Momentus Plasma Water Propulsion Will Be Two to Three Times Better Than Chemical Rockets

Momentus will provide in-space transportation services to various orbits all the way out to deep space. They will receive $8.3 million in funding today.

The funds will go towards in-orbit technology demonstration of the company’s in-space rocket scheduled to launch in the 1st quarter of 2019.

Prime Movers Lab led the round for Momentus, a 2018 graduate of the Y Combinator program, with participation from Liquid 2 Ventures, One Way Ventures, Mountain Nazca, Y Combinator and numerous other VCs.

Dakin Sloss, Founder and General Partner at Prime Movers Lab (which invests in physics-powered startups) said:
“Momentus has not only developed groundbreaking and efficient water-powered, in-space rockets, but also validated the massive market demand for their services with hundreds of millions of dollars in LOIs. We are thrilled to back this extraordinary team of seasoned entrepreneurs and space industry veterans in their impressive pace of introducing novel technology to space — which we expect will continue with the upcoming in-space demonstration in the first half of 2019.

Momentus Founder, President, and veteran space entrepreneur Mikhail Kokorich said: “We are building in-space rockets that, once in space, move spacecraft from one orbit to another. Our goal is to make in-space rides affordable and fast. Democratization of in-space transportation will enable a lot of new business models beyond low earth orbit.”

According to a recent report by the Satellite Industry Association, prepared by Bryce Space and Technology, the space economy hit almost $270 Billion in 2017. The first market Momentus will address is low-earth orbit (LEO) transportation, mostly through orbital altitude adjustments for satellites. The trans-GEO market will be driven by applications like satellites tugging from LEO to higher orbits such as mid-earth orbit or geostationary orbit, in-space services and satellite de-orbiting. Currently this market is served either by chemical booster stages, or by ion propulsion onboard, which is overkill for the requirements and not as efficient as water for the fuel to mass ratio.

Vigoride, Momentus’ smallest ESPA class in-space rocket service will be providing rides from LEO with wet mass less than 250 kg, which will be ready and space qualified in 2019.

Back on Earth, Momentus is focused on the following milestones:
● 2019: Flight demonstration of our technology in space
● 2020: Start providing Vigoride service using our first in-space rocket;
● 2020: Test next-gen Ardoride engines for our in-space rockets in Simulated Space Environments.

Momentus Technology

Momentus will use microwaves to heat water to super-high temperatures.

They are using proven components in an innovative way.

Future systems will be able to gather water from asteroids and planets for easy refueling. Missions will be able to travel anywhere in the solar system and get fuel. Power can be from solar or other power sources.

Two to three times the ISP – fuel efficiency- of chemical rockets

VIGORIDE™ is the name of the first Momentus commercial service in 2020.

Main propulsion for small spacecrafts
Orbit raising from LEO, orbit inclination change
Satellite deorbiting missions
Main thruster for deep space spacecrafts
In-space boosters for micro-launchers

SPECS
Starting mass: 180kg (ESPA) or 300kg (ESPA GRANDE)
∆V: up to 6km/sec
Propulsion: water plasma-powered Vigor™
Specific Impulse: up to 700 seconds

Double the performance of chemical rockets
Solar power: 500W

ARDORIDE™ for service start in 2021

In-orbit servicing
Space debris removal
Platform for small telecom satellites
In-space boosters for small-lift launch vehicles
Deep space exploration
Near-Earth asteroid scouting

SPECS
Payload from LEO: up to 180kg to Lunar orbit
Payload from GTO: up to 250kg to Mars orbit
∆V: up to 6km/sec
Propulsion: water plasma-powered Ardor™
Specific impulse: 700 sec
Solar power: 2-3kW

FERVORIDE™ sometime after 2021 a reusable system

Boosting of large satellites from LEO to GEO
Moon exploration resupply
Deep space missions
Asteroid mining infrastructure

SPECS
Payload: over 10,000kg to GEO
∆V: up to 8km/sec
Reusable
Propulsion: water plasma-powered Fervor™
Specific impulse: 900 sec
Solar power: over 10kW

VALORIDE™ is the goal of a large 100 ton system

Water delivery from asteroids to cis-lunar space
Water bunkering
Deployment of asteroid mining infrastructure
Moon and Mars exploitation resupply
SPECS
Payload: over 100tn
Reusable
Propulsion: water plasma-powered Valor™
Specific impulse: 1100 sec
Solar power: over 100kW

166 thoughts on “Momentus Plasma Water Propulsion Will Be Two to Three Times Better Than Chemical Rockets”

  1. Regenerative braking.

    At the axis of the tether, make it a ring. A trough with a mass “rolling” around within. Think of a mag-lev train.

    When a load is taken on, the tether slows, but the mass continues forward in the trough. Coils in the trough use magnetic fields to drag down the forward momentum of the mass, re-imparting it into the tether.

    Solar can be used to spin the mass up in between loads; to “top it off”.

    All electric, no fuel.

  2. Hi Michael. Of course you’d only do it to bank propellant for refueling Space Tugs, not as part of an inflight propulsion system. Low-Power plasma propulsion is a commitment to taking 180 days or so to deliver to GEO, while soaking up Van Allen Belt radiation the whole trip. While there are Comm-Sats that can self-power to GEO from LEO, it’s not recommended and means tying up expensive equipment for no good reason if there’s an alternative high-thrust system available.

  3. On-orbit electrolysis, but not just-in-time electrolysis. You’d spend more energy splitting the water than you’d get back burning the hydrolox, so if you have the sort of power to split enough water just-in-time to get high thrust, you’re better off just using a high power high thrust plasma rocket.

    Otherwise, you’d be using low power over an extended period of time, and storing the hydrolox for when you need it. In which case, the low power plasma rocket may be more appealing after all, or if not, you may consider throwing carbon into the mix to make methalox. It’s easier to store than hydrolox, and you need pretty much the same equipment to make it.

