I saw that this weeks Space Access '09 conference, http://www.space-access.org/, will have several presentations by companies working on suborbital flights for tourism.
According to this article, Virgin Atlantic is planning on marketing just suborbital flights at $200,000 and it reports a survey said orbital flights might be commercially viable at $500,000:

Space tourism survey targets cost factor.
Online results hint at future price points for suborbital and orbital flights.
By Leonard David
Senior space writer
updated 4:53 p.m. ET, Tues., Oct. 3, 2006
"Pricey seats.
"So far, orbital space tourism has been the propelled
province of well-heeled millionaires. Even for projected
suborbital jaunts — up to the edge of space and return to
Earth — the price tag for a Virgin Galactic spaceliner
seat slaps your purse or wallet for roughly $200,000.
Several key results of the space tourism survey point out:
The prices of current space treks into suborbital and
orbital are generally too high at present, with only 7
percent registering for a suborbital flight and 4 percent
for an orbital adventure at current price levels.
Suborbital flights would really take off at $25,000, and
orbital flights at $500,000, if such price levels were
compatible with an operator’s business plan. If price were
not an issue, nearly two-thirds of the respondents would
want to go on a round-the-moon adventure."
http://www.msnbc.msn.com/id/15120091/

I want to argue here that it would be feasible to provide service also for a much larger market: suborbital, hypersonic passenger flights for transcontinental and intercontinental transportation.
A round trip cross-Atlantic ticket on the Mach 2 Concorde cost around $10,000. I don't think it's out of the question that a substantial number of business executives and wealthy vacationers would be willing to pay $100,000 to make a cross-Atlantic or cross-U.S. trip that took less than an hour, especially when it included making a short stint to space in the process.
Likewise I think there would be a substantial market at $100,000 per ticket for a trip to Asia that only took 2 or 3 hours, compared to a full day as it does now.

You can make a calculation for how much fuel you would need for a rocket flying horizontally to reach a certain distance by using the rocket equation for velocity:

Vf -Vi = Ve*ln(Mi/Mf), where Vf, Mf are the final velocity and final mass, and Vi, Mi are the initial velocity and initial mass, and Ve is the exhaust velocity. The formula still works for intermediate points in the trip where you burned only a portion of the fuel, where Vf and Mf are the values at these intermediate times.
Let's say you're burning propellant at a rate r kgs/sec. Then the mass of the vehicle at time t will be Mf = Mi-rt. I'll say the initial velocity Vi is zero, and let the velocity at time t be V(t). Then the formula becomes:

V(t) = Ve*ln[Mi/(Mi-rt)]. Then we can integrate this formula for velocity to get the distance traveled, S(t):

S(t) = Ve*t - (Ve/r)*(Mi-rt)*ln[Mi/(Mi-rt)]

