
Thruster for Mars mission breaks records - skolos
http://ns.umich.edu/new/releases/25192-thruster-for-mars-mission-breaks-records
======
nickik
The hole of Space exploration is really hindered by the approach to nuclear
power. Many missions that could fly with nuclear batteries don't use them.
Rosetta would have been a far better mission with one.

On a larger scale we should have nuclear reactors in space. If we ever want a
mars colony, nuclear is way, way better then solar. Elon Musk is gone try with
solar but he really doesn't have any other options.

NASA is the one place there can actually be progress on this stuff, no private
company can reasonable attempted this stuff because of regulation. We need
more nuclear batteries, we need small reactors for space and we need nuclear
thermal rockets engines.

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Gravityloss
It's not so easy to make space nuclear power light and reliable. Most likely a
nuclear powered spacecraft with electric thrusters would be a dog.

Nuclear thermal rockets aren't that great either, the temperature and thus the
specific impulse is not very high, and they have high dry mass and would be
really expensive to develop and hard to make reliable.

In space you have 1.3 kW per square meter sun power constantly without the
atmosphere or clouds in the way, and solar cells improve constantly.

~~~
snerbles
At Earth orbit, yes. Recall that the inverse square law applies for light
emitted by the sun.

On Mars, solar power per square meter is a bit over 550W.

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redcalx
That number sounds high. I make it about 300W for Earth.

[http://heliosphan.org/solarenergy.html](http://heliosphan.org/solarenergy.html)

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snerbles
I should have clarified - this is raw irradiance, not the power you'd see from
a photovoltaic cell.

~~~
redcalx
Ahh, I forgot that my calc was based on an average for the Earth's surface -
so including high latitudes and day/night. On that basis I figure our numbers
broadly agree.

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Symmetry
Doing the math on this 5.4 netwons in 108 kilowatts would give you a maximum
exhaust velocity of 38 km/s which is in line with what you expect from a Hall
effect thruster. You can get much higher exhaust velocities (and thus more
fuel efficient engines) from gridded ion engine but that requires more power
for a given thrust and the wear on the grid is a concern.

I'm not really sure why it's important that we have big hall thrusters,
though? My impression was that you could just keep adding more of these to a
spacecraft if you needed to.

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sp332
It seems like the bigger ones are more efficient. Looking at the design I
think they nested several hall effect thrusters which could improve focus or
something.

Edit:
[http://pepl.engin.umich.edu/projects/NCHETs.html](http://pepl.engin.umich.edu/projects/NCHETs.html)

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sp332
102kW? How do they plan to provide power for that on a spaceship?

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Symmetry
For Mars probably solar. The ISS's panels provide that much. Any time you're
looking at electric propulsion your power plant is going to be a big fraction
of your vehicle weight.

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sp332
The current prototype weighs 500 pounds (226 kg) so it could just accelerate
itself at 1/400 g. After 100 hours it could be moving at 8,500 m/s but that's
not including cargo or solar panels.

~~~
Someone
The Voyagers do around twice that at the moment.

So, (very much ballpark, and ignoring all additional weight for fuel, etc.),
would that mean this could reach three times their speed in a month, and,
after that, catch up with one of them in 15 years or so?

If so, is it feasible to build one with enough fuel to accelerate for a year
or so?

If so, where’s the billionaire willing to spend a few quid on a machine that
goes out to photograph one of the Voyagers from close up while it zooms by, or
even bring one of them back to earth before the century is over?

~~~
Symmetry
So, getting up to 25.5 km/s with a rocket with an exhaust velocity of 30 km/s
means you need the wet weight to be 2.33 times the dry weight. Last I checked
[1] you can get 77 W/kg with photovoltaics so you need you'll need 1402 kg of
those in addition to the 226 kg of engine for a total of 1626 kg. Round that
up to 2200 kg for structure and tankage and so on for a total we mass of 5126
kg where 2926 kg of that is fuel. You're using that at 5.4/30000=.00018 kg/s
for a total of 16255555 seconds of acceleration or about six months. So six
months instead of one but basically yes.

[1][http://hopefullyintersting.blogspot.com/2015/03/rockets-
elec...](http://hopefullyintersting.blogspot.com/2015/03/rockets-electric-
propulsion.html)

EDIT: Of course, as it accelerates it'll get further away from the sun leading
to less power from the solar panels and a slower acceleration.

~~~
sp332
Xenon is apparently pretty expensive, like $1,200/kg. Just running it for 100
hours at 0.00018 kg/s will cost $76,800 for the propellant. Plus 10,200 kWh of
electricity!

