Author Topic: LEO is halfway to anywhere in solar system. Fact or fiction ?  (Read 26774 times)

Offline savuporo

  • Senior Member
  • *****
  • Posts: 5155
  • Liked: 988
  • Likes Given: 343
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 ?
Orion - the first and only manned not-too-deep-space craft

Offline M129K

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.

Online Robotbeat

  • Senior Member
  • *****
  • Posts: 28853
  • Minnesota
  • Liked: 9044
  • Likes Given: 5798
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.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline savuporo

  • Senior Member
  • *****
  • Posts: 5155
  • Liked: 988
  • Likes Given: 343
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 ?

Orion - the first and only manned not-too-deep-space craft

Offline jabe

  • Regular
  • Full Member
  • ****
  • Posts: 1123
  • Liked: 83
  • Likes Given: 5
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

Offline M129K

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".

Offline savuporo

  • Senior Member
  • *****
  • Posts: 5155
  • Liked: 988
  • Likes Given: 343
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.
Orion - the first and only manned not-too-deep-space craft

Offline M129K

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".

Online Robotbeat

  • Senior Member
  • *****
  • Posts: 28853
  • Minnesota
  • Liked: 9044
  • Likes Given: 5798
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.)
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline savuporo

  • Senior Member
  • *****
  • Posts: 5155
  • Liked: 988
  • Likes Given: 343
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.
Orion - the first and only manned not-too-deep-space craft

Offline savuporo

  • Senior Member
  • *****
  • Posts: 5155
  • Liked: 988
  • Likes Given: 343
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.


« Last Edit: 01/03/2014 10:16 pm by savuporo »
Orion - the first and only manned not-too-deep-space craft

Offline QuantumG

  • Senior Member
  • *****
  • Posts: 8830
  • Australia
  • Liked: 3832
  • Likes Given: 916
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.)
Human spaceflight is basically just LARPing now.

Offline R7

  • Propulsophile
  • Senior Member
  • *****
  • Posts: 2738
    • Don't worry.. we can still be fans of OSC and SNC
  • Liked: 957
  • Likes Given: 662
I reckon Heinlein didn't mean it as exact astrodynamical law, just as an catchy inspirational saying ???
AD·ASTRA·ASTRORVM·GRATIA

Offline savuporo

  • Senior Member
  • *****
  • Posts: 5155
  • Liked: 988
  • Likes Given: 343
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.
Orion - the first and only manned not-too-deep-space craft

Offline RonM

  • Senior Member
  • *****
  • Posts: 2720
  • Atlanta, Georgia USA
  • Liked: 1488
  • Likes Given: 1128
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.

Offline Andrew_W

  • Full Member
  • ****
  • Posts: 769
  • Rotorua, New Zealand
    • Profiles of our future in space
  • Liked: 15
  • Likes Given: 12
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.
I confess that in 1901 I said to my brother Orville that man would not fly for fifty years.
Wilbur Wright

Offline savuporo

  • Senior Member
  • *****
  • Posts: 5155
  • Liked: 988
  • Likes Given: 343
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.
« Last Edit: 01/03/2014 11:48 pm by savuporo »
Orion - the first and only manned not-too-deep-space craft

Offline DMeader

  • Full Member
  • ****
  • Posts: 956
  • Liked: 100
  • Likes Given: 47
"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.

Offline Solman

  • Full Member
  • ****
  • Posts: 675
  • Liked: 9
  • Likes Given: 9
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?



Offline Andrew_W

  • Full Member
  • ****
  • Posts: 769
  • Rotorua, New Zealand
    • Profiles of our future in space
  • Liked: 15
  • Likes Given: 12
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.
I confess that in 1901 I said to my brother Orville that man would not fly for fifty years.
Wilbur Wright

Tags: