Best propulsion method for a "low cost" SSTO?

[Idobox]

This reminds me of Jules Verne's work about going to the Moon via space gun.

If the gases are to be confined to a single segment of the tube, be burned by the passing vehicle, then disappear, why use doors? Membranes could do the job; the vehicle will penetrate it as it goes from one mix to the next.

Also, the vehicle would need some fuel for orbital insertion. Combining a ramjet with a rocket engine gives you an air-augmented rocket, which works as a ramjet while still in the tube, and burns fuel in atmosphere to combat atmospheric drag. After that, do circularization burn, and you're done. Now, we have to somehow cram all those, plus fuel and payload, in a 1m-diameter vehicle short enough to be carried by a truck that can climb mountains. But I'll leave that to our ingenious engineers.

The gases are at rather high pressure in the later stages, and you're going to hit it at several km/s. A membrane strong enough to hold this kind of pressure might be dangerous for your craft.

Mass drivers, whatever the technology, still require you to have a small rocket for circularization. Ducted rockets are good if you plan to stay long in the atmosphere, which is not the case here, and it is much easier to have a bullet shaped ship in a tube rather than having a ducted rocket fitting the tube (friction vs gas flowing around it). The typical design is a bullet shape ship and a small conventional rocket, even if the gun starts you "only" at 4km/s, making a SSTO is considerably easier.

[shynung]

The gases are at rather high pressure in the later stages, and you're going to hit it at several km/s. A membrane strong enough to hold this kind of pressure might be dangerous for your craft.

Mass drivers, whatever the technology, still require you to have a small rocket for circularization. Ducted rockets are good if you plan to stay long in the atmosphere, which is not the case here, and it is much easier to have a bullet shaped ship in a tube rather than having a ducted rocket fitting the tube (friction vs gas flowing around it). The typical design is a bullet shape ship and a small conventional rocket, even if the gun starts you "only" at 4km/s, making a SSTO is considerably easier.

Looks like we could drop the ducted rocket, then. The rocket would only be used for circularization and stationkeeping.

Also, membranes could be designed to resist high pressure, but breaks easily if punctured from a single point, but that requires advanced materials. Since said membrane would be expendable, material costs need to be taken into account.

[Nibb31]

Chicken and the egg problem: You couldn't start decreasing launch costs without more demand, and demand is limited because of high launch costs. Now how do we solve this?

You do it progressively over a long period of time. It's not a problem that will be solved with some sudden breakthrough.

The problem is that there is no "killer app" for space. The lack of demand is partly due to the cost, but mostly due to the lack of any worthwhile return on investment. Simply put, nobody really needs to go to space.

The only profitable business up there is com sats and government contracts. Space fanboys talk about tourism, mining, and microgravity manufacturing, but those activities all lack a viable business model, regardless of cost. Even if you cut prices by 50%, they still won't be queueing up for tickets.

[Sillychris]

What about a zero stage to orbit space elevator?

[Nibb31]

Already discussed many times. It falls into the fantasy megastructure category, with the giant railgun, the rotovator, the launch loop. It has all sorts of problems, like developing 36000km long carbon nanotubes instead of the 10 millimeter ones that we currently have, and building self propelled elevator cabins that go fast enough to make the thing worthwhile.

And of course, it assumes that someone is ready to spend billions of dollars to build the thing and that people are willing to massively buy tickets to go to GEO. For what?

It takes a 7 days to reach the GEO station of a space elevator at 200km/h. 2 weeks for a round trip. To make it worthwhile, you need a decent payload, something like 10 or 20 tons. For people, you need food and supplies and decent comfort for those 2 weeks.

Imagine a high-speed train, with enough grip on the cable to carry its own weight including its own power source and heat dissipation equipment, plus the payload, and without damaging or eroding the cable.

Major engineering challenge here and not realistic with current technology.

Edited April 17, 2014 by Nibb31

[Sillychris]

Carbon nanotubes are just barely strong enough, but what about spider silk?

I'd be down with camping out in an elevator car for 2 weeks.

[Rakaydos]

Carbon nanotubes are just barely strong enough, but what about spider silk?

I'd be down with camping out in an elevator car for 2 weeks.

Spider silk compares favorably with steel. Carbon nanotubes compare favorably with diamond. No contest here.

I'm still a fan of Airship to Orbit. So you have to replace a little helium each flight... so what?

