Author Topic: Intercontinental Single-Stage Sub-Orbital  (Read 17022 times)

Offline sanman

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Intercontinental Single-Stage Sub-Orbital
« on: 01/03/2011 05:19 PM »
Tell me, would it be feasible to design a sub-orbital vehicle that could serve the rapid intercontinental travel market?

So it would take off vertically, and land horizontally somewhere on the opposite side of the world. And it would be traveling through the vacuum in between.

Imagine it being used only for cargo at first, but then much later it would eventually achieve a man-rating to allow rapid intercontinental passenger flights.

So the goal of this vehicle would not be to achieve orbit, but to provide rapid intercontinental suborbital travel/transport. We're talking about being able to land on the other side of the world in less than an hour.

Economics would dictate that this be a single-stage vehicle, for ease of turnaround.
Beyond that, what design features would this market niche role compel?
« Last Edit: 01/03/2011 05:22 PM by sanman »

Offline RanulfC

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #1 on: 01/03/2011 05:23 PM »
Well to keep you trajectory out of the lower Van-Allen belt you'd haved to shallow up the angle and probably have to have some sort of "skip-glide" air-breathing portion of the flight. IIRC you're looking at a 'cruise' velocity of Mach-6 or greater and a high hypersonic L/D in order to carry it off. (External burning fuel/air as a ramjet engine helps with the L/D issue)

Randy

Offline sanman

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #2 on: 01/03/2011 09:36 PM »
But what if we don't want an airbreathing hypersonic solution? Why must we have one?

What if you want to ballistically coast through the vacuum, to minimize your flight time?

It says here that the inner Van Allen radiation belt begins at 200km:

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

That's above LEO, so why would a suborbital vehicle be in danger of traveling into the Van Allen belts? I don't think anybody worries about SpaceShipOne/Two hitting the Van Allen belts.

The idea behind this vehicle is that it should use rocket propulsion through the vacuum in order to achieve rapid intercontinental transit.

Because it would be used for commercial transport purposes, it should be designed to maximize payload capacity. Hopefully this would not necessarily balloon the size of the vehicle, since it only has to achieve a suborbital trajectory rather than achieving orbit.


Online Jorge

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #3 on: 01/03/2011 10:15 PM »

It says here that the inner Van Allen radiation belt begins at 200km:

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

That's above LEO,


Incorrect. 200 km is not above LEO.
JRF

Offline sewand

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #4 on: 01/03/2011 11:08 PM »
Do a search on Philip Bono's Icarus/Pegasus VTOVL concepts for intercontinental sub-orbital transport.   As I understand it, he was optimistic on the mass fractions.  But they are interesting ideas... and I think suborbital transport could be the killer app for rocket transport. 
« Last Edit: 01/03/2011 11:11 PM by sewand »

Offline Ronsmytheiii

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #5 on: 01/03/2011 11:54 PM »
Well if you dont mind a vertical landing, it has already been invented:

« Last Edit: 01/03/2011 11:57 PM by Ronsmytheiii »

Offline kkattula

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #6 on: 01/04/2011 03:36 AM »
Basically, the delta-v required to go inter-continental, point to point, is quite close to what's required to get to orbit. That's why the early satellite launchers were often re-purposed ICBMs, with reduced payload.

A purely ballistic trajectory needs to go thousands of km into space.  Depressed trajectories designed to stay at lower altitudes reduce range or payload.

Another option is to launch into LEO, then do a re-entry burn after a fraction of an orbit. But that requires a full SSTO capable vehicle.

IIRC, the Saenger antipodal bomber skip-glide concept has been shown to be rather optimistic in its assumptions. Specifically in hypersonic L/D and re-entry thermal load.

Offline sanman

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #7 on: 01/04/2011 05:06 AM »
The energy requirements to go intercontinental may be similar to what's required to achieve orbit. But the market demand for rapid intercontinental transport will likely outpace demands for orbital satellite launches for quite some time.

Optimized economics trumps optimized physics. I'm assuming that a rocket-based intercontinental transport would be the most economical form of rapid intercontinental transport. Is that a reasonable assumption?

Hypersonic flight is still vapoware, but rockets have been carrying humans for over half a century. (I assume the X-15 rocketplanes were rockets and not jetplanes.)

So why not a Skylon that uses rockets instead of scramjets? What's the disadvantage from using the more proven rocket technology?


Offline butters

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #8 on: 01/04/2011 05:43 AM »
Rapid intercontinental transport via a vertical takeoff rocket is largely oxymoronic because of the logistical overhead in placing payloads on top of vertical rockets and/or erecting vehicles from horizontal to vertical.

