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#4160 by Bob Woods on 08 Aug, 2016 17:55
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Does anyone know what the time spent in sunlight versus shadow with an orbit that low? If you're only able to use the thruster for half the time due to lack of sunlight, wouldn't that change the requirements for staying in orbit?
Also it would be interesting to know if they did have a small nitrogen thruster on there, how long it would likely be able to hold that orbit. If ~6 months it would certainly make one wonder. I hope like hell they have what they say they have.
You use a battery to store power from solar cells to provide power during dark periods. Dark/light is probably 50/50 on a "normal" orbit, as satellites in orbits don't really care what the tilt of the earth is compared to the solar plane. -
#4161 by Monomorphic on 08 Aug, 2016 21:42
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Spent all day completely rearranging my work area. With the torsional pendulum and draft enclosure taking up so much space, I consolidated all the storage racks on the other side of the room. This freed up a lot of extra surface space. I'm also purchasing a couple of 10' kayaks that will be stored on the wall to the far left.
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#4162 by Bob Woods on 08 Aug, 2016 21:54
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Spent all day completely rearranging my work area. With the torsional pendulum and draft enclosure taking up so much space, I consolidated all the storage racks on the other side of the room. This freed up a lot of extra surface space. I'm also purchasing a couple of 10' kayaks that will be stored on the wall to the far left.
Kayaks with EM drives. You must be feeling very confident.
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#4163 by CorvusCorax on 08 Aug, 2016 22:08
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You use a battery to store power from solar cells to provide power during dark periods. Dark/light is probably 50/50 on a "normal" orbit, as satellites in orbits don't really care what the tilt of the earth is compared to the solar plane.
50/50 (with battery buffering) is a good guess for most LEO orbits, especially as low as 150km, as they have to be more or less circular, but it should still be possible to put the sat into a heliosynchronous polar orbit at 150 km ish altitude that keeps it in the dawn/dusk area for almost 100% of the time all year through.
If you allow higher apoapsis, and eccentric orbits, you would always end up with more sun time. Also generally, the higher an orbit is compared to earth radius, the less time it spends in earth shadow, with 50/50 being the maximum (even at just 150 km it would already trend towards 60/40 since you can use dusk+dawn)
(Example: The moon spends only a few hours in partial eclipse with a month long orbital period. Also it only ever "hits" shadow during certain alignment constellations, twice a year. Similar is true for sats in GEO orbits, they are almost never in shade)
I think you'd have to get to an orbit around earth/sun L2 lagrange point to ever get more than 50% shade.
So if you can harvest twice your average energy requirements during the sun time and battery-buffer it for the night-duration, you're always in the green
that'd be around 40 minutes at 10W, (during a 85minute orbit) so you'd need 24 kJ of energy storage. Assuming a 12 V bus that'd be 555 mAh battery pack. Let's assume a power efficiency of 50% in the total system, then you'd need a 12V 1000 mAh battery pack (space rated). Using LiPolymers (if they are allowed) that'd be roughly 400g of cell mass, plus thermal control.
EDIT: 400g is the wrong weight, a pack of that size would weigh around 110g. I confused the weights of two different batteries
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#4164 by dustinthewind on 09 Aug, 2016 00:01
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Hi RERT, once again Cannae sort of pulls the rug out from underneath us: They state <10 Watts for the thruster not 12, and an altitude of under 150 miles. What happens if you calculate using 10 or less? Did you use 150 miles for your calculation, I looked back and couldn't find it. I believe Cannae is so secretive that they leave themselves open to speculation: e.g.: who knows if there are cold gas thrusters aboard the Cubesat to help maintain orit...etc.
Just like there experiments, they are all behind closed doors with results reported, but nothing about materials and methods. No independent validation. Don't get me wrong , I'd give parts off my body for EM drive to be "truly" true. But Cannae leaves us with no way of "knowing" anything.