This formula is for the case of constant thrust, where the acceleration will gradually increase since the mass is decreasing as the fuel is used up. It might be more comfortable for the passengers if instead we used a constant acceleration flight. This would be accomplished by making the fuel flow rate, and therefore thrust, decrease as the weight decreases. The formulas for this case can be constructed in an analogous fashion to those of the classic rocket equation. I haven't calculated it but my guess is the total fuel usage would be the same as for using the fuel at a constant rate.
In any case, I will assume that just as for SpaceShipOne it will have aerodynamic shape to allow lift so that most of this propulsion can go towards providing horizontal thrust. I didn't include the drag in this first order calculation of the constant fuel rate case, but it can be added in a more detail examination. You can reduce the drag by having the craft undergo the hypersonic flight at high altitude. You can save fuel to reach this altitude by using a carrier craft such as the White Knight for SpaceShipOne. Note that you don't have to use the fuel on the carrier craft or suborbital vehicle to get to a height of say 100 km, but only to get to high enough altitude to reduce the drag and heating on the vehicle at the hypersonic velocities.
XCOR is planning on using kerosene and LOX for their engines so I'll use this type of engine for getting the Ve number. Kerosene/LOX engines can have Isp of 360 s at high altitude, which I am assuming will be the only time the rocket will be used. So Ve will be in the range of 3600 m/s at high altitude.
Let's say you want to go across the continental U.S., 4500 km. For a first generation transport vehicle let's say it's comparable in size to SpaceShipOne about 1,000 kg empty and 3,000 kg fully loaded with fuel to carry one pilot and two passengers.
Let's put in some numbers in order to calculate the distance, S(t): say t = 2500 s, about 42 minutes, r = 1 kg/s, and Mi consists of a 1000 kg vehicle with passengers and 2500 kg fuel, for a total of 3500 kg. Then we calculate: S(t) = 3600*2500 - (3600/1)*(1000)*ln(3500/1000) = 4,490,000 meters, or 4,490 km. The time of 42 minutes compares to about 6 hours for a normal passenger jet to travel this distance.
The maximum speed would be Vf = 3600*ln(3500/1000) = 4500 m/s, or Mach 15, quite a high speed. The X-15 was able to reach Mach 6.7 and was planned on being able to reach Mach 8. It had an Inconel skin with a titanium frame to resist the heat loads at these high Mach numbers.
Still for Mach 15 you might need materials even more heat resistant. In this article Burt Rutan says SpaceShipOne's carbon composite structure would not be sufficient for even the Mach 6.7 speeds of the X-15:

X-15 and today’s spaceplanes.
by Sam Dinkin
Monday, August 9, 2004
http://www.thespacereview.com/article/204/2

Still carbon-carbon composites are used for the leading edges of the wings for the Space Shuttle which have to withstand the highest temperatures of re-entry even at Mach 25, so presumably would also work at Mach 15. These carbon-carbon composites became infamous though for how they fractured under impact by foam in the Columbia accident. It turned out they are even more brittle than fiberglass.
This is a bit puzzling because the type of carbon composites used extensively for example in modern race cars is actually more fracture resistant than steel. This makes them an ideal material for race cars since they have greater strength than steel while being more fracture resistant and at a fraction of the weight. I can only assume that at the time the shuttle was being designed, these highly fracture resistant carbon composites were not available. Then the recommendation for the thermal protection is the carbon-composites of this highly fracture resistant type.
For the vehicle to be useful as a transport craft it will have to be able to take-off and land at least at international airports. Airport safety managers might not be too enthusiastic about rocket takeoff at their airports, and certainly not enthusiastic towards deadstick landings. At least for the takeoffs this uncertainly be could ameliorated by the jet engine carrier craft.
For the landings I suggest these rocket craft also have their own small jet engines so that they can do powered landings. There are some lightweight jet engines that could work for our 1000 kg first generation craft. For instance there is the TRS-18-1 engine that can produce 326 pounds of thrust and only weighs 85 pounds:

Microturbo TRS-18-1
Engine Specifications.
http://www.bd-micro.com/FLS5J.HTM#ENGINE

Two of these would probably be sufficient for landing our 1000 kg rocket plane assuming at subsonic speeds the craft had a lift/drag ratio typical for jets, which can be at 10 and above.
A more high performance and more extensively tested jet engine to use might be the PW610F. This weighs 260 pounds and can produce 900 pounds of thrust:

Pratt & Whitney Canada PW600.
http://en.wikipedia.org/wiki/Pratt_%...y_Canada_PW600

One of these would probably sufficient for our purposes. For this more high performance engine we might even be able to use it for takeoff to reach high altitude for the rocket plane, dispensing with the need for the carrier craft.
At this early stage, we would have separate jet engines and rocket engines. The jet intakes would be closed off when the rocket is operating and opened to be used only during low speed, subsonic flight. However, we can imagine with further development we would get a type of hybrid engine, as for example envisioned for the Skylon craft, where the jet and rocket engine are combined into one.


Bob Clark

I'm only glossing over all your calculations because I'm not sure if that is a major component of the feasability of the plan.

