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B Hyperloop - Orbital Space Launch

  1. Jan 4, 2019 #1
    I'm hoping I can get my idea debunked or with some words of encouragement, continue my investigation in what could be an ideal way to solve some propulsion issues in space travel.

    What I'm suggesting is building a large circular "maglev" accelerator in space, similar to CERN, which wouldn't need to be depressurized since already in the vacuum of space therefore cutting down on materials/costs, the "tube" wouldn't need to be built as such, only the interior/bottom half would need to be constructed. A possible location would be surrounding the moon, in it's orbit.

    In theory, the spacecraft or payload would be accelerated to the required velocity then launched. The only fuel then required would be for minor course adjustments and to decrease velocity upon arrival. In the distant future, if a regular transit destination was determined, ie: Alpha Centauri - A habitable world, a duplicate system could be built to "Catch" a spacecraft and/or launch in the opposite direction towards earth.

    Thoughts?
     
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  3. Jan 4, 2019 #2

    russ_watters

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    Because the accelerator is not tethered to a giant rock, it still needs the same propulsion system the rocket was supposed to have. I'm not sure if putting the rocket engines on the launcher vs the rocket conveys a momentum/fuel advantage though....someone else can maybe address that.
     
  4. Jan 4, 2019 #3
    I see what you're saying, so the whole "loop" would want to rotate in the opposite direction, in this case it could be tethered to the moon in multiple areas. I would suppose to offset any variation on spin, each payload could be launched in the opposite direction. Now being that the loop's mass would be much greater than the payload, I'm not even sure if the impact would negate a tethering system. ??

    As for any advantage without a tethering system, even if a rocket system (or other propulsion) was required for the "loop", at the bare minimum, the payload would be significantly smaller since it wouldn't require the acceleration fuel/mass for the trip.
     
    Last edited: Jan 4, 2019
  5. Jan 4, 2019 #4

    russ_watters

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    Hmm, that could potentially work.
    I may have created a little mess: "tethered to a giant rock" was a slightly tongue in cheek way of saying our launch pads are mounted on Earth, which is also the origin point for almost all of our launches. It has, in fact, been proposed that giant linear accelerators be used to launch payloads into space, but there are technical issues such as acceleration rate and aerodynamic stress that make it impractical.

    Your idea, I think, would work, but it is a fabulously expensive way to fulfill a need that doesn't exist.
     
  6. Jan 4, 2019 #5
    So you're not the first person to think about this. This is essentially a StarTram: https://en.wikipedia.org/wiki/StarTram

    You're not going to achieve a meaningful percentage of c with that, as others have explained.
     
  7. Jan 4, 2019 #6
    I don't think this is the same idea - similar but not the same. I'm proposing an accelerator IN SPACE, this wouldn't be used to get into orbit, the main purpose would be to accelerate cargo/craft to a vary fast speed before launching it into deep space, thus not having to rely on an onboard propellant.
     
  8. Jan 4, 2019 #7

    Janus

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    Let's assume you want a top speed of 1% of c, making a trip to Alpha C 430 yrs long. As the payload accelerates up to speed, the centripetal forces it will feel will grow larger. If we are talking passengers, then there is a limit to how much they could take. let's be generous and put this at 5g. In order to reach a speed of 1% of c, and keep the g forces on the passengers down to 5g, the accelerator would have to have a radius of 1.2 AU, or 20% larger than the Earth's orbit.

    If we built the ring entirely circling the Moon at 100 km above its surface, then that same 5g restriction would limit the top exit velocity to under 10 km/sec, This is less than the over 12 km/sec you would need just to escape the solar system from Earth's orbit around the Sun. To reach that earlier speed of 1% of c with an accelerator of this radius would subject the payload to nearly 490,000g
     
  9. Jan 4, 2019 #8
    Glad someone came up with the equation. I was actually concerned with the g forces as well, just wasn't sure on the calculation. Back to the drawing board.
     
  10. Jan 7, 2019 #9
    Basically, your idea is not useful with current power technology. When every space structure is powered with solar panels, it makes more sense to bring solar panels along spacecraft, to power fuel-efficient ion thrusters for several months or years in row is cost-efficient and weight-efficient manner.
    Having much oversized solar panels on linear accelerator which stays idle for 99.999% of time is not a valid proposal. Super-capacitors charged by smaller solar panels are slightly better solution, but still terribly bulky and expensive.

    For device like you imagine to be built (basically a mass driver), you need
    1) Good pulse power but stationary power source (fusion stellarator powering MHD generator?)
    2) Have thousands time more space traffic compared to today, to have a meaningful load of that pulse power source

    When both pre-requisites are meet, you can attach linear accelerator (mass driver) to said power source and utilize it with good effect for space travel.
     
