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

[brockrwood]

[I am re-posting this musing here, as it was starting to get very far afield of the original message thread it was in...]

In the other thread, we were discussing whether Virgin Galactic's "Spaceship 2" is really a spaceship because it does not seem to ever get to the "Karman line" that most experts agree is where Earth's atmosphere ends and "space" begins.

While I admit that some might just dismiss Spaceship 2 as just a really high flying "rocket plane", still, I like the idea of the air-launched "spaceship", a la "Spaceship 2" and the old, venerable, X-15 rocket plane.

It seems to make sense: You make a really big, high-flying, but still air-breathing aircraft. Then you launch or drop a rocket powered "spaceship" from the aircraft. Maybe the spaceship is both "scramjet" and "rocket" craft, or some sort of hybrid. Wouldn't that be the most economical, most elegant way to get into space? Here we are in 2021, 60 years after Yuri Gagarin became the first human in space, and we are still, basically, doing this the same way: We point a large, chemically fueled rocket at the sky and then we light that roman candle. Then the rocket goes (essentially) straight up, vertically, against the gravity well of Earth, expending enormous amounts of fuel in the process. Ultimately, a fairly small payload on the top of the rocket gets into space.

I love rockets! I am a BAR model rocketeer. But as a space enthusiast, I think we ("we" being humanity) need a more elegant way to get into space. Space elevator? Some sort of rail gun that magnetically hurls a payload into space? An air-launched spaceship? A horizontal take off craft that begins as an air-breathing jet airplane, turns into some sort of hybrid jet/rocket craft at some point, and then finally becomes a pure rocket craft that enters space?

 

[Charles_McG]

I always wondered if Burt Rutan had a plan to get Spaceship One in and out of orbit. My thought was a tether. Launch a tether-end-seeking robot near apogee. Catch the tether. Get one hell of a lift into orbit. Reverse to get back down, putting the tether back into higher orbit and dropping the Ship back at the top at the atmosphere with low relative ground velocity.

 

[Sandy H.]

It would be interesting to know what percentage of energy is used for different phases of flight. We know a model rocket using a piston launcher goes higher than conventional launch, so affecting the initial phase going from zero movement to acceleration up is important. (I'm guessing if Elon wanted to use a conventional LPR piston, he'd need to use LOC heavy wall tubing at least. . . )

As a thought experiment, as I doubt there is any version of practicality, what if you could make the launch pad accelerate the rocket upward from zero movement to 50mph at 5ft/s^2 before the engines light? f=ma, so we'd know how much force from the external system you'd need to put in, but at the end of the day, how much more mass (or less fuel) would it use over the whole flight? Guessing it wouldn't be much and the cost to build a pogo-pad would be huge and the new systems that could cause a failure would also be bad. Complex=bad, simple=good. . .

Still fun to talk about, though.

Sandy.

 

[brockrwood]

I always wondered if Burt Rutan had a plan to get Spaceship One in and out of orbit. My thought was a tether. Launch a tether-end-seeking robot near apogee. Catch the tether. Get one hell of a lift into orbit. Reverse to get back down, putting the tether back into higher orbit and dropping the Ship back at the top at the atmosphere with low relative ground velocity.

Space tether! Once you have something in orbit, just lower a rope?

 

[brockrwood]

It would be interesting to know what percentage of energy is used for different phases of flight. We know a model rocket using a piston launcher goes higher than conventional launch, so affecting the initial phase going from zero movement to acceleration up is important. (I'm guessing if Elon wanted to use a conventional LPR piston, he'd need to use LOC heavy wall tubing at least. . . )

As a thought experiment, as I doubt there is any version of practicality, what if you could make the launch pad accelerate the rocket upward from zero movement to 50mph at 5ft/s^2 before the engines light? f=ma, so we'd know how much force from the external system you'd need to put in, but at the end of the day, how much more mass (or less fuel) would it use over the whole flight? Guessing it wouldn't be much and the cost to build a pogo-pad would be huge and the new systems that could cause a failure would also be bad. Complex=bad, simple=good. . .

Still fun to talk about, though.

Sandy.

The Russian Solution: Build it big. Build it simple (and thus reliable). Good, old, vertically launched, expendable chemical rockets work fine if they don’t cost too much.

