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Super-Earths in Need for Extremly Big Rockets (2018)

arxiv.org

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Re: Super-Earths in Need for Extremly Big Rockets (2018)

#11

Post by perihelions »

There's a lot of loopholes you could plausibly escape through. For one: you could use hybrid atmosphere-breathing engines to get most of the way to low orbit. (Using ambient atmosphere as a reaction mass circumvents the rocket equation). From low orbit, you can switch to electric thrusters with Isp much higher than the engines considered here: it's no longer necessary to have a thrust/weight ratio greater than unity.

A hydrogen planet would be particularly easy, since the light molecules would maximize Isp for a (non-combustion) thermal engine. A nuclear scramjet on a Hycaean world would have some truly impressive performance.

Re: Super-Earths in Need for Extremly Big Rockets (2018)

#12

Post by captainmuon »

Perhaps "slow" ascent would be a option, i.e. not reaching escape velocity but just steadily ascending until you are far enough away that gravity is lower. I know here on earth it is far more inefficient, which is why you always go for "ballistic" trajectories where you gain enough velocity that inertia carries you on.

Maybe there is something you could "ratchet" against? Thrust a bit upward and have something prevent you from falling back down. Maybe the denser atmosphere would provide an option. You could deploy large sails as intermediate launch pads in the atmosphere for example.

Re: Super-Earths in Need for Extremly Big Rockets (2018)

#13

Post by helpfulContrib »

jqpabc123 wrote: post #4

Bottom line: Chemical rockets are never going to take us any place interesting in the universe.

16-Psyche[1] is finally conquered.

The first remote factory ships arrive, and not long after the pile collectors go out, the machines start building new rockets.

New starships, constructed from the mineralogical ultra-super-mega-wealth that is this remote asteroid treasure, begin to rise among the golden landscape. These are not Earth-rated rockets, but rather planetary transfer super-structures that can move entire cities worth of materials, slowly and surely, out to somewhere great.

We might find a spot to park some of these cities where the weather is always going to be great. We might find a way to build them into mini Dyson-spheres, parked around a bit of fusion, or so.

I think rockets can take us to great places. Imagine a single-pass 3D printed Starship made out of titanium and other such alloys 16 Psyche might provide ..

Its a pretty big universe. A lot of it is interesting.

[1] - https://en.wikipedia.org/wiki/16_Psyche

Re: Super-Earths in Need for Extremly Big Rockets (2018)

#14

Post by sdenton4 »

captainmuon wrote: post #12

Perhaps "slow" ascent would be a option, i.e. not reaching escape velocity but just steadily ascending until you are far enough away that gravity is lower. I know here on earth it is far more inefficient, which is why you always go for "ballistic" trajectories where you gain enough velocity that inertia carries you on. Maybe there is something you could "ratchet" against? Thrust a bit upward and have something preven…

I once had a fun week playing Kerbal Space Program building solar-powered quadcopter launch platforms...

Basically a quadcopter which is mostly a big platform with a rocket payload in the middle. The quadcopter slowly ascends to the highest feasible altitude, bypassing all of the worst of the air resistance, and greatly reducing the delta v needed to get into orbit as a result.

This was mainly helping with the atmospheric drag problem, though; you would presumably need a lot of atmosphere to get far enough from the planet to help with the increased need for horizontal speed with a super massive planet.

Oh hey I found an old screenshot: https://imgur.io/zq8iyV0?r

Re: Super-Earths in Need for Extremly Big Rockets (2018)

#15

Post by Retric »

daltont wrote: post #3

Read a sci-fi book recently with that being a central plot point. Reasonably advanced species unable to escape the gravity of its home world. There is also a dearth of fissile material in the solar system that prevent a "nuclear option". Book was written as a bit of homage to "The Mote in God's Eye" with wanting to leave to planet being seen as a "Crazy Eddie" idea. https://www.goodreads.com/book/show/59554147-cold-e…

It’s clearly more difficult, but authors are a few individuals briefly thinking about a problem not entire civilization attacking the problem across generations.

