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I believe I’ve found out where the extra energy is supposed to come from in order to reduce ascent times to less than a week.

The mesosphere and lower thermosphere experience heating and cooling over the course of the day, causing them to expand and contract on a daily basis (expansion during the day, and contraction at night).  This expansion and contraction occurs on a broad scale and is quite dramatic in scope.  Continuity (basically, conservation of mass for fluids) requires airflow for the uneven change in volume of that much gas.  That means wind.  However, the expansion/contraction doesn’t just occur across the day/night terminator but up and down as well.  This creates regular updrafts and downdrafts in the upper atmosphere (Upward in the day, downward at night).  The air rises and falls on a daily basis, creating a huge wave of thermal expansion that travels around the globe once per day. 

An ATO vehicle can ride this wave, gaining energy from it.

These updrafts can reach speeds of up to 100m/s, depending on latitude, altitude and time of year.  However, 15m/s to 50m/s appears to be about average.  The updrafts start to make themselves felt at 50km and can be observed as high as 250km – well above the altitude where the ATO’s terminal velocity exceeds orbital velocity.  The vehicle will not ascend much faster than this during the updraft “crest” of the expansion wave.  However, the wing area of the craft is so great that even a relatively slow updraft will carry it heavenward with more force than all the aerodynamic lift it can produce on its own, and a climb rate of 15m/s with an updraft beats the climb rate of 0.05m/s to be expected without it. 

This upward boost, once per transit around the earth, lifts the vehicle up to altitudes where its terminal velocity is faster, allowing it to accelerate more rapidly.  The boost happens relatively gradually, allowing the vehicle to accelerate up to terminal velocity and maintain lift at its new altitude.  The contraction “trough” encountered on the Earth’s night side does create a downdraft and cause the vehicle to descend, but under roughly constant density conditions (no collapse of the gas cells) and does not completely negate the gains in altitude and velocity acquired during the day.  It’s able to retain a little bit more energy from each pass of the expansion wave.

The airship is ratcheted into the sky, courtesy of the upper atmosphere’s day/night cycle, obtaining progressively higher altitudes and velocities with each pass.  Given that the vehicle doesn’t start at orbital speeds, it may be possible to use a highly inclined spiral trajectory starting at the Earth’s pole to take maximum advantage of this effect, minimizing the amount of time it spends in the wave “trough” and maximizing its time in the “crest”. 

The effect is strongest in the mesosphere and peters out near the top of the ATO’s trajectory due to thinning air. 

There are still portions of the ascent where the ATO must produce at least 80% of its own weight in aerodynamic lift alone (no centrifugal lift, updrafts, or other sources), and preferably more.  One such critical point occurs at the start of the trajectory when its buoyancy peters out before updrafts are sufficient to support it, and the other occurs at the end of the trajectory when the atmosphere is no longer dense enough for updrafts to provide any support.  However, the effect of mesospheric updrafts pretty much removes the critical points in between.

If it can surmount these two critical points in its trajectory (and I think it can), an ATO can fly to orbit in less than two weeks. 

What are the political realities driving these trends?

If you're going to drive a stake through the heart, you'd better know where to aim...

I’m continuing my own analysis of this propulsion method. 

It’s capacity is likely somewhat less than my previous estimates, primarily because it turns out that  the most obvious configurations can’t be launched from lower altitudes.  The vehicle must start from an altitude in excess of 40km.  This limits the vehicle mass to less than 200 tons, because that’s about the most that can be lifted into the thin air at that altitude..

Euler, the aerodynamic lift is indeed roughly constant, as it depends on relative velocity and engine thrust.  However, there are other sources of lifting force available during the ascent, some of them important for an airship even though they would be negligible for a garden variety airplane. 

The airship experiences forces in the horizontal and vertical directions, which can be described as the conventional Thrust, Drag, Lift, and Weight.  However, they can be further resolved into: Engine Thrust, Tail Wind Force, Drag, Aerodynamic Lift, Bouyancy, Centrifugal Lift, and Weight.  Many of them are variable, and their interplay creates several critical points in the Lift Force curve during the ascent.  Those critical points have to occur at a Lift greater than zero, or they can’t be surmounted.  Finding parameters that will get the vehicle over one critical point without catastrophically reducing available lift at the next is challenging. 

At this point, I can say that the original estimate of 5 days to orbit from JP Aerospace may have merit after all.  Wind speeds in the mesosphere and higher approach large fractions of orbital velocity, and the airship is large enough to be carried along with them just like a kite if it can be given the lift to reach them.  The centrifugal force of this motion provides additional lift, and the wind force provides far greater acceleration than can be gotten from an ion engine alone.  It may even be enough to reach orbit in 5 days.

Losing the ability to lift 1000T to orbit has reminded me that my usual success rate with evaluating such concepts is only about 50/50.  However, I still believe an Airship To Orbit vehicle of the type described by JP Aerospace can fly, and with a reasonable payload.

