A cheap and easy way to space.

[scottb50]

samkent,

The reason to go to Low Earth Orbit is that that is the place where space begins, and that is the place where we should transfer to space vehicles designed to travel exclusively in an airless environment. The current shuttle is a all-purpose vehicle, designed to reach altitudes of hundreds of miles, while carrying large payloads. We have to get away from that concept if we are going to lower the cost of putting people into space. And it is those costs which are the greatest impediment to progress off-planet right now.

I think we need just those capabilities to get from the surface to LEO and back. Beyond that we should look to vehicles brought up by a Shuttle clone and assembled in LEO. Getting to LEO and back to Earth are the two things we have to do to operate in Space. Once there it can be a simple matter of assembling vehicles from various components brought up to Leo.

 

[Jazman1985]

Halman, I also entertain similar thoughts to yours for what the safest and most cost effective Earth-LEO transportation device would be. I have heard that Single Stage to Orbit using LOX/Kerosene as fuel is just barely beyond current technology with a dry mass fraction of 7% or so. So this is where people stop? Unfortunately, engineering this type of craft is not what I am qualified to do, but it seems like instead of dividing the problem into several steps, the problem has been looked at and deemed undoable. If a dry mass fraction of 7% is unatainable, what about 15%, 10%? Are those easily feasible without having to spend billions on over-engineering? Design the highest performance possible for an orbital vehicle and then backwards engineer the first stage to compensate for the difference. A quick bit of math tells me that a dry mass fraction of 12% on a second stage should impart approximately 7000 m/s delta v to a vehicle. Meaning that a speed of mach 5 and altitude of 50,000 ft should about cover the remaining delta v. Most of this can be covered with turbojet technology developed 50 years ago. Using a flying wing and lifting body, similar to what you proposed, should increase the ease of this.

It's amazing to me that neither NASA nor a private company hasn't advanced any further on this front. Similar to what others have commented, more companies than ever before are currently building rockets. With this in mind it's really only a matter of time before someone decides to strap a few together with an airplane and figures out what the true physical limitations are. Hopefully whoever does it first will survive to return to earth and try again.

 

[halman]

Jazman1985,

Part of the problem, I believe, has been the Space Shuttle. So many people figured that it was what the engineers wanted, so doing anything better would be impossible. What is not widely known is that the Space Shuttle was the LAST thing that the engineers wanted. Politics designed the space shuttle, which is why it has been so expensive to operate. The engineers just made sure that it would work.

When a brilliant aircraft designer approached the problem of getting payload to altitude, he created a vehicle which was the first of its kind, a carrier wing. Up until the White Knight came on the scene, designers were hobbled by beliefs about what an aircraft should look like, how it should haul its payload. The White Knight has got to be one of the most efficient aircraft in the world when judged by its power to weight ratio. We have forgotten the days when engines were weak, and lift had to be created by structure, not by speed.

Mach 5 at 50,000 feet is a recipe for disaster, because the air is still dense enough at that altitude that high speeds are dangerous. But, rockets work much more efficiently in that realm than they do at the surface, and a vehicle can accelerate fast enough that it doesn't actually climb, the Earth curves away beneath it. Single-stage to-orbit designs have to deal with the high density of the atmosphere at the surface, without benefiting from that density. Two-stage to-orbit designs utilize that density for lift and oxidizer, while the orbiter does not require the huge amounts of power that a vertically launched vehicle must have to counter the force of gravity trying to pull it straight down.

We need to do everything possible to reduce the energy production requirements of the launch system. A wing could reach take-off speed on its own, but that would require a very long runway. Plus, the wing would have to support a tremendous amount of weight on its landing gear, which would make that gear very heavy in itself. By supporting the wing with a cradle that is riding on a track which is part of a magnetic catapult, we tremendously reduce the power requirements for the wing. We also have an opportunity for the wing to use fuel which it does not have to carry in its own tanks during the acceleration phase, so that it can have completely full tanks when it begins to fly.

