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kbd512 the post 24 I think is in one of the directions that I would work towards and also altering the Cygnus so that it could hold more fuel would be another especially the extended length unit. It could even be stretched such that we can even provide an even greater amount with rework engines and solar panels to be launched on a Falcon 9 Heavy as well.
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I quite agree with Kbd512 that near-continuous thrusting with an electric propulsion thruster would be the better way to re-boost the ISS. Even micro-gees of reboost acceleration, over long periods of time, should do the job. Just as long as that acceleration balances or exceeds the drag deceleration number. Surely there's a few KW of electricity available somewhere on the ISS to power a couple of such thrusters.
I just looked at Dragon as a rebooster, because I happened to know how much propellant it carries, and roughly what its thruster Isp is. Either it or Cygnus could do the job Progress did, except that it works better if you can plumb your cargo propellant into your thruster propellant supply. Otherwise, you don't have very much impulse to offer for station reboost. You need most of that propellant to deorbit, and to maintain attitude until the chutes open, in the case of Dragon.
GW
Last edited by GW Johnson (2022-03-15 12:05:32)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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I made a mistake on the designation for Aerojet-Rocketdyne's engine. It's supposed to be "X3", not "X200". The X3 is capable of accepting up to 200kW of input electrical power. At 100kW, the X3 thruster generates 5.4N of thrust. X3 is purported to be capable of 7 different firing configurations that consume input power ranging between 2kW and 200kW. As-tested, each X3 thruster weighs 230kg and is 80cm in diameter. The "flight weight" X3 engines could weigh a bit less than that, but 230kg is acceptable for an orbital station that never leaves LEO. The specific impulse ranges between 1,800s and 2,650s.
I would like to see brand new MegaFlex panels add to ISS and remove / de-orbit the existing 20-year-old panels. Orbital ATK (now Northrop Grumman Innovation Systems) says they can package a pair of 150kW "wings" (300kW total) into a Falcon 9 fairing. I want to attach 4 brand new 150kW "wings" / "panels" to ISS, for a total of 600kW, same concept as Lockheed-Martin's "Mars Base Camp" orbital station. The pair of 200kW-class X3 thrusters provides redundancy and the 600kW of input power provides a very generous margin for both recharging the station's batteries, powering all the scientific experiments, and the power required for station-keeping.
The estimated daily drag force on ISS at its current altitude is a little less than 1N, so any thruster that can supply 2N of thrust or more, 50% of the time (if the input power comes from solar arrays), is sufficient to continually reboost the ISS to maintain its orbit around the Earth. ESA's ATV fired a pair of its R-4D-11 thrusters for about 40 minutes. Those thrusters have a vacuum specific impulse of 312s, so each firing consumed about 770kg of fuel. If we presume that the X3 thruster can operate at a minimum of 1,800s of specific impulse, then the monthly reboost maneuver would consume about 128kg of fuel, and yearly reboost propellant consumption is 1,540kg, down from 7,000kg to 9,000kg using chemical engines. If it operates closer to 2,650s at full power, then yearly propellant consumption falls to 1,088kg.
VASIMR's specific impulse starts at 3,000s using Argon and goes all the way up to 12,000s using H2 as the propellant. At 12,000s, the yearly propellant consumption falls to 240kg. As such, H2 propellant from the supplied H2O feedstock (for onboard O2 breathing gas generation) consumes 38.5X less propellant mass than the storable chemical propellants we use today.
If we needed to get an object with the payload mass of the ISS into LMO, then VASIMR engines with an attached SLS LH2 tank containing 733,000 gallons (196,357kg) of LH2, could supply 42.6km/s of delta-V. ISS doesn't need to get there at any great speed, it just needs to get there and come back.
We can use Starship to provide enough propellant to send large ships all the way to Mars and back without refueling using existing technology. After you have the orbital refilling station set up at Mars, then you only need to supply half as much fuel to send the ship back to Earth and only need to ship half as much fuel.
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Sounds like we would want to do an upgrade rather than see it in the bottom of the Ocean.
We know that Water is costly to bring to the station and making use of the Hydrogen is problematic for getting it cold so that we control its use.
Do the other heavy gases have similar issue of boil off and control that hydrogen has?
So why not use the methane created from the co2 waste stream as the ISS already does do.
They are more expensive so why not keep what we know works just use it when its needed.
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kbd512,
I have always been skeptical of VASIMR. It uses a magnetic bottle to contain plasma. Hydrogen power generators have tried to do that, and found the magnetic bottle consumes more power than the generator produces. However, VASIMR is not supposed to be a power generator, it's a thruster. So just accept the fact it consumes a lot of power. It promised to produce 9,000 seconds with H2 propellant when first proposed. I haven't followed developments in a few years, but last I read they hadn't demonstrated it with H2. Performance with argon was lower.
Another issue is gas available on ISS. The oxygen generator uses electrolysis to split water into O2 and H2, however the H2 is piped to a Sabatier reactor. The Sabatier consumes all the H2 and half the CO2 from cabin air, converting it into methane and water. The water is added to the station's water, both for drinking water and the electrolysis tank. That leaves methane and the other half of CO2. I have also proposed direct CO2 electrolysis to recover oxygen from the CO2 currently dumped in space, that would convert 80% of the CO2 into O2 and carbon monoxide (CO), so effectively only recover 40% of the oxygen. However, 40% is better than 0%. Others have proposed other systems that convert that CO2 into heavier hydrocarbons. But currently ISS has none of that, the CO2 not used by the Sabatier is dumped in space. But that leaves you with methane and CO2, not H2.
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I would have thought that the heavier element would have produced more thrust.
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Roscosmos head revises comments about quitting ISS after 2024
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Today's Internet feed contained a number of links to a story about the latest Progress shipment.
Apparently out-gassing of something in the vehicle (not fuel) caused concern, and the air was scrubbed for a while.
https://www.space.com/space-exploration … uts-on-iss
There are at least four versions of this story available.
The story brings the Svezda module back into focus. It reports that the Russians have been keeping the module closed except for when transferring cargo, which seems like a good idea, in light of GW Johnson's warnings about a catastrophic blowout that might occur if the tunnel which carries air pressure lets go.
The article **also** reminded readers that the Russians have not committed to staying with ISS past 2026, and they could pull the plug at any time in 2025.
(th)
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