By the time you set up the rocket with its payload and have it tanked up for launch, you might as well have sent the payload via cargo jet. Explain to me a vertical launch system that can handle 10 or more launches per day from a single pad and then maybe we can begin to consider the practical economics.

Otherwise we're talking about a horizontal takeoff system with airport-like logistics, and that to me optimizes out to something rather like the Reaction Engines A2 hypersonic transport concept that would do Mach 5 at 85,000 feet with antipodal range (anywhere in the world from anywhere in the world).

But it's still tough to sell a few hours across the world over less than 24 hours across the world if it costs several times more. Overnight intercontinental transport is quite sufficient for most time-sensitive business, and it stands to question whether the value of faster transport would be worth the associated price.

Finally, I'll just briefly note that Skylon does not involve scramjets and does indeed involve a staged-combustion rocket cycle with a precooled turborocket cycle and bypass ramjets for the airbreathing portion.

Offline kkattula

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #9 on: 01/04/2011 06:16 AM »
The energy requirements to go intercontinental may be similar to what's required to achieve orbit. But the market demand for rapid intercontinental transport will likely outpace demands for orbital satellite launches for quite some time.

What I was trying to explain is that a VTVL rocket-based intercontinental transport is effectively the same thing as a VTVL orbital transport. That's how difficult it is.

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Optimized economics trumps optimized physics.

Really? I don't understand what you mean by that, but I don't think I want to fly in your rocket. :)

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I'm assuming that a rocket-based intercontinental transport would be the most economical form of rapid intercontinental transport. Is that a reasonable assumption?

No.  Teleportation could be cheaper, and a lot faster. 

Or for a more practical solution, mag-lev trains running in vacuum tunnels at hypersonic speeds. Very expensive to build, but massive throughput of passengers.


Offline Archibald

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #10 on: 01/04/2011 06:26 AM »
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For example, a flight of about 10,000 kilometers would require a delta-V of over 7,300 meters/second, which is already about 80% of that required to reach low Earth orbit.

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During my involvement with a hypersonic vehicle program in the late 1980s, the rule of thumb was that once you got over about 5,000 meters/second, the difference between that and an orbital reentry environment were small.

There's certainly a "sweet spot" between the two - I mean a reasonable distance balanced with a reasonable speed. 
Perhaps rocket powered hypersonic point-to-point transportation could be done for a range of 1000 to 3000 km
« Last Edit: 01/06/2011 06:38 AM by Archibald »
That logarithm in the rocket equation is rather annoying...

Offline sanman

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #11 on: 01/04/2011 04:36 PM »
I don't understand how a fraction of an orbit is different from a purely ballistic trajectory - both involve unpowered coasting. I don't see why every ballistic trajectory has to go thousands of miles into space, when you can have a shallow ballistic trajectory.

Let's imagine a powered "flatter" trajectory, rather than one that goes thousands of km into space. But that flatter rocket trajectory would still for the most part take place in a vacuum, as opposed to the upper-atmospheric flight of a hypersonic vehicle.

Since it was mentioned in previous posts that a horizontal takeoff vehicle is more economical to load than a vertical takeoff one, then let's assume that one.

An SSTO vehicle is considered beyond the range of current state of the art capabilities. But there's no reason to say that Single-Stage SubOrbital vehicle is beyond the state of current technology.

Let's suppose that our SSS vehicle uses LOX-Kerosene, as an economical fuel, and is traveling from NewYork to Tokyo, or from London to Sydney.

What kind of flight time can we expect, and what kind of G-forces along the way?

Offline RanulfC

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #12 on: 01/04/2011 05:05 PM »
IIRC, the Saenger antipodal bomber skip-glide concept has been shown to be rather optimistic in its assumptions. Specifically in hypersonic L/D and re-entry thermal load.
Quite optimistic given the lack of knowledge at the time. When the idea was examined again in the late 60s the entire concept was pretty much found to be less viable than originally assumed. However, a LOT of the information was simply rejected out of hand simply because it was part-and-parcel of the concept. Another more critical review was undertaken in the late '80s to mid-'90s which used both the gained knowledge data-base and high end CFD modeling among other things to examine the idea of "hypersonic-skip-gliding" without specifically connecting a vehicle concept to the technique.

It was found that skip-gliding actually WOULD work and work quite well given some minimum design criteria and since then suggestions have been made to improve both the basic concept and to provide "up-grades" and work-arounds for some of the efficiency and Hypersonic Lift-to-Drag ratio issues.

