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How do a go from a thrust of 66.28 t to kilonewtons?

thrust:  66.28 t
isp:     237.2 s
burn:    34 s

These values are from spacelaunchreport under Vehicle Components, for the Ariane 4 PAP solid booster.

Russell Borogove
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Justin808
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    Are those metric tons, in other words 1 ton = 1000 kg? In that case, they might be referenced to standard gravitational acceleration g = 9.80665 m/s^2 and if that is true, and only if that is true, you would multiply tons by 1000 to get kg-equivalent, then by g to get Newtons (kg m /s^2), or just multiply tons by g to get kiloNewtons directly. Always pay close attention to the units, they will help suggest how to use your values. You can also read this: http://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication330e2008.pdf – uhoh Feb 22 '18 at 03:30
  • Someone has down voted your question, probably because it is not clear, and you haven't included enough information really. (They should have left a comment as well). Can you explain where these numbers are coming from? – uhoh Feb 22 '18 at 03:32
  • @uhoh - Thanks. I added a bit more detail (where I got the numbers from). – Justin808 Feb 22 '18 at 03:46
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    @uhoh - Your comment is correct, I'd checked with some other numbers where I knew the kN. – Justin808 Feb 22 '18 at 03:55

1 Answers1

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In this case, the figure appears to be in metric tons-force, so the conversion factor to kN is "standard gravity"†, ~9.81 m/s2. 66.28 tons-force is therefore 650 kN, which is the figure I see on Wikipedia for the Ariane 4 PAP solid booster.

† Not to be confused with the standard gravitational parameter.

Russell Borogove
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  • Being (apparently) the "resident stickler" it might be better to just quote the correct value for standard gravity since "gravity at Earth's surface" actually varies by roughly a percent from place to place. It even has an ISO thingy! – uhoh Feb 22 '18 at 05:03
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    As the converted value came out suspiciously close to the suspiciously round figure of 650kN, I suspect that three decimal places is overkill to begin with. I'm idly considering formulating a question about uncertainty in engine thrust figures, but haven't decided if I care enough about it. – Russell Borogove Feb 22 '18 at 05:15
  • I still believe the correct answer is to multiply metric tons by exactly 9.80665 m/s2 the standard value, and if an example is found somewhere which suggests a different value was used, it means that they did it wrong. – uhoh Feb 23 '18 at 01:11
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    The correct answer is not to pretend you have significant figures that you don't actually have, but I'll meet you halfway on terminology. – Russell Borogove Feb 23 '18 at 01:51
  • That applies to how one would display a result, but not the underlying procedure that one should use when performing the calculation, or especially when answering how others should perform the calculation. "Pre-rounding" before you are done is not a good ideal. Someone might have more digits in the future. – uhoh Feb 23 '18 at 02:01
  • I don't know how to get it across to you that "exactly 9.80665" IS "approximately 9.81". ¯\(ツ)/¯ – Russell Borogove Feb 23 '18 at 02:04
  • I'm just replying to the use of the word "pretending". My meaning is that the correct answer to this "how to" question is to multiply by the correct number. Using all available digits during the calculation is the correct procedure, there is no "pretending" in doing so. Subsequent calculations might involve subtraction of two large numbers for example. The edit looks good (as does your sketch!) – uhoh Feb 23 '18 at 03:16