By flying the orbiter off of the back of the wing, we can avoid losing critical altitude. We also make the design of the carrier wing less complicated, because the wing does not have to straddle the orbiter. The orbiter engines can be started and run up while the orbiter is still attached to the wing, which reduces the urgency of making sure the engines are running right when the nose is pointed at the ground. During this pre-separation burn, the orbiter engines can be burning kerosene carried in the tanks of the carrier wing, preserving its own supply.

 

[EarthlingX]

What about altitude compensating nozzle ?
http://en.wikipedia.org/wiki/Altitude_c ... ing_nozzle
If it would be possible, to get Isp over 400s at the beginning, and keep it over 400s, it would allow fuel/structure ratios over 10%.
(Single-Stage-to-Orbit)
http://www.tsinghua.edu.cn/docsn/lxx/ma ... age586.htm
If ship then refuels in orbit, it can loose most of it's speed above the atmosphere, and have much less requirements for heat shielding, and more mass available for other uses.

Biggest difference in atmosphere pressure is in the first 20 km, and we are pretty at home at that height. For example, i like the idea of a big platform, built upon a stack of helium balloons, controlled like airship, for launch platform.
Existing tech is also going through evolution, which brings lower prices and better performance.

We already did some talk about it here :
(New Shuttle, Let's dust off Venture Star!)
viewtopic.php?f=15&t=19679

 

[halman]

EarthlingX,

The primary reason for my proposal is to make access to space cheap and reliable as soon as possible. Therefore, I am against using, at this stage, anything other than standard turbopump engines, with conventional bells, that burn kerosene and lox. The advantages that theoretical designs have over existing motors is rarely substantial, while contributing to the complexity of the design unnecessarily. What we need right now is something to ferry people to and from space with, at the lowest possible price, with the highest possible reliability.

This is why the design that I champion is a two-stage system, because it creates two distinctly different vehicles for dealing with two distinctly different regimes. During the initial moments of a vertical launch, the vehicle is fighting gravity, losing 20 miles per hour in velocity every second. And that velocity is straight up, because the lower atmosphere is too dense to travel very fast in. By the time that the vehicle has entered the lower density atmosphere, it has already burned nearly 1/2 of its propellant, just fighting gravity.

By using aerodynamic lift instead of engine power, we can rise to the top of the dense part of the atmosphere without using any of the orbiter's fuel. If the orbiter can burn all of its fuel gaining speed, the amount of fuel required to reach orbit diminishes substantially. This is what the engineers back in the 1960's were shooting for when they first proposed a shuttle, and their idea is still probably the best, most achievable concept.

Single-stage to-orbit ships will come, someday. But we need cheap, easy access to space right now. to support the economic development that is so essential there. Once we create a thriving industrial zone off-planet, money for improved designs, and different designs, will be easy to get. But we need to get that economic development going to insure that we maintain access to space.

 

[EarthlingX]

Halman,

i agree, start with existing and proven, avoid unnecessary development where possible, and after do incremental evolution, like changing engine nozzle or flying computer.
I think that something very Shuttle like could be SSTO, with humans only. Getting better Isp with attitude compensating nozzle would do a lot to make it possible, but if staging is currently proven better and cheaper, so be it, while it is so.

Shuttle could be a family of ships, if money for Constellation would go to Shuttle evolution.

 

[Jazman1985]

"Getting better Isp with attitude compensating nozzle"
if a vehicle is launched at altitude(50 70 kft), should it need any compensation for altitude? Is this close enough to a vacuum to consider it one?

 

[EarthlingX]

"Getting better Isp with attitude compensating nozzle"
if a vehicle is launched at altitude(50 70 kft), should it need any compensation for altitude? Is this close enough to a vacuum to consider it one?

Sure, this is one way to solve it, but wouldn't it be much neater, if you could just adapt relatively small part of your ship, instead of creating complicated additional infrastructure ? If it can't be done, you do what you can, use what's best available thing for the purpose.

Approximately 90 % of Earth atmosphere is under 16 km, and engines adapted for that height have Isp about which rocket tech can only dream, not to mention their maturity and safety record comparing to rocket engines, so yea, why not.

Thing is, that Shuttle stack, which puts in orbit about 130t if you include orbiter, weighs around 2000t all together, and i have trouble envisioning this monster or something with similar capabilities on top of a carrier airplane. Empty orbiter (78 t) needs a jumbo for a lift.

