wls@astrovax.UUCP (William L. Sebok) (02/25/86)
Some context (attempting to edit it down to size): In article <2803@amdahl.UUCP> ems@amdahl.UUCP (E. Michael Smith) writes: >>How you gonna bring back that locomotive sized payload when you >>want to fix it, retire it, analyse it, sell it, etc. if you don't have >>a nice big cargo bay to put it in? In article <740@astrovax.UUCP> I reply: )It seems that we eventually need a small payload launch system and a large )payload launch system (and even further down the road a spectrum of launch )system sizes). And in article <484@ecn-pc.UUCP> wdm@ecn-pc.UUCP (Tex) writes: > You didn't answer the question - what do you do when it is time to bring > back something large? You use the large payload launch system. I spoke of having both available. Of course, I was speaking of an ideal world where development costs are already paid, but it seems that we will eventually want to to go in the direction of more than one size of launch vehicle (just as other forms of transportation have done). )One doesn't always need an 18 wheel truck to carry something that would fit )in the trunk of your small car. > There are few items of interest in LEO that would > fit in the trunk of a small car. I was making an analogy. The proper spectrum of launch vehicle sizes would best be determined from the spectrum of payload sizes. ) Reusability is (to some extent) a separate issue: it would be ) nice if the the small payload lauch system were reuseable. The small launch ) system could either be unmanned or have a single pilot. > Reuseabiltiy is a critical issue because > it is tied so closely to cost. I also disagree that a small payload > launch system is the way to go - once you start putting the mass of a > launcher into orbit, the incremental cost of additional payload is small- > Putting a several thousand pound launcher into orbit to deliver a one > hundred pound payload does not make any sense. At any time a hardnosed look at the economics must be made. At some point the cost saving of not having to rebuild the whole vehicle balances the cost of launching the mass of the vehicle. This point may change in time as we progress up the learning curve. In the mean time there are 2 more advantages to having a small launch vehicle available 1) if it is manned more experience with manned launches could be had under different conditions than that of the large vehicles, 2) manned or unmanned our ability in space wouldn't be so dependent on the well-being of few large launchers. Since the small vehicles would presumably be cheaper to build than the large vehicles, one could build more of them and the loss of one would be less of a disaster. -- Bill Sebok Princeton University, Astrophysics {allegra,akgua,cbosgd,decvax,ihnp4,noao,philabs,princeton,vax135}!astrovax!wls
dietz@SLB-DOLL.CSNET (Paul Dietz) (03/02/86)
[debate between E. M. Smith and Bill Sebok on reusuability and size of launchers] There are additional advantages to small launchers. Generically, building a small ANYTHING is a good way to get experience before building a large economy-sized model. Small jets were built before 747s. Small rockets were launched before the Saturns. It's generally easier to try out competing technologies at the prototype stage. The motto "plan to throw one away, you will anyway" applies to any complex system, not just to software. > Reusability is a critical issue because > it is tied so closely to cost. One of the shuttle's problems is that it's not really reusable. The ET gets thrown away ($40 million (?) right there). The SRB's require extensive refurbishment. The tiles need to be inspected. The main engines require constant maintenance and rebuilding. I'd like to see hard numbers on the number of man-years of effort needed for one shuttle flight vs. a similar number for one expendable flight (including the effort in building the shuttle, amortized, and the effort in building the expendable booster). I expect the ratio is quite small.