
The Tyranny of the Rocket Equation (2012) - brudgers
https://www.nasa.gov/mission_pages/station/expeditions/expedition30/tryanny.html
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koverda
Nice that we live on a planet with low enough gravity to get off of it. The
article states that if the Earth was about 50% bigger, chemical rockets
wouldn't be able to achieve escape velocity. Any species on a planet like that
has a much much harder time getting into space.

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Florin_Andrei
We almost had a nuclear space program. It got cancelled for non-technical
reasons. On a planet with harder take-off, that program would get all the
funds it could possibly need.

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knodi123
> We almost had a nuclear space program.

built on the success of a rocket-based program! no way would a country fund a
vehicle that spews out a constant stream of nuclear bombs as their species'
_first_ foray into orbit!

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Florin_Andrei
> _a vehicle that spews out a constant stream of nuclear bombs_

That's not how the NERVA was supposed to work.

[https://en.wikipedia.org/wiki/NERVA](https://en.wikipedia.org/wiki/NERVA)

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exrook
I believe the GP is referring to Project Orion[0], which did propose using
repeated nuclear detonations behind a spacecraft to propel it forward.

[0]
[https://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propu...](https://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29)

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maxxxxx
What amazes (and saddens) me is that we don't seem to have not even a far
fetched theoretical approach to dramatically improve rockets within the next
few decades.

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mickronome
It's a bit sad, I do long for the stars and planets.

However, rramatically improving rockets might be like trying to improve the
carriage to get a much faster personal transport, while keeping the horse.

It seems to be the case, that the cost of launching commercial payloads are
still "low" enough compared to the cost of the payloads since there are few
big budget ventures that tries to make lifting _much_ cheaper through
alternative methods.

I'm not saying that space elevators or other alternative lift devices are
feasible, but we tend to get huge investments even into tech that seems
absolutely implausible if there is a big market. The lack of these makes
investments makes it plausible that the current launch costs are actually
acceptable for all current, and expected near future commercial actors.

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philwelch
The nice thing about rockets is that you can start as small as you'd like and
build progressively larger and larger rockets and get the engineering details
right before you have to worry about getting into space.

Space elevators, skyhooks, and launch loops are all big enough that it's an
all-or-nothing deal. You can test individual components, but a whole end-to-
end space elevator has to be exactly the distance between ground and geosync
or else it just doesn't work. At best, you could build smaller versions of
this stuff on the moon first and then scale up to Earth-size later, taking
into account such factors as water, atmosphere, and the fact that the Earth is
not tidally locked with the sun. But that requires hauling metric fucktons of
parts and equipment to the moon, even if you're using lunar resources to build
the space elevator itself, so there's no guarantee you end up ahead in the
end.

The basic physics behind rockets is simple as all hell, and it still required
von Braun to spend his entire adult life building progressively bigger and
bigger rockets and refining the design details. The V2 only needed to be able
to land nose-first 200 miles from where it was launched, but without that
knowledge and experience, the Saturn V would have been impossible. That's the
kind of iteration that's fundamentally impossible with these other launch
systems.

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snovv_crash
With a space elevator, don't you need a mass some distance above geosync to
hold the weight of the cable and the payload as it ascends?

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yellowapple
I think the counterbalance is more to make sure that the center of gravity is
actually the thing in geostationary orbit.

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drostie
In six years nobody has corrected the fact that one of the propellants listed
is not "Methane-Oxygen" but "Earth orbit to near-Earth asteroids", and the
following is not "Methane-Oxygen" but "Hydrogen-Oxygen."

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mrfusion
Keep in mind this equation only applies if you insist on bringing all your
fuel with you.

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neolefty
Where else would you get it? Unless it's beamed in the form of light, I don't
know of many options.

The challenge is to get from the Earth's surface, to orbit. Yes, there's
oxygen along the way, but the speeds you have to go will wreck you if you stay
in the atmosphere at all. So you get into vacuum ASAP.

Once you're in orbit, you have a lot more options. For example, you don't need
a high-thrust engine—instead, high-efficiency is fine, even if it's low
thrust. Etc.

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dangerbird2
He's probably implying mining or synthesizing fuel on smaller gravity wells
like Mars. Being able to synthesize fuel for the return trip could massively
cut back on initial launch weight. Energizing propellant with a microwave beam
([https://en.wikipedia.org/wiki/Beam-
powered_propulsion](https://en.wikipedia.org/wiki/Beam-powered_propulsion))
has been hypothesized, while a solar sail is much more realistic with modern
technology.

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klodolph
> As humans, we are powerless to change this number. We simply have to accept
> its consequences. I like to think of this as the travel cost.

This is selling rocket science a little short, I think. The availabilty of
gravity assists and aerobraking make it possible to achieve large variations
in delta V necessary for a trip, as long as you can make the right tradeoffs
elsewhere (travel time, etc).

See:
[https://en.wikipedia.org/wiki/Interplanetary_Transport_Netwo...](https://en.wikipedia.org/wiki/Interplanetary_Transport_Network)

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pasabagi
It's occurred to me that a rocket is perhaps the perfect metaphor for a
pessimistic reading of the fermi paradox. It's a device that perfectly
encapsulates how much easier it is to destroy society, than it is to pull
society out of a gravity well. In the first instance, by blowing up on the
launchpad. In the second, by providing the means for competing societies to
nuke the whole world into a mass extinction.