    Speaking of carbon, a methane or CO/CO2 plasma rocket might work nicely too.

  4. Nice start there GG. What the Water Rocket headline about x2-x3 efficiency doesn’t tell you is that low thrust trajectories have higher delta-vees too. Basically the Oberth Maneuver can’t be used, so inter-orbital transfer means the rocket does work against gravity the whole journey. From LEO to escape, for example, the delta-vee is 7.75 km/s vs 3.3 km/s for a single high-thrust impulse.

  5. I object: Historically, radioactive spider bits and bat costumed vigilantes have been solutions, not problems.

  6. “the supply IS finite” – true, in the sense that the Sun is finite. Short term (this side of a thousand years), I don’t see a way around the rocket equation, other than light sails, laser propulsion, etc. That is, unless we get some new physics – a fairly high probability, given we can only find 5% of the Universe.

  7. You can still get by with a very high ISP, low acceleration propulsion system. You just need more of it as the traffic increases, scaled to the traffic. The real question is whether it’s an economic ratio.

    The system still allows your rotovator to supply brief high g acceleration using low acceleration systems.

    Kind of like renting moving vans, where when there’s an imbalance they just offer really cheap rentals in the opposite direction of the prevailing traffic, the rotovator operator would adjust the incoming and outgoing charges to encourage traffic to balance. Sure, we’d end up importing a lot of asteroidal steel due to the really low shipping rates…

  8. I think they’re just being vague, in the hope that people will fill in the holes for them, each according to their own preference.

  9. If the rotovator is only used for brief periods, it probably won’t be economically viable. You’d want to use it to a good fraction of as much as physically possible (aka of max capacity). Same as any expensive infrastructure.

  10. No, it’s a real problem. I read a comic once where the Earth ran out of water and it was a real problem.
    The Oceans running out of water is an urgent a problem as mutant Kangaroo insurgents, radioactive spider bites, evil government conspiracies to conceal alien contact, Bat costumed vigilantes and every other major issue that comic books bring up.

  11. They are very vague and confusing when talking about the advantages of their drive over competitors, but what I THINK they meant was:
    Our typical (2018 or projected near future) ion drives run on materials like argon or other noble gases, which means that storing the fuel requires a pressurized gas tank. This means that on your space probe only a small % of the propulsion system mass can be the actual propellant. However, water is dead easy to store. It is trivial to have a big water tank that would let you have say 50% of the propulsion system mass as useable water propellant, for the same probe size as would have 2 or 5% of propulsion system mass as stored argon propellant.
    Hence, although an ion drive might give more impulse per kg of propellant, the water plasma drive will give more impulse per kg of propulsion system. Which is what you actually have to pay for.

  12. PS: at the low end — 500 watts and ISP 700, you’re talking 0.014 newtons. For a 315 kg spacecraft, that turns into 0.000045 m/s² or 338 km/day² … GoatGuy

  13. If you want a real improvement, you don’t start with water. You start with rocket fuel, and *end* with water. That way the microwaves are added on top of the chemical energy; You’ve got a sort of microwave “afterburner” for the chemical engine. Should work just fine with methane/O2, not just H2/O2; Sure, the CO2 won’t absorb the microwaves, but the water still will, and heat the CO2.

  14. Over at Centauri Dreams, they’ve proposed using the water generated by crew after consuming food as reaction mass.

  15. Mmm… overcomplicated. H₂O has a few VERY well defined microwave absorption bands of high efficiency. Merely heating water to vapor, sending it thru a microwave-transparent ceramic plasma heating chamber, blasting it with appropriate wavelength microwaves, heating to perhaps 5,000° to 6,500° K, letting it escape through a magnetically shielded expansion cone… extracts the most kinetic energy from the process.

    Problem is, that while the ISP is high, as is impossible to overcome, the energy-per-thrust is also pretty high.

    P = 50 ISP² Δm/ΔT approximately.
    P = 50 × 700² × 0.00002 kg/s (20 milligram/sec)
    P = 472 W

    If 60% of the mass of the probe is water, at ISP 700, the ΔV is 6.2 km/s, and in particular it takes 122 days to use up the water fuel. Acceleration is abysmally low of course — a mere 0.00004 m/s² (300 km/day²), but over those 122 days, it builds up. Gradual. Further, over the 122 days, the probe will have travelled 0.022 AU (astronomical units).

    Anyway.
    Calculating away.
    GoatGuy

  16. The law of gravity already takes care of that. If you can find water somewhere outside of earth’s gravity well it will be cheaper to use that for propellant than to move water from earth’s surface a long way uphill.

  17. we need laws to regulate how much water people
    can use from earth for propulsion.if earths water content gets below a certain level people with spaceships would not be able to take any more.i prefer they mine asteroids planetoids and moons for water.

  18. If I were trying to make a low thrust, high ISP rocket using water for reaction mass. I’d pressurize water well above it’s critical pressure, preheat it in a steel tube to somewhere around it’s critical temperature with a resistance heater, heat it to the highest temperature the material would take in a secondary boiler made of an electrically nonconductive material like silicon nitride with microwaves, and then expand it through an electrically non conductive nozzle, where it would be irradiated with microwaves. or an infrared laser during expansion. I’d try to come up with a scheme so that the expansion would take place within an optical resonant cavity. Perhaps a copper jacket, completely surrounding a silicon nitride nozzle except for an exit hole for the reaction mass.

  19. Not much 2-way traffic today but if there is going to be humans beyond LEO, it’s reasonable to plan for them returning to earth. Asteroid mining of metals and volatiles will be a big thing and the mass needs to be hauled down to consumers both in orbit and on the surface of the moon, Earth and Mars. People, supplies, electronics, robots and advanced equipment will be going up.

