Author Topic: LEO is halfway to anywhere in solar system. Fact or fiction ?  (Read 26404 times)

Offline gbaikie

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LEO is far more than 'half way' to the Moon/Mars, etc..... judged by cost/energy required... in part because a launch requires you to beat aerodynamic and gravity drag...

ApolloEnergyRequirements: https://en.wikipedia.org/wiki/File:ApolloEnergyRequirementsMSC1966.png

As I read it, it took 5.6 million pounds of fuel to get to low earth orbit...  only about 200,000 lbs for the entire rest of the mission...
So, by fuel/energy required, LEO was 96% of the way to the Moon..and back.
Btw...
LEO to Low Lunar Orbit Delta V is 4.04 km/sec...
LEO to Mars Transfer Orbit is only 4.3 km/sec..
LEO to escape velocity is only 3.2 km/sec... remember that LEO velocity = 17,000 mph, escape velocity is only 25,000 mph

Ok so you making an economic argument.
A simpler type of economic argument is what is seat cost difference between LEO and Lunar surface.
Or roughly 50 million to LEO and 500 million to lunar surface.
But either of these arguments are based on viewing it in terms a commercial operation.
And to imagine what NASA is doing is vaguely related to some kind of commercial operation
is a mistake.
So in commercial operation, one can have lower seat cost by having more seats. Therefore if flying 7 vs 2
one can considerably lower costs per seat.
Or if want to look at terms mass, Apollo put 200,000 lbs crew and machine to LEO, and 33,000 lbs
on the lunar surface. Or 1/6th mass was put on moon as compared to put in LEO.

A better metric for NASA [and applies to commercial] is time.
One has set amount of money and how much can you do in a year or decade.
With commercial one can attempt to put dollar amount on whatever the activity is.
With NASA one has establish what is the value.
And this very difficult, particular when a significant value is as a job program.
But it easy to see that if shorten a program in terms of time, one lowers
cost of program. If you also see that if there is no shortage of programs
one doesn't have worry too much about the "job program value" unless
one imagines that people doing repetitive things or same thing is something
desired for your job program- it certainly requires less ability for the management
of the job program. So there is less meaningful work for management in terms of
managing. Which not to say management can't fill it's schedule with endless
activity- they very practiced at doing this.

The other aspect of shortening a program time has to do with having a defined
goal, and having enough time to achieve this goal.
If the goal is to have lunar base forever, one can get confused over the matter
of time. But for lunar base "forever" what obvious is the cost per year should
be low.
I would say doing something forever is not something NASA should focus on,
but rather should focus on what it do in the shortest time period.
So for example I think NASA could explore the Moon as a program in about 6
years, whereas such relatively short time period would insufficient for a
Manned Mars program.
For anyone imagining that we have explored the Moon, one tend to think
that any additional exploration should not require much time. But the actual
fact is that we have not explored the polar regions of the Moon. And safe to
say that polar region are radically different on the Moon compared to other regions
of the Moon. Or there is less difference between Antarctic and rest of Earth,
as compared to lunar poles and rest of the Moon.
Another aspect is lunar poles are a tiny area- though this does depend somewhat
what meant by lunar polar region. But in any case it's relatively small area.
And relatively small- oh say, 1/10th or Antarctic. Say a part of southern peninsula
being one pole and some other small chunk of Antarctic being the other lunar pole.
So, this could be someone entire world if they don't travel much, but it's something
one could explore fairly well in a few years.

With Mars distance is a factor which will make any exploration take longer. And one can't
really narrow the area down much by any reasonable criterion. But limited it to
one of Mars' poles it's around 10 times more area than lunar poles, and general planet
is hundreds times more area. So generally speaking one should not limit Mars exploration
by less than 2 decades. Probably 3 decades could be a reasonable  limitation- if you want to actually
consider it.

   
« Last Edit: 01/06/2014 01:26 PM by gbaikie »

Offline Hop_David

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Obviously we all know the original quote is from a guy famous for fiction.

I think its a bad myth that keeps getting propagated too much.

In no relevant measure is LEO halfway to .. really, anywhere significant in the solar system.

There are many reasons why, starting with the harsh realities of building hardware that works and lasts in space for any period of time.

Discuss ?

I've always disliked Heinlein's viral meme.