Here is a NASA calculator to play with different nozzle configurations and altitudes:
RocketThrust Simulator
Biggest change in Isp is in lower 40 km.

 

[halman]

EarthlingX,

You have fallen into the trap which commonly gets most people considering my concept. They try to envision the Space Shuttle, fully fueled, sitting on top of a carrier wing, and boggle at what they see. So would I. The Space Shuttle is a vehicle designed to carry a large (physically and pound-wise,) payload to altitudes as high as 600 miles. It is designed for vertical take-off, so it has very large engines, which consume huge quantities of fuel. The airframe is entirely metal, and was designed with a very conservative attitude, seeing as no one had ever flown anything like it.

So, toss that image of the Space Shuttle riding on the back of a wing out the window, and imagine a much lighter vehicle, perhaps about the same size as the Shuttle, but with internal tanks instead of a payload bay. Or, a payload bay which is much smaller, accommodating a 15 passenger van-sized life support module instead of a city bus. This vehicle is built primarily of composites, and the engines are much smaller, although there might be more than three of them. Because the vehicle never has to climb straight up against gravity, total thrust to weight ratio of less than 1 to 1 is acceptable, but a ratio of .75 to 1 is desirable.

Total vehicle weight at separation would be on the order of 1 million pounds, but probably more like 750,000. That seems like a lot, but we are carrying large fractions of that amount half way around the world using conventional aircraft with only four engines. Using a specially designed airframe, and as many as 12 engines, plus a catapult to accelerate the stack to take-off speed, I am confident that we can lift a payload of 1.5 million pounds to 50,000 feet. Going any higher reduces the efficiency of the carrier wing, while imparting little benefit to the orbiter.

All of my figures are guestimates, based upon actual weights and capabilities of existing vehicles.

Space shuttle orbiter: Empty weight 172,000 pounds Maximum payload 55,000 pounds Gross lift-off weight 240,000 pounds Payload bay 15 X 59 feet Service ceiling 600 miles On-orbit endurance 14 + days with crew of 7.

External tank: 534,900 gallons Gross lift-off weight 1,670,000 pounds.

This is considerably different than a vehicle with a service ceiling of 140 miles, and a payload of 2,500 pounds, which has an on-orbit endurance capability of only 72 hours.

 

[SpaceForAReason]

I do believe that the piggy back option would certainly work but captive carry is still pretty darned effective and saver. A previous post mentioned that SpaceShip One dropped 15,000 feet. I think the figure was more like 1,500. That kind of drop is trivial and is certainly safer for the stage 1 ship. Using the atmosphere as part of the fuel saves an awful lot on cost and weight.

Another idea that had been brought up many years ago was the X-30. After the program was cancelled the x-43 took over as the technology demonstrator and reached a speed of Mach 9.68. Unfortunately they had to use a missile just to get the thing lit, but it did work. I wonder if that might be something that could be resurrected?

The X-30 was designed to have a max velocity of 23,000 mph. More than ample for any mission. The service ceiling was listed as 284 miles. Sounds like a sweet ride up if you can get it lit. I guess the engineers thought it might be a challenge: "After the X-43 tests in 2004, NASA Dryden engineers said that they expected all of their efforts to culminate in the production of a Two-Stage-To-Orbit Crewed Vehicle in about 20 years." (wikipedia)

There is still alot of research being done. Boeing is testing the hypersonic X-51 this December. Alas, fruits of these programs will likely be may years off still. That being the case I think the captive carry will be the first best method of cheap, manned space flight. Lets leave the HLV work to the big rockets... for now.

 

[Jazman1985]

I'm wondering if either a piggyback or captive carry option need to be used. What about a horizontal stack with the orbiter sitting in front of the added wing and fuel? When ready to release, use the same stage separation as they currently use. Vehicle length shouldn't be a problem, it can be made to be fatter than VTVL vehicles. Weight isn't the problem, the new Airbus A380 has a Max takeoff weight of well over 1 million pounds. I'm wondering if a vehicle about half that size would do.