 

[Charles_McG]

Not quite - it spins end over end to keep it taught. When you catch the bottom - timed so the end spinning down is nearby and near zero relative velocity, it then lifts the payload up and releases it again 180 degrees of spin later. Momentum is exchanged - the average momentum stays the same, so the payload is in orbit and the tether is in a lower orbit. Payload lowering reverses that. Residual losses could be made up by solar electric reboost between cycles.

It takes some of the material advances of a space elevator - but less extreme. Note: I haven't seen recent estimates of how long a momentum exchange tether like this needs to be to keep the Gs survivable.

 

[Funkworks]

I think an important decision to make is whether you just want to reach the Karman line, or to reach orbit and stay there. Reaching the Karman line and falling back (like Spaceship 2 and New Sheppard) is one thing, but if you want to keep accelerating to an orbital 17 000 mph after that (like Falcon 9), nothing can do it but humungous fuel tanks that will dwarf any other propulsion system.

For example, SS-520 is the smallest rocket to place a payload into orbit (2.6 tons of rocket and fuel for a 4kg payload). Maybe one could carry that with a B-52 but why bother.

In fact, I just realized Blue Origin named its 2 rockets based on just that: New Sheppard refers to Alan Sheppard who "only" reached space, and New Glenn refers to John Glenn who reached orbit. Now compare the size of their fuel tanks:

 

[Sandy H.]

[snip]

For example, SS-520 is the smallest rocket to place a payload into orbit (2.6 tons of rocket and fuel for a 4kg payload). Maybe one could carry that with a B-52 but why bother.

If it was launched from a B-52, how much more payload would get to orbit. Honest question, not being snarky. If it becomes 4.5kg, then not worth it. If it became 15kg, still might not be worth it, but it would at least be interesting to know.

Sandy.

 

[brockrwood]

I think an important decision to make is whether you just want to reach the Karman line, or to reach orbit and stay there. Reaching the Karman line and falling back (like Spaceship 2 and New Sheppard) is one thing, but if you want to keep accelerating to an orbital 17 000 mph after that (like Falcon 9), nothing can do it but humungous fuel tanks that will dwarf any other propulsion system.

For example, SS-520 is the smallest rocket to place a payload into orbit (2.6 tons of rocket and fuel for a 4kg payload). Maybe one could carry that with a B-52 but why bother.

So getting the rocket ship to, say 40,000 feet by hitching ride on an airplane doesn’t help that much?

 

[kuririn]

You are correct that it would be nice to have a more elegant solution for delivering payloads into space. Burning tons of chemicals uses a lot of resources and depending on the propellant can pollute the atmosphere. Also costs many millions of dollars.
But it is where our technology is currently at.
Something like this


Or this


would be more sustainable but we are nowhere close to making it happen.
But we can dream.

 

[teepot]

I think for us to be a true space faring race, and by that I mean easy access to space for anyone. It should be no different than buying a plane ticket now. To do that we need to understand gravity and be able to manipulate it. Think of a very large platform that can lift large structures to space. I have thought for many many years that UFO's and now UAP's use gravity for propulsion. At least in a gravity well. How the get from star to star would be a different matter. Lots of theories about that.

 

[cerving]

It's the velocity, not altitude, that gets you in orbit. Although it seems inefficient, a rocket is the best way to get that velocity... after you've fired your rockets for awhile, that velocity adds up real quick. Trying to put that rocket on an airplane to gain altitude does buy you some efficiencies because the air is thinner, but adds a whole lot more complexity and ultimately reduces your carrying capacity because the airplane has to lift itself as well as the rocket.

 

[neil_w]

You are correct that it would be nice to have a more elegant solution for delivering payloads into space. Burning tons of chemicals uses a lot of resources and depending on the propellant can pollute the atmosphere. Also costs many millions of dollars.

Cost of fuel for a Falcon 9 flight is estimated at about $200K, and $500K for a Falcon Heavy. Presumably a Starship flight will use more and cost more. But those numbers are actually far lower than what I ever would have guessed.

Source: https://space.stackexchange.com/que...falcon-heavy-use-what-is-the-price-rp-1#32732, agrees at a high level with numbers I've seen in the past

 

[kuririn]

Cost of fuel for a Falcon 9 flight is estimated at about $200K, and $500K for a Falcon Heavy. Presumably a Starship flight will use more and cost more. But those numbers are actually far lower than what I ever would have guessed.

