[blakesterz]

"A massively scaled up version running at 200 MW could make the one-way transit to Mars in as little as 39 days, but generation of this amount of in-space energy isn’t currently anywhere near possible and would require both an advanced onboard nuclear reactor as well as super-efficient heat radiators. "

200 MW is a helluvalotta power! Disappointing to see it's so far off.

[avmich]

If we're talking of this kind of efforts, why not to discuss this - https://toughsf.blogspot.com/2019/10/the-expanses-epstein-dr... . Seems in the realm of physics, with some more impressing results...

[jessaustin]

One would have expected a narrative published in the last decade could have featured a more felicitously named phlebotinum.

[marta_morena_25]

Yeah this sounds cool. Essentially you could design a large spacecraft and put a fusion reactor in it (we will have viable, positive yield reactors soonish). It should be possible then to power a fusion drive as well by building a sort of "half-open" fusion reactor chamber into which we dispense some of the plasma without any pressurization. It should essentially cause a massive explosion, that if somehow controlled by magnetic fields, should yield an enormous forward thrust.

Technically, does it even matter how fast we eject? Shouldn't relativity allow us to reach speed of light with any positive thrust velocity? If the speed of the shuttle was of any concern, that should directly invalidate relativity, since passengers would suddenly not perceive any acceleration anymore, even though nothing about the spaceship and its physical reaction has changed.

[UnpossibleJim]

To my understanding of physics, there is almost no amount of thrust that would actually propel us to the speed of light, in reality. The energy costs alone would simply be too enormous.

"Folding space"/"Warping space", or shrinking the space in front of the craft while expanding the space, would seem to be the only theoretical way to achieve speeds that not only would match light speed but could surpass it and not break the laws of physics as we understand them. The drive Alcubierre proposed in the 80's, I think... maybe the 90's. I'm not sure when. A Spanish mathematician or physicist who was a fan of Star Trek.

EDIT: My understanding of physics is pretty minimal. I'm more than happy for someone to correct me and explain what I got wrong. This type of stuff is fascinating.

[thatcherc]

It's actually that there is no amount of thrust that would propel you to the speed of light - no 'almost' about it.

From the perspective of an outside observer, a constantly-accelerating spaceship will approach the speed of light, but never quite get there. This will happen regardless of the level of thrust.

Alcubierre drives are pretty sweet - the only trick is they seem to require negative mass [0]... at least they've gotten down the requirement from a negative Jupiter mass to a mere -700 kg!

[0] - https://en.wikipedia.org/wiki/Alcubierre_drive#Mass%E2%80%93...

[krastanov]

Alcubierre is a Mexican physicist, not Spanish.

[UnpossibleJim]

Whoops, sorry =/ Like I said, my understanding of this stuff is very surface. Thank you.

[AnimalMuppet]

Even without relativity, the ejection velocity matters. To get the same change in momentum, you need to eject more mass if you have a lower ejection velocity. That means that you have to carry more mass to eject. And that means that, to accelerate that mass, you have to eject more mass. And so on. It just becomes really unworkable really quickly. (This is called the "rocket equation".)

As for the rest of your second paragraph: Look into how relativistic velocity addition works.

[Florin_Andrei]

That's cartoon physics.

[api]

How much thin film PV is that? There's no wind and the solar constant is a lot higher in space even further from the sun.

Also remember that space is not dark. Unless you are behind something you are always in daylight if you are near a star.

[a_crc]

It's a lot of solar panel. A quick search gives us a figure of 220 watts of power per square meter of space based solar panel. This would mean a 200MW solar collector would need to be almost a million square meters in size. For reference that would be a square the length of 155 NYC city blocks on each side.

[SECProto]

> A quick search gives us a figure of 220 watts of power per square meter of space based solar panel. This would mean a 200MW solar collector would need to be almost a million square meters in size. For reference that would be a square the length of 155 NYC city blocks on each side.

200MW/(220w/m2) gives us an area of 1,000,000m^2, a square 1000m on each side.

(side note: a NYC block isn't a very good length reference - they vary[1] from 250ft to 750ft depending which direction you're measuring. So the square would be 4 to 12 blocks on each side)

[1] https://streeteasy.com/blog/how-many-nyc-blocks-are-in-one-m...

[api]

Hmm... or maybe some smaller panels plus a really enormous and very very thin reflective collector for concentrating solar. Keep in mind that things can be very thin in space.

It would still weigh a lot though, and heat would be a major issue. You wouldn't want to melt the solar panels.

This would require someone much more knowledgable to determine if it's feasible.

Edit: I wonder if you'd get some amount of solar sail effect in addition to the plasma rocket? Of course this would help you one way and hurt you the other way.

[codeduck]

A million square metres is one square kilometre. It could be built but it would be heavy. A circular sail with a radius of just over 600 metres would do it.

[chasd00]

wouldn't a million square metered be a megametre and not kilometre?

[codeduck]

no. 1000m * 1000m = 1000000m^2 or 1 km^2

[jcims]

That's if it's illuminated by the sun. Blast it with a 500MW space-based laser and you'll up the tempo.

[adrianN]

On Earth a commercial solar panel produces around 150W per square meter peak. I don't think you can improve this by more than an order of magnitude. Solar power drops off with the square of the distance to the sun. 200MW is a lot of solar panels.

[ben_w]

Not by a factor of ten, but you can get 47.1% of the sunlight (which at 1 AU with no atmosphere is 1360 W/m^2), or 640 W/m^2.

Even then, 200 MW is a square 560 meters on each side.

[Majromax]

The linked article also makes a comparison with the ISS solar arrays, which provide 120kW of power. They're not the most efficient panels out there, but it's hard to make up three orders of magnitude.

[tectonic]

But usage on smaller, uncrewed probes could be much closer.