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a discussion about spaceflight

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a discussion about spaceflight
Post by drinksmuchcoffee   » Mon Jul 25, 2016 5:53 pm

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This was moved from another thread where it was considered a hijacking. My bad :(

OrlandoNative wrote:
drinksmuchcoffee wrote:
...

I am sorry but you've hit upon one of my pet peeves. There is this meme that says, "except for the lack of political will we'd have Lunar Colonies, Space Cities, and manned missions to the outer planets by now."

I don't buy it.

Costs to orbit are on the order of $10k per kg. We are never going to have any space colonies at those prices. It just isn't possible economically. And lots of smart people have been working on the problem of lowering launch costs for decades without a whole lot of progress. Similarly, manned vehicle failure rates are unacceptably high, on the order of one out of 100 launches for the Shuttle and probably one out of 500-1000 launches for Soyuz. Getting to a more reasonable rate of one out of 10000 or more will require technology that we do not yet possess.

For my money (and some of it is my money) the considerable resources and effort spent on ISS would be more productively spent pursuing order-of-magnitude improvements in launch costs and vehicle reliability and safety.

I'm not saying it's entirely political. It's also social. Anyone who thinks the government can fix anything and everything obviously hasn't been very observant for the past half century or so.

I'm not going to say we'd have bases on Mars or routine journeys to the outer planets, but had we persevered after the original moon landings we could certainly have a decent orbital infrastructure and even moon bases by now.

As long as the government regulates travel; and controls certain technological experimentation and use, costs will remain high. What is needed to bring the cost down is some way of replacing chemical rockets with something else. Whether it's some sort of nuclear engine (which, of course, the government is loathe to let ordinary commercial entities to work on) or some breakthrough in physics, like the discovery of some way of generating anti-gravity, who knows? I doubt the latter is likely soon, but some sort of "hybrid" craft that used typical jet engines for lower altitude flight combined with some sort of non-combustion engine for higher altitude might be more cost effective. What brings the cost down is (1) adapting current technology to new usages, (2) doing away with "one time" usage, and (3) thinking "outside the box" whenever possible.

As for "manned vehicle failure" rates, tens of thousands of people are killed yearly in automobile crashes in the US alone. How many die in space or rocket accidents in the same time frame? If we still can't expect 0 fatalities utilizing vehicles that have been undergoing constant improvement for the past 100 years, why should we worry about every space fatality? Most auto accidents - even with fatalities - often go unreported by the media. Or at least relegated to the back pages of the "local news" section. I can't think of a *single* space accident that was so ignored, however.

*If* our ancestors had the same timid outlook we seem to have today, we'd either still be in Europe; or else the US would consist of only the Atlantic coast states. There was nothing "safe" about what the pioneers faced in moving westward. Why would we expect the exploration of space to be any different? If people are willing to take the risk, I say let them. Don't hold them back. Encountering problems leads to solutions. It's impossible to fix all problems if you don't know what they are to begin with, and the only way to really find them is to do something.

We seem to have forgotten that.


I think the relative risks of spaceflight are still extremely high, and high enough to be qualitatively different than the risks we accept from passenger vehicles or commercial air travel.

Space Shuttle (1981-2011) -- 135 flights, 2 vehicle losses with fatalities
Soyuz (1967-present) -- 130 flights, 2 flights with fatalities

Commercial Air Travel (Worldwide) (2014) -- 30 million flights, 21 accidents with fatalities
Passenger Vehicles (USA) (2015) -- 411 billion trips, 38300 fatalities

So spacecraft, according to our limited sample size (but over a time period of decades) seem to have fatalities on around 1 percent of flights. Soyuz probably actually does better, because the fatalities occurred on earlier flights (Soyuz 1 and Soyuz 11) and might be considered test flights. How much better we can't and don't know, but it is unlikely the failure rate is much better than 1 out of 1000 flights with present technology.

Commercial air travel in 2014 had over 30 million flights with 21 accidents with fatalities. So that argues their "failure rate" per flight is better than 1 out of 100000.

Passenger Vehicles, which on a per-mile basis are more dangerous than commercial air travel, still show a "per trip failure rate" that is better than 1 out of 10000000.

