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Single Stage to Orbit

KASASpace

By KASASpace
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KASASpace

KASASpace

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I know this has probably been made a hundred times now, but I want to show you guys my idea.

So, you have a runway at the Spaceport. This is only for landing, however. Initial takeoff is done with a sort of maglev track which accelerates the craft to 300 m/s. Now, this is way faster than necessary speed for a ramjet or a scramjet. So very little moving parts in initial ascent engines. Make them like the Sabre engines, only ram/scram jets. This would mean those same engines could eventually be used as the upper stage, probably either RP-1 or Methane as fuel. Primarily because they are awesome. Possible cargo to LEO over 10 tons.

Launch Sequence(revised):

1. Acceleration by something, perhaps a sled with rockets and then rams onboard, to about 300 m/s

2. start of ramjet

3. Exiting of launch track

4. Midair refueling

5. Scramjet activates

6. Runout of air between 50 and 60 km

7. biprop engine begins, scram cut-off an instant later

8. MECO

9. perform mission

10. Return to Earth

The bonus here is that if you build enough of them, you can get a HUGE amount of launches per year, making the SSTO an effective cheap launcher, not to mention not having to actually, you know, LAUNCH! From a launch pad extremely slowly, wasting huge amounts of precious fuel.

Edited by KASASpace
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Camacha

Camacha

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Or perhaps a sort of catapult like on aircraft carriers, but it would be a big one.

The problem with that is that your speed will bleed off fast, meaning you need incredible speeds just where the atmosphere is thickest. Taking your propulsion along will go a long way in reducing speed in the thickest part of the atmosphere and increasing it in the thinner part.

Or you could build a vacuum or hydrogen tunnel that goes way up, but I am not sure that is practical.

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KASASpace

KASASpace

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The problem with that is that your speed will bleed off fast, meaning you need incredible speeds just where the atmosphere is thickest. Taking your propulsion along will go a long way in reducing speed in the thickest part of the atmosphere and increasing it in the thinner part.

Or you could build a vacuum or hydrogen tunnel that goes way up, but I am not sure that is practical.

Hello, RAM/SCRAMJET!

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K^2

K^2

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I don't think building a maglev is going to be economical here. You are probably better off using solid rocket JATOs to get yourself up to ramjet speeds. That way, you can take off from conventional runways. Cost of JATOs is going to be lower than cost of building and operating a maglev, even in the long run.

Other than that, yeah, the idea of using ramjet for early portions of ascent is pretty appealing. I was thinking of something similar for a hybrid rocket. Basically, you have your solid fuel chamber, you can feed liquid oxidizer into it to run as a conventional hybrid, but you also have a ram intake sitting at the top which can let you run the whole thing with external air. Now, a solid fuel ramjet might sound pretty crazy, but honestly, it's not that different from operation of a hybrid. And you get some limited throttling with this.

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KASASpace

KASASpace

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How are you going to get a ramjet or scramjet to function at 300 m/s? The speed of sound in air at sea level under ISA conditions is 340 m/s.

No, the type of jet is a ramjet that can also operate as a scramjet, it's a variable type ramjet. Ramjets can work at subsonic speeds.

Also, what happened to that effect where you can make fluid speed increase by making it go into a smaller place than it was? Same applies here. You make an intake that's a large-ish area flow into a much smaller area before combusting.

Edited by KASASpace
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KASASpace

KASASpace

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I don't think building a maglev is going to be economical here.

Well, if you have solar farms (IE giant solar panels in the desert) and "ship" the electricity down, or perhaps the idea some guy had, where you beam down electricity with a microwave from a giant solar power station in a a HUGE orbit. And plus, maybe more of a giant railgun, but either way it's magnets.

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K^2

K^2

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How are you going to get a ramjet or scramjet to function at 300 m/s? The speed of sound in air at sea level under ISA conditions is 340 m/s.

You only need the speed of sound at the narrowest part of the intake. As the intake narrows, incoming air speeds up, so you can get Mach 1 at the narrowest part even at subsonic speeds. You still need to be going fast, but 300m/s is quite reasonable for ramjet operation.

Well, if you have solar farms (IE giant solar panels in the desert) and "ship" the electricity down, or perhaps the idea some guy had, where you beam down electricity with a microwave from a giant solar power station in a a HUGE orbit. And plus, maybe more of a giant railgun, but either way it's magnets.

Maintaining magrail operation isn't just about energy. It's still going to cost you a lot of money to operate, even if energy is free.

Besides, electricity is cheap. Taking a 100T ship to 300m/s would take 1.1MWh. Magrail can be over 80% efficient. Even if you have to pay 15 cents per kWh, that's less than $200/launch. That's nothing. The entire cost is going to come from crews that will have to operate, maintain, and inspect it. All of the replacement parts, etc. Take a look at how much money goes into running a facility like JLab. There are a lot of similarities between running large magrail and particle accelerator.

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KASASpace

KASASpace

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Maintaining magrail operation isn't just about energy. It's still going to cost you a lot of money to operate, even if energy is free.

Besides, electricity is cheap. Taking a 100T ship to 300m/s would take 1.1MWh. Magrail can be over 80% efficient. Even if you have to pay 15 cents per kWh, that's less than $200/launch. That's nothing. The entire cost is going to come from crews that will have to operate, maintain, and inspect it. All of the replacement parts, etc. Take a look at how much money goes into running a facility like JLab. There are a lot of similarities between running large magrail and particle accelerator.

