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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Douglas SASSTO | 2/2 | https://en.wikipedia.org/wiki/Douglas_SASSTO | reference | science, encyclopedia | 2026-05-05T13:22:13.739601+00:00 | kb-cron |
== Design == Although the SASSTO claimed the S-IVB as its starting point, this was a conceit, and the vehicle had little in common with the S-IVB except its size. The internal fuel tankage was considerably different from in the S-IV. The LH2 was no longer cylindrical, but spherical, and moved to the forward location in the fuselage. The LOX tankage, originally on top of the LH2, was re-positioned into a series of smaller spherical tanks arranged in a ring below the LH2. The tanks were all moved forward within the airframe compared to the engine, all of these changes being made in order to reduce changes in the center of gravity as the fuel was burned off. The fuselage section immediately above the engine was necked down, forming what appeared to be a larger single plug. The upper section of the fuselage, over the top of the hydrogen tank, was likewise necked down. In order to increase the amount of LH2 being carried, given the fixed dimensions, SASSTO proposed freezing 50% of the fuel to produce a slush hydrogen mixture. This improvement was not uncommon in designs of the era, although it was not until the 1990s that any serious development work on the concept was carried out. The rearmost portion of the spacecraft was a single large plug nozzle, fed by a series of 36 injectors operating at 1500 psia, producing 277,000 lbf (1,230 kN) of thrust. Since plug nozzles gain efficiency as they grow larger, the 465 sec specific impulse (compared to the J-2's 425) was not particularly aggressive. The engine also served as the primary heat shield, actively cooled by liquid hydrogen that was then dumped overboard. Four landing legs extended from fairings on the fuselage sides, retracting to a point about even with the "active" portion of the engine area. Four clusters of small maneuvering engines were located between the legs, about half-way from front to back along the fuselage. A series of six smaller tanks arranged in the gaps between the LOX and LH2 tanks fed the maneuvering engines. SASSTO delivered 6,200 lb (2,800 kg) of cargo to a 110 nmi (200 km) orbit when launched due east from the Kennedy Space Center. Empty weight was 14,700 lb (6,700 kg), considerably lighter than the S-IVB's 28,500 lb (12,900 kg), and gross lift off weight was 216,000 lb (98,000 kg). The typical payload was the Gemini, which was covered with a large aerodynamic fairing. Re-entry maneuverability was through a blunt-body lifting profile, similar to the Apollo CSM. The cross-range was limited, about 230 miles (370 km), and there was basically no maneuverability at all on final approach. There was enough fuel for about 10 seconds of hovering and small maneuvers to select a flat landing spot. Because SASSTO was the same basic size as the S-IVB, Douglas proposed transporting it in the existing Aero Spacelines Super Guppy after landing at either Wendover Air Force Base in Utah, or Fort Bliss outside El Paso, Texas.
== Developments == Dietrich Koelle used SASSTO as the starting point for a similar development at Messerschmitt-Bölkow-Blohm in the late 1960s. Unlike Bono's version, Koelle used as much existing technology and materials as possible, while abandoning the need for the specific S-IVB sizing. The result was a slightly larger spacecraft, the Beta, that launched 4,000 lb (1,800 kg) of payload without the use of slush fuel, advanced lightweight construction, or a real aerospike engine. As part of the Beta proposal, Koelle pointed out that even the existing S-IVB could reach orbit, with zero payload, if equipped with a high-pressure LOX/LH2 engine of 460 Isp. Gary Hudson, in 1991, pointed out that such an engine existed, the RS-25, using a RS-25-powered S-IVB as a thought experiment to demonstrate the real-world feasibility of SSTO launchers. This study was part of his "Phoenix" series of launchers, all similar to the SASSTO.
== See also == List of space launch system designs
== References ==
=== Notes ===
=== Bibliography ===
=== Further reading ===
== External links == SASSTO - Encyclopedia Astronautica PC-compatible flight simulation for the SASSTO. Requires prior installation Orbiter general space flight simulator package, both Orbiter and SASSTO are freeware.