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

[boomtube-mk2]

But it is not all about going straight-up, you have to go latterly and build speed.
Not sure how any laser could do that.

Oddly enough if you could keep going "Straight-up" and away from earth and get far enough away from Earth that you are no longer attracted by Earth's gravity you could do this going 100mph.

 

[Grog6]

This is true, but you would not be in Orbit, if the power holding you away from earth goes away, you fall. If you can get the 7Miles/sec earth departure speed straight away, you would not fall back, but you're still not in earth orbit.

 

[Grog6]

I forget where I read it---possibly in Heinlein's "Expanded Universe"---but a theoretical way to reach orbit would use an extremely powerful ground-based laser that fires pulses into the combustion chamber of the rocket. The heat vaporizes fuel in the chamber with each pulse. Possibly the fuel is carried in the rocket and a portion is released with each pulse. Or possibly some of the fuel could come from the atmosphere; partly air-breathing, so to speak, until it left most of the atmosphere.

Those are all the details I remember. But it would certainly be an extremely cheap system, and could likely use any fuel. Plain water would work.

Best -- Terry

The use of any fuel is the best part, I've seen several authors postulate on Nuclear-based engines that can use anything.
Lol; I loved rereading Heinleins older stuff After I actually learned Nuclear Physics; "Blowups Happen" Read a lot differently at 40.

Niven and Pournelle's Motie books used laser drives for powering solar sails; interesting. I'm sure there are others.

 

[smstachwick]

But it is not all about going straight-up, you have to go latterly and build speed.
Not sure how any laser could do that.

Oddly enough if you could keep going "Straight-up" and away from earth and get far enough away from Earth that you are no longer attracted by Earth's gravity you could do this going 100mph.

You are ALWAYS attracted by Earth’s gravity.

Sorry, couldn’t resist. Captain Technicality strikes again!

 

[rocket_troy]

The use of any fuel is the best part, I've seen several authors postulate on Nuclear-based engines that can use anything.

I always liked the idea of using water for the propellant ie. heat it via nuclear reactor to the point of dissociation in the chamber and throat and let it (exothermally) recombine in the expansion process. This might require a long exit cone (perhaps), and it also might not be achievable - dunno. It's never been anything more than a thought bubble.

TP

 

[Grog6]

Yeah, that one would be tough for several reasons; few materials will take being hit by water when it's that hot, free radical water at high temperatures is unbelievably corrosive, and the combustion would melt most ceramics. And those issues are just the problems I've had in the past, with various things.
The NERVA rocket attempts pretty much shattered the cores, and blew them out in the desert.

 

[Jeff Lassahn]

I forget where I read it---possibly in Heinlein's "Expanded Universe"---but a theoretical way to reach orbit would use an extremely powerful ground-based laser that fires pulses into the combustion chamber of the rocket. The heat vaporizes fuel in the chamber with each pulse. Possibly the fuel is carried in the rocket and a portion is released with each pulse. Or possibly some of the fuel could come from the atmosphere; partly air-breathing, so to speak, until it left most of the atmosphere.

Those are all the details I remember. But it would certainly be an extremely cheap system, and could likely use any fuel. Plain water would work.

Best -- Terry

Someone was making the rounds at science fiction conventions and stuff a few years ago with a proposal for laser powered rockets to launch small payloads to orbit.
It was basically the Laser Thermal Rocket described here: https://en.wikipedia.org/wiki/Laser_propulsion

The design performance was limited by how hot you could run the heat exchanger, and one of the benefits is the effective Isp is a lot higher than chemical rockets, so total reaction mass is lower and the rockets are smaller.

 

[brockrwood]

Here’s an idea: Attach the tether to the Moon, not to the Earth. The Moon’s lower gravity puts less stress on the tether so you can make it out of existing materials.

https://futurism.com/scientists-cable-earth-moon/amp

 

[Antares JS]

Here’s an idea: Attach the tether to the Moon, not to the Earth. The Moon’s lower gravity puts less stress on the tether so you can make it out of existing materials.

https://futurism.com/scientists-cable-earth-moon/amp

...No.

https://what-if.xkcd.com/

 

[shockie]

SSTO is the way to go. Someday soon AI will tell us how to do it.