I'm looking at it from a completely different angle relating to spaceship1, and am commenting not as a "I don't think so", but more of a "I don't know how it adds up".

SS1 goes 2200mph for 15 minutes. I'm not sure how much of that is actually acceleration, but it is only to get to that speed and not to maintain the speed for any amount of time.

You are proposing a faster speed for a sustained flight. That sounds to me like a considerably larger fuel load than your calculations indicate.

The only other option is ballistic, which would take an even higher speed.

And; you are proposing doing it for half the current cost. Somethings got to be missing.

__________________
Numbers are not case sensitive. (me)

It's called realistic engineering.

Describing SS1, SS2 or even X-15 as "suborbital" can be misleading. Technically that is true -- they didn't achieve orbit. However there's a vast difference between those and a suborbital transoceanic trajectory.

The best current example we have is the space shuttle doing a Transoceanic Abort Landing (TAL). That would actually cross the Atlantic under rocket power, just like the proposed suborbital hypersonic transport.

TAL altitude trajectory peaks at about 360,000 ft (68 miles). Required velocity varies with destination landing site, but is very high. E.g, the shuttle doesn't even attain single-engine TAL (ability to cross the Atlantic with two failed engines) until about 17,000 feet per second (11,500 mph, 5181 m/s).

Your actual required velocity for a trans-atlantic hypersonic transport would be similar to the shuttle's TAL abort MECO (Main Engine Cut Off) velocity. I don't remember that off hand, but it's close to orbital velocity.

Reentry heating and required thermal control for a TAL trajectory is similar to orbital entry, actually worse in some ways.

The required vehicle would be nothing like SS1, SS2, or even the X-15 in terms of energy required, thermal protection, etc. It would be more like the current space shuttle on a TAL abort.

However this same exercise shows a hypersonic suborbital transport is potentially feasible both technically and (surprisingly) economically.

Technically it's feasible since it has already been achieved -- the shuttle TAL abort.

Economically the shuttle's marginal launch cost (incremental cost of adding a single flight) is around $200 million -- and it's not a cheap vehicle. From a mass standpoint, the shuttle could carry 200 people in the cargo bay. They wouldn't all fit, so it's space-constrained.

If you could cram 50 people in there, for $4 million per ticket, the shuttle could be a suborbital transport right now.

If a vehicle not even designed for that role could approach that goal, it's logical a safer, cheaper, purpose-built vehicle is possible.

Something like a properly-designed, scaled-up, passenger-carrying X33 might work.

You need to take into consideration the Isp of the engine for the fuel requirements. This is a measure of how much fuel you need to reach a specified thrust. The SpaceShipOne engine specifications are given here:

Scaled Composites SpaceShipOne.
Specifications.
http://en.wikipedia.org/wiki/SpaceSh...Specifications

SpaceShipOne uses an engine with an Isp of 250 sec, significantly lower than the Isp possible with kerosene/LOX engines when used in vacuum (actually near vacuum) of about 360 sec.


Bob Clark

Ok, so that's about 1.4x the efficiency.
But; we are talking 5x just the speed alone. More for extra fuel, and more for distance.

__________________
Numbers are not case sensitive. (me)

That is an important question you ask. The overwhelmingly key fact that makes space travel to orbit difficult is that the defining equation for rocket travel called the "rocket equation" specifies that the amount of fuel you need to reach a certain speed increases exponentially with the speed. Since the speed to attain orbit is so high, this means at least for a rocket you may need 10 times as much weight in fuel as what you wish to get in orbit.
There is also an exponential dependence on the velocity of the exhaust, i.e., small changes in the exhaust velocity causes exponentially large changes in the fuel required. This is true for all speeds not just the speed to reach orbit. So the difference in Isp from 250 s to 360 s which corresponds to a difference in exhaust velocity from 2500 m/s to 3600 m/s results in a large difference in the amount of fuel required.
See the explanation here:

Tsiolkovsky rocket equation.
http://en.wikipedia.org/wiki/Rocket_equation


Bob Clark

Right. I'm not sure the calculations which is why I'm giving vague references. But; you have me confused as to what your OP is about.

