Author Topic: Larger than ITS - The next generation  (Read 9986 times)

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 27019
  • Minnesota
  • Liked: 6911
  • Likes Given: 4873
Re: Larger than ITS - The next generation
« Reply #40 on: 07/15/2017 11:17 PM »
Fissionable nuclear fuel is less dangerous than the radioisotope fuel we launch on every outer planets mission.

And NASA has recently tested an actual active fission reactor (although of a very simple design different than would be used in flight) with DoE's help in the last few years. This could be used for nuclear electric propulsion, probably for robotic missions.

Nuclear is not prohibited. Just need to use common sense. Doesn't make sense to use for Earth launch (chemical rockets work very well and affordably for launching into LEO), but could be useful once in orbit.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline DAZ

  • Full Member
  • *
  • Posts: 119
  • Everett WA
  • Liked: 82
  • Likes Given: 1
Re: Larger than ITS - The next generation
« Reply #41 on: 07/16/2017 01:09 AM »
Fissionable nuclear fuel is less dangerous than the radioisotope fuel we launch on every outer planets mission.

And NASA has recently tested an actual active fission reactor (although of a very simple design different than would be used in flight) with DoE's help in the last few years. This could be used for nuclear electric propulsion, probably for robotic missions.

Nuclear is not prohibited. Just need to use common sense. Doesn't make sense to use for Earth launch (chemical rockets work very well and affordably for launching into LEO), but could be useful once in orbit.

I readily agree with all of your statements except for your last sentence.  Chemical rockets donít work very well they barely work at all.  Any object they place into orbit ends up costing more than their weight in gold or platinum.  SpaceX and Blue Origin are working very hard to get the price down below the cost of gold.  This is essentially what the whole ITS project is about.  By scaling up to such a large size they hope to bring the cost down.  This is primarily the reason why a smaller ITS doesnít make economic sense.  Making it half the physical size costs 80 to 90% of the full-size version but you only get 10 to 20% of the economic advantages.  A very much larger ITS (which is what this topic is about) could possibly be even more economically advantageous.  But no matter how big you make the ITS it may not be as economically advantageous as an NTTR that is the same size as the presently envisioned ITS.  In fact, as you scale up both vehicles the NTTR will always come out ahead for the same size vehicles.  Of course, that assumes that the NTTR works as envisioned.

Up thread, it was mentioned about different generations of these vehicles.  It is definitely possible that a much bigger version of the ITS type vehicle could be built.  But it will be approaching the physical limits for just handling such a large vehicle.  And as mentioned up thread some much more advanced concept will need to come along.  The NTTR may be that concept.

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 27019
  • Minnesota
  • Liked: 6911
  • Likes Given: 4873
Re: Larger than ITS - The next generation
« Reply #42 on: 07/16/2017 02:41 AM »
Nah, brah, that's completely off-base. Gold and platinum are on the order of $100,000/kg. Falcon Heavy is on the order of $2000/kg. ITS is hoped to get around $10/kg because the actual cost of chemical propellants is very low. It's not the chemical aspect that makes current space launch expensive, it's the cost of throwing away aerospace hardware every flight.

And you think nuclear thermal would help?

A nuclear thermal rocket would be a very fast way to make your space launch even more expensive and approach the cost you mentioned before.

And you don't even get the benefit of lower propellant costs as nuclear thermal rockets generally use pure hydrogen, which is a LOT more expensive per kilogram ($10 or so) than liquid oxygen ($0.10 per kilogram or even less) which makes up the vast majority of a chemical rocket's propellant and liquified natural gas is also super cheap ($0.25/kg in the US). So even though an NTR would use less propellant, the cost of that propellant would be actually more.

This is only partly why nuclear thermal (especially the high Isp kind) is not a good idea for Earth launch. There are also technical reasons why it's a bad idea.

Might be good for very high delta-V trajectories.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline DAZ

  • Full Member
  • *
  • Posts: 119
  • Everett WA
  • Liked: 82
  • Likes Given: 1
Re: Larger than ITS - The next generation
« Reply #43 on: 07/16/2017 03:01 PM »
Nah, brah, that's completely off-base. Gold and platinum are on the order of $100,000/kg. Falcon Heavy is on the order of $2000/kg. ITS is hoped to get around $10/kg because the actual cost of chemical propellants is very low. It's not the chemical aspect that makes current space launch expensive, it's the cost of throwing away aerospace hardware every flight.

And you think nuclear thermal would help?

A nuclear thermal rocket would be a very fast way to make your space launch even more expensive and approach the cost you mentioned before.

