Why L1 for a staging point?

[j05h]

Good Singapore comparison! <br /><br />This is what I picture for an L1 Halo station: A keel of trusswork, several hundred feet long. At the center is a stack of BA and SunDancer modules clipped to the keel. At one end of the keel is a nuclear reactor, Solar-Dynamic or photovoltaic arrays. Along the keel are docked clusters of reused upper stages clustered as tankage, others being used as departure stages and tugs. The non-power end of the keel is used as a jig for building real Spaceships that go places, such as 1000t flights to Mars. Extra SunDancer and upper-stages are used for periodic station-keeping. The system really shines with propellant and reusable transfer stages coming back to it. <br /><br />The habitat is expandable- it is clipped longitudinally to the keel, consists of a series of 4 BA-330s docked to a 5m Node, stacked as many downward as partnership can afford. SunDancer baseblocks are positioned as needed to the Nodes or 330s. Clients can bring their own, just plug-n-play. Or they can rent time in a module. Several modules would be hotels, one might be restaurant/media suite, another two might be NASA, another module Hughes. Clients would include everyone from the rich and famous to satellite techs to National Geographic or NASA expeditions. The goal is to aggregate interests. <br /><br />The truss, power and first cluster of crew modules would be operated by "L1 Aggregators, Inc". The propellant storage, including redesigning Centaurs (etc) to be tugs, practical prop transfer, and exploring new sources of volatiles would be the duty of a separate "Prop Stop, Inc." Both would work in partnership with NASA and many industrial partners, especially Bigelow Aerospace and US launch providers.<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[samkent]

>>Most of, say a Mars stack, could spiral out to EML1 with an ion drive over 6 months needing only a fuel fraction of 10%.<br /><br />I can totally support this method of fuel savings, but EML1 is not required to do it.<br /><br />You could spiral the Mars stack farther over a longer period of time for greater savings. It doesn't have to be the sweet spot of EML1.

 

[j05h]

<i>> I can totally support this method of fuel savings, but EML1 is not required to do it.<br /><br />You could spiral the Mars stack farther over a longer period of time for greater savings. It doesn't have to be the sweet spot of EML1.</i><br /><br />As you say, EML1 is the sweet spot. The main advantage is that L1 enables use of components from many launch points on Earth, something that individual LEO orbits or a slow spiral outward don't allow. Instead of building the stack in LEO and spiralling it, the components are flown from all over to L1, then put together, checked out and flown. <br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[josh_simonson]

>You could spiral the Mars stack farther over a longer period of time for greater savings. It doesn't have to be the sweet spot of EML1.<br /><br />Indeed you could, however in a moon-mars-and-beyond plan EML1/2 is a good kick off point for all the potential destinations. This would allow a single model of SEP space tug to be used in all those campaigns. Any lunar infrastructure placed at EML1 could also be used for Mars and beyond. We don't want to repeat the mistake of the ISS, putting it somewhere that isn't suitable to be used in the next step in exploration. <br />

 

[quasar2]

i don`t believe i`ve seen this on here yet: i`ve heard that artifacts "in" emily could be seen during lunar transit. this is also a way to see the ISS. naturally since atrifacts in emily would be larger than those in leo, this would be good & bad. good in that people would finally be able to see "our" progress in space. ya know the one about th hoax, when we can`t see lunar surface artifacts, could be avoided. bad in that it could eventually be shameless advertising. <div class="Discussion_UserSignature"> </div>

 

[j05h]

L1's visibility from Earth is something I mentioned above. Put a big enough truss-module stack there, it creates permanent, visible presence to anyone looking up. A massive, cooperative L1 station would be progress, there is nothing wrong with advertising, per se, and that kind of advertising is priceless. <br /><br />The best feature of an L1 station is that it can be accretionary. Flights can arrive from anywhere on Earth (using a tug) and any extra hardware can be reused, adding to the station.<br /><br />"Emily" is a cool name for EML1, would the station be "Emily Transfer Station"? From an advertising viewpoint, "Emily" has strong branding possibilities that the space community should consider adopting - we can campaign for "Emily Station" more successfully than for "Logisitics And Manpower Extension Base". <br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[comga]

