Author Topic: LIVE: Full Committee Hearing - A Review of NASA's Space Launch System  (Read 338746 times)

Offline sergeante

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By shipping material and fuel to those points through various efficient means such as high delta t low delta v ballistic trajectories or ion propulsion and doing your in space assembly there, delta v can be accumulated and stockpiled at lower cost than simply building and fueling a big Earth Departure Stage (EDS) in LEO and lighting it off to go on your way to a NEO or Phobos or Mars.

You still have to lift all of it into LEO to begin with. Moving it someplace else doesn't change that cost. Moving it to a higher orbit* is an extra cost. Why do it, if everything starts in LEO at some point anyway?

*Lest we forget, an orbit at an EML point is still just an orbit. It's not magic. You have to spend the energy to enter a transfer trajectory, and then the energy to insert into the orbit.

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Also, as Robotbeat says, an EML assembly point is inclination neutral for purposes of terrestrial launch sites. Therefore, less politics is involved.

That's true, as far as it goes. But I've never seen numbers that justify the extra impulse to get there, just to even out the mission impulse for participants with differently inclined launch sites.

Offline 93143

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Let me just point out here that delta-V doesn't add linearly.  If you fully fuel a transfer vehicle at an L-point, the delta-V bonus from an Earth swingby can be larger than you could ever get starting from LEO.  This could increase the achievable transit speed.

Alternately, you could achieve Earth escape with an electric stage without the weeks-long spiral out of LEO, which also improves mission time.

These are in addition to the advantages cited by Bill White.

There's also the possibility of mining the lunar polar craters for ice (current indications are that there is a lot of it, and relatively pure), cracking it into LOX and LH2, and sending it to an L-point depot on a reusable lander for a lot less delta-V than would be required from Earth.  This is a much nearer-term possibility than you seem to think.

...

On the subject of reusability, wasn't that part of the idea of the NAUTILUS-X?  I suppose using the same ship for multiple Mars missions would be further down the line...

Online Robotbeat

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Jason,
Do you have any idea how difficult it is to build a 100% reusable rocket engine that you can trust crews lives to, that CAN'T BE INSPECTED between uses?   That's what you're assuming all-too-casually there.

Also, cryogenic pressure tanks (LOX, LCH4 and LH2 alike) have to go through far more heat and load cycles in orbit than they ever would for a launch vehicle.   Shuttle ET's are a case in point -- they can only go through, what, 13 thermal/pressure cycles?   Yet a stage on orbit is going to have to go through those, plus long durations of cold-storage interspersed with intense sunlight.   And radiation, molecular oxygen and other factors that aren't immediately apparent.   The requirements for that are far more demanding than anything we've done to date.

Don't get me wrong, I'm all for an in-space infrastructure to reduce our dependence on Earth-launched materials and equipment,   But its unrealistic to expect to use any existing hardware.   NOTHING has so far been built to do any of these things with humans in the mix -- and its going to take a MAJOR effort to develop the necessary systems to a safe enough level that we can depend on them "unseen".

Ross.
So, you just design the stage for more thermal cycles. Big deal. It only adds very marginally to the mission mass for an order of magnitude increase in number of thermal cycles.

ISS's thrusters on the Russian segment are examples of rocket engines that are plenty safe enough for a manned spacecraft and have burned tons of fuel (and have been refueled) and have been on-orbit for a decade and will be up there being used for another decade or two (and they are DECADES old, having been originally built--structurally, at least--in the 1980s). That's about what a multi-mission exploration craft would be expected to do for many, many missions. It's clearly possible because it has already been done. ISS goes through many more thermal cycles (plus more orbital debris and atomic oxygen, etc) than infrastructure placed at a Lagrange point would.

It's possible to do on-orbit inspection, and to design engines to be easier to remotely inspect (SSME, which must be torn down, is not the only way to do it).
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Offline Jason1701

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the exploration vehicles mass is a small fraction of propellant, supplies, crew, and any auxiliary vehicles (sats, landers, etc.)

