Content deleted Content added
Line 71:
:I get your two points. I don't have time to relook a the sources just now, but in the long news conference by the SES executive Halliwell I recall him mentioning the extra push, and impact on the probability that SpaceX successfully landing the first stage would go down. It seemed to me, as I heard that and other sources, that given SpaceX's loss of flight 19, and subsequent 6 or so month delay to the return-to-flight, it pushed SES back a bunch, and thus reduced SES near-term revenue statements (SES were going public on that in securities regulation announcements), and since SES is a really good (though not exclusive) SpaceX customer, SpaceX decided to "take one for the customer" and burn harder/longer, and reduce landing probability of the experimental controlled-descent first stage. No problem; all good business. But the push or extra burn or whatever was mentioned by Halliwell, and picked up by space media who covered that. So I think the extra push should not be left out of the article. On your second point, I have not seen sources that clarify how much of the extra push was first stage vs. second stage. Given the extra push was talked about, and sourced, it is not at all clear that just because the second stage did a "burn to (safe) depletion" rather than a "burn to target orbit", then that would mean the first stage didn't give some extra push also, and thus use up some of the propellant that would have been part of its return and landing prop margin; SpaceX clearly decided to do a special 3-engine landing burn on flight 22, never before even tested, in order to have a (small probability) shot at bringing the thing in and landing it. [[User:N2e|N2e]] ([[User talk:N2e|talk]]) 18:55, 9 April 2016 (UTC)
::I fully agree with [[User:C-randles|crandles]] on {{diff||714371128||this edit}} which improves the reader's understanding that mass and speed are the key factors in setting practical limits to booster recovery. Here we had a rocket which couldn't reduce its re-entry velocity as much as would be feasible on a LEO Dragon launch, for example. That being said, I would assume that the negotiated supersynchronous trajectory had an impact on the first stage as well as the second stage, taking both of them to their limits? However we are surely going down the sweet and sour path of [[WP:OR]]... This case was undoubtedly a great way to push the envelope on what these Falcons can withstand! — [[User:JFG|JFG]] <sup>[[User talk:JFG|talk]]</sup> 07:26, 10 April 2016 (UTC)
:::Looking again at the ref http://spaceflightnow.com/2016/02/24/falcon-9-rocket-to-give-ses-9-telecom-satellite-an-extra-boost/] "Halliwell said SES’s contract with SpaceX called for the rocket to deploy SES 9 into a “sub-synchronous” transfer orbit with an apogee around 16,155 miles (26,000 kilometers) in altitude. ... The change in the Falcon 9’s launch profile will put SES 9 into an initial orbit with an apogee approximately 24,419 miles (39,300 kilometers) above Earth." 26000km to 39300km is quite a difference that doesn't seem likely to come from just a couple of extra seconds burn from the second stage. This makes it seem to have a more significant effect than I was thinking when reading the change was just a slightly longer burn on the second stage. Would still suggest payload weight "heavier than the Falcon 9 rocket’s advertised lift capacity to geosynchronous transfer orbit" is likely a major effect but without reference we shouldn't indicate which is more important. Can we find a wording that suggests both are factors without indicating one is more important than the other? Perhaps I will have a go at adding a little more. [[User:C-randles|crandles]] ([[User talk:C-randles|talk]]) 11:05, 10 April 2016 (UTC)
| |||