    Fuel is still by far the biggest cargo so logically, this is the first thing that will be mined outside Earth. Having a tug-boat or rotavator delta-V service from LEO and to beyond will result in a very big boost of usable payload from Earth. Not having to bring fuel for anything beyond launch to LEO will give us a much higher payload fraction and reduce costs. Second stages can be refueled in LEO and do propulsive landing. Or a rotavator can extract the kinetic energy and deorbit at velocities that makes reuse possible.

    Rotavators can be staged so each one does not have to be huge. I don’t know what would be a realistic dimensioning of a rotavator for the transition from Earth to LEO. It would be great if if was possible to use a suborbital rocket and let a rotavator add the final delta-V to LEO.

  20. Those larger engines get 900/1000 sec impulse, in vacuum. That handily beats even best future raptors performance of ~380 sec.

    However BFR having swappable engine bays would make it alluring to change up the deep space engines for these. Unfortunately the tank design would get complicated (Methalox + H2O)

  21. This is an interesting perspective, as Orbit Fab is going to be demoing water tanker tech on ISS shortly, with the end goal of an orbital propellant depot service. Then there’s Jon Goff’s recent 3 burn departure paper that gives justification for a propellant depot than can be refueled from upper stage ullage, and provide a start point for reusing/refueling an upper stage for that 3 burn departure.

  22. Estimate the weight of a decently sized spacecraft with say a dozen people, like a SpaceX BFS. What area of solar panels would it take to provide 1 G (or even part of a G) of thrust? I suspect that the spacecraft will be mostly solar panels. My personal preference would be for a ship that isn’t dependent on the sun. That means nuclear (fission or fusion).

  23. Rotavators will win.
    They gain energy when de-orbiting stuff so they need very little energy if there is 2-way traffic.

  24. No, from their website – “(ISP) Faster than electrical power provided by ion propulsion due to higher thrust for the same size solar panel.”
    This approach focuses on the initial key to space expansion, H20 (fuel, air, shielding & life support). It’s simple, efficient & scaleable (helped exponentially by zero g).

    I like it.

  25. I assume this is being water is being “energized” by using a nuclear reactor’s heat. Yes? This is not something that will launch from Earth. It will be built and used in space. Sure, they could have that up and running in 20 years or so. You just need the infrastructure and some nuclear fuel.

  26. Thinking about it, better to have four equally spaced masses to keep the center of the tether system from wobbling around.

    Too, it would be more efficient to keep pushing the masses around the trough, like roller coaster cars on a closed loop-the-loop, moving in the opposite direction as the tethers rotation, speeding them up when necessary to compensate for the momentum lost when snagging a load.

  27. Forgot to add, if you can electrolyse H2/O2 and chill them to liquid form, you have all the gear (and power) needed for zero boiloff tankage. Space storable is an issue for spacecraft fuel tanks, not for propellant making storage depots.

  28. That latter aspirational application of the concept (which is *just* a helicon thruster using water propellant, thus a ‘Water Rocket’) is interesting. Water delivery to orbital depots via Water Rockets makes a lot of sense. On-Orbit Electrolysis can then split the water into H2/O2 for high-thrust chemical propulsion Space-Tugs to haul CommSat payloads to GEO delivery – cutting out the multi-month transfer time for a Water Rocket. For interplanetary crewed missions, high thrust chemical propulsion is needed for Earth escape. Once out of Earth’s Sphere of Influence then switching to helicon thrusters would be quite effective. Aerocapture into Mars or Titan orbit would then be indicated, to minimise the gee-losses climbing into and out of gravity-wells. Braking into Ceres orbit via helicon thruster would beat chemical propulsion due to Ceres’ inclined and elliptical orbit. NEA missions would be Water Rocket missions too.

  29. VASIMR isn’t a panacea – it’s an electric rocket too and suffers from the same power-to-mass limitation. Plus the efficiency is lower for lower delta-vee missions like the Water Rocket is intended for, as the ionization energy fraction of the power budget is much higher. Helicon thrusters, like the Water Rocket, are more efficient for these sort of missions.

  30. I’m not a watermelon by any means, but the idea of wasting 90% plus of the volatiles you’re shipping still irks me. They’re in large supply, but we’re going to be inhabiting this solar system for a long time yet, and the supply IS finite.

  31. One can of course also hook up any of the existing very efficient electric style propulsion systems (ion, mag sail, solar sail, etc) to your rotovator and use it to regain any momentum lost by accelerating a package to higher velocities.
    The slow, but very efficient ion drives can spend days or weeks regaining the momentum lost during the brief periods when the rotorvator is actually used.

    Regular commenter here, Dan Ravensnest, studied rotorvators (and other space launch tech) for Boeing and has written books on the subject. Which I can’t link to with this stupid comment system.

  32. Yes. This.

    Where are the numbers? The diagrams? The schematics?
    Even the people using magic unicorn propulsion still have pages of how it is supposed to work, even if there is vague handwaving at some points.

    But this? The closest thing I could find to any technical detail at ALL was a vague line about the plasma being heated to the same temperature as the surface of the sun. Which is about 6000K.

    Are they using magnetic or electrostatic nozzles? Presumably, (because that’s above the melting point of even Tantalum hafnium carbide (Ta4HfC5) of 4215 K) but I couldn’t find any mention, let alone a sketch.

    Yet they claim they are doing a launch in the first quarter of 2019. Unless they are using the Muslim calendar they must have the probe built and most of the way through final testing by now.

  33. Starting with rocket fuel and ending with water suffers from the problem of fuel storage requiring cryogenic tanks. The use of water has two main advantages
    1. Super easy long term storage under all sorts of conditions in tanks that are basically just the minimum shell to prevent the stuff leaking out. A technology that we have had for literally tens of thousands of years.
    2. You can refuel from just about anywhere in the solar system, without needing to make a rocket fuel factory.

