How Fast Would Directed Gravity Field Travel Be?

[Spacescifi]

 

While it is easy to totally make up scifi drives, it is still interesting when a bit of real force is in play.

Quin-gravity Drive: Causes vessel using it to fall in FIVE directions under gravity other than down....up, left, right, forwards and backwards. When turned off you will return back to normal gravitational pull.

Drive is modular and installed against spaceship hull....so five of them, four cross-ways along the sides, and one along the top in the center.

Travel from Earth: You get free 1g fall away from Earth and can even reach orbital velocity!

 

Questions:

 

How long would it take to reach Earth orbit speed? Less than the usual 8 minutes that IRL rockets take I presume since this gravity drive has a quick start (immediately starts falling up at 1g, no slow take off here).

Possible problems: Earth's 1g gravity field is awesome, but the farther you travel the weaker it becomes to the point where you're gravity drive will probably barely accelerate if at all.

It would be nice to use Earth gravity acceleration as long as possible but realistically it would probably be smarter to turn it off if destination has less than 1g.

Why? You will come in too fast otherwise, and the local gravity may or may not be enough to curb enough of your excess speed in time.

For examlple, from Earth to the moon, would it NOT prolong travel time if the vessel used Earth gravity until moon gravity became stronger and started to then try to use moon gravity to slow down for landing?

Or would it be faster to just use Earth gravity directed acceleration drive to put along a trajectory, coast and then use moon gravity to land with less excess kilometers per second?

 

Travel options: You could go anywhere in the solar system, although the 'dead zones' would be interplanetary space far between planets.

At points such as these you could burn some rocket propellant I presume, since I am rather certain sun gravity is still rather weak at Earth orbit ranges and won't even be a fourth of a g acceleration.

 

You guys and gals likely know better though....

 

 

Edited May 15, 2021 by Spacescifi

[SOXBLOX]

Since this is pure magic, as fast as you like.

[Spacescifi]

38 minutes ago, SOXBLOX said:

Since this is pure magic, as fast as you like.

 

Faster than IRL travel for sure. As the 1g has diminishing returns the farther the vessel is from Earth until lunar gravity has more acceleration anyway.

 

Wonder how long it would take to reach Mars?

The real irony?

 

It would STILL take months of coasting...just somewhat less if you expend a few rocket boosts in interplanetary space.

[wumpus]

59 minutes ago, SOXBLOX said:

Since this is pure magic, as fast as you like.

Magic: For when you want a reason for your spaceship to arrive at the precise time the plot requires.

("speed of plot" doesn't require magical drives, but it certainly helps with unspecified thrust & delta-v).

[Spacescifi]

6 minutes ago, wumpus said:

Magic: For when you want a reason for your spaceship to arrive at the precise time the plot requires.

("speed of plot" doesn't require magical drives, but it certainly helps with unspecified thrust & delta-v).

 

True.

Chances are high I will use something a lot easier than this, I just wanted to get a good laugh when as per the usual...even doing what is impossible still has a travel time of months LOL.

[kerbiloid]

Spoiler

 

[K^2]

11 hours ago, Spacescifi said:

How long would it take to reach Earth orbit speed? Less than the usual 8 minutes that IRL rockets take I presume since this gravity drive has a quick start (immediately starts falling up at 1g, no slow take off here).

Nothing slow about rockets taking off. They do tend to have a bit less than 1g of acceleration from the pad, but not by a lot. And once some of the fuel burns off, it can be well over 2g.

You can also do the math really easily. You need about 7.5km/s to orbit. Ignoring losses and ascent trajectory, that's a bit over 750s at 1g or 12.5 minutes. This is very rough estimate, but still, clearly far greater than ~8 minutes taken by typical rocket.

[cubinator]

7 hours ago, Spacescifi said:

 

Faster than IRL travel for sure. As the 1g has diminishing returns the farther the vessel is from Earth until lunar gravity has more acceleration anyway.

 

Wonder how long it would take to reach Mars?

The real irony?