The advanced work done in the United States was a program concept called "Hyper-Soar" which would have a hypersonic spaceplane launched from the US which would use a combination of skip-gliding trajectory and ram/scramjet "power-boosts" during the atmospheric "skip" portions of the flight, generally extending each "glide" segment and maintaining a higher average flight speed over the entire mission.

An early 2000-ish ESA report showed that a vehicle with a hypersonic L/D ratio of around 4.0 using external burning combustion during a skip-glide trajectory could do an Earth circumnavigation flight at an averge speed of Mach-10 using much less overall fuel/energy than previously assumed.

But what if we don't want an airbreathing hypersonic solution? Why must we have one?
What if you want to ballistically coast through the vacuum, to minimize your flight time?
A ballistic trajectory isn't necessarily the "least-time" trajectory in fact it is usually not. "Ballistic missile" is somewhat a misnoumer as they don't actually fly a "ballistic" trajectory but a highly depressed angle powered trajectory.

Nothing says you HAVE to have an "airbreathing" solution, you can replace the external-burning ramjet with rocket engines and just fire them at the bottom of each "skip" to re-accelerte the vehicle and extend the next glide phase. However that would require more on-board storage as you're providing both fuel and oxidizer for the engines, and you also loose the L/D boost that external burning provides. So it's a trade off.

And you DO want vacuum "coasting" time to allow radiation cooling of your vehicle between "skips" but with a purly ballistic trajectory you only GET one "reentry" event so your TPS has to be able to handle the higher-heat pulse.

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It says here that the inner Van Allen radiation belt begins at 200km:

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

That's above LEO, so why would a suborbital vehicle be in danger of traveling into the Van Allen belts? I don't think anybody worries about SpaceShipOne/Two hitting the Van Allen belts.
::::grin::: Lets recall that 100km is "officially" the start of space, and that "LEO" is not a single defined orbit and is actually a "speed" rather than an altitude :)

Having said that, common Low-Earth-Orbits usually end up being somewhere between 100-300 "nautical" miles or 115 to 300 "actual" miles or between 185-556km with the majority of orbits filling the space between the inner and outer belts simply because the air-drag below the inner belt is pretty bad at orbital speeds.

Nobody worries about a "suborbital" tourism vehicle like SpaceShip-Two hitting the Van Allen belts because their maxium altitude which is determined by their maximum speed in a Class-1 (Suborbital: Straight-up/Straight-down) trajectory is far too low to achieve the needed altitude. (SS-2 will top out at around Mach-4 or around 1.3kps)

For Class-2 trajectories, (Suborbital: Point-To-Point) which is what you're talking about, your velocities have to be higher because you are adding significant horizontal velocity as well as vertical climb. The further you "aim" to go the higher your peak altitude will be because the faster you will have to travel. In a ballistic flight path as you near speeds of around Mach-8 to Mach-10 your flight path climbs into the lower Van-Allen belt quickly.

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The idea behind this vehicle is that it should use rocket propulsion through the vacuum in order to achieve rapid intercontinental transit.
So...

1) Rocket powered take off to around Mach-4 at an angle of around 70 or more degrees to exit the atmosphere. Maximum Altitude would be around 100km.
2) Once "in-space" you apply the rockets to achieve horizontal velocity to around Mach-10. A bit more, a bit less depending on various factors but close enough for this example. Cut engines and coast.
3) Re-fire engines occasionally to adjust trajectory to increase range and avoid falling back to Earth short of your goal.
4) Reenter at around Mach-10 and slow to a glide and fly to destination to land.

Does that sound about like what you're thinking?

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Because it would be used for commercial transport purposes, it should be designed to maximize payload capacity. Hopefully this would not necessarily balloon the size of the vehicle, since it only has to achieve a suborbital trajectory rather than achieving orbit.
It would depend on a huge amount of more specific information but no matter what your overall "payload" would be less than a similar capacity/range subsonic aircraft simply because of nature of a rocket powered suborbital vehicle.

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Do a search on Philip Bono's Icarus/Pegasus VTOVL concepts for intercontinental sub-orbital transport. >>snip<<  But they are interesting ideas... and I think suborbital transport could be the killer app for rocket transport.
While the concepts are very interesting, part of the overall issue was that the only actual "suborbital" transport of the group of concepts (the Pegasus) couldn't achieve the needed flight perameters without a major boost from a rocket powered sled and track up the side of a mountain.