All I'm saying is that the SS1 comparisons of weights in the OP don't add up considering these issues.
I read the following that you can add 500kg of fuel to SS1(or equivalent craft) and reach 5x the speed.

__________________
Numbers are not case sensitive. (me)

I've never thought of it like that! So we have a vehicle capable of point to point suborbital travel already, it's just not it's main function.
Would there be enough people needing and able to pay 4 million or so a flight to get to their destination in a couple of hours? I'm sure among businessmen and politicians there'd be some who value in person negotiations enough to pay, but would that be enough market? I'm sure there'd be military interest.

__________________
For me it's enough for the garden to be beautifull; why do so many want to see fairies at the bottom?

"Many of those people are not getting four when adding two and two; many of them aren't even getting five or twenty-two. They're getting potato."
Gillianren

Thanks. Some good points.
The focus of the suborbital flight companies is just on tourism: you go up, take a look at the black night of space and come back to where you started from. But it's obvious that there would be a much bigger market if the passengers could actually travel somewhere they needed to get to quickly.
BTW, in your estimation of the speeds needed to make the hypersonic flight transatlantic, remember we are only going high speed to make the travel time short. We could of course even go subsonic and get across the Atlantic, as is done now. We don't necessarily even have to go to the altitude to be considered space, just high enough to reduce the drag at the highest speeds of the trip.
In the example of the shuttle TAL that's for when you cut-off the engine and the vehicle glides the rest of the way. However, you can in the case of the hypersonic transport trips have powered flight the entire trip.


Bob Clark

The year is 2009 and not 1969. The population no longer worships at the feet of technology whether it be the Concord or the 'tallest building'. Bigger and faster had better have much better 'raison d'tre' than being the latest thrill for the rich and famous. Getting a businessman to Tokyo in half the time just won't cut it.

There are so many regulatory issues that this is dead in the water. The safetyhoops to take on paying customers as the focus would be insurmountable. These aircraft would just not have the numbers or infrastructure to even begin to meet safety standards. Large airlines with fleets of hundreds of planes can barely do it now.

No, a few tens of thousands of passenger seats in not enough....one needs repeat business and yes, the Concord 'only' cost ten thousand...but no, it was rarely full. Wealthy people are wealthy because they DON'T spend a hundred thousand on a seat when they can pay 900 for a first class ticket on a passenger airline. AND...as of this latest economic crisis no executive of any major corporation would fly at a hundred thousand since out of PR necessity many of them are now flying economy class instead of first class.

If someone wants to invest billons in airflight today. It should be, as in the automotive industry, in methods to improve energy efficiency. The Concord would not be approved today...too inefficient, too noisy and so on. For the rest of this century any large technology developments are going to have to jump environmental hurdles...PR hurdles and so on. Grandma won't be taxed for turning her thermostat up while the wealthy jaunt around in hundred thousand dollar seats.

No, there wouldn't be. Seriously - the training, checkout etc for a sub-orbital flight like that will totally eliminate any possible savings.

LHR - LAX on a Jumbo is 11 hrs on a bad day. Add on 3 hrs checkin and baggage claim - 14 hrs. basically, a full day.

Now imagine a vehicle that's only slightly less performance orientated than a full space shuttle orbital launch - the training, the fitting out of suits, the safety briefings...that, in itself, is a day, maybe a week.

What possible benefit is there for long distance travel (the answer is none)

Sub-orbital joyrides in the SS2 / Lynx style will be it for a very VERY long time to come.

When I was a kid, you could fly to New York in 2 hrs 59 minutes.

Now, check in for that route opens 3 hours before take off.

Think about it.

The regulatory, safety and financial issues are being resolved for Virgin's SpaceShip 2: http://en.wikipedia.org/wiki/SpaceShipTwo

Virgin plans on a fleet of 3-5 vehicles and beginning passenger service by 2011.

