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General Discussion => General Discussion => Topic started by: savuporo on 01/03/2014 08:45 pm

Title: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/03/2014 08:45 pm
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 ?
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: M129K on 01/03/2014 08:55 pm
In terms of delta V, it's definitely halfway or better than halfway to many places. You need 9.3 km/s to enter LEO. From there, you need 4 km/s for lunar orbit, 4.3 for a fast transfer to Mars, 6.3 for Jupiter, 6.2 for the lunar surface, etcetera.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Robotbeat on 01/03/2014 09:06 pm
Yeah, in terms of delta-v, it's definitely true. Imagine a fully fueled Proton or Falcon 9 in LEO (picked Proton because it's hypergolic... thus storable), assuming the proper modifications. You could fly anywhere in the solar system. You'd have as much delta-v capability as Dawn but better because you have very high thrust so you can take full advantage of the Oberth effect. You could enter and leave orbit about different bodies.

With 9-10km/s of delta-v in LEO, not only could you go anywhere in the solar system, but in many cases you have enough delta-v to get there very quickly or even return back to Earth.

Delta-v wise, it's entirely true. Obviously in delta-t terms it isn't, but that should be obvious to anyone with even a smidgen of a clue.


....aaannnd this is why people are such big fans of propellant depots or in-orbit refueling.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/03/2014 09:24 pm
Delta-v wise, it's entirely true. Obviously in delta-t terms it isn't, but that should be obvious to anyone with even a smidgen of a clue.

How about more meaningful measures like delta-dollars, delta-manpower, delta-failure rate, delta-tracking capability, delta-commlink, delta-longevity or things along these lines ?

Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: jabe on 01/03/2014 09:29 pm
In terms of energy change it is pretty close to halfway.  Simplifying the summary...Using Ep (potential energy =- GMm/r)  while on Earth surface you have Ep, in a low circular orbit you have 0.5Ep, upon just escaping it has zero energy.  So looking at the change from one to another delta-E is O.5 Ep so once in orbit you could argue you are hallway out of Earth's grasp
My 2 worth...
jb
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: M129K on 01/03/2014 09:31 pm
Delta-v wise, it's entirely true. Obviously in delta-t terms it isn't, but that should be obvious to anyone with even a smidgen of a clue.

How about more meaningful measures like delta-dollars, delta-manpower, delta-failure rate, delta-tracking capability, delta-commlink, delta-longevity or things along these lines ?
Payload for an Ariane 5 is 21 tonnes to LEO or 7 tonnes TLI. So that's one third in "delta-payload".
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/03/2014 09:34 pm
Payload for an Ariane 5 is 21 tonnes to LEO or 7 tonnes TLI. So that's one third in "delta-payload".
Again a very meaningless measure, unless the payload is a bag of bricks. Or you want it to become a brick very quickly after the TLI.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: M129K on 01/03/2014 09:41 pm
Payload for an Ariane 5 is 21 tonnes to LEO or 7 tonnes TLI. So that's one third in "delta-payload".
Again a very meaningless measure, unless the payload is a bag of bricks. Or you want it to become a brick very quickly after the TLI.
Why is that a meaningless measure? Everybody knows that in terms of distance, it's a myth. But "distance" and "range" in spaceflight are measured in delta V. And the "cost" is usually measured in cost/kg of useful payload, at least when comparing the cost-effectiveness of comparable systems. But you discredit both units as "meaningless".
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Robotbeat on 01/03/2014 09:43 pm
Delta-v wise, it's entirely true. Obviously in delta-t terms it isn't, but that should be obvious to anyone with even a smidgen of a clue.

How about more meaningful measures like delta-dollars, delta-manpower, delta-failure rate, delta-tracking capability, delta-commlink, delta-longevity or things along these lines ?
The launch environment is also one of the most difficult parts of the trip. You're likely to fail very soon in a mission, on launch or deployment or soon after. Failure rate drops as time goes on, so I'd actually say that it's fairly true for delta-failurerate, too.