ALL the other vehicles were in essance Single-Stage-To-Orbit Vehicles used to provide ballistic point-to-point service instead. Even the Pegasus was designed as a viable upper stage spacecraft able to handle all aspects of orbital flight and a bit more simply because it WAS a suborbital vehicle primarily.

IS suborbital point-to-point (P2P) high-speed/fast package-delivery (as it's listed currently) "THE" killer-ap for rocket transports? Opinions still differ on the idea with major questions over the "assumption" that the world is even ready for point-to-point delivery services.

Some reading:
http://www.suborbitalinstitute.org/FAQ.html

http://www.space.commerce.gov/library/reports/2002-10-suborbital-LowRes.pdf

http://www.nss.org/tourism/Suborbital_presentation.pdf

http://www.sei.aero/com/projects/displayindex.php?id=3
(I highly recommend the papers here as the "Fast-Forward-Group" is an industry self organized group doing actual money and economic studies in order to quantify the current technical and economic challenges that need to be addressed to move this concept into reality.)

NOTE TO ALL: This is the "final" report just issued (March, 2010) by the Office of Commercial Space Transportation, FAA so is of interest to everyone.
http://www.faa.gov/about/office_org/headquarters_offices/ast/media/point_to_point.pdf

(Found here with a lot of other interesting pointers: http://www.faa.gov/about/office_org/headquarters_offices/ast/)

And a few more:
http://www.isunet.edu/index.php?option=com_docman&task=doc_download&gid=519

http://spaceinvestmentsummit.com/lcr3/presentations/7_Services_Splinter_Session_Materials/7.1_Transport_Matrix.ppt

http://dspace.mit.edu/bitstream/handle/1721.1/9253/45537132.pdf?sequence=1

Randy

Offline RanulfC

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #13 on: 01/04/2011 05:36 PM »
Rapid intercontinental transport via a vertical takeoff rocket is largely oxymoronic because of the logistical overhead in placing payloads on top of vertical rockets and/or erecting vehicles from horizontal to vertical.
While I won't argue the overall assumptions per se...

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By the time you set up the rocket with its payload and have it tanked up for launch, you might as well have sent the payload via cargo jet. Explain to me a vertical launch system that can handle 10 or more launches per day from a single pad and then maybe we can begin to consider the practical economics.
Any Soviet era ICBM site can handle multiple launchers per day with only a few hours needed to load the "next-shot" rocket with pre-packaged payload. There ARE some downsides to this as an economical example though :)

Payload intergration with rocket vehicles is CURRENTLY time-consuming simply because it is an exacting tasking with variable and complex operations and handling issues due to the very much "one-of-a-kind" payload and launcher interaction and connection. Given an actual "need" for the development of a more intergrated and faster payload system the majority of current aircraft payload operations and equipment is quite suitable for payload/launcher operations.

However this would mean actually designing and building reusable rockets and the infrastructure to go with and support them.

YOU assume that current launch operations are "required" for any vertical take off and/or landing rocket vehicle but this is simply not true. Example launch facilty for high-flight rate launch and landings? The reinforced concrete pad(s) the DC-X flew from in New Mexico proved that the currently over-regulated and quite expensive launch facilities in current use are NOT required for a properly designed vehicle. However that same pad would have to have added equipment and facilites to handle any "normal" launch vehicle so it is quite clear the launch facilites are much less an issue than the vehicles themselves.

The key is the questions of "practical-economics" and market for suborbital point-to-point versus current long range air transport.

While you feel that the Mach-5, A-2 transport would "economical" for the suggested mission however the fact that it ONLY travels at Mach-5 and remains inside and is dependent ON the atmosphere is self limiting in capability and economics in and of itself. A subsonic take-off and landing, rocket boosted suborbital vehicle with an average speed of Mach-10 actually faces less stress and is easier to engineer than the A-2 and using denser fuels would probably be smaller and carry more payload.

This doesn't mean such a vehicle has any more of an opportunity in being built, but looking at the situation honestly it is easier and more practical to build such a vehicle as I've described for long-distance fast-package delivery services than a Mach-5 air-breathing only transport aircraft.

So we are back to the original question:
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Optimized economics trumps optimized physics. I'm assuming that a rocket-based intercontinental transport would be the most economical form of rapid intercontinental transport. Is that a reasonable assumption?
Is it a "reasonable" assumption? It really depends on what your assumptions concerning the economics and market for and of intercontinental transport are, but currently the answer would be "NO" because current transportation systems and market studies show no great clamoring for faster transport.