That's what I meant when I said the reliability and safety of space travel need to improve by orders of magnitude. Sometimes I think the best thing for NASA would be a reincarnation of Hyman Rickover who could spend several decades pissing everyone off while keeping them alive.

As an added thought, I never realized there were more Shuttle flights than Soyuz flights, although Soyuz will likely surpass the Shuttle in the next couple of years.
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Re: a discussion about spaceflight
Post by HB of CJ   » Wed Jul 27, 2016 3:24 am

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Excellent post and thank you. It is all about time, money and tech. For a thousand years or longer, brave sailors set sail and never returned.

Then as time and tech allowed, the ships became stronger and better. Better sail plans. Winds and currents began to be understood much better.

Towards the very end of the sailing ship era, captains and strong ships actually sought out heavy blowing weather ... it got them home quicker with rich cargo.

The sailing ship era was a classic risk/reward situation. If a ship survived just one return voyage during the heyday of the sailing ship, the vessel was paid for.

Sometimes the cargo from one safe return trip was a 100 to 1 value reward. Until we make space travel profit oriented there may be no real tech development driving it.

We need some sort of economic incentive for expanded space explorations. The problem is that there is nothing to go to visiting the moon and mars.

Tech must improve until we reach a point where private starship ownership is common and mundane. Similar to private car ownership. This will eventually happen.

But not for the foreseeable future. It might take 1000 years of tech development but eventually mankind will explore and enjoy our solar system. Perhaps the stars?

Someday. Not today. Not next year. But someday. Ya gotta have heart and faith in the future history of mankind. We will do it, it is just a matter of when and how.

Edited by HB. I need to read my own posts. Big mistake made. I meant to say equal and mundane to private aircraft ownership ... not automobile ownership. My mistake. Yikes!!
Last edited by HB of CJ on Thu Aug 04, 2016 6:15 pm, edited 1 time in total.
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Re: a discussion about spaceflight
Post by cthia   » Wed Jul 27, 2016 6:05 am

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The industrial might and resourcefulness of Earth as a whole is much greater than the sum of its parts. Perhaps what is holding Earthlings back from spaceflight is their lack of cohesion, collusion, teamwork, participation and partnership. A point made by my niece at 12-yrs of age.

We only have to consider the success of the international space station. I'm primed to think that her intimations are correct - what currently governs the success of Earth spaceflight isn't so much as time or tech but the inability to work in concert.

My niece and I began this conversation in my sister's company. Everyone has a family member that abhors sci-fi don't they? "What makes you two think that Earth will ever rise above its own solar system when we don't seem to even be able to conquer safe travel into outer space?"

That was the lead-in for my niece's point. And she supported it by a, rather insightful for any age I think, supposition that any species' success in space travel was probably fueled by necessity. Necessity born of a dying planet. A planet suffering or threatened by natural causes or self-destruction by accident or by arrogant design. A planet that coalesces as a whole to fight a common enemy as was part of the premise of the movie Independence Day.

The swinging pendulum of death is what kick started cooperation in the Honorverse on Old Earth during the Final Wars.

Son, your mother says I have to hang you. Personally I don't think this is a capital offense. But if I don't hang you, she's gonna hang me and frankly, I'm not the one in trouble. —cthia's father. Incident in ? Axiom of Common Sense
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Re: a discussion about spaceflight
Post by Imaginos1892   » Wed Jul 27, 2016 7:35 pm

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We still have to get into orbit in the first place, and we currently lack a practical means of doing that. There has been some discussion of different ways of getting there but most of them are not possible at present.

Until we find a way to spin carbon nanotubes 40,000 miles long the Beanstalk will remain just wishful thinking, and nuclear rockets are never going to fly - literally. Even if the engineering issues can be solved, tree-huggers and anti-nukers will gang up and bury them under a billion lawyers; more effective than a neutron star's gravity at keeping things stuck on the ground. For the forseeable future, we must make do with chemically propelled spacecraft, but we have GOT to do it better than the way it's being done now.