BTW, if you use an electric stage, you can put more than half your LEO payload on a trajectory to anywhere in the solar system (co-launching with the electric-stage, too, so not using two launches). Once you get into LEO, there are all sorts of tricks you can do besides the usual chemical rocket.

And a lot of the reason everything else is expensive beyond LEO is because access to even the minimum orbit (LEO) is incredibly expensive and likely to remain so for a while, even if big strides are made with reusable rockets.

If we magically had free, safe, ultra-routine access to LEO (as if it were just an island or something), all the other steps would seem far easier.

But right now, everything has to be designed to work perfectly the first time after being put through huge accelerations, huge aerodynamic loads, aeroheating, enormous vibrations, etc. If we could instead launch straight from LEO, everything else would seem far easier. (I'm not suggesting here that building and launching from a space station is magically better, but if LEO was as easy to get to as a launch site on Earth, it WOULD be magically much better.)
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/03/2014 10:05 pm
And the "cost" is usually measured in cost/kg of useful payload,
Only up to earth orbits, but not beyond.

Deep space mission costs in real world have very little do to with the delta-V capabilities.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/03/2014 10:06 pm
And a lot of the reason everything else is expensive beyond LEO is because access to even the minimum orbit (LEO) is incredibly expensive and likely to remain so for a while, even if big strides are made with reusable rockets.
That is an often claimed myth, but it has very little basis. Deep space craft are expensive for other reasons.

Quote
But right now, everything has to be designed to work perfectly the first time after being put through huge accelerations, huge aerodynamic loads, aeroheating, enormous vibrations, etc.
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.


Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: QuantumG on 01/03/2014 10:15 pm
Let's try to make savuporo's case for him..

A typical two stage launch vehicle has a booster stage that essentially just throws the second stage above the atmosphere and gives it a little kick. In essence, it's close to the total delta-v of a suborbital tourism flight (about 4.5 km/s).

So, clearly, suborbital tourism is half way to orbit.

Disagree? Okay, now you get savuporo's point. (I think.)
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: R7 on 01/03/2014 10:39 pm
I reckon Heinlein didn't mean it as exact astrodynamical law, just as an catchy inspirational saying ???
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/03/2014 10:47 pm
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.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: RonM on 01/03/2014 11:03 pm
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.

Heinlein was referring to sci-fi rockets with incredibly powerful 'torch drives' that probably defy the laws of physics. Yes, it is a catchy phrase, but it doesn't apply to today's technology.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Andrew_W on 01/03/2014 11:24 pm
Heinlein was simply pointing out that the same delta v that will get you from Earth's surface into LEO, will get you from LEO to anywhere (in the solar system), which is essentially true.

No need to look for any more profound explanation.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/03/2014 11:43 pm
Heinlein was simply pointing out that the same delta v that will get you from Earth's surface into LEO, will get you from LEO to anywhere (in the solar system), which is essentially true.
"essentially true" is stretching it a bit as landing on Io will be pushing it. However the point of this thread is exactly that, delta-V ( or Isp , or Mass fraction or radiation environment or solar flux or any other metric ) alone gives a very misleading impression about the difficulty of getting there.

The scary "tyranny of rocket equation" is not really the only or even the most significant factor that makes space difficult. And funny - the tyranny was broken ages ago by first multistage rocket.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: DMeader on 01/03/2014 11:49 pm
"essentially true" is stretching it a bit as landing on Io will be pushing it. However the point of this thread is exactly that, delta-V ( or Isp , or Mass fraction or radiation environment or solar flux or any other metric ) alone gives a very misleading impression about the difficulty of getting there.

You are taking that old aphorism far, far too literally.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Solman on 01/04/2014 12:02 am
Delta-v wise, it's entirely true. Obviously in delta-t terms it isn't, but that should be obvious to anyone with even a smidgen of a clue.