[Exosphere]

Regarding SpaceX's use of a lot of engines to make it easier to achieve economies of scale with a low launch rate, wouldn't that be effective early on, but more costly as launch rates increase and it becomes easier to achieve economies of scale without an excessive number of engines? Twenty-eight engines per Falcon Heavy launch would allow you to produce a greater quantity of engines, but it would also mean you'd have to pay for twenty-eight times the number of turbopumps, injectors, etc every time you built a rocket. So, if the mass production advantage is reduced, it would seem like it would be most effective to use fewer engines, not more.

As an aside, I'd say that space planes do seem more cost effective, now that I think of the whole picture. You don't have to disassemble the entire vehicle to load a cargo, bolt it together again, have engineers test all the connections, load the rocket onto a crawler, pull the whole thing out to the pad, and lift it into position every time you launch. With a Skylon-style vehicle, the whole thing could be loaded via overhead gantries, pulled out by a standard aircraft hauler to a fueling apron, fueled, hauled to the runway, and launched -- which seems cheaper than the rocket approach, especially considering that the cost of maintaining, assembling, and testing the vehicle is the greatest contribution to launch costs.

The more I think about it, the more I like the Skylon. I hope it actually gets funded, though...

Edited April 17, 2014 by Exosphere

[Rakaydos]

As an aside, I'd say that space planes do seem more cost effective, now that I think of the whole picture. You don't have to disassemble the entire vehicle to load a cargo, bolt it together again, have engineers test all the connections, load the rocket onto a crawler, pull the whole thing out to the pad, and lift it into position every time you launch. With a Skylon-style vehicle, the whole thing could be loaded via overhead gantries, pulled out by a standard aircraft hauler to a fueling apron, fueled, hauled to the runway, and launched -- which seems cheaper than the rocket approach, especially considering that the cost of maintaining, assembling, and testing the vehicle is the greatest contribution to launch costs.

But a spaceplane that isnt SSTO has the same kinds of overhead a multistage rocket would have. That was part of the problems with the Space Shuttle. And a SSTO like Skylon pays for the capability with a much lower mass fraction, making it equivilant to a smaller and cheaper multistage rocket.

As for the long term problems of clustering compared to long term use of larger engines... first you have to get through short term to get to long term.

Edited April 17, 2014 by Rakaydos

[Exosphere]

But a spaceplane that isnt SSTO has the same kinds of overhead a multistage rocket would have. That was part of the problems with the Space Shuttle. And a SSTO like Skylon pays for the capability with a much lower mass fraction, making it equivilant to a smaller and cheaper multistage rocket.

As for the long term problems of clustering compared to long term use of larger engines... first you have to get through short term to get to long term.

Personally, I see the Skylon as more of a crew transfer vehicle. Like all space planes, the Skylon can't match the payload to LEO figures of a heavy lift vehicle, so it probably makes more sense to use a reusable Falcon Heavy rather than a Skylon for heavy cargo missions. However, since a crew tank to take people to dock with a station in LEO isn't particularly heavy (the Skylon holds thirty people), a smaller payload craft makes more sense, since the extra payload the Falcon Heavy can carry is wasted on a small payload that doesn't need to go any further than LEO, but the cost per launch is the similar regardless of the payload.

Of course, this is not the case if demand is high enough that it's economical to launch huge groups of people at once. I'm not going to be that optimistic, though.

Edited April 17, 2014 by Exosphere

[KASASpace]

Scramjets for initial ascent.

Then switch over to chemical engines.

Scramjets are typically lighter than turbojets and turbofans, so they are ideal, however they do have less Isp......

[Red Iron Crown]

Scramjets for initial ascent.

Then switch over to chemical engines.

Scramjets are typically lighter than turbojets and turbofans, so they are ideal, however they do have less Isp......

How are you accelerating to a speed where scramjets work well enough to take over?

[cantab]

The only profitable business up there is com sats and government contracts. Space fanboys talk about tourism, mining, and microgravity manufacturing, but those activities all lack a viable business model, regardless of cost. Even if you cut prices by 50%, they still won't be queueing up for tickets.

Spaceliners, either suborbital or fractional-orbital, may be a good one. Though even then the main issue is whether enough people are willing to pay enough money to get from Europe to America in 60 minutes.

