Why is not a SSTO useful today?

[Wesley01]

Why is a SSTO not useful today? My chief complaint is that it is because ever sinse beginning folks have though of a SSTO as using one single chemical rocket burn from start to finish and this simple is not very effiecnt at all. My idea is with the SSME like 25 years ago SSTO started to be feasable when you look at most effient three dimensional solution I am presently suggesting. I have done the figures and came up with a one million GLOW rocket seven percent empty bit over three percent useable payload thrust weight ratio 1.5/1 and nearly 10 kilometer/second burn out velocity too. Thanks 

[Red Iron Crown]

Welcome aboard!

Care to show your workings?

[Shpaget]

Wasn't it proven that, using same propellant and structural materials, SSTO will always be less efficient than a multistage rocket?

[Scotius]

[snip] don't be nasty to the kid. Don't you think he deserves to keep his wide-eyed enthusiasm a bit longer? All too soon he will realise how much politicking and money issues is bogging down the greatest adventure humanity is trying to push forward, and he will become just as frustrated as we are.

 

As for your question, Wesley - we are not quite there yet. There is little incentive to re-use the same craft, because with only a handful of launches every year it's simpler and cheaper to use multi-staged rockets. But we are getting there, with SpaceX and British team working on Skylon blazing the trail.

[Elthy]

As SpaceX showed SSTOs arent realy needed. Why not a 2 stage design, first stage returns to launchpad, the second one could use a lifting body like an SSTO, but it would have a way better payload ratio...

[Scotius]

Nothing new under the Sun Arthur Clarke envisioned such progression way back in 1946. I have a copy of his book "Interplanetary Flights" on my shelf, i read it every now and then - and i'm still amazed how his predictions continue to hit close to what we actually do.

[Bill Phil]

They need better efficiencies than what we can currently accomplish. There's generally a lot of problems, but that's a big one.

[Mitchz95]

If Elon Musk assumed that the industry knew better than anyone else how to build a rocket and didn't bother trying to come up with his own ideas, SpaceX wouldn't exist and we'd be no closer to reusable rockets than we were twenty years ago. Don't discourage people from trying new angles.

[Bill Phil]

1 minute ago, Mitchz95 said:

If Elon Musk assumed that the industry knew better than anyone else how to build a rocket and didn't bother trying to come up with his own ideas, SpaceX wouldn't exist and we'd be no closer to reusable rockets than we were twenty years ago. Don't discourage people from trying new angles.

Then why does the Merlin use a lot of ideas that are industry normal? The only difference is that they're trying to land it, and they succeeded. But we're still no closer to reusability, except for that small amount that's just getting the hardware back, but the shuttle did that, too, to an extent.

[Tiber9]

I'd also be curious to see more about what you're working on, Wesley. The SSTO issue is really complex and interesting, as it really feels at times like we are very close. I remember reading that the Titan missile was orbit-capable, assuming that there was no payload at all other than the rocket itself. 

Escape Dynamics is i believe working on applying a beamed power concept to enable an ssto, so another interesting approach in addition to skylon and reusable multi-stage rockets. I'd be curious to know how much the disposable nature of spacecraft really hinders the industry. We throw A LOT away in general. I would hope that in the long run reusable vehicles could make space more accessible, but in the short term the development costs to invent those vehicles are probably a major issue. 

It was a Vsauce video that pointed out how it only took about 60 years to go from the first plane to the first people in space, but it took i think twice that to go from the invention of the motorcycle to the first complete backflip on a motorcycle. People like Clarke do seem to be right a lot, but no one ever seems to have good predictions of how long some steps really take. 

 

[Vanamonde]

Some posts have been removed from this thread or edited. Please do not insult each other. 

[fredinno]

5 hours ago, Tiber9 said:

I'd also be curious to see more about what you're working on, Wesley. The SSTO issue is really complex and interesting, as it really feels at times like we are very close. I remember reading that the Titan missile was orbit-capable, assuming that there was no payload at all other than the rocket itself. 

Escape Dynamics is i believe working on applying a beamed power concept to enable an ssto, so another interesting approach in addition to skylon and reusable multi-stage rockets. I'd be curious to know how much the disposable nature of spacecraft really hinders the industry. We throw A LOT away in general. I would hope that in the long run reusable vehicles could make space more accessible, but in the short term the development costs to invent those vehicles are probably a major issue. 

