a discussion about spaceflight

munroburton wrote:

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...

Spaceplanes are already being worked on, or rather, the engines needed to propel them into space.
Here is a link to a company that is in active development & has already received funding:

http://www.reactionengines.co.uk/

All indication are is that they have a viable system.

Rincewind wrote:
Large snip

http://www.reactionengines.co.uk/

All indication are is that they have a viable system.

Once a good basic idea is invented, comes the hard work of making it practical. For those who don't want to click on this - they are making good use of the high temperature of the incoming air at high speeds. The front is a turbine, the center uses the cryogenic fuel to cool the air to a lower temperature, and the turbine shaft energy compresses the cooled air into the combustion chamber. This improves efficiency, and most of all, reduces material related high temperature problems.

I read something about this some years back. My bad, I didn't think it would be possible to make heat exchangers with the needed combination of capability and low weight.

Three cheers for good research engineering!

Hip, Hip, Hooray


Since the oxygen is a much heavier fraction of the fuel load in a rocket than the reducing fuel, the primary advantage would be not having to lift that oxygen for the first stage.

Of course, the reward for overcoming a challenge is meeting another one , such as the need for pure rockets at the top of and above the atmosphere

Common and mundane private aircraft ownership and use is pretty common and mundane ALREADY. At least here in SW OR USA.

Our excellent local, (County) airport enjoys an excellent one mile long paved runway. 5280 feet. C130 Herky Birds have easily landed.

So have older private Gulf Stream private jets. Many friends own light sports aircraft. Others ultra lights. Some have older Cessnas.

Others share an Air Coop. A good private used Cessna 172 can be had for about $50,000. Less than a good SUV. But some maintenance.

However, like outer space tomorrow, air flight today remains a steep learning curve for the private citizen. Not for the stupid.

Hopefully, 500 to 1000 years of future tech will change things. The advanced suit case family Star Ship might be quite common.

DDHv wrote:

Rincewind wrote:
Large snip

http://www.reactionengines.co.uk/

All indication are is that they have a viable system.

Once a good basic idea is invented, comes the hard work of making it practical. For those who don't want to click on this - they are making good use of the high temperature of the incoming air at high speeds. The front is a turbine, the center uses the cryogenic fuel to cool the air to a lower temperature, and the turbine shaft energy compresses the cooled air into the combustion chamber. This improves efficiency, and most of all, reduces material related high temperature problems.

I read something about this some years back. My bad, I didn't think it would be possible to make heat exchangers with the needed combination of capability and low weight.

Three cheers for good research engineering!

Hip, Hip, Hooray


Since the oxygen is a much heavier fraction of the fuel load in a rocket than the reducing fuel, the primary advantage would be not having to lift that oxygen for the first stage.

Of course, the reward for overcoming a challenge is meeting another one , such as the need for pure rockets at the top of and above the atmosphere

Hopefully this project doesn't suffer a mischief as a result of Brexit.

Imaginos1892 wrote:

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.

The issue isn't just the weight of the engines. If you're going for jet powered horizontal take-off you also need lots of additional surface area for aerofoil (whether wings, blended wing, or lifting body design), the weight of aerodynamic control surfaces, actuators, etc, and (unless the thing is expendable) you also need even more extra mass to provide heat shielding for all that extra surface area so the rocket can survive reentry. Lugging all that up to orbital velocity is tons of extra mass a 'classic' staged rocket doesn't have to handle.

You can solve some of that if the jet powered atmospheric part acts as a first stage and drops clear of the rocket before it boosts into orbit. But if you want the horizontal delta-v you talk about then it's a supersonic separation - that's a dicey and dangerous operation. The only attempt I'm aware of offhand was the D-12 drone designed to be launched from the back of a supersonic SR-71 - the attempts ending after a fatal collision between drone and aircraft. (The drone was later modified to be dropped from a B-52, so at subsonic speeds)

Basically there are engineering reasons why it's hard to do spaceplanes. It's not just NASA being stuck in a rut (though I agree they do seem to be - they give the impression of being willing to study any new launch system to death because people don't get fired for more studies; they do for launch accidents).

drinksmuchcoffee wrote: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

It needs to be mentioned though, that both accidents with the Soyuz were with FIRST generation systems, Soyuz-1 was essentially the prototype, while Soyuz-11 was a redesign to allow docking with a spacestation.

2nd generation Soyuz, 1973 to 1981 had a single notable malfunction(the only engine malfunction in the programme ever), but did not result in an accident, merely a mission aborted after already being in orbit.

