Southwest Virginia Blogs

NASA Cancels Mission to Visit 2 Asteroids.

The Dawn mission was put on standdown last October after going over budget and suffering several setbacks that included the rupture of two xenon fuel tanks during testing, forcing engineers to reduce the amount of xenon to be loaded in the tanks.

For background reading on the mission and its difficulties, I suggest the paper by C. T. Russell et al: Dawn Discovery Mission: Status Report (pdf). The report includes some useful insight into the typical problems with spacecraft development:

Dawn has not been immune from the difficulties generally encountered by spaceflight projects that have fixed, tight schedules. Manufacturers have fluctuations in their workloads when unexpected orders arrive. Small changes in process may be made without much concern or documentation, until the subsystem fails inspection or test. Advanced planning may be inadequate so that needed parts are not on hand on assembly day, etc. These lapses all lead to delays which must be overcome with the expenditure of schedule or cost reserves. Thus far Dawn has delayed its launch date only by three weeks, principally due to an early lapse in support for the project, rather than any of the many technical issues experienced in system development. It is the Dawn project’s self-assessment at the present time that it can continue to move on schedule to launch, barring a major technical problem outside the control of the project, such as the perennial problem of the possibility of a launch vehicle standdown. A potential issue of this nature does exist with the processes used to fabricate Dawn’s xenon tank. However, we expect that Dawn will not be affected by the questions associated with the processes used to build the tank for the reasons outlined below.

Design, analysis, and test of the titanium tank for the xenon propellant are also discussed in the report:

The flight tank installed in Dawn has been tested to well above the pressures needed for ground and flight operations and it has been taken to theses high pressures repeatedly. However, when tanks similar to the flight tank have been ruptured by increasing the pressure on them until they cracked, the tanks ruptured at pressures above that needed by Dawn but below the theoretical estimates, necessitating a review of the construction processes, assumptions and the actualities of the as-built tanks. The root causes for the reduced pressure at rupture are now known and how to build stronger tanks understood. Thus there should not be problems with future tanks, but what to do with Dawn’s tank now in the spacecraft?

This mission might make a nice case study in spacecraft design. In the words of Mario Salvadori’s mother-in-law, commenting on his book Why Buildings Stand Up:

This is nice, but I would be much more interested in reading why they fall down.

Spacecraft failures are interesting too, and I wrote about them in this 2003 conference paper:
When Spacecraft Won’t Point (pdf).

Dang, I missed it: Cassini Spacecraft Returns to Titan on Monday. We’re thinking a lot about Titan around here, as we have a team of 18 seniors and 6 freshmen working on a mission to Titan. The novel project involves a fleet of buoyancy-driven gliders, a ground-based docking station, and a space-elevator. Great fun.

I mentioned a couple of weeks ago that Elon Musk would be here to give a lecture at Virginia Tech. He was here last week, for a few hours on February 21. His lecture was the second in a series sponsored by our distinguised alumnus Dr. Pat Artis, and his wife Nancy. The first in that series was in February 2005, and the lecture was given by Commander Brian Binnie. I discussed Commander Binnie’s lecture here.

Mr. Musk was here for dinner at Virginia Tech’s Inn. The 40 guests at the dinner included various Deans, Department Heads, and staff from the College Engineering, as well about half a dozen engineering undergraduate students. During the reception before dinner, I had a chance to chat briefly with Mr. Musk, discussing Falcon 1 and its payload FalconSat-2, built by cadets at the USAF Academy, under the supervision of some of my former USAF colleagues and students.

After dinner, we made our way over to Burruss Hall where the auditorium was set up for Mr. Musk’s presentation. The auditorium seats over 2000, but was probably less than half full. By contrast, Binnie’s talk filled the auditorium; however, the reason for the difference in attendance is almost certainly because all engineering freshmen were required to attend Binnie’s talk, and for some reason the same requirement was not imposed for Musk’s talk.

After introductions, Mr. Musk began his 30-minute powerpoint presentation, in which he described how SpaceX got started, what lines of rockets were in development, and what he expected regarding the upcoming launch. I especially liked his line about making “the human race multi-planetary.” The best part of his talk was when he invited questions, and there were many. I didn’t take notes, but I recall the gist of a few of the questions: What kind of car does a guy like you drive? Will you sell launches to foreign agencies? Can you describe your pre-SpaceX business experiences? How did you recruit the ~175 people who work for SpaceX. What are your plans for human spaceflight systems? What’s going on with SpaceX, Lockheed-Martin, and Boeing? What could Lockheed-Martin and Boeing do to be competitive with SpaceX?

As I said, the Q&A was the most interesting part of the talk, and it went on for more than half an hour. Some of the questions were asked by a reporter for the campus paper, who had interviewed me earlier in the day. Amusingly, the reporter’s article referred to me as Professor Charles Hill. Well, at least some of the letters were correct.