 

It would STILL take months of coasting...just somewhat less if you expend a few rocket boosts in interplanetary space.

Ah, but gravity pulls on everything equally, so you can just accelerate everyone in the ship to not squash them when going faster.

[Spacescifi]

3 hours ago, K^2 said:

Nothing slow about rockets taking off. They do tend to have a bit less than 1g of acceleration from the pad, but not by a lot. And once some of the fuel burns off, it can be well over 2g.

You can also do the math really easily. You need about 7.5km/s to orbit. Ignoring losses and ascent trajectory, that's a bit over 750s at 1g or 12.5 minutes. This is very rough estimate, but still, clearly far greater than ~8 minutes taken by typical rocket.

 

I see...I thought that may be the case

 Reaching space itself can be faster, but reaching prbital velocity is what takes the time.

Edited May 15, 2021 by Spacescifi

[Codraroll]

On 5/15/2021 at 8:09 AM, Spacescifi said:

Chances are high I will use something a lot easier than this

I just wonder, have you ever written anything or are you just churning around with hypotheticals?

I must admit I get slightly tired of the endless flood of threads asking questions for which the answer is always "You're making stuff up for sci-fi, the answer can be anything you like".

Edited May 16, 2021 by Codraroll

[SpaceFace545]

Something like this would be FTL, so whatever max speed would be would be faster than light.

[Spacescifi]

5 hours ago, Codraroll said:

I just wonder, have you ever written anything or are you just churning around with hypotheticals?

I must admit I get slightly tired of the endless flood of threads asking questions for which the answer is always "You're making stuff up for sci-fi, the answer can be anything you like".

 

Depends....on what you mean by written anything. Since the answer to 'anything'  can easily be yes. If you are being specific then I can actually answer. That said, I have scrapped some long held tropes I intended to use as the following shows:

Scifi must match the setting one wants. Which means complete realiism has to go. Cannot justify it otherwise.

Right now, there is no scenario in which a massive human space colonization effort happens for reasons several are very aware of. Mostly because it is more reasonable not to given the challenge and expense. If it were easier and the challenge was reduced to more reasonable levels then we could see something.

For a while I wanted something that could prevent RKV's, but eventually I realized I don't have to make common assumptions scifi makes and that alone can fix it.

Common assumption: Scifi aliens exist.

What if they don't? What if it's just us?

That means Earth is a lot safer from RKV's even if they we do develop high thrust constant acceleration. You do not destroy your home. As for scifi aliens....who really cares? No one really wants to read what they don't know nor understand, they are stand-ins for humans or beasts anyway in scifi,  much like fantasy settings. You can even still have them via bioengineering fiction from human science.

This even makes space colonization easier, since it is just humanity and it's descendants spreading out over the cosmos.

Lots of resource stations on uninhabitable worlds going on to ressupply or grow or add to space habitats.

Cities in space.
 

Edited May 16, 2021 by Spacescifi

[Spacescifi]

45 minutes ago, SpaceFace545 said:

Something like this would be FTL, so whatever max speed would be would be faster than light.

 

No.

Planet gravity won't let you reach luminal let alone lightspeed because gravity assisted gravity field redirection drive would pass on.

To make another pass you would have to kill your speed anyway.

The sun has 27g but you would die along the way unless you had an EM cloak. Constant 27g would also kill.

Edited May 16, 2021 by Spacescifi

[Codraroll]

8 hours ago, Spacescifi said:

Depends....on what you mean by written anything. Since the answer to 'anything'  can easily be yes. If you are being specific then I can actually answer. That said, I have scrapped some long held tropes I intended to use as the following shows:

Stories. Prose. Scripts. Literature. Any lengthy bit of text that actually uses the information you keep asking for. If the point is to just explore new concepts, you might as well make a "Spacescifi's questions thread" or use the existing questions thread rather than flooding the forums with one new one every single day.  Especially if you think it through and figure that the answer to the question might possibly be "It's your sci-fi, you make the rules, have it however you want" like seems to be the case for 90% of those threads.