And you don't even get the benefit of lower propellant costs as nuclear thermal rockets generally use pure hydrogen, which is a LOT more expensive per kilogram ($10 or so) than liquid oxygen ($0.10 per kilogram or even less) which makes up the vast majority of a chemical rocket's propellant and liquified natural gas is also super cheap ($0.25/kg in the US). So even though an NTR would use less propellant, the cost of that propellant would be actually more.

This is only partly why nuclear thermal (especially the high Isp kind) is not a good idea for Earth launch. There are also technical reasons why it's a bad idea.

Might be good for very high delta-V trajectories.

Well, you are partly right and Iím partially wrong.  In the last 10 to 15 years the price of gold (and platinum) has gone totally wacky.  It is gone up multiple hundreds of percent.  Traditionally platinum is more expensive than gold but at this time itís the other way around.

So at the present price of gold, you are correct.  I was speaking and thinking of the more traditional prices of gold and launch costs from like 10 to 15 years ago.  This incidentally was before SpaceX.  SpaceX has managed to bring the price to launch into orbit to below the traditional costs of gold that I was thinking of.  They are on course with the ITS to get launch costs down to the traditional costs of silver.  The problem is weíre still thinking of these launch costs like the costs of precious metal.  Ideally, we need to get the cost down to below dirt and water like most of our other transportation costs.  We will obviously not reach that idea but the closer we can get the better.  The ITS will probably get down into the hundreds of dollars but is doubtful that this type of system will get all the way down to $10.  A 2nd generation ITS will probably get us very close but still not as low as obviously desirable or that can be obtained.

As you said, the cost of the fuel is not the most important parameter.  It is more how often you can use the vehicle AND how much it can carry at one time for a given size vehicle.  This is why a bigger ITS would be better.  This is also why a theoretical NTTR could be better.  It could carry more for the same size vehicle.  Possibly as much is 2 to 3 times more.  And yes it does use hydrogen (which is more expensive than methane obviously) but it will use more air than hydrogen.  When you take into account the free air as propellant it could be as cheap as methane/LOX.

The NTTR is among the 1st truly new ideas to launch much cheaper into orbit that is come out in decades.  Another has been a laser launch system.  To get past limitations of a chemical system a new system not based on chemical propellants will be needed.  Maybe this will be a laser derived launch system but such a system would require an absolutely huge ground infrastructure be built to compete with something like an ITS at each launch location.  On the other hand, maybe it could be something like an NTTR that would still require a large upfront investment to develop but once developed could be scaled at a much lower cost than a laser launched system.  No matter how you look at it the future looks to be very interesting past the ITS.

Offline DreamyPickle

  • Full Member
  • *
  • Posts: 146
  • Home
  • Liked: 60
  • Likes Given: 14
Re: Larger than ITS - The next generation
« Reply #44 on: 07/16/2017 09:11 PM »
People seem to assume that the main point of ITS is the scale but I think it's actually the full reusability that is key to reducing costs. Since reusability eats into payload fraction you still need a bigger rocket, but not that much bigger. I suspect Elon's initial presentation was scaled up intentionally so that people wouldn't see it as a threat to projects like SLS.

In order for the project to be successful all it needs is a payload capacity similar to the Falcon Heavy, maybe even smaller. Then you complete with EELV-class launchers by having high flight rates and not throwing away hardware. Key features would be:

* Fully reusable second stage entering on it's side.
* No manual inspection of the heat shield.
* Second stage capable of reentering from higher orbits like GTO or Mars/Moon return.
* Payload bay instead of disposable fairing.
* Orbital refueling for sending large payloads outside LEO.
* Three configurations: cargo, tanker and manned.

There are also benefits to scaling up such as the fact that you don't need to split manned missions into small chunks. But these additional advantages are small.

Offline JamesH65

  • Full Member
  • ****
  • Posts: 621
  • Liked: 360
  • Likes Given: 8
Re: Larger than ITS - The next generation
« Reply #45 on: 07/17/2017 12:53 PM »
Nah, brah, that's completely off-base. Gold and platinum are on the order of $100,000/kg. Falcon Heavy is on the order of $2000/kg. ITS is hoped to get around $10/kg because the actual cost of chemical propellants is very low. It's not the chemical aspect that makes current space launch expensive, it's the cost of throwing away aerospace hardware every flight.

And you think nuclear thermal would help?

A nuclear thermal rocket would be a very fast way to make your space launch even more expensive and approach the cost you mentioned before.

And you don't even get the benefit of lower propellant costs as nuclear thermal rockets generally use pure hydrogen, which is a LOT more expensive per kilogram ($10 or so) than liquid oxygen ($0.10 per kilogram or even less) which makes up the vast majority of a chemical rocket's propellant and liquified natural gas is also super cheap ($0.25/kg in the US). So even though an NTR would use less propellant, the cost of that propellant would be actually more.

