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# Gravitationally coupled spaceship

 (+8) [vote for, against]

Sooner or later we (and by "we" I mean humanity, rather than Sturton, the intercalary and myself) will develop decently powerful space propulsion systems, capable of accelerating a spaceship up to a large fraction (say 0.99999...) of C. This is good, because at 0.99999...C, you can get anywhere in the universe in about 5 minutes, thanks to time dilation.

But wait - Houston, we have a problem! If we accelerate our spaceship at 1G, it will take about 1 year to reach 0.99999...C. For most of that year, the crew will not experience significant time dilation, and hence they will experience most of that full year of acceleration. This is a drag.

The solution, of course, is to accelerate at more than 1G, and ideally at about 1000G. This will reduce the acceleration period to something like 8 hours (mostly experienced) - enough time to watch a movie, have an in-flight meal, and catch a little sleep. To give a 1000G acceleration, all we need is a bigger engine. So that's OK.

But wait - obviously a major malfunction! With an acceleration of 1000G, our intrepid crew will be reduced to a thin, multi-layered paste on the back wall of the spacecraft. Even if we fill the spaceship with water to cushion the force, 1000G will still be enough to fractionate your bones from your fat. Not at all good.

This, then, is the coupling problem - how to transmit a force equally to all components of the body, so that it can be accelerated very intensely without dying.

So, here's what we do. First we build the spaceship with its super-duper engine, and we build it strong enough to survive 1000G of acceleration. Fine.

Now, in the nose of the ship, we put a large mass. A quite very much large mass. For compactness, and to leave room for the in-flight catering supplies, we will use a black hole of perhaps a few trillion tons. Of course, it's notoriously hard to fix a black hole in place (duct tape is hopeless, for instance), so we'll use a charged black hole and hold it in place with a big electric field.

So, we have a big big mass at the nose of the ship. The ship, by the way, is quite long (maybe a few hundred kilometres). By dint of careful calculation and use of the right mass of black hole, there will be a space further down the ship at which (a) the black hole is exerting 1000G of upward pull and (b) the G-gradient is only about 1G per metre, so tidal forces aren't too bad.

Now we're all set. We put the crew in the spaceship, initially at the very bottom (quite far from the black hole), and then we fire up the engines. The ship starts to accelerate upward at, initially, a few G. The crew, meanwhile, take an elevator that brings them closer to the top of the ship, and hence closer to the black hole.

At some point, the crew will be close enough to the black hole that its upward gravitational pull exactly matches the acceleration of the ship as a whole, and the crew feels themselves weightless. We then open the throttle and ramp up the acceleration to 10G, 100G....1000G, and during this time the elevator is rising and bringing the crew closer to the black hole in the nose.

Once we reach 1000G acceleration (of the ship), the elevator stops at the point where the black hole is providing 1000G of upward pull on the crew. (The actual pull will be slightly greater at their head, and slightly less at their feet. For this reason, they would find it convenient to stand upside down, feet facing the black hole.)

And - gadulka! - the spaceship can now accelerate at 1000G, with the delicate, squishy crew members coupled to it gravitationally and able to enjoy their in-flight drinks service in the usual way.

 — MaxwellBuchanan, Oct 29 2017

Neutron Star http://www.unexplor...ulp/htm/rpulp88.htm
Prior art for my annotation. [Wrongfellow, Oct 29 2017]

Wandering Star aural art
[normzone, Oct 30 2017]

Alcubierre drive https://en.wikipedi...ki/Alcubierre_drive
Quantum gravity [8th of 7, Nov 02 2017]

 Can the tidal force be used to provide artificial gravity for the passengers?

 I'm imagining a passenger module divided into three pieces:

 An aforeships compartment, closer to the hole, where people stand with their feet towards the hole, experiencing 1001g of gravitational acceleration counterbalanced by 1g of locally upwards mechanical force from the floor;

 A behindships compartment, further from the hole, where people stand the other way up, feeling 999g of gravitational acceleration supplemented by 1g of locally upwards pressure from the floor;

 An inthemiddleships compartment, locally weightless, where the passenger module is attached to the main spine of the ship.

