henry@zoo.toronto.edu (Henry Spencer) (04/05/91)
[March issue of Spaceflight mentions that astronaut William F. Fisher has left NASA to return to medical practice. No big surprise, on thinking about it: he was co-chair of the group that reported the bad news about EVA requirements for Fred, which probably killed his chances of future flight assignments.] Editorial urging that SDIO get sensible about tactical-missile defence, dumping the silliness of applying Brilliant Pebbles to every problem and concentrating on urgent near-term availability of competent ground-based interceptors with better coverage than Patriot. Aerojet gets modest research contract from Army Strategic Defense to build a 33klb rocket engine using gel propellants, in the hopes that gels will give safer field handling than liquids while retaining stop-start and throttling capability. Bush signs new commercial space policy guidelines, stressing government purchase of commercial products and services when possible. OMB orders independent engineering review of NASA's EOS plan, reportedly to look particularly at the wisdom of large multi-sensor platforms. SDI estimates worldwide limited-attack protection system at $41G. The design target is complete destruction of a 200-warhead attack, including coverage for US territories, allies, and military forces in the field. Third-world tactical missiles and the possibility of accidental and unauthorized attacks from a politically-unstable Soviet Union are the major threats seen. The only real technical surprise is a willingness to consider shipboard and airborne launch platforms. Patriot succeeds as tactical missile interceptor in the Gulf, with a 100% interception rate for Scuds engaged over Saudi Arabia in the first three weeks of Desert Storm. (Some Scuds were not engaged because they were headed for water or open desert.) Study indicates that Navstar is not suitable for use by itself as a precision approach system for aircraft blind landings, although it could be very useful in combination with the new ground-based Microwave Landing System [which is somewhat controversial due to conversion costs from the older ILS now in use]. Various improved forms of Navstar, e.g. differential systems and phase-tracking receivers, could achieve "Category 1" accuracy, or nearly, but not "Category 3" [the really heavy-weather blind-landing standard]. The fundamental problem is that Cat 3 requires a maximum 2s delay between a system failure and a warning to aircraft on final approach, and even an extensive ground-receiver network with a new data link to the aircraft would have trouble meeting this. A further complication is that a satellite failure that kills Cat 3 capability at one airport will affect other airports in the area too. Finally, the non-military part of Navstar is not really accurate enough for Cat 3 even with differential methods, due to substantial altitude errors. It could, however, give much better accuracy than MLS for the early phases of landings, plus better coverage of possible abort trajectories in case of trouble, while leaving MLS (which gets more accurate as range closes) to handle final approach. Soviets reveal details of their N1 booster, meant as their Saturn V equivalent for manned lunar missions. The N1 used massive clustering of engines, and reliability problems in the 30 (!) first-stage engines were its Achilles' Heel. Early reports suggesting that the N1 would carry up the lunar spacecraft and rocket stages while a Soyuz launch carried the crew up appear to have been incorrect; it now appears that a single N1 launch would do the whole job. The first three stages would put a Soyuz, a lander, and three more rocket stages into Earth orbit. The fourth stage would boost the rest toward the Moon. The fifth would brake the rest into lunar orbit, and then do most of the deceleration of the lander, being jettisoned shortly before landing to crash on the Moon. [This "lunar crasher" approach was seriously considered for Apollo for a while.] The lander engine would then complete the landing, and later be used to boost back to lunar orbit. Finally, the sixth stage would boost the Soyuz back toward Earth. The total crew would be two, with only one descending to the lunar surface, and crew transfer between Soyuz and lander would be by EVA. [Actually, various elements of this resemble rejected alternatives in the US program; similar problems, similar solutions.] -- "The stories one hears about putting up | Henry Spencer @ U of Toronto Zoology SunOS 4.1.1 are all true." -D. Harrison| henry@zoo.toronto.edu utzoo!henry