 

[Cape Byron]

SSTO is the way to go. Someday soon AI will tell us how to do it.

Like this?

https://en.wikipedia.org/wiki/McDonnell_Douglas_DC-X

 

[Jeff Lassahn]

Here’s an idea: Attach the tether to the Moon, not to the Earth. The Moon’s lower gravity puts less stress on the tether so you can make it out of existing materials.

https://futurism.com/scientists-cable-earth-moon/amp

If you're going to catch a cable above the atmosphere using a suborbital booster, seems like a Skyhook would be an easier way to do it:
https://en.wikipedia.org/wiki/Skyhook_(structure)Also the idea of a bunch of spinning cables attached to nothing in particular flinging stuff around orbital space seems really satisfying to me.

 

[brockrwood]

SSTO is the way to go. Someday soon AI will tell us how to do it.

We just need an air-breathing rocket engine to make SSTO happen. Must be hard to do.
https://en.m.wikipedia.org/wiki/Skylon_(spacecraft)

 

[Antares JS]

We just need an air-breathing rocket engine to make SSTO happen. Must be hard to do.

It's called a "Ramjet" or a "Scramjet," and they have been around for a long time. The huge problem with these ideas, which often gets ignored by armchair engineers, is that by not launching vertically and moving that fast through atmosphere, you are basically performing a reentry - with all the heat, drag, and aerodynamic problems that entails - in reverse, while under power, and feeding that re-entry plasma into your air-breathing engine.

The concept of a spaceplane is very, very overrated. To be practical, a space vehicle needs to get the atmosphere out of the way as quickly as possible, which necessitates vertical launch.

 

[OverTheTop]

Remember it is not a vertical launch that is needed. You need horizontal velocity to achieve orbit, which is not zero gee, just free fall. To put things in perspective the ISS has about 93% of the gravity we have acting on us on the ground.

So the horizontal component is a requirement. The launches nowadays are optimised to get the maximum out of each launch vehicle/payload/fuel combination with regard to their moving from vertical to horizontal flight.

The concept of SSTO is not dead in the water but will have different optimisation constraints compared to what traditional rockets have. Not having to carry oxygen, and its associated gravity losses, is a paradigm shift.

Think how SpaceX has revolutionised spaceflight by going non-traditional. So many naysayers quoting the inefficiencies of their system as a cause for it to fail. Look where they are now.

 

[Pete.D]

Remember it is not a vertical launch that is needed. You need horizontal velocity to achieve orbit, which is not zero gee, just free fall. To put things in perspective the ISS has about 93% of the gravity we have acting on us on the ground.

So the horizontal component is a requirement. The launches nowadays are optimised to get the maximum out of each launch vehicle/payload/fuel combination with regard to their moving from vertical to horizontal flight.

Yes the needed dV is mostly horizontal for orbital trajectories, but you need to FIRST get above most of the atmosphere to reduce drag and thermal stresses to manageable levels.

If you could develop a vehicle that didn't have to carry fuel for overcoming that drag, and didn't carry a weight penalty for the engine, heat shielding and structural components, a ramjet/scramjet (or other air-breathing engine) could work.

You've likely seen what heat and aerodynamic stresses do to our sub- and low-Mach high-power model rockets; they increase exponentially as you accelerate to orbital velocity. SSTO and Falcon would disintegrate if they had to accelerate entirely within the atmosphere; even though they go nearly straight up for the first minute of flight they must throttle down until they pass max-Q.

A better way would be to carry just reaction mass (hydrogen or water); no chemical propellants of any kind, and beam the needed energy up from the ground.

 

[OverTheTop]

but you need to FIRST get above most of the atmosphere to reduce drag and thermal stresses to manageable levels

No. You don't get above most of the atmosphere first. Look at any of the vehicle flight profiles and there is a gradual transition to horizontal, to reduce gravity loss associated with lifting the fuel. The profiles for different vehicles/missions are different, but NONE of them go up then horizontal.

 

[Pete.D]

No. You don't get above most of the atmosphere first. Look at any of the vehicle flight profiles and there is a gradual transition to horizontal, to reduce gravity loss associated with lifting the fuel. The profiles for different vehicles/missions are different, but NONE of them go up then horizontal.

