profac/profac.html><br /><br />That is a fascinating link, nice artwork and interesting details. The PROFAC is very much like the concept presented by Paul, except the PROFAC uses an electric rocket for propulsion instead of an electrodynamic tether.<br /><br />The point that PROFAC uses a nuclear power plant for energy in order to reduce the drag from low-orbit is important. I can see that the combined drag of solar power panels and a kilometer long tether might make Paul's concept impractical. And using a nuclear powerplant in a low-altitude high-drag orbit might be politically infeasible. Damn, that's terrible. The idea has such great potential.<br /><br />Hmmm...maybe there is still a politically viable use for this concept. What if instead of putting the self-filling refuelling depot in very low Earth orbit, we placed it in Mars orbit instead? Hear me out...<br /><br />ORBITAL DEPOT IN MARS ORBIT<br /><br />1)could it work?<br /><br />Because of the dynamics of heavy carbon dioxide in combination with the low gravity of Mars, the Martian atmosphere weirdly enough has about the same effective pressure at 400,000 ft elevation as the Earth's atmosphere does. That means an orbiting molecular pump could collect mass in Martian orbit! But because Mars has no practical magnetic field, an electrodynamic tether wouldn't work, sadly. Some kind of rocket propulsion would have to be used for stationkeeping and orbital maneuvering.<br /><br />2)how would it work?<br /><br />What I contemplate is a nuclear electric powered orbital depot very much like the PROFAC; only instead of using an electric rocket expelling nitrogen, waste heat from the reactor would expell excess carbon-dioxide for rocket propulsion. As carbon-dioxide was collected, heat from the reactor would be u

 

[gunsandrockets]

<I hear plenty of "can't be done" on this website, but the reasons so far boil down to "no one has wanted to try it". Is that who you want to be?><br /><br />Dude, in case you haven't noticed, I'm on your side!<br /><br />I just think you should focus more on the stronger aspects of your concept than get trapped trying to defend outlier applications.

 

[gunsandrockets]

<If you placed some atmosphere gathering surfaces in positions where the atmosphere would just have impacted on the station anyway, then you havent lost anything you hadnt bugeted on losing anyway. In fact merely by stopping a particle instead of letting it bounce off forwards again, you could up to halve the momentum loss of each particle impact, reducing the propellent cost you eventually need to spend to remain in orbit. ><br /><br />That doesn't sound right. I don't think it would work that way.<br /><br />

 

[kelvinzero]

well it works within my highly simplistic model. The two major simplifications are<br />(a) the particle isnt really going to bounce exactly backwards. However so long as it bounces roughly backwards the general argument applies.<br />(b) the collision wont really be elastic. It is going to create some heat so it clearly cant bounce backwards with the same relative speed.<br /><br />My model might be wrong to the degree that particles dont bounce at all at those velocities. Perhaps they just embed themselves like radiation?<br /><br />Nevertheless Im pretty sure that if the particles are going to hit you anyway, collecting them does not create additional drag. This also has the exception of streamlined surfaces where perhaps the collision does not rob the air particle of all its velocity. <br /><br />Here is an example of the simplistic model though. Consider the impacting air and the station to both have mass 1. The air has speed 0 and the station is moving with speed 1.<br /><br />Following an elastic collision, the air would be moving forwards with speed 1 while the station has speed zero. This is just what you see in a newtons cradle.<br /><br />Following a purely inelastic collision, the air+station would be moving forwards with speed 0.5 and combined mass of 2.<br /><br />So the station wins in this case because it still has half its velocity AND it has all this extra mass it could consider using for some purpose.

 

[paul_klinkman]

"In the mean time, is there a way of getting some idea what the design would look like? eg, a flat square panel attached to a spherical tank?"<br /><br />There's more than one way to gather ions approaching from one direction at roughly 17,500 mph. If you look up "molecular pump" on Wikipedia you'll see a turbine. Turbines work, but they're heavy and the turbine's blades would have to be pitched almost straight up to match the incoming velocities of the ions.<br /><br />An older technology, the Langmuir mercury vapor vacuum pump, vaporizes mercury atoms in a certain direction, creating a laminar flow of mercury atoms which traps other gaseous atoms in its flow. The mercury sticks to the walls of the vacuum pump, and the other atoms are pushed to the pump's back wall where they can be drained into a pipe. We favor the laminar flow idea because it's lightweight and allows us to close off our gatherer during solar storms when we'll get too much low-value gases. <br /><br />However, we still have to deal with ions coming in to our gatherer at orbital velocity. That's why we're looking at creating an inward laminar flow of microparticles along the edges of a circular tube. Ions will generally penetrate down the center of the tube, strike a microparticle and usually bounce violently toward a wall, where on the second bounce the ion will get trapped in the laminar flow of microparticles. The incoming ions will transfer their incoming force to the microparticles, increasing the flow velocity as the particles go down the collector tube. At the bottom we have to separate the gas molecules from the microparticles, but that can be done. We expect to incur experimentation costs in the development of our new collector, and we won't know for sure that our molecular pump works until we launch a tiny prototype and collect a few grams of gases in orbit. <br /><br />After capture we're going to be radiating away all kinds of heat. Incoming ions lose their tremendous velocity, then

