6 ms·
This article is mostly fluff. It doesn't get into any interesting technical details. The core bits are: > Mr. Kokorich, 44, is one such entrepreneur. In 2017 h
by sxp 6y ago
This article is mostly fluff. It doesn't get into any interesting technical details. The core bits are:
> Mr. Kokorich, 44, is one such entrepreneur. In 2017 he founded Momentus, a California-based company that seeks to revolutionize transport in space by developing in-space transfer vehicles that use water as a propellant. These would “complement low-cost gigantic rockets, like Starship from SpaceX and New Glenn from Blue Origin,” he says. Craft built by Momentus would enable the outer-space equivalent of the connecting flight. A satellite would reach orbit by “ride-sharing on a big rocket,” then transfer to a Momentus vehicle for the next leg farther out.
> The choice of water as a propellant, Mr. Kokorich says, would “not only enable extremely low-cost in-space vehicles—built in a ‘Mad Max’ steampunk style—but eventually allow the use of water mined from the moon and from asteroids.”
It would be nice if journalists did some actual investigating and reporting instead of just regurgitating non-technical PR.
I think there's some info at https://momentus.space/ https://momentus.space/ but no interesting technical details.
- y04nn 6y agoFrom https://momentus.space/development/ https://momentus.space/development/ it looks like they are using a microwave generator with water to generate a plasma thruster. The technical name seem to be microwave electro-thermal thruster (MET). There is more info on the thurster in the abstract here: https://ieeexplore.ieee.org/abstract/document/1420619 https://ieeexplore.ieee.org/abstract/document/1420619
- DavidSJ 6y agoSo in a sense it’s a steam engine powering a space ship.
- hnuser123456 6y agoWonder what an effective steam rocket in lower atmosphere would look like.
- tobmlt 6y agoSSME’s? Or does it count if the water started off in separate pieces?
- TheAdamAndChe 6y agoSteam is a gas, meaning the thrust is a function of the pressure. Plasma is made of ions, which can be significantly accelerated by electromagnets, meaning the thrust depends on the acceleration caused by those magnets, and can be a lot higher than steam. (Technically, the thrust generated is more complicated than just pressure, heavily affected by temperature too, but I digress)
- walrus01 6y agoHow does the specific impulse compare to the current state of the art hall effect / ion thrusters that use xenon as a fuel?
- Rebelgecko 6y agoProbably worse. Raw steam has an ISP of around 100s. There was an experimental ion thruster from U Michigan a few years ago that got that up to nearly 700s. Some of the more efficient ion thrusters are like 20,000s (although they're operating at a different scale so idk if that's an apples to apples comparison) Edit- I looked at the Momentus paper linked above and apparently their ISP is 800s
- walrus01 6y agoIt's my understanding that current state of the art very low kN, but high ISP efficiency hall effect/ion grid thrusters can achieve 6000-8000 specific impulse without an absolutely ridiculous amount of electricity. There are designs that have been ground tested but not flown which could achieve 15000-20000 ISP but would also require immense photovoltaic arrays, or a small nuclear reactor. Once in orbit unless you need to achieve a lot of delta-v in a relatively short period of time, I'm not sure why an engine/fuel combo with only 800 ISP would be a logical choice. It's certainly a whole lot more efficient than a bipropellant chemical rocket engine, which maxes out around 385-400 ISP. Although it's never flown I believe the theoretical efficiency of a NERVA would be around 800.
- supernova87a 6y agoI am really surprised that this story got the weekend interview slot of the WSJ, no less.
- callamdelaney 6y agoThere's a Romanian space company trying to make first stage boosters out of super heating water.. https://www.youtube.com/watch?v=WKHI5VXisEc https://www.youtube.com/watch?v=WKHI5VXisEc https://www.youtube.com/watch?v=O50kL6am6U8 https://www.youtube.com/watch?v=O50kL6am6U8
- 7373737373 6y agoOnce in space, does it not make more sense to split water into hydrogen and oxygen using solar energy and use that as fuel?
- callamdelaney 6y agoPerhaps, but the intended purpose of these is to actually help get the payload to space.
- aphextron 6y agoAt that point it would be far more efficient to just skip the electrolysis, fill your spacecraft with xenon, and use the solar power for ion propulsion. No need for an oxidant when you have sufficient electrical power, so a large portion of the water's mass would be dead weight.
- marcosdumay 6y agoWater is certainly cheaper and easier to handle than xenon. But the company's site claims a "3x increase in efficiency" (WTF that is), so I guess they didn't manage to get any high isp.
- simonh 6y agoYou would generate the fuel extremely slowly so would have to wait ages between brief burns for thrust. But why settle for the Isp of a hydrolox engine, when you can have the efficiency of an ion it hall thruster?
- avian 6y agoScott Manley has a video with a more realistic view on this company [1]. [1] https://www.youtube.com/watch?v=qT9HBkWGg7s https://www.youtube.com/watch?v=qT9HBkWGg7s