I Love Chemically-Fueled, Vertical Take-Off Rockets But Doesn't Humanity Need a More Elegant Way to Get into Space?

[Antares JS]

I have significant doubts that any oxidizer weight savings from using an air-breathing engine for the first few tens of thousands of feet (before the air gets too thin to support an air-breathing engine) is worth the added complexity. What you are talking about doing results in making a two-stage rocket into a three-stage rocket where the first stage is used for less than a minute.

Not to mention, ramjets and scramjets require some kind of boost to get going in the first place; they are not capable of moving a stationary vehicle as they require supersonic air to be forced through their intakes by the vehicle's motion, adding yet another layer of complexity and taking away from the practicality.

So in the end, you need a rocket boost to get your air-breathing first stage going, then the air-breathing stage has to start up, then it's only good for a brief time before the air gets too thin, at which point it has to be separated or shut down and the actual rocket has to be started, but you're still low and slow enough that you're probably going to still need two more rocket stages.

Technically feasible? Probably. Practical? Unlikely.

 

[MidOH]

The F15 Eagle launched a missile into orbit to shoot down a satellite. So it has been done.
https://avgeekery.com/that-time-an-f-15-pilot-shot-down-a-satellite-32-years-ago-this-week/
But the F15 is about 20 times larger and heavier than the weapon it launched. So do the math and scale that up. How much of a rocket do you need to get your payload from 50,000 feet to orbit? 50,000 pounds? 100,000 pounds? Multiply that by at least 20 for the aircraft.

That's one big aircraft. Anyone that thinks that a giant aircraft, is more elegant than a rocket with only a handful of moving parts, obviously hasn't spent anytime wrenching on jets.

For now. A simple fuel tank, over a simple rocket engine, is the best way up. Solve the equation of gravity, or create inertia dampers if you want something elegant.

 

[brockrwood]

How about a railgun to get the vehicle to a hogh enough speed yo start the scramjet. Then. The scram jet gets it to hypersonic speed. Then, when the sir gets too thin, the intakes close and a small rocket engine gets it into orbit?

 

[smstachwick]

How about a railgun to get the vehicle to a hogh enough speed yo start the scramjet. Then. The scram jet gets it to hypersonic speed. Then, when the sir gets too thin, the intakes close and a small rocket engine gets it into orbit?

Again, additional complexity and weight of the entire system for not much usable burn time.

While theoretically feasible, it might not be entirely practical and it would introduce additional points of failure.

 

[Antares JS]

How about a railgun to get the vehicle to a hogh enough speed yo start the scramjet. Then. The scram jet gets it to hypersonic speed. Then, when the sir gets too thin, the intakes close and a small rocket engine gets it into orbit?

High enough speed to start a scramjet is about Mach 5. You're already hypersonic at that point and dealing with all that heat and wave drag before leaving the rail. Remember that the one and only scramjet demonstrator had to be accelerated to the point where it could be started by an air-dropped Pegasus rocket.

Magnetic launch rails also have to be either extremely long to spread out the acceleration with sensitive cargo (like humans) on board or they can be shorter and accelerate quickly, but in that case they could only be used to chuck water tanks and other g-insensitive cargo into space.

You can start a ramjet at Mach .5, but now you're adding more weight and yet another level of complexity by using a ramjet to get up to the speed where you can use a scramjet. Ramjets also are not very efficient unless you are going Mach 2-3.

 

[brockrwood]

Again, additional complexity and weight of the entire system for not much usable burn time.

While theoretically feasible, it might not be entirely practical and it would introduce additional points of failure.

Hmm. Maybe lots of cheap, reliable conventional, vertical launch rockets may be the way to go, huh? Especially if those tockets are mostly recoverable and reusable, a la SpaceX?

 

[Antares JS]

Hmm. Maybe lots of cheap, reliable conventional, vertical launch rockets may be the way to go, huh? Especially if those tockets are mostly recoverable and reusable, a la SpaceX?

For the time being, yes.

I would highly suggest people who really want to dive into this kind of stuff play Kerbal Space Program. I learned more about how space flight works from playing Kerbal than from my college courses. You can see for yourself how impractical an SSTO is by flying one for yourself and see just how much smaller you can make an orbital rocket by dividing it into two stages.