My first thought is balloons work based on relative densities so they can still reach very low density air on a high gravity world. That doesn’t help much with rockets, but firing a gun or using something like spin launch is much easier if you can start from very low atmospheric pressure.

No idea what actual engineers could come up with.

Re: Super-Earths in Need for Extremly Big Rockets (2018)

#16

Post by dr_orpheus »

captainmuon wrote: post #12

Perhaps "slow" ascent would be a option, i.e. not reaching escape velocity but just steadily ascending until you are far enough away that gravity is lower. I know here on earth it is far more inefficient, which is why you always go for "ballistic" trajectories where you gain enough velocity that inertia carries you on. Maybe there is something you could "ratchet" against? Thrust a bit upward and have something preven…

Yes and no. So the slow/efficient acceleration is realized today with electric propulsion [0] which is very efficient in terms of fuel consumption because it accelerates the particles to such high speeds. But, it is very low thrust so it is something that is on for days/weeks/months at a time versus the small amount of time that chemical rockets are on. Because it's so low thrust though its not something that will actually generate enough acceleration to get you off the ground in the first place. You will still need a high thrust device (i.e. rocket or something more exotic like SpinLaunch) to get you off the ground and in to a low orbit. So while you wouldn't have to reach escape velocity (11.2 km/s on Earth) you still need to get to a very large fraction of that (6-7 km/s for low-earth orbiting satellites).

https://en.wikipedia.org/wiki/Spacecraft_electric_propulsion

Re: Super-Earths in Need for Extremly Big Rockets (2018)

#17

Post by mcbutterbunz »

onlyrealcuzzo wrote: post #10
jqpabc123 wrote: post #8

Earlier quoted context omitted.

Even within our own solar system, anywhere beyond the moon is likely to end up as a one way, dead end trip.

Why is it so important to get back? That implies people need to go there, I think? Why? And would it really not be possible to get to Enceladus and back (w/o people)? The gravity there is so much less than the moon. Or is it just the distance to and from Enceladus, and possibly nothing for a slingshot?

I can look at pictures of Machu Picchu on Google Maps but the experience of being there is so much better (from what I hear). That's why we want to send people. Presumably those people want to survive and come back too.

Re: Super-Earths in Need for Extremly Big Rockets (2018)

#19

Post by 1970-01-01 »

captainmuon wrote: post #12

Perhaps "slow" ascent would be a option, i.e. not reaching escape velocity but just steadily ascending until you are far enough away that gravity is lower. I know here on earth it is far more inefficient, which is why you always go for "ballistic" trajectories where you gain enough velocity that inertia carries you on. Maybe there is something you could "ratchet" against? Thrust a bit upward and have something preven…

As gravity increases, buoyancy also increases. A high-g civilization with access to hydrogen would be able to float to the top of their atmosphere, and then proceed to launch into space.

Re: Super-Earths in Need for Extremly Big Rockets (2018)

#20

Post by sjducb »

perihelions wrote: post #11

There's a lot of loopholes you could plausibly escape through. For one: you could use hybrid atmosphere-breathing engines to get most of the way to low orbit. (Using ambient atmosphere as a reaction mass circumvents the rocket equation). From low orbit, you can switch to electric thrusters with Isp much higher than the engines considered here: it's no longer necessary to have a thrust/weight ratio greater than unity.…

Yea. Some kind of nuclear scramjet would be the way to get off a big planet with a dense atmosphere.

To explain for all of the non engineers:

On earth scramjets work because airflow enters the front of the engine and the shape of the inlet compresses the gas, fuel is added and burnt, then the exhaust gasses go out the back really fast.

With a nuclear scramjet the fission reaction heats up the middle of the scramjet so air comes in, is compressed then heated so it expands and goes out the back really fast.

That would move you very quickly and efficiently through the dense atmosphere, using almost no fuel, and you do not have to carry much reaction mass.

Then once in space you feed compressed hydrogen into the front of the engine heat it up and send it out the back really fast, just like the nuclear rocket motors that nasa is developing right now.

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