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Aviation History
1984
1984 - 0052.PDF
SPACEFLIGHT How to make Orbiters fly longer DOWNEY For several years, Rockwell has been looking at ways of extending a Space Shuttle Orbiter's time in space, currently limited by the ability to generate electrical power. Its latest proposal, now in detailed study, is a set of cryogenic tanks, grouped together in a "wafer" shape and carried in the payload bay. Orbiters generate elec tricity through the combina tion of oxygen and hydrogen, in a process which takes place inside the three fuel-cells on board. The spacecraft store liquid oxygen and hydrogen in spherical tanks below the payload-bay floor—three tanks of each in the baseline configuration, giving a maximum continuous power of 21kW for up to seven days (2,640kWhr total deliverable energy). Two more pairs of tanks can be accommodated below the floor, increasing mission duration to 12-5 days at the same power level (see graph at foot of page). Each additional tank-pair adds 840kWhr. Orbiter Columbia was upgraded to the full complement of five tank-sets before STS 8, on which Spacelab 1 was the main payload. "People are looking more and more at keeping the Orbiter up longer," says Drew Hayes, Rockwell's project manager for cryogenic wafers. Lack of space rules out carriage of further cryogenic tanks in the Orbiter's fuse lage, but it is possible to house them in the payload bay, at Cryogenic wafer comprises four tank-sets supported on an aluminium alloy framework, and would almost double mission duration the expense of some payload volume and weight. Rockwell calls its solution a cryogenic wafer. It com prises an aluminium alloy framework supporting four liquid-oxygen and four liquid- hydrogen tanks. The wafer like shape is designed to use the least amount of payload bay, leaving plenty of room for cargo. It almost doubles mission duration of the five- tank set, providing 21kW of maximum continuous power for 23-5 days. Missions most likely to benefit from the cryogenic wafer include Spacelab flights and those involving materials processing. Hayes anticipates that 20-30 per cent of missions could be in the market for a wafer, but points out that the unit would be flown only when needed. He adds that the wafer is a short-term solution that "buys more time quickly", and that so far Rockwell has financed work on it from its own money. Nasa has been working with the company on mission extension for several years, however, and could be in the market for a wafer within the next year or two. Rockwell says that it could have a cryogenic wafer flying within 2=1-3 years of go-ahead. It estimates development cost „ 7,500 _iz 5 6,000 >, CD a 4,500 c CD •§ 3,000 1,500 Tanks below payload bay .Tanks in payload bay "2-^A wfi i \ i 6 7 \ • • 8 v ^X • 9 \ i 21 \ \ 18 in \^16% \ \ \ \ , \i ,\ , \ 0 8 10 12 14 16 Mission duration (days) 18 20 22 24 How mission duration varies with the number of liquid oxygen and hydrogen tank-sets carried by the Orbiter. The light tone represents Rockwell's cryogenic wafer 72 at $50 million-$60 million, including construction of a flight unit. Cryogenic wafer uses the same Beech-built tanks already used in the Orbiter, and many of the valves and other parts are also common. The only major new part is the support framework, which Rockwell would design and build. Hayes adds that Orbiter modifications are minimal. Cryogenic wafer weighs about 3,630kg fully loaded, and would take up 2- lm of the payload bay length. This compares with a weight of 2,600kg for the baseline system (three tank-sets). Nasa is looking at other ways of augmenting Orbiter duration, including solar arrays. Rockwell's cryogenic wafer appears to be the only short-term, medium-power solution, however, and could get the go-ahead soon. Solar arrays would be able to provide significantly more power than cryogenic wafer, for an indefinite length of time. They are a longer-term solution, however, and wou) " probably require more eyfiS. sive Orbiter modificftWy Any solar array is alpayload to be carried in t1 FLIGHT Inte-><iUonal '
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