The two "locally upwards" forces point in opposite directions, placing the module as a whole under tension, but cancelling each other overall.
 — Wrongfellow, Oct 29 2017

It even serves to protect from space dust [+]
 — Voice, Oct 29 2017

 //Can the tidal force be used to provide artificial gravity for the passengers? // Well, yes.

 At any point along the ship, the experienced G-force will be:

 N=A - gM/d^2 (or something like that), where N is the net experienced G-force, A is the actual acceleration of the ship in space, g is the gravitational constant (should be capital G, I think, actually) and d is the distance from the black hole.

 So, at some point along the ship, for any given set of circumstances, N will go from being positive (toward the bottom of the ship, i.e. pulling you to the floor of the rocket) to negative, and obviously zero somewhere in between.

 Assuming that you want something like 1G acting on your centre of mass, you could have two "floors", one nearer and one further from the top of the rocket. People would walk around upside-down on the upper floor, and right way up on the lower floor. So, in effect it would be a room where you could walk on the floor or ceiling, but be weightless mid-way between the two.

Could make for interesting cricket matches.
 — MaxwellBuchanan, Oct 29 2017

 // enough to fractionate your bones from your fat. Not at all good //

 ... unless you want to make healthier kebabs ?

 Ohh .. Kay ...

 Are you listening ? Are you ? THAT MEANS YOU, PRODBURY ... Now, open your text books atSTOP THAT BLUDGEWICK, IT'S DISGUSTINGLY UNHYGIENIC, DON'T YOU HAVE A HANDKERCHIEF ? chapter six ... right ...

Now, pay attention. YOU DON'T DO IT LIKE THAT. Newtonian reaction drives are fine for minor changes of orientation, but if you want to cross interstellar distances in reasonable timescales, something a trifle more sophisticated is obligatory.
 — 8th of 7, Oct 29 2017

Yes, [8th], we assumed that you would like to make some oblique reference to a hypothetical poorly-defined alternative to reaction drives. If you would care to give a little more detail, obviously, we will be happy to take it under consideration.
 — MaxwellBuchanan, Oct 29 2017

 // unless you want to make healthier kebabs ? //

We can probably manage this without needing a black hole.
 — Wrongfellow, Oct 29 2017

 (+)//N=A - gM/d^2 (or something like that)//

You defined N,A,g and d. What's M?
 — 2 fries shy of a happy meal, Oct 30 2017

Cured pork, boiled and thinly sliced; half of the popular breakfast dish M n X ...
 — 8th of 7, Oct 30 2017

 IAmNotAScientist, [2 fries], but Wikipedia tells me that the unit of measure for that Gravitational Constant includes an inverse kilo (always useful to pack in your checked luggage); so, there's probably a "mass" term in the vulgar fraction on the right hand side of that equation, measured in right-way-up kilos, to cancel it out, so that the whole thing can then be subtracted from acceleration without semantic embarrassment

... or something.
 — pertinax, Oct 31 2017

Using a similar approach, we can solve intergalactic travel by simply directing a black hole that affects the position of the sun to take the entire show on the road
 — theircompetitor, Oct 31 2017

That would be an excellent idea. The problem with very fast space travel is that, although you may be back in time for tea, it's likely that tea itself will have evolved in the meantime. Taking the whole planet along with you would solve that problem.
 — MaxwellBuchanan, Oct 31 2017

Here's another idea: don't travel at all but instead recreate your destination where you are now. It doesn't matter how accurate your recreation is because you can never be confident what your destination looks like, so any recreation of it is as good as any other. The reason for this is that, because information can not be transmitted faster than light, any information you may think you have about your destination will always be out-of-date; You can never be sure what your destination looks like now or will look like when you arrive. Any opinion as to what your destination looks like is equally valid.
 — hippo, Oct 31 2017

That's all very well and good unless you want to travel to Milton Keynes. Everyone knows what Milton Keynes looks like, always.
 — MaxwellBuchanan, Oct 31 2017

//unless you want to travel to Milton Keynes// luckily that situation never arises
 — hippo, Oct 31 2017

I’m not exactly certain how you accelerate a black hole at that speed, but that’s details. Maybe with a black hole apult?
 — RayfordSteele, Oct 31 2017

<marked for tagline> I’m not exactly certain how you accelerate a black hole at that speed, but that’s details. </marked for tagline>
 — theircompetitor, Oct 31 2017

Well, as hawking is often the prelude to spitting, perhaps the Hawking radiation could be followed by the ejection of some sort of reaction mass?
 — pertinax, Oct 31 2017

Like [2Fries] said, At an environment of such chaotic ranges, would M mean mass.
 — wjt, Nov 01 2017

 Thanks [pertinax]. I didn't want to assume. I thought maybe gM was the symbol for gravitational constant.