 

[justdoit2]

The things mentioned in this thread seem to make so much scense why on earth, pun intended, has none of the brains at the top of the chain made this leap of faith years ago, we would be in such a good position now had this been done 10 or 20 years ago, surely we can all agree on that.

This being the case, the fact that we haven't surely means that the sooner we do, the sooner we will be in that good position in the future. Surely we can agree on that too. This being the case, can someone at the top please take all this on board and MAKE IT HAPPEN.

One thing I would say though is it's all very well being able to get a lot of manpower cheaply into LEO but they need to be able to do things when they get there which will involve lifting not just manpower to LEO but also equipment and infrastucture so presumeably we would need to have a cargo lifting version at the same time, not to be developed years later.

I think there was a mention earlier about a transfer of crew to a craft designed only to work in space which would make scense but how would such a craft get there? Could a very large rocket do the trick or are we looking at assembly in orbit and would that really be possible, just a thought. I know I'm getting a bit ahead of ourselves here but the thing is they need to be done more or less at the same time or there is no point getting the manpower to LEO.

 

[halman]

Jasman1985,

For some reason, I don't quite grasp what you are driving at. Putting the payload in front of the wing would unbalance the wing, to where it would end up pointing straight down. A wing must support its payload, either underneath it or above it. Remember, the stack is accelerated on a catapult to about 350 miles per hour, to insure that the wing has sufficient lift to climb. We are not shooting it into space directly.

 

[halman]

Justdoit2,

Welcome to the SDC boards!

Probably nothing has been done with this concept for the same reasons that the U.S. did nothing to build a space station on its own. A lack of understanding of the nature of space exploration, considering it to be just for scientific research, not for expanding the sphere of human activity beyond Earth. To date, the Russians seem to be the only folks who have a clear idea of what they want to do in space, and how to go about it.

This concept that I am advocating depends on keeping the payload of the orbiter to a minimum, so that the take-off weight of the carrier wing does not grow too large. Personally, I believe that we will eventually see a wing large enough to carry the entire 4.5 million pound Space Shuttle stack to 50,000 feet, but not for some time. For one thing, when it comes to launching REALLY large payloads, step rockets are still more efficient or cheaper than a reusable space plane, because all of the payload stays in space.

There is also an aerodynamic law which makes large rockets more efficient than small ones. Something about mass versus the cross section of the vehicle. So, we will need the Ares-5, or the Proton, or some other large step rocket to work with the advanced shuttle. This vehicle would be used for launching the Orbital Transfer Vehicles, the components for space stations, and the modules of a lunar shuttle and deep space exploration vehicle.

Once private industry has an assured way of getting its people into space, investment into space stations will accelerate. Initially, research into materials processing will be the main activity, but once materials from the Moon become available, large scale processing will begin. To insure that these space platforms are in constant sunlight, they may be put into orbit around the Sun, rather than in the Earth-Moon system. Using the Lagrange points requires some station keeping, whereas a simple solar orbit does not.

What really has me incensed is the idea that some 6 TRILLION dollars is wrapped up in equity markets (stock markets) around the world, yet money for developing space exploration systems is so hard to come by. China could fund the development of this entire system without seriously denting its foreign reserves, if we would let it. The capital outlays are not all that large, and corporations are putting up money in similar magnitudes right now in the energy industry. But so few people see any urgency to space exploration, just considering it to be regular old scientific research.

 

[Jazman1985]

Halman, what I envisioned is a Two Stage rocket(with the necessary turbojets) with a large wing running down the length of both stages. Upon separation, 90% of the wing falls away with the first stage, leaving the orbiter to burn to orbit. Using a combination of both dense and solid fuels in the orbiter(2nd Stage), and dense fuels in the first stage, keeping the C.O.G somewhat stable should be possible, considering that even empty, the first stage should outweigh the orbiter, considering the much larger wing structure. The smaller wing area on the orbiter should be adequate, considering landing weight will be significantly lower than when a fully fueled second stage. Since the orbiter has already left most of the atmosphere at separation, a large size wing relative to the full weight of the orbiter will not be useful for lift. I think the specific wing sizes and weight for reentry characteristics are going to be the most difficult thing to determine in the whole structure.

