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Posted: |
Jan 14, 2015 - 11:55 AM
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By: |
Grecchus
(Member)
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The most important thing was to re-supply the crew on the ISS. It seems the american module has had an ammonia leak. It's like the old age problems of Mir are now besetting the ISS. Hope they resolve the problem asap.
The launch had been postponed. At the time I was half-listening in and the American controller was suggesting the sensors were accounting for some kind of drift while the launch vehicle was stationary on the pad. They'd planted the idea something was wrong with the stabilizer gyros on the rocket's instrumentation because it was audible and not too hard to relate.
Then, when the launch finally goes ahead it's in the dark. The gyros don't seem to have had a problem getting the payload into orbit, at least from the 2nd stage instrumentation sensory apparatus. The problem was with the 1st stage section which spread it's legs, then plonked itself down hard on the crosshairs (we are told) a considerable distance off the coast of Florida. The implication is it would have worked but for some measly hydraulic fluid needed to manipulate the aerofoils for controlled flight, located somewhere on the landing stage.
What I find extraordinary is that the space shuttle's SRBs were always recovered after parachutes were deployed to soft-land them into the sea. Why on earth can't SpaceX use that tried and tested method? You see, when a launcher lifts off, it's under constant, never-ending acceleration until it meets its target altitude either in the atmosphere or in orbit. That's one of the physical principles that allowed the extremely complex Saturn V rocket to keep together on it's way up. All the joins between stages were being compressed together due to the acceleration. The point being they are designed to go faster and faster, not slower and slower. The only instance I can think of when a vehicle used rocket engines to land was when the LEM met with moondust in zero atmosphere. That is to say with no wind currents to buffet it all the way down.
The problems of trying to keep a long cylindrical mass upright most of the way down within the atmosphere imply that a considerable fuel reserve is required to decelerate and cushion the landing. We've all seen failed rocket launches where they've exploded on the pad - it's a difficult proposition at best for a long limbed rocket to maintain stability at slow speed close to the ground. But as I've pointed out, launch vehicles aren't called "rockets" for nothing. Sure, I'm no rocket scientist, but I've been following the technology as it's been developed over decades and the idea of landing an oversize missile with pinpoint accuracy on it's arse seems just a little bit strange.
Don’t get me wrong. I'm really enthusiastic about any practical method being perfected to re-use hardware, it's just that my sense of the possible is sorely tested by the technique SpaceX is touting as it's claim to fame. I've always thought that each launch requires a new build. The trick is to employ the simplest tried, tested and proven assembly line there is. And I truly believe that is as cheap as it can get (this obviously applies to the 2nd stage, which needs renewal for all launches.)
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Posted: |
Feb 3, 2015 - 2:02 PM
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By: |
Grecchus
(Member)
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They can always raise the ISS orbit when that suits. What doesn't make sense is that the russian Progress is a tried and tested vehicle. Maybe if the ISS orbit is a little less eccentric then rendezvous is less tricky? Playing catch-up in orbit is an interesting 'game.' The higher you are, the less orbital velocity is required. The lower you are, the faster you will go - these are the laws of physics at play. Rendezvous is dependant on precise thruster vectoring at the point of closest contact, and has to be continuous until station keeping means the vehicle is "merged" with the station. Hohman transfers are usually good enough to do the job.
Actually, now that I'm in the groove, going back to Apollo, the most interesting part of the entire experience (for me) was blasting off from the base of the lander whilst on the moon (using it as a launch platform), followed by the ascent to the point at which the LM's upper stage turned off it's single rocket engine, which couldn't be throttled or reignited once turned off. It was either full "on" or "off." That rocket engine and the vernier thrusters were the only "tether" the two guys had to the CM - and hence, to life itself. Now, if you really think about it, that is freaking incredible. That rendezvous is out of this world in the conception and the execution! My admiration for the 12 men who performed that feat is unlimited. Without doubt the single most incredible accomplishment of flight and navigation ever to be performed by man. Of course, the entire journey is one monumental feat of scientific precision. Though when you break it down into the various segments, that ascent takes the biscuit. Now, you might think the landing itself is the greater feat (especially 15's mountian hugging all the way down to Hadley Rille,) but that dash for an intitial parking slot between the moon and the CM is tops for me!
As for SpaceX, I think the Falcon 9 is expected to be reliable for at least 40 launches. In the animation from SpaceX, the rocket engine bells are bearing the brunt of heating on reaching denser air, so they must be very strong to absorb so much "punishment." Some components will be prone to differences in mtbf and will need replacement according to inspection, I should think.
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Maybe they are letting their imagination get the best of themselves and can't escape the nostalgia of Buck Rogers science. (fiction) 