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TOPIC: Dawn spacecraft
Blobrana


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RE: Dawn spacecraft
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Send your name to the asteroid belt on the Dawn spacecraft. Your name will be recorded onto a microchip that will be placed aboard the spacecraft accompanying it on its mission to the asteroid belt. After entering your name below, you will have the opportunity to print a document that verifies your journey aboard the spacecraft.

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Blobrana


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Dawn continues to keep its human handlers very busy as preparations continue on schedule to meet the planned opening of the launch period on June 20, 2007.

Much of June 2006 was devoted to conducting the comprehensive performance tests (CPTs) described in the previous log. In these tests, most of the hardware and software subsystems already on the spacecraft were exercised to help uncover problems ranging from incomplete solder connections on a microchip or a broken wire, to software bugs, to unexpected interactions between subsystems that must work together. Of course, each subsystem was tested extensively as it was being built, but some afflictions may remain hidden until the subsystem is operating on the spacecraft with other subsystems. As thorough as the CPTs are, testing will become more and more demanding over the coming months as the spacecraft is asked to perform in ways progressively more like what it will encounter during its voyage to the asteroid belt and its explorations of Ceres and Vesta, the most massive bodies in that region of the solar system. The upcoming tests will be described in future logs.

The CPTs yield a tremendous volume of data, and engineers are still analysing the details of their subsystems' performance, but all indications are that the tests went extremely well. As our humble human readers know, some errors are inevitable in a design as intricate and complex as one of Earth's interplanetary spacecraft. So far it appears that all such flaws are easily correctable.

Some subsystems have not yet had their first CPT. The ion propulsion subsystem and the instruments for collecting scientific data are awaiting their tests in August. We will introduce each of Dawn's subsystems in the next log.

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Blobrana


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On March 27, NASA Associate Administrator Rex Geveden reinstated the Dawn mission, after it had been cancelled on March 2nd. The Dawn team is very grateful that NASA recognized the work that the project has accomplished to reduce technical, schedule and cost risk, and committed the funds needed to complete the mission. The project team has been directed to resume integration and testing activities, and develop a detailed project schedule and cost profile to support a launch between June and August of 2007.

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During the stand down the team has been working on developing and vetting test procedures and dry-running them on the testbed. The team is anxious to integrate the instruments, which have been stored at Orbital since November, and begin comprehensive spacecraft testing. Final delivery of the second (re-worked) Attitude Control Electronics Unit, the PPUs, and re-worked Digital Control Interface Units are pending. The ion thrusters are the last items to be integrated.

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Blobrana


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The Dawn mission to visit a pair of asteroids has been reinstated following a mission review.

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Blobrana


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NASA will host a media telecon at 2:30 p.m. EST today to discuss results of the committee reviewing the decision to terminate the DAWN mission.
The DAWN spacecraft was scheduled to orbit Vesta and Ceres, two of the largest asteroids in the solar system. During its mission, the
spacecraft would observe the properties of the two asteroids providing insight into the formation of the early solar system.

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Blobrana


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Mission Cancelled
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NASA has cancelled the mission to visit two asteroids after the program was told to stand down because of cost overruns and technical problems.

The cancellation is the latest setback for NASA, which has been forced to delay science missions to focus on developing a new manned spacecraft to return to the moon in the next decade.
The Dawn spacecraft was to reach Vesta, 220 million miles from Earth, in 2011. It was then supposed to have reached Ceres, about 258 million miles from Earth, in 2015.

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Blobrana


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RE: Dawn spacecraft
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In mid-October, the Dawn mission team was asked by NASA Headquarters to cease all work except that which was critical to maintaining the viability of the Dawn mission to launch on a delayed schedule, still achieving all of its scientific objectives. This action was taken in response to concerns about the availability of funding in FY2006 to cover any problems that might arise during environmental and performance testing, particularly with regard to several pieces of subsystem hardware perceived to have experienced significant problems. The chief items of concern are the Power Processing Units (PPUs) that provide the high voltage power to the thrusters in the ion propulsion system, one of the redundant Attitude Control Electronics (ACE) boxes, and the xenon tank.

Concern regarding the flight xenon tank arose because two qualification tanks ruptured at lower than expected pressure during testing, instigating a thorough review of the integrity of the flight tank. The Dawn team chose to reduce the xenon load in the flight tank from 450 to 425 kg to increase the safety margin (reducing a generous fuel load margin but not affecting the science return). A recommendation from the group charged with reviewing the Dawn tank, chartered by the NASA independent Technical Authority guidelines, is expected in early December.

The "stand down" order reduces expenditures while an independent assessment of the project is performed by a team assembled by the Discovery Program Office at Marshall Space Flight Centre. This Independent Assessment Team (IAT) has visited the PPU manufacturer (L3, which took over from Boeing), and will spend time during November and December with

Dawn is currently in the Assembly, Test and Launch Operations (ATLO) project phase. To date, nearly all the hardware has been successfully delivered to Orbital and integrated to the spacecraft. Delivery of the remaining PPU and ACE are pending. The solar array arrived and a deployment test was conducted at Orbital. Power has been applied to the high voltage system as the first step towards testing of the ion propulsion system, which will culminate in a hot-fire test next year.
Flight software delivery 5.1.1, which includes all functionality, has been delivered to the flight system and to the dual testbeds.

ATLO work will proceed at a slower pace during the stand down. The goal is to fully integrate the spacecraft and perform a Comprehensive Performance Test (CPT), which fully exercises the spacecarft subsystems. This will be followed by a flight system CPT, in preparation for bakeout and instrument integration. Thermal vacuum testing, originally scheduled for January at the Goddard Space Flight Center, has been postponed until the project restart.

Assuming the project receives authority to proceed to launch, a replanning effort will be undertaken beginning in February to develop a schedule, taking into account the funding constraints. At that time, the operations teams will be reconstituted, and the test program will ramp up. A series of end-to-end information system flow tests and mission scenario tests have been already planned and partially scripted.

Because of the flexibility afforded by the ion propulsion, Dawn's launch period extends at least into late 2007. The original launch period in June 2006 was chosen based on projected readiness to launch at that time. The baseline trajectory includes a Mars Gravity Assist in 2009, which fixes the timing of subsequent events. The neutral mass margin presently increases as the launch date moves toward 2007. Work is underway to define the sensitivity of the new trajectory to launch date in order to facilitate the replanning effort.

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Blobrana


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NASA has told the team developing an asteroid mission to "stand down" from launch preparations.
The Dawn spacecraft was scheduled for launch in June 2006 on a missiom to the large asteroids Ceres and Vesta, but has been told to defer work preparing the spacecraft for launch until further notice. According to the report budget pressures at JPL, which is managing the mission, is the cause for the delay. Project officials said they were asked to stand down "while an independent assessment team reports back to headquarters" on a number of technical issues, not specified in the report.
There is no sign that NASA intends to cancel the mission, officials insist. Dawn has a launch window that lasts more than a year, unlike other planetary missions whose launch windows are typically no more than a few weeks long.

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