Author Topic: Water-propelled satellite into Deep Space  (Read 17975 times)

Offline vyoma

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Water-propelled satellite into Deep Space
« on: 12/04/2013 03:10 AM »
Quote
CubeSat Ambipolar Thruster (CAT), a new rocket propulsion system powered by the Sun and propelled by water, which will push small spacecraft like CubeSats around and far beyond the Earth.

http://www.theverge.com/2013/12/2/5166398/cubesat-kickstarter-water-for-satellite-propulsion
http://www.kickstarter.com/projects/longmier/cat-launch-a-water-propelled-satellite-into-deep-s
« Last Edit: 12/04/2013 03:11 AM by vyoma »

Offline Falcon H

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Re: Water-propelled satellite into Deep Space
« Reply #1 on: 12/04/2013 03:27 AM »
Water propelled spacecraft....sounds like something from an Isaac Asimov story. :)   
"Sooner or later, we must expand life beyond our little blue mud ball--or go extinct" Elon Musk

Offline Stormbringer

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Offline Nilof

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Re: Water-propelled satellite into Deep Space
« Reply #3 on: 12/04/2013 04:44 PM »
Water as a propellant is a stretch goal though, with the initial propellant choice being Xenon.

Xenon has a higher performance due to it's higher density, and it does lessen issues with corrosion. On the other hand, water would make things simpler for the average cubesat builder, and there's the possibillity of ISRU in the future. It's definitely easier to store in LEO with a vapor pressure three orders of magnitude lower than Xenon at 300K.
« Last Edit: 12/04/2013 04:46 PM by Nilof »
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Asteroza

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Re: Water-propelled satellite into Deep Space
« Reply #4 on: 12/05/2013 12:41 AM »
Note this is round 2 on kickstarter for the CAT, as the first run failed to get funded ($200K vs $50K, and now the $50k has been cleared), so this kitty definitely has 9 lives. But it did generate a lot of interest and secondary support, which is why they are farther along and have different goals this time around.

The first kickstarter is here
http://www.kickstarter.com/projects/597141632/cat-a-thruster-for-interplanetary-cubesats

Note that using a pressurized xenon tank has its own issues in terms of satellite handling and transport to the launcher payload integration facility, requiring special clearances if traveling by air, while a water fueled cubesat should be easier to develop for less well funded outfits, barring battery material clearance issues for air transport. Some makers bypass this by sending the battery pack by other means and reintegrate at the destination.

This coupled with a cubesat only massive cluster launch, say on the first demo flight of Falcon Heavy reusable (would that be MOACL, the mother of all cluster launches?) to disperse multiple constellation fleets of polar or sunsync orbit cubesats would be very interesting. The payload adapter would look like a supersized submunition bomblet dispenser too...
« Last Edit: 12/12/2013 10:54 PM by Asteroza »

Offline Hanelyp

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Re: Water-propelled satellite into Deep Space
« Reply #5 on: 12/05/2013 01:29 AM »
Reading Ignition!, mention is made of space storeable propellants that remain liquid at something like -40 or -65 C.  A matter of not freezing in the tank in orbit.

Online ChrisWilson68

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Re: Water-propelled satellite into Deep Space
« Reply #6 on: 12/05/2013 07:20 AM »
Wow, this is really exciting!  Communication is still an issue, but if this is successful, it greatly lowers one of the big barriers to entry for research and innovation in deep space.

Offline ssshock

Re: Water-propelled satellite into Deep Space
« Reply #7 on: 12/07/2013 03:36 AM »
I did ask about whether they would keep the water liquid, and in LEO in their satellite, they said the avg temp was 10-20 degrees C. Deep space would be a bit different though!

Offline colbourne

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Re: Water-propelled satellite into Deep Space
« Reply #8 on: 12/08/2013 05:52 AM »


Just to give an idea of a water rocket

Online aero

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Re: Water-propelled satellite into Deep Space
« Reply #9 on: 12/08/2013 07:19 AM »


Just to give an idea of a water rocket
I liked the "Giant Water Rocket" clip better.  ;D
Retired, working interesting problems

Offline A_M_Swallow

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Re: Water-propelled satellite into Deep Space
« Reply #10 on: 12/08/2013 03:34 PM »

Online avollhar

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Re: Water-propelled satellite into Deep Space
« Reply #11 on: 12/11/2013 06:16 AM »
Plenty of things do not add up here.. doing some basic math and rocket equations:

given (http://pepl.engin.umich.edu/thrusters/CAT.html):
Up to 2 mN thrust for 10W
Up to 20,000 m/s plasma exhaust velocity
Up to 10 Watts continuous (or higher power when pulsed)
3U CubeSat (30 cm x 10 cm x 10 cm)
20 W of power produced from deployable solar panels

Now the math:
thrust = massflow*exhaust velocity.. results in a mass flow of 0.1grams/sec (plausible)
mechanic power = 1/2 * massflow *exhaust_velocity^2 = 20 Watt (huh? it said 10 Watt continous el power)
Looking at the drawing, we can assume that the long sides of the 3U cubesat can be deployed to form a 100% area efficient solar panel of 30cm*10cm*10cm*4panels = 0.012m2 area. The solar constant is 1400W/m2, so we have 16.8W solar (!) power on this area. To produce 20W of this would require 120% efficient cells.. (again: huh?)