Delta V is part of the exponent in the rocket equation. If you have very good chemical propellant, each 3 km/s added to your delta V budget doubles the starting mass. Actually more than doubles if it means extra staging and throwing away more mass enroute.

So I would say 9 km/s is less than halfway to 12 km/s. And 12 km/s is less than halfway to 15 km/s. Etc.

And delta V isn't the only metric. Depending on your goals, frequency of launch windows, trip times can be important.

You correctly point out delta V isn't the only consideration. But from there you contend the difficult mass fractions required by the rocket equation is a minor problem. A very silly conclusion.

Offline gbaikie

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Obviously we all know the original quote is from a guy famous for fiction.

I think its a bad myth that keeps getting propagated too much.

In no relevant measure is LEO halfway to .. really, anywhere significant in the solar system.

There are many reasons why, starting with the harsh realities of building hardware that works and lasts in space for any period of time.

Discuss ?

I've always disliked Heinlein's viral meme.

Delta V is part of the exponent in the rocket equation. If you have very good chemical propellant, each 3 km/s added to your delta V budget doubles the starting mass. Actually more than doubles if it means extra staging and throwing away more mass enroute.

So I would say 9 km/s is less than halfway to 12 km/s. And 12 km/s is less than halfway to 15 km/s. Etc.

And delta V isn't the only metric. Depending on your goals, frequency of launch windows, trip times can be important.

You correctly point out delta V isn't the only consideration. But from there you contend the difficult mass fractions required by the rocket equation is a minor problem. A very silly conclusion.

Fair enough. Or you talk about rocket fuel cost. LEO: 2000 per lb. 12 km is 4000 per lb. And 15 is $8000 per lb.
So lunar surface is around 15 km/s. And so 8000 per lb.
And happens if can sells rocket fuel made on Moon for $2000 per lb or 1/4 price to ship from Earth. And can ship it for same price to 12 km/sec?
You get Commercial lunar water mining. with cost for crew to leave the Moon or ship from the moon being 1/4 cost. PLUS one can reuse the spacecraft- easier than reusing launch vehicles from Earth.

Add a decade or two commercial activity on the Moon, and instead lunar rocket fuel $2000 per lb, it's 1000 or less per lb, and drops to lower price each year IF there is more market demand for the rocket fuel. And meanwhile every thing you do related to doing things on the Moon lowers in cost. And you new things happened, like solar panels made on the Moon at competitive price to solar panels shipped from Earth.
As solar panels made on Moon capture entire lunar market for solar panels, and more solar panels are used, lunar solar panels become ever cheaper than solar panels shipped from Earth, even if costs to ship from Earth lower significantly. And cost to ship from Earth will lower significantly, because increase yearly demand of earth launches.
But when lunar rocket is still 1000 per lb, one halves the 12 km/s from earth. Which means you halved the cost pf rocket fuel in Mars orbit, or any other planets orbit or at some asteroid or minor planet destination.
Etc. Or Mars settlements.
« Last Edit: 01/06/2014 09:40 PM by gbaikie »

Offline savuporo

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You correctly point out delta V isn't the only consideration. But from there you contend the difficult mass fractions required by the rocket equation is a minor problem. A very silly conclusion.
I didn't conclude that its a "minor problem", i said that propulsion issues are just one among multiple hard problems for going beyond LEO. Judging just by the manhours and money spent on the propulsion vs rest of the spacecraft systems, it's fair to say propulsion is not the most difficult issue.

It's hard to find a single metric that supports Heilein's meme.
« Last Edit: 01/06/2014 04:28 PM by savuporo »
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Offline DMeader

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It's hard to find a single metric that supports Heilein's meme.

Especially if you insist on taking it so literally and arguing every point into the ground.

It was an off-hand remark, made back at the dawn of spaceflight before it was realized that many of these issues were, in fact, issues.

Offline savuporo

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It was an off-hand remark, made back at the dawn of spaceflight before it was realized that many of these issues were, in fact, issues.
Exactly - which was the entire point of this thread. The remark was catchy and insightful at the time, but really doesn't have any relevance or basis today. Hence, fiction.
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Offline R7

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Hence, fiction.