  34. I provided it indirectly. Since

    ⇒ P = 50 ISP² Δm/Δt (mass flow rate, kg/s) and inverting:
    ⇒ Δm/ΔT = P / ( 50 ISP² )

    ⇒ F = ISP Δm/Δt … so substitute in
    ⇒ F = ISP P / ( 50 ISP² )
    … F = P / (50 ISP)

    You just substitute in P (variously 500 watts, 900 watts, 3.5 kW, 10 kW, 100 kW per article) and the respective ISP ratings projections (700, 700, 900, 1100, 1300…) and come up with actual expected thrust. Of course, you need to derate for coupling efficiency from power-in all the way to exhaust-out, which I wouldn’t expect to be better than 50%. more likely 35% or less.

    Still, there you go.
    Math self-help.

    Just saying,
    GoatGuy

  35. Start & end “with thin film mirrors” for the lowest mass, simplest, “Solar Furnace” spacecraft (except for Electronics, Comms, Humans/AI, etc). Add rocket & fuel (which could be almost anything). Get to your chosen NEO & start making water. Return to Lunar orbit & sell.

  36. For anything but a poor man’s ion engine, you’d do better to use a vasimr design. One thing that intrigues me, is the idea of storing reaction mass as ice, and using it as shielding around electronics, or biologics. That, and harvesting reaction mass during exploration. If you could come up with a design that could use somewhat dirty water, you could explore the outer solar system on the cheap.

  37. *In theory*, (In theory theory is the same as practice, but in practice it isn’t.) solar panels built to be in near zero G vacuum, and ONLY near zero G vacuum, could be enormously lighter for their power output than current solar panels used in space, because most of the weight of the latter is still structural.

    Also, you should be able to rely on solar panels out to at least Jupiter orbit, if you supplement them with thin film mirrors to concentrate the light. Which could even be engineered to be frequency selective, and only concentrate the range of wavelengths the panel could efficiently convert.

  38. And if there is a shortage of downwards traffic that results in energy deficit for a chain of rotavators, one could just use any old rock in space as “fuel” for them. Just hook it up at the most outward rotavator and bring it down. All the rotavators will be refueled with potential energy in the process.
    Rocks and gravity are fuel…

  39. Snazzy website, beautiful graphics, fancy names, but I can’t find any links to, you know, *technical details* at their website. Just projected capabilities.

    They’re talking about their technology, but they just got their funding, so, how do they already have the technology?

    In my experience that’s a major flag of a scam, because people working on real technology are excited about the technology, and want to brag about how it works.

    And I’m sad about that, because the basic idea isn’t bad, it’s been kicking around for a long while in the form of, “Let’s take a chemical rocket, and *dump external energy into it!*”

  40. Just a small error. This is not as efficient as ion drives at 700 seconds(ion drive=3300) but it does have more thrust. Great article!

  41. There is power and fuel in low earth orbit to make a tug boat feasible.

    A simple tug boat could be a solar panel and a resistance heater. The cargo pod could carry its own fuel. The tug would grab the cargo pod and boost it into higher orbit or launch it into interplanetary space.

    A more complicated tug would either use a magnetic field to push against the ionized gas in space or to use induction current to push against the earth’s magnetic field.

  42. Why won’t that work for people?
    At an ISP of 1100 sec, using fuel that’s ubiquitous throughout the Solar System, using free, 24/7 energy, that is scaleable (proving difficult w/Hall effect, etc), seems a practical approach. Who else is trying this? Granted, a 1MW nuclear reactor could accelerate efforts; even better a fusion torch.
    But large amounts of ice work well as shielding. Add a space-temperature superconducting magnetic field generator & longer trips might be OK.
    And it will take 20+ years for any of the recent space launch/travel innovations to matter. 😉

  43. Solar? Ok, this isn’t for people then. This is for moving unmanned machines around the solar system. Meh. It will still take 20+ years for this to matter.

  44. How much water do you think they need? Relax buttercup.. the earth isn’t melting nor is it drying up. Education is life.. ignorance is everything else.

  45. Rotavators will win.They gain energy when de-orbiting stuff so they need very little energy if there is 2-way traffic.

  46. There is power and fuel in low earth orbit to make a tug boat feasible. A simple tug boat could be a solar panel and a resistance heater. The cargo pod could carry its own fuel. The tug would grab the cargo pod and boost it into higher orbit or launch it into interplanetary space. A more complicated tug would either use a magnetic field to push against the ionized gas in space or to use induction current to push against the earth’s magnetic field.

  47. I assume this is being water is being “energized” by using a nuclear reactor’s heat. Yes? This is not something that will launch from Earth. It will be built and used in space. Sure, they could have that up and running in 20 years or so. You just need the infrastructure and some nuclear fuel.

  48. Those larger engines get 900/1000 sec impulse, in vacuum. That handily beats even best future raptors performance of ~380 sec. However BFR having swappable engine bays would make it alluring to change up the deep space engines for these. Unfortunately the tank design would get complicated (Methalox + H2O)

  49. Just a small error. This is not as efficient as ion drives at 700 seconds(ion drive=3300) but it does have more thrust. Great article!

  50. This is an interesting perspective, as Orbit Fab is going to be demoing water tanker tech on ISS shortly, with the end goal of an orbital propellant depot service. Then there’s Jon Goff’s recent 3 burn departure paper that gives justification for a propellant depot than can be refueled from upper stage ullage, and provide a start point for reusing/refueling an upper stage for that 3 burn departure.

  51. we need laws to regulate how much water peoplecan use from earth for propulsion.if earths water content gets below a certain level people with spaceships would not be able to take any more.i prefer they mine asteroids planetoids and moons for water.