Not even talking about a claimed 90% DC-efficient RF generator, the requirement of anti-freeze for the water (why water??) and the lack of active attitude control (you fire the engine, but cannot control which direction you go) and the lack of a comms concept for larger distances.

If I am very polite, I would say this needs some serious work.. I certainly would not put a penny into the funding before more coherent numbers appear. But maybe my math is completely wrong: in that case, I am open for corrections.

Offline corgius

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Re: Water-propelled satellite into Deep Space
« Reply #12 on: 12/11/2013 07:00 AM »
Looking at the drawing, we can assume that the long sides of the 3U cubesat can be deployed to form a 100% area efficient solar panel of 30cm*10cm*10cm*4panels = 0.012m2 area. The solar constant is 1400W/m2, so we have 16.8W solar (!) power on this area. To produce 20W of this would require 120% efficient cells.. (again: huh?)

30cm*10cm*10cm is not an area, is a volume!

30cm*10cm*4=0.12m2 -> 168W

;-)



Online avollhar

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Re: Water-propelled satellite into Deep Space
« Reply #13 on: 12/11/2013 07:12 AM »
Bugger! I stand corrected, thank you.. at least this seems to add up now as 20W solar power are in reach, but still optimistic without panel gimbals and active attitude control.

(Should I drink more coffee or less ?)

Thanks corgius!

Offline corgius

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Re: Water-propelled satellite into Deep Space
« Reply #14 on: 12/11/2013 08:52 AM »
Bugger! I stand corrected, thank you.. at least this seems to add up now as 20W solar power are in reach, but still optimistic without panel gimbals and active attitude control.

(Should I drink more coffee or less ?)

Thanks corgius!

if I correctly read there, an attitude control is present

Quote from: PEPL Thrusters: CubeSat Ambipolar Thruster link= http://pepl.engin.umich.edu/thrusters/CAT.html
...
While the CAT thruster is firing, the satellite will be aimed with a space qualified control system consisting of small reaction control wheels (four small gyroscopes) and magnet torque rods.   Flight qualified solar panels mounted on the outside of the CubeSat will power the CAT and other onboard systems like the radios and computers. All of these core satellite components have flown previously on CubeSats from the University of Michigan.
...

Online avollhar

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Re: Water-propelled satellite into Deep Space
« Reply #15 on: 12/11/2013 10:12 AM »
On the same page it says:
'Passive magnetic attitude stabilization from nozzle magnets interacting with Earth's magnetic field.'

I think we will have to see. Anyway, for travel out of LEO they need cold gas thrusters to de-saturate the gyros once in a while.

Anyway, thanks for pointing it out.

Offline A_M_Swallow

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Re: Water-propelled satellite into Deep Space
« Reply #16 on: 12/11/2013 11:40 AM »
On the same page it says:
'Passive magnetic attitude stabilization from nozzle magnets interacting with Earth's magnetic field.'

I think we will have to see. Anyway, for travel out of LEO they need cold gas thrusters to de-saturate the gyros once in a while.

Anyway, thanks for pointing it out.

Could the gyros be de-saturated against the main thruster?

Online avollhar

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Re: Water-propelled satellite into Deep Space
« Reply #17 on: 12/11/2013 11:43 AM »
Could the gyros be de-saturated against the main thruster?
Shouldn't.. de-saturation implies getting rid of angular momentum. Main thruster cannot do this.

Offline cordwainer

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Re: Water-propelled satellite into Deep Space
« Reply #18 on: 12/12/2013 04:37 AM »
Could lower the necessary energy needed to vaporize the water by doping with metallic salts, couldn't they. Could lead to corrosion issues though.

Offline AJA

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Re: Water-propelled satellite into Deep Space
« Reply #19 on: 12/14/2013 01:39 PM »
Reading Ignition!, mention is made of space storeable propellants that remain liquid at something like -40 or -65 C.  A matter of not freezing in the tank in orbit.

That doesn't exclude water though. You could have a storage tank, a reverse osmosis system, and a prop tank. Add salt/mineral (also ISRU - biological waste in case of manned, orbital complexes like ISS, and the minerals of the celestial body you land on - in case of surface exploration - cometary/asteroid - extremely low gravity well ones) to the water to depress the freezing point and keep it from freezing. You don't even need a reverse osmosis system if you can just do the good old evaporate-purify-condense in different tank. (Tech already flying on ISS - the passive heat pipes)

Plenty of things do not add up here.. doing some basic math and rocket equations:

The key phrase is

Up to
i.e. those numbers aren't the values of the parameters at the same time.


I think we will have to see. Anyway, for travel out of LEO they need cold gas thrusters to de-saturate the gyros once in a while.
Surely the same magneto-torquers work with the solar magnetic field? Yeah, it's weaker; but it's not zero. Being in deep space, and away from eclipses wouldn't require large rates of attitude change thermal management wise, or communications wise...




Could lower the necessary energy needed to vaporize the water by doping with metallic salts, couldn't they. Could lead to corrosion issues though.
All solutes raise the boiling point of water. But I don't think the energy'd be a problem, given that they're in space, and have access to a vacuum.. (Have a tank of flexible dimensions.. drive a "wall"..expanding the tank, and you get boiling..? On earth, you're fighting the atmospheric pressure opposing the expansion, but we won't have that up there)
« Last Edit: 12/14/2013 01:44 PM by AJA »

Tags: cubesat water