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The solar arrays provide about 100 kW of power, so we can put the two HiPEP thusters providing 1 N (1000 mN) power combined, with the specific impulse as high as 6000–9000. Such an acceleration force for 419,700 kg mass does not look very good for meeting any possible timelines and deadlines of gaining velocity.

Still, would the 1 N force be sufficient to start raising the orbit, or atmospheric drag is more even at that altitude?

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Yes, according to multiple sources, including the answer to this question. The estimated drag forces on the ISS, on average, appear to be about 0.25N (although some estimates put it as high as 0.9N). So yes, in theory, a constant thrust could do it. Now, you'd have to contend with the power drain. I believe HiPEP thrusters use somewhere in the range of 25-50KW, so you'd max out the power on the ISS just keeping it in orbit, which kind of nullifies the point of having it there in the first place...

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  • $\begingroup$ I've got to wonder if the estimated life of those thrusters would be lowered if you planned to fire it 24/7 over long periods of time as well. Given that they're meant to be doing long, low-impulse thrusts I'd don't know if it would matter; but I don't think they were ever planned to be doing many year-long impulses. $\endgroup$
    – Magic Octopus Urn
    Nov 18, 2019 at 20:47
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    $\begingroup$ Fair, and they've never been used in space AFAIK, so we can't really say for sure. But previous ion powered spacecraft have had crazy long burn times (think Dawn) and they ended up just fine after those long thrust times. Plus redundancy and load sharing might help a lot there $\endgroup$
    – Michael Stachowsky
    Nov 18, 2019 at 20:49
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    $\begingroup$ This picture makes it seem like there was not 100% constant thrust for Dawn. Then again, some of those blue sections would still be an impressive amount of time. Thanks regardless, the Dawn page helped clear up some misconceptions I was having about how Ion thrusters are used in practice :)! $\endgroup$
    – Magic Octopus Urn
    Nov 18, 2019 at 20:59
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    $\begingroup$ Indeed. Apparently Dawn's total mission thrusting time was 5.9 years (although I'm certain it wasn't all at once, it's still amazing what the thrusters could do) $\endgroup$
    – Michael Stachowsky
    Nov 18, 2019 at 21:02
  • $\begingroup$ The ISS spends a significant fraction of its time in darkness. It's somewhat less than 50% and as it's highly inclined orbit precesses there are periods with no eclipse, but overall it's a big effect. $\endgroup$
    – uhoh
    Nov 19, 2019 at 1:21

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