Propelling deep space flight with new fuel source, Momentus prepares for liftoff

Re:Propelling deep space flight with new fuel source, Moment... by Animats on Monday July 23, 2018 @01:47PM (#17594393)

with water as a power source

No, no. Water is just the reaction mass. The power source is solar. This is a steam rocket.

[ Parent | on HN ]

Re:Propelling deep space flight with new fuel source, Moment... by syntaxing on Monday July 23, 2018 @03:26PM (#17595206)

Yup, people do not understand how stable water is (hence the low energy density). Phase change on the other hand, is a extremely effective method to harness work from heat.

[ Parent | on HN ]

Re:Propelling deep space flight with new fuel source, Moment... by Animats on Monday July 23, 2018 @06:52PM (#17596688)

They're going all the way to plasma. The idea is to pump as much energy as possible into small amounts of reaction mass, to maximize momentum while minimizing reaction mass consumption. They can get more energy from solar panels over time, but not more reaction mass.

Remember, not only do rockets need something to push against, you have to bring that something with you.

[ Parent | on HN ]

Re:Propelling deep space flight with new fuel source, Moment... by GW150914 on Monday July 23, 2018 @06:55PM (#17596702)

Remember, not only do rockets need something to push against, you have to bring that something with you.

Rockets do not need to push against anything... they expel reaction mass out one end ensuring an equal and opposite reaction. Hence the term “reaction mass” in the first place. Rockets would work just as well in a vacuum as in atmosphere, but it is true that you have to carry your fuel with you.

Downvote if you must, but Newton’s third law still exists. ;)

[ Parent | on HN ]

Re:Propelling deep space flight with new fuel source, Moment... by lgats on Monday July 23, 2018 @10:35PM (#17597701)

I suppose the rocket is "pushing against" the particles as they are exhausted

[ Parent | on HN ]

Re:Propelling deep space flight with new fuel source, Moment... by outworlder on Monday July 23, 2018 @03:47PM (#17595384)

Yeah, I call water hydrogen ash.

[ Parent | on HN ]

Re:Propelling deep space flight with new fuel source, Moment... by mrfusion on Monday July 23, 2018 @02:57PM (#17594946)

Why use a microwave? Why not just a heating element?

[ Parent | on HN ]

Re:Propelling deep space flight with new fuel source, Moment... by syntaxing on Monday July 23, 2018 @03:22PM (#17595173)

Probably mode of energy transfer. Microwaves are extremely efficient with transferring energy to water since you do not need to have something with higher temperature to produce heat flow. Also, you can heat up a contained area (especially water vapor) easily where as heating elements are limited to surface area (and the heat flow will be extremely low since the mass is low).

[ Parent | on HN ]

Re:Propelling deep space flight with new fuel source, Moment... by sbierwagen on Monday July 23, 2018 @07:01PM (#17596744)

Their Zeal thruster uses a heating element: http://momentus.space/services/

To answer your question, I would guess that a microwave can get the reaction mass hotter than just a resistive heating element, and thus get higher exhaust velocity.

[ Parent | on HN ]