games@max.u.washington.edu  writes: Re; Response from CoB of Boeing on SSTO ... >"As far as single stage to orbit technology, we think that we have >a better answer in a two stage approach, and we are talking to some >of our customers about that.  As far as commercialization, that is >a long ways off.  ... > Anybody know anything further? Is this really news? Does this >threaten further work on DC-? ?       Boeing has been looking at several TSTO vehicles and has carried out extensive conceptual studies of advanced launch systems for some time.  A good reference on this might be: "Comparison of Propulsion Options for Advanced Earth-To-Orbit (ETO) Applications (IAF-92- 0639)." by V.A. Weldon and L.E. Fink from Boeing.   The paper describes a propane-fueled TSTO launch system claimed to achieve aircraft-like operational efficiencies without the problems associated with liquid hydrogen fuel.  Basically, it's a high-speed airplane launching a Hermes-type spaceplane    The design (the concept is also called "Beta") as laid out in the paper can launch at least 10,000 pounds into polar orbit, or 20,000 pounds to space station orbit including a crew of eight persons and life support.  System design reliability is .9995.    Beta is a 360-foot-long first stage powered by two large ramjets and 12 high- speed civil transport (HSCT) turbofans.  A 108-foot- long reusable orbiter is trapeze-mounted in the belly of the first- stage aircraft, which also could accommodate a longer and heavy payload on an expendable second stage.    To launch the orbital vehicle, the first stage takes off like a normal HSCT and accelerates to Mach 3.  At that point the turbofans, modified to burn catalyzed JP-7, would shut off and the ramjets, would take over.  At Mach 5.5 the orbiter or the ELV would swing out, ignite and proceed to orbit. Both vehicles would land like aircraft at the conclusion of their respective missions.    Estimated total weight of the combined configuration at takeoff is about 1.5 M lbs, roughly equivalanet to a fully loaded An-225. The orbiter stages weighs about 400,Klbs including 335 Klbs of LOX and subcooled propane to power two 250 Klbs vacuum thrust rocket engines. Propellants would be stored at 91 degrees Kelvin, with the propane in a spherical tank mounted forward of the 15-by- 25-foot cargo bay and the two-seat orbiter crew station. LOX would be stored aft.  Weldon and Fink claim the key to this design's success is the structurally efficient airframe and the compact tankage allowed by the high-density supercooled hydrocarbon fuel.      The paper compares TSTO design to SSTO design.  They conclude while a SSTO has a slightly lower recurring cost, a TSTO is easier, cheaper, and less risky to develop, simpler to build, has greater safety and mission versatility and doesn't carry the hard-to-handle and bulky hydrogen fuel. The conlcude "In conjunction with its major use of airplane type engines and fuel, as well as its inherent self- ferry capability, it is probably the system most likely to provide as close to airline-like operations as possible with a practical configuration, until a single stage airbreather/rocket concept can be shown to be operationally viable."    >Is this really news? Does this threaten further work on DC-?    Weldon and others at Boeing have been working on TSTO designs for some time.  I expect this, or a similar concept (perhaps the HTHL SSTO they proposed for the SDIO SSTO first phase) is being re- examined as a basis for a bid on the first phase of SpaceLifter.    Does it threaten DC-???.  Possibly -- There is a set of on-going studies trying straighten out the government's future space transportation strategy.  MDC and Boeing (as well as other firms) are providing data to a joint study team back in DC.  There are various factions and options vying for attention -- including shuttle upgrades, shuttle replacement (what was called the "4-2-3" architecture), SpaceLifter, ELV upgrades, and various advanced vehicles (ALES, Beta, DC-??, NASP, FSTS, SSTOs of several types, etc.)  NASA/DOD/DOT are trying to put together a coherent strategy for future US gov't space transportation systems, and trying to juggle near-term launch needs (like for DoD and NASA) against medium-term needs (including commercial considerations), and against the investment and risk of going to "leap frog" new technologies like SDIO/SSTO and NASP and Beta.    It's a heck of a problem.  The worst part of the problem isn't that there aren't promising ideas and concepts -- there are dozens of them -- but how they balance cost and risk versus real needs in the near term.  They should have a draft report in mid-June, with a final report coming by the end of the fiscal year.  ------------------------------------------------------------------  Wales Larrison                           Space Technology Investor