5 ms·

The citation for the wikipedia page (240s ISP) gives an exhaust velocity of 2,300m/s : https://en.wikipedia.org/wiki/SuperDraco#cite_note-DragonFlyEAI201403-4

by delibes 11y ago

The citation for the wikipedia page (240s ISP) gives an exhaust velocity of 2,300m/s : https://en.wikipedia.org/wiki/SuperDraco#cite_note-DragonFlyEAI201403-4 https://en.wikipedia.org/wiki/SuperDraco#cite_note-DragonFly... - page 12 of the PDF. So taking a rough 2300/9.8 gives about 235s

irrelative 11y ago
FWIW, Isp is measured in seconds and by multiplying it times gravity, you get the exhaust velocity. I believe this was done to more easily compare rocket efficiency regardless of units of gravity. It looks like you're doing this calculation: Isp * Gravity / Gravity If you're trying to predict the hover duration, that will depend on the delta V of the vehicle. Then, a hover duration would be: Delta v / Gravity Not sure what the expected delta V is for the Dragon though.
ChuckMcM 11y ago
Yes I read that (and the spaceflight insider article (http://www.spaceflightinsider.com/organizations/space-exploration-technologies/spacexs-superdraco-engine/ http://www.spaceflightinsider.com/organizations/space-explor...), all numbers that are derived by third parties. So while I do not doubt that the numbers for that vehicle and that test are accurate, I keep hoping to find actual data from SpaceX on the performance of the production rocket slated for use in the production Dragon Module. I understand that SpaceX plays this information close to its vest given the competition with Boeing for Commercial Crew and perhaps Blue Origin should SpaceX ever decide to sell rockets for sub orbital tourist jaunts[1]. Anyway I'm just interested in more official specs so that I can have more confidence in my understanding of their capabilities. [1] If you think about it, they have all the hardware, an F9r with a Dragon Crew mounted on top, they boost up to 100km, separate, the Dragon gets a nice ballistic arc for that weightless feeling and then both the booster and the capsule go back and land back at the pad for re-use.

by delibes 11y ago

irrelative 11y ago

FWIW, Isp is measured in seconds and by multiplying it times gravity, you get the exhaust velocity. I believe this was done to more easily compare rocket efficiency regardless of units of gravity. It looks like you're doing this calculation: Isp * Gravity / Gravity If you're trying to predict the hover duration, that will depend on the delta V of the vehicle. Then, a hover duration would be: Delta v / Gravity Not sure what the expected delta V is for the Dragon though.

ChuckMcM 11y ago

Yes I read that (and the spaceflight insider article (http://www.spaceflightinsider.com/organizations/space-exploration-technologies/spacexs-superdraco-engine/ http://www.spaceflightinsider.com/organizations/space-explor...), all numbers that are derived by third parties. So while I do not doubt that the numbers for that vehicle and that test are accurate, I keep hoping to find actual data from SpaceX on the performance of the production rocket slated for use in the production Dragon Module. I understand that SpaceX plays this information close to its vest given the competition with Boeing for Commercial Crew and perhaps Blue Origin should SpaceX ever decide to sell rockets for sub orbital tourist jaunts[1]. Anyway I'm just interested in more official specs so that I can have more confidence in my understanding of their capabilities. [1] If you think about it, they have all the hardware, an F9r with a Dragon Crew mounted on top, they boost up to 100km, separate, the Dragon gets a nice ballistic arc for that weightless feeling and then both the booster and the capsule go back and land back at the pad for re-use.