Beaming laser power to ion drive is 300-400 times more thrust than just laser photonic sail

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1

"They are claiming lithium ions do not degrade the grid which is why they are putting up with the crappy momentum/energy."

Choice of propellant has little to do with the momentum you get for a given amount of energy; That's all down to the exhaust velocity, e=1/2mV^2, while momentum is m*V. There's a contribution from the energy needed to ionize the fuel, but the higher the exhaust velocity, the less significant that becomes. This system is aimed at higher exhaust velocity, lower fuel requirement, which costs you on the power consumption end of things.

That's why the thrust is poor for the power input, not because they're using lithium.

2

Alpha Centauri in only 40,000 years. πŸ™‚

3

Seriously, "attuned to the Lithium ion"?

Actually, a photovoltaic array can be pretty darned efficient, if fed monochromatic light of exactly the right wavelength. They tend to waste any energy in the photon in excess of the bandgap, and fed just the right wavelength can approach 100% efficiency.

And the latest advance in ion engines is a magnetically insulated grid, that doesn't degrade.

4

Array is not going to be 70% efficient and thruster is not going to be 58,000s ISP. You're trying to tell me you're going to exhaust Lithium ions at 580,000 m/s without degrading the grid?

5

The array only adsorbs photons at one frequency. 70% should be easy.

Grid arrays have expelled Xenon at 240,000 m/s 10 years ago. Lithium is much lighter than xenon so 580,000 m/s is less energy and much less momentum per ion. They are claiming lithium ions do not degrade the grid which is why they are putting up with the crappy momentum/energy.

6

I'm just glad the article doesn't mention Elon Musk.

7

Yes so you can tell it will cost 10-20 times more than it should πŸ˜‰

8

All that's well and good but how does it slow down once it's at a considerable distance from the Sun???

9

gary oblock, gravitational lens will still work further out. It needs a minimum distance. Should get gradually dimmer with distance. The sun's photosphere is low density so the effect will not be noticeable for awhile. And there would be decreased interference from the corona and flares further out. Bigger problem is that it you can only point it at one point. It will take one picture for a few years.

10

There are a lot of missions where the probe doesn't slow down. Yes, it sucks to spend 10 years getting your $billion probe to Pluto or where ever only to have 3 days of observation and that's it.

At least with this scheme you are waiting for less time. You zap by the target even faster though πŸ™

Of course what they do is try to time it so that their probe passes close by more than one thing.

11

Why not use the ion thruster to decelerate into orbit? You could use 1 array to push the women to Jupiter and propel/decel the Kuiper belt probes during the Jupiter mission's coast phase.
Also slow missions with lower launch weight would be cheaper. Or launch a bunch at same price.

12

"...push the women to Jupiter..."?????

13

I figure it's got to be autocorrect, (Nobody's ever claimed Jupiter needs women.) but from what.

BTW, notice that nesting is turned on now? Now Brian just needs to get the code installed that clues browsers in on the fact that there are user names and passwords in need of autofilling.

14

It doesn't. Slowing down isn't needed for this mission.

15

I think the laser is used simply to provide the power via a tuned pv array to run the very high power ion drive, so it’s not a light sail.

16

I didn't hear much new, except maybe use of lithium as reaction mass for the drive?