Heinlein, fiction? How dare you...

http://www.projectrho.com/public_html/rocket/surfaceorbit.php

Quote
    Mr. Heinlein and I were discussing the perils of template stories: interconnected stories that together present a future history. As readers may have suspected, many future histories begin with stories that weren't necessarily intended to fit together when they were written. Robert Heinlein's box came with "The Man Who Sold the Moon." He wanted the first flight to the Moon to use a direct Earth-to-Moon craft, not one assembled in orbit; but the story had to follow "Blowups Happen" in the future history.

    Unfortunately, in "Blowups Happen" a capability for orbiting large payloads had been developed. "Aha," I said. "I see your problem. If you can get a ship into orbit, you're halfway to the Moon."

    "No," Bob said. "If you can get your ship into orbit, you're halfway to anywhere."

    He was very nearly right.

From A Step Farther Out by Jerry Pournelle (1979)
AD·ASTRA·ASTRORVM·GRATIA

Offline gospacex

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I reckon Heinlein didn't mean it as exact astrodynamical law, just as an catchy inspirational saying ???

Of course. Its too catchy and a lot of space advocades seem to subscribe to the notion that "once we can get to LEO on the cheap, we can go anywhere easily in a cheap modified Cadillac Coupe the Ville!". That is not the case now, and it wont be in the future.

Not unless you have a very peculiar definition of word "half".

For me, "halfway" means that effort (money/time/design challenges/...) involved in getting a spacecraft to LEO is, roughly, half of the effort of getting a similarly massive and complex craft to e.g. Jupiter.

You somehow think that Heinlein meant "after you got to LEO, the rest is easy". He did not.

Offline imspacy

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For me, "halfway" means that effort (money/time/design challenges/...) involved in getting a spacecraft to LEO is, roughly, half of the effort of getting a similarly massive and complex craft to e.g. Jupiter.

You somehow think that Heinlein meant "after you got to LEO, the rest is easy". He did not.
IMO, Heinlein's quote remains today insightful and valid.... if anything, an understatement..

Take Apollo, where producing/flying the Saturn V (just to reach LEO) was over half the project cost/problems... with most of the remainder being getting the CM/SM/LM weight down to fit within the single Sat V BFR weight to LEO...
Designing a moon lander (LEM) was not a problem...the LEM was designed, and could have been built in 1962... The basic problem of space travel is pretty simple... fuel (storable like hydrazine), rocket engine (like super Draco), power (solar cells), life support, guidance...
What took 8 years was building a LEM light enough to fit on Sat V... the SWIP (Super Weight Improvement Program), etc...
I believe that a lot of engineering folks around America and the world can fairly easily/cheaply design/build a vehicle on earth (say in a hanger somewhere) to get to Mars... of say 1 million pounds.. hardware, fuel, oxy/water, lander, etc..

The problem (engineering and economic) remains today to get that 1m lbs weight, that vehicle/fuel/supplies to Low Earth Orbit....
If you try to either create a single BFR to orbit it, or slim it down to fit on a single BFR.

But once you solve the 'get it to LEO' problem... e.g. buy into launching the modules/fuel tanks/supplies separately on reusable, volume produced/launched CFRs (Cheap Frigging Rockets), the problem is both engineering and economically straightforward/doable.

« Last Edit: 01/07/2014 03:38 PM by imspacy »
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Online Elmar Moelzer

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I think that Heinlein got it pretty much spot on. DeltaV to LEO is more than half way to anywhere in the solar system and if you look at gross vehicle mass, then we are way more than half way (just look at the mass of the spacecraft compared to the launch vehicle). I also think that there is a mindset problem. If going to LEO was as routine and cheap as a transatlantic flight, missions that go BEO could be handled much more efficiently.

Online KelvinZero

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It was an off-hand remark, made back at the dawn of spaceflight before it was realized that many of these issues were, in fact, issues.
Exactly - which was the entire point of this thread. The remark was catchy and insightful at the time, but really doesn't have any relevance or basis today. Hence, fiction.

It may become more true in the future. delta-v will always be hard work and relevant, but ISRU, lifesupport, reliability and guidance may become mundane when they are everyday problems for hundreds of thousands of people.

I think what you are objecting to is the interpretation that implies the only big hurdle facing us is cheap access to space, so people propose focusing all our effort on this and none on ISRU, lifesupport, reliability and guidance etc, as if they will solve themselves as a side effect.