Source: https://space.stackexchange.com/que...falcon-heavy-use-what-is-the-price-rp-1#32732, agrees at a high level with numbers I've seen in the past

Well then, sign me up!

 

[brockrwood]

It's the velocity, not altitude, that gets you in orbit. Although it seems inefficient, a rocket is the best way to get that velocity... after you've fired your rockets for awhile, that velocity adds up real quick. Trying to put that rocket on an airplane to gain altitude does buy you some efficiencies because the air is thinner, but adds a whole lot more complexity and ultimately reduces your carrying capacity because the airplane has to lift itself as well as the rocket.

I guess this is why Orbital Science's (now Northrop Grumman's) "Pegasus", air-launched rocket, is still pretty small. If there were a practical way to make it bigger, and thus able to put a bigger payload into orbit, they would have done it by now.

https://en.wikipedia.org/wiki/Northrop_Grumman_Pegasus
(BTW, I love that the Pegasus is launched from a converted L-1011. The L-1011 is still the best looking tri-jet ever to fly.)

 

[Cape Byron]

I'm thinking a really, really big rubber band.

Or a giant balloon lofted by the hot air from politicians.

 

[brockrwood]

Cost of fuel for a Falcon 9 flight is estimated at about $200K, and $500K for a Falcon Heavy. Presumably a Starship flight will use more and cost more. But those numbers are actually far lower than what I ever would have guessed.

Source: https://space.stackexchange.com/que...falcon-heavy-use-what-is-the-price-rp-1#32732, agrees at a high level with numbers I've seen in the past

SpaceX takes a different approach: Use conventional, vertical take off chemical rockets, but add super smart computer control and servos and such so you can land and re-use the boosters. If you can reduce the cost of the launch to just the cost of fuel (or primarily the cost of the fuel), them cost to launch goes way down. The reusability of the Space Shuttle was supposed to lower the cost of each flight but it never worked out that way.

 

[smstachwick]

SpaceX takes a different approach: Use conventional, vertical take off chemical rockets, but add super smart computer control and servos and such so you can land and re-use the boosters. If you can reduce the cost of the launch to just the cost of fuel (or primarily the cost of the fuel), them cost to launch goes way down. The reusability of the Space Shuttle was supposed to lower the cost of each flight but it never worked out that way.

The real cost inflator on the shuttle was the heat shielding, which had to be inspected and largely replaced after every reentry. A rocket vehicle in which all or most of the non-reentering parts are reusable and the re-entering spacecraft is expendable would appear to be the best solution, hence SpaceX’s work with returning boosters.

To be fair to the shuttle system, the SRBs were useable for about 20 flights, which is more than I’ve gotten out of many, many model rockets, so they weren’t entirely on the wrong track with the concept.

(BTW, I love that the Pegasus is launched from a converted L-1011. The L-1011 is still the best looking tri-jet ever to fly.)

 

[Funkworks]

So getting the rocket ship to, say 40,000 feet by hitching ride on an airplane doesn’t help that much?

I haven't crunched the numbers yet, but I don't think so. 40 000 ft is a big proportion (%) of the Karman line, but a small proportion (%) of low Earth orbit altitudes. I don't mind finding out the numbers but I can't decide if I should do it in feet or meters. Decisions, decisions.

 

[Bravo52]

I guess this is why Orbital Science's (now Northrop Grumman's) "Pegasus", air-launched rocket, is still pretty small. If there were a practical way to make it bigger, and thus able to put a bigger payload into orbit, they would have done it by now.

The Pegasus launch apparatus is a solution to a very defined problem. It was done because they could and it is more efficient based on the size and scope of the Pegasus (which had already been defined). Industry has even looked at launching orbital devices from C-17s that amounted to nothing more than pushing the booster out of the back of the plane at altitude. The carriage/release part is fairly basic and simple.

 

[brockrwood]

The real cost inflator on the shuttle was the heat shielding, which had to be inspected and largely replaced after every reentry. A rocket vehicle in which all or most of the non-reentering parts are reusable and the re-entering spacecraft is expendable would appear to be the best solution, hence SpaceX’s work with returning boosters.

