Nh - The Launch Thread, Godspeed little one |
Nh - The Launch Thread, Godspeed little one |
Jan 16 2006, 03:08 PM
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Founder Group: Chairman Posts: 14433 Joined: 8-February 04 Member No.: 1 |
I thought it was time, with the Atlas V about to roll out - for a new thread for NH for the launch etc.
Someone asked over at the HZ just how NH can go so fast, this was my reply.... QUOTE How do you get a spacecraft to Jupiter in under a year? Easy. Make it very very light, and put it on a very very big rocket. The config of Atlas V rocket being used to launch NH (551 - 5m fairing, 5 solids, and one engine on the Centaur stage ) would typically put 8,670kg into GTO or 20,520 into LEO. New Horizons is 478kg, and it's Star 48B 3rd stage is 2,137kg - so instead of hauling 20 tons, this vehicle is hauling about 2.5 tons thus you get a HUGE velocity out of it. AND, once it's done that, you have the final kick of the 48B, 591 thousand kgs-s (thus accelerating is all a further 3.5 - 4km/s ball park speed, if my maths is right) At launch - the vehicle is 573,160kg. NH is 0.083% of it. Imagine the Apollo entry capsule on top of a Saturn V...tiny tiny tiny... that was 5,800 kg on a 3,038,500kg rocket - 0.191% - more than double that percentage of NH. The cutaway's are almost comical, with this tiny gold-clad box on an enormous vehicle. Basically - it's a LOT of rocket, and not a lot of payload. For comparison, look how much fuss was made of Stardust that entered so quickly. It took >16 hrs to get from the distance of the moon to Utah. NH makes that journey in 9 hours One thing the NH mission is not short of, is superlatives. I'm not one for good luck charms (although I'll eat peanuts during a Martian EDL with the best of them), but this mission has been so long in coming, that it deserves every ounce of luck it can have - the best, most accurate launch possible, the cleanest checkout, and incident free cruise to Jupiter. Goodluck and Godspeed little one, we're with you every step of the way. Doug PS - Alan, you're a credit to your field, spending so much time answering questions and writing the PI Perspectives, it's been a hell of a journey! |
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Jan 23 2006, 02:05 PM
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Senior Member Group: Members Posts: 2998 Joined: 30-October 04 Member No.: 105 |
QUOTE It's not uncommon for LV's to turn, quite a lot, after SRB sep. Are we talking about the turn NH did at the end of this groundtrack map? That map confused the dickens out of me. I figured that the reverse-track was an illusion, but it's still confusing. http://www.spaceflightnow.com/atlas/av010/...roundtrack.html I can see pitching down after getting above the atmosphere, that adds vectors to trade the "upward, out of the air" velocity for "horizontal, orbital, velocity". --Bill -------------------- |
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Jan 23 2006, 02:55 PM
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
QUOTE (Bill Harris @ Jan 23 2006, 03:05 PM) Are we talking about the turn NH did at the end of this groundtrack map? That map confused the dickens out of me. I figured that the reverse-track was an illusion, but it's still confusing. That retrograde groundtrack is logical once you think about how it happens. After the Centaur 2nd burn and especially after the solid kick motor burn the spacecraft is on a hyperbolic escape trajectory. To a crude approximation you could imagine it as a tangent leaving a point some few hundred km above Earth's surface. The spacecaraft is no longer constantly following Earth's curvature and beating Earth's rotation beneath. Instead, as the spacecraft moves away from the Earth, the tangential part of its velocity (relative to Earth's surface) starts to rapidly drop-off (becoming radial) and eventually Earth's rotation catches up and overtakes the sub-spacecraft point. From there on, the groundtrack becomes retrograde. A similar retrograde trajectory "loop" is likely also present in satellites in geostationary transfer orbit, only they eventually come to a still in the groundtrack point of view when they reach GEO orbit and circularize it. -------------------- |
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