True, but propellant and supplies are extremely cheap. I should have stressed in my last post that reusing value is important, not mass alone.


1. how difficult it is to build a 100% reusable rocket engine that you can trust crews lives to, that CAN'T BE INSPECTED between uses? ...

2. cryogenic pressure tanks (LOX, LCH4 and LH2 alike) have to go through far more heat and load cycles in orbit than they ever would for a launch vehicle.   Shuttle ET's are a case in point -- they can only go through, what, 13 thermal/pressure cycles?   Yet a stage on orbit is going to have to go through those, plus long durations of cold-storage interspersed with intense sunlight.   And radiation, molecular oxygen and other factors that aren't immediately apparent.   The requirements for that are far more demanding than anything we've done to date.

1. Then have multiple redundant rocket engines, or launch a new engine module for each mission. The value of the engine is small compared to the value of the rest of the ship.

2. One solution is to not use cryogenic propellants, which wouldn't be a huge handicap because of the low dv that the L-points enable. Your point is good, but it will have to be solved for any exploration architecture that uses chemical propellants, whether or not the bulk of the hardware is reusable.

Many of these issues have been addressed in the Nautilus thread.

Offline sergeante

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Very likely, if you're going to Mars (since very-low-boiloff is already a requirement for a cryogenic chemical or NTR Mars mission for the return). Also, the amount of delta-v you need once at EML1/2 is much smaller, meaning that hypergolic or other non-hydrogen stages would be not such a big hit.... And besides, you're going to be hanging out in LEO for any kind of Mars mission because it'd take multiple launches (i.e. likely months) of even the monster Ares V to get enough propellant. So yes, you still need very-low-boiloff technology.

Low boiloff technology in a small stage (i.e. Earth return stage) is probably more accessible than in a large one (i.e. EDS).

As for the delta-v you need from an EML, to borrow a phrase, so what? You still had to spend the energy to get there. TANSTAAFL.

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Your assumption, then, is that all the industrial infrastructure will always be on Earth (not counting the far future). Then, your conclusion is that we should not build industrial infrastructure (multi-mission depot, etc) off of Earth? Interesting logic. If I agree with your assumption, then of course I'd agree with your conclusion.

Not so much an assumption as educated judgment. The problem with a space industrial infrastructure is that you wind up lofting hundreds or thousands of tons of infrastructure with lift you could have invested in exploration resources. You need a huge investment in exploration to justify it. I don't see that for decades, perhaps centuries.

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...(by the way, if you're using chemical rockets, you can use the Oberth effect twice, thus giving you more benefit... like as if your rockets had twice as much thrust... and you can use both the Earth and the Moon as gravitational levers... so there IS some fundamental benefits in the idealized sense)

I wouldn't base an overall plan on the occasional Earth-Moon alignment. Also, to take advantage of that alignment, you have to what? That's right, expend propellant. It might not be much delta-v to drop from EML1/2 to a lunar orbit that gives you an Oberth opportunity, but you still spend propellant within that opportunity to get less of an energy gain than the same propellant would get you in an Earth orbit. And you can only use any quantity of propellant exactly once.

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An EML1/2 gateway or depot or rendezvous point or whatever does have the benefit that we can take advantage of all the launch infrastructure on Earth instead of just the launch infrastructure at a certain latitude, while also avoiding the cost of launching to a high-inclination (say, ISS) orbit from a mostly-equatorial launch site... everyone can launch with the most efficiency. Unless, of course, you're assuming that we launch a single enormous HLV straight to Mars, we're going to have to do some assembly in orbit. Apollo was built assuming NO infrastructure in orbit because space was entirely new and there was a race. That is no longer true... we have many satellites for communication, for instance.

Can't get something for nothing. You still have to haul all that stuff uphill to the EML before you can use it. And when you get there, it might be relatively cheap to make your plane change, but you still had to haul it all uphill.