Right, they can't make a right-angle turn (that would increase the aerodynamic stress excessively); it's a gradual curve. But they always get up above most of the atmosphere before they can increase speed; that's between 50,000 and 80,000 ft. They use full power to get up to Mach, then back off until they're above the high drag zone, then go back to full power.

But air-breathing engines don't work very well above 80,000 ft.

The radically different profiles aren't for orbital insertion; they're for escape trajectories.

 

[OverTheTop]

Right, they can't make a right-angle turn (that would increase the aerodynamic stress excessively)

If it is done "outside" the atmosphere as you suggest then there would be very little lateral force on the airframe. The reason they don't do it is because it doesn't make sense.

The radically different profiles aren't for orbital insertion; they're for escape trajectories.

Not necessarily. Look at the Ariane 5 flights and they even go downhill on their way to orbit, under power, for part of the flight. It depends on the mission/payload/orbit as to what works best.

But they always get up above most of the atmosphere before they can increase speed

They get above ENOUGH of the atmosphere, not most of it. Remember it is still present even at altitudes of hundreds of km where the ISS travels. It comes down to definition of "most". The rate of the gravity turn is chosen to maximise outcome for the mission.

They use full power to get up to Mach, then back off until they're above the high drag zone, then go back to full power.

Not necessarily. Some payloads cannot take the high accelerations that the launch vehicles are capable of as they are burning their fuel mass down. These flights need to throttle back for the sake of the payload, even after MaxQ.
Also, some rockets can't throttle back and thus go through MaxQ at full throttle. It comes down to the launch vehicle capabilities and strength, flight profile and other factors.



SUMMARY: It is very difficult to make generalisations without getting into details about where the generalisations are not applicable.

 

[MJW]

They get above ENOUGH of the atmosphere, not most of it.

Most as in linear elevation from ground to 'edge', no. Most as in portion of integral mass along the same line, me thinks yes. Do you have a specific flight profile and definition of atmospheric edge that you're using?

 

[Pete.D]

Not necessarily. Look at the Ariane 5 flights and they even go downhill on their way to orbit, under power, for part of the flight. It depends on the mission/payload/orbit as to what works best.


They get above ENOUGH of the atmosphere, not most of it. Remember it is still present even at altitudes of hundreds of km where the ISS travels. It comes down to definition of "most". The rate of the gravity turn is chosen to maximise outcome for the mission.


Not necessarily. Some payloads cannot take the high accelerations that the launch vehicles are capable of as they are burning their fuel mass down. These flights need to throttle back for the sake of the payload, even after MaxQ.
Also, some rockets can't throttle back and thus go through MaxQ at full throttle. It comes down to the launch vehicle capabilities and strength, flight profile and other factors.

SUMMARY: It is very difficult to make generalisations without getting into details about where the generalisations are not applicable.

It depends mostly upon the desired orbital altitude (or escape), and the acceleration.

Rockets with large boosters are essentially throttling back as their boosters complete their burn; their total thrust declines throughout the burn.

 

[MJW]

The Skylon project for SSTO and it's SABRE engine is something I'd love to see come to fruition. An Is of 3,600s at sea level is pretty much the Holy Grail of rocket engine efficiency, short of direct fusion drives with an Is of approx 10,000s obviously.

https://en.m.wikipedia.org/wiki/SABRE_(rocket_engine)

 

[RocketPro]

If it is done "outside" the atmosphere as you suggest then there would be very little lateral force on the airframe. The reason they don't do it is because it doesn't make sense.

…snip…

SUMMARY: It is very difficult to make generalisations without getting into details about where the generalisations are not applicable.