 

[JonClarke]

Your idea for using PROFAC in Mars orbit is an intriguing one.<br /><br />It would involve a major rethink of propellant options for NTRs though, using CO2 rather than H2. I can't recall the exact numbers but CO2 isp's for an NTR aren't very good. But having a source in space might make the difference overall. <br /><br />If something like NIMF is developed it might even share a common reactor.<br /><br />I can't see any reason why a PROFAC could not be made to work in any atmosphere. Venus for CO2, Titan for methane, Jupiter or Saturn for H2.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[gunsandrockets]

<[Mars PROFAC] would involve a major rethink of propellant options for NTRs though, using CO2 rather than H2. I can't recall the exact numbers but CO2 isp's for an NTR aren't very good. But having a source in space might make the difference overall.><br /><br />NTR with carbon dioxide propellant has about 26% of the ISP of hydrogen propellant. Zubrin uses a figure of 260 ISP for the NIMF. My preference is for PROFAC to break the CO2 down into carbon monoxide and oxygen. A bi-propellant chemical rocket engine which burns those propellants has an ISP of 300. The only advantage I can think of that CO2 NIMF has over CO/O2 chemical is easier long term storage of liquid CO2.<br /><br /><br /><br /><I can't see any reason why a PROFAC could not be made to work in any atmosphere. Venus for CO2, Titan for methane, Jupiter or Saturn for H2. /><br /><br />Titan yes. Venus I'm pretty sure should work. I suspect PROFAC would end up so deep in the gravity well of Jupiter or Saturn to function that the propellant payoff wouldn't be worth the delta-V cost to refuel there. <br />

 

[kelvinzero]

Hey Paul, what is the power supply for the orbital gatherer's design?<br /><br />I thought solar panels, but assume you dont want their drag to be a significant fraction of the total drag since that directly cuts into your efficency. The panels would have to be aligned parallel to the particle direction (and perhaps behind the collector)? The only way you can align them this way AND keep them square on to the sun would be to have an orbit along the 'twilight zone'. This would also keep you permanently in sunlight BUT I think a tether can only push you in an east/west direction. It could keep you in the twilight zone during the year, but not recover momentum.<br />Nuclear would be great but more difficult politically?<br /><br />Also, how often are the incoming particles ionised? That suggests the possiblity of slowing them magnetically so their kinetic energy is converted to electricity instead of heat. <br /><br />(been thinking about how that might work. It could be as simple as two plates edge-on to the particle flow with a magnetic field aligned to twist incoming particles to impact one or the other dependent on charge sign, so the plates gain opposite charges that can be drained off as current. Uncharged particles could simply pass through and be ignored.)

 

[paul_klinkman]

"The panels would have to be aligned parallel to the particle direction (and perhaps behind the collector)?"<br /><br />My current design is to place all of the solar panels in a line behind the collector. In this sheltered space, the solar panels turn in parallel, in 2 dimensions, to face the sun.<br /><br />In an equatorial orbit, this system fails for several minutes per orbit on March 21 and on September 21, as one panel (or the collector) blocks the next panel. We can pay that price.<br /><br />Near-shadings of one panel by another are also a problem. We can reduce near-shadings by backing the panels away from each other.<br /><br />I realize that this method is a bit more expensive than simply throwing out a big wing of solar panels. <br /><br />I also realize that our device eats electricity for breakfast. Essentially we're taking out a huge component of NASA's big dumb lifting and replacing it with solar. Yes, NASA shall go green, whether they like that kumbayah image or not. NASA will do its part to fight global warming.<br /><br />"Also, how often are the incoming particles ionised?"<br /><br />100% of the time.<br /><br />"That suggests the possiblity of slowing them magnetically so their kinetic energy is converted to electricity instead of heat."<br /><br />I noted that in January's patent application, thank you. For the prototype we're going to keep it simple, but later on we'll take all the cheap amperage we can get.<br /><br />Furthermore, we can boost our proportion of hydrogen ions with electromagnetic superconducting coils out in front of the gatherer. Hydrogen ions (simple protons) bend far more than other ions, and a few circular coils out in front of the gatherer will deflect more hydrogen right into the gatherer. As I have said, we want to maximize our profitable products, and water may be our most important end product. Water is a propellant, water is a stable way of ferrying oxygen to the space station and water is shielding. Also, water is the foun

 

[JonClarke]