~~~
Symmetry
That's cheap! The launch'll set you back about $100m so another $3.5m for
propellant isn't going to be worth worrying about. At some point we'll be
wanting to start finding more fuel for our rockets at our destinations. There
are ways we know how to do this for oxygen, hydrogen, and methane but getting
more xenon on Mars or Titan just isn't doable. So at that point I expect
people to switch over to Argon which doesn't ionize quite as easily but can be
found all over the solar system.

~~~
sp332
Or we could set up a Xenon distillery at Jupiter, where it's more abundant :)

~~~
Symmetry
I don't envy whoever would have to haul it up _that_ gravity well.

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ctdonath
What's the mass consumption/ejection rate for this thing? What's the power
consumption rate? Wondering if a non-solar power source (batteries, nuclear,
etc) could cannibalize its waste fuel as ejection material.

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zlynx
One of the best things about these thrusters is how they look exactly like a
science fiction space thruster should. This would not look out of place on a
Star Destroyer or a Federation Constitution class cruiser.

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the8472
Isn't corrosion an issue with hall thrusters, especially at high power and
long-duration firings? At least that was one of the selling points of VASIMR
over ion thrusters.

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je42
how does this compare to Space-X Raptor engines ?

~~~
lutorm
Raptor is a conventional chemical rocket engine. The thrust is much higher (of
order 1 million N vs 5N) but the specific impulse is much worse so your
ability to reach speeds is limited by the amount of propellant you need to
carry.

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dang
Url changed from [https://newatlas.com/x3-hall-thruster-test-record-
nasa/51869...](https://newatlas.com/x3-hall-thruster-test-record-nasa/51869/),
which points to this.

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jtchang
Weren't we still unsure how the thruster actually worked? As in where the
thrust was coming from?

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Elv13
No, that's the EM drive. This engine is less or more a particle accelerator
shooting high velocity noble gas. It's like a rocket (less or more), but
instead of using a lot of slow matter, it use a little, but very fast, matter.
It still requires a supply of matter to trow from the back of the spacecraft,
it just uses it in a way to minimize the amount required (by trading it by
silly amount of power).

It's based on the classic `F=m*a` Newtonian second law. But uses high `a`
instead of high `m`.

The Hall and Ion engines just replace chemical energy with electricity.

Edit: Added the `F=ma` part. Edit2: Added that it still requires matter.

~~~
samstave
But you still need to give it a supply of noble gas, correct?

So how many AU per unit of noble gas do you reach at terminal velocity of the
thing?

Also what are the manufacturing limitations for noble supply - given all the
talk about us running out of helium.

Aside: it would be ironic if they had helium balloons at the launch party of
some such rocket...

Finally, what is the state of the noble gas when consumed by this engine in a
full vacuum of space? Is it destroyed into a state that is unrecoverable?

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JumpCrisscross
> _terminal velocity of the thing?_

What?

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samstave
Assume you have a thing: rocket, satellite, probe, etc, and you’re pushing it
to mars or whatever, and you have an engine that, based on the comment states
in consumer noble gasses as fuel, one would assume you have to provide the
noble gas, correct?

So after you falcon9 the thing into orbit, and push it along, and it then uses
this engine to go the distance, will it constantly increase or hit a max
terminal velocity. In either case, would that not tell you how much fuel to
give it; which comes down to “if it is powered by helium and we are supposedly
running out of helium, how much helium would it use vs how much helium is
available?”

Is that not a sound question?

The second part of the question is “if we give it one ton of fuel, how far can
it get?”

Pretty simple MPG question in my mind...

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camiller
There are a lot of variable not accounted for, like the mass of the ship(and
cargo) you are going to attach it to. In theory it can keep accelerating as
long as it has fuel, and the maximum speed would be related to the speed of
the exhaust. At very high velocity we would have to account for friction with
the interstellar medium, space isn't entirely empty just the density is very
(very) low.

In the real world you probably have a destination in mind... and maybe want to
come back. For one way mission, accelerate till half your fuel is gone,
perhaps coast for a bit, then decelerate with the remaining fuel (maybe keep
some reserves for maneuvering).

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samstave
So basically, step two of getting to Mars is to setup interstellar refulling
stations.

Once you get to mars, or any destination, you need fuel to get back/other
things...

So assuming we have an engine that can deliver us back and forth in a
reasonable time, then we need to think about deploying intermediate refueling
drones... and then drones to refill them... and then how to manufacture and
deliver that fuel to the various nodes...

And if we are running out of helium, on earth, we need to find the most
harvestable noble gas we can in the solar system...

What are the atmospheres of the other planets made up of, specifically
Jupiter, how could we slurp off its atmosphere to Bush is around the solar
system?

Assuming other energy sources don’t pan out

~~~
Armisael16
Interstellar refueling stations don't make any real sense because you spend as
much fuel rendezvousing with the refueling station as you'd get back.

