20121022, 22:59  #23  
Basketry That Evening!
"Bunslow the Bold"
Jun 2011
40<A<43 89<O<88
3×29×83 Posts 
Quote:
Quote:


20121022, 23:43  #24  
"Forget I exist"
Jul 2009
Dumbassville
2^{6}·131 Posts 
Quote:
Last fiddled with by science_man_88 on 20121022 at 23:44 

20121023, 00:29  #25 
6809 > 6502
"""""""""""""""""""
Aug 2003
101Γ103 Posts
21A6_{16} Posts 
Why not build in a TAU mission? Would that not provide some ROI earlier? There are some other side missions that could be part of it.

20121023, 00:43  #26 
(loop (#_fork))
Feb 2006
Cambridge, England
6358_{10} Posts 
So: you're saying that we can pass the cost of monitoring the probe after it passes 30AU to an organisation with an infinite budget. Alpha Centauri is 280,000AU away; 7AU/year is just about attainable with a hot launch, Jupiter and Saturn flybys, and an only marginally unreasonable supply of ASRGs powering ion engines that we know how to build.
An RTG of the ASRG type has a halflife of 80 years, weighs 20kg and produces 140 watts; unfortunately it has moving parts. If we use something with a halflife of 8,000 years instead (americium243 or curium245), it would weigh two tons for the same power output; and after 40,000 years we'd still have three watts. (of course this is insane, nothing with moving parts will last 40,000 years, a convincing explanation of why a proposed design could be expected to last 40,000 years would probably exhaust the $10^10 in experiment alone, arranging that the last three watts are still usable at 40,000 years is absurd) Voyager 1 has a 23watt radio and can be heard reasonably happily at 120AU with a 3.7metre dish at its end and a 34metre DSN dish at ours. Our radio has one ninth the power, so would be audible at 40AU without antenna gain. Let's add some antenna gain. There's a satellite currently in orbit (TerreStar1) known to have an 18metre deployed antenna; there's a satellite USA202 currently in orbit which is suspected to have a 100metre deployed antenna. Let's get the NRO director some really good cigars and get a spare one of those; doubling the antenna diameter at either end doubles the range, so with our 100m transmitting antenna and our 3watt radio we'd be audible with a 34metre DSN dish at 1000AU. Which means the dish that the infinitely wealthy organisation has to have at Earth has to be about 10km; this is at the absurdbutnotridiculous level. So this is a probe consisting of two tons of ludicrously overspecced radioisotope generator and let's say two tons of huge antenna (and some kind of sensor pack, but that's a trivial weight); it's assembled in orbit, and attached to a last stage containing four tons of Pu238 ASRGs at 7W/kg, which provide 28kW of power to a cluster of twelve NSTAR ion thrusters (which weigh 50kg each and provide 92mN thrust each using 5g/hour of xenon each), and tankage for thirty tons of xenon. Two Falcon Heavy launches for the probe and the xenon; call the stack fifty tons since we do need some kind of spacecraft structure. And then you use the remainder of the budget on launching Falcon Heavy second stages and stacking them as the departure stage  $100 million per secondstage delivered to the assembly site is almost reasonable. Deliver 40 of them; they weigh 50 tons each, 90% of which is fuel, and each provide 445kN of thrust for 345 seconds. We're starting off in the ISS's orbit at 7.7km/s orbital velocity Fire the first 27: 12MN of thrust applied to 750 tons of payload plus 1300 tons of enginesandfuel, accelerate at 6m/s for about 300 seconds; off we go at 2km/s. Fire the next nine: 4MN of thrust applied to 300 tons of payload plus 450 tons of enginesandfuel, accelerate at 6m/s for about 300 seconds; 2km/s more, and we've reached Earth escape. Fire the next three: 1.3MN of thrust applied to 150 tons of payload plus 150 tons of enginesandfuel, 2km/s more, we're on the way to Jupiter. Fire the last one when you're at perijove for the Oberth manoeuvre, then light up the ion engines; thirty tons of xenon gets half a million thrust hours on a 1newton engine on 50 tons of vehicle and an additional 36km/s which is our 7AU/year. The laughter as you propose this to a NASA congressional hearing can clearly be heard at the other end of the Mall. Last fiddled with by fivemack on 20121023 at 00:51 
20121023, 00:54  #27 
"Forget I exist"
Jul 2009
Dumbassville
2^{6}×131 Posts 
lets say one robot is TAU to earth and one is TAU to the other star system this only cuts down on the transmission time by about 277278 hours and that assumes the robot around earth is in control of the whole mission if earth control is needed it adds back 499 004.784 seconds of transmission time at very least which is 138139 hours.

20121023, 01:29  #28 
6809 > 6502
"""""""""""""""""""
Aug 2003
101Γ103 Posts
21A6_{16} Posts 

20121023, 01:44  #29 
"Forget I exist"
Jul 2009
Dumbassville
2^{6}×131 Posts 
what's your time constraint again (a close look shows 4.37 light years/(0.1 light years/year) = 43.7 years to get there at 29979245.8 meters/second) ?
Last fiddled with by science_man_88 on 20121023 at 02:03 
20121023, 05:48  #30 
Oct 2004
Austria
4662_{8} Posts 
Just two questions:
* What was the cost of Apollo 11 in today's money? * What was the cost of the Curiosity mission (let's say until the end of primary mission, not taking in account any extension of the mission)? 
20121023, 06:46  #31 
Bamboozled!
"πΊππ·π·π"
May 2003
Down not across
10,253 Posts 
Fine. You're working to two significant digits, I'm working to the nearest factor of two at best and to the nearest order of magnitude much of the time. You didn't pick up, for instance, that at 0.1c it takes only 43 years travel time. The figure 10,000 g acceleration was picked almost arbitrarily as something which ruggedized hardware might be able to withstand for minutes at a time; I've no idea whether that's plausible. Even a tenth of that may be infeasible.

20121023, 06:49  #32 
Bamboozled!
"πΊππ·π·π"
May 2003
Down not across
10,253 Posts 
Oh, I can design one all right, well under budget and well within the time limit. The point is that the mission is then pointless. Throwing an upper stage rocket to Alpha Cen is straightforward and it will get there in a few tens of kiloyears. So?

20121023, 06:58  #33 
Bamboozled!
"πΊππ·π·π"
May 2003
Down not across
24015_{8} Posts 

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