The airship, before launch, floats at some equilibrium altitude.  To compute it's thrust to weight ratio, it's important to note that the parameter of interest is the net weight, not just the displacement.  (Airplanes don't float, and thus have no equilibrium altitude.)  Before launch, the net weight is zero, and the thrust to weight ratio is effectively infinity.  It's not hard to get smaller than that, and any little change in lift or  weight will raise the airship (ion engine thrust, thermals, a dropped screw, etc.). 

The drag is very small as well -- nearly equal to the thrust, just a tiny amount less.  So the lift doesn't need to be stupendous, either.  The climb rate for a vehicle of this type would start out at about 2 inches per minute.  All that's required is that the tiny amount of lift developed stays greater than the net weight. 

The net weight does increase as the vehicle climbs above its equilibrium altitude, but it does not jump from zero to the full displacement at the moment motion starts.  The lift increases with altitude as well (as a result of greater speed), and does not decrease as long as the speed does not decrease and the lifting body holds its shape.  Acceleration does decrease as the net weight increases, but never quite goes to zero.  In fact, the ascent speeds up again during the last leg of the flight because the net weight begins decreasing back to zero again as the vehicle enters the microgravity conditions of near orbital velocity.

Theoretically, an airplane could do the same thing, if it could withstand the correspondingly higher initial velocities it needs to reach the same altitude.  An airship can start with zero velocity, and needn't worry about how many times the speed of sound it's travelling until it's actually ready to light its engines.

The thrust:weight and lift:drag ratios can be favorably maintained all the way up.  This thing can fly.

Now, who's interested in a 1000T to orbit heavy lift vehicle?

LOL!

Looking for a ticket back to Earth!    :laugh:

There really wouldn't be that much helium in such an airship.  Sure, it's huge, but most of that volume is filled with gas at lower pressure than on the surface of Mars. 

Hydrogen is not unusable for this application, and although it is flammable, would not be explosive or even burn particularly hot at the pressures involved.

I finally got curious enough about this scheme to crunch some numbers.  I think JP Aerospace's Airship To Orbit plan will work.

First, you should know that, while I don't know about an airship 1.6km long, it should be possible to carry this off with vessels of smaller size (closer to the size of the largest balloons flown to date, using similar materials).  The vehicles to do this can be built.

Second, drag is not a limiting factor.  Don't get me wrong: it's a factor, but it's just a parameter, not a show stopper.  The airships in question are so large that atmospheric drag quickly slows them to some terminal velocity no matter how much thrust they get.  At 61km altitude, atmospheric drag is very small, even on a 1.6km airship, but so is the thrust of an ion engine.  Shortly after starting its ion drive, the airship can expect to reach a terminal velocity of only a few meters per second.  However, the ship also gets a small amount of additional dynamic lift, which starts it ascending (also at some upward terminal velocity).  This ascent lifts the airship to atmospheric regions where the air density is lower, and thus the air drag is correspondingly less and the terminal velocity is correspondingly higher.  The vehicle goes faster as it rises.  It still feels drag and still has a terminal velocity; the terminal velocity just keeps increasing as it goes higher.

What's more fascinating, the vehicle will never quite lose all of its dynamic lift.

Drag and dynamic lift both vary linearly with air density and vary as the square of relative air velocity.  They'll stay in roughly the same proportion.  The air density varies exponentially with altitude, eventually diminishing to near zero.  But the terminal velocity increases exponentially with altitude, just on a different curve.  So the effect of diminishing air density never quite completely cancels out the effect of increased velocity on the dynamic lift. 

Similarly, because the air drag keeps decreasing as the ship climbs, the air drag never quite balances the engine thrust.  Outside of a certain range of parameters, the rate of increase for terminal velocity can eventually diminish below useable levels.  (An airship can only stay airborne for so long, and the gradual velocity increase must be sufficient to accomplish the ascent to orbit in that time, or it's all for nothing.)  However, the acceleration merely falls below useful levels; it never goes to zero.

The airship continues accelerating _and_ climbing the entire time its engine produces constant thrust.

Constant thrust is important.  A jet engine using ambient atmosphere for thrust would suffer an exponential loss of thrust as the atmosphere thinned out.  It would reach the point where it couldn't produce any useful thrust long before it had reached orbital speed.  Any engine capable of flying an airship to orbit must have its own fuel supply. 

Higher thrust is obviously better than lower thrust.  An ion engine producing 10N thrust could bring a twenty ton airship to orbital speeds in a year.  That's really pushing the envelope as far as reliability and flight time.  I think engines capable of at least 100N would be necessary for something like this, but that demands a power supply, fuel and rocket engine that a vehicle of this type might not be able to carry, and would still require a month or more of ascent time.  (The 5 days advertised by JP Aerospace is unrealistic.)

Also, it's important to note that the orbital velocity eventually attained is itself a terminal velocity.  The vehicle is so large that it still feels substantial drag at that speed and altitude.  If more thrust isn't used to ascend to a higher orbit, or the airship's envelope isn't cast off to reduce drag, air drag will eventually slow the vehicle back down and cause it to re-enter the atmosphere.  The re-entry shouldn't be violent though.  If the envelope holds together in the plasma of the upper atmosphere, it may be possible for an airship to rondevous with a smaller orbiting satellite and go right back down the way it came up.

It's slower than advertised, but it will still work.