Third generation has a perfect safety record for its 5 years of use.

4th generation have gone through several iterations, and have a perfect record except for the Soyuz-TMA, which was a redesign to integrate a number of changes on request by NASA, as well as updating equipment overall and to function better with the ISS, probably another version of trying to change to much at once, and it had two instances of touching down too roughly after deorbiting( 8-9g impacts), no lasting injuries caused from what i could find though.


Anyway, the HUGE difference between the shuttles and the Soyuz accidents is the fact that ALL Soyuz accidents have happened after major changes to the craft spawned problems that were not found during testing, and both the accidents with fatalities happened in the first 4 years, with the last one being 45 years ago.

While the shuttle accidents happened after 5 and 22 years in service, when it was effectively a "known" system.

And if you look at all the incidents, the shuttle really doesn´t feel very safe at all, Challenger almost had a multiple main engine failure a year before it did crash, something that easily could have caused it to crash, Columbia had a fire onboard during landing in 1983 due to a leak, Atlantis had massive damage to its thermal shielding in 1988, Columbia had a short circuit AND a hydrogen fuel leak in 1999 either of which could have caused a fatal accident...

So while the statistics look similar at a glance, reality is VERY different. The shuttles were plagued by troubles throughout their lifetime, while Soyuz had teething issues but after that has generally been the safest mode of spacetravel you can find.

You could also compare with the Apollo/Saturn program, less than 20 manned missions but managed to have 3 notable incidents(Apollo-1, -13 and -15(notable as in not caused by random bad luck, like Apollo-12 getting hit by lightning twice during launch, or during the Apollo/Soyuz mission where a switch left in the wrong position almost killed the crew during reentry)) where the latter two escaped unharmed despite probabilities looking bad.

Yet the Apollo/Saturn program was overall a much higher quality show than the shuttle, and had it been retained, would probably have become almost as safe as the Soyuz(it´s a more complex system so probably hard to reach the same level).

Essentially, the space shuttle was an ( stupid ) attempt at getting into space cheapskate style.
Ended up at least as expensive as what it was meant to replace, and much more unsafe and with limitations that slowed down space exploration something dreadful.

Imaginos1892 wrote:My proposal is methane/air and methane/oxygen. Is it really that hard to design and build methane-fueled jet engines?

Yes. Come back in a century or two and it might be realistic. MAYBE. Methane has a number of issues in regards to the extreme cold and heat that tends to be involved during spaceflights.

In short, sounds great in theory but doesn´t actually work. Desktop general style spaceflight theory.

Imaginos1892 wrote: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.

Because when vertically launched, this causes no troublesome inbalance.
It is one of THE big issues with horizontal takeoff/launch. For a tiny craft with little to no real usefulness, it´s relatively easy to compensate for. For heavy lifters it´s a nightmare.

Imaginos1892 wrote:This is not to be built on government contracts, so will you allow me to believe they won't be stuck-on-stupid?

...

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.

Funny thing you know... That was basically the idea behind the Space Shuttle.
Yet in the end, it became drastically LESS reliable, MORE expensive and mostly less useful than the Apollo/Saturn.

Imaginos1892 wrote: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.

Do you REALLY think you´re the only one who reached that conclusion?

https://en.wikipedia.org/wiki/MAKS_%28spacecraft%29 USSR
https://en.wikipedia.org/wiki/Buran_%28spacecraft%29 USSR
https://en.wikipedia.org/wiki/Kliper Russia
https://en.wikipedia.org/wiki/HOPE-X Japan
https://en.wikipedia.org/wiki/RLV_Techn ... _Programme India
https://en.wikipedia.org/wiki/Da_Vinci_Project private project
https://en.wikipedia.org/wiki/Hermes_%28spacecraft%29 France
https://en.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-105 USSR test
https://en.wikipedia.org/wiki/HOTOL British
https://en.wikipedia.org/wiki/MUSTARD British
https://en.wikipedia.org/wiki/XCOR_Lynx private project

Now lets see, what´s the common thing about all of them? Oh yeah, they were dumped for being MORE EXPENSIVE AND LESS RELIABLE than vertical launch systems.

Imaginos1892 wrote:If you shoot something straight up, it must have a thrust-to-weight ratio greater than 1 at the worst possible time

Yeah, so what? Horizontal launch means instead you get the fun of requiring a drastically LONGER boost phase because you´re travelling through atmosphere much longer.