  52. If I were trying to make a low thrust, high ISP rocket using water for reaction mass. I’d pressurize water well above it’s critical pressure, preheat it in a steel tube to somewhere around it’s critical temperature with a resistance heater, heat it to the highest temperature the material would take in a secondary boiler made of an electrically nonconductive material like silicon nitride with microwaves, and then expand it through an electrically non conductive nozzle, where it would be irradiated with microwaves. or an infrared laser during expansion. I’d try to come up with a scheme so that the expansion would take place within an optical resonant cavity. Perhaps a copper jacket, completely surrounding a silicon nitride nozzle except for an exit hole for the reaction mass.

  53. Snazzy website, beautiful graphics, fancy names, but I can’t find any links to, you know, *technical details* at their website. Just projected capabilities.They’re talking about their technology, but they just got their funding, so, how do they already have the technology?In my experience that’s a major flag of a scam, because people working on real technology are excited about the technology, and want to brag about how it works.And I’m sad about that, because the basic idea isn’t bad, it’s been kicking around for a long while in the form of, “Let’s take a chemical rocket, and *dump external energy into it!*”

  54. Thinking about it, better to have four equally spaced masses to keep the center of the tether system from wobbling around.

    Too, it would be more efficient to keep pushing the masses around the trough, like roller coaster cars on a closed loop-the-loop, moving in the opposite direction as the tethers rotation, speeding them up when necessary to compensate for the momentum lost when snagging a load.

  55. Regenerative braking.

    At the axis of the tether, make it a ring. A trough with a mass “rolling” around within. Think of a mag-lev train.

    When a load is taken on, the tether slows, but the mass continues forward in the trough. Coils in the trough use magnetic fields to drag down the forward momentum of the mass, re-imparting it into the tether.

    Solar can be used to spin the mass up in between loads; to “top it off”.

    All electric, no fuel.

  56. Forgot to add, if you can electrolyse H2/O2 and chill them to liquid form, you have all the gear (and power) needed for zero boiloff tankage. Space storable is an issue for spacecraft fuel tanks, not for propellant making storage depots.

  57. Hi Michael. Of course you’d only do it to bank propellant for refueling Space Tugs, not as part of an inflight propulsion system. Low-Power plasma propulsion is a commitment to taking 180 days or so to deliver to GEO, while soaking up Van Allen Belt radiation the whole trip. While there are Comm-Sats that can self-power to GEO from LEO, it’s not recommended and means tying up expensive equipment for no good reason if there’s an alternative high-thrust system available.

  58. On-orbit electrolysis, but not just-in-time electrolysis. You’d spend more energy splitting the water than you’d get back burning the hydrolox, so if you have the sort of power to split enough water just-in-time to get high thrust, you’re better off just using a high power high thrust plasma rocket.

    Otherwise, you’d be using low power over an extended period of time, and storing the hydrolox for when you need it. In which case, the low power plasma rocket may be more appealing after all, or if not, you may consider throwing carbon into the mix to make methalox. It’s easier to store than hydrolox, and you need pretty much the same equipment to make it.

    Speaking of carbon, a methane or CO/CO2 plasma rocket might work nicely too.

  59. That latter aspirational application of the concept (which is *just* a helicon thruster using water propellant, thus a ‘Water Rocket’) is interesting. Water delivery to orbital depots via Water Rockets makes a lot of sense. On-Orbit Electrolysis can then split the water into H2/O2 for high-thrust chemical propulsion Space-Tugs to haul CommSat payloads to GEO delivery – cutting out the multi-month transfer time for a Water Rocket. For interplanetary crewed missions, high thrust chemical propulsion is needed for Earth escape. Once out of Earth’s Sphere of Influence then switching to helicon thrusters would be quite effective. Aerocapture into Mars or Titan orbit would then be indicated, to minimise the gee-losses climbing into and out of gravity-wells. Braking into Ceres orbit via helicon thruster would beat chemical propulsion due to Ceres’ inclined and elliptical orbit. NEA missions would be Water Rocket missions too.

  60. VASIMR isn’t a panacea – it’s an electric rocket too and suffers from the same power-to-mass limitation. Plus the efficiency is lower for lower delta-vee missions like the Water Rocket is intended for, as the ionization energy fraction of the power budget is much higher. Helicon thrusters, like the Water Rocket, are more efficient for these sort of missions.

  61. Nice start there GG. What the Water Rocket headline about x2-x3 efficiency doesn’t tell you is that low thrust trajectories have higher delta-vees too. Basically the Oberth Maneuver can’t be used, so inter-orbital transfer means the rocket does work against gravity the whole journey. From LEO to escape, for example, the delta-vee is 7.75 km/s vs 3.3 km/s for a single high-thrust impulse.

  62. “the supply IS finite” – true, in the sense that the Sun is finite. Short term (this side of a thousand years), I don’t see a way around the rocket equation, other than light sails, laser propulsion, etc. That is, unless we get some new physics – a fairly high probability, given we can only find 5% of the Universe.

  63. I’m not a watermelon by any means, but the idea of wasting 90% plus of the volatiles you’re shipping still irks me. They’re in large supply, but we’re going to be inhabiting this solar system for a long time yet, and the supply IS finite.

  64. You can still get by with a very high ISP, low acceleration propulsion system. You just need more of it as the traffic increases, scaled to the traffic. The real question is whether it’s an economic ratio.

    The system still allows your rotovator to supply brief high g acceleration using low acceleration systems.

    Kind of like renting moving vans, where when there’s an imbalance they just offer really cheap rentals in the opposite direction of the prevailing traffic, the rotovator operator would adjust the incoming and outgoing charges to encourage traffic to balance. Sure, we’d end up importing a lot of asteroidal steel due to the really low shipping rates…

  65. If the rotovator is only used for brief periods, it probably won’t be economically viable. You’d want to use it to a good fraction of as much as physically possible (aka of max capacity). Same as any expensive infrastructure.

