Tim Furniss/LONDON
Flying more than seven Space Shuttle missions a year could jeopardise safety, says astronaut Brewster Shaw, who heads the Boeing International Space Station programme. This conclusion - supported by NASA - has important ramifications for the International Space Station (ISS), already six years late.
With some Shuttle missions required for non-ISS needs such as servicing the Hubble Space Telescope, just five missions may be left each year to continue the ISS' assembly to keep it on track for a target completion date in 2004. Of the 46 missions required to complete the assembly, the Shuttle will make more than 30.
Completion in 2004 will be 10 years later than the target set when President Ronald Reagan inaugurated the programme - once called Freedom - in 1984.
Shaw, who clocked up 22 days space time on Shuttle missions STS9, 61B and 28 between 1983 and 1989, twice as commander, and once head of the Space Shuttle programme, says trying to fly eight or more Shuttle missions a year "would tax the system", especially with employee cuts at United Space Alliance, the Boeing-Lockheed Martin company which operates the Space Shuttle for NASA. United Space Alliance is "doing quite well, but it would be difficult to sustain a high flight rate", says Shaw.
Hundreds of jobs were lost as a result of privatising Shuttle operations and through cuts at the Kennedy Space Center (KSC) in Florida, creating fears that safety and fleet viability would jeopardised.
More staff would be required to support more flights. "It takes time to process the system, get the ISS elements together, do the testing and integration-The plan we have laid out is probably as good as we can hope to do," says Shaw.
Even with a full seven Shuttle ISS missions a year, completing assembly by 2004 would still be difficult, suggesting to some observers that the ISS is too Shuttle-dependent. For example, there are seven Shuttle missions planned between next February and November, excluding two other non-ISS manifested missions, including a science research flight. That totals nine missions, so two will have to go. Translate that to the ISS and the assembly-complete date falls further into 2004, or even perhaps 2005.
The other issue, aside from maintaining the flight rate, is the possibility of a Shuttle accident. Losing or damaging an orbiter - or particularly the loss of a crew - could ground the Shuttle programme, and therefore the ISS.
It took 20 months to get the Shuttle flying again after the Challenger accident in 1986. Dan Goldin, NASA's administrator, says that if there was another accident, the Shuttle, like an airline, would keep on flying. But this is an "airline" with just four vehicles.
Shaw believes there is a will in the USA for the Shuttle to keep flying and for the ISS to continue. "We have international obligations," he says.
Components are being contributed by Canada, Japan, Europe and Brazil. "Being a space-faring person, I would hope that we can keep going. Would Columbus have turned back if he lost one of his ships? I don't think so." He adds, however, that "another thing to stress is the fleet issue". Three of the four Shuttle orbiters - the Discovery, Atlantis and Endeavour - can fly ISS missions. The Columbia is too heavy. "If one of these was grounded or lost, together with the ISS hardware it was carrying, the effect would be even worse," he says.
The main problem is getting the Space Shuttle ISS missions off the ground. No launches can take place until the Russian service module, Zvezda, takes off. Already over a year late in delivery, the module is at Baikonur in Kazakhstan, scheduled for launch on 12 November.
Russia is taking no chances, and is even training an emergency Soyuz TM crew to fly into orbit to hard-dock the Zvezda if for some reason it fails to join properly with the Zarya control module. The Zarya and its attached US node, Unity, have limited attitude control capability and the Zvezda is required. It will also provide additional work and living space.
Once the Zvezda is attached to the ISS, the Shuttle can start flying again, with a logistics mission in December and an ambitious sequence of major assembly missions next year.
There is no guarantee that the Zvezda will meet its launch date, however, and it could conceivably be lost in a launch failure. NASA has contracted the Naval Research Laboratory to build an Interim Control Module (ICM). If the Zvezda fails or it is delayed beyond February, NASA will launch the ICM in its place.
The ICM will be a modified version of a previously classified 12.5t spacecraft bus originally designed for a Shuttle launch. The bus was used to launch Naval Ocean Surveillance System satellites on Titan IV boosters. The ICM has been built but needs modification before it can fly. Changes include use of a smaller propulsion engine, three inertial measurement units, three-axis stabilisation control and an attitude control system designed to maintain the attitude of a changing configuration.
The ICM will have to be launched on the Space Shuttle - further altering and delaying the assembly schedule. The Zvezda delay will have to be significant to make this worthwhile. The ICM will dock to the Zarya module and would provide propulsion and attitude control for up to three years.
Another option is to use the ICM to refuel the Zvezda in place of Russian Progress M tankers. The ICM, however, will not provide living space for continual manning by three crew, as would the original Zvezda design.
The ICM would give the ISS a flexibility that will not be allowed later. "The assembly sequence may be slightly flexible early on, for example, putting something on one side rather than on the other, but in the later stages there isn't flexibility. You can't send something up unless it has something to attach to. The assembly is from the inside out," Shaw says.
Despite the ISS delays, Boeing has been delivering its Space Station components regularly as part of its contract. The Space Station Processing Facility at the KSC is "chock full" of ISS components waiting to fly, so much so that a former Spacelab processing building nearby has been called into service to house the truss components for the station.
"Our philosophy is that we are going to continue to deliver hardware as close to the delivery date as we can, as part of our contract and we will support the government between then and the time of launch in some sort of sustaining arrangement," says Shaw. "If there are further delays, it will not have an impact on Boeing, but obviously the programme will be affected."
Source: Flight International
