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Planetary News: Dawn (2007)Dawn Aims for July 7 Launch, But Delays Make for Tight Window of OpportunityBy Emily LakdawallaJune 26, 2007 Despite several nagging "issues that need to be resolved," NASA's Dawn mission to Vesta and Ceres is "pressing full steam ahead for a July 7 launch readiness date," NASA's Deputy Associate Administrator for Programs Todd May said in a press briefing today. Minor but time-consuming problems with the preparation of the launch vehicle have caused repeated delays for Dawn's launch readiness date from June 20 to July 7. The delays have pressed the Dawn launch up against the launch period for the Phoenix mission to Mars, causing scheduling headaches and forcing NASA to consider delaying Dawn's launch until September. The recent delays have nothing at all to do with minor damage (now repaired) that happened to one of Dawn's solar panels two weeks ago. They have been caused by problems with the Boeing Delta II 7925H-9.5 rocket that will carry Dawn into space. Dawn's launch period was supposed to open on June 20. However, in April, a late delivery of some rocket hardware delayed the launch date to June 30. Then, on May 30, a problem with the crane used to assemble the hardware forced another week's delay, to July 7, the current launch readiness date.
Dawn's planned mission to Ceres and Vesta can be accomplished with launch dates any time from now until mid-July, and again from early September through mid-October. However, Dawn does not have all these launch dates available to it, because there are conflicts with other launches. Dawn will launch from Pad B at Cape Canaveral's Space Launch Complex 17. The Phoenix mission to Mars is planned for a launch from Pad A. Phoenix must launch in the three-week period between August 3 and August 24, or its mission will be delayed two years until the next Mars launch opportunity. But a launch from one pad cannot occur when there is a rocket sitting on the other pad. Dawn has to launch no later than July 11 to avoid impinging on the Phoenix launch opportunity (because there must be time after the first launch to assemble and test the launch vehicle for the next launch).
A five-day launch window is extremely short, especially given Florida's iffy afternoon weather. During the routine spaceflight readiness review of the Dawn mission, NASA considered postponing their attempt to launch Dawn until September, after Phoenix launches. "There are other options for Dawn, but they come at a fairly large cost," May said. "If we were to jump over the Phoenix launch, we get in to hurricane season; and it's a fairly large budget hit to do that. And frankly, there's no guarantee to get off at that time either." It could cost NASA around $25 million to delay to September, May said. They will consider the possibility of a delay again on Tuesday, July 3, when the launch readiness review takes place. Between now and the July 3 launch readiness review, several issues must be resolved. None of these is particularly out of the ordinary for a planetary launch, but the short launch period available to Dawn this July appears to be making NASA nervous. One minor problem arose in their analysis of the attachment of the solid rocket boosters to the first stage of the Delta II rocket. Another problem is that the ship they intended to use for their required downrange tracking of the rocket following the launch is will not be in place because of mechanical problems, delays in its passage through the Panama Canal, and storms encountered en route to Puerto Rico. There is an airplane that can probably be in position to track the rocket, but it requires repairs to its landing gear before it will be ready. May reported that they do expect all these issues to be "clear" by Tuesday. The reason that July 3 is such an important date is because that is the day on which they must decide whether or not to load the Delta II rocket's second stage with hydrazine fuel. Once it is loaded with hydrazine, the second stage must be used within a fairly short time frame of several weeks. If NASA decided to postpone the launch after fueling the second stage, they would be required to purchase a new second stage for the launch vehicle, May said. The new second stage would not be available until mid-October, near the close of Dawn's launch window. So they must decide on Tuesday whether Dawn will launch in July or in September.
As of today, NASA plans for Dawn to be ready for a July 7 launch. But there is no room for further delays. Absolutely everything must be in place on July 3 for a July 7 launch to go forward. If any problem -- including sufficiently unpleasant-looking weather forecasts -- makes a launch in the July 7-11 period look unlikely, NASA may choose not to fuel the second stage of the rocket and push to a September launch. Bad luck has dogged Dawn's launch preparations until now; the mission now needs to catch a break for the launch to happen as scheduled. For updates on the status of the preparations for Dawn's launch, stay tuned to The Planetary Society Weblog. |
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