It was a Vsauce video that pointed out how it only took about 60 years to go from the first plane to the first people in space, but it took i think twice that to go from the invention of the motorcycle to the first complete backflip on a motorcycle. People like Clarke do seem to be right a lot, but no one ever seems to have good predictions of how long some steps really take. 

 

Only problem is that most of the costs are labour, not materials.

5 hours ago, Bill Phil said:

Then why does the Merlin use a lot of ideas that are industry normal? The only difference is that they're trying to land it, and they succeeded. But we're still no closer to reusability, except for that small amount that's just getting the hardware back, but the shuttle did that, too, to an extent.

Because those are cheaper. Merlins were also designed for reuse, the only other ones I'm sure of that were operational being the SSMEs.

[Sandworm]

6 hours ago, Mitchz95 said:

If Elon Musk assumed that the industry knew better than anyone else how to build a rocket and didn't bother trying to come up with his own ideas, SpaceX wouldn't exist and we'd be no closer to reusable rockets than we were twenty years ago. Don't discourage people from trying new angles.

Musk didn't argue with anyone about building the rocket.  The spacex is pretty conventional in terms of being a rocket.  It just flies a radically different profile.  Fins at one end, legs at the other, this isn't anything remarkable from an engineering perspective, kinda obvious really.  The difference comes in the control and automation departments, and having the will to actually make the attempt.

[sojourner]

Single Stage To Orbit? it's been done. Heck, Falcon 9 first stage can do that.  There's even a thread on this forum about it.

Single Stage To Orbit, reusable?  Possible, not demonstrated yet.

Single Stage To Orbit, reusable and with a useful payload capability?  Ah, there's the hard part.  No one has been able to do it yet.  Skylon thinks it has a way, but they have a lot of work to do to prove it.

Edited January 10, 2016 by sojourner

[Exoscientist]

13 hours ago, Shpaget said:

Wasn't it proven that, using same propellant and structural materials, SSTO will always be less efficient than a multistage rocket?

 

 True but can make up for it in simplicity.

 

  Bob Clark

[A35K]

When people say an SSTO is less efficient, they usually refer to a pure rocket SSTO. As far as I know, nobody is building or planning to build one of these, exactly because they are not efficient. What they are doing though, with the Skylon, is an SSTO that uses air-breathing engines for the first part of its flight until hypersonic speeds, which means its rocket will need to provide much less d-V and fight against much less gravity and drag than in conventional rockets, where a rocket is used throughout the whole flight. As a result (I think) it will be able to use much less fuel per launch than a normal rocket. That's where its usefulness lies at, not to mention it is completely reusable, so unlike the Space Shuttle which dropped its main fuel tank, and then needed to be refitted, with the Skylon, technically all you have to do is refuel and do some checks and you're ready to go, like a normal airplane. This will result in much more frequent launch capabilities. I'm not sure, but I think another advantage may be that when it returns, it could use its airbreathing engines to actually fly, (but I'm not sure if it will have enough fuel left).

[magnemoe]

19 hours ago, Shpaget said:

Wasn't it proven that, using same propellant and structural materials, SSTO will always be less efficient than a multistage rocket?

It is, even an air breathing engine like skylon would have better performance if going suborbital and drop an second stage as it don't have to accelerate itself to orbital speeds. 
if something like skylon is build it would probably do this for many missions not to LEO anyway.
If you need an upper stage anyway its not very expensive to make it larger.

 

 

[Kaos]

Escapedynamics also tries to build an SSTO.

The downside of SSTO is, that they are quite inefficient, as long as the ratio of payload to structure is so small. This ratio can be increased by more stable materials, smaller celestial bodies to start from, or fuel with higher Isp. These superstable and lightweight materials are not developed, yet. From moon we started SSTO. The higher Isp is why companies as Skylon and Escapedynamics think, they can build efficient SSTO. All methods to get an Isp high enough and usable on rockets are considered experimental, that is why this is only used in current research and not in application, yet. If it will be some day, we will see.

[Rune]

Actually, the problem with SSTOs is that we could very well build a SSTO, but it is very unlikely that we could build a REUSABLE one, and then why not making it multistage if we are throwing it away. Getting something to stop from 7,2km/s can be just as hard as getting to that speed in the first place. Even the most optimistic people budget something like 10% of weight in thermal protecion to survive reentry, and there goes you payload and then some. Amd the actual, operational TPS systems have much worse weight fractions than those optimistic estimates...