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Launch efficiency (expressed in mission-total IMLEO) isn't the only metric that matters (and even then, there are some advantages to EML rendezvous/depot/etc).

Only with technological and budget assumptions that I find wildly optimistic.
« Last Edit: 07/27/2011 06:10 PM by sergeante »

Offline Jason1701

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Launch efficiency (expressed in mission-total IMLEO) isn't the only metric that matters (and even then, there are some advantages to EML rendezvous/depot/etc).

Only with technological and budget assumptions that I find wildly optimistic.

You're saying that mass is more important to minimize than total integrated mission cost? I think everyone here would disagree.

Offline sergeante

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Let me just point out here that delta-V doesn't add linearly.  If you fully fuel a transfer vehicle at an L-point, the delta-V bonus from an Earth swingby can be larger than you could ever get starting from LEO.  This could increase the achievable transit speed.

You still had to spend the energy to lift the propellant uphill. You can't get more energy into propellant by dropping it from a high orbit than you spent to put it there.

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Alternately, you could achieve Earth escape with an electric stage without the weeks-long spiral out of LEO, which also improves mission time.

Or you could just spend the energy used to put the stage into an EML to give it a kick from LEO into an almost transfer orbit, and use the electric propulsion to do the rest.

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There's also the possibility of mining the lunar polar craters for ice (current indications are that there is a lot of it, and relatively pure), cracking it into LOX and LH2, and sending it to an L-point depot on a reusable lander for a lot less delta-V than would be required from Earth.  This is a much nearer-term possibility than you seem to think.

I alway love this option. How many hundreds or thousands of tons of industrial base do you have to put on the Moon and in cislunar space to extract, refine, and deliver this lunar propellant resource? Nobody knows, but they assume it has to be less than just using the same machinery and lift to do something more directly useful.

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On the subject of reusability, wasn't that part of the idea of the NAUTILUS-X?  I suppose using the same ship for multiple Mars missions would be further down the line...

Way further down the line...

Offline sergeante

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You're saying that mass is more important to minimize than total integrated mission cost? I think everyone here would disagree.

I'm saying that, given a certain lifting capacity, payload to objectives is more important to maximize.

And I'm simply not seeing how the costs are going to be less for using the lifting capacity to goof around with infrastructure projects than it will be to use it to go places. That's what the lunar resources and EML1/2 people miss -- that infrastructure costs real shekels and real payload space. It would take an enormous continuous exploration investment to make it pay off.

Offline sergeante

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True, but propellant and supplies are extremely cheap. I should have stressed in my last post that reusing value is important, not mass alone.

You're already committed to expending the value of propellant, cargo, and crew shuttles. Those are not cheap.

Offline JohnFornaro

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Quote from: Seargente
Guys...stick with me -- we are not going to have an industrial base anyware except the Earth for the deep foreseeable future.

This is well known.  Everything is built on Earth, dry.  The only possibility of a new technique is to make prop in the dark lunar craters, and drop it to a convenient point; L1 or LEO.  This would help the very massive issue of propellant launch from Earth's surface, altho such a scheme is only in the early design stages.

Orbital assembly is a given as well.  Should that be in LEO, and if so, at ISS, or a better inclination for lunar or martian orbit injection.  Should the assembly take place at L1 or L2?

I'm not sure what your objection is.

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The exploration vehicle would have to be reconditioned after each mission.

While this is certainly true, the only alternative would be to construct a new one for each mission.  WRT Mars, unless official strategies can be changed, there will only be one photographic mission, and the flag will cost a bit more, but it would probably be within that budget.  WRT the Moon, reusability seems to be desirable.

That whole restartability and reliability thing that Ross mentions also comes into play, and the cost of this new capability far outweighs the delta-vee costs by any measure.  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.

IMLEO is not the only metric that matters.

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...that infrastructure costs real shekels and real payload space...

This is quite well known, too.  One of the biggest complaints about SLS is that it is a huge rocket for no known or budgeted missions.

Again, it's not clear where you're headed with your line of reasoning.
Sometimes I just flat out don't get it.

