6 ms·

"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 energ

"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.

tectonic 6y ago
But usage on smaller, uncrewed probes could be much closer.
api 6y ago
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.
- Majromax 6y ago
  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.
- adrianN 6y ago
  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 6y ago
    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.
- a_crc 6y ago
  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.
  - api 6y ago
    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 6y ago
    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 6y ago
      wouldn't a million square metered be a megametre and not kilometre?
      - codeduck 6y ago
        no. 1000m * 1000m = 1000000m^2 or 1 km^2
  - SECProto 6y ago
    > 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-mile/ https://streeteasy.com/blog/how-many-nyc-blocks-are-in-one-m...
avmich 6y ago
If we're talking of this kind of efforts, why not to discuss this - https://toughsf.blogspot.com/2019/10/the-expanses-epstein-drive.html https://toughsf.blogspot.com/2019/10/the-expanses-epstein-dr... . Seems in the realm of physics, with some more impressing results...
- marta_morena_25 6y ago
  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 6y ago
    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.
    - krastanov 6y ago
      Alcubierre is a Mexican physicist, not Spanish.

tectonic 6y ago

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

api 6y ago

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.

Majromax 6y ago
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.
adrianN 6y ago
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 6y ago
  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.
a_crc 6y ago
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.
- api 6y ago
  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 6y ago
  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 6y ago
    wouldn't a million square metered be a megametre and not kilometre?
    - codeduck 6y ago
      no. 1000m * 1000m = 1000000m^2 or 1 km^2
- SECProto 6y ago
  > 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-mile/ https://streeteasy.com/blog/how-many-nyc-blocks-are-in-one-m...

avmich 6y ago

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

marta_morena_25 6y ago
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 6y ago
  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.
  - krastanov 6y ago
    Alcubierre is a Mexican physicist, not Spanish.