Eh, spoilsport.
Quote from: Bill White on 07/27/2011 09:26 pmEh, spoilsport. Check this out -- if the pass at your longitude happened right around evening or morning nautical twilight, the Sun would still be on the vehicle. That might give you a pretty good show if it was also close to perigee, because it would be going really freakin' fast.See, I'm not just a taker.
But yes, sometimes it's actually superior to the direct route.)
Quote from: Robotbeat on 07/27/2011 09:42 pm But yes, sometimes it's actually superior to the direct route.)In delta-v terms. In delta-t terms, it's juuust a bit pokey.
Quite right... Now I'm all interested in this topic... Going to start a new thread.
Quote from: Robotbeat on 07/27/2011 09:56 pmQuite right... Now I'm all interested in this topic... Going to start a new thread.Please drop a link here, if you could.
We are quite a bit off topic here.I will make my final comment on this thread:At this point, we:1. Do not know what the details of the report are2, Know that nothing can move forward until this report is made public and Congress approves of it.3. Do not know for sure if there will or will not be a congressional investigation to determine what if any laws NASA leadership has broken4. Know that the next hearing and associated processes are now stalled until after the debt crisis is either resolved, or until how the government will function in a default is known.5. Know that NASA is not likely to continue function in the event of a default, which seems all the more likely to happen. The first effects would be felt on Tuesday of next week. With that said, I don't really think there is anything more we can do or talk about in the short term. We will have to watch and wait, and we will have to see how much damage is done to the agency if the federal government defaults. Its time to lock this thread.
And I'm with Bill White in that I think kerolox, to power the cis-lunar tug, should get much more consideration. I believe that ease of handling will outweigh the ISP advantages of H2, at least when coming from Earth.
Quote from: JohnFornaro on 07/27/2011 06:26 pmAnd I'm with Bill White in that I think kerolox, to power the cis-lunar tug, should get much more consideration. I believe that ease of handling will outweigh the ISP advantages of H2, at least when coming from Earth.I too can imagine that hydrogen might turn out not to be worth the deep-cryo hassle for some applications, but my first fall-back would be methane rather than kerosene, especially for a re-usable system. The reason is that methane evaporates cleanly, whereas a heavy hydrocarbon like kerosene tends to leave residues behind, which could explode on contact with lox during a re-start.Methane's specific impulse is also better. It is less dense than kerosene, meaning tanks will be heavier, but gravity losses aren't going to be big deal anyway for chemical-propelled cis-lunar systems.Maybe it would also be possible to mix in a bit of propane (or maybe propene [propylene]) to make a VAPAK self-pressurizing system, eliminating the needed for a separate pressurant.
Propane might be better than methane, and not because it can be self-pressurized. Propane has nearly the Isp of methane but if cooled to near liquid oxygen temperatures, it has just as high bulk density as using kerosene... Thus your mass fraction would be better.
Quote from: Robotbeat on 07/28/2011 02:43 amPropane might be better than methane, and not because it can be self-pressurized. Propane has nearly the Isp of methane but if cooled to near liquid oxygen temperatures, it has just as high bulk density as using kerosene... Thus your mass fraction would be better.That's a good point. I had rejected chilled propane for deep-space use, because it wouldn't self-cool through evaporation. But if you have a tank full of oxygen that boils a bit below the fuel's freezing point, the oxygen vapor could be used to cool the fuel.From what I've heard, you may not want to chill propane all the way to the freezing point, because of increasing viscosity. And let's not forget propylene, which I suspect would turn out to be a bit better than propane.
The capability is already being rebuilt, Aerojet already is setting up production for it's AJ-26, new build over the warehoused 1970's engines it is currently rebuilding.
Again, it's not clear where you're headed with your line of reasoning.
It's a very accessible destination, but only if one wants to go there -- realism about technology and economics, and accepting the implication thereof.
And I simply don't believe anybody is going to invest the payload capacity to do it, not for a long time.
It should be in the orbit that best uses the injection impulse for the specfic opportunity ...
That all of this speculation about the utility of an EML assembly point ignores technological and economic reality.
Remember, I don't believe in the utility of the Moon any time soon. So my concern is with how to optimize interplanetray exploration payload utilization.
We're crawling right now. Even a beginning EML/lunar infrastructure is well into walking.
In-space infrastructure is basically what we need in order to keep the boundaries pushed back.
I also believe we need to look plug-n-play cryogenic tanks rather than fuel transfer. ...And these issues suggest at least looking at kerolox ...
It's really slow, but sometimes uses next to no energy... which is how we get Mars meteorites...
{snip}Which just brings up yet another one of those things I don't know. Where do the meteorites keep their computers for figuring out their orbital mechanics?
QuoteAnd I simply don't believe anybody is going to invest the payload capacity to do it, not for a long time.Well, Orbital, SpaceX and the several other players, are investing money to deliver payloads. True, their major customer seems to be NASA, but there are other customers as well. So somebody is investing something in payload capacity, most likely with the expectation of economic return. How sufficient an investment is all that? Clearly, more than is in my checking account, and less than would be necessary to do the whole thing.
QuoteIt should be in the orbit that best uses the injection impulse for the specfic opportunity ...That is the current paradigm for NASA's robotic exploration missions. When I was in college in Albemarle County in the sevnties, a group of us virtually memorized the Albemarle County VDOT map, which showed all the itty bitty dirt roads that permeated the county. Informally, we explored them all; we knew which route was the shortest between two points, as the wheel rolls. However, the less "efficient" "orbits" between destinations sometimes involved taking I-64 to Route 29: a few more miles, a bit more gas, but less time and less wear and tear on the suspension. As with all analogies, this one only goes but so far, and it should not be stretched to where it no longer applies.IOW, the ISS could become Wheeling, West Virginia. Etc.
QuoteThat all of this speculation about the utility of an EML assembly point ignores technological and economic reality.The utility of an EML assembly point has been demonstrated for decades in older papers.
Quote from: JohnFornaro on 07/28/2011 02:58 pm{snip}Which just brings up yet another one of those things I don't know. Where do the meteorites keep their computers for figuring out their orbital mechanics?I am sure that they use virtual computers. They need new software, something that can handle planetary gravity wells without crashing.
Quote from: A_M_Swallow on 07/28/2011 05:54 pmQuote from: JohnFornaro on 07/28/2011 02:58 pm{snip}Which just brings up yet another one of those things I don't know. Where do the meteorites keep their computers for figuring out their orbital mechanics?I am sure that they use virtual computers. They need new software, something that can handle planetary gravity wells without crashing. NASA computers should be able to do just about anything. This still ticks me off.....NASA has awarded HP a $2.5 billion contract over four years for desktop services and devices, HP said Thursday. http://news.yahoo.com/s/zd/20110428/tc_zd/263749read # 254 onward.....NASA waste of funds IMHO. Lets say these funds went into Commercial. What could SpaceX etc have done 600 million a year?or Should these funds been assigned to the new launcher?