Talk:SpaceX reusable launch system development program/Archive 1: Difference between revisions

Revision as of 04:57, 3 April 2017

Revision as of 05:42, 13 May 2017

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So the article will definitely need an update, and I don't have time to do it just now. [[User:N2e|N2e]] ([[User talk:N2e|talk]]) 12:57, 24 February 2016 (UTC)

== Flight 22 landing: Significance of extra push - consequently phrasing looks wrong ==

{{ping|N2e}}

There was an agreement that an extra push would be given to reduce time to reach final orbit. This came from '''second''' stage being run until depletion of fuel rather than shutting down when a target orbit was reached. This has very little, if any, effect on amount of fuel left in '''first''' stage. I don't mind this piece of information being given - Not quite sure where I would move it to. Seems well covered in [[Falcon_9_Flight_22]] and not sure it needs to be here as well. However, I do object to phrasing that indicates that because of the extra push there is little fuel left to land the first stage. Far, far, more important is that the payload was heavy for being lifted to GTO. Unless you have or there is a reference indicating such importance, such a level of importance should not be implied by the article. So the phrasing should reflect this. If other editors want to insist on including mention of the extra push fine but for accuracy don't phrase to indicate this is primary reason for little fuel being left to land first stage. Can we please change the phrasing or remove it? [[User:C-randles|crandles]] ([[User talk:C-randles|talk]]) 14:12, 9 April 2016 (UTC)

: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]] ^{[[User talk:JFG|talk]]} 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. Hope bit added serves. [[User:C-randles|crandles]] ([[User talk:C-randles|talk]]) 11:05, 10 April 2016 (UTC)

::::Sure, give it a go. That was why I suggested we beat it around on the Talk page for a bit. Just was a shame to lose that aspect of the extra energy added for movement of the trajectory to a higher energy orbit, and one that was beyond what the contract called for. [[User:N2e|N2e]] ([[User talk:N2e|talk]]) 02:23, 12 April 2016 (UTC)