 

[MJW]

Space planes, like Skylon, that use a single stage to orbit overcome a lot of the issues with vertically launch rockets. By using lift from wings to gain altitude while accelerating towards orbit using a turbo-jet/closed loop engine, like SABRE, the mass fraction is dramatically improved. Sure, it takes 10+ minutes to gain the same altitude a conventional rocket gains in 1 minute, but does that really matter for putting cargo into space? Only ICBMs ”need” to reach orbit as fast as possible. Everything else humans launch can afford a little longer journey.

 

[Antares JS]

Space planes, like Skylon, that use a single stage to orbit overcome a lot of the issues with vertically launch rockets. By using lift from wings to gain altitude while accelerating towards orbit using a turbo-jet/closed loop engine, like SABRE, the mass fraction is dramatically improved. Sure, it takes 10+ minutes to gain the same altitude a conventional rocket gains in 1 minute, but does that really matter for putting cargo into space? Only ICBMs ”need” to reach orbit as fast as possible. Everything else humans launch can afford a little longer journey.

Skylon is a paper vehicle at this point, and the air is too thin to feed jet engines at around 50,000 feet, less than 1/6 of the way to the Karman Line. Wings become dead weight around 120,000 feet, only a little more than 1/3 of the way to the Karman Line.

I reiterate, going very fast through the atmosphere is a really bad idea due to the heat and wave drag. You are basically trying to do a re-entry in reverse while under power. You need to get the thick parts of the atmosphere out of the way as quickly as possible, otherwise you are just wasting propellant.

 

[MJW]

It's got well over a decade of funding from the European Space Agency (and DARPA, among other sources) and its SABRE engine has passed every test so far. As I recall it's compressor is functional to over 80k feet and M5.4. That's a lot of altitude and velocity to gain without burning any oxidizer and only hydrogen for fuel... Somebody in charge somewhere must see potential in the concept.

 

[Antares JS]

It's got well over a decade of funding from the European Space Agency (and DARPA, among other sources) and its SABRE engine has passed every test so far. As I recall it's compressor is functional to over 80k feet and M5.4. That's a lot of altitude and velocity to gain without burning any oxidizer and only hydrogen for fuel... Somebody in charge somewhere must see potential in the concept.

There is a long, long history of aerospace projects that received funding but never got off the ground. Just because they have funding is not a reason to get excited that it's actually going to happen.

Assuming those numbers are accurate, 80,000 feet is a quarter of the way to the Karman line and Mach 5.4 is 1/5 of orbital velocity. It's way too soon to get excited. And it's just what the compressor is capable of, not what the whole vehicle is capable of. See my previous posts for major problems still to be overcome.

 

[OverTheTop]

I have significant doubts that any oxidizer weight savings from using an air-breathing engine for the first few tens of thousands of feet (before the air gets too thin to support an air-breathing engine) is worth the added complexity. What you are talking about doing results in making a two-stage rocket into a three-stage rocket where the first stage is used for less than a minute.

Skylon is a paper vehicle at this point, and the air is too thin to feed jet engines at around 50,000 feet, less than 1/6 of the way to the Karman Line. Wings become dead weight around 120,000 feet, only a little more than 1/3 of the way to the Karman Line.

I reiterate, going very fast through the atmosphere is a really bad idea due to the heat and wave drag. You are basically trying to do a re-entry in reverse while under power. You need to get the thick parts of the atmosphere out of the way as quickly as possible, otherwise you are just wasting propellant.

The scramjet will open up a paradigm shift in how we get to space if they get the tech sorted out. I can imagine a method of having the SSTO vehicle go to a height and then deliberately hold that height (thrust vector partly downwards) whilst accelerating and breathing enough atmospheric oxygen. At some point (probably determined by mechanical strength of the vehicle ) you point towards space and switch over to internal oxidiser as the atmospheric oxygen runs out.

It will be a completely different set of flight optimistation parameters compared to the regular "get out of the air ASAP" trajectories we see now.

The idea has to be viable or they would not be investing so much in the project. The numbers have to stack up or they would be told "You're dreaming. Go away" by those holding the purse-strings.

 

[Antares JS]

(...) if they get the tech sorted out.

That's the trick, isn't it? I think a lot of people really don't grasp how difficult this is.

The idea has to be viable or they would not be investing so much in the project.

If only that was true. Sadly, the ones holding the purse strings are usually not engineers familiar with how difficult these kinds of ideas really are to execute. Aerospace history is littered with projects that attracted investors and attention only to peter out because they couldn't "get the tech sorted out." My cynicism is born from that history. I will be happy to be wrong about Skylon, but I don't think I am.

