Orbiter missions with no (or little) fuel usage for deceleration, Target planet capturing the spacecraft w/o extensive fuel usage |
Orbiter missions with no (or little) fuel usage for deceleration, Target planet capturing the spacecraft w/o extensive fuel usage |
Sep 1 2015, 10:58 PM
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#16
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
Getting a stable circular orbit around an outer planet it energy intensive. Indeed. The examples I cited ( MRO, Cassini, Galileo, MESSENGER, Uranus orbiter ) almost all end in exceptionally eccentric orbits - they are pretty much the minimum delta V you could possibly use whilst remaining gravitationally bound to the spacecraft. MESSENGER wasn't hugely excentric - but far from circular. It's already highly energy intensive to get into ANY orbit - let alone a circular one. in the case of Cassini and Galileo, multiple gravity assists from moons were used to manipulate the orbit thereafter. In the case of MRO - it's aerobraking that makes up the difference. The spare NRO hardware equates to enough hardware for one telescope. It's to be used as the basis for the proposed WFIRST mission. Getting a spacecraft that massive ( >11 tons ) into some sort of orbital tour of Mars, asteroids and the outer solar system would require extraordinary amounts of Delta V that would pretty much require next gen solar-electric prop ( which obviously isn't going to work beyond Jovian like distances ) |
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Sep 2 2015, 02:19 AM
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#17
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Member Group: Members Posts: 684 Joined: 24-July 15 Member No.: 7619 |
Getting a spacecraft that massive ( >11 tons ) into some sort of orbital tour of Mars, asteroids and the outer solar system would require extraordinary amounts of Delta V that would pretty much require next gen solar-electric prop Correct. Except when it isn't. The beauty of chaotic orbits that require little to no delta-v is that 0 x anything = 0 Zero x 350kg craft = zero thrust. Zero x 11 ton craft = zero thrust. http://www2.esm.vt.edu/~sdross/talks/ross-csulb-2003.pdf http://forum.nasaspaceflight.com/index.php?topic=26217.0 Idea is, old spy satellite and icbm components could be reporposed into a group of space telescopes. If we aren't using them to spy on each other, might as well send them out to get pictures of other planets and moons. Take a spy satellite telescope, add a Dawn style ion engine powered by a RTG, and a big antenna to transmit back to earth. Send it out to Earth's L2 point, then let it traverse the roughly zero-delta-v chaotic orbit pathways from earth's L2 out to the gas giants and beyond. While it is in-between planets, telescope could look at stars and galaxies just like hubble. But when it closes in on planetary sytems, we get great images of planets, moons etc. That takes lots of time, but, if the telescope does science on the way out, who cares as long as our kids and grand-kids get great photos? |
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Sep 2 2015, 02:56 AM
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#18
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Member Group: Members Posts: 684 Joined: 24-July 15 Member No.: 7619 |
Cool map, with classical transfer orbit delta-v
http://www.dailymail.co.uk/sciencetech/art...solar-Tube.html Cooler map, with chaotic minimal delta-v http://www.gg.caltech.edu/~mwl/publication...SAndOrigins.pdf |
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Sep 2 2015, 03:11 PM
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#19
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
Zero x 350kg craft = zero thrust. Zero x 11 ton craft = zero thrust. You say zero thrust - then talk about an RTG powered Dawn Thruster. Dawn's thrusters require approx 10x the output of a typical RTG. Also - assuming you could apply every ounce of Delta V that Dawn has generated and apply it to a Hubble sized payload, the total Delta-V it would impart would drop from approx 10km/sec to 1.4 or so. Exploring the Earth-Moon region with little Delta-V is easy. It's been done time and again. That Scientific American article is somewhat disingenuous to talk about the '300 million miles' that Genesis traveled....when it actually just went to L1 and back, via L2... in an geocentric frame, a few million miles, not hundreds of millions. It also negates the fact that getting from LEO to L1 requires >3.5km/sec in the first place. Getting out to Mars, Jupiter, Saturn and beyond....I see no reference to the zero Delta-V trajectories in either of the papers you cite. I'd be delighted to see a realistic trajectory that gets 11 tons from LEO or even L1 to Mars, Jupiter and beyond with zero delta V in a time frame realistic for the lifetime of a spacecraft. Say, 10-20 years. |
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