The only info. we have for Cannae is the NASA testing: 10 Watts would generate 17.32 micro Newtons, which is below the amount you calculated to sustain orbit (if I didn't screw up my math). Please tell me where I'm right or wrong thanks, FL
You are overthinking this IMHO. The cubesat will stay in orbit, or it won't. The rest of the details aren't anyone's business but theirs. If it does stay in orbit, mainstream press exposure and scrutiny from all quarters will increase exponentially regarding the details of that cubesat.
Also, regarding hidden gas thrusters. The FAA will conduct a Part 414 safety review of the launch. The review doesn't cover the satellite per se, but the launch vehicle operator will disclose any propellants on board because it'd affect the safety of the launch vehicle, so the launch operator would be taking a major risk with their business by not disclosing this. If we know the launcher and specific flight, we can look up the safety review specific details in the Federal Register.
I would guess if they are being honest, and they are building a cubesat, that they would have tested the cube sat on earth as a closed system. If they got a force measurement out of it then maybe the next test would be a low orbit test to prove the concept? Unless this is their one and only test, yikes. I guess the low orbit test takes care of space litter if it doesn't work. I wonder if this is a test they are hoping will work, or their claims are more grand than, it is just a test. I find it odd the shape of their cavity, that it doesn't appear to be conical, unless I mistook the image. -
#4165 by JonathanD on 09 Aug, 2016 02:46
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You use a battery to store power from solar cells to provide power during dark periods. Dark/light is probably 50/50 on a "normal" orbit, as satellites in orbits don't really care what the tilt of the earth is compared to the solar plane.
I get that, but it's a cubesat and batteries are not light! I'm just trying to understand how that would work. -
#4166 by sghill on 09 Aug, 2016 12:57
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Hi RERT, once again Cannae sort of pulls the rug out from underneath us: They state <10 Watts for the thruster not 12, and an altitude of under 150 miles. What happens if you calculate using 10 or less? Did you use 150 miles for your calculation, I looked back and couldn't find it. I believe Cannae is so secretive that they leave themselves open to speculation: e.g.: who knows if there are cold gas thrusters aboard the Cubesat to help maintain orit...etc.
Just like there experiments, they are all behind closed doors with results reported, but nothing about materials and methods. No independent validation. Don't get me wrong , I'd give parts off my body for EM drive to be "truly" true. But Cannae leaves us with no way of "knowing" anything.
The only info. we have for Cannae is the NASA testing: 10 Watts would generate 17.32 micro Newtons, which is below the amount you calculated to sustain orbit (if I didn't screw up my math). Please tell me where I'm right or wrong thanks, FL
You are overthinking this IMHO. The cubesat will stay in orbit, or it won't. The rest of the details aren't anyone's business but theirs. If it does stay in orbit, mainstream press exposure and scrutiny from all quarters will increase exponentially regarding the details of that cubesat.
Also, regarding hidden gas thrusters. The FAA will conduct a Part 414 safety review of the launch. The review doesn't cover the satellite per se, but the launch vehicle operator will disclose any propellants on board because it'd affect the safety of the launch vehicle, so the launch operator would be taking a major risk with their business by not disclosing this. If we know the launcher and specific flight, we can look up the safety review specific details in the Federal Register.
I would guess if they are being honest, and they are building a cubesat, that they would have tested the cube sat on earth as a closed system. If they got a force measurement out of it then maybe the next test would be a low orbit test to prove the concept? Unless this is their one and only test, yikes. I guess the low orbit test takes care of space litter if it doesn't work. I wonder if this is a test they are hoping will work, or their claims are more grand than, it is just a test. I find it odd the shape of their cavity, that it doesn't appear to be conical, unless I mistook the image.
If we actually see it go up into orbit, we can rest assured they are entirely confident that it works. No one would pay for a satellite launch-even a cubesat -without tabletop confidence. Their investors would never allow it.
I view this as great news, but they aren't on the pointy end of a rocket just yet...