Everything about the way NASA puts stuff into orbit is wrong. They build a huge, complex, hideously expensive rocket, stand it up on its ass end and light it off. Then they start building another one just like it to carry the next load because each one is completely consumed in the course of its single flight! That's planned obsolescence with a vengeance, coupled with institutional inertia. NASA is no longer the organization it was back in the 1960's; it's been taken over by bureaucrats, bean-counters and pencil-pushers. Decisions are based on politics and pandering instead of physics and engineering.

Some of you here make the same mistake and persist in misusing "the rocket equation" where it does not apply, to "prove" that the ONLY way to reach orbit is with vertical-launch staged rockets, when it is in fact the WORST way.

If you shoot something straight up, it must have a thrust-to-weight ratio greater than 1 at the worst possible time: when weight is maximum and rocket performance is degraded 18% by atmospheric back pressure. Under these adverse conditions the engines have to generate at least twice as much thrust as the entire vehicle's initial weight unless you want liftoff to be even more outrageously inefficient than it is already. This requires the engines and their support structure to be huge, and heavy - exactly what you don't want.

It also loses 9.85 meters per second for every second it spends pushing up against gravity. All that energy and reaction mass is completely wasted - you get NOTHING for it, neither altitude nor velocity. In 2 1/2 minutes of vertical boost, your rocket throws away enough fuel to generate 1.5 KPS delta-V just holding its own dead weight up against the static force of gravity.

Next, it loses another 500 MPS or so gaining radial velocity. Any stable orbit has a net radial velocity of zero, so most of the energy and reaction mass spent generating radial velocity is wasted.

Right there, you've just added a completely unnecessary 2 KPS to the wrong side of your "rocket equation". Worst of all, this waste takes place during the most expensive part of the flight, when you're already spending the most fuel to get the least return. If we did nothing else and just changed the launch profile from vertical to horizontal it would make getting into orbit a lot easier.

A vehicle using jet engines and aerodynamic lift is subject to completely different, and much more forgiving, equations. A jet engine produces 10 to 40 times more specific impulse from its fuel than a rocket can get from an equal mass of fuel and oxidant. Taking off horizontally, it has no need of huge, heavy engines that have to hoist its entire takeoff weight into the air, it does not waste fuel holding itself up, and it's primarily gaining angular velocity which translates directly into orbital velocity.

We know that a jet aircraft can reach Mach 3.3 at 25KM altitude because the SR-71 did that 50 years ago. If it's going east near the equator, that adds up to 1.5 KPS. It now needs rockets to produce another 6.5 KPS and reach low orbit, which can be achieved with a fuel fraction of less than 0.7. If it spent 6% of its takeoff weight in fuel to reach this point, that makes its overall fuel fraction around 0.75 and puts a big dent in "the tyranny of the rocket equation".

So, just a few advantages of a hybrid spaceplane over a rocket:

Much higher specific impulse during the critical early phase of flight
More efficient use of both energy and reaction mass
Much smaller (lighter!) engines, even with two separate engine systems
Rocket nozzles optimized for vacuum, instead of a compromise between 1 Bar and zero
Lighter structure overall due to lower G loading
Can actually maneuver for landing, with engines ON
You can fly it again tomorrow!
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Re: a discussion about spaceflight
Post by munroburton   » Thu Jul 28, 2016 5:59 am

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Imaginos1892 wrote:So, just a few advantages of a hybrid spaceplane over a rocket:

Much higher specific impulse during the critical early phase of flight
More efficient use of both energy and reaction mass
Much smaller (lighter!) engines, even with two separate engine systems
Rocket nozzles optimized for vacuum, instead of a compromise between 1 Bar and zero
Lighter structure overall due to lower G loading
Can actually maneuver for landing, with engines ON
You can fly it again tomorrow!


All true... theoretically. So why hasn't it been done?

Only five spaceplanes have reached space. The three which made it further into orbit used rocket-powered vertical take-off.

The other two were as you proposed - except they had to be carried to the edge of the atmosphere by much larger aircraft. Hauling that aircraft's fuel tanks and air-breathing engines further into space is expensive - never mind orbit. Then you've got to deal with the consequences of partially emptied tanks affecting the center of mass.

