J. Taylor Ridgeway (jridgewa@bellsouth.net) Betreff: RE: Sänger
Where can I find more information about the progress and proven specifications
of the Sänger aerospace plane?
Feb. 11th. 98
The concept of an Aerospace plane goes back to Eugen Sänger's WW II plans for an "antipodal bomber", a winged hypersonic aircraft, which would be able to deliver a bomb to New York and then circle the earth to return to base. There must be plenty of literature, both German and English. Derivatives of the idea are the British HOTOL, US Aerospace plane etc.
Sänger was a BMFT (German Ministry for Research and Technology) funded study project, which was carried out by then MBB, Munich, to study the concept, materials and thrust unit, and for which MBB received more than 330 million DM (then apprx. 200,000,000 US-$). This was around 1990. A very good popular style article is in GEO 12/91 (the German equivalent of the Ntl. Geographic).
The biggest lobbyist of Sänger was then Mr. Ernst Högenauer (Munich). Mr. Sängers son also lives near Munich (spoke to him once on the phone). MBB has been aquired by DASA. In fact, for technical details, specifications etc. I would write to the DASA, Munich PR office.
With regard to progress, there is none. The project was officially terminated a few years ago, largely, because the estimated 40 Billion DM to build two planes were considered unaffordable, due to environmental objections and because the project outcome in technical terms was far from certain. Because of the way public funding works here, all tools, wind tunnel models etc. had to be kept on hand in case the project would be revived. This period has elapsed last autumn and DASA may have destroyed it. Or they may have given some items to the Technical University TU Munich. Inofficially, some people still try to do some work on Sänger and quietly divert some money, so I was told. But it is no longer an official project for some years now. Personally, I think the decision to terminate was right. Sänger is a brilliant project and should be revived when we have an infrastructure to supply (space stations and bases on Moon and Mars), but it is unsuited to build that infrastructure up.
Personally, I think the decision to terminate was right. Sänger is a brilliant project and should be revived when we have an infrastructure to supply (space stations and bases on Moon and Mars), but it is unsuited to build that infrastructure up.
The person to contact for further information at the TU Munich is Gerd Hofschuster. He presides the space student group, called WARR. They have a web page with a downlink at DLR's page. Mr. Hofschuster is very nice and knows Mr. Sänger, Mr. Högenauer and some people at DASA. Good luck. Tom Stinnesbeck
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Mr. Zehringer on the cost of space travel:
Mr. Zehringer is a well-known, now retired rocket engineer who has specialised in solid propellants. He has also published a book on the subject. Mr. Zehringer has developed the Asphalt/KClO4 mixture which was the most widely used mixture, in particular in military rockets, until the advent of Ammonium Perchlorate. Mr. Zehringer now devotes time to the comparative cost analysis of various space access systems. He writes:
Mr. Zehringer: ...
What is the cost comparison with other types of transportation systems ? .. We know what it costs to ship goods via car, or air, or via ship. How does this compare with present and projected rocketry? Chemical versus nuclear ? .... Right now and in the forseeable future, my current data suggests that we are several orders of magnitude higher than existing systems. And for this reason, space flight will be in the realm of governments and/or political motives...
Tom Stinnesbeck:
Indeed, space access cost is several orders of magnitude from current earth transport systems. The Shuttle, being on the more expensive side, is about 300 times more expensive for 1 kg of transport to LEO than is the Concorde (18.000 $ vs. 60 $). Cheaper rockets such as the Delta are still apprx. 150 times more expensive (9.000 $ vs. 60 $). However, earth transport systems are also several orders of magnitude apart. The Concorde costs $ 60 per kg, regular air freight is about $ 3,- (20:1), the slow boat costs only pennies per kg. We must also take in account what a transport system is designed for. Hence, earth transport systems, even though all will take you from A to B, are also several orders of magnitude apart. Obviously, we would never fly crude oil on the Concorde. Yet, in some cases we find it economical to fly even gasoline in aircraft, for the purpose of refueling military airplanes. Space transport is difficult to compare with earth transport. The Voyager space craft has covered many billions of miles in over 10 years. That's pretty economical when compared with 10 years of uninterrupted airplane operation.
What is "economical" after all? Obviously, a transport system is economical as long as it permits us to make a profit. Thus, even current rockets are economical for the transport of communication satellites, which is good (and private) business. For an extended exploration- and exploitation program of the solar system, they are not. The real question, in my oppinion is, what could the cost of space access be. Must it be so high ? We (and an increasing number of people around the world) believe not. Currently and in the forseeable future, we only have rockets to get us into space. Hence, we must ask what we can do to make rockets cheaper. This is what my article tries to deal with. The official school of thought is that more high tech will bring the cost down. In the past, however, this has clearly failed. Some suggest to build aerospace planes, Sänger etc. Such systems would have front-up cost in the range of $ 50 Billion. I don't think that's realsistic. Another school of thought (Arthur Schnitt's) is that less technology is the answer. After intensive analysis I have decided for myself that I agree with that.