Imaginos1892 wrote: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!

Yup. Because face the facts man, massproducing rockets and capsules this way is by far the cheapest way to get into space.

The Space Shuttle was designed EXACTLY for this reason.
Yet in the end, for smaller loads the Soyuz system costs a fraction per kg to put in orbit, while for large loads, the previous Saturn rockets were eventually found to have been considerably cheaper. And better. And safer. And more capable.

I would absolutely LOVE it if there was a better way, but right now, you´re just spouting old rehashed news that was PROVEN A MISTAKE.

Imaginos1892 wrote: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:

Except you´re never going to get an SR-71 to actually be able to reach orbit. And even if you did, how exactly are you going to protect such an extremely nonoptimal shape against reentry heat?

And if you got it into orbit, you DO remember that the SR-71s fueltanks are designed to be leaky while cold, to offset the problems of heat during highspeed flight. Which means while it is in space, you´re going to have a spacecraft leaking fuel. This was something that almost caused a fatal accident for a space shuttle and you want to do it deliberately? Not so bright.

So, i´ve already identified TWO CRITICAL FAILURES in your example. Either of which just on their own completely kills your claims.

Imaginos1892 wrote:You can fly it again tomorrow!

That´s what the slogan was for the space shuttles! Before they were actually built at least. Ended up being an extremely unrealistic pipedream.

Imaginos1892 wrote: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".

Where the hell did you get 6% from? An SR-71 did not get to topspeed at max altitude without an inflight refuelling.

And funny thing is, it´s those "last" KPS you dismiss so easily that are the hardest to reach.

In case you forgot, as long as you´re in atmosphere, the faster you go, the hotter it gets because the more friction you generate.

So your idea for reaching space basically has the prerequisite of reaching space first, because otherwise you don´t have enough thrust or fuel to reach space so you can reach space...

How are you going to cool the lift surfaces while at high speed in atmosphere?
How are you going to keep those same areas from misbehaving once they reach the mix of overheating and cold that you get in space?

The SR-71 is a horrible starting point for a spaceplane.

The MiG-25 managed similar speeds and might work slightly better, but that´s because it´s a fricking flying BRICK, due to being built to a large extent with steel, because aluminium couldn´t handle the stress.

The SR-71 in turn used a mix of titanium and corrugated aluminium to overcome the same issues. Unfortunately, its design would NOT survive spaceflight.

The SR-71 was an awesomely neat aircraft, but it´s NEVER going to get anyone into space.

Ya'll need to check out Kerbal Space Program.

MaxxQ wrote:Ya'll need to check out Kerbal Space Program.

Just waiting for it to drop a bit in price.

I started long ago though(mid 90s) with the original "Buzz Aldrin´s Race into Space".

And nowadays there´s the freeware version of that, simply called "Race into space".
AND just a couple of weeks ago i found that there´s what is essentially a remake by Slitherine games.

http://www.raceintospace.org/ freeware version, just download and play
http://www.slitherine.com/products/prod ... atformID=1 sort of remake

Tenshinai wrote:
snip

Yeah, so what? Horizontal launch means instead you get the fun of requiring a drastically LONGER boost phase because you´re travelling through atmosphere much longer.

snip

A Canadian patent suggests an alternative for getting into space. They patented the idea of making a very large structure (miles high, sticking out of the atmosphere), which is supported by compressed gasses underneath it. IIHIR, they have giant tubes around the outside with high pressure air in them and area sufficient to hold up the platform at the top. These are arranged and connected into a complete slanted surface, which in turn is supported by lower pressure compressed air underneath the whole structure. It would be like a gigantic conical mountain in shape.

http://www.gizmag.com/canadian-firm-pat ... tor/38773/

I ran some calculations, and the major problem with such an artificial mountain (besides expense) is the target it would make for people who don't like it, or perhaps don't like those building it. Fuels could go up some of the tubes as gasses and be turned into liquids at the platform. Vehicles could be raised on tracks up the sloping sides. It does have one major advantage over the tethered tower concept - a tension structure, if severed in the middle, has the lower part fall to earth over a very large area, at very high speeds. A compressed air supported tower, although much lower, would have untoward effects limited to local areas. The platform could have an electromagnetic catapult to start the launch with some initial velocity.

Over all, I'd prefer Murray Leinster's launch grids, or Honorverse's antigravity, but don't see any way they could be built. It is too bad that this launch mountain structure, like tension tethers, would be so vulnerable