Business spacecraft for the super-rich will work too I reckon. Some of the biggest yachts out there are estimated to have cost comparable sums to the development cost of SpaceShipTwo.

[KASASpace]

How are you accelerating to a speed where scramjets work well enough to take over?

That's a matter of what's good for that kind of purpose.

I suggest having the SSTO on a sled that gets accelerated to the required velocity, and once it gets there it detaches and flies on upward.

[Armchair Rocket Scientist]

That's a matter of what's good for that kind of purpose.

I suggest having the SSTO on a sled that gets accelerated to the required velocity, and once it gets there it detaches and flies on upward.

Traveling mach 5 at ground level sounds like a recipe to have your vehicle either incinerated or torn apart, not to mention that the scramjets would be unlikely to overcome the huge drag forces. All hypersonic aircraft so far have only gone that fast in the stratosphere.

Also, one of the major advantages of SSTOs is supposed to be reduced infrastructure costs. Your proposal requires a railgun or other sled capable of accelerating a 100+ ton vehicle to mach 5 or higher. Even if you accelerate at 10 gs, you'll need nearly 15 km of track. I'm estimating that the price tag would be somewhere between "high" and "absurd." Even after leaving the track, the vehicle will likely travel hundreds of kilometers before it gets high enough for the sonic boom to reach acceptable levels. Your launch sites are pretty much limited to the Sahara desert, or MAYBE the Australian outback; Nevada doesn't have large enough uninhabitated spaces. Either that, or you could build your 15+ km long track in the middle of the ocean, which would make it even more expensive.

[DerpenWolf]

For doing something cheap and realitivly simple technologically I would go with a tripropellant rocket/spaceplanes/craft/thing that switched out h2 and kerosene when appropriate, maybe even use different fuel mixtures for optimal performance. Then use an aerospike for a nozzle in order to keep your ISP up.

[shynung]

For doing something cheap and realitivly simple technologically I would go with a tripropellant rocket/spaceplanes/craft/thing that switched out h2 and kerosene when appropriate, maybe even use different fuel mixtures for optimal performance. Then use an aerospike for a nozzle in order to keep your ISP up.

Downside to this design would be needing to carry 3 separate tanks for each propellant mix, complicated valving systems (especially if variable fuel mixture is implemented), and an engine that works well with both fuels (most are designed specifically for one type of fuel/oxidizer mix).

If droptank-carrying rockets/spaceplanes are considered SSTO, one fuel-type could be carried in the droptank, and the other in the internal tankage.

[Dwayne_Knight]

As others have mentioned I think the two lowest cost solutions are beamed power and air augmented rockets.

Microwave beamed power using ground based nuclear seems cheaper since you can use existing reactors and of less cost politically. You won't get permission to create anything like a fission reactor rocket anywhere near earth any time soon. I'd suggest space based microwave emitters and a fan jet mother ship but a similar community of people object to "deathrays" from space as object to nuclear anything.

Air augmented rockets should be simpler and with more versatile launch windows.

I've seen a little comparison to the sabre engine suggesting temperature resistant materials are a problem offsetting some of sabres complexity.

So right now I'm imagining a LNG/LOX air augmented rocket, with an adjustable scram jet intake, some type of aerospike nozzle, and fuel cooled engine and intake surfaces to reduce the material thermal load.

So a sabre with the expensive radiator and turbo machinery gutted.

Liquified natural gas should be a lot easier to store and handle than hydrogen and offers a somewhat middle ground between kerosene and hydrogen.

Just spit balling needs a lot of math to back up the idea.

Got me thinking so I did a little poking around and found an interesting concept for a space blimp. High altitude balloon ascent using a ion or similar efficient engine potentially solar powered. Pretty speculative.

http://en.wikipedia.org/wiki/JP_Aerospace#Orbital_Ascender

Edited April 18, 2014 by Dwayne_Knight
found something new and interesting

[shynung]

So right now I'm imagining a LNG/LOX air augmented rocket, with an adjustable scram jet intake, some type of aerospike nozzle, and fuel cooled engine and intake surfaces to reduce the material thermal load.

Liquified natural gas should be a lot easier to store and handle than hydrogen and offers a somewhat middle ground between kerosene and hydrogen.