Furthermore, most rockets have at least two and typically three stages - launch, transition(atmo-to-vac) and vacuum optimised thrusters. Since each successive stage abandons the mass of the empty fuel tanks and now less-optimised engine, its capabilities are maximised. A spaceplane has to keep carrying all its 'stages' from launch to touchdown, as well as a mission payload to orbit.

HB of CJ wrote:Tech must improve until we reach a point where private starship ownership is common and mundane. Similar to private car ownership. This will eventually happen.


Perhaps it will eventually, but the fact remains that we don't currently have private aircraft in 'common and mundane' ownership. Frankly, I think it's a terrible idea, considering we can't even keep commerical airline pilots sober, plus the daily volume of drink-related automotive mishaps...
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Re: a discussion about spaceflight
Post by HB of CJ   » Thu Jul 28, 2016 12:10 pm

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Great subject matter and thank you again. One of the puzzling things about the Honorverse is that after 2000 years or more, there is not more high tech. Make that tech equal to magic.

"Honey, why don't we go to Terra Nova for vacation? They have that new sea and surf resort on the South Island. I want to go. Six days, 5 nights. All we need is us and our credit cube."

"OK, I will go ask Jennifer. (Jennifer is the private family owned starship) Jennifer, we want to go to Terra Nova for vacation. Can you take the two, (2) of us? How long, how $much$. How fast?"

Jenifer answers ... "I can do it, but I need that current maintenance upgrade. Then I need to contact all the powers that be to get departure, space trip permits and course clearances."

"OK, let me know how long, how fast and how much it will cost. If within our family monthly budget, go ahead and make all preparations to leave. Let us know ahead the time the schedule."

Jenifer quickly answers. "OK boss, it is all laid on. We leave in 3 hours. Two hours to clear the system, then about 5 hours to Terra Nova at Warp 7. If we leave now, very clear space.

An example of eventual space tech available to the average working family. Not cheap but doable. The family starship looks like a big suitcase when shut down. It is mostly force fields.

Most of the starship resides in alternate dimensions. That is how it works. Once deployed, it looks like a kinda big pumpkin seed. Very safe old space tech. Tech beyond our imagination today.

Will we ever get to that point? Again, there must be some important benefit of doing so. Population pressures come to mind. Also resource potential. It will take much time and tech.
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Re: a discussion about spaceflight
Post by Imaginos1892   » Thu Jul 28, 2016 8:47 pm

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munroburton wrote:The other two were as you proposed - except they had to be carried to the edge of the atmosphere by much larger aircraft.

Carried to the edge, yeah, but but dropped there subsonic. Meaning the rockets still have to make 7.6 KPS or more. Fuel fraction increases geometrically with delta-V and hits 1 at less than 10 KPS. I'm talking about reducing the rockets' job to 6.5 KPS or less, which allows a fuel fraction of under 0.7.

munroburton wrote:Hauling that aircraft's fuel tanks and air-breathing engines further into space is expensive - never mind orbit. Then you've got to deal with the consequences of partially emptied tanks affecting the center of mass.

Only if the designers are stupid enough to use different fuels for the two engine systems. This is not to be built on government contracts, so will you allow me to believe they won't be stuck-on-stupid? My proposal is methane/air and methane/oxygen. Is it really that hard to design and build methane-fueled jet engines? The fuel tank needs to be 10-15% bigger, but it's more than made up by reduction of the oxygen tank. The rocket needs almost 4 kilograms of oxygen for every kilogram of methane. Running a slightly rich mixture actually produces a bit more specific impulse.

Horizontal takeoff means the jet and rocket engines combined are smaller (and lighter) than the rockets required to shoot it off vertically. Fuel (and oxygen) tanks get emptied no matter what kind of engines you're using, so I don't see why you even mentioned that.
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Re: a discussion about spaceflight
Post by Dilandu   » Fri Jul 29, 2016 6:40 am

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Imaginos1892, the main problem of traveling to space is a velocity, not the altitude. Various air-launch systems were proposed and tested, but basically the only thing they do is the optimisation of the initial part of the flight.

Carried to the edge, yeah, but but dropped there subsonic. Meaning the rockets still have to make 7.6 KPS or more. Fuel fraction increases geometrically with delta-V and hits 1 at less than 10 KPS. I'm talking about reducing the rockets' job to 6.5 KPS or less, which allows a fuel fraction of under 0.7.


