# Which one of these Isp's for the Dawn spacecraft is wrong?

The Wikipedia article NASA Solar Technology Application Readiness says:

The ions are accelerated through two fine grids with roughly a 1300 V difference between them for 2.3 kW operation, with a thrust of 20-92 mN, a specific impulse of 1950-3100 N·s/kg and a total impulse capability of 2.65 x106 Ns.

and the Wikipedia article subsection Dawn (spacecraft); Propulsion system says:

The Dawn spacecraft was propelled by three xenon ion thrusters derived from NSTAR technology used by the Deep Space 1 spacecraft, using one at a time. They have a specific impulse of 3,100 s and produce a thrust of 90 mN.

Both numerical values are about 3,000.

But Isp in seconds is obtained by dividing Isp in N·s/kg (which has units of velocity) by Earth's standard gravity of 9.80665 m/s^2, so one of those numbers is off by roughly a factor of 10.

• Which one is wrong, or are they both wrong?
• If so, then what's the right number?
• thought tempting, identify-this-error is probably a bad idea for a tag
– uhoh
May 18 '19 at 19:07
• It's possible that some future person will be searching for the correct Isp for Dawn. Such a person is more likely to come here if the question title asks for the correct answer, rather than disputing the wrong answer. May 19 '19 at 1:25
• Maybe that's how they nearly missed their initial target... May 19 '19 at 1:37
• @DrSheldon I understand the concept, but in this case I think it's most appropriate to leave it as-is. This is exactly the question I needed answering, and it is exactly the question that has been addressed in the posted and accepted answer. If a future person queries a search engine, they will now get the right number in either article in Wikipedia. People don't usually come to Stack Exchange to get a specific numerical value like an engine's Isp, and this question will serve as a warning that even if they do move on to a more encyclopedic website like Wikipedia, numbers there can be wrong!
– uhoh
May 19 '19 at 1:42
• @uhoh validate-my-hypothesis might be a good one :). I've wanted one for validating a line of thinking for awhile now. There's a lot of open-ended questions, but I've seen a lot of people asking with an attempt at the question first (E.G. this). May 23 '19 at 16:41