The problem is the same for all of the ideas like space-elevators, or asteroid
mining, or spacetravel as a normal thing - given our current politics, there's
no way you'd avoid occasional rock-droppage with catastrophic consequences for
people still stuck on earth. It would just be too easy. If you start thinking
along the lines towards nuclear-fueled rockets, the problem just gets worse.

Non-weapon rockets are high-energy, fiddly devices - and their dumb purely-
destructive siblings are far simpler.

If launching rockets became cheap enough to put people on Mars, that would
also mean they'd be cheap enough so even small states could afford ICBMs.
Because rockets are ICBMs.

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neolefty
_how much easier it is to destroy society_

Lots of modern technologies do that. Like a child growing up—at what age do
you use sharp knives? a lawnmower? a car?—humanity has matured ethically
alongside our technology.

I agree we have to be careful not to _Great Filter_ ourselves.

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pasabagi
>humanity has matured ethically alongside our technology

That's exactly the problem. I don't think we have at all. We do no serious
study of ethics in our schooling, and frankly don't devote serious thought to
the subject. It's very uncommon to meet somebody who has read even a single
book about ethics. We're a society of meat-eaters who consider people who harm
animals to be scum, a society that simultaneously considers the protection of
children fundamental, and where the most likely age to die on a world scale is
in childhood. These are reflections of a deep lack of ethical maturity.

Regardless of all of the inconsistency, I think it's hard to look at the times
in which the world came to the brink of nuclear catastrophe in the cold war,
and state confidently that this is a society with the maturity to hold nuclear
weapons.

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AgentOrange1234
This is really fascinating. I still don’t have an intuitive understanding of
why getting into space takes so much more propellant than flying an airplane,
but it seems like it’s definitely a hugely more difficult thing to do. Thanks
for posting.

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yellowapple
It's about speed. Getting into space is relatively easy (it does take a lot
more propellant than flying an airplane, but it's understandable since
spaceships tend to fly a lot higher than airplanes). _Staying_ there means you
have to be flying so fast that you fall continuously around Earth instead of
into it. Even the fastest airplanes in the world can't get that fast on their
own (at least not yet). More speed requires more fuel (and since that fuel
makes you heavier, you need even more fuel to counteract the added weight -
that's the rocket equation).

Even more intuitively: it's about distance. Flying from Los Angeles to Salt
Lake City requires less fuel than flying from Los Angeles to New York City.
Flying from Los Angeles all the way around the world and landing again in Los
Angeles takes even more fuel.

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AgentOrange1234
That... makes perfect sense. Thanks!

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ur-whale
Since I first got interested in science, I've been presented a number of times
with this idea (that lifting things in orbit is subject to very simple physics
that have harsh economic implications).

I've always felt uneasy about this, as it seems to imply that the only way to
put things in orbit is via rockets.

For example, there is the idea of a space crane (assuming it can be built)
that is simply a very, very tall building, assembled one chunk at a time, and
that once built can simply lift things in orbit.

Would a space crane be slave to the same equations?

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ohazi
No, it wouldn't, but "assuming it can be built" is a pretty tall order.

We don't really know how to reliably manufacture materials that can sustain
the loads required for something like this.

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ur-whale
Yes, I do understand that we have an unsolved material science problem for the
space elevator, but my question was more theoretical (hence the "assuming
that") and boiled down to:

"doesn't the hypothetical space elevator break the tyranny of the rocket
equation?" (which you did answer).

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woodandsteel
SpaceX’s BFR plans to overcome the propellant problem for getting to Mars by
refueling in orbit. I am surprised the article didn't mention the refueling
possibility. Maybe NASA didn't want to admit they are making a mistake putting
all their cash into the SLS.

Also, the economic implications of the equation don't matter so much when you
have a reusable rocket, and the BFR is supposed to be able to reuse both
stages.

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neolefty
_I am surprised the article didn 't mention the refueling possibility._

NASA source is from 2012, before BFR was fleshed out.

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woodandsteel
Ok, but it still should have been included as a theoretical possibility.

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hackerpacker
there are more tyrannical equations if you are promoting space colonization. I
mean if you compare earth to a petri dish, what do you think a small domed
shelter on some other planet will be?!?

I like space, lots of neat things to learn, but the discussion always seems to
get a little religious and doomsday-ish, and I find it less than genuine. Like
have people thought about where the energy to get massive numbers of people
off the planet will come from, and how that will leave the planet in even
worse shape for those that can't leave?

It is folly to think technology can fix everything, and I sometimes wonder if
it has actually "fixed" anything, aside from helping to enable overpopulation.

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groby_b
The energy to get a human off the planet is relatively small. Let's call it an
MWh. (It's 9.1 KWh/kg)

A billion people is a PWh. That's 0.5% of the earth's annual energy use. It's
a blip on the radar, especially since it will subsequently reduce annual
consumption in the 10% range.

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hackerpacker
factoring in Tsiolkovsky's equations, it seems more like 30mwh, and that is
just one person, and just the fuel, not the processing or the preparation or
even building a rocket, without any life support, or landing plan.

plus where are you going to send %10 of the population where they will be
immune to human nature, whatever that is.

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ilugaslifk
The tyranny of the rocket equation has done an order of magnitude less damage
to the progress of human space exploration than the mind-blowing waste of the
Shuttle program.