  66. No, it’s a real problem. I read a comic once where the Earth ran out of water and it was a real problem.
    The Oceans running out of water is an urgent a problem as mutant Kangaroo insurgents, radioactive spider bites, evil government conspiracies to conceal alien contact, Bat costumed vigilantes and every other major issue that comic books bring up.

  67. One can of course also hook up any of the existing very efficient electric style propulsion systems (ion, mag sail, solar sail, etc) to your rotovator and use it to regain any momentum lost by accelerating a package to higher velocities.
    The slow, but very efficient ion drives can spend days or weeks regaining the momentum lost during the brief periods when the rotorvator is actually used.

    Regular commenter here, Dan Ravensnest, studied rotorvators (and other space launch tech) for Boeing and has written books on the subject. Which I can’t link to with this stupid comment system.

  68. They are very vague and confusing when talking about the advantages of their drive over competitors, but what I THINK they meant was:
    Our typical (2018 or projected near future) ion drives run on materials like argon or other noble gases, which means that storing the fuel requires a pressurized gas tank. This means that on your space probe only a small % of the propulsion system mass can be the actual propellant. However, water is dead easy to store. It is trivial to have a big water tank that would let you have say 50% of the propulsion system mass as useable water propellant, for the same probe size as would have 2 or 5% of propulsion system mass as stored argon propellant.
    Hence, although an ion drive might give more impulse per kg of propellant, the water plasma drive will give more impulse per kg of propulsion system. Which is what you actually have to pay for.

  69. Yes. This.

    Where are the numbers? The diagrams? The schematics?
    Even the people using magic unicorn propulsion still have pages of how it is supposed to work, even if there is vague handwaving at some points.

    But this? The closest thing I could find to any technical detail at ALL was a vague line about the plasma being heated to the same temperature as the surface of the sun. Which is about 6000K.

    Are they using magnetic or electrostatic nozzles? Presumably, (because that’s above the melting point of even Tantalum hafnium carbide (Ta4HfC5) of 4215 K) but I couldn’t find any mention, let alone a sketch.

    Yet they claim they are doing a launch in the first quarter of 2019. Unless they are using the Muslim calendar they must have the probe built and most of the way through final testing by now.

  70. Starting with rocket fuel and ending with water suffers from the problem of fuel storage requiring cryogenic tanks. The use of water has two main advantages
    1. Super easy long term storage under all sorts of conditions in tanks that are basically just the minimum shell to prevent the stuff leaking out. A technology that we have had for literally tens of thousands of years.
    2. You can refuel from just about anywhere in the solar system, without needing to make a rocket fuel factory.

  71. we need laws to regulate how much water peoplecan use from earth for propulsion.if earths water content gets below a certain level people with spaceships would not be able to take any more.i prefer they mine asteroids planetoids and moons for water.

  72. PS: at the low end — 500 watts and ISP 700, you’re talking 0.014 newtons. For a 315 kg spacecraft, that turns into 0.000045 m/s² or 338 km/day² … GoatGuy

  73. I provided it indirectly. Since

    ⇒ P = 50 ISP² Δm/Δt (mass flow rate, kg/s) and inverting:
    ⇒ Δm/ΔT = P / ( 50 ISP² )

    ⇒ F = ISP Δm/Δt … so substitute in
    ⇒ F = ISP P / ( 50 ISP² )
    … F = P / (50 ISP)

    You just substitute in P (variously 500 watts, 900 watts, 3.5 kW, 10 kW, 100 kW per article) and the respective ISP ratings projections (700, 700, 900, 1100, 1300…) and come up with actual expected thrust. Of course, you need to derate for coupling efficiency from power-in all the way to exhaust-out, which I wouldn’t expect to be better than 50%. more likely 35% or less.

    Still, there you go.
    Math self-help.

    Just saying,
    GoatGuy

  74. Start & end “with thin film mirrors” for the lowest mass, simplest, “Solar Furnace” spacecraft (except for Electronics, Comms, Humans/AI, etc). Add rocket & fuel (which could be almost anything). Get to your chosen NEO & start making water. Return to Lunar orbit & sell.

  75. If I were trying to make a low thrust, high ISP rocket using water for reaction mass. I’d pressurize water well above it’s critical pressure, preheat it in a steel tube to somewhere around it’s critical temperature with a resistance heater, heat it to the highest temperature the material would take in a secondary boiler made of an electrically nonconductive material like silicon nitride with microwaves, and then expand it through an electrically non conductive nozzle, where it would be irradiated with microwaves. or an infrared laser during expansion. I’d try to come up with a scheme so that the expansion would take place within an optical resonant cavity. Perhaps a copper jacket, completely surrounding a silicon nitride nozzle except for an exit hole for the reaction mass.

  76. If you want a real improvement, you don’t start with water. You start with rocket fuel, and *end* with water. That way the microwaves are added on top of the chemical energy; You’ve got a sort of microwave “afterburner” for the chemical engine. Should work just fine with methane/O2, not just H2/O2; Sure, the CO2 won’t absorb the microwaves, but the water still will, and heat the CO2.

  77. *In theory*, (In theory theory is the same as practice, but in practice it isn’t.) solar panels built to be in near zero G vacuum, and ONLY near zero G vacuum, could be enormously lighter for their power output than current solar panels used in space, because most of the weight of the latter is still structural.Also, you should be able to rely on solar panels out to at least Jupiter orbit, if you supplement them with thin film mirrors to concentrate the light. Which could even be engineered to be frequency selective, and only concentrate the range of wavelengths the panel could efficiently convert.