Edited May 16, 2021 by Codraroll

[SpaceFace545]

38 minutes ago, Spacescifi said:

 

No.

Planet gravity won't let you reach luminal let alone lightspeed because gravity assisted gravity field redirection drive would pass on.

To make another pass you would have to kill your speed anyway.

The sun has 27g but you would die along the way unless you had an EM cloak. Constant 27g would also kill.

But isn’t this like an Alcubierre drive where you essentially “surf” a warp in space time, in this case your craft is perpetually falling forward. And there wouldn’t be any acceleration because only space time moves, you don’t.

[wumpus]

On 5/15/2021 at 7:59 AM, K^2 said:

Nothing slow about rockets taking off. They do tend to have a bit less than 1g of acceleration from the pad, but not by a lot. And once some of the fuel burns off, it can be well over 2g.

You can also do the math really easily. You need about 7.5km/s to orbit. Ignoring losses and ascent trajectory, that's a bit over 750s at 1g or 12.5 minutes. This is very rough estimate, but still, clearly far greater than ~8 minutes taken by typical rocket.

Didn't the Saturn V lift off at something like .1g?  Adding lots more fuel to the first stage is way cheaper than developing even more powerful engines, and increases delta-v a little.  Saturn V also shut off an engine to avoid going over 3g, which for all I know is pretty standard with crewed rockets.

There's a Japanese orbital rocket where the first 3 stages are all solid (so increasing thrust mostly requires thicker walls), that takes off at ~2.4g and the acceleration keeps increasing.  This nearly eliminates gravity losses, but I don't know  how much they lose through  aero drag losses.

[K^2]

3 hours ago, wumpus said:

Didn't the Saturn V lift off at something like .1g?  Adding lots more fuel to the first stage is way cheaper than developing even more powerful engines, and increases delta-v a little.

Yeah, but that's somewhat uncommon. The marginal utility of fuel is really low at that point, so it only makes sense when you need just a bit more oomph and you are using high I_SP fuel, like LH2.

3 hours ago, wumpus said:

Saturn V also shut off an engine to avoid going over 3g, which for all I know is pretty standard with crewed rockets.

Yes. Not just crewed, either. You rarely want to go much above 3g if you can help it even purely from perspective of efficiency while still ascending through atmosphere. Of course, if you're going up on solids, you might be forced into higher acceleration. So it varies, but generally, you don't see anything much above 3 - 3.5.

3 hours ago, wumpus said:

This nearly eliminates gravity losses, but I don't know  how much they lose through  aero drag losses.

So like I pointed out above, it's really not optimal. Ideally, you want to start your ascent at 2g and ramp up to 3 through gravity turn, then ease out a bit as you're exiting atmosphere and settling into your orbit. But this is wishes being horses kind of thing. With constraints of real engines, you usually start bellow 2g to build up to these 3-3.5 I've mentioned above.

Getting 2.4g from the pad is an interesting choice. I have a feeling they're optimizing for something other than fuel use, exploiting the fact that solids are relatively cheap, and you can just have a bigger booster. I should take a look at what their ascent looks like.

[Starman4308]

6 hours ago, wumpus said:

There's a Japanese orbital rocket where the first 3 stages are all solid (so increasing thrust mostly requires thicker walls), that takes off at ~2.4g and the acceleration keeps increasing.  This nearly eliminates gravity losses, but I don't know  how much they lose through  aero drag losses.

I doubt it comes close to eliminating gravity losses: you still have to start with a substantial pure-upwards component to get out of the thickest of the atmosphere, otherwise the aero losses are going to be absurd.

As to why 2.4G, my guess is that it's a combination of shared hardware (i.e. the SRBs are also components of other rockets) and use of short-duration SRBs intended to get the core stage up to speed.

My other guess, that it's an adapted ICBM*, doesn't really square with Japan's lack of ICBMs.

*ICBMs intentionally have very high TWR to help get them through weather and get some distance from their launch site, which is a rather obvious high-priority target for enemy counter-force strikes.