In fact the first statement explains why this should be reversed. Saying these technologies may become mundane is the same as saying we can make good progress on them with less effort. Solving these can make it practical to do something out there, which will create a reason for transportation on a large commercial scale, which is the best way to encourage cheap access to space.

Offline RanulfC

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I reckon Heinlein didn't mean it as exact astrodynamical law, just as an catchy inspirational saying ???

Of course. Its too catchy and a lot of space advocades seem to subscribe to the notion that "once we can get to LEO on the cheap, we can go anywhere easily in a cheap modified Cadillac Coupe the Ville!". That is not the case now, and it wont be in the future.

Shall we get the context AND the quote correct first??
From: http://www.projectrho.com/public_html/rocket/surfaceorbit.php#id--The_Hefty_First_Step
Jerry Pournelle:
"Mr. Heinlein and I were discussing the perils of template stories: interconnected stories that together present a future history. As readers may have suspected, many future histories begin with stories that weren't necessarily intended to fit together when they were written. Robert Heinlein's box came with "The Man Who Sold the Moon." He wanted the first flight to the Moon to use a direct Earth-to-Moon craft, not one assembled in orbit; but the story had to follow "Blowups Happen" in the future history.

Unfortunately, in "Blowups Happen" a capability for orbiting large payloads had been developed. "Aha," I said. "I see your problem. If you can get a ship into orbit, you're halfway to the Moon."

"No," Bob said. "If you can get your ship into orbit, you're halfway to anywhere."

He was very nearly right."

No it doesn't mean you can then go to Saturn in a "cheap modified Cadillac Coupe the Ville" but it DOES mean you can throw more payload for less propellant with lower Delat-Vs.
Now I haven't hit the end of the thread yet so this MAY have been addressed but I can't believe, Savuporo, that you make a very fundamental and basic mistake in your argument here:
Its not about the "first time" so much as about that a deep space craft has to keep working for a long long time in a very harsh environment. Barring magical leaps in propulsion technology, the launch windows to Jupiter come around only every so often, and even if launch to LEO was at its theoretical minimum, you would still have to design your hardware to last for years because you cant go after it and fix it.
Extra mass budget only helps with limited aspects of spacecraft engineering.
(Bolding mine)

WHAT? Extra mass budget helps with ALL aspects of spacecraft engineering, not just a "limited-few" how could it not? More mass allowance means:
1) More spare parts
2) More supplies
3) Deeper and more robust life support
4) More tools and equipment to FIX anything that goes wrong
5) More redundant systems
6) More robust equipment and spacecraft structure
7) Did I mention more spare parts and the tools and equipment to fix anything that goes wrong?

Seriously the list goes on and on. Part of the "challenge" of HLV-single-shot-to-anywhere architecture is simply the fact that your mass budget doesn't allow for much "spare" room or mass in "wiggle" room to back up your various systems. In reality you have to shave every "non-essential-ounce" and more often than not the definition of "non-essential" includes back ups and spares so that if anything DOES break you have a potential loss of mission and/or crew.

Think about Apollo-13 and how that would have turned out if the CM/SM was the size and build of the early VonBraun "Moonships" from the Colliers series. "Damn we had one of our O2 fuel-cell feed tanks blow up!"
"Really? Damn, well switch to back up and we'll have to cut the stay on the Moon down by a week"

Is it "just" a catchy phrase? Well yes, but really really no. No matter how you look at it the HARDEST step is going from the Earths surface into LEO. Everything AFTER that is a matter of optimizing your outbound mass with the most efficent propulsion method. Easy? No but no "harder" than designing a vehicle that can go from Earth to LEO on a regular basis and in some ways a lot easier and most definitly a lot "cheaper" than the alternative.

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline Hop_David

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Price of satellites and size of satellite industry  still far eclipses the launch costs.

Far eclipses? From Space.com: "The average satellite price over the next decade will be $99 million, compared to $97 million in the past 10 years. The per-satellite launch price is predicted to remain flat, at $51 million, according to Euroconsult."

So launch costs are more than a third.

Moreover, some of the satellite expense is related to launch costs. For example launch costs make it uneconomic to maintain and/or upgrade sats. To mitigate lack of maintenance, massive redundancy is part of sat design.

Radiation shielding would be a lot easier with some extra mass. With extra mass larger radiators make it easier to dump waste heat. I would expect much of the engineering expense comes from making sats that can endure harsh conditions with minimum mass.

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