Mr. Zehringer:
So, although the rocketry area was first dominated by the military, it is now a large aerospace business, particularly for launching the large number of communication satellites on order and projected. But, NASA is only slowly mooving forward. However, it may well be that the work of the amateurs will gradually increase. They have already reached very high altitudes. And I soon expect that someone will launch a small, private, amateur satellite. And after that, I expect some person or some country will enter in the realm of orbital flight. But that it not right now. But it is coming!
Tom Stinnesbeck:
I fully agree. It will come (and we are working on it, as are many others). There are some groups in England ("Aspire Space") and Wales (also working on hybrids), one in The Netherlands, and certainly some in the US. If we could somehow work together and exchange knowledge, we might get there faster .....
Mr. Zehringer has mentioned nuclear rockets:
Will nuclear rockets bring a break-through in terms of cost ?
My opinion:
I don't think so. First, I think we all agree that nuclear rockets are only for transport within space, that is, between celestial bodies, but not for launch into space. And even there, orbits must be high enough to be stable for many thousands of years in case of accident. Such orbits, however, only need a relatively small Delta-V to reach escape velocity. Thus, the anticipated benefit is largely offset. Furthermore, the public, which, after all, has to pay the ticket, is generally not favourable towards nuclear propulsion. The word of "Tschernobyls in the sky" has already made rounds. For those reasons, I wuldn't be surprised, if nuclear rockets, assuming they will ultimately come, will be fully "Made in Space", for ex. built on the Moon. And this is certainly another two or so decades away (at the current pace of things). There may be other nuclear propulsion concepts to change the picture, for ex. a laser-induced Helium 3 pellet fusion acting on a pusher plate. This reaction hardly yields any radioactive waste or long- lived hazards. But for now, this is only a paper concept. Last but not least, we must also consider the cost reviveing a nuclear rocket program. Such a program existed 3 decades ago, but was terminated in 1972. Until then, it had costed more than $ 2 Billion. So, in order to revive that effort, re-establish facilities, build the teams and knowlege base etc., we would probably have to invest in the order of 10 to 15 Billion $s in today's money. I think that's unlikely given the current state of public finances and public sentiment towards nuclear concepts.
There are also technical difficulties. Nuclear propulsion has a simple underlying idea (heating Hydrogen in a nuclear fission core), but in actual technical terms is far from trivial. The "Case for Mars" series has a very good summary on the past programs, their results and their technical obstacles. In a typical Mars mission, for ex., the reactor would have to work and stay operative over a period of 3 or so years. It would have to be reactivated after extended dormant periods of more than a year. All this without service. Given the reliability record of nuclear power plants here on earth with their big technical and operational teams, I think this is very unlikely (and I am not a No-Nuke person)!
But let's assume for a moment, we had nuclear propulsion, that it
was safe etc. Would it be an economical concept then ? Let's let mathematics
speak for itself: Energy expenditure of space travel is usually expressed
in terms of Delta-V. A typical LEO to escape Delta-V would be 3500 m/s.
This is a very basic space maneuver and the building block for any exploratory
regime, be it Mars or Moon. A major cost component of such a maneuver is
the fuel we have to bring from the Earth's surface into space. Tsiolkowsky's
formula tells us what the fuel fraction of the space craft would have to
be for several propulsion concepts:
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This very simple screening calculation shows that nuclear performance is obviously much better than that of chemical rockets. However, there is no compare to electric propulsion. Furthermore, we must also note that a c of 9000 m/s for nuclear motors already marks the theoretical end of that propulsion concept (there are exotic ideas around gas core reactors, which would, at most, reach into the lows electrical range). The c of electric propulsion, by contrast, has only one theoretical limit - the speed of light. Electric propulsion is well established. It is by no means exotic. Electric propulsion has prooved to be reliable over many months of operation. A well-known and long standing advocate of electric propulsion is Prof. Ernst Stuhlinger, companion and "right hand" of Wernher von Braun. Hence, electric is our way to go. Perhaps it's biggest disadvantage is low thrust, which means that we will slowly have to spiral out of orbit. But then again - cargo is usually in no hurry.
For those reasons I believe that nuclear propulsion is a (costly) dead end.