  11. Jan 12, 2019 at 2:48 PM #10

    sophiecentaur

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    IMO, however many systems are going to be useful for getting equipment into remote places, the timescales that our bodies and societies work will mean that human star travel won't be on the cards for a very long time, if ever. Actually, i don't feel the same urge as the enthusiasts have. What space exploration actually needs humans on board (bearing in mind that those humans won't be you or me)? There is far more to life than just going places. We should be far more centred on the mind and building a worthwhile society than on spending money on unfeasible manned trips. Manned trips are only approved of by politicians for political reasons and the reasons are nothing to do with improving the human condition. Just take Trump's 'Space Force' idea. Straight out of Hollywood but it could well end up being funded.
     
  12. Jan 12, 2019 at 7:10 PM #11

    mfb

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    Crewed trips to unknown places are the reason humans can be found outside Africa.
     
  13. Jan 13, 2019 at 3:40 AM #12

    sophiecentaur

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    That's a frequently used argument but the analogy is extremely thin. Dispersion of the Human Species was highly incremental and it was a very low tech process. One may as well say that people swim the English Channel so it's only a matter of time before they swim the Atlantic all in one go. The actual numbers count much more than enthusiasts about anything tend to acknowledge.
     
    Last edited: Jan 13, 2019 at 3:51 AM
  14. Jan 14, 2019 at 12:32 AM #13

    mfb

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    Going to the Americas needed more technology than going from Africa to Asia. Going to remote islands in the Pacific needed more technology than going to the Americas (probably). Going to the South Pole needed more technology than exploring all of the Pacific. Going to Mars will need even more technology.
    No one said you had to swim. You want a ship. People invented ships. People did cross the Atlantic.
     
  15. Jan 14, 2019 at 4:43 AM #14

    sophiecentaur

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    A bit more, in the 16th century, agreed. But many species of life have made it across the Atlantic, one way or another. Human presence all over the World was not due to 'manned expeditions' it was achieved way before Columbus' times in pre-history. They more or less just waited for the land bridge between Asia and America and then moved house. The only parts of the Earth that humans have not colonised are Antarctica and particularly high mountain regions and, strangely, they are the only regions with little or no other advanced life forms present. All Earthbound ' colonising expeditions' have taken humans to a place where there is Air, Water and Food Sources and individual journeys have taken no more than a few years. Also, the participants were always looked upon as expendable. I can't see modern politics accepting that.

    I am always surprised that the numbers seem to be ignored by start travel enthusiasts. There is a timescale, beyond which humans do not plan - never have. The timescales are actually getting shorter. No one plants trees, for use in 500 years' time these days. It's taken several decades for the majority World opinion to have swung in the direction of acknowledging Climate Change because of inability to consider long time scales. People are 'scared' that the Sun will swallow us up because the concept of billions of years is just beyond them.

    It's quite amazing that the Space industry thinks as far ahead as it does with the decade-long plans for projects. Some very sophisticated thinkers involved there, I think. But I am sure the attention span of society will max out when the first results of an interstellar space travel project will take generations to reach Earth. Great as a thought exercise but billions of dollars would be required. Who would vote for that level of spending?
     
  16. Jan 14, 2019 at 6:11 PM #15

    mfb

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    No one was talking about Columbus. I was talking about the first settlers that probably came over/along the land bridge, but needed tools for that. Clothes, for example, probably fishing equipment, boats and so on. Columbus was not even the first one to come from the European side.
    Don't switch the topic please. The discussion was about exploration. We did explore all these places. Humans have been on nearly every high mountain, humans have been all over the place in Antarctica. We have a permanently inhabited station at the South Pole (and a few more at the coast).
    All high jump records were below 2 m - until someone jumped higher. See the previous posts, you start with the easy things and then go to more ambitious things. Of course everything before the age of spaceflight went to a place with air and water. Where else would it go.
    We did have expeditions to places without food, and since the 1960s we also had expeditions to places without air or water.

    "This has never been done before" is the main point of an expedition. You don't make an expedition to New York.
    Who knows how long a generation will be by then.
     
  17. Jan 15, 2019 at 4:12 AM #16

    sophiecentaur

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    You may have been but your words were "crewed trips", which doesn't sound like early tribes following a food source. And you continue with :
    which confirms my view.
    How was it a switch of topic to compare human occupation with that of other living species, which are not technically developed? It just proved my point.

