Quote from: spacenut on 04/09/2021 01:54 pmOn Mars I don't think they will release any water to the atmosphere. You apparently missed my complaint, that Ncb was responding to- that a rocket engine fired in orbit (with an exaust velocity less that twice orbital velocity) "recycles" it's propellant back to the planetary atmosphere in the form of exaust gasses, but that a constant thrust ion engine, if it cant point it's drive directly at a planet the whole trip, can eject propellant into interplanetary space, lost forever.Ncb's point of atmospheric erosion is taken, but there are measures that can be taken to compensate, such as a superconductor ring around the equator for an artificial magnetic field.
On Mars I don't think they will release any water to the atmosphere.
Agreed it should be Advanced Concepts.
https://www.solestial.com/
Yeah, imagine SEP bigger than 300 meters, with these solar panels and the evolution of the Krypton ion Engine...Mars could be much more realistic with this technology...
At some point refueling Starships 6 times just for one trip to Mars may get too expensive. 6 cargo flights to dock with a large SEP cargo ship could get the cargo at least 5 flights of cargo and one to fill up of Argon to get a tug ship on its way. It may only take one cargo Starship of argon to be able to take 1000 tons of cargo, not just 500 tons to Mars. Something to think about.
1.3% of earth's atmosphere is Argon.
As Musk himself said, the nitrogen/oxygen plant will also be producing Argon.
Quote from: ncb1397 on 04/08/2021 08:58 pm1.3% of earth's atmosphere is Argon.Likewise, ~ 1% of the lower thermosphere is argon.Quote from: Robotbeat on 04/08/2021 03:02 pmAs Musk himself said, the nitrogen/oxygen plant will also be producing Argon.And likewise, a nitrogen/oxygen thermosphere ASCENT propellant trawler would produce argon as unavoidable byproduct. -VASIMR-argon Isp exceeds 5000 s. Greater thrust is needed but planned.One could imagine a rotating high-thrust VASIMR SEP tug with enormous, ultra-lightweight solar panel films, centripetally extended. Hypothetically, if engines were rated at, say, 10,000 s, a 10-t SEP tug could give a 100-t payload 4 km/s delta-v with < 5 t of argon. Fly-back to the depot would use ~ 1 ton. That would be highly mass-efficient cargo-delivery propulsion, and more economical if the argon were free trawler waste.(This assumes some efficient cargo landing system. Maybe simple, reusable monopropellant ASCENT top-mount rocket packs, burning the other thermosphere propellant harvest? On Mars, you might reuse for simplified point-to-point delivery of smaller cargoes to unprepared landing sites.)
One could imagine a rotating high-thrust VASIMR SEP tug with enormous, ultra-lightweight solar panel films, centripetally extended. Hypothetically, if engines were rated at, say, 10,000 s, a 10-t SEP tug could give a 100-t payload 4 km/s delta-v with < 5 t of argon. Fly-back to the depot would use ~ 1 ton. That would be highly mass-efficient cargo-delivery propulsion, and more economical if the argon were free trawler waste.
Quote from: LMT on 10/17/2022 03:57 amQuote from: ncb1397 on 04/08/2021 08:58 pm1.3% of earth's atmosphere is Argon.Likewise, ~ 1% of the lower thermosphere is argon.Quote from: Robotbeat on 04/08/2021 03:02 pmAs Musk himself said, the nitrogen/oxygen plant will also be producing Argon.And likewise, a nitrogen/oxygen thermosphere ASCENT propellant trawler would produce argon as unavoidable byproduct. -VASIMR-argon Isp exceeds 5000 s. Greater thrust is needed but planned.One could imagine a rotating high-thrust VASIMR SEP tug with enormous, ultra-lightweight solar panel films, centripetally extended. Hypothetically, if engines were rated at, say, 10,000 s, a 10-t SEP tug could give a 100-t payload 4 km/s delta-v with < 5 t of argon. Fly-back to the depot would use ~ 1 ton. That would be highly mass-efficient cargo-delivery propulsion, and more economical if the argon were free trawler waste.(This assumes some efficient cargo landing system. Maybe simple, reusable monopropellant ASCENT top-mount rocket packs, burning the other thermosphere propellant harvest? On Mars, you might reuse for simplified point-to-point delivery of smaller cargoes to unprepared landing sites.)That's actually an interesting propellant economy point. Assuming you had PROFAC style atmosphere propellant trawlers (largely based in earth SSO), you could have a rather large economy of nitrogen, oxygen, and argon for cislunar and outbound ops, feeding propellant depot stations. If ASCENT propellant can be made locally in orbit at a propellant depot using uplifted hydrogen, then you have bulk nitrogen (cold gas thrusters, VASIMR propellant, etc), oxygen (life support, oxidizer), argon (for interplanetary electric propulsion), and ASCENT propellant for landers. With a nascent orbital propellant economy with a near term use case, ASCENT propellant manufacturing on orbit brings the secondary argon propellant economy to maturation.The cumbersome issue is sourcing the hydrogen for ASCENT. If you lift water or ammonia, you are left with excess oxygen or nitrogen which you were ostensibly trawling the atmosphere for already. Liquid hydrogen is a hard cryogen that adds a lot of headaches.The secondary problem is, you are already collecting so much nitrogen with an atmosphere trawler that running VASIMR on nitrogen may be more economical despite the mass/ISP penalty.