I don't see where you have mentioned the visibility of EML-1, but it is not obvious that it would be visible. It is centered on the line between the Earth and the Moon. As such, the center is always in front of the Moon, when seen from Earth. <br />What are the dimensions of stable pseudo-orbits? That is, are they larger than the Moon, and so make an object orbiting EML-1 visible against dark space, instead of the Moon? Or would such an object be visble only between last and first quarter, where more than half of the visible Moon is dark? <br /><br />At least we would always know where to look. <br /><br />Edit: A bit of research indicates that stable pseudo-orbits exist at L4 and L5, but not L1, L2, or L3. Those are metastable, and as such, corrective maneuvers will increase the farther the object gets from the stable point. Therefore, the most efficient location is on the Earth-Moon line, and a station at EML-1 would not be visible from Earth.

 

[samkent]

It sounds like a truck stop in space. Truck stops need a lot of traffic to be viable, and I just don’t see it happening. I would suspect you would need something at least as big as the ISS. And how many of us think we will try that again?<br /><br /> More likely the assembly would take place in an ISS type orbit and then the ion tugs will push the whole thing farther out over time.<br /><br />It’s like bio-diesel, it’s a nice idea but will never amount to more than a hand full of people collecting grease and batching their own.<br /><br />Besides, if you block my view of the Moon, I’ll sue!<br />

 

[j05h]

<i>> It sounds like a truck stop in space. Truck stops need a lot of traffic to be viable, and I just don’t see it happening. I would suspect you would need something at least as big as the ISS. And how many of us think we will try that again? </i><br /><br />A truck stop is exactly what I'm talking about. The L1 station accretes over time, it could start as a couple of Centaurs docked with a SunDancer and grow from there. The "keel + modules" approach would be much larger than ISS eventually. In the private-public-open architecture the "we" is mostly investors and business, unlike the govt-govt-corporate architecture of ISS. <br /><br />Any future stations will have much larger internal volume than ISS, while being lighter, cheaper structures. The Bigelow Aerospace BA-330 is going to change how we think of "space stations". The internal volume in a simple station consisting of node with 4 BA-330s and 2 SunDancers would be about twice ISS volume in a ~150t package. Price for something like that, delivered and assembled in LEO circa 2015, is perhaps $1-1.5G, from an avowed prime-builder of new-type space stations. Ordering early and ordering many would probably get you significant discounts, esp. coupled with bulk launch. My suggestion is that the bulk of the L1 "Emily" station be corporate owned-n-operated, including pressurized volume, tank-farm and the keel with an open-access policy between the station's partners. Clients would rent rooms or dock their own modules to the Habitat or separately on the keel. (and the keel is just an idea, it could just as easily be a half-dozen cooperative free-flyers or whatever works)<br /><br />This "new economy" approach can significantly change how spaceflight happens. put together many clients and a few anchor tenants and go for it. The truth of the L1 base as "truck stop" is that it is the perfect meeting point between LEO and the rest of anywhere. A single LEO orbit is cheaper to reach from a single Earth launch site, but if yo <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[h2ouniverse]

What about moving the ISS to EML1 after 2015? It would be so frustrating to have spent all that money to lift the tens of tons of the ISS, and seen them go back to ground...

 

[josh_simonson]

The delta-v to do that is prohibitive. <br /><br />I don't see any reason for anything but a temporary manned presence at EML1. Missions could even be staged there without any permanent station at all. Instead of EOR-LOR for lunar missions we could do L1R-L1R, and the lander could take a high-ISP route to L1. The Ares-IV concept (Ares 1 SS+CEV on Ares V instead of EDS) was suggested for it's ability to launch the CEV all the way to LLO or Lagrange points. This could even be done with LH2 if the SEP tug could also re-liquefy hydrogen. Sort of a mobile depot.<br /><br />There are many interesting archatectures that can be implemented with depots, tugs and various staging points. NASA's current plant is pretty much the simplest bare bones plan possible, but isn't the best as far as scalability goes.

 

[h2ouniverse]

Has anyone done the calculation with ion engines (or vasimr), for the LEO to EML1 transfer?