    You seem to be wilfully ignoring the essential difference between Earth exploration and colonisation, (which requires virtually no essential technology) and space missions which must rely entirely on technology and which would involve many generations and far longer term planning than humans have ever managed. PF normally requires high factual accuracy and the quotation of precedents yet the star travel enthusiasts exhibit an amazing level of blind optimism about the way humans may or may not behave in a timescale that's totally unprecedented. Just because one can do calculations which may be accurate and justified, doesn't imply that humans will succeed in a project that's based on those calculations.
    I am pragmatic and I have no particular optimism about the future for humans (in the long term it is none of my business) but there is evidence of a very limited lifetime for all past 'civilisations'. Why should we expect any difference - just because the technology is very attractive and exciting?

    PS The Swimming the Atlantic bit was clearly just an analogy to demonstrate that the magnitude of any project is highly relevant. Actually getting across oceans does not require technology - just luck, in many cases. Study the spread of many species over tens of millennia.
     
  18. Jan 15, 2019 at 5:06 AM #17

    mfb

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    Which other species? This thread was always about human exploration.
    I'm not ignoring it. I'm pointing out that we did several big steps in the past already. The next one is always more challenging than the steps before. I know that, you don't have to repeat it again. You think the first trip over an ocean was easy with the tools at that time? I'm sure many people told the few that did the trip to stay. Because no one did it before, and blah blah blah.
    There is no such rule and it would be completely against the idea of the forum. Science is always about doing something new.
    I don't get that impression from most here. Or maybe the group you call "enthusiasts" is way smaller than I think. I see it acknowledged everywhere that it will be an unprecedented challenge, and no one claims that it will certainly happen.
    The timescale is not new, at least not for missions within our solar system. As an example, plans for the LHC started ~1990, the project is expected to run until 2035 or longer, with data analysis taking at least 5 more years. A 50 year project, longer than the working life of people. Compared to that a crewed mission to Mars, Jupiter or even Saturn, including the planning, is much faster.
    You know what typically comes before the decline (unless it caused by a natural disaster)? Stagnation. A phase where people stop doing something new, stop exploring the world, stop expanding even if they could.
     
  19. Jan 15, 2019 at 8:19 AM #18

    sophiecentaur

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    So now we're back into exploration and not migration? I already made the point that there are very few places on Earth that were not reached by other species, unsupported by technology so humans getting there is no big deal (comparatively).
    Big by what standards? The biggest steps, interns of impact, were actually colonisation by totally primitive tribes. The biggest step of 'a man' was 350,000km for a short while. Good but no cigar in terms of hundreds or thousands of years to the stars. Extrapolation that far could be very optimistic. An interesting thought experiment, don't get me wrong (I guess you may do).
    You call that a long timescale - all self respecting Emperors took that long to organise their mausoleum and look where they are now.
    Look on my Works, ye Mighty, and despair!
    Nothing beside remains. Round the decay
    Of that colossal Wreck, boundless and bare
    The lone and level sands stretch far away.”
    Ozymandias. Percy Shelley
    (In a timescale of just a few hundred years. We are dealing with more than ten times that timescale.

    I would have thought that a healthy skepticism would be the reasonable attitude to such long term plans. (Who's POTUS these days?) World stability is one thing we cannot count on, these days.
     
  20. Jan 16, 2019 at 12:56 AM #19

    mfb

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    You started it:
    By the standards of what had been done before. You are presenting history as if everything was a trivial exercise. With modern knowledge and tools it would be, but that is not the point.
    It is over 5 times the length of the whole Apollo project. It is longer than any proposed project to get humans to Mars. It is longer than any future project about getting humans to Jupiter's or Saturn's moons would probably be. If you don't see a problem with projects up to 50 years in length then I don't understand your previous objection to them.
     
  21. Jan 16, 2019 at 7:21 AM #20

    sophiecentaur

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    That's my point. 50 years is 'a very long time' in the minds of people funding projects. Mars is by far the lowest hanging fruit, too. The long term benefits of some of the longest running space probes (70 years or so) were not actually planned for by the money sources, even if the designers had it up their sleeves. Sending a crewed ship on a long (star) trip could not rely on that kind of lucky extension of the project ( as in Voyager) it would need to be planned to operate over many hundreds of years. That is many times the 10X ratio that you have quoted.
    Imo, you are far too optimistic about the way governments might behave and also about how much money the population of the Earth would be prepared to contribute on a personal basis. How much money would you personally sacrifice, at the expense of your children's welfare or your own comfort?
    You have misinterpreted my objections all along. I am prepared to suspend my disbelief about the possibilities of future technology but, in all conscience, I cannot contemplate FTL travel or believe that humans have a future of unlimited advance. That would be very out of character.
     
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