Maybe we could nudge a small-ish black hole to slingshot around our sun and have the ship catch up to it.
 — 2 fries shy of a happy meal, Nov 01 2017

 /recreate your destination where you are now/

Genius! And maybe people will pay me for a trip there! I am pretty sure Istanbul looks like the dog couch, plus a bunch of blankets...
 — bungston, Nov 01 2017

It certainly smells like it ... unless you've washed the blankets in the past six months, in which case the dog couch is much more fragrant.
 — 8th of 7, Nov 01 2017

I take it, then, that you're not a fan of black tobacco, [8th]?
 — pertinax, Nov 02 2017

 It's absolutely fine until some idiot sets fire to it.

While we have no objection to setting fire to things as a general principle, there are some substances which are better uncombusted.
 — 8th of 7, Nov 02 2017

And the other 997G?
 — MaxwellBuchanan, Nov 02 2017

 Why does the propulsion unit have to accelerate at the same speed as the hab module? Couldn't we simply fasten the habitat module onto a very long, very stretchy bungee cord or stick of chewing gum?

<Somewhere out in space> Huge explosive acceleration takes place, accelerating the end of a stretchycord in the direction of Planet NewEarth where ever it happens to be. At the other end of the stretchycord, a huge hab module is accelerating at a rate that is a ratio of its inertia to the faster moving end, eventually getting up to an appreciable speed.
 — RayfordSteele, Nov 02 2017

 //Could make for interesting cricket matches//

I found it all entirely plausible until you got to this bit.
 — AusCan531, Nov 02 2017

 There might be something that higgs bosons could do to create a gravitational singularity sized gravity field without the gravitational singularity.

One advantage: Higgs bosons have already been produced, so just make more of them, and get them to cooperate.
 — beanangel, Nov 02 2017

 //eventually getting up to an appreciable speed.//

 Yes, but 'eventually' is quite a long time.

We want to accelerate people at 1000G, so they can get up to near-light-speed quickly. The only way to do that, survivably, is to apply a force to each atom in the person, proportional to that atom's mass. Gravity is, as far as I know, the only way to do this.
 — MaxwellBuchanan, Nov 02 2017

 //a gravitational singularity sized gravity field without the gravitational singularity//

So, a sized gravity field?
 — Wrongfellow, Nov 02 2017

 No.

 — 8th of 7, Nov 02 2017

Re. [8th]'s link - it seems that the only place Alcubierre could find the right kind of negative density was in a Casimir vacuum. Now, there's plenty of vacuum in interstellar space, but a Casimir vacuum has to be very, very flat. So, if you first reduced your crew to minimal lamina by unbalanced acceleration, then you could fit them into the sub-micron-thick vacuum in which Casimir forces would enable the Alcubierre drive required to protect them from unbalanced acceleration. Job done.
 — pertinax, Nov 03 2017

This asks the question, how sharp a gravity gradient would be needed to separate quarks. The energy to separate quarks should be equatable to a gravitation force differential over such a minuscule distance.
 — wjt, Nov 03 2017

How tall is a football field?
 — lurch, Nov 03 2017

African or European ?
 — normzone, Nov 03 2017

Oh, European ... African ones are non-migratory.
 — 8th of 7, Nov 04 2017

Small black holes have short lifetimes. How long will this one last?
 — notexactly, Mar 11 2019

 I was reading this post, nodding approvingly as there were no apparent flaws, until I got to the part which said “duct tape is hopeless” whereupon I knew it was all bollocks and stopped reading.

You. Take.That. Back.
 — AusCan531, Mar 11 2019

You forgot about the time-dilation effects of the black hole itself. I can't remember how it all goes (G and M's and square-roots and such...) but it will definitely make a difference to the time-span of such an endeavour.
Of course, capturing a black hole in the first place, with-out it capturing you, is the tricky bit...