 

[j05h]

ISS is designed for LEO, not L1; it is a research station not a transfer station, it lacks the tooling and liquid storage for what i'm talking about. ISS should continue to be what it is: a government research station. <br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[h2ouniverse]

in reply to<br />"The Delta V requied is exactly the same no matter what propulsion technique is used. "<br />---------<br />I know.<br />I was talking about the needed propellant mass (that is highly dependent on Specific Impulse, knowing that ion/plasma drive can be already better than 4000s)(12 times better than bi-propellant chemical propulsion). I'll make a calculation to feel how much Xe supply that would represent.

 

[spacester]

<font color="yellow">The Delta V required is exactly the same no matter what propulsion technique is used.</font><br /><br />Not true.<br /><br />[ *gasp* goes the crowd! Some guy is trying to correct SG!! ]<br /><br />I'm sorry folks, but this thread is too good to let that unqualified statement stand. I saw this claim the other day and let it pass, but not here, OK?<br /><br />Gravity losses matter, and you get a LOT of gravity losses with ion drive because you aren't burning at an apse.<br /><br />Trajectory matters. Anything other than Hohmann takes more Delta V.<br /><br />Eccentricity matters. Hohmann isn't even *defined* for non-circular orbits.<br /><br />Navigational precision matters. If you aren't pointed the right direction when you burn your rockets, you get gravity losses of another kind.<br /><br />Burn times matter - different propulsion techniques deliver differing thrust, so for a given trajectory different burn times are required, and that means different gravity losses. <br /><br />SG, perhaps you meant to qualify your statement?<br /> <div class="Discussion_UserSignature"> </div>

 

[spacester]

SG, I don't have time for this this morning, and I know for sure that you're a very busy guy as well, doing important work.<br /><br />What would it take for you to accept the fact that I *am* an expert? How many correct results are required? Or is the main thing having 'credentials?'<br /><br />I've been waiting for 6 years for a "pro" to show up here and back me up. It ain't gonna happen, they don't give their precious expertise away. Which is the main reason I started this course of study 6 years ago: to provide my fellow poor slobs who are not in the industry access to the numbers needed to flesh out our dreams. I do not take this task lightly. I am a Mechanical Engineer with a strong ethic of not speaking to subjects beyond my knowledge.<br /><br />A guy can learn a lot in 6 years of continuous study.<br /><br />Math is math. You appeal to authority, I appeal to mathematics. You are wrong on several points. More tonight. <br /><br />BTW, I'd appeal to Keermalec for a few points here, but he doesn't seem to be around this year so far. <div class="Discussion_UserSignature"> </div>

 

[j05h]

Instead of arguing about gravity losses from low-thrust engines, how about fleshing out the numbers for the craft we have now? I'm thinking of things like Centaur and IUS, Fregat and whatevs the Ariane uses. What are the numbers like for those stages going to L1? No, I'm not discounting ion/Hall thrusters, just that they aren't currently built into a long-duration Tug architecture.<br /><br />Spacester, so-called "amateurs" change the world in every field of endeavor. <br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[samkent]

There are just sooo many reasons why this truck stop will never happen.<br /><br />1. There is just no need for it.<br /> We can barely justify keeping men in orbit now let alone to man a depot. <br /> We may put boots back on the Moon, but I see it as 50/50. As for Mars, not in this century.<br /><br />2. Cost.<br /> For the amount of money spent on this truck stop, you could have numerous robotic missions. What percentage of time would it actually be used for its intended purpose? Would you purchase a new car if you only drove it once a year?<br /><br />3. Risk to humans.<br /> Assembly of huge modules is very dangerous work. If an astronaut has a crushed arm or a torso puncture, he might survive the 2-3 hours it takes to get him on the ground. But how many hours would it take from L1?<br /><br />IMO<br />The mythology of the advantages are based in a Star Trek world.<br />

 

[j05h]

Not prop needed (though that'd be useful), more mass each common, existing stage can deliver to L1. <br /><br />J <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[j05h]