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#4167 by RERT on 09 Aug, 2016 17:09
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CorvusCorax -
Your logic on the LiPoly battery solution seems to put it well in scope for a cubesat.
Just curious though: I've seen figures for Li-ion energy density in the region of 180 Wh/kg. Your sums say they'd need about 14 Wh of storage, which works out at more like 80g than 400g. Is it the 'space rated' characteristic which raises the cell weight? -
#4168 by rugo on 09 Aug, 2016 18:40
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This is a link to the standard battery module from a cubesat kit:
http://www.cubesatkit.com/docs/datasheet/DS_CSK_BM_1_710-01006-A.pdf
In total 40Wh energy stored. -
#4169 by frobnicat on 09 Aug, 2016 20:17
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Concerning the Cannae intended cubesat and battery, every comment seem to assume that a continuous operation is needed, but it doesn't take a continuous thrust to keep a satellite into orbit against atmospheric drag. Clearly the thrusters on ISS don't operate continuously, there is only a burn now and then to "up" the orbit.
So I don't see why a battery is needed at all : instead of storing half of solar power when in sun and release it later when in shadow, just use 100% power for thrusting when in sun and fly around as a dead weight when in shadow, the inertia of the sat as a whole is the "buffer" for power off periods. Isn't the added weight of a battery worth 10W for half an orbit worse than the added weight of a double power system (RF generator and frustum running at 20W instead of 10W) ? Or is it not possible to keep a proper circular orbit when thrusting only dayside (assuming appropriate vector) ?
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#4170 by CorvusCorax on 09 Aug, 2016 22:53
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Concerning the Cannae intended cubesat and battery, every comment seem to assume that a continuous operation is needed, but it doesn't take a continuous thrust to keep a satellite into orbit against atmospheric drag. Clearly the thrusters on ISS don't operate continuously, there is only a burn now and then to "up" the orbit.
So I don't see why a battery is needed at all : instead of storing half of solar power when in sun and release it later when in shadow, just use 100% power for thrusting when in sun and fly around as a dead weight when in shadow, the inertia of the sat as a whole is the "buffer" for power off periods. Isn't the added weight of a battery worth 10W for half an orbit worse than the added weight of a double power system (RF generator and frustum running at 20W instead of 10W) ? Or is it not possible to keep a proper circular orbit when thrusting only dayside (assuming appropriate vector) ?
The 10W were a number coming from Cannae. We don't know how much thrust they get out of that, but based on available numbers achieved in other experiments referred in this thread, it was assumed that this might just barely be enough to overcome atmospheric drag at 150 km. (if at all)
The ISS thrusters are chemical rockets and have thrust a few orders of magnitude higher. At these thrust levels one operates in "impulse mode" - same as other satellites who use chemical rockets for station keeping.
very low thrust engines (like ion engines, hall thrusters, solar sails, and very likely early EM drives if they work) tend to operate over much longer times - with continuous thrust over sometimes several orbits to achieve the required delta/vCorvusCorax -
Your logic on the LiPoly battery solution seems to put it well in scope for a cubesat.
Just curious though: I've seen figures for Li-ion energy density in the region of 180 Wh/kg. Your sums say they'd need about 14 Wh of storage, which works out at more like 80g than 400g. Is it the 'space rated' characteristic which raises the cell weight?
My bad. I took the wrong weight. I was off by a factor of 4.
I based that on the weight of a high performance 12V 1500 mAh pack I have here - but I didn't remember its weight correctly, the pack weights only 113g, not 400g.