Interesting that the isp of CO-O2 is higher than a CO2 NIMF. It certainly makes NIMF less attractive. <br /><br />The main advantage of NIMF as I see it is its theoretically infinite range. But several 1000 km using a chemical fuel may be good enough. The main disadvantage if NIMF I see would be the shielding required when its own the ground.<br /><br />OT, but I find the possibility of fuels that burn in CO2 interesting. In addition to exotics like silane, aluminium, magnesium and silicon will do so, and generate useful thrust.<br /><br />Good point about the gravity wells of Jupiter and Saturn.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[paul_klinkman]

"Dude, in case you haven't noticed, I'm on your side!"<br /><br />Sorry, I've been getting a bunch of flak.<br /><br /> "I just think you should focus more on the stronger aspects of your concept than get trapped trying to defend outlier applications."<br /><br />If we can perform propellant gathering at a very cheap price, and if we can master these rendezvous maneuvers, then our launch options open up. Scramjets no longer have to reach Mach 25. Single stage rockets don't have to reach orbit. Orbit gets cheap fast. This is what you have dreamed of. I'm sitting on some other outlier applications and this is no outlier, this is the main course.

 

[kelvinzero]

Im glad you can clearly take this to a much higher level of science than I can. It allows me to concentrate on the important problems such as how to render the earth to look sort of fuzzy around the edges <img src="/images/icons/smile.gif" /><br /><br />With the equatorial orbit of course the big loss is the <50% of time that is spent in shadow. What I am taking you to mean is that when not in shadow, the panels can be angled to exactly face the sun (without self-shadowing) almost 100% of the time. I have a fairly good image in my head now.

 

[jimfromnsf]

"Given a 10 ton device in orbit gathering and refining 1000 tons of propellants over its 10 year lifespan, I don't know if boosting suborbital spacecraft is completely harebrained. I hear plenty of "can't be done" on this website, but the reasons so far boil down to "no one has wanted to try it". Is that who you want to be?"<br /><br />the reasons aren't "no one has wanted to try it". It is basic physics that prevent it.<br />

 

[jimfromnsf]

300 km cir parking orbit – 7727 m/s velocity<br />300 x 0 km “launch†orbit<br />Perigee - 7996 m/s<br />Apogee – 7637 m/s<br /><br />The launch “orbit†is representative of a suborbital trajectory. It is a “real†orbit and would be if there was no atmosphere on earth. It has almost the same energy as the circular orbit which means relatively little energy is needed to change the launch “orbit†to the parking orbit (which really means the bulk of the energy needed has been already expended)<br />A true suborbital trajectory (like a ICBM or a sounding rocket) would have less energy and therefore less velocity at apogee. <br />As it is there would be a 90 m/s velocity difference for two spacecraft to meet at apogee. If a more suborbital trajectory is used, the velocity difference would be greater. <br /><br />If the chaser were to reduce its velocity by 90m/s, it would quickly enter the atmosphere. Also it is not really providing any reall benefit since the "lob" vehicle is already near orbital velocity<br />

 

[paul_klinkman]

"If the chaser were to reduce its velocity by 90m/s, it would quickly enter the atmosphere."<br /><br />The shuttle can surf on its heat shield for half an orbit before it comes to earth. <br /><br />The chaser will quickly enter? Where does the atmosphere officially start that it could quickly enter? Remember how I once said that the atmosphere never really stops, it just gets consistently thinner with altitude all the way into space?<br /><br /><br />"As it is there would be a 90 m/s velocity difference for two spacecraft to meet at apogee." <br /><br />Now, remember that the average rocket is 95% big dumb booster and 5% orbital payload. That 90 m/s velocity difference is as expensive (from the viewpoint of launch weight) as an 1800 m/s velocity difference on earth, because the propellant to make that 90 m/s velocity difference has to be launched by 20 times more propellant. If the chaser uses 2 times more propellant, to slow down 90 m/s and then accelerate the payload 90 m/s, that would still a factor of 10 savings if earth and orbital fuel procurement and handling costs were equal.<br /><br />We might be performing the rendezvous anyways, preparatory to boosting the payload to GSO, for example. Saving an extra 90 m/s would just be a little gravy that we could add. We could put just a bit more payload on an undersized launch rocket and still get our payload up.<br />

 

[jimfromnsf]

"The shuttle can surf on its heat shield for half an orbit before it comes to earth. "<br /><br />It isn't a half an orbit and it is heating up and losing more energy<br /><br />"We could put just a bit more payload on an undersized launch rocket and still get our payload up. "<br /><br />Still not going to work. This "scenerio" is for an instantenous rendezvous. It can't happen, real work effects com into play. LV trajectory variations due to actual launch time, winds, actual performance from engines, guidance errors, and other influences will prevent the LV from arriving at the proper position. The depot on orbit can not adjust for these