How about more meaningful measures like delta-dollars, delta-manpower, delta-failure rate, delta-tracking capability, delta-commlink, delta-longevity or things along these lines ?
If we magically had free, safe, ultra-routine access to LEO (as if it were just an island or something), all the other steps would seem far easier.

But right now, everything has to be designed to work perfectly the first time after being put through huge accelerations, huge aerodynamic loads, aeroheating, enormous vibrations, etc. If we could instead launch straight from LEO, everything else would seem far easier. (I'm not suggesting here that building and launching from a space station is magically better, but if LEO was as easy to get to as a launch site on Earth, it WOULD be magically much better.)

Kinda bolsters the idea of tele-robotic on-orbit assembly and check out of payloads using launched and ISRU derived elements as espoused by the Phoenix Project doesn't it?


Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Andrew_W on 01/04/2014 12:02 am
So what you're saying is that there are different measures to delta v some of which make LEO far less than half way, others that make it far more than half way. Yep.

 So the inference is that even if it was cheap and easy to get to LEO the rest of the journey would still be hard?
 I'd argue that easier to LEO makes the rest easier, as once you're in LEO there's no need to expend energy at the prodigious rate that a launch vehicle must, you can get to about anywhere in the solar system with far more conservative engineering.

That initial and costly launch is why the engineering on probes needs to be at the cutting edge, the last 10% is 90% of the cost, it's worth spending that 90% to get launch costs down, and because you don't want to face those launch costs again if the probe fails.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Lee Jay on 01/04/2014 12:09 am
When New Horizons separated from its Atlas V January 19, 2006, would you say it was "most of the way" to Pluto, since it wasn't going to get much more delta-V (well, from rockets anyway)?

The web page says, "The New Horizons spacecraft, now more than halfway between Earth and Pluto...".

I think when most people say "half way", they're thinking of time or distance, not energy or velocity.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: QuantumG on 01/04/2014 12:12 am
I'd argue that easier to LEO makes the rest easier, as once you're in LEO there's no need to expend energy at the prodigious rate that a launch vehicle must, you can get to about anywhere in the solar system with far more conservative engineering.

Well, the same is true of getting above the atmosphere. If you had a way to "start" at 100 km, with no atmospheric penalty to worry about to get there, a much simpler rocket could get you to orbit than existing second stages of launch vehicles - because they have to go through supersonic transition in the lower atmosphere.

I can think of a few ways to do that, some more realistic than others, but I think that's a much more complicated argument than saying 100 km is half way to orbit.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: jabe on 01/04/2014 12:13 am
Another way of looking at it....As this kickstarter (http://www.kickstarter.com/projects/longmier/cat-launch-a-water-propelled-satellite-into-deep-s) seems to suggest ..they can go "anywhere" on a modest budget..hard part for the project, if development is succesful, is getting to LEO.
jb
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/04/2014 12:21 am
So what you're saying is that there are different measures to delta v some of which make LEO far less than half way, others that make it far more than half way. Yep.
I'm saying that all the delta-v maps drawn up are missing many, and more important map layers.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Oli on 01/04/2014 12:42 am
It's not only delta-v, but the fact that you don't need huge thrust to fight against gravity anymore. Thrust is expensive and heavy.

Quote from: Quantum
A typical two stage launch vehicle has a booster stage that essentially just throws the second stage above the atmosphere and gives it a little kick. In essence, it's close to the total delta-v of a suborbital tourism flight (about 4.5 km/s).

So, clearly, suborbital tourism is half way to orbit.

4.5km/s is Mach 13+, that's roughly 4x the delta-v of suborbital tourism.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: MATTBLAK on 01/04/2014 12:46 am
"LEO is halfway to anywhere in solar system. Fact or fiction?" 

Sadly, it's been more fact than fiction since December 1972... :(
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Patchouli on 01/04/2014 12:59 am
It depends on your definition of half way and what the mission parameters are.