There's however a number of factors that make the theoretical energy density unachievable and that 1500mAh pack representable:
1. Additional weight factors in the cell:
- Metal conductors to cathode/anode to get electrons in and out of the cell at low resistance
- Insolator to separate individual cell layers
- Casing/Outer insulation
2. Then you'd have to charge/dischage once every 85 minutes. That's around 6000 charge/discharge cycles over the course of one year. To make a LiPo cell survive that you can't utilize it to maximum capacity. You'd use a lower charge voltage to increase lifetime (reducing energy density by around 25%), and also use spare capacity to still have enough "left" at the end of the lifetime. (another 25%-50%)
http://www.cubesatkit.com/docs/datasheet/DS_CSK_BM_1_710-01006-A.pdf
gives the weight of the actual 40Wh cubesat pack with 310g.
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#4171 by RERT on 10 Aug, 2016 11:39
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Quote
...
I based that on the weight of a high performance 12V 1500 mAh pack I have here - but I didn't remember its weight correctly, the pack weights only 113g, not 400g.
There's however a number of factors that make the theoretical energy density unachievable and that 1500mAh pack representable:
1. Additional weight factors in the cell:
- Metal conductors to cathode/anode to get electrons in and out of the cell at low resistance
- Insolator to separate individual cell layers
- Casing/Outer insulation
2. Then you'd have to charge/dischage once every 85 minutes. That's around 6000 charge/discharge cycles over the course of one year. To make a LiPo cell survive that you can't utilize it to maximum capacity. You'd use a lower charge voltage to increase lifetime (reducing energy density by around 25%), and also use spare capacity to still have enough "left" at the end of the lifetime. (another 25%-50%)
http://www.cubesatkit.com/docs/datasheet/DS_CSK_BM_1_710-01006-A.pdf
gives the weight of the actual 40Wh cubesat pack with 310g.
OK great, and thanks. So battery capacity isn't an issue. The unit you point to looks to do the job, and there is no particular reason to assume they would be limited to a single such unit, given its dimensions and weight. Presumably, now I come to think of it, they didn't just pluck '6U' out of the air, and might have thought this through... -
#4172 by Gilbertdrive on 10 Aug, 2016 15:32
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I notice than the drag will give a small proper acceleration opposite to the propulsion of the Cannae Drive.
So, if ever Shawyer/traveller theory about the need of proper acceleration is true, the drive will be in generator mode, and it would decelerate the cubesat, that would fall back most quickly than without propulsion system.
I still have no position about the strange "acceleration needed theory" but I found interesting to notice that, if the Cannae test is positive, this acceleration needed theory will be nullified.
At the opposite, if the Cannae cubesat fall quickly, it may be "acceleration needed theory" is right, or the Cannae Drive thrust was an artifact, of it does not work into space, or something else. A positive will tell much more that a negative one
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#4173 by CorvusCorax on 10 Aug, 2016 17:15
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Yeah, that's the great thing about engineering solutions. There is a "positive proofing" paradigm, as opposed to the "falsification" paradigm used in theoretical sciences.
If that thing remains in orbit,that still doesnt proof any specific EM drive theory, after all the effect could be due to interaction with the earth magnetic field and fail in deep space. But it would proof that EM drives are feasible as propellantless in space propulsion
If the sat falls, it really proofs nothing. How many attempts to build the airplane fell from the sky before flight as a principle was proven. People like Lilienthal also built the theory as they went, to match and improve their experimental results -
#4174 by X_RaY on 10 Aug, 2016 20:44
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Concerning the Cannae intended cubesat and battery, every comment seem to assume that a continuous operation is needed, but it doesn't take a continuous thrust to keep a satellite into orbit against atmospheric drag. Clearly the thrusters on ISS don't operate continuously, there is only a burn now and then to "up" the orbit.
You are right
So I don't see why a battery is needed at all : instead of storing half of solar power when in sun and release it later when in shadow, just use 100% power for thrusting when in sun and fly around as a dead weight when in shadow, the inertia of the sat as a whole is the "buffer" for power off periods. Isn't the added weight of a battery worth 10W for half an orbit worse than the added weight of a double power system (RF generator and frustum running at 20W instead of 10W) ? Or is it not possible to keep a proper circular orbit when thrusting only dayside (assuming appropriate vector) ?