 

Rune. I never get tired of talking about this stuff.

[Shpaget]

1 hour ago, Kaos said:

All methods to get an Isp high enough and usable on rockets are considered experimental, that is why this is only used in current research and not in application, yet.

And when they do mature, they'll be used on multistage rockets as well and further improve them, setting the bar for SSTO even higher.

Edited January 10, 2016 by Shpaget

[Kaos]

1 hour ago, Shpaget said:

And when they do mature, they'll be used on multistage rockets as well and further improve them, setting the bar for SSTO even higher.

If the technologies are far enough developed, the disadvantages of multistage would be bigger. I am not sure, where this limit is, but if you make the values for strength and Isp big enough, SSTO would be preferable, as the advantage of staging shrinks.

Take for example a material strong enough that you could build a sufficient strong structure with a fuel ratio of 99.9%. One would gain merely advantage with staging, so why would someone go into the effort of staging then? With incredible Isp this effect would be even more obvious: Given a fuel that can be handled as well as todays fuels, but has an Isp of 100 km/s. You could build rockets with only 15% fuel tank which are fully reusable. What would staging gain then for reaching the orbit?

Of course, slightly stronger materials oder slightly more efficient fuels would be first used to make non-SSTO more efficient.

[Bill Phil]

I think we just need a high enough thrust and ISP.

[mikegarrison]

On 1/10/2016 at 3:25 AM, A35K said:

When people say an SSTO is less efficient, they usually refer to a pure rocket SSTO. As far as I know, nobody is building or planning to build one of these, exactly because they are not efficient. What they are doing though, with the Skylon, is an SSTO that uses air-breathing engines for the first part of its flight until hypersonic speeds, which means its rocket will need to provide much less d-V and fight against much less gravity and drag than in conventional rockets, where a rocket is used throughout the whole flight. As a result (I think) it will be able to use much less fuel per launch than a normal rocket. That's where its usefulness lies at, not to mention it is completely reusable, so unlike the Space Shuttle which dropped its main fuel tank, and then needed to be refitted, with the Skylon, technically all you have to do is refuel and do some checks and you're ready to go, like a normal airplane. This will result in much more frequent launch capabilities. I'm not sure, but I think another advantage may be that when it returns, it could use its airbreathing engines to actually fly, (but I'm not sure if it will have enough fuel left).

That's kind of two stages anyway, an air-breathing stage and a rocket stage.

[mikegarrison]

On 1/10/2016 at 0:52 PM, Kaos said:

If the technologies are far enough developed, the disadvantages of multistage would be bigger. I am not sure, where this limit is, but if you make the values for strength and Isp big enough, SSTO would be preferable, as the advantage of staging shrinks.

Take for example a material strong enough that you could build a sufficient strong structure with a fuel ratio of 99.9%. One would gain merely advantage with staging, so why would someone go into the effort of staging then? With incredible Isp this effect would be even more obvious: Given a fuel that can be handled as well as todays fuels, but has an Isp of 100 km/s. You could build rockets with only 15% fuel tank which are fully reusable. What would staging gain then for reaching the orbit?

Of course, slightly stronger materials oder slightly more efficient fuels would be first used to make non-SSTO more efficient.

If the staging is free, then a staged launch vehicle will always perform best. It will always mean you are getting rid of dead weight. I mean, even fighter airplanes drop their extra fuel tanks in order to extend range and yet still be light enough to fight when they reach the target.

A single-stage only makes sense if the weight penalty for keeping the empty tank is small enough that the simplicity pays more than the loss of performance.

[ModZero]

Skylon won't actually win all that much dV from the jet mode, just enough to be viable at all, really (I don't remember exact numbers, but they've shown up multiple times in NasaSpaceflight forums, with sources and knowledgable (and not-so-knowledgable) people reading it, if you want to dig for sources). It's not really a heavy lift launcher, and it will need an upper stage (hopefully reusable? They made some noises about it, but that's a lot of mass for questionable win) to get things into high orbits. 

They're hoping for a business model efficient in terms of profits, not really a lifter efficient in terms of mass-to-LEO.