A space probe can take a slow trajectory though they don't always do, but with a crewed mission on the other hand you usually want to follow the fastest economically feasible trajectory.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Oli on 01/04/2014 01:30 am
4.5km/s is Mach 13+, that's roughly 4x the delta-v of suborbital tourism.

Gravity and aerodynamic losses eat 2 km/s, potential energy eats about 2 km/s. Suborbital vehicles that make it over 100 km, should they ever start flying, require about 4.5 km/s of delta-v. About the same as a first stage of a launch vehicle.

Apparently Space Ship One required a delta-v of roughly 1.4km/s...

http://en.wikipedia.org/wiki/Delta-v_budget

Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: QuantumG on 01/04/2014 01:44 am
4.5km/s is Mach 13+, that's roughly 4x the delta-v of suborbital tourism.

Gravity and aerodynamic losses eat 2 km/s, potential energy eats about 2 km/s. Suborbital vehicles that make it over 100 km, should they ever start flying, require about 4.5 km/s of delta-v. About the same as a first stage of a launch vehicle.

Apparently Space Ship One required a delta-v of roughly 1.4km/s...

http://en.wikipedia.org/wiki/Delta-v_budget

Ahh, okay. My mistake. I think the point still stands: "100 km altitude with 2 km/s of velocity is halfway to orbit" is a misleading statement, even though it's technically correct in terms of delta-v.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: sdsds on 01/04/2014 02:02 am
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.

I think your point presupposes that, upon reaching "anywhere in the solar system," your spacecraft isn't going to return to Earth. What would Elon say to that?
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: aero on 01/04/2014 02:12 am
Conversations such as these almost always confuse LEO, Low Earth Orbit, with LOA, Low Orbit Altitude. To stay in a stable LEO the vehicle must have both orbital altitude and orbital velocity.

For Earth, orbital velocity is 7,791.99 m/s at 185,000 meters altitude. At that altitude but no velocity your space vehicle will fall directly to earth under the influence of gravity. With insufficient velocity your vehicle will move a distance down range falling all the while before it encounters the earth. With exact orbital velocity your vehicle will fall past the side of the earth at exactly the same orbital altitude and with excess velocity it will pass the side of the earth at a higher altitude.

The "LEO" in LEO is halfway to anywhere includes both the altitude and the velocity needed for orbit. And note that if your vehicle is stationary at orbital altitude it has very little time to reach orbital velocity because it starts to fall immediately, and gravity will not wait for you to build your speed. Your vehicle needs to be ruggedly built in order to withstand the high accelerations needed to reach orbital velocity before gravity causes it to reach earth.

Two stage rockets overcome the need for extremely high acceleration of the second stage in part by giving the second stage a percentage of the horizontal orbital velocity and a very significant upward velocity. Gravity must overcome this upward velocity before it can accelerate the second stage downward hence the second stage has more time to accelerate through the remaining percentage of horizontal orbital velocity. With more time and less velocity increment the second stage acceleration can be lower and the vehicle somewhat less rugged. But note, as second stage fuel is burned off even the most wimpy ( but successful) second stage engines do provide the stage with high acceleration.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: pathfinder_01 on 01/04/2014 03:27 am

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.

Every Flight including deep space flights to the moon by Apollo start in LEO and even flights to far places like Jupiter start from parking orbits. Sure you would have to design a craft to last a bit longer if assembling in LEO but there are limits to how much one can put on the top of an rocket no matter how big you make the thing.  Some assembly may be required no matter what(i.e. Even Apollo had to give up on Direct landing for various reasons. )

You don't have to design the hardware to last for years, it just needs to last long enough to pull the mission. This may push you towards different solutions but that is that. We have spacecraft that work without humans for years already. Probes that go to distant planets likewise and Voyager is still ticking at 36 years. There is only so much simplicity to be had by designing for short periods of time(i.e. One of the problems with Apollo is the fact that the LM was only built for short trip..i.e. you would require some redesign for it to serve as a craft that could support a lunar base.)
Title: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Lars_J on 01/04/2014 05:32 am
Savuporo, I think you are fundamentally misunderstanding the "halfway to anywhere" idea.