Online Robotbeat

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Very likely, if you're going to Mars (since very-low-boiloff is already a requirement for a cryogenic chemical or NTR Mars mission for the return). Also, the amount of delta-v you need once at EML1/2 is much smaller, meaning that hypergolic or other non-hydrogen stages would be not such a big hit.... And besides, you're going to be hanging out in LEO for any kind of Mars mission because it'd take multiple launches (i.e. likely months) of even the monster Ares V to get enough propellant. So yes, you still need very-low-boiloff technology.

Low boiloff technology in a small stage (i.e. Earth return stage) is probably more accessible than in a large one (i.e. EDS).
The technology needed is the same, and because of the larger surface-area-to-mass ratio of the smaller stage (and the longer time it needs to have low-boiloff), design of a larger stage at a certain boil-off rate should actually be a lot easier than for a smaller one, so actually the opposite of what you said.

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As for the delta-v you need from an EML, to borrow a phrase, so what? You still had to spend the energy to get there. TANSTAAFL.
Yes, there is such a thing as a free lunch. You can leverage incredibly high SEP (which has the benefit of the enormous improvements in specific power for solar arrays) for a huge portion of the mission delta-v if you so decide. If you don't do EML (or, I suppose, high Earth-orbit) rendezvous, you can't really take advantage of this unless you intend to buy into the difficulty of an entirely SEP (or NEP)-propelled spacecraft.

Another large benefit is that of safety. Most spacecraft failures occur at the beginning of the mission, and the rate of failure drops gradually as the time in space increases. Thus, by rendezvous just at the edge of Earth-escape, you don't have to commit to the mission  until most of the things that are going to fail have already failed and you can plan accordingly (or fix them before leaving Earth-Moon). The environment at an EML point is much closer to deep space than it is in LEO (where you have much quicker and more intense thermal cycles, atomic oxygen, and greater drag which may mean you have to wait to deploy large structures like solar arrays, radiators, etc), so it gives you the opportunity to test your craft before leaving the Earth-Moon system. You get rid of all the infant-mortality failures and are left mostly with the better-understood-and-modeled-and-predicted fatigue-type failures.
« Last Edit: 07/27/2011 06:29 PM by Robotbeat »
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Offline Bill White

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You're saying that mass is more important to minimize than total integrated mission cost? I think everyone here would disagree.

I'm saying that, given a certain lifting capacity, payload to objectives is more important to maximize.

And I'm simply not seeing how the costs are going to be less for using the lifting capacity to goof around with infrastructure projects than it will be to use it to go places. That's what the lunar resources and EML1/2 people miss -- that infrastructure costs real shekels and real payload space. It would take an enormous continuous exploration investment to make it pay off.

sergeante, I agree with this:

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It would take an enormous continuous exploration investment to make it pay off.

However I am not persuaded human spaceflight is worth funding UNLESS we intend to make a continuous exploration investment.

Unless we are going to stay (at least eventually) just send robots.

= = =

Also too, EML assembly would not require massive infrastructure or permanent human presence. Think human tended, not human occupied.

= = =

Also, also too - - despite being a DIRECT / SLS supporter I would not be confident in a single launch Mars or NEO mission and once we start doing on orbit assembly of missions using EML to assemble just makes more sense to me than using LEO to assemble.

As I have said for years and years, I believe the Jupiter 246 would be an ideal launch vehicle to support a robust EML based program of lunar and beyond cis-lunar exploration.

It can be done with smaller rockets, just not as efficiently.
« Last Edit: 07/27/2011 06:37 PM by Bill White »
EML architectures should be seen as ratchet opportunities

Online Robotbeat

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True, but propellant and supplies are extremely cheap. I should have stressed in my last post that reusing value is important, not mass alone.