The cost of the human labor to perform all of the analyses that you mention dwarfs the cost of the consumables and is an appreciable fraction of the total cost of the LV per mission (up to 20%). Right now, those analyses are all done multiple times in a custom manner per mission. SpaceX is focused on getting the flight rate up so that those costs can be regularized to the point that they’re minimized. I know this because I‘ve bought an F9 in the last year. We’ve spent multiple millions of the purchase price already on preliminary loads, separation, and trajectory analysis.
Space is hard…

 

[OverTheTop]

The cost of the human labor to perform all of the analyses that you mention dwarfs the cost of the consumables and is an appreciable fraction of the total cost of the LV per mission (up to 20%). Right now, those analyses are all done multiple times in a custom manner per mission. SpaceX is focused on getting the flight rate up so that those costs can be regularized to the point that they’re minimized. I know this because I‘ve bought an F9 in the last year. We’ve spent multiple millions of the purchase price already on preliminary loads, separation, and trajectory analysis.
Space is hard…

I'm jealous! Good to hear you are progressing through the flight development process. Not many people realise just how much work is involved in getting these things into space. The fact that the early part of the flight is all calculated a priori (first part of flight is open-loop control) is not something many people take into account. So much more complex than HPR or suborbital shots. I wish your mission success . I hope you let us know which one it is when the time comes!

 

[brockrwood]

Remember it is not a vertical launch that is needed. You need horizontal velocity to achieve orbit, which is not zero gee, just free fall. To put things in perspective the ISS has about 93% of the gravity we have acting on us on the ground.

So the horizontal component is a requirement. The launches nowadays are optimised to get the maximum out of each launch vehicle/payload/fuel combination with regard to their moving from vertical to horizontal flight.

The concept of SSTO is not dead in the water but will have different optimisation constraints compared to what traditional rockets have. Not having to carry oxygen, and its associated gravity losses, is a paradigm shift.

Think how SpaceX has revolutionised spaceflight by going non-traditional. So many naysayers quoting the inefficiencies of their system as a cause for it to fail. Look where they are now.

I think that is the key. To not have to carry it’s own oxidizer but get it from the atmosphere saves a huge amount of weight. I guess that, theoretically, you could do that even with a vertical take off rocket, but a scramjet type design seems more feasible, no?

 

[brockrwood]

beam the needed energy up from the ground.

? With a laser of some sort?

 

[RocketPro]

I'm jealous! Good to hear you are progressing through the flight development process. Not many people realise just how much work is involved in getting these things into space. The fact that the early part of the flight is all calculated a priori (first part of flight is open-loop control) is not something many people take into account. So much more complex than HPR or suborbital shots. I wish your mission success . I hope you let us know which one it is when the time comes!

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

 

[brockrwood]

Like this?

https://en.wikipedia.org/wiki/McDonnell_Douglas_DC-X

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.

 

[brockrwood]

I was always fond of the “launch multiple smaller rockets and assemble whatever you wish in space” approach. It seems to lower the overall risk of a space launch mission.

The cancelled Constellation project also seemed like a good idea: Launch the hardware and other non-human stuff on a bigger, riskier rocket that can lift heavy things. Launch the humans on a second, more reliable, safer, smaller rocket. The humans can just dock with the previously launched hardware already in orbit.

 

[OverTheTop]

Do you have a specific flight profile and definition of atmospheric edge that you're using?

Nothing specific. As I stated earlier it is a set of trades that are made to get the most efficient use of the fuel and depends on the vehicle, payload and mission objectives.

Rockets with large boosters are essentially throttling back as their boosters complete their burn; their total thrust declines throughout the burn.

They will throttle back as necessary to protect the structure of the flight vehicle and payload. Other than that the most efficient use of the fuel is to burn it as quickly as possible to reduce gravity loss. Gravity loss is the amount of energy you need to expend to lift the fuel to the point where it is actually burned and turned into thrust.

I guess that, theoretically, you could do that even with a vertical take off rocket, but a scramjet type design seems more feasible, no?

Scramjet will change the optimisation profile for the flight. It still won't be straight up, but I suspect it will be more vertical in the early flight phase. Gain the most height to get out of the thicker atmosphere with least fuel. Same as standard rockets really, but with a tweak because of being able to gather O2 along the way, and it will also be constrained by the amount of onboard stored O2 for later phases of the flight. I suspect there are some second-order effects that will kick in too, and we could end up with quite a peculiar flight profile on that one.

I really hope the SABRE engine works its way up the TRL scale and help getting us to space.
https://en.wikipedia.org/wiki/Technology_readiness_level