Rocket Science

I was watching something on the planets and learned something about rocket power. So I thought of a trivia question:

Using rocket power *alone*, what approximate area of the solar system can be reached? The choices represent an increase in distance.

Quote: odiousgambit

Using rocket power *alone*, what approximate area of the solar system can be reached?

Once you reach escape velocity for this planet... you just keep going subject to occasional solar winds and the gravitational attraction of large objects. If you time the launch to avoid the larger known planets you keep going and going like that Battery Bunny using only a few little puffs of energy to change your attitude or kick your speed up to avoid collisions or the effects of sailing "upwind".

Quote: Fleastiff

avoid the larger known planets

nope

thanks for voting. Same selection I would have made prior to a few days ago

Can I make the rocket as big as I want to?

Perhaps the question you're asking differs from the question you intended to ask. Otherwise, velocity is a scalar vector and acceleration will increase until fuel exhaustion, at which time your velocity will remain constant unless slowed by atmosphere or mass sufficient to affect it. You will, eventually, leave the solar system under those conditions.

Quote: Mosca

Can I make the rocket as big as I want to?

After thinking about it, probably one condition that applies and was not mentioned in the program was that the rocket takes off from Earth. In the early days of space exploration, they knew that it is not possible to reach Earth's orbit velocity without making a two stage rocket, discarding stage one. Possibly if you built a huge rocket in, say, moon's orbit and took off from there, it would change the claim that the rocket can only reach [answer in spoiler]. From Earth, there are probably also limits that are practical engineering limits rather than just theoretical limits [I'm not sure]

Quote: beachbumbabs

Perhaps the question you're asking differs from the question you intended to ask. Otherwise, velocity is a scalar vector and acceleration will increase until fuel exhaustion, at which time your velocity will remain constant unless slowed by atmosphere or mass sufficient to affect it. You will, eventually, leave the solar system under those conditions.

I guess the physics of orbit velocity and escape velocity still apply, though. Bear in mind this was a surprise to me too. As far as your thought experiment goes, remember that, say, a rifle pointing straight up fires a bullet going faster than the speed of sound, but still the bullet fights gravity and eventually falls back to Earth. So, the Sun also slows objects as they try to escape the solar system. It is not correct to imagine something in orbit is not affected by gravity; in one sense the object is falling at the same rate it is climbing. Something on the way to outer planets also is slowing down; it either has the right ultimate speed or not. [IMO; this can get over my head]

At this point let's grant a minor spoiler, that escape velocity from the Sun can't be obtained by rocket power *alone* [that emphasis is critical]. I can't find the exact statement that planet X [per spoiler] is as far as you can get in Wikipedia, the closest statement I found is here:

Quote: wikipedia (exact URL is a spoiler)

Rocket engines can certainly be used to accelerate and decelerate the spacecraft. However, rocket thrust takes propellant, propellant has mass, and even a small increment Δv (delta-v) in velocity translates to far larger requirement for propellant needed to escape Earth's gravity well. This is because not only must the primary stage engines lift that extra propellant, they must also lift more propellant still, to lift that additional propellant. Thus the liftoff mass requirement increases exponentially with an increase in the required delta-v of the spacecraft.

This is all seeming pretty complicated, but the answer to "how could Voyager I and II do it?" is simple and you'll be glad you found out what it is.

Quote: odiousgambit

This is all seeming pretty complicated, but the answer to "how could Voyager I and II do it?" is simple and you'll be glad you found out what it is.

Gravity assists from Jupiter and Saturn, maybe from Uranus and Neptune for Voyager 2. Why not use the free momentum when it's so easy to do so.

But you're wrong. Unless you state the problem in such a way as to limit the kind of rocket used, there is no limit to how far a rocket-propelled anything can go, even if launched from the Dead Sea.

Quote: Nareed

Gravity assists from Jupiter and Saturn, maybe from Uranus and Neptune for Voyager 2.

Your answer is the correct answer.

http://en.wikipedia.org/wiki/Gravitational_slingshot

Quote: Nareed

But you're wrong. Unless you state the problem in such a way as to limit the kind of rocket used, there is no limit to how far a rocket-propelled anything can go, even if launched from the Dead Sea.

I guess I have realized that the program made an over-simplified statement. They just stated that planet X was as far as they could get without the slingshot effect. But I'm guessing that the statement derived from what practical limitations were accepted as to how many stages etc. can really be done in practicality.

I have reached the limit for what I should be "hosting" here. Nonetheless I thought it was pretty interesting. There is a story involved about realizing the very rare planet alignments that allowed Voyagers to do what they did. So I guess the old Astrology thing about "planets being in alignment" portending something proves to be true [g]

Quote: odiousgambit

I guess I have realized that the program made an over-simplified statement. They just stated that planet X was as far as they could get without the slingshot effect. But I'm guessing that the statement derived from what practical limitations were accepted as to how many stages etc. can really be done in practicality.

It depends on the type of rocket. A strict limit on chemical rockets does limit you severely. If you allow ion-drive rockets (for the payload), solar sails (not rockets), fission-powered rockets (on every stage or just for the payload). That's just limiting to the likely option. If you had a fusion rocket you could not simply leave the Solar System, but likely do so very fast.

Quote:

There is a story involved about realizing the very rare planet alignments that allowed Voyagers to do what they did. So I guess the old Astrology thing about "planets being in alignment" portending something proves to be true [g]

It's a great deal more complicated than that. It depended on where Jupiter, Saturn, Uranus and Neptune would be when Voyager 2 could reach them in turn, if the launch could be undertaken by a certain time.

This was the TV series:

http://www.imdb.com/title/tt0283775/

I watched it again. There are a number of possibilities as to why the narrator said what he did, but with certain assumptions that are not laid out, one of the possibilities might be that even today, with the type of rocket engines actually being used, *without the slingshot effect* the approx 400 million miles to Jupiter [at closest point] is about all that can be obtained from an Earth launch for practical purposes.

The program said Mariner "barely made it" to Mars. They seemed to be emphasizing the difficulties of getting to these places.