Why would the regulatory and safety issues differ for a transatlantic flight vs SpaceShip 2's up/down trajectory? In both cases you're carrying paying passengers, the only difference is the velocity and destination.

Ridiculous. Of course the two are different. If an airline had a crash every 50 or so flights it would be bankrupt in 2 seconds and have FAA launching massive investigtions as to how the aircraft was ever approved in the first place. Even if an an airline had a crash every 5,000 flights the same....immediate grounding forever.

Yup, save a couple of hours but go through a weeks training and full medical before and after every flight. You have to be kidding. 'Bye, dear I'm off to a meeting in Tokyo...it's three weeks from toady so I better get off to training school now....also, don't want to miss the special rates....only $100,000 if one stays only an extra month while the aircraft is refurbished'.

The most technically developed ideas for ballistic transport AFAIK were Pegasus, Ithacus and Hyperion...

http://www.astronautix.com/craft/pegvtovl.htm

http://www.astronautix.com/lvs/ithacus.htm

http://www.astronautix.com/craft/hypnssto.htm

Thanks for that. Hadn't heard of those before.


Bob Clark

None of two I mentioned were a conventional airliner.

You said regarding a hypersonic transport: "There are so many regulatory issues that this is dead in the water. The safetyhoops to take on paying customers as the focus would be insurmountable."

My point was SpaceShip 2 is a hypersonic transport, albeit not transoceanic. It's not dead in in the water due to regulatory issues. It plans on taking paying customers.

Since this is already in progress, how can it be "dead in the water"?

If you mean a transoceanic hypersonic transport, how are the regulatory and safety issue different between that and SpaceShip 2? They both carry passengers, are both hypersonic and both suborbital. They differ only the max velocity and destination.

What exact regulatory issues would render a transoceanic hypersonic passenger transport "dead in the water", and not likewise affect SpaceShip 2?

You're right. The increase in the engine exhaust velocity is not enough to explain the difference. For SpaceShipOne the entire purpose is getting to that high altitude of 100 km. So alot of the thrust is working against gravity. And since its engine is lit at about 41,000 feet, about 14 km, there is still a alot of air drag in the initial part of the trip.
For the transport flight in contrast you don't need to get to the altitude of 100km. You can use your carrier craft to get you to the high altitude you need and the entire rocket thrust would be used just for increasing your horizontal velocity.


Bob Clark

Just saw this article on Rocketplane XP, which plans to offer suborbital, tourism rocket flights, while using jet engines for take-offs and landings:

Rocketplane reset
by Jeff Foust
Monday, November 5, 2007

The revised Rocketplane XP design (above) is intended ultimately to be more competitive in the emerging suborbital space tourism conference.
http://www.thespacereview.com/article/994/1

The Second Space Age.
March 6, 2008
Patrick Mahoney
"Ready for a space cruise? The technology is taxiing to the runway."
http://machinedesign.com/article/the...space-age-0306

Rocketplane XP's current design was modified from the original Lear Jet base airframe but still has the look of a passenger business jet, with a rocket in the tail.
It has some titanium and steel portions to withstand the heat of reentry in addition to an aluminum frame. This makes it heavier than a Lear Jet and it has to use a long military base runway for take-offs and landings. However, quite likely if it used all composite materials, as does SpaceShipOne, to replace the heavy steel, titanium, and aluminum it could take off and land from a standard sized airport runway.


Bob Clark

The Europeans have also proposed a business jet model for a suborbital tourism rocket:

DATE:14/06/07
SOURCE:Flightglobal.com
PICTURES: Astrium aims for 2012 suborbital tourism flights.
By Rob Coppinger

The space jet will take off from a conventional runway, powered by two jet engines, and fly to 39,300ft (12,000m), where it will ignite its liquid oxygen, methane rocket engine providing an ascent acceleration of 3g. After 80s the jet will reach 196,000ft and coast to its apogee.
http://www.flightglobal.com/articles...m-flights.html

Interestingly, they consider this as a precursor to a point-to-point transport.