<i>> 1. There is just no need for it.<br />We can barely justify keeping men in orbit now let alone to man a depot.<br />We may put boots back on the Moon, but I see it as 50/50. As for Mars, not in this century. </i><br /><br />Yeah, optimism! An L1 station does not make sense with the current number of space launches, but with projects that potential double or more current launches, it does begin to make sense. The Moon project done with ELV and aimed at ISRU does this. So does a single "Bigelow" type hotel if only counting launches to support human flight. It definitely requires more payloads and new ways of procuring them. <br /><br /><i>> 2. Cost.<br />For the amount of money spent on this truck stop, you could have numerous robotic missions. What percentage of time would it actually be used for its intended purpose? Would you purchase a new car if you only drove it once a year? </i><br /><br />The stations intended purpose as outlined is legion - whatever makes money. It's not another ISS, it needs to be built and operated mostly privately to work. NASA can't afford it, but would make an ideal anchor tenant. Other potential tenants include Hughes and other comsat manufacturers, Bigelow-based Hotels and the propellant depot operator. <br /><br />The number of scientific robotic missions is irrelevant, that kind of measure makes no sense from a business perspective because separate robots don't make a "place" to make money. The station could easily start man-tended and grow from there, be completely automatic or start with only a single client/customer and grow from there. If you read above, however, you will see that I'm discussing a heavily-aggregated model where as many stakeholders as possible are brought together to make L1 make sense. <br /><br />This is not about "exploration" alone. <br /><br /><i>> 3. Risk to humans.<br />Assembly of huge modules is very dangerous work. If an astronaut has a crushed arm or a torso puncture, he might survive the 2-3 hours it ta</i> <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[josh_simonson]

At isp of 450, the fuel fraction for the L1 burn is about 58%. At isp of 4500, the fuel fraction is 8%. With that kind of savings, who cares which one is slightly less efficient due to second, third and fourth order effects.<br /><br />L1 staging doesn't require anything except the SEP tug, with a big bonus for re-liquification capability. All the tug needs is a physical connection to push through, and perhaps a couple fuel lines for re-liquification. That would not require EVA, and is hardly sci-fi. All components needed for an SEP tug exist as mature technologies that would only need to be implemented on a larger scale.<br /><br />Without reliquification, it could still be done with LOX/methane, for a fuel fraction penalty of 6% on the lander. 42% to 48%. <br /><br />An added benefit of EML-1/2 is that the DV to get to earth from them is 0.77 and 0.33km/s respectively - as opposed to 1.31km/s from the moon. This reduces the size of the CEV SM considerably. It would even fit on the Ares 1. <img src="/images/icons/wink.gif" /> The lower return DV from EML-2 is a big part of why some prefer it.

 

[h2ouniverse]

To shuttle_guy and spacester,<br /><br />Imho, you are not talking exactly about the same thing, hence your dispute.<br /><br />Spacester, you are considering the general case. If you talk about the actual increase in orbit energy for the spacecraft after a thrust, then, granted, it will depend on how efficient your thrust is (alignment vs velocity vector), and on whether you boost at peripapsis (when S/C velocity is large) or at apoapsis (when S/C velocity is low)(Oberth effect). The delta-V is then dependent on the trajectory.<br /><br />But in system engineering, we tend also to consider the <br />"delta-V" between the two velocities of initial and final orbits, when achieving a slow transfer between two circular orbits (the case there, as ISS current orbit is quasi-circular, as EML1 orbit around the CoG of Earth-Moon). The difference due to the offset of the centers of rotation (Earth's centre in first case, Earth-Moon cog in the second) is too low to result into a significant EML1 orbit "non-circularity" in Earth-centered referential. (<2%). <br /><br />As first approximation, it is therefore most convenient to infer propellant mass from "delta-V" between the two orbits, especially in the case of ion/plasma prop (quasi-circular spiralling up over several months!). And that was the issue there. That is why there is ground for using delta-V to compute fuel mass.<br /><br />Note that: the very high Isp of ion/plasma will far more than compensate the efficiency loss due to the deviation from the perfect Hohmann transfer.<br />Note too that even with chemical propulsion, maneuvers are often split into 3 or 4, to limit stress on thrusters, enable control of the burst parameters and avoid fuel-consuming overshoots!.<br /><br />Best regards.<br />