 

[smstachwick]

That's the trick, isn't it? I think a lot of people really don't grasp how difficult this is.

One only has to look at the flurry of designs offered to the USAAC/USAAF/USAF between 1924 and 1962. In that time they designated 111 aircraft with the P or F identifier. While many of early designations were merely borne out a simple engine switch, many more were either unworkable prototypes or designed to fill a role that was conceptually flawed. Obviously none of these ever made it into production.

Curtiss-Wright produced a number of these designs, of which one (the XF-87 Blackhawk) spelled the end for the company as an aircraft manufacturer.

 

[brockrwood]

For the time being, yes.

I would highly suggest people who really want to dive into this kind of stuff play Kerbal Space Program. I learned more about how space flight works from playing Kerbal than from my college courses. You can see for yourself how impractical an SSTO is by flying one for yourself and see just how much smaller you can make an orbital rocket by dividing it into two stages.

Where do I obtain this Kerbal Space Program?

 

[bwayne64]

Until they figure out anti gravity or find material strong enough for a space elevator, I think we're stuck with chemical rockets. I personally think that Liquid ox/hyd isn't that bad environmentally. But I know the extreme Climate change folks don't like it. It's only water vapor coming out those nozzles. But they act like you're spewing hydrochloric acid. Now I don't know about the exhaust of the Space X engines. Some bi product of Ox/kerosene. It would be nice to have something less explosive to carry people up. Anti grav would be awesome, but so would super powers, LoL.

 

[Antares JS]

Where do I obtain this Kerbal Space Program?

https://store.steampowered.com/app/220200/Kerbal_Space_Program/

 

[Antares JS]

Now I don't know about the exhaust of the Space X engines. Some bi product of Ox/kerosene.

Hydrocarbons burning with pure oxygen produce primarily water vapor and carbon dioxide, with traces of other carbon-oxygen-hydrogen compounds.

 

[RocketPro]

SPHEREx is the mission. Press release about our science coming late next week.

Press Release as mentioned:
NASA Finalizes Plans for Its Next Cosmic Mapmaker: https://www.jpl.nasa.gov/news/nasa-finalizes-plans-for-its-next-cosmic-mapmaker

 

[Sooner Boomer]

Hydrocarbons burning with pure oxygen produce primarily water vapor and carbon dioxide, with traces of other carbon-oxygen-hydrogen compounds.

*Anything* burning (above a certain temperature) in Earth's atmosphere will produce nitrogen oxides. Rocket exhaust is certainly above that temperature. And a rocket launch produces more than a trace. This is one reason internal combustion engines need catalytic converters. NOx is a major component in photochemical smog.

 

[Antares JS]

*Anything* burning (above a certain temperature) in Earth's atmosphere will produce nitrogen oxides. Rocket exhaust is certainly above that temperature. And a rocket launch produces more than a trace. This is one reason internal combustion engines need catalytic converters. NOx is a major component in photochemical smog.

Except that rocket fuel doesn't burn "in atmosphere." It burns in an environment of 100% oxygen, except for the first split second. After the engine gets going, the internal pressure keeps atmosphere out.

The only way you're getting significant amounts of nitrogen compounds is if you are using propellants that contain nitrogen, such as hypergolics. Nitric acid was also used as an oxidizer back in the day, but not so much anymore.

 

[boomtube-mk2]

We should count ourselves lucky that we can even get anything into orbit, much less fairly big things.
Our measly 9.81 meters per second^2 G-force can, with a lot of effort, be overcome using chemical fueled rockets.
Bump that to 13-14 meters per second^2 or more and the math falls apart.
Your rocket is heavier as is the fuel, yet that fuel isn't producing any more energy, specific impulse, than it does here on Earth.

Google "The Tyranny of the Rocket".

 

[Sooner Boomer]

Except that rocket fuel doesn't burn "in atmosphere." It burns in an environment of 100% oxygen, except for the first split second. After the engine gets going, the internal pressure keeps atmosphere out.

The only way you're getting significant amounts of nitrogen compounds is if you are using propellants that contain nitrogen, such as hypergolics. Nitric acid was also used as an oxidizer back in the day, but not so much anymore.