Bob Clark

I agree, but a very long time isn't never, and at least this wild idea has a functioning, if totally impractical, example.
If one day you could walk onto a craft like we do 747's, and developments in related areas (like orbital and suborbital tourism) brought the cost of the technology down, and it's reliability and performance up, I expect someone would be there to make money from it.

__________________
For me it's enough for the garden to be beautifull; why do so many want to see fairies at the bottom?

"Many of those people are not getting four when adding two and two; many of them aren't even getting five or twenty-two. They're getting potato."
Gillianren

Another article on the proposed Astrium suborbital, tourism rocketplane:

Space planes 'to meet big demand'.
By Jonathan Amos, Science reporter, BBC News
Monday, 17 March 2008, 13:38 GMT
"Aerospace giant EADS says it will need a production line of rocket planes to satisfy the space tourism market."
http://news.bbc.co.uk/2/hi/science/nature/7298511.stm

There is a link to a nice video of a simulated flight on this page. In the video the passengers are wearing helmets with closed visors. But it doesn't look like they are wearing actual spacesuits with independent air supplies because the helmets are not connected to the rest of the suits. The helmets have more the look of motorcycle helmets. I don't know if this is really supposed to be accurate.


Bob Clark

Another suborbital, tourism rocket plane based on a business jet model:

Bristol Spaceplanes - Ascender.

http://www.bristolspaceplanes.com/pr...ascender.shtml

There have been several studies showing just for tourism there would be a sufficient market for such suborbital flights to be profitable. I have to think there would be a bigger market for cases where the traveler would actually want to go somewhere and this method could get him there in 1/10th the time.
As a point of comparison I did a search on the Japan Airlines site for round trip business class tickets from my town of Philadelphia to Tokyo.
It ranged from $6,600 to $21,000:

Note also, that the $200,000 ticket price mentioned for suborbital flights on SpaceShipOne is only for the first few flights. After, a few years the price is expected to come down to $20,000.


Bob Clark

Another suborbital tourism project was posted on the SpaceFellowship.com forum:

Project Enterprise.
http://www.european-spacetourism.eu/index2.html

I noted in their simulated video of the trip, it has the passengers wearing oxygen masks.


Bob Clark

In this animation of the SpaceShipTwo trip, the passengers also do not appear to be wearing actual spacesuits, though they do have helmets:

Virgin Galactic SpaceShipTwo Animation.
http://www.youtube.com/watch?v=Cw1WaW8JsFs


Bob Clark

I have always liked this idea since I read about it in Heinlein's book, Friday. He didn't explain the technical details, just the basics of how it was part of the infrastructure.

That is, perhaps, where this argument should begin. We know it's techically possible. What we need to know is if it is financially plausible. Start by estimating the market and the potential demand. Include other issues not related to the technology, such as time and space and infrastructure restraints as well as possible regulatory necessities.

A purpose-built point-to-point hypersonic transport will not look like the Space Shuttle or those other ballistic rockets shown above. If it spends a lot of time in the hypersonic flight regime, it will probably best resemble a wave-rider (an inverted half-cone that creates compression lift) or something that resembles the simpler Sears-Haack body with wings, like the Skylon.

I also wouldn't consider the costs of the SST as much of that is government waste and labor retention. You need to estimate realistic fuel and labor costs for operations, while amortizing R&D (unless subsidized by a government) in order to arrive at an estimated ticket cost that is within an order of magnitude of reality. Additional real costs would be infrastructure acces and regulatory fees, security, etc.

