Tim Furniss/LONDON
Late this month, technicians at NASA's Space Station Processing Facility (SSPF) at the Kennedy Space Center (KSC), Florida, will begin interlinking International Space Station (ISS) components for one of the largest test operations ever conducted by the space agency. The test will imitate the assembly in orbit of the ISS, due to begin on 20 November.
The Multiple Element Integrated Testing (MEIT) rehearsal will link in function the ISS components destined for the first six assembly missions (which includes one Russian flight) as they are being prepared for launch.
Virtually empty 18 months ago, the 42,500m² (457,000ft²) SSPF is now packed with ISS components being prepared for the first assembly launch in 16 weeks' time. The assembly sequence begins with the launch by a Proton booster of the Russian Zarya Control Module. More than 250,000kg of station equipment will be "on the home stretch towards Earth orbit by the end of the year", says NASA.
The first Space Shuttle ISS assembly mission, STS88/Endeavour, is due for launch on 3 December. Its main payload will be the US Unity Node 1, which will link to the Zarya. Five more ISS Shuttle missions are planned by December 1999. Another Proton will launch the Russian Service Module on 20 April, 1999.
CHECK PROCEDURES
"One of the major objectives of MEIT work is to mimic the early assembly of the Station," says Bill Arceneaux, ISS integrated test and verification manager. "We will build up the test in the same sequence as we will fly. The objective is to check not only the hardware and software, but also the procedures we will use in orbit."
The tests will join together a functional imitation of the Unity and Zarya - the two components to be connected on Shuttle mission STS88 - with the Z-1 truss framework to be launched on STS92. Then the tests will add the power system, batteries and cooling radiators to be launched on STS97, the US Laboratory to be launched on STS98, and the logistics module, equipment racks and Canadian robotic arm to be launched on STS99.
The Unity flight module is not included in the tests, to avoid interfering with preparations for its forthcoming launch. Final checks are being made of the Unity emulator to be used during the test, comparing it with the flight module to ensure that it is an accurate imitation. The emulator imitates the functions of the Unity, although it does not resemble the module in structure, Arceneaux says.
The tests will not physically join the components, as will be the case in orbit, but will link them via electrical, data and fluid lines, using the same cables that will form the connections in space. Extension cables will be used in some cases where components cannot be moved close enough together for the connections.
"A majority of the links that will be made in space will be made first at KSC," Arceneaux says. "We will do commands just like the crews are going to do. We'll go through activation procedures and then check out the operation of the components in several modes, testing all the command and signal paths."
Crews of the Shuttle missions involved and ISS crewmembers will also be participating in tests at the SSPF, practising and evaluating the planned flight procedures.The systems that will be tested include data processing, command and control systems, communications and tracking, electrical, and cooling.
The multi-element testing plan was a late addition to the ISS programme, which capitalised on an opportunity presented by launch delays during the past year. With the new schedule, components for the first six launches will now all be at KSC simultaneously for several months, opening a window for the tests.
PLANNING AHEAD
The success in putting together this first multi-element testing plan has led to a drive to formulate plans to continue such testing throughout the programme, Arceneaux says.
A second phase of testing during assembly may link together a majority of the segments that will compose the 110m-long ISS truss structure, focusing on the centre segment through which will pass a maze of connections and critical equipment links. A third phase of testing may encompass the Japanese laboratory module, advanced logistics module and other Station components.
"There are a lot of people who think that this is the best thing this programme has done recently to strengthen itself," Arceneaux adds.
"We won't use this approach to test all of the interfaces throughout assembly, but we will certainly test the most critical ones," he says. "You are going to find every problem with your spacecraft eventually. Our goal is to make sure we find them and fix them on the ground."
Source: Flight International