You're already committed to expending the value of propellant, cargo, and crew shuttles. Those are not cheap.
...hmmm... big on Mars... fan of HLVs... not a fan of in-space infrastructure... Robert Zubrin, is that you? ;)
« Last Edit: 07/27/2011 06:46 PM by Robotbeat »
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Offline kraisee

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So, you just design the stage for more thermal cycles. Big deal. It only adds very marginally to the mission mass for an order of magnitude increase in number of thermal cycles.

That doesn't worry me.   Neither the raw material costs, nor even the weight penalties are all that big of an issue.

Its the likely 8 years and $10 billion in development costs for a new FULLY REUSABLE AND HUMAN-RATED stage and engine system, that concern me considerably.

Ross.
« Last Edit: 07/27/2011 06:47 PM by kraisee »
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Offline sergeante

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This is well known.  Everything is built on Earth, dry.  The only possibility of a new technique is to make prop in the dark lunar craters, and drop it to a convenient point; L1 or LEO.  This would help the very massive issue of propellant launch from Earth's surface, altho such a scheme is only in the early design stages.

And I simply don't believe anybody is going to invest the payload capacity to do it, not for a long time.

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Orbital assembly is a given as well.  Should that be in LEO, and if so, at ISS, or a better inclination for lunar or martian orbit injection.  Should the assembly take place at L1 or L2?

It should be in the orbit that best uses the injection impulse for the specfic opportunity the spacecraft is built for. IOW, it should be in an orbit analogous to the pre-interplanetary parking orbits used for robotic exploration spacecraft.

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I'm not sure what your objection is.

That all of this speculation about the utility of an EML assembly point ignores technological and economic reality.

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While this is certainly true, the only alternative would be to construct a new one for each mission.  WRT Mars, unless official strategies can be changed, there will only be one photographic mission, and the flag will cost a bit more, but it would probably be within that budget.  WRT the Moon, reusability seems to be desirable.

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.

Also, even if on-orbit refurbished spacecraft became acceptable, there is a cost to lofting, manning, and supplying you refurbishment facility. There's no guarantee -- and IMO little hope -- that the expense would be justified over just using new spacecraft each time.

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IMLEO is not the only metric that matters.

It's the driving metric with realistic economic and technological assumptions.

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This is quite well known, too.  One of the biggest complaints about SLS is that it is a huge rocket for no known or budgeted missions.

There's even less budgeted mission for EML1/2 infrastructure. EML1/2 infrastructure literally puts the cart before the horse. we're in the crawling phase, which is direct throw to the objective. Someday, in several decades or a few centuries, we'll be in the walking phase, with some in-space infrastructure making sense. Someday after that, in the unpredictable far future, well be in the runnin phase, with a reasonable selfsufficient space civilization. Let's keep things in their proper order.

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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.

Offline sergeante

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...hmmm... big on Mars... fan of HLVs... not a fan of in-space infrastructure... Robert Zubrin, is that you? ;)

Not at all that big on Mars. I'm for expanding the boundaries of human exploration incrementally, but making sure those boundaries stay put once pushed back. I'd start with NEO rendezvous, then Mars flyby, then Mars orbit, then Mars landing. After that, which I think will take at least thirty years, we'll see what kind of technology and funding we have and where we should go with it.

Not a fan of super heavy launch vehicles. Just convinced that they represent the correct technological direction to take exploration launch vehicles.

Not convinced that in-sapce infrastructure is economically justifiable or technically useful in the next several decades.

Robert Zubrin...I always tell people to hold on to their wallets with him. He's trying to sell you something.

Offline sergeante

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The technology needed is the same, and because of the larger surface-area-to-mass ratio of the smaller stage (and the longer time it needs to have low-boiloff), design of a larger stage at a certain boil-off rate should actually be a lot easier than for a smaller one, so actually the opposite of what you said.

Superficially, I would agree with you. But a smaller stage is easier to shade. You can also configure it so that it has the same diameter of a larger stage and optimize it's orientation towards the Sun (i. e. PTC AKA "barbecue" roll) during transit.