You (and many others) seem to read it as "once you get to LEO, everything else is EASY". But that is NOT true, and not what the saying implies.

Getting to LEO is hard. Getting to the rest of the solar system from there is ALSO hard. A different set of challenges, but still very challenging.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/04/2014 06:22 am
Getting to the rest of the solar system from there is ALSO hard. A different set of challenges, but still very challenging.
That's what i'm trying to call out here. In fact, getting to rest of the solar system is much, much harder in many ways, seeing as there are plenty of organizations that can put payloads to orbit, but only so few that have operated a spacecraft beyond earth orbits.

A lot of space enthusiasts seem to think its all about mass, delta-vee and orbits, whereas the real challenges are elsewhere.

Give you an example. If launch was free, you can probably build a decently working LEO cubesat with modest mission goals for about five figures.
If launch and insertion to lunar orbit was free, you could not build a working moon orbiting cubesat for a similar amount, you'd have to pay about 10x more.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: QuantumG on 01/04/2014 06:26 am
Give you an example. If launch was free, you can probably build a decently working LEO cubesat with modest mission goals for about five figures.
If launch and insertion to lunar orbit was free, you could not build a working moon orbiting cubesat for a similar amount, you'd have to pay about 10x more.

Citation needed.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/04/2014 06:30 am
Citation needed.

Here you go
https://www.csulb.edu/colleges/coe/mae/views/courses/
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Robotbeat on 01/04/2014 06:56 am
The statement says absolutely nothing about what it's like to /operate/ anywhere in the solar system, just what it takes to get there.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/04/2014 07:10 am
The statement says absolutely nothing about what it's like to /operate/ anywhere in the solar system, just what it takes to get there.
Ah, ok - if thats what we are talking about then Heinlein is exactly correct - give or take a few km/s. LEO is halfway to anywhere in solar system as long as we are talking bricks or dead bodies.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Robotbeat on 01/04/2014 07:13 am
What kind of twisted understanding would it take to interpret the phrase as meaning it's just as easy to operate in LEO as it is, say, in Io orbit? The statement is about getting there, not about operating there.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Andrew_W on 01/04/2014 08:03 am

Give you an example. If launch was free, you can probably build a decently working LEO cubesat with modest mission goals for about five figures.
If launch and insertion to lunar orbit was free, you could not build a working moon orbiting cubesat for a similar amount, you'd have to pay about 10x more.

If launch were free I'd be booking a ticket, along with millions of others, and all those billions of tourist dollars would push Manned activities far out into the solar system.

Imagine being able to launch from LEO without the cost of getting there, the cost of all interplanetary operations would plummet to a fraction of present costs. The several thousands of tons launching from the Earth's surface each year could be several thousands of tons launching from LEO, without the need to use high thrust chemical rockets those thousands of tons in LEO could, with higher Isp propulsion, launch far more mass to the planets than we currently put into LEO.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Hop_David on 01/04/2014 06:24 pm
The scary "tyranny of rocket equation" is not really the only or even the most significant factor that makes space difficult. And funny - the tyranny was broken ages ago by first multistage rocket.

Eyup. Those multi-stage rockets got rid of the need for expendable, throw-away hardware decades ago. (rolling eyes).
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/04/2014 06:29 pm
Imagine being able to launch from LEO without the cost of getting there, the cost of all interplanetary operations would plummet to a fraction of present costs.
That fraction is much much bigger than many people think, because costs are not driven only by propulsion issues.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/04/2014 06:32 pm
Eyup. Those multi-stage rockets got rid of the need for expendable, throw-away hardware. (rolling eyes).