To be fair to the shuttle system, the SRBs were useable for about 20 flights, which is more than I’ve gotten out of many, many model rockets, so they weren’t entirely on the wrong track with the concept.



View attachment 485456

Sorry, DC-10, the L-1011 is much cuter than you are. ;-)

 

[boomtube-mk2]

I'm thinking a really, really big rubber band.

Or a giant balloon lofted by the hot air from politicians.

How about a million really strong peasants and a big blanket.

If we continue to use rockets and aero-breaking for bringing things down, we will eventually reach the point were the "Pollution" from the burning rocket fuel becomes a measurable/significant percentage of the total "Green-House gases pumped into the atmospheres. Then there's the heat directly introduced into the atmosphere by the aero-breaking.
Currently this is negligible but if we are too get to a point where we can truly exploit our solar systems resources then we won't be launching a few rockets each year but hundreds if not thousands assuming we don't run out of the resources needed to build those numbers.

I have often thought that this is why there are no "Super-Civilizations" wandering around in the Milky Way, they, like us, hit the point where the required technology to really and truly "Get out there" is simply not available, that in this instance; the science doesn't support the imagination.

 

[brockrwood]

To be fair to the shuttle system, the SRBs were useable for about 20 flights, which is more than I’ve gotten out of many, many model rockets, so they weren’t entirely on the wrong track with the concept.

Did they re-use the big fuel tank?

 

[boomtube-mk2]

Did they re-use the big fuel tank?

No.
It was pointed out that with just a small sacrifice in payload weight, they could have put those tanks into orbit, where they could have been used in many interesting ways.

 

[brockrwood]

Sorry, DC-10, the L-1011 is much cuter than you are. ;-)

The ugliest, but most capable, tri-jet ever was Tu-154. Take a 727 but make it so that it can land and take off on an unimproved runway. In Sibera. At 40 degrees below zero. That's a Tu-154. https://en.wikipedia.org/wiki/Tupolev_Tu-154

 

[brockrwood]

No.
It was pointed out that with just a small sacrifice in payload weight, they could have put those tanks into orbit, where they could have been used in many interesting ways.

Dang. Each Shuttle launch could have used the tank as a mini-Skylab!

 

[boatgeek]

Cost of fuel for a Falcon 9 flight is estimated at about $200K, and $500K for a Falcon Heavy. Presumably a Starship flight will use more and cost more. But those numbers are actually far lower than what I ever would have guessed.

Source: https://space.stackexchange.com/que...falcon-heavy-use-what-is-the-price-rp-1#32732, agrees at a high level with numbers I've seen in the past

Part of the point of using LNG for Starship (other than less coking = easier reusability) is that LNG is cheaper than rocket-grade kerosene (aka RP-1). Starship should cost on the order of $150K for the fuel. I'm not sure if the $200K to fuel F9 includes the LOX or not, so it may not be apples to apples. Regardless, on a cost-of-fuel-per-pound-to-orbit basis, Starship will be quite a bit cheaper.

 

[boomtube-mk2]

But what is the specific impulse of LNG vs Kerosene?

A couple of N. American Class 1 railroads have experiment with the use of LNG to power their "Diesel Electric" locomotives.
It takes a separate tank-car to haul around enough LNG to replace the 5,000 or so gallons of diesel fuel a typical DE locomotive has.

 

[boatgeek]

But what is the specific impulse of LNG vs Kerosene?

A couple of N. American Class 1 railroads have experiment with the use of LNG to power their "Diesel Electric" locomotives.
It takes a separate tank-car to haul around enough LNG to replace the 5,000 or so gallons of diesel fuel a typical DE locomotive has.

View attachment 485489

That's part of why Starship and New Glenn (should it ever emerge from its burrow!) are so big--LNG isn't all that energy dense. It still appears to be cheaper per million BTU than diesel, especially once you start considering the cost of emissions aftertreatment on new diesel engines. DEF doesn't come cheap and has its own set of storage requirements.

 

[boomtube-mk2]

It still appears to be cheaper per million BTU than diesel, especially once you start considering the cost of emissions aftertreatment on new diesel engines. DEF doesn't come cheap and has its own set of storage requirements.

And yet no Class1 RR has actually taken the plunge and invested in the infrastructure required to make the switch to LNG and show no signs of doing so in the near future.