Quote from: LMT on 10/17/2022 03:57 amOne could imagine a rotating high-thrust VASIMR SEP tug with enormous, ultra-lightweight solar panel films, centripetally extended. Hypothetically, if engines were rated at, say, 10,000 s, a 10-t SEP tug could give a 100-t payload 4 km/s delta-v with < 5 t of argon. Fly-back to the depot would use ~ 1 ton. That would be highly mass-efficient cargo-delivery propulsion, and more economical if the argon were free trawler waste.Your numbers are optimistic. It's best to show first-order kinematics to make sure you are in the ballpark.4km/sec is barely enough to get you from LEO to Mars Injection, but how are you braking when you get there?Back-calculating the mass flow rate, assuming 30 days of acceleration, you need 4000 / 86400 / 30 = 1.54mm/sec^2 acceleration on 110t, or a force of 170N. The mass flow rate = 170N/100km/sec = 1.7g/secThat's 4.4t of Argon.The exhaust energy flow is 1/2*.0017kg/sec * 100000^2 = 8.5MW.VASIMR is 73% efficient, so input power is 8.5MW/.73 = 11.6MW.I don't think VASIMR is rated to 11.6MW, they've tested 200kW. They need a 58x factor of power improvement. I note Raptor-1 to Raptor-2 was about a 1.3x improvement. No engine type in history has showed 50x improvement over a span of < 20 years.State of the art solar panels are 1kw/kg so you need 11.6t of solar panels.There are 11.6 - 8.5 MW of waste energy so 3MW of radiators are needed. At 1kg/kw that's 3t of radiators.Overall just the power component requires 3 + 11.6 = 15T of power/cooling. I'm unable to find anywhere that mentions VASIMR's engine mass per kw of thrust. For X3 it's about 1.41kg/kw but let's say VASIMR is has better power density and is at 1kg/kw of thrust. That's 8.5T of VASIMR.So your tug, just for power, cooling, and engine, will mass 23.5t. Added structure and you are probably over 30T.Add in another 2t of Argon in order to brake at Mars, and we're at 32T so we're at 78t of cargo.You've also added about 50 days to your mission for acceleration and braking. You could accelerate quicker but you quickly move into the gigawatt power range. For reference, 6 raptors is 25GW of exhaust power.Speaking of cargo, how were you planning on transferring cargo from Starship to the tug? Transferring fuel is challenge enough, solid, bulky cargo will be even worse.I note the cost to add fuel for Mars to an existing 100t of cargo on a Starship is about $12M. That's the only cost SEP is saving. Orbital transfer operations for cargo will probably eat up a large chunk of that savings.I've run the numbers on almost any target in the solar system and extra-solar. All electric drive tech is obsolete compared to cheaply refueled StarshipsHere's an example for X3 clusters: https://docs.google.com/spreadsheets/d/1mrlKefLWzGxsYtBXWF92a0cXqsPZoKLGlPbQizKHI3g/edit#gid=0
"How are you braking," is a cargo EDL topic, unrelated to ion engines here.
"State of the art solar panels are 1kw/kg," but thin-film PV is more plausible for the application and timeframe. Perovskite and quantum dot films give 10-30 kW/kg, GaAs gives ~ 50, and CVD might give 70 (Islam et al. 2022).-VASIMR needs large radiators, and heat rejection scales with T^4 (Stefan-Boltzmann). What are the hottest radiator designs on the board today? Example: A potassium radiator might have an effective radiative temperature of 670 K (Tomboulian 2014).
Quote from: LMT on 10/18/2022 04:13 am"How are you braking," is a cargo EDL topic, unrelated to ion engines here.So, you're just tossing the VASMIR and acres of solar panels away for each trip?Please describe how such a system will be reused. You will find you'll need more deltaV to enter Mars Orbit, and you aren't aerobraking with acres of solar panels and cooling arrays.
Quote from: LMT on 10/18/2022 04:13 am"State of the art solar panels are 1kw/kg," but thin-film PV is more plausible for the application and timeframe. Perovskite and quantum dot films give 10-30 kW/kg, GaAs gives ~ 50, and CVD might give 70 (Islam et al. 2022).-VASIMR needs large radiators, and heat rejection scales with T^4 (Stefan-Boltzmann). What are the hottest radiator designs on the board today? Example: A potassium radiator might have an effective radiative temperature of 670 K (Tomboulian 2014).What's the operating temperature of VASIMR? You aren't getting temps above that in your radiator unless you go with a compression style heat pump, and those have ~60% efficiency at best, which makes your solar panels even bigger (and your radiators too).Nice thing about chem/nuke rockets - the waste heat all goes out the tailpipe, everything internally is regeneratively cooled.Speaking of solar panels, those are the mass of the actual solar / electricity devices. Not the frame to support them, deploy them, route the power back to the VASMIR, condition/regulate the power, etc. etc.1kw/kg was for all that and was an optimistic projection from this article:http://www.spacefuture.com/archive/early_commercial_demonstration_of_space_solar_power_using_ultra_lightweight_arrays.shtml
I don't think VASIMR is rated to 11.6MW, they've tested 200kW. They need a 58x factor of power improvement. I note Raptor-1 to Raptor-2 was about a 1.3x improvement. No engine type in history has showed 50x improvement over a span of < 20 years.
Quote from: InterestedEngineer on 10/18/2022 12:28 amI don't think VASIMR is rated to 11.6MW, they've tested 200kW. They need a 58x factor of power improvement. I note Raptor-1 to Raptor-2 was about a 1.3x improvement. No engine type in history has showed 50x improvement over a span of < 20 years.Technology can evolve very quickly from prototype to production if there is a need.Is using multiple engines cheating?The Heinkel He 178 first flew in 1939 with 4.4kN of thrust.The 707-120 first flew in 1957 with 4x60kN of thrust.Is nuclear an "engine"?Chicago Pile-1 operated at 200W in 1942.Shippingport Nuclear power plant reached 60,000,000We in 1957.