A TWO STAGE SYSTEM with catapult (SEE one stage Nuclear later)
The present excessive cost of launch in $/ kg in low earth orbit (LEO) is much too high. This is a result of a series of very bad political decisions and wishful thinking on the part of politicians who were NOT scientists and wanted - even demanded - single stage to orbit. That just is not the best way to go. They were told that repeatedly, and they ignored the advise of numerous major contractors who were almost unanimous in the right way to get low cost launch. This was very thoroughly studied between 1959 and 1970 by Boeing, Convair (General Dynamics), Lockheed, etc. and they all came up with a two stage system,
The space shuttle was a politically proposed monstrosity, a "stage and a half" system which was selected by those half wits who "wanted" single stage to orbit. It was an ill advised emotional decision that resulted in the cost nightmare we now are using.
Multistage rockets, like the Saturn V system and the failed Russian (Soviet) equivalent could launch large payloads into orbit for about $2000 per Kg. (all costs here are on 1999-2000 basis $). That is just the cost of any purely rocket system. It suffers from the huge first stage fighting gravity and you expend 3/4 the total weight (that huge first stage) just to get to 15,000 meters (50,000 feet) and mach 2. It is an absurd option. Yet we continue to do that because we have done it that way in the past.
A better option is to use WINGS, and an aircraft lower stage, letting the air provide both oxidizer (80% of the fuel weight in a rocket system is LOX) as well as primary lift to gain initial altitude and speed.
The technology and materials used in that first stage winged vehicle will fix the staging altitude and velocity. For B-52 mach near 1 we stage at 50,000 ft. For an aluminum vehicle (ignoring cooling of structure) the speed limit before melting / softening the skin of the vehicle is about mach 2.7 which stages at about 100,000 feet. Un-cooled Titanium (think SR-71) allows mach 3.5 and about 120,000 feet. There is a distinct flight corridor that demands the mach number match a certain altitude. Try to fly any lower, the dynamic pressures get too high and the structure becomes excessive. Go any higher and you run out of air. The velocity rams air efficiently only in such a way that the flight corridor narrows at higher mach numbers to a rather narrow altitude zone on the fringe of space. Titanium cooled with a hydrocarbon fuel (thermally stable Jet Fuel like JP7X or JP7 TS) allows mach 5 and 125,000 ft. Ti with liquid methane (LCH4) allows mach 7 (Aurora type vehicles). and 120-130,000 ft. Liquid hydrogen (LH2) allows mach 12 and 125-135,000 ft. Note the velocity is determined by the heat sink available.
LH2 has the highest heat sink, and also the highest heat of combustion, (50,000 BUT/Lb) but demands super insulation (14 degrees K boiling point - demands vacuum, as air is a solid at that temperature) thus increasing structural weight. LCH4 is next best with more moderate insulation demands and second best heat of combustion 35,000 BUT/lb and JP7 TS is least with 20,000 heat of combustion. Any of these can be made to work. As a matter of practicality since we have experience with LCH4 - it is cheap and plentiful, that probably is the better choice. Any velocity difference at staging is made up by shifting weight from the lower winged stage to the second stage vehicle, so the staging velocity is not all that critical.
The upper stage that goes to orbit will still look very like the Space Shuttle. That shape is fixed by re-entry conditions. It is winged for both airlift goign out and re-entry.
The upper stage will almost certainly be LH2 rockets with perhaps an Supersonic Combustion Ramjet (SSCRJ or Scramjet) for initial boost to orbit. Tests of Scarmjets to mach 12 and beyond have already been done so the range between mach 7 and mach 12-15 can be Scramjet. The final delta V to orbit must be rocket in any case. LH2- LOX is always the economic winner there. Once you have paid the price of lower stage energy you can not afford anything but top performance and LH2- LOX gives that at lowest risk cost.
There also is one more option, correctly proposed (Prelude to Space) by Arthur C Clarke (father of communications satellites - for which he got not a dime) and that is a catapult system for the initial boost to about mach 1. The gourd based catapult can be built very cheaply with highway construction brute force technology; it never flies so weight is no problem. Just build it as strong as is required,. That allows major reduction in landing gear and associated structural weight as it no longer has to carry full take off weight, only empty landing weight That also gets rid of a "low speed propulsion system" to get to mach 1. The propulsion weight fraction thus drops, allowing more "payload".
The best guess for 2 stages + catapult launch cost is about $50-100 per Kg. That is more than a decimal point below Space Shuttle costs ($2500/kg) . There also is a lowest possible cost limit. Taking the energy required, E= 1/2 m v2 and knowing orbital velocity and the lowest cost of energy just paying for the energy demands about $2 to $4 per kg into orbit. So the proposed launch system is only about 10% efficient, at best, but that is better than ten current 1% efficient systems!
In the Motion Picture 2001 a Space Odyssey Arthur C. Clark used a nuclear powered vehicle to get to a space station. Arthur C. Clark has probably not been adequately appreciated. He for example invented orbital satellite communications, a multi billion-dollar industry giving global real time communications, and cheap Internet to anywhere. He also got the launch vehicle right.
In the late 1950’s there was a project ANP Airplane Nuclear Powered. One of the first things President J. F. Kennedy did was to cut the program. It was an Eisenhower left over and politically incorrect. It was incorrect more than one way, as the Soviet Union had built a nuclear engine and tried to test it. It stalled, went into meltdown, and went nuclear supercritical, killing about half the Soviet upper military brass in the resultant atomic explosion.
That was a Khrushchev bragging point that literally blew up in his face while he was at a UN Meeting (the one wit h the shoe pounding). He had planned to announce the USSR had a nuclear aircraft engine, and instead had a sudden silence, and over the next few weeks over 20 generals died in “airplanes crashes” etc. They never did admit to the disaster until after the collapse of the USSR which became Russia.
The American design was much safer, and worked…. Sort of. A reactor was flown in a highly modified B-36 in the late 50’s and a major flaw in the whole design concept was found. The ANP was to be a flying command center that would stay aloft orbiting the USA for about a month at a time. After which the crew would retire from all Nuclear exposure, having reached the lifetime radiation limit. Oops! The reactor could be shielded from all direct radiation exposure, but radiation going out into the air and bouncing back provided enough “sky shine” to be intolerable.
That is why the B-36 had a nose with foot thick aluminum and lead glass windows about 8 inches thick. They needed the huge weight lift capacity of that giant airplane just to lift the cockpit shielding for the sky shine. The reactor could be up loaded /off loaded up / down a rail into a pit over which the aircraft taxied. There was sufficient direct shielding in the forward bomb bay protecting the crew from the radiation coming form the rear bomb bay where the reactor was stowed, but the sky shine defeated the project. An ANP class vehicle could be designed to about half a rad per day by putting the retractor as far to the rear as possible, but the B-36 was already fixed in possible geometry and had higher dosage.
BUT SKY SHINE IS NOT ALL THAT SERIOUS FOR A SPACE LAUNCH VEHICLE GOING INTO SPACE! NO AIR!
The vehicle spends about 15 to 20 min on climb out to where there is no air to reflect radiation, and even the last part of that climb is in very rarified air. Thus the total exposure is well within acceptable limits, under .005 rads per trip. The other radiation from other sources while in orbit is far greater than the aircraft dose. That major difference has been ignored and, with that problem out of the way, a one stage to orbit aircraft is eminently possible. Clark was right again!
The key here is the nuclear power density per weight so far exceeds chemical energy density that nuclear works while chemical lower energy density demands a two-stage system.
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