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Yes, there is such a thing as a free lunch. You can leverage incredibly high SEP (which has the benefit of the enormous improvements in specific power for solar arrays) for a huge portion of the mission delta-v if you so decide. If you don't do EML (or, I suppose, high Earth-orbit) rendezvous, you can't really take advantage of this unless you intend to buy into the difficulty of an entirely SEP (or NEP)-propelled spacecraft.

Once again, if I were doing mission design, I'd invest my chemical propellants in Earth escape and use my SEP to get a quicker transit.

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Another large benefit is that of safety. Most spacecraft failures occur at the beginning of the mission, and the rate of failure drops gradually as the time in space increases. Thus, by rendezvous just at the edge of Earth-escape, you don't have to commit to the mission  until most of the things that are going to fail have already failed and you can plan accordingly (or fix them before leaving Earth-Moon). The environment at an EML point is much closer to deep space than it is in LEO (where you have much quicker and more intense thermal cycles, atomic oxygen, and greater drag which may mean you have to wait to deploy large structures like solar arrays, radiators, etc), so it gives you the opportunity to test your craft before leaving the Earth-Moon system. You get rid of all the infant-mortality failures and are left mostly with the better-understood-and-modeled-and-predicted fatigue-type failures.

The flip side of that is that you trade infant mortality for extra operational service time in space in which the equipment can fail. I'm not sure you could justify that with an honest trade study.
« Last Edit: 07/27/2011 07:10 PM by sergeante »

Offline sergeante

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sergeante, I agree with this:

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It would take an enormous continuous exploration investment to make it pay off.

However I am not persuaded human spaceflight is worth funding UNLESS we intend to make a continuous exploration investment.

Unless we are going to stay (at least eventually) just send robots.

Continuous investment I'm for. Enormous continuous investment to unprecedented levels is not worth wasting analysis time on. It ain't in the cards.

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Also too, EML assembly would not require massive infrastructure or permanent human presence. Think human tended, not human occupied.

Docking type and maybe a few EVAs type assembly is not going to require a lot of human involvement. A spacecraft refurbishment architecture will.

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Also, also too - - despite being a DIRECT / SLS supporter I would not be confident in a single launch Mars or NEO mission and once we start doing on orbit assembly of missions using EML to assemble just makes more sense to me than using LEO to assemble.

Docking is docking, wherever you do it.


Online Robotbeat

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In-space infrastructure is basically what we need in order to keep the boundaries pushed back.

What happened after Apollo, when we ran out of the launch vehicles we had stopped building halfway through? We stayed on the ground.

What happened to us after we stopped flying Shuttle? Well, the first time, we sat on the ground until we fixed Shuttle. The second time, after we had in-space infrastructure built, we stayed in orbit. Now that Shuttle has stopped flying altogether, ISS is now entirely going to be supported by launch vehicles which have other military and commercial uses (like Shuttle was supposed to be... how I wish that would've worked out!), thus they're not going to just sit on the ground anymore.

If we build an EML gateway and a reusable lunar lander using multiple launch vehicles (which have continual military and commercial use), we will not have to be tied to the canceling of any one launch vehicle or any one launch vehicle's grounding after an accident. The in-space infrastructure would keep us there, at the boundary of human exploration, and not retreating like what happened after Apollo. The Soviets also had in-space infrastructure and basically, once they launched their first space station, they had a nearly-unbroken continual presence in space for much less money than the US's approach (until ISS) of relying almost entirely on ground-based infrastructure and only doing short missions of only a week or two at a time.

In-space infrastructure seems to be the only proven way of "making sure those boundaries stay put once pushed back."

(Now Jim comes on and says that's not in NASA's charter. :) )
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Offline sergeante

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In-space infrastructure seems to be the only proven way of "making sure those boundaries stay put once pushed back."

Even in-space infrastructure needs funding. Funding can be pulled. A much better model is a national policy commitment to never doing less than we have already accomplished, which you would need anyway, whether your program was exploration or building an EML/Lunar infrastructure. (I don't think it's realistic to do both at once, politically and economically.)

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