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.
Quote from: Robotbeat on 01/03/2014 09:06 pmDelta-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".
Quote from: M129K on 01/03/2014 09:31 pmPayload 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.
And the "cost" is usually measured in cost/kg of useful payload,
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.
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.
I reckon Heinlein didn't mean it as exact astrodynamical law, just as an catchy inspirational saying
Quote from: R7 on 01/03/2014 10:39 pmI 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 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.
Quote from: savuporo on 01/03/2014 09:24 pmQuote from: Robotbeat on 01/03/2014 09:06 pmDelta-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.)
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.
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.
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.
Quote from: Oli on 01/04/2014 12:42 am4.5km/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.
4.5km/s is Mach 13+, that's roughly 4x the delta-v of suborbital tourism.
Quote from: QuantumG on 01/04/2014 01:03 amQuote from: Oli on 01/04/2014 12:42 am4.5km/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
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.
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.
Getting to the rest of the solar system from there is ALSO hard. A different set of challenges, but still very challenging.
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.
The statement says absolutely nothing about what it's like to /operate/ anywhere in the solar system, just what it takes to get 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.
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.
Eyup. Those multi-stage rockets got rid of the need for expendable, throw-away hardware. (rolling eyes).
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.
That fraction is much much bigger than many people think, because costs are not driven only by propulsion issues.
Quote from: savuporo on 01/04/2014 06:29 pmThat 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.
Quote from: Hop_David on 01/04/2014 06:24 pmEyup. 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.
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.
A big part of the cost of the deep space missions you talk about is R&D.
Electric propulsion helps beat the tyranny of the rocket equation
"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.
. $10 Arduino gets fried really fast really good near Jupiter.
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....
Quote from: gbaikie on 01/05/2014 03:58 pmI 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.
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.pngAs 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
Quote from: savuporo on 01/03/2014 08:45 pmObviously 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.
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.
It's hard to find a single metric that supports Heilein's meme.
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.
Hence, fiction.
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)
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.
Quote from: DMeader on 01/06/2014 04:37 pmIt 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.
Price of satellites and size of satellite industry still far eclipses the launch costs.