There are certainly some untested aspects of this vehicle, especially..... pogo..... History is a guide.
Pogo oscillation is exactly what it sounds like – a violent up-and-down motion that could make anybody sick, but makes rockets really really sick. It results from a variation in thrust from different engines, and with thirty unreliable ones, you can get a lot of variation. Once it starts, it's very hard to correct, as the variable acceleration leads to variable fuel pump pressures, which leads to more variables acceleration, and so on and so on until eventually you match the vehicle's resonance frequency and vibrate the whole thing to death.https://jalopnik.com/this-insane-rocket-is-why-the-soviet-union-never-made-i-1448356326
Quote from: edkyle99 on 12/29/2017 04:05 pmThere are certainly some untested aspects of this vehicle, especially..... pogo..... History is a guide. I don't think "torque", or force of rotation around an axis, is the right word or focus. Where is everyone seeing so many spinning parts that can go wrong? From everything I've Googled today, pogo oscillations appear to be the real risk, up and down variations in thrust & LOX & fuel flow. They brought down the 4th & final 30-engine N-1 launch, and have a long history of plaguing US launches as well. They also have a long history of mitigation by various kinds of engineering, the latest written up by our own Philip Sloss just this month, a 3D-printed POGO Suppression Accumulator built by Aerojet Rocketdyne for NASA's Space Launch System R-25 engines. In the past NASA instituted a safety level of G forces to be tolerated by such oscillations, +/-0.25G.Here's one description related to the 4th N-1 launch:QuotePogo oscillation is exactly what it sounds like – a violent up-and-down motion that could make anybody sick, but makes rockets really really sick. It results from a variation in thrust from different engines, and with thirty unreliable ones, you can get a lot of variation. Once it starts, it's very hard to correct, as the variable acceleration leads to variable fuel pump pressures, which leads to more variables acceleration, and so on and so on until eventually you match the vehicle's resonance frequency and vibrate the whole thing to death.https://jalopnik.com/this-insane-rocket-is-why-the-soviet-union-never-made-i-1448356326
I see very little (if any) risk for POGO for FH, since they are flying the same stages as F9. Same engines, same tank lengths. POGO - if present - will show up in early launches. All this talk of possible failure points - one more dramatic than the next - starts to border on concern trolling, IMO. “Surely SpaceX has not thought of *this*?”
Emily Lakdawalla points out that the FH demo launch is too early for an optimal earth-mara trajectory:https://twitter.com/elakdawalla/status/946941586373451776Can someone with the technical chops compute if FH has to capability to put a roadster-sized payload arbitrarily close to Mars (ie, for purposes of computation, on a path impacting Mars) even if launched mid-January?
So...let me get this strait. We have the most eagerly-awaited rocket roll-out in decades, and all we get are long-distance shots and no up-close hi-res's from SpaceX?
I don't think that there is any realistic prospect of SpaceX confirming actively that the roadster gets to its destination orbit. All they will be able to do is monitor the second stage for as long as possible to confirm its trajectory. All they'll ever be able to say is: "With a high degree of confidence..."
I know I am not going to make any friends by saying this but it needs to be said.I would majorly hate to be a member of the generation that just can't stand to wait until it [whatever "it" may be] actually happens. I get the impression that they would never be able to stand the wait time of several YEARS while a probe makes its way to Jupiter, Saturn, Uranus, Neptune, Pluto or the Ort cloud. Their heads would explode. Try launching a probe like that knowing that you yourself may very well not live long enough to see it arrive and that children who are in 4th grade at launch date would likely be the scientists that would monitor and record the arrival. Do you have the patience for that?Jeepers people. The solar system isn't your back yard that can be crossed in a leap and a bound. SpaceX will provide photographs when it wants to and not one second before - they don't owe any of us a thing.Falcon Heavy will launch when it is ready. - Give it a rest and have a cup of tea or coffee or latte-mocha-chi-whatever.Chill. It will happen when it happens. THIS site will be the first to let you know it's happening so just stay tuned and quit complaining.
Quote from: clongton on 12/30/2017 01:13 pmI know I am not going to make any friends by saying this but it needs to be said.I would majorly hate to be a member of the generation that just can't stand to wait until it [whatever "it" may be] actually happens. I get the impression that they would never be able to stand the wait time of several YEARS while a probe makes its way to Jupiter, Saturn, Uranus, Neptune, Pluto or the Ort cloud. Their heads would explode. Try launching a probe like that knowing that you yourself may very well not live long enough to see it arrive and that children who are in 4th grade at launch date would likely be the scientists that would monitor and record the arrival. Do you have the patience for that?Jeepers people. The solar system isn't your back yard that can be crossed in a leap and a bound. SpaceX will provide photographs when it wants to and not one second before - they don't owe any of us a thing.Falcon Heavy will launch when it is ready. - Give it a rest and have a cup of tea or coffee or latte-mocha-chi-whatever.Chill. It will happen when it happens. THIS site will be the first to let you know it's happening so just stay tuned and quit complaining.Ah, the impatience of youth, assisted by a culture hell bent on instant gratification, topped by the photos-or-it-didn't-happen dogma.
Yeah, judging from some coincidentally accurate porkchop plots and a few articles, Roadster can certainly make it to a rather close encounter with Mars, it just might take anywhere from a 12-24 month coast period to get there.