Well, on the note of the magrail thing, I admit that's where cost comes in the most, but the parts to replace are typically hte most costly if I remember right. So you mass produce replacement parts. As cost per launch not counting the magrail maintenance cost, it's till pretty cheap.

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K^2

K^2

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I think maglev are pretty much maintenance free, as in Inductrack design the maglev rails are nothing more than stacked sheet metal

While you can use that for suspension, you can't use that design for propulsion. Inductrack relies on train to generate its own propulsion. That's fine for a train, because it can be heavy without serious consequences. If you are launching an SSTO, it needs to be as light as possible. So all of your propulsion system has to be in the track. That means that you can't have an unpowered track. You have to have an active linac pushing your SSTO, and that's going to be way more complicated.

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PakledHostage

PakledHostage

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You only need the speed of sound at the narrowest part of the intake. As the intake narrows, incoming air speeds up, so you can get Mach 1 at the narrowest part even at subsonic speeds. You still need to be going fast, but 300m/s is quite reasonable for ramjet operation.

It sounds like I have some reading to do. The tone of KASASpace's posts are in line with a socially awkward highschool student rather than any sort of authority, but I will take your word for it.

It surprises me that you can get one to work at speeds that low. The diffusers (inlet cowls) on the large turbofan engines that I am familiar with work the opposite way. They slow down and compress the ~Mach 0.82 free stream air before it reaches the engine's fan and compressor. Diffusers ahead of the turbojet engines in fighter aircraft do the same as well.

Edited by PakledHostage
fixed a spelling mistake
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3_bit

3_bit

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Remember that Scramjets rely upon extremely high input air speeds, after all there are essentially no moving parts in the combustion chamber. I can't find any numbers right now, but you'll probably need more than 300 m/s to start it, not to mention a higher altitude.

I do definitely think Maglev launches are the future.

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Nibb31

Nibb31

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RATO + Rocket engine = no longer single stage to orbit.

SSTO is actually quite trivial. The old Titan II first stage would have been capable of SSTO (with a tiny payload), and old Mercury-Atlas was nearly an SSTO (it only dropped the engines). Those had ancient engines with a crappy Isp. With current rocket engines, it would be easy.

The reason most modern commercial launchers use an upper stage is because of flexibility and precision. Commercial launches have variable requirements for specific orbits which often require multiple burns with parking orbits and insertion manoeuvers. Restartable engines are more complex, so it makes sense to have a big first stage to do most of the work with big fat heavy non-restartable engines and to keep the restartable upper stage as small as possible.

Edited by Nibb31
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K^2

K^2

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It surprises me that you can get one to work at speeds that low.

If that surprises you, wait 'till you see how low it can go.

Although ramjets have been run from as low as 45 m/s (162 kph, 100 mph)[8] upwards, below about Mach 0.5, they give little thrust and are highly inefficient due to their low pressure ratios.

In principle, there isn't really an absolute cutoff for minimum speed, but it gets more and more challenging as you drop the lower speed. And you get less and less thrust out of it, so it becomes incapable of sustaining speed before it actually becomes inoperable. But at 300m/s you can actually get enough thrust out of one to accelerate. I doubt I'd be able to find good references right now, but some experimental flights Soviets have done were dropped from another airplane at under 900km/h. That's less than 250m/s, and these ram jets were able to go supersonic afterwards.

Remember that Scramjets rely upon extremely high input air speeds, after all there are essentially no moving parts in the combustion chamber. I can't find any numbers right now, but you'll probably need more than 300 m/s to start it, not to mention a higher altitude.

Absolutely. While scram jet is a type of a ram jet, it's designed for much higher intake speeds. I don't think there is a specific cutoff for these either, but in practice, you need to be well into supersonic before you can start using a scramjet.

In principle, the only part that has to be different is the combustion chamber. Scramjet and ramjet can share an intake. So you might be able to build a scram/ram jet at expense of just a few moving parts to switch from one mode to the other. I don't know if you could get both maximally efficient, but since ram jet only needs you to get to scram speeds, if you can make operation at the hypersonic speeds as efficient, it's probably good enough.

So I still think this idea has promise for a small, reusable shuttle.

RATO + Rocket engine = no longer single stage to orbit.

So? It's a technicality. Reason we want an SSTO is to cut launch costs by reusing the craft as much as possible. Yes, R/JATO boosters would technically be a stage. But in terms of practical use, they are just consumables. We aren't talking about Shuttle SRBs, here. We are talking about small boosters attached to pylons which just get the ship off the ground.

With what you are going to save on weight with (sc)ram jets, you are still going to end up way ahead even if your R/JATO are single use. In fact, you might even still be ahead compared to using a true SSTO with SABRE-like engines.

P.S. While I still think maglev to 300m/s would be too expensive to be worth it, I'd definitely look into pneumatic catapults, similar to these used on aircraft carriers. Nothing new to invent, hardware exists, and it can get you to a pretty good fraction of that starting speed.

Edited by K^2
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K^2

K^2

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A lot. For the most famous example, SR-71 Blackbird used a hybrid ram/turbojet. Basically, it had a ram air bypass leading straight to the afterburner, allowing it to operate as a ram jet at Mach 3.2 cruise.

These days, people are more interested in scramjets for hypersonic flights. Off the top of my head, the Boeing X-51 WaveRider is a great example of a currently operational test platform.

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rpayne88

rpayne88

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Just to offer some constructive criticism, 10 tons to LEO (almost typed LKO) is a pretty small payload. Look at something like a Saturn V or SLS which can put 100+ tons into LEO. Or the Space shuttle that, IIRC, could put 30 tons up. Its a good start, but we'd need larger SSTOs.

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