 

[scottb50]

For some reason, I don't quite grasp what you are driving at. Putting the payload in front of the wing would unbalance the wing, to where it would end up pointing straight down. A wing must support its payload, either underneath it or above it. Remember, the stack is accelerated on a catapult to about 350 miles per hour, to insure that the wing has sufficient lift to climb. We are not shooting it into space directly.


That still leaves the problem of the upper stage being released at a very low speed compared to what it would be with a TSTO. Compare the infrastructure needed for a rail launcher as compared to a vertical launch. A two to three mile rail and ramp opposed to a fairly simple launch platform. The Shuttle Launch platform would be much better if it followed the Russian model, A simple rail line to tow the launch assembly to the pad, no crawler with huge tracks, on a special roadbed, just a platform rolled along a train track.

The difference then becomes whether you use brute force or spread it out. If you use brute force you use massive force to get to a point the upper stage can be released with the maximum payload possible to get to orbit. With a rail launch you still have to compromise and make up the speed not imparted by the launch vehicle. Basically it sounds good but in reality it severely reduces the payload.

The only feasible system is basically what the Shuttle could, and was designed to provide, a huge launch stage and flexible upper stages. The payloads never evolved or were broken down into smaller vehicles to launch on other launchers.

If done right Shuttle should have been able to put any satellite into position as well as return to it for service, both of which have been proven but not exploited. There is no difference docking to the ISS then docking to any other satellite so pretty much any should be able to be reached and serviced. That alone would have extended their lifespan exponentially. That half the Shuttle bay would contain propellant tanks to extend it's range to reach the satellites was never pursued either.

That it has to be Shuttle is also not correct, it could be any vehicle, which opens the probability of a Tug. While getting off Earth is the primary problem, keeping what is off working is the next consideration. Sending up parts and sending down only those parts that need major overhaul or recycling makes more sense. Anything in LEO is an asset and cost a ton of money to get there. Why burn it up? If it could be reached and serviced it could be built a whole lot cheaper.

 

[Jazman1985]

scottb50, I think the idea is that the second stage is not released immediately at liftoff, it is released once the vehicle has reached a certain speed and altitude, presumably using the most efficient method in the atmosphere, turbojet engines on the carrier wing. Of course, it could use a combination of turbjets and rockets if that would be more efficient or could attain a high enough altitude and high enough separation speed. The main purpose is not to place something the size of the Space Shuttle in orbit, I can't see any reason we need to place 205,000 lbs(including orbiter weight) in orbit on a strictly crewed flight. Granted, if successful, any RLV could be cheaper than an ELV for sending up smaller supplies like food, oxygen, etc..., so short of large payloads like a space station section or large satellites, I can't imagine we'd need much else.

I think the orbital space tug operations you mentioned are a perfect example of what else is needed to compliment a RLV. Once in orbit at approximately 100~120 km, little delta v is required to move to a higher orbit, but something that a tug using electric propulsion could accomplish much better(and cheaper) than having to sacrifice safety in a RLV because someone tried to squeeze another 500 m/s delta v onto the vehicle.

Considering the increased safety and the size that we now know is possible with airplanes, I'm trying to figure out why air launching hasn't been done successfully yet.(with crewed RLVs)

 

[thermionic]

>>Considering the increased safety and the size that we now know is possible with airplanes, I'm trying to figure out why air launching hasn't been done successfully yet.(with crewed RLVs)

Scaled has an initiative to develop LauncherOne, using WKII to loft 200Kg orbital payloads. WKII is a pretty big aircraft, and Rutan is a smart dude. Maybe they'll eventually be able to optimize the system up to, say, 500Kg. That might be enough to get one person orbiting for a little while and back down...

 

[scottb50]

Scaled has an initiative to develop LauncherOne, using WKII to loft 200Kg orbital payloads. WKII is a pretty big aircraft, and Rutan is a smart dude. Maybe they'll eventually be able to optimize the system up to, say, 500Kg.

The problem is it would take a vehicle with more then twice the capability of WKII. A 757, modified like the Orbital L-1011 might do it, with uprated C-17 engines.