However, there is a clear indication that industry and the market would leap on the chance to have access to more effective timely transport, but this is tempered with an overall caution due to the relative immaturity of, and lack of economic data-base for rapid inter-continental transport.
The current case stands at someone needing to "build-it" (prove out the concept AND the economics) and the market and public will come. But not until then.

Note: You wrote:
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Hypersonic flight is still vapoware, but rockets have been carrying humans for over half a century. (I assume the X-15 rocketplanes were rockets and not jetplanes.)
Learn your history! Especially if you are planning on using it to bolster your argument! :)

Point of fact: The X-15 rocket PLANES were in fact built to fly and study the hypersonic (above-Mach-5) flight regime and did so extensivly. They proved out the techniques, materials, and issues with flying for extended times at hypersonic speeds. It should be noted that almost all "manned" rockets have traveled routinly at hypersonic speeds both going into space and returning from space. Hypersonic speeds above Mach-6 have proved mostly probematical due to high aerodynamic stress and heating which is why a lot of the study for hypersonic transport systems include some means of active cooling (using the assume cryogenic fuel) or a "skip-glide" type flight to allow radiative cooling.

Hypersonic flight is NOT "vaporware" and neither is hypersonic Air-Breathing flight, but then again "intercontinental" rocket flight is on the same level being quite possible, just not proven to be economical or practical.

Randy

Offline sanman

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #14 on: 01/05/2011 04:09 AM »
Nothing says you HAVE to have an "airbreathing" solution, you can replace the external-burning ramjet with rocket engines and just fire them at the bottom of each "skip" to re-accelerte the vehicle and extend the next glide phase. However that would require more on-board storage as you're providing both fuel and oxidizer for the engines, and you also loose the L/D boost that external burning provides. So it's a trade off.

Fair enough - it's understood that rockets have to carry the extra LOX weight, since they're not burning in air. On the other hand, scramjets have to withstand the prolonged atmospheric frictional heating, which probably entails its own weight penalty. Plus, even scramjets have inferior power-to-weight than rockets, right? (I'm talking about the apparatus, not the fuel+LOX)



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So...

1) Rocket powered take off to around Mach-4 at an angle of around 70 or more degrees to exit the atmosphere. Maximum Altitude would be around 100km.
2) Once "in-space" you apply the rockets to achieve horizontal velocity to around Mach-10. A bit more, a bit less depending on various factors but close enough for this example. Cut engines and coast.
3) Re-fire engines occasionally to adjust trajectory to increase range and avoid falling back to Earth short of your goal.
4) Reenter at around Mach-10 and slow to a glide and fly to destination to land.

Does that sound about like what you're thinking?

Yes, that's it! That's roughly what I was picturing, for HOTOL.
But if you do it the DC-X VTVL way, perhaps steps 1 & 4 would be more abbreviated.


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It would depend on a huge amount of more specific information but no matter what your overall "payload" would be less than a similar capacity/range subsonic aircraft simply because of nature of a rocket powered suborbital vehicle.

Fair enough - it's understood that you'll be flying at a higher price point than regular intercontinental atmospheric flights, but on the other hand you're getting rapid transit time for that extra money. The early applications could be military of course, but then gradually infiltrate the commercial world.

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IS suborbital point-to-point (P2P) high-speed/fast package-delivery (as it's listed currently) "THE" killer-ap for rocket transports? Opinions still differ on the idea with major questions over the "assumption" that the world is even ready for point-to-point delivery services.

Well, the world should be ready to move on, since commercial air travel hasn't evolved for a long time. It's still being done the same way as it was during the 1960s. Since then, momentum has been lost. If this were still the 1960s, we would all still be marveling at the new wonders of the "Jet Age" - but a half century later, we're all yawning at the Jet Age.

With commercial air travel now increasingly a commoditized business dominated by price-wars, there should be room to compete in a differentiated and much higher-margin space, where currently no competition exists.

If you can't come up with a broader market base in the long run, then you're condemned to living at the mercy govt contracts. If Chinese and Russian launchers prove to be too cost-competitive in the space launch business, even people like Elon Musk will be reduced to showing up at congressional hearings fretting over the meager amount of govt contracts and subsidies coming his way, and will eventually quit in frustration.

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YOU assume that current launch operations are "required" for any vertical take off and/or landing rocket vehicle but this is simply not true. Example launch facilty for high-flight rate launch and landings? The reinforced concrete pad(s) the DC-X flew from in New Mexico proved that the currently over-regulated and quite expensive launch facilities in current use are NOT required for a properly designed vehicle. However that same pad would have to have added equipment and facilites to handle any "normal" launch vehicle so it is quite clear the launch facilites are much less an issue than the vehicles themselves.