Boarding and loading times will vary depending upon the capacity of the vehicle. The mention of 3 hours for pax is due to issues of security, curb-to-gate pedestrian transit time, general queing time, vehicle turn-around-time and built in delays, and actual boarding and loading time. If you plan to shuttle hundreds of people in one of these proposed vehicles, then it may take a while to load. So, if you load fewer people, the time is reduced. Howeover, if you require larger runways or other facilities more distant from the airport, then intra-terminal transit time can increase, or costs may increase if you desire to install a rail-line in between.

Life and health concerns are valid, but may not need to be prohibitive. Roller coasters already exclude people based on height and post disclaimers regarding ailments that may be problematic. Current air travel can be problematic for certain people. Deep Vein Thrombosis is also a risk of air travel, but that does not prevent airlines from operating or people from taking the risk. A viable business model will need to use a technology that does not require weeks of training, and/or include the cost of lobbying for regulatory changes to remove a training requirement. Pressure suits may or may not be required, depending on regulations and risk assessments and backup systems and probabilities or breach-and-repair or breach-followed-by-catastrophic-failure (in which case a p-suit is useless). A helmet-alone may indeed be more helpful on a mass/usefulness risk assessment.

__________________
"What you think you thought you saw you did not see." Agent J, MiB - Manhatten Bureau

But enough to count for 80% of the thrust?
Just exactly how high would the carrier get you? And how much of that drag is reduced?
Sure you can reduce some, but the very reason you have drag is the very reason the mother ship can carry the craft in the first place.
I would imagine that SS1 is near that point of diminishing returns now.

__________________
Numbers are not case sensitive. (me)

The velocity requirements to overcome gravity and drag just for getting to the altitude for space are quite high, nevermind that required for orbital velocity:

Delta-v budget.
"The delta-v requirements for sub-orbital spaceflight can be surprising. For the Ansari X Prize altitude of 100 km, Space Ship One required a delta-v of roughly 1.4 km/s. To reach low earth orbit of the space station of 300 km, the delta-v is over six times higher -- 9.2 km/s.
Launch/landing budget
* Launch to LEO — this not only requires an increase of velocity from 0 to 7.8 km/s, but also typically 1.5–2 km/s for atmospheric drag and gravity drag"
http://en.wikipedia.org/wiki/Delta-v...ral_principles

I'm estimating an altitude for low drag transport flight in the range of 100,000 to 150,000 feet, 30km to 50 km. Remember all the energy for getting to this altitude is made by the carrier craft. The U-2 and SR-71 aircraft were capable of reaching 85,000+ ft with payload. This was using 1960's technology, with steel, aluminum, and titanium materials.
Using all composites they could be made significantly lighter and very likely could reach 100,000 to 150,000 feet with payload. A variant of a 1960's era Russian aircraft, the MiG-25, was already able to reach 120,000 ft altitude in a test flight in 1977:

Mikoyan-Gurevich MiG-25.
# 1.2 Aircraft design phase
http://en.wikipedia.org/wiki/MiG-25#...t_design_phase

The air drag is linearly dependent on air pressure. This page gives some air pressure values at altitude:

Atmospheric pressure.
http://en.wikipedia.org/wiki/Atmospheric_pressure

Judging from the information there, the pressure at 41,000 feet where SpaceShipOne is released is between 1/5th to 1/10th that at sea level. However, the pressure at 100,000 feet is 1/100th that at sea level, and at 150,000 feet it's 1/1000th that at sea level. Keep in mind though that in my estimate of the fuel requirements I didn't include the extra amount that would be required to overcome drag.


Bob Clark

None of the new space tourism rocket planes can really be compared to a hypersonic transport. Really, the only design I've seen that would ever be practical and cost effective is the Reaction Engines A2.
http://en.wikipedia.org/wiki/Reaction_Engines_A2

__________________
"Duct tape is like the Force. It has a light side, a dark side, and it holds the universe together." -Carl Zwanzig

In their usual good reporting, the BBC discusses directly the safety issues for these suborbital tourism flights:

Space ships: the next generation - Space Tourist- BBC Science & Nature.
http://www.youtube.com/watch?v=g_ROk...eature=related

Bob Clark