I'm trying to figure out why air launching hasn't been done successfully yet.(with crewed RLVs)

First of all air launching has been done successfully many times, X-15, Space Ship I, anti-satellite rockets fired from F-15's. It just restricts the available payload too much to consider as a launch alternative. And they all had crews that returned.

Scaled has an initiative to develop LauncherOne, using WKII to loft 200Kg orbital payloads.

That's pretty much the whole point. Look at Orbital The Pegasus XL weighs 51,000 pounds and can put 971 pounds into orbit when launched from an L-1011. The Minotour uses a two stage Minuteman booster, has an 80,340 pound launch weight and can put 1200 ponds into orbit. At 35,000 feet the Minotour is doing mach 3, instead of Mach .80. The biggest advantage is the Minotour continues to an even higher altitude and speed before it releases Pegasus.

White Knight II was developed to launch a suborbital vehicle and more then meets the requirements. That it can orbit less then 1/4 the payload of Pegasus reflects the scale of the vehicle needed for usable payloads. ISS supply needs thousands of pounds per launch and if you scale up from 200 for WKII to 971 for an L-1011 a usable payload would take one big airplane, or one re-usable first stage using rockets and jet engines.

 

[thermionic]

Yes, that was my point, if I have a point, and if I understand your point. WKII was designed from the ground up to do air-launches, yet it is only likely to be able to put an half-ton of pie in the sky. And it's more or less best-in-class at the moment. There's a reason why there haven't been crewed orbital air launches. Rutan will tell you that the biggest advantage of air-launch is safety, with flexible orbit second. 50K feet and a few hundred or thousand MPH don't make that much difference in the total energy required for orbit.

 

[EarthlingX]

Here's a result from messing with that calculator above:

After getting to 1:100 ratio at 17891,76 m, i couldn't over expand a nozzle anymore, due to the calculator limitations.

Ship would be still rather slow at that altitude to try stage separation, i think, but that depends on a total mass and fuel/structure ratio, which all together would define, how much thrust is needed for the constant acceleration.

Here is an Open Office spreadsheet i used as a basis for this picture:
http://rapidshare.com/files/298539942/V ... 0.27.1.ods

 

[halman]

scottb50,

As it was originally conceived, the Space Shuttle was not to be a heavy-lift launch vehicle. Only compliance with Air Force payload requirements made it such. Budget restrictions caused left-over Apollo hardware to be put back in service for transporting the stack to the launch site, not the desires of the engineers. What is flying now is a massive compromise, which is exactly what we should avoid.

Launching straight up means using tremendous amounts of energy, which requires the utmost in performance, absolutely perfect conditions, and very few abort options. By the time the Space Shuttle separates from the Solid Rocket Boosters, it has burned nearly half of the fuel in the External Tank, yet the vehicle is only traveling about 1 mile per second. Over 3 million pounds of the 4.5 million at launch have been discarded at that point, and 4 miles per second still must be added to the vehicle's velocity.

The speed of the orbiter at separation in my concept is inconsequential, because the orbiter is at an altitude where it can use nearly all of it's energy to accelerate, instead of expending 50 percent or more just fighting gravity. If the orbiter can reach 5 miles per second from a standing start at 50,000 feet, what difference does it make if it going 200 miles per hour or 500 miles per hour? We have to stop thinking in terms of a vertical launch, where each stage must add as much velocity as possible. The first stage, the carrier wing, is required only to lift the orbiter to an altitude where it can accelerate as rapidly as possible, not to impart velocity to the orbiter.

Until the White Knight came along, we had never seen an aircraft designed specifically for lifting mass. Every air-launch system up to that time used an existing airframe. The White Knight II still only uses two engines, in spite of the larger payload it is to carry. Burt Rutan made a remark back when Space Ship One was flying about a carrier wing with eight 747-size engines. That is the kind of power that is needed to lift large payloads to launch altitude.

Using a catapult to launch the stack has two advantages: The wing does not have to have an undercarriage capable of supporting over 1 million pounds, and a runway 15 miles long does not have to be built. Getting the stack up to take-off velocity using just the onboard engines would take a long time, and an engine failure would mean having enough runway to safely stop after reaching 99 percent of take-off speed. The catapult would support the stack, accelerate it fairly quickly, and provide a means of slowing it down in case of an abort.