The key is the questions of "practical-economics" and market for suborbital point-to-point versus current long range air transport.

Yes, this DC-X VTVL mode of transport would be an interesting one to consider for sub-orbital point-to-point intercontinental. Imagine being able to get some lifesaving medicines, supplies, or transplant organs, etc, to some other place on the globe very quickly. While converting DC-X to SSTO would be too difficult, it seems like it could be scaled up for sub-orbital flight.

Or what about even the Roton concept? Couldn't that likewise be adapted for sub-orbital point-to-point? I haven't heard anybody propose that yet. Roton ultimately could not be made workable as an SSTO, but its design could probably be adapted to achieve suborbital point-to-point.
At least Roton's overhead rotor design could be a robust way to address that "last-mile" leg of the journey (and even the "first mile" as well).


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Learn your history! Especially if you are planning on using it to bolster your argument! :)

Point of fact: The X-15 rocket PLANES were in fact built to fly and study the hypersonic (above-Mach-5) flight regime and did so extensivly. They proved out the techniques, materials, and issues with flying for extended times at hypersonic speeds. It should be noted that almost all "manned" rockets have traveled routinly at hypersonic speeds both going into space and returning from space. Hypersonic speeds above Mach-6 have proved mostly probematical due to high aerodynamic stress and heating which is why a lot of the study for hypersonic transport systems include some means of active cooling (using the assume cryogenic fuel) or a "skip-glide" type flight to allow radiative cooling.

Hypersonic flight is NOT "vaporware" and neither is hypersonic Air-Breathing flight, but then again "intercontinental" rocket flight is on the same level being quite possible, just not proven to be economical or practical.

LOL, yes, I'm aware of what the X-15 program was about - I read plenty about it as a fascinated kid. But I was talking about scramjet propulsion vs rocket propulsion. X-15 craft were rocket-propelled and not air combustion. While rockets have been flying for over a half-century, no scramjet vehicle other than the rare test model has really flown. No actual practical missions are being carried out by scramjet vehicles today. They are still for the most part VAPORWARE.

My point in saying that, is that it's more logical to try to develop a suborbital point-to-point vehicle based on the more mature and proven rocket technology, as compared to the as yet unproven, expensive and precariously complex scramjet technology.
« Last Edit: 01/05/2011 04:14 AM by sanman »

Offline kkattula

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #15 on: 01/05/2011 04:20 AM »
I don't understand how a fraction of an orbit is different from a purely ballistic trajectory - both involve unpowered coasting. I don't see why every ballistic trajectory has to go thousands of miles into space, when you can have a shallow ballistic trajectory.

Orbit is not about altitude, except that you have to be high enough that air-drag is not significant. It's about having sufficient speed that you fall around the Earth rather than falling into it.

A point to point ballistic trajectory won't quite reach orbital velocity, but has to go high to avoid hitting the Earth before it's gone far enough sideways.

A fraction of an orbit is different from a purely ballistic trajectory in that you do reach orbiat velocity, then have to fire a retro engine to reduce your speed back to sub-orbital.



Offline sanman

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #16 on: 01/05/2011 05:32 PM »
Or what about even the Roton concept? Couldn't that likewise be adapted for sub-orbital point-to-point? I haven't heard anybody propose that yet. Roton ultimately could not be made workable as an SSTO, but its design could probably be adapted to achieve suborbital point-to-point.
At least Roton's overhead rotor design could be a robust way to address that "last-mile" leg of the journey (and even the "first mile" as well).

Gee, the more I think about it, the more I like this idea. If you were to do Suborbital Point-to-Point, you certainly want a controlled landing, and even a powered landing. Coming down by parachute is too primitive.

HOTOL allows you the elegant airport departure and arrival, but then you've got to include the large heavy wings, and you need the heat shielding for a broad section of the vehicle. You may need an extra long airstrip.

The Roton concept with its overhead rotor offers the same nifty airport departure and can even land on unprepared terrain, and has a simpler trajectory, and only needs the heat shield at the bottom.

It could start out as an automated unmanned point-to-point rapid transport. Eventually,

I'm not saying that there's an immediate market for thousands of these things. But if you look at those 2 giant Antonov An-225 aircraft in existence, I'd read that they're always booked solid because of their unique ability to carry large-sized items that everybody else can't carry.