The fact that you're generating heat in an oxygen/nitrogen environment causes the formation of NOx. Tne nitrogen does not take part in the reaction between the propellant and oxidizer. And, until it gets fairly high, it *is* burning in the Earth's atmosphere. Once it gets high enough, the atmosphere thins: less pressure, less nitorgen, less NOx.

 

[Antares JS]

The fact that you're generating heat in an oxygen/nitrogen environment causes the formation of NOx. Tne nitrogen does not take part in the reaction between the propellant and oxidizer. And, until it gets fairly high, it *is* burning in the Earth's atmosphere. Once it gets high enough, the atmosphere thins: less pressure, less nitorgen, less NOx.

I was talking about the inside of the combustion chamber (in which any ambient atmosphere is shoved out when the engine starts), but I see you are not. It seems you are saying the heat from the exhaust causes NOx to form around it, not actually in the engine. In that case, apologies for the misunderstanding.

 

[Sooner Boomer]

I was talking about the inside of the combustion chamber (in which any ambient atmosphere is shoved out when the engine starts), but I see you are not. It seems you are saying the heat from the exhaust causes NOx to form around it, not actually in the engine. In that case, apologies for the misunderstanding.

Sorry I didn't explain better. You're right, too. Inside the combustion chamber, the only things that should be there are the propellant, oxidizer, and their products. The chemistry of combustion, and what forms at what pressure/temperature is quite fascinating!

 

[aerostadt]

If you want to be technical as I mentioned earlier in this thread, you would be amazed how much hydrogen can be in rocket exhaust. Liquid H2/LOX rocket engines will have a lot of unburned hydrogen. You get higher exhaust velocity(lower molecular weight) and/or specific impulse with hydrogen in the exhaust with a lower combustion chamber temperature. Even composite solid rocket motors have a lot of unburned hydrogen in the exhaust for the same reason to increase specific impulse.

 

[Cape Byron]

Why did development of the DC-X stop? It seemed promising. Plus, the “fly a little, break a little” development approach has been shown to work and provide rapid development. Example: SpaceX.

Found this today. Also posted in the Cool things I found on YouTube or other videos... thread.

 

[brockrwood]

SpinLaunch is fascinating but could this really be scaled up to handle bigger payloads and orbital launches?
https://www.space.com/spinlaunch-nasa-suborbital-test-flight-agreement

 

[rocket_troy]

Even composite solid rocket motors have a lot of unburned hydrogen in the exhaust for the same reason to increase specific impulse.

Depends on what your definition of "a lot" is. For a typical 70/15/15 mix of AP/Organic/Al, the H2 in the exhaust would theoretically be less than 3% of exhaust mass flow irrespective of Pc or Pa. I have to admit, that's more significant than I would've guessed, but it might be under the threshold of "a lot" for many... but maybe not...

TP

 

[aerostadt]

Depends on what your definition of "a lot" is. For a typical 70/15/15 mix of AP/Organic/Al, the H2 in the exhaust would theoretically be less than 3% of exhaust mass flow irrespective of Pc or Pa. I have to admit, that's more significant than I would've guessed, but it might be under the threshold of "a lot" for many... but maybe not...

TP

Depends on how you look at a NASA-Lewis Thermochemical run. On a weight basis the amount of free hydrogen will be low. On a molar basis the amount of free hydrogen is startlingly high. The net effect is that the average molecular weight of the combustion products is reduced dramatically. Although, at some point the Al2O3 becomes a liquid and then a solid most thermochemical runs will include the aluminum oxide in the average molecular weight calculation. I find this to be no problem, because I have seen specific impulse predictions to be more accurate than sophisticated CFD runs that allow some of the aluminum oxide to precipitate out. Just think, sit down and calculate the molecular weight of Al2O3. You will find that it is in the 90's. The molecular weight of H2 is 2. The average molecular weight of the Space Shuttle SRB's is around 26, which is a drastic reduction from the 90's. This is why I was excited several years ago when I heard researchers were putting aluminum/lithium alloy in composite solid propellant. The lithium was scavenging the chlorine from the hydrogen in the HCl in the combustion products and producing more free hydrogen and sure enough the average molecular weight went down and the specific impulse went up pretty good, maybe 10 seconds. Does that make a difference? It sure can. In the submarine launched ballistic missiles the addition of the explosive HMX only increases the specific impulse by about 2 or 3 seconds. Even though though SLBM propellant can be shock sensitive, U.S. Navy considers the enhanced performance worth the risk.