In deep space, there are far less restrictions on vehicle geometry than earth to orbit launches. So you can do parallel staging and drop tanks, keep the engines, avionics and everything else. There is no real reason why staging in space would mean throwing away expensive bits of your propulsion system.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: M129K on 01/04/2014 06:36 pm
What kind of twisted understanding would it take to interpret the phrase as meaning it's just as easy to operate in LEO as it is, say, in Io orbit? The statement is about getting there, not about operating there.
I think Savuporo fundamentally misunderstands the phrase and has decided to deny it can possibly make any sense.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Hop_David on 01/04/2014 06:38 pm
That fraction is much much bigger than many people think, because costs are not driven only by propulsion issues.

The fact that space ships are disposable have a big effect. Imagine the cost of a plane ticket if a 747 were thrown away each trip.

A big part of the cost of the deep space missions you talk about is R&D. When a mission is one-off, it bears the entire burden of R&D expense.

If many units are made, R&D expense is amortized over many units.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Patchouli on 01/04/2014 06:57 pm
That fraction is much much bigger than many people think, because costs are not driven only by propulsion issues.

The fact that space ships are disposable have a big effect. Imagine the cost of a plane ticket if a 747 were thrown away each trip.

A big part of the cost of the deep space missions you talk about is R&D. When a mission is one-off, it bears the entire burden of R&D expense.

If many units are made, R&D expense is amortized over many units.

I read somewhere the second MER rover was less the half the cost of the first one.

I'm surprised they haven't made a standardized bus for space probes though the Mariner and Viking programs did appear to reuse a lot of hardware.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Hop_David on 01/04/2014 07:02 pm
Eyup. Those multi-stage rockets got rid of the need for expendable, throw-away hardware. (rolling eyes).

In deep space, there are far less restrictions on vehicle geometry than earth to orbit launches. So you can do parallel staging and drop tanks, keep the engines, avionics and everything else. There is no real reason why staging in space would mean throwing away expensive bits of your propulsion system.

Limited re-use is done by deep space probes. For example after after Dawn took a look at Vesta, it moved onto Ceres.

Dawn's thrusters are low thrust, high ISP xenon thrusters are used. (I guess the Dawn folks hadn't heard your argument that hydrazine beats higher ISP propellants). It also helps that delta V from Vesta to Ceres isn't 9 km/s. High exhaust velocity, low delta V budget -- maybe Tsiolkovsky's rocket equation does have something to do with Dawn being reused.

Dawn was launched on a throwaway Delta II. If NASA wanted to replenish DAWN's xenon, they would have to launch it with another throw away craft.

Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Robotbeat on 01/04/2014 07:30 pm
Electric propulsion helps beat the tyranny of the rocket equation by vastly increasing the Isp, making the whole thing seem much more like filling up a car... The tank doesn't take up nearly the entire volume of the vehicle like it does for a launch vehicle.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Hop_David on 01/04/2014 07:34 pm
Electric propulsion helps beat the tyranny of the rocket equation by vastly increasing the Isp, making the whole thing seem much more like filling up a car... The tank doesn't take up nearly the entire volume of the vehicle like it does for a launch vehicle.

Just so.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/04/2014 07:59 pm
A big part of the cost of the deep space missions you talk about is R&D.
True, but not only. The cheapest bill of materials cost of a GN&C board you can fly on LEO is in the range of 10 dollars.

I'll let you take a guess of what the the equivalent cost of one that would orbit Jupiter is - ignoring NRE costs.

And NRE costs are not ever going away, even if you can standardize and reuse some designs.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: R7 on 01/04/2014 08:14 pm
Electric propulsion helps beat the tyranny of the rocket equation

But it adds the tyranny of external energy requirement, which leads to tyranny of time. But is this relevant to OP's concern which appears to be;

"Bunch of space geeks misunderstand Heinlein's maxim!!!"

So? Should we do something? I doubt anyone's launch contract, xLV development or other space related livelihood is under a threat because of that.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/04/2014 08:17 pm
"Bunch of space geeks misunderstand Heinlein's maxim!!!"