  78. And if there is a shortage of downwards traffic that results in energy deficit for a chain of rotavators, one could just use any old rock in space as “fuel” for them. Just hook it up at the most outward rotavator and bring it down. All the rotavators will be refueled with potential energy in the process.Rocks and gravity are fuel…

  79. Snazzy website, beautiful graphics, fancy names, but I can’t find any links to, you know, *technical details* at their website. Just projected capabilities.They’re talking about their technology, but they just got their funding, so, how do they already have the technology?In my experience that’s a major flag of a scam, because people working on real technology are excited about the technology, and want to brag about how it works.And I’m sad about that, because the basic idea isn’t bad, it’s been kicking around for a long while in the form of, “Let’s take a chemical rocket, and *dump external energy into it!*”

  80. Not much 2-way traffic today but if there is going to be humans beyond LEO, it’s reasonable to plan for them returning to earth. Asteroid mining of metals and volatiles will be a big thing and the mass needs to be hauled down to consumers both in orbit and on the surface of the moon, Earth and Mars. People, supplies, electronics, robots and advanced equipment will be going up.Fuel is still by far the biggest cargo so logically, this is the first thing that will be mined outside Earth. Having a tug-boat or rotavator delta-V service from LEO and to beyond will result in a very big boost of usable payload from Earth. Not having to bring fuel for anything beyond launch to LEO will give us a much higher payload fraction and reduce costs. Second stages can be refueled in LEO and do propulsive landing. Or a rotavator can extract the kinetic energy and deorbit at velocities that makes reuse possible.Rotavators can be staged so each one does not have to be huge. I don’t know what would be a realistic dimensioning of a rotavator for the transition from Earth to LEO. It would be great if if was possible to use a suborbital rocket and let a rotavator add the final delta-V to LEO.

  81. For anything but a poor man’s ion engine, you’d do better to use a vasimr design. One thing that intrigues me, is the idea of storing reaction mass as ice, and using it as shielding around electronics, or biologics. That, and harvesting reaction mass during exploration. If you could come up with a design that could use somewhat dirty water, you could explore the outer solar system on the cheap.

  82. Mmm… overcomplicated. H₂O has a few VERY well defined microwave absorption bands of high efficiency. Merely heating water to vapor, sending it thru a microwave-transparent ceramic plasma heating chamber, blasting it with appropriate wavelength microwaves, heating to perhaps 5,000° to 6,500° K, letting it escape through a magnetically shielded expansion cone… extracts the most kinetic energy from the process.

    Problem is, that while the ISP is high, as is impossible to overcome, the energy-per-thrust is also pretty high.

    P = 50 ISP² Δm/ΔT approximately.
    P = 50 × 700² × 0.00002 kg/s (20 milligram/sec)
    P = 472 W

    If 60% of the mass of the probe is water, at ISP 700, the ΔV is 6.2 km/s, and in particular it takes 122 days to use up the water fuel. Acceleration is abysmally low of course — a mere 0.00004 m/s² (300 km/day²), but over those 122 days, it builds up. Gradual. Further, over the 122 days, the probe will have travelled 0.022 AU (astronomical units).

    Anyway.
    Calculating away.
    GoatGuy

  83. The law of gravity already takes care of that. If you can find water somewhere outside of earth’s gravity well it will be cheaper to use that for propellant than to move water from earth’s surface a long way uphill.

  84. we need laws to regulate how much water people
    can use from earth for propulsion.if earths water content gets below a certain level people with spaceships would not be able to take any more.i prefer they mine asteroids planetoids and moons for water.

  85. If I were trying to make a low thrust, high ISP rocket using water for reaction mass. I’d pressurize water well above it’s critical pressure, preheat it in a steel tube to somewhere around it’s critical temperature with a resistance heater, heat it to the highest temperature the material would take in a secondary boiler made of an electrically nonconductive material like silicon nitride with microwaves, and then expand it through an electrically non conductive nozzle, where it would be irradiated with microwaves. or an infrared laser during expansion. I’d try to come up with a scheme so that the expansion would take place within an optical resonant cavity. Perhaps a copper jacket, completely surrounding a silicon nitride nozzle except for an exit hole for the reaction mass.

  86. Those larger engines get 900/1000 sec impulse, in vacuum. That handily beats even best future raptors performance of ~380 sec. However BFR having swappable engine bays would make it alluring to change up the deep space engines for these. Unfortunately the tank design would get complicated (Methalox + H2O)

  87. Just a small error. This is not as efficient as ion drives at 700 seconds(ion drive=3300) but it does have more thrust. Great article!

  88. *In theory*, (In theory theory is the same as practice, but in practice it isn’t.) solar panels built to be in near zero G vacuum, and ONLY near zero G vacuum, could be enormously lighter for their power output than current solar panels used in space, because most of the weight of the latter is still structural.

    Also, you should be able to rely on solar panels out to at least Jupiter orbit, if you supplement them with thin film mirrors to concentrate the light. Which could even be engineered to be frequency selective, and only concentrate the range of wavelengths the panel could efficiently convert.

  89. And if there is a shortage of downwards traffic that results in energy deficit for a chain of rotavators, one could just use any old rock in space as “fuel” for them. Just hook it up at the most outward rotavator and bring it down. All the rotavators will be refueled with potential energy in the process.
    Rocks and gravity are fuel…

  90. Snazzy website, beautiful graphics, fancy names, but I can’t find any links to, you know, *technical details* at their website. Just projected capabilities.

    They’re talking about their technology, but they just got their funding, so, how do they already have the technology?

    In my experience that’s a major flag of a scam, because people working on real technology are excited about the technology, and want to brag about how it works.

    And I’m sad about that, because the basic idea isn’t bad, it’s been kicking around for a long while in the form of, “Let’s take a chemical rocket, and *dump external energy into it!*”

  91. Not much 2-way traffic today but if there is going to be humans beyond LEO, it’s reasonable to plan for them returning to earth. Asteroid mining of metals and volatiles will be a big thing and the mass needs to be hauled down to consumers both in orbit and on the surface of the moon, Earth and Mars. People, supplies, electronics, robots and advanced equipment will be going up.