So even if you only built a dozen Roton-type suborbital rapid transports, you could probably expect that their niche capabilities would keep them quite busy. And as operations matured, operating costs would come down to reduce the pricing, resulting in more demand and more vehicles being built.








Offline baldusi

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #17 on: 01/05/2011 07:27 PM »
Or for a more practical solution, mag-lev trains running in vacuum tunnels at hypersonic speeds. Very expensive to build, but massive throughput of passengers.
I've heard a speed of 6000km/h for such trains. So you have any paper on that? South America would be the ideal place since the distance between big cities are big (thousands of km), and there are no techtonic plates boundaries.

Offline RanulfC

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #18 on: 01/05/2011 07:39 PM »
Fair enough - it's understood that rockets have to carry the extra LOX weight, since they're not burning in air. On the other hand, scramjets have to withstand the prolonged atmospheric frictional heating, which probably entails its own weight penalty. Plus, even scramjets have inferior power-to-weight than rockets, right? (I'm talking about the apparatus, not the fuel+LOX)
'Couple of points out front:

1) Scramjets aren't neccessarily needed as a standard subsonic-combustion ramjet can be effective up to speeds of Mach-8.

2) Ramjets or in fact most Air-Breathing engines can have higher Thrust-To-Weight ratios if you really need them, but the economics aren't usually there for them to be in general use. (Military engines for example)

3) Air-Breathing engines are "accellerator" and "cruise" type engines in that they steadly and efficently continue to accellerate the vehicle to the limits of their performance. This is not as much of an issue if the vehicle is using the atmosphere as a 'support' medium as well, (think "lifting-trajectory" using wing/body lift) however rockets are very inefficent at any sort of "cruise" mode and are pretty much just straight accelleration engines. They tend to require very high T/W ratios simply because they demand Vertical Take Off, high angle trajectories in order to get up and out of the atmosphere as soon as possible.

3) Thrust-To-Weight isn't as important in the type of suborbital flight we're discussing.

Drag and such for a ramjet is pretty low overall, better the more you "intergrate" the intake/exhaust system into the vehicle. An "external-burning" ramjet uses the body of the vehicle and the shockwaves generated by hypersonic speeds as the "walls" of the engine. By injecting fuel into a specific point the body/shockwave dynamics are used to compress the fuel air mixture which then uses the body/shockwave dynamics to allow optimum expansion of the exhaust.

You CAN do a skip-glide with rocket burns instead of air-breathing, but as I noted you lose some of the advantages available.

Quote
So...

1) Rocket powered take off to around Mach-4 at an angle of around 70 or more degrees to exit the atmosphere. Maximum Altitude would be around 100km.
2) Once "in-space" you apply the rockets to achieve horizontal velocity to around Mach-10. A bit more, a bit less depending on various factors but close enough for this example. Cut engines and coast.
3) Re-fire engines occasionally to adjust trajectory to increase range and avoid falling back to Earth short of your goal.
4) Reenter at around Mach-10 and slow to a glide and fly to destination to land.

Does that sound about like what you're thinking?

Yes, that's it! That's roughly what I was picturing, for HOTOL.
But if you do it the DC-X VTVL way, perhaps steps 1 & 4 would be more abbreviated.[/quote]
Step 1, not so much. Step one pretty much covers all types of "take-offs" that are possible. It only concerns itself with the portion of the flight from where you decide to start the suborbital run through the speed needed to get above most of the atmosphere.

Step 4 you just shorten the "flying" portion with a terminal velocity fall into range to restart your propulsion system for landing.

In the end the overall flight mechanix are the same.

Quote
Well, the world should be ready to move on, since commercial air travel hasn't evolved for a long time. It's still being done the same way as it was during the 1960s. >snip good stuff<
With commercial air travel now increasingly a commoditized business dominated by price-wars, there should be room to compete in a differentiated and much higher-margin space, where currently no competition exists.

One would think. Proving it however is the issue :)

[quotet]Or what about even the Roton concept? Couldn't that likewise be adapted for sub-orbital point-to-point? I haven't heard anybody propose that yet. Roton ultimately could not be made workable as an SSTO, but its design could probably be adapted to achieve suborbital point-to-point.
At least Roton's overhead rotor design could be a robust way to address that "last-mile" leg of the journey (and even the "first mile" as well).[/quote]
Actually? The original "two-person" (no cargo) ROTON was designed from the start as an SSTO vehicle. It was only when it grew bigger that it lost the SSTO ability and started having heavier issues.

I don't see any reason it wouldn't work.

