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
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 ?
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)
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.
I reckon Heinlein didn't mean it as exact astrodynamical law, just as an catchy inspirational saying
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.
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.
Price of satellites and size of satellite industry still far eclipses the launch costs.