    Fuel is still by far the biggest cargo so logically, this is the first thing that will be mined outside Earth. Having a tug-boat or rotavator delta-V service from LEO and to beyond will result in a very big boost of usable payload from Earth. Not having to bring fuel for anything beyond launch to LEO will give us a much higher payload fraction and reduce costs. Second stages can be refueled in LEO and do propulsive landing. Or a rotavator can extract the kinetic energy and deorbit at velocities that makes reuse possible.

    Rotavators can be staged so each one does not have to be huge. I don’t know what would be a realistic dimensioning of a rotavator for the transition from Earth to LEO. It would be great if if was possible to use a suborbital rocket and let a rotavator add the final delta-V to LEO.

  92. This is an interesting perspective, as Orbit Fab is going to be demoing water tanker tech on ISS shortly, with the end goal of an orbital propellant depot service. Then there’s Jon Goff’s recent 3 burn departure paper that gives justification for a propellant depot than can be refueled from upper stage ullage, and provide a start point for reusing/refueling an upper stage for that 3 burn departure.

  93. Estimate the weight of a decently sized spacecraft with say a dozen people, like a SpaceX BFS. What area of solar panels would it take to provide 1 G (or even part of a G) of thrust? I suspect that the spacecraft will be mostly solar panels. My personal preference would be for a ship that isn’t dependent on the sun. That means nuclear (fission or fusion).

  94. Rotavators will win.They gain energy when de-orbiting stuff so they need very little energy if there is 2-way traffic.

  95. There is power and fuel in low earth orbit to make a tug boat feasible. A simple tug boat could be a solar panel and a resistance heater. The cargo pod could carry its own fuel. The tug would grab the cargo pod and boost it into higher orbit or launch it into interplanetary space. A more complicated tug would either use a magnetic field to push against the ionized gas in space or to use induction current to push against the earth’s magnetic field.

  96. Why won’t that work for people?At an ISP of 1100 sec, using fuel that’s ubiquitous throughout the Solar System, using free, 24/7 energy, that is scaleable (proving difficult w/Hall effect, etc), seems a practical approach. Who else is trying this? Granted, a 1MW nuclear reactor could accelerate efforts; even better a fusion torch.But large amounts of ice work well as shielding. Add a space-temperature superconducting magnetic field generator & longer trips might be OK.And it will take 20+ years for any of the recent space launch/travel innovations to matter. 😉

  97. Solar? Ok, this isn’t for people then. This is for moving unmanned machines around the solar system. Meh. It will still take 20+ years for this to matter.

  98. No, from their website – “(ISP) Faster than electrical power provided by ion propulsion due to higher thrust for the same size solar panel.”This approach focuses on the initial key to space expansion, H20 (fuel, air, shielding & life support). It’s simple, efficient & scaleable (helped exponentially by zero g).I like it.

  99. I assume this is being water is being “energized” by using a nuclear reactor’s heat. Yes? This is not something that will launch from Earth. It will be built and used in space. Sure, they could have that up and running in 20 years or so. You just need the infrastructure and some nuclear fuel.

  100. Those larger engines get 900/1000 sec impulse, in vacuum. That handily beats even best future raptors performance of ~380 sec.

    However BFR having swappable engine bays would make it alluring to change up the deep space engines for these. Unfortunately the tank design would get complicated (Methalox + H2O)

  101. How much water do you think they need? Relax buttercup.. the earth isn’t melting nor is it drying up. Education is life.. ignorance is everything else.

  102. This is an interesting perspective, as Orbit Fab is going to be demoing water tanker tech on ISS shortly, with the end goal of an orbital propellant depot service. Then there’s Jon Goff’s recent 3 burn departure paper that gives justification for a propellant depot than can be refueled from upper stage ullage, and provide a start point for reusing/refueling an upper stage for that 3 burn departure.

  103. Estimate the weight of a decently sized spacecraft with say a dozen people, like a SpaceX BFS. What area of solar panels would it take to provide 1 G (or even part of a G) of thrust? I suspect that the spacecraft will be mostly solar panels. My personal preference would be for a ship that isn’t dependent on the sun. That means nuclear (fission or fusion).

  104. There is power and fuel in low earth orbit to make a tug boat feasible.

    A simple tug boat could be a solar panel and a resistance heater. The cargo pod could carry its own fuel. The tug would grab the cargo pod and boost it into higher orbit or launch it into interplanetary space.

    A more complicated tug would either use a magnetic field to push against the ionized gas in space or to use induction current to push against the earth’s magnetic field.

  105. Why won’t that work for people?
    At an ISP of 1100 sec, using fuel that’s ubiquitous throughout the Solar System, using free, 24/7 energy, that is scaleable (proving difficult w/Hall effect, etc), seems a practical approach. Who else is trying this? Granted, a 1MW nuclear reactor could accelerate efforts; even better a fusion torch.
    But large amounts of ice work well as shielding. Add a space-temperature superconducting magnetic field generator & longer trips might be OK.
    And it will take 20+ years for any of the recent space launch/travel innovations to matter. 😉

  106. No, from their website – “(ISP) Faster than electrical power provided by ion propulsion due to higher thrust for the same size solar panel.”
    This approach focuses on the initial key to space expansion, H20 (fuel, air, shielding & life support). It’s simple, efficient & scaleable (helped exponentially by zero g).

    I like it.

  107. I assume this is being water is being “energized” by using a nuclear reactor’s heat. Yes? This is not something that will launch from Earth. It will be built and used in space. Sure, they could have that up and running in 20 years or so. You just need the infrastructure and some nuclear fuel.

Comments are closed.