 

[spacester]

Hi josh_simonson,<br /><br />I never have figured out out to respond to a post such as this one of yours. <br /><br />I've spent years providing detailed calculations in an effort to establish credibility. IMHO certain people here just cannot handle the concept of someone not in the industry being capable of digging deeper and providing more detail than they got in their textbooks. <br /><br />Even after all my work, SG refuses to show me any respect. The fact is, I can out-orbital mechanic him with one semi-latus rectum tied behind my back. An expert can tell the level of expertise of others by their language. SG is NOT an expert on the subject, but he wants to play the role. Fine, I let him, until he spreads dis-information and confusion.<br /><br />You made a post, I'm sure you're trying to help. But all it amounts to is a series of claims, with nothing to back it up.<br /><br />So what you're asking me to do is ignore the fact that although I've provided for years every detailed step for every calc I offer, I get not even the 'benefit of doubt', and then I'm to turn around and accept your numbers without question.<br /><br />Can you see my position here? What is it you want me to do with your statements? Accept the numbers without any support, and agree with your conclusions? Sure, OK, yeah, brilliant analysis there josh, I guess. So you say, anyway. To verify the numbers you base your conclusions on, I need to reconstruct the calculations from scratch. When do I get the benefit of the kind of detailed presentation I provide?<br /><br />IOW, if you want to throw some numbers out there without any support, go right ahead, 'it's a free country'. But all it does is make matters worse for me. (Who cares, right?) I've posted 100 times the math you have here, and no one can find errors in it, because I check and double check and write it all out and show all my work, and I don't post until I am *SURE*. How am I to be expected to just accept your numbers without any support? Not <div class="Discussion_UserSignature"> </div>

 

[gunsandrockets]

<BTW, I'd appeal to Keermalec for a few points here, but he doesn't seem to be around this year so far.><br /><br />Check out this older thread from SB&T that begins...<br /><br />http://uplink.space.com/showthreaded.php?Cat=&Board=businesstech&Number=814501&page=0&view=collapsed&sb=5&o=0&vc=1<br /><br />... in that thread Keermalec and I had a very productive discussion regarding low-thrust propulsion for a Mars mission. The rule of thumb as I understand it is low-thrust propulsion suffers a roughly 50% penalty compared to high-thrust propulsion for TMI.

 

[spacester]

I wrote this last night, it didn't meet my editorial standards so i didn't post it. But this morning I say wth and so here it is.<br />***<br />H2Ouniverse, yes I think we are talking about two different things. But my usage is correct, and SG's is wrong. It just is.<br /><br />First of all, I am responding to the statement SG made. IIRC it was verbatim the same as a post from him a few days earlier. Scroll up and look at what he said. Notice the word 'exactly'? SG is like a god around here, and I'm sure he has the best of intentions but his statement is disinformation. Does 'exactly' mean what I think it means? I didn't write such a silly thing as '. . . exactly the same, no matter . . . '. Also, BTW, this thing between me and him goes way back. I show him respect, he does not return the favor. But he is much less condescending towards folks than he used to be, so I let a lot of his mistakes go by these days. Still, some things are just too far off the plantation to let pass.<br /><br />Allow me to present some background material for folks first, before I respond to your points. I feel I have to try to establish credibility to start every post here. It ended up being a long post, but I'm not just arguing, I'm trying to educate.<br /><br />When we talk of Delta V, we are in the typical case talking about the quantity used in the rocket equation. Take the dV required for your mission, divide by your engine's exhaust velocity (which is the constant 'g' times the specific impulse). Use that result as the exponent of the number 'e' and you get a dimensionless number which you can interpret to tell you what percentage of your craft has to be propellant.<br /><br />But dV also serves as the link to the orbital mechanics problem. IOW you have to solve the trajectory problem and get dV before you can use the rocket equation. IOW where and when you want to go someplace on orbit represents a performance requirement called dV, and the rocket equation needs to know the dV so you can des <div class="Discussion_UserSignature"> </div>