So? Should we do something? I doubt anyone's launch contract, xLV development or other space related livelihood is under a thread because of that.
Again, the difficulty of getting to and doing anything in deep space is only partially driven by the propulsion issues.

A delta-V map is like a city map of vegetation, without any other layers.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: R7 on 01/04/2014 08:38 pm
Again, the difficulty of getting to and doing anything in deep space is only partially driven by the propulsion issues.

A delta-V map is like a city map of vegetation, without any other layers.

I was addressing your concern, not the proofs against maxim's factuality. Because the sentence is void of accurate metrics one could argue it's both fact and fiction depending on what metrics the observer chooses. Delta-v wise pretty much a fact. Many-other-v wise fiction, as for instance your GNC board example obviously proofs. $10 Arduino gets fried really fast really good near Jupiter.

Again, as far as the space geeks that might not get this; so what? Always someone out there to misunderstand things, not Heinlein's fault.

Anyhow the new motto is: Mumbai slum is halfway to Venus.

Don't ask.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/04/2014 08:39 pm
Another point: GEO comsat satellite buses and payloads are standardized, in a commercial supplier commercial customer industry that has existed for decades.
Price of satellites and size of satellite industry  still far eclipses the launch costs.

NRE costs ? Yes but not really
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Patchouli on 01/04/2014 08:41 pm
Electric propulsion helps beat the tyranny of the rocket equation by vastly increasing the Isp, making the whole thing seem much more like filling up a car... The tank doesn't take up nearly the entire volume of the vehicle like it does for a launch vehicle.

Dawn visiting both Vesta and Ceres would have been impossible without electric propulsion.
At least not while staying within the payload capacity of a Delta II.

With chemical propulsion the mission probably would have required a Delta IV Heavy.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/04/2014 09:30 pm
. $10 Arduino gets fried really fast really good near Jupiter.
I'm sure this can be addressed by a careful application of superdraco thrusters.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: gbaikie on 01/05/2014 03:58 pm
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 think it's based on assumption, that we moving out into the solar system.
And so part of what it assumes one would have fuel depots.

So it's not the same as saying putting something LEO, should only be 1/2 the cost of landing on Mars, for example.
Whereas if we have fuel depots in LEO, this obviously leads fuel depots elsewhere, and with such system,
Mars would be about twice the cost of getting to LEO.

Or if there was lunar water mining and the production of rocket fuel on the Moon. The greater part of cost of going to the Moon, would be getting to LEO.
Even if we had a system of delivering earth rocket fuel to Lunar orbit, it would lower costs by a significant degree.
And by a "system" I mean a market of rocket fuel in space- or if people think something is actually better than market- then they can think of it as this being this " system "

So the path NASA took to lower costs was to try to develop a cheap way to get to orbit- Shuttle.
But rather if NASA had developed fuel depots- something anyone could have expected NASA would done without question- then NASA would have lowered the cost of getting *in-to* space. As in, Space is not LEO. Space is *mostly* quantitatively, beyond LEO.

So with depots in LEO. Falcon-9 would been an example of  one biggest rockets needed. And heavy launch vehicle for Mars would be something like a Atlas-V or Delta-IV heavy. Instead dreaming of 130 ton to LEO launch vehicle.

Because if we had a depot at LEO, then naturally we would extend depots to L-1 and Mars orbit. And with this one does not need a enormous launch vehicle [but can't do it with one launch anyhow].

So since NASA has not developed any system, that allows us to go into space, LEO is not half way to anywhere. And we are not using LEO in way which is rational.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: imspacy on 01/06/2014 02:44 am
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
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/06/2014 04:18 am
I think it's based on assumption, that we moving out into the solar system.
And so part of what it assumes one would have fuel depots.
...

Good start of the post, but in my opinion you took a sharp left turn in second sentence and i couldn't finish reading.

Lets look at the first sentence though. Assume the measure "halfway to anywhere" means our progress in space in general - i.e. how much of humanity's reach is actually extending into solar system.