If one uses an air-augmented rocket, one couldn't simply use an aerospike nozzle; too much air being forced through a small nozzle opening will create a lot of drag, and puts more stress on the hardware. Instead, the ducting should converge to a chamber, inside of which is where the aerospike/regular nozzle sits in. This chamber mixes the rocket exhaust with ambient air, then shoots this mixture out of its own nozzle, separate from the rocket motor's.

LNG is about 97% methane and about 2-3% ethane, along with traces of heavier hydrocarbons mixed in. Methane/LOX rockets are currently being developed by SpaceX, the first of such design being named Raptor engine.

[KASASpace]

Traveling mach 5 at ground level sounds like a recipe to have your vehicle either incinerated or torn apart, not to mention that the scramjets would be unlikely to overcome the huge drag forces. All hypersonic aircraft so far have only gone that fast in the stratosphere.

Also, one of the major advantages of SSTOs is supposed to be reduced infrastructure costs. Your proposal requires a railgun or other sled capable of accelerating a 100+ ton vehicle to mach 5 or higher. Even if you accelerate at 10 gs, you'll need nearly 15 km of track. I'm estimating that the price tag would be somewhere between "high" and "absurd." Even after leaving the track, the vehicle will likely travel hundreds of kilometers before it gets high enough for the sonic boom to reach acceptable levels. Your launch sites are pretty much limited to the Sahara desert, or MAYBE the Australian outback; Nevada doesn't have large enough uninhabitated spaces. Either that, or you could build your 15+ km long track in the middle of the ocean, which would make it even more expensive.

Or, we could take advantage of the Vespucci effect, where a fluid's speed increases as it moves into a lower volume area.

Of course, it would probably start as a quasi-ramjet, and then change it's respective geometry to "scram" mode once sufficient altitude has been reached (not to mention speed)

[shynung]

Or, we could take advantage of the Vespucci effect, where a fluid's speed increases as it moves into a lower volume area.

Did you mean Bernoulli?

[Red Iron Crown]

Did you mean Bernoulli?

Or Venturi effect, perhaps.

[KerikBalm]

Seems to me an X-15/Spaceship 1 style craft would be the most cost effective way... except neither of those were orbital.

I imagine something like a gutted C-5/An-124 ...

or this:

http://en.wikipedia.org/wiki/Conroy_Virtus

It would not be outside the realm of possiblity that you could have a carrier aircraft get a payload of 100 tons to 1,000 km/h at 14km

From there a 100 ton Scramjet craft* is dropped, hopefully you'd get something like 10-20 tons to LEO with it.

Then they both return to base

*I'm not sure if a Sarbe engine would be of much use in that situation

The first stage - the massive cargo plane, shouldn't be much more expensive to operate than a normal heavy cargo aircraft.

The second stage - the scramjet spaceplane, would probably be about as expensive to refit as the shuttle orbiter, so you'd save on the SRBs and the big external tank.

[rkman]

wouldn't it make more sense just to use a chemical rocket-powered SSTO?

Not from the perspective of cost. Why an SSTO when it is cheaper to use a staged rocket?

[Dwayne_Knight]

If one uses an air-augmented rocket, one couldn't simply use an aerospike nozzle; too much air being forced through a small nozzle opening will create a lot of drag, and puts more stress on the hardware. Instead, the ducting should converge to a chamber, inside of which is where the aerospike/regular nozzle sits in. This chamber mixes the rocket exhaust with ambient air, then shoots this mixture out of its own nozzle, separate from the rocket motor's.

LNG is about 97% methane and about 2-3% ethane, along with traces of heavier hydrocarbons mixed in. Methane/LOX rockets are currently being developed by SpaceX, the first of such design being named Raptor engine.

Thanks for the link to the raptor will take a look.

I was thinking about the nozzle geometer and looking at some rocket based combined cycle papers on the web. Aerospike for the central rocket for space and entrainment would be fine and some more tradition geometry for the duct while in atmosphere.

I like the look in the link bellow of profile C from figure 3.1 on page 36.

Let me know what you think.

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCkQFjAA&url=http%3A%2F%2Ftrace.tennessee.edu%2Fcgi%2Fviewcontent.cgi%3Farticle%3D1754%26context%3Dutk_gradthes&ei=DLNSU5GjIqP52wWF54CgDQ&usg=AFQjCNHUcJ77eZrq4WBgO6rYUCV4M_s1dA&sig2=m5oCjg2Zn56lpoC6P7VjFg&bvm=bv.65058239,d.b2I