Traffic and Sun Angles May Affect STS-100 Launch Date
NASA is giving consideration to postponing the launch of STS-100. This issue will come up at tomorrow’s STS-100 FRR (Flight Readiness Review). The main reason has to do with Soyuz lifetime and traffic management in and around the Space Station. Sun angles and Shuttle cooling – and some software constraints – are also an issue.
The Soyuz currently attached to the ISS is coming to the end of its 6 month on orbit stay time. The Russians are remaining rather firm with regard to their desire to change out that Soyuz with a new spacecraft. Russia has expressed an interest in getting the new Soyuz spacecraft up no later than 12 May – although they are still working toward a 28 April launch date.
STS-100 is scheduled to launch on 19 April and return to Earth on 30 April. The Soyuz ferry flight is scheduled to launch on 28 April with the crew returning in the older Soyuz 10 days later. Russia has agreed in principle to slip their Soyuz launch date by one day for every one day that the launch of STS-100 slips. At some point, however, Russia would like the U.S. to consider doing a scheduling leapfrog over their Soyuz mission if delays begin to mount.
The main concern of both NASA and Russia is having two spacecraft performing proximity operations at the same time. They would prefer to have, at minimum, a one day buffer between one spacecraft’s arrival and the other’s departure.
If the STS-100 launch date slips too much, moving to a new launch date of 6 May would be one day after the older Soyuz undocks from the ISS.
There is another factor that is influencing the prospect of a 6 May launch date. After mid-May there is a high beta angle constraint that would prohibit Shuttle operations at the ISS. This constraint arises when the orbital parameters (orbital plane) and the amount of sunlight hitting and heating a Shuttle (due to the sun’s seasonal position/direction with respect to the Earth) place considerable strain on the spacecraft’s cooling systems. Missions during such periods are avoided whenever possible. As such a mission needs to be completed before mid-May so as to avoid the high beta angle conditions. This high beta angle situation will continue until early June – and is actually a driver in the scheduling of the next (ISS-7A) Shuttle mission to the ISS.
One additional factor affecting launch dates has to do with software. STS-100 will not have a software upgrade that allows them to have the ability to dock on FD-3 (flight day 3). Launching on 20 April would lead to docking on FD-4.
NASA has already expressed concern that flying Dennis Tito to the ISS at this point in its assembly would be inopportune given the complexity of what is going on. According to NASA sources, the issues leading towards a possible change in Shuttle launch dates, however, would be given the same consideration regardless of whether Mr. Tito was or was not aboard this particular Soyuz mission. NASA has said that it would continue to oppose Mr. Tito’s flight regardless of when either the Soyuz or Shuttle launches occur.
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