I guess right around the time Apollo 17 departing LEO people could have made an argument that just by the ratio of people that have been to LEO vs people that have been further than that you could consider it halfway.

As of today, the ratio according to wildly unscientific estimate is 536 to 24. 4% of travelers have made it past the half way point.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: gbaikie on 01/06/2014 11:26 am
I think it's based on assumption, that we moving out into the solar system.
And so part of what it assumes one would have fuel depots.
...

Good start of the post, but in my opinion you took a sharp left turn in second sentence and i couldn't finish reading.
Well, I think there was concern about difficulty of getting into space, and that it was known that LEO required the least amount delta-v. Therefore any interest in LEO was mostly about it requiring the least amount of delta-v to enter the space environment, that LEO would a location to refuel spacecraft so one could go beyond LEO.
Or if lived on world similar to Mars and therefore getting into space was less difficult in terms of delta-v, the issue having some atmospheric drag in LEO would made any orbit in LEO which had a significant amount of drag, less appealing.
Quote
Lets look at the first sentence though. Assume the measure "halfway to anywhere" means our progress in space in general - i.e. how much of humanity's reach is actually extending into solar system.
That's a way looking at it. Not what I meant.
But that Soviets achieved getting to orbit was seen a large step towards this goal. Or a major step forward in this direction. Just as landing people on Moon could be considered a major step towards this goal.
But could say that the steps of needing to refuel in LEO was bypassed, so in sense, it less of milestone that one would generally would assume in terms of progress.
Or Saturn V was a gimmick- though a very impressive trick. Plus building such a large and capable rocket
would in itself can be seen as significant progress.
And that Saturn V allow people to fooled by the idea that we would be sending people to Mars- soon.
And so, the thinking being, that a slightly bigger launch vehicle could developed to do this.
Quote
I guess right around the time Apollo 17 departing LEO people could have made an argument that just by the ratio of people that have been to LEO vs people that have been further than that you could consider it halfway.
But few thought of couple hundred miles above them as a goal. The point of what I am saying is that they considered LEO as a way to go the Moon and beyond.
And as said above some people were fooled by the illusion.

But also some also would considered "getting back to the plan" was to again focus on LEO, so that we can go beyond LEO.
Plus of course they were things one could do in regard to ISS, and these could be important. They could be important because they could lead to markets in space. So, such as possibility of making various material in microgravity.
And of course consequence to a human body of being in microgravity environment- something on one needs to understand if humans could travel to Mars [or anywhere other than the Moon].

One could say the plan of ISS was to be fuel depot. And other things would added, and the fuel depot was subtracted as not something as the first thing to do, and then remained left out, due the ramification of these other choices.
Or the baby was tossed out with the bath water.
Or simple human insanity.
Or you could call it Groupthink. Or also include numerous other rationalizations, though they are all part of how one chooses to characterize the insanity.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: gbaikie on 01/06/2014 01:07 pm
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.

   
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Hop_David on 01/06/2014 02:04 pm
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.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: gbaikie on 01/06/2014 03:12 pm
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.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/06/2014 04:26 pm
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.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: DMeader on 01/06/2014 04:37 pm
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.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: savuporo on 01/06/2014 05:41 pm
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.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: R7 on 01/06/2014 08:08 pm
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)
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: gospacex on 01/07/2014 12:16 am
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.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: imspacy on 01/07/2014 03:34 pm
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.

Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Elmar Moelzer on 01/08/2014 03:04 pm
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.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: KelvinZero on 01/09/2014 09:54 pm
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.
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: RanulfC on 01/09/2014 09:59 pm
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
Title: Re: LEO is halfway to anywhere in solar system. Fact or fiction ?
Post by: Hop_David on 01/11/2014 03:56 pm
Price of satellites and size of satellite industry  still far eclipses the launch costs.

Far eclipses? From Space.com (http://www.space.com/6839-space-forecast-predicts-satellite-production-boom.html): "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.