I.e. you need something ramjet-powered, that would be capable of going at least Mach 3-4.

The problem is, ramjets aren't good for start, so you need initially to accelerate near Mach 1 before your ramjets would start to work.
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Re: a discussion about spaceflight
Post by munroburton   » Fri Jul 29, 2016 8:22 am

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Empty fuel tanks impose a mass and volume penalty. Virtually all vertical launch systems get rid of this by jettisoning spent stages. If you don't want to do that, you have to haul this dead mass around in orbit.

A spaceplane could do the same thing with drop tanks. But then it'd need more engine power to push this additional weight, more lift... and all these extras are completely unnecessary in orbit. Worse than unnecessary, really.

It's the tyranny of the rocket equation all over again.

Dilandu wrote:Imaginos1892, the main problem of traveling to space is a velocity, not the altitude. Various air-launch systems were proposed and tested, but basically the only thing they do is the optimisation of the initial part of the flight.

Carried to the edge, yeah, but but dropped there subsonic. Meaning the rockets still have to make 7.6 KPS or more. Fuel fraction increases geometrically with delta-V and hits 1 at less than 10 KPS. I'm talking about reducing the rockets' job to 6.5 KPS or less, which allows a fuel fraction of under 0.7.


I.e. you need something ramjet-powered, that would be capable of going at least Mach 3-4.

The problem is, ramjets aren't good for start, so you need initially to accelerate near Mach 1 before your ramjets would start to work.


Accelerating and lifting the mass of 7.6 KPS worth of fuel(the absolute quantity of which goes up exponentially as payload mass increases) is no trivial matter, never mind trying to get something like a 747 or A360 to Mach 5. Believe me, I'd love to see a real SSTO spaceplane too, but pushing through the atmosphere is a secondary problem to be avoided not embraced(Gravity being the primary problem).
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Re: a discussion about spaceflight
Post by HB of CJ   » Fri Jul 29, 2016 6:33 pm

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Edited by HB because he does not read his stuff. Yikes! Oh boy! Corrections are provided where needed and boy are they needed!

No matter how far in the future ones thinks, we will always have that pesky planetary gravity well. No way around it if we want to mostly stay and live on earth or many other colony planets.

Thinking about 500-1000 years down the road into the intermediate human future history which has not happened yet because it is in the future .. a "Star Ship" will need the following "stuff" plus probably a lot more "things", (tech) we have not yet considered.

1) Lift. "Gravs" it will be called. Anti gravity. It will be easy to "float" above the ground. Mundane.

2) Inertial compensator's. Good and certified for civilian use. About 1000 gees maximum. Also known as "compensators".

3) Drive. Normal space. Civilian use limited to about 500 gees.

4) Lift. About the same as drive. You just aim the starship straight up or nearly so.

5) Impulse power or normal space drive. Good to about .1 Cee maximum normal space velocity at the aforementioned 500 gees nominal acceleration.

6) Navigational normal space deflectors. Not quite the same as shields. Civilian Deflectors are good to about .1 Cee. This actually requires most of the star ships available power.

7) Warp Drive. Civilian use good to about Warp 5 or 6. Very fast. Warp 5 is about one light year in 1.4 hours. Warp 6 is one light year in about 10.3 minutes.

8) Extremely good sensors to see where you are going at Warp Speed. Easy to outrun your sensors. Not good. Good sensors mostly dependent upon very well charted space.

9) Screens, deflectors and shields while running in Warp. Even when in warp, a small part of the star ship remains anchored in normal space. Extremely important to deflect normal space debris.

10) Jump Drive. For big distances where Warp Speed is too slow. Navigation is very very important. Civilian use limited to about 100 light year jumps.

Except for everything we don't have yet, the home owned Star Ship of the future is quite doable. But, eventually we will get there. Expensive but doable. Upper middle class.

Edited by HB. Forgot to mentioned the power source or sources. Probably something we have not even thought about yet. Maybe borrowing energy from alternate dimensions? Dunno. :)
Last edited by HB of CJ on Mon Aug 08, 2016 9:24 pm, edited 1 time in total.
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