 

[Jazman1985]

Just for some more information, White Knight 2 has 4 P&W 308's for a total thrust of ~28,000 lbf with a payload of ~37,000 lbs. A 747-400-Freight version has a total thrust of ~250,000 lbf with a payload of ~250,000 lbs. So the payload to thrust is quite a bit better. So, scaling up, a vehicle with a payload capacity of at least 350,000 lbs should be quite capable of being made using turbojets comparable to a 747. Considering WK1 to WK2 scaled payload 4.5 times, it stands to reason that Rutan's WK3 would pull a payload of at least 150,000 lbs. If you're going to deliver a bigger carrier airplane, you might as well make it alot bigger.

 

[scottb50]

Launching straight up means using tremendous amounts of energy, which requires the utmost in performance, absolutely perfect conditions, and very few abort options. By the time the Space Shuttle separates from the Solid Rocket Boosters, it has burned nearly half of the fuel in the External Tank, yet the vehicle is only traveling about 1 mile per second.....

Which is more than 3000 mph faster than White Knight and 200,000 feet higher.

Over 3 million pounds of the 4.5 million at launch have been discarded at that point, and 4 miles per second still must be added to the vehicle's velocity....

At 250,000 feet you are well above most of the atmosphere while at 50,000 feet you still have to expend energy to counter drag as well as gain altitude and speed.

The speed of the orbiter at separation in my concept is inconsequential, because the orbiter is at an altitude where it can use nearly all of it's energy to accelerate, instead of expending 50 percent or more just fighting gravity. If the orbiter can reach 5 miles per second from a standing start at 50,000 feet, what difference does it make if it going 200 miles per hour or 500 miles per hour?

Again you have to get considerably higher to even go that fast, the X-15 made 4519 mph and 36.3 miles, slightly below 200,000 feet.

We have to stop thinking in terms of a vertical launch, where each stage must add as much velocity as possible. The first stage, the carrier wing, is required only to lift the orbiter to an altitude where it can accelerate as rapidly as possible, not to impart velocity to the orbiter.

The White Knight II still only uses two engines, in spite of the larger payload it is to carry....

I think it uses four engines, nowhere near 747 size, used on the Falcon 2,000 and other bigger biz jets.


Using a catapult to launch the stack has two advantages: The wing does not have to have an undercarriage capable of supporting over 1 million pounds, and a runway 15 miles long does not have to be built. Getting the stack up to take-off velocity using just the onboard engines would take a long time, and an engine failure would mean having enough runway to safely stop after reaching 99 percent of take-off speed. The catapult would support the stack, accelerate it fairly quickly, and provide a means of slowing it down in case of an abort.[/quote]

I'm not disputing that, but if the first stage has jet engines only it would still need a massive upper stage to reach orbit say the equivalent of three Centaur stages or nearly 150,000 pounds of propellant, add the weight of the stage and payload and your closer to 250,000, not including the first stage.

 

[mj1]

The cheap and easy way to get humans to LEO is have a private sector company that is forced to consider its bottom line use simple, proven, and reliable kerosene-fueled rockets to put them there. We don't need the complexities and ineffeciencies of a large government space agency to do it. In fact, having NASA work on it almost guarantees that it will neither be cheap or easy because that is not how they design things.

What we DO need NASA for is the things that we haven't discovered yet. New technologies, new frontiers, new planets, new science. These are things that are difficult for the private sector to finance because there is often no profit horizon, making the attainment of investment capital problematic.

This seems to be the most senisble view I have seen in here. NASA has been there and done that with boosters. Why waste billions developing new boosters like Ares, when a company like SpaceX is already doing that faster, better, and much cheaper. Let guys like that worry about getting stuff to LEO. What we need from NASA is to start figuring out how to get a manned ship to Mars, the asteroids, and other places in the Solar system once a ship is actually IN space. They should be looking at options like down the road figuring out if and how a ship could be launched in parts by private launchers and built in space by NASA constructions crews, and then launched to points in the Sol system. NASA can work with the private contractors to insure that their boosters can get their stuff into space and spend the rest of their resources on the actual business of living and working in space, on the surface of Mars, or wherever.