Airships can fly to orbit.  Who knew!   

We don't need any "properly rich" Mars Society members. (Though all are welcome!  :;): )  Donations of any size greater than $1.00 can be put to use if we can get enough of them.  A trust fund would not need to start out relatively large -- $200000, or about 5% to 10% of the overall cost of a Mars Analog Research Station, will do nicely for small projects.  We can raise that kind of money -- the Mars Society has already secured sponsorships for at least 20 times that amount in less than 5 years.  There's no need to be chasing any Mars Society member around with our hands out.

So far, Mars Society membership has grown roughly linearly by about 1000 members per year since 1998.  It should have roughly 6500 members now, and this formula projects it will have roughly 7000 members by this year's end. 

If we took $1.00 US from the dues of each renewing member and each new member starting in January 2005, depositing it in an account earning 5% interest, we would accrue $100000 US from a starting balance of zero in eight years.  (This assumes membership increased at a constant rate to 15000 members in 2013.)  In sixteen years we would reach $350000, and after twenty-seven years, one million dollars.

That compares poorly with the overall cost of projects like the analog stations, but could be accomplished with no initial investment and relatively meager interest, using just 2% of membership dues.  With 4% to 6% of the dues, you could fund several small projects, provided you were willing to wait five years for each.

Regarding the quality of amateur research, no, it isn't always of the same caliber as an R&D program funded by a big corporation bent on profit any more than interest accrual over time is necessarily superior to rapid funding by a profit driven sponsor.  However, it does work, even if slowly, and in many fields it's the only thing flying.  When you find a big name sponsor willing to fund research in those areas where amateur research currently holds sway, be sure to let us know.     

I should point out that while no one can know everything, the whole 7000 and growing of the Mars Society can know a lot.  Individually, we're small, but we can think and act together and that makes us big. 

I should also point out that if you know how, it's always cheaper to build your own.  Colonization will involve mass production as much as R&D.  The Mars Society should consider how to get in on that just as much as how to conduct preliminary research.

I've been reading Frank W. Crossman's paper, ”Building Earth's Ark to Mars - Another Strategy for the Mars Society”, in the book _On to Mars: Colonizing a New World_.  The article includes a call to Mars Society members to begin their own projects, on a volunteer basis, for research and development of critical systems and mission architecture for the colonization of Mars.  He also advocates the progressive use of interest bearing investments to raise money for projects as being  superior to constantly relying on outside investors.  (See Clifford McMurray's article in the same book for a more detailed discussion).  He employs some unnecessary romanticism in his discussion of selection criteria; however, I think that his main points are realistic.  Relying on our own labor over time rather than seeking enough money to buy quick gratification, the Mars Society could advance its goals.  The time scales required are longer than the organization's current grant & sponsor oriented financing, but sustainable results become more certain.  It's just a question of which one we prefer: results or returns.  (A plan that gets us to Mars in one year has a faster return than one that gets us there in ten, but they both have the same result.)

Amateur science is my hobby.  Engineering may have been regulated to the point where only licensed professionals are allowed to practice it, but important scientific research can still be performed by twelve year old nerds studying ice cubes in their kitchen freezer.  In dealing with others with similar interests, I've learned not to evaluate anyone's observational abilities and technical skills based on who their employer is.  I have no problem believing that everyone in the Mars Society is capable of doing original research on a topic that could provide knowledge directly applicable to the colonization of Mars, without a vast budget or a new job.  There's also a lot of well developed technical expertise floating around here (professionals AND amateurs), and many of us are capable of the development of actual infrastructure useful for interplanetary colonization. 

“It's rocket science” is a description, not an excuse.  With the exception of proprietary information (which, thanks to growth of the field of rocketry, is no longer an insurmountable obstacle), there is no information that an aerospace engineer knows that you personally cannot learn and use.  This applies to any technical information that you will ever encounter in your life.  You just have to be willing to invest the effort necessary to obtain the knowledge and assure your grasp of it.  You can't ever let ignorance scare you off.  Just find something you're interested in enough to work on, reach down into yourself for the strength to admit “I don't know crap about that”, and get to work finding crap out. Do you want to know if useful amounts of food can be grown on Mars?  There are experiments you, personally, can run to find out.  Do you want to know how to build an orbital launch vehicle?  Somewhere, someone knows how, and thus you can, too. 

The members of the Mars Society can go a long way toward getting people to Mars by donating their own labor and resources to make it happen.  You don't have to work on a schedule, or even spend much money.  Just find something that needs doing or studying in order to get people to Mars, find out if you can do it, and then do it.  Make Mr. Crossman proud -- do your own R&D.  Believe me, you're able.

We could do this.  All that is required is the commitment.

One-way tickets don't promise to be cheaper than return, because of all the extra stuff colonists have to develop, test, and bring with them.  However...

Given a choice between two missions with the same cost, I prefer the one that yields a return, not just a return ticket.

Colonization is the way to go.

Hmm... Given the common occurence of the word "megawatt" in articles on the famous VASIMR drive, how much power is too much power? 

The tabletop, non-rocket version of the fusor draws about as much power as a large TV - no megawatts there.