Quote
My point in saying that, is that it's more logical to try to develop a suborbital point-to-point vehicle based on the more mature and proven rocket technology, as compared to the as yet unproven, expensive and precariously complex scramjet technology.

Don't get stuck on "hypersonic" meaning "scramjet" because you don't NEED scramjets to fly at hypersonic speeds. Just saying...

Randy

Offline sanman

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Re: Intercontinental Single-Stage Sub-Orbital
« Reply #19 on: 01/05/2011 08:56 PM »
'Couple of points out front:

1) Scramjets aren't neccessarily needed as a standard subsonic-combustion ramjet can be effective up to speeds of Mach-8.

2) Ramjets or in fact most Air-Breathing engines can have higher Thrust-To-Weight ratios if you really need them, but the economics aren't usually there for them to be in general use. (Military engines for example)

3) Air-Breathing engines are "accellerator" and "cruise" type engines in that they steadly and efficently continue to accellerate the vehicle to the limits of their performance. This is not as much of an issue if the vehicle is using the atmosphere as a 'support' medium as well, (think "lifting-trajectory" using wing/body lift) however rockets are very inefficent at any sort of "cruise" mode and are pretty much just straight accelleration engines. They tend to require very high T/W ratios simply because they demand Vertical Take Off, high angle trajectories in order to get up and out of the atmosphere as soon as possible.

3) Thrust-To-Weight isn't as important in the type of suborbital flight we're discussing.

Drag and such for a ramjet is pretty low overall, better the more you "intergrate" the intake/exhaust system into the vehicle. An "external-burning" ramjet uses the body of the vehicle and the shockwaves generated by hypersonic speeds as the "walls" of the engine. By injecting fuel into a specific point the body/shockwave dynamics are used to compress the fuel air mixture which then uses the body/shockwave dynamics to allow optimum expansion of the exhaust.

You CAN do a skip-glide with rocket burns instead of air-breathing, but as I noted you lose some of the advantages available.

Well, perhaps a smaller suborbital craft wouldn't bother with skip glide, just to keep things simple.

Quote
Step 1, not so much. Step one pretty much covers all types of "take-offs" that are possible. It only concerns itself with the portion of the flight from where you decide to start the suborbital run through the speed needed to get above most of the atmosphere.

Step 4 you just shorten the "flying" portion with a terminal velocity fall into range to restart your propulsion system for landing.

In the end the overall flight mechanix are the same.

Okay, but somehow it seems like unmanned autonomous flights are better suited to vertical landing, as compared to horizontal landing.

Quote
One would think. Proving it however is the issue :)

Well, hopefully Virgin/Branson will see enough demand to give a solid answer.

But I noticed that Branson had commented early on about the idea of using SpaceShipTwo for quick intercontinental travel. Obviously it's not designed for that. But it then makes me wonder if a flashy-yet-conventional enterprise like his would have more eagerly leapt at the idea of a rapid intercontinental transport over a space tourist vehicle.
Aiming at space tourism means you get to be flashy first, and worry about paying the bills later. With suborbital intercontinental transport, you get to serve a more conventional market first, to pay the bills, and you have the possibility of evolving into something more flashy and Buck Rogers later on.


Quote
Actually? The original "two-person" (no cargo) ROTON was designed from the start as an SSTO vehicle. It was only when it grew bigger that it lost the SSTO ability and started having heavier issues.

I don't see any reason it wouldn't work.

I remember reading that "2 guys and a ham sandwich" slogan for original Roton, but I recall the original design also had other hangups, like trying to position the rocket combustion chambers on each of the rotor-tips, etc. That seemed a little weird and eccentric. When they switched to the FASTRAC engine, that seemed more mainstream and sober.




Quote
Don't get stuck on "hypersonic" meaning "scramjet" because you don't NEED scramjets to fly at hypersonic speeds. Just saying...

Randy

Okay, fair enough - I see that there are probably already various hypersonic designs that use rockets instead of scramjets. But if you're going to use rockets, why not free yourself from the atmosphere and pass frictionlessly through the vacuum? Yes, you'll need to carry the LOX, but for a smaller-sized vehicle it shouldn't add too much weight.

During the early period, the market for rapid intercontinental flight would be smaller, so it could probably be served by smaller-sized vehicles.
Once that market is catered to and becomes more established and experiences greater growth, then you might want to scale up and have really large transports with greater carrying capacity. That might then push you to switch away from rocket to ramjet/scramjet, so that you could get rid of the oxidizer weight and scale up your vehicle size and capacity.

« Last Edit: 01/05/2011 09:04 PM by sanman »

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