This is only partly why nuclear thermal (especially the high Isp kind) is not a good idea for Earth launch. There are also technical reasons why it's a bad idea.

Might be good for very high delta-V trajectories.

Gold right now is $39k per kilo. Nowhere near $100k and platinum is about $29k, even further away. I didn't look up any of the other figures.

Offline envy887

  • Senior Member
  • *****
  • Posts: 2701
  • Liked: 1243
  • Likes Given: 776
Re: Larger than ITS - The next generation
« Reply #46 on: 07/17/2017 01:01 PM »
People seem to assume that the main point of ITS is the scale but I think it's actually the full reusability that is key to reducing costs. Since reusability eats into payload fraction you still need a bigger rocket, but not that much bigger.
...

Exactly. Doubling the size only nets a ~10% reduction in cost per kg to orbit. Doubling the reusability nets a ~50% or more reduction.

I suspect there will eventually be a larger rocket than the 42 Raptor ITS, if only to eke out a few more 10 percents reduction in cost. But that size isn't necessary to start with.

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 27019
  • Minnesota
  • Liked: 6911
  • Likes Given: 4873
Re: Larger than ITS - The next generation
« Reply #47 on: 07/17/2017 01:06 PM »
Nah, brah, that's completely off-base. Gold and platinum are on the order of $100,000/kg. Falcon Heavy is on the order of $2000/kg. ITS is hoped to get around $10/kg because the actual cost of chemical propellants is very low. It's not the chemical aspect that makes current space launch expensive, it's the cost of throwing away aerospace hardware every flight.

And you think nuclear thermal would help?

A nuclear thermal rocket would be a very fast way to make your space launch even more expensive and approach the cost you mentioned before.

And you don't even get the benefit of lower propellant costs as nuclear thermal rockets generally use pure hydrogen, which is a LOT more expensive per kilogram ($10 or so) than liquid oxygen ($0.10 per kilogram or even less) which makes up the vast majority of a chemical rocket's propellant and liquified natural gas is also super cheap ($0.25/kg in the US). So even though an NTR would use less propellant, the cost of that propellant would be actually more.

This is only partly why nuclear thermal (especially the high Isp kind) is not a good idea for Earth launch. There are also technical reasons why it's a bad idea.

Might be good for very high delta-V trajectories.

Gold right now is $39k per kilo. Nowhere near $100k and platinum is about $29k, even further away. I didn't look up any of the other figures.
39k is proportionally much closer to 100k than it is to 2k, but correction noted.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Online spacenut

  • Senior Member
  • *****
  • Posts: 2150
  • East Alabama
  • Liked: 310
  • Likes Given: 195
Re: Larger than ITS - The next generation
« Reply #48 on: 07/17/2017 01:50 PM »
If they build "in space" nuclear spacecraft for transfer of goods and people to and from Mars.  There is no danger of nuclear problems on earth on in the atmosphere.  An ITS would be sufficient for transfer of goods to a large space only vehicle.  Then another ITS at Mars for off loading stuff.  Trips to Mars would be greatly reduced in time traveled to and from Mars with a nuke spacecraft.  It could be assembled in LEO from components brought up by ITS.  It would be like a large NautilusX type spacecraft.  Standardized cargo modules could be transferred.  Also, standardized human modules could be transfered without anyone getting out.   

Offline alexterrell

  • Full Member
  • ****
  • Posts: 1516
  • Germany
  • Liked: 46
  • Likes Given: 31
Re: Larger than ITS - The next generation
« Reply #49 on: 07/19/2017 04:42 PM »
I would build the next generation of space craft on Phobos. Perhaps an inflatable torus could be made on earth, and inflated and out fitted at Phobos, where most of the mass is shielding (radiaton and micro meteorite). I was thinking two torus, of major radius 12m and minor radius 6m, counter rotating, inside a non rotating shield.

They would just shuttle between Phobos and High Earth Orbit. If there's fuel at Phobos (ie water or hydrocarbons) they would fuel up there for the return trip.

These would carry a few hundred people - probably no reason to go for more as economies of scale break down. A 40m diameter ship could still have a heat shield for some form of aerocapture.

Offline DnA915

  • Member
  • Posts: 49
  • United States
  • Liked: 24
  • Likes Given: 30
Re: Larger than ITS - The next generation
« Reply #50 on: 07/19/2017 05:00 PM »
I would build the next generation of space craft on Phobos.

Not really understanding the benefit of this vs assembly in LEO. LEO would have plenty of radiation shielding and micro-medeorites have yet to destroy the ISS. Also, if assembled in LEO, you have way less fuel use during assembly and you can also lift larger parts at a time with smaller rockets.

Tags: ITS SpaceX Mars BFR