Don't forget the losses while storing would reduce the total effectivity of the system, therefore the total thrust over time would be even lower at the end of the day. -
#4175 by zen-in on 11 Aug, 2016 03:04
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Concerning the Cannae intended cubesat and battery, every comment seem to assume that a continuous operation is needed, but it doesn't take a continuous thrust to keep a satellite into orbit against atmospheric drag. Clearly the thrusters on ISS don't operate continuously, there is only a burn now and then to "up" the orbit.
So I don't see why a battery is needed at all : instead of storing half of solar power when in sun and release it later when in shadow, just use 100% power for thrusting when in sun and fly around as a dead weight when in shadow, the inertia of the sat as a whole is the "buffer" for power off periods. Isn't the added weight of a battery worth 10W for half an orbit worse than the added weight of a double power system (RF generator and frustum running at 20W instead of 10W) ? Or is it not possible to keep a proper circular orbit when thrusting only dayside (assuming appropriate vector) ?
You are right. In order to achieve an increasing circular orbit thrust has to be uniform in the orbit. Batteries are required. -
#4176 by ThinkerX on 11 Aug, 2016 06:52
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Quote
You are right
Don't forget the losses while storing would reduce the total affectivity of the system, therefore the total thrust over time would be even lower at the end of the day.
Perhaps this accounts for the six month duration for the mission? -
#4177 by 1 on 12 Aug, 2016 00:25
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Concerning the Cannae intended cubesat and battery, every comment seem to assume that a continuous operation is needed, but it doesn't take a continuous thrust to keep a satellite into orbit against atmospheric drag. Clearly the thrusters on ISS don't operate continuously, there is only a burn now and then to "up" the orbit.
So I don't see why a battery is needed at all : instead of storing half of solar power when in sun and release it later when in shadow, just use 100% power for thrusting when in sun and fly around as a dead weight when in shadow, the inertia of the sat as a whole is the "buffer" for power off periods. Isn't the added weight of a battery worth 10W for half an orbit worse than the added weight of a double power system (RF generator and frustum running at 20W instead of 10W) ? Or is it not possible to keep a proper circular orbit when thrusting only dayside (assuming appropriate vector) ?
You are right. In order to achieve an increasing circular orbit thrust has to be uniform in the orbit. Batteries are required.
I believe, in general, a satellite will need a battery for some purpose or another; unless raising your orbit is truly your only goal. Still, sun-side only operation should be completely possible at the expense of transfer efficiency. Since the lifetime of an EM-drive-like device wouldn't be limited by your supply of reaction mass, we can perform an arbitrarily high number of sub-optimal (read: off-axis) 2-burn maneuvers to achieve whatever orbit raising / lowering needs to be done.
The question then returns to, is 'continuous operation' or 'keeping a proper circular orbit' actually needed; something which would probably be determined by mission requirements rather than technical feasibility.
edit: wording -
#4178 by MaxIsp on 12 Aug, 2016 00:59
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A sun synchronous orbit riding on the terminator could allow continuous operation in sunlight, constant orbital altitude raising, and eventually reaching escape velocity. albeit in a high inclination plane.
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#4179 by Gilbertdrive on 12 Aug, 2016 10:01
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You are right.
But sun synchronous is not the most ordinary orbit, so maybe they can have a lower price on other LEO launch.
It would be interesting if somebody knows if there is a price difference for a cubesat in SSO, or any LEO
Also, maybe there are reasons if it stays in LEO instead of rising it's orbit.
1 : Communication from a higher orbit may need more expensive material, and more precise orienting.
2 : Their cubesat could take damage in Van Allen Belt, between 700 km and 10 000 km high.
So, it is probable than LEO and not rising orbit until escape means the cheaper and quicker mission.
Also, even if the propulsion system is On only when the cubesat exposed to the sun, it still needs battery for maintaining warm the satellite when it is in the night side...
