Spacecraft Crashes Into Satellite

Juha-Matti Laurio writes "A robotic NASA spacecraft designed to rendezvous with an orbiting satellite instead crashed into its target. Unbeknownst to engineers at the time, DART's main sensor mistakenly believed it was flying away from the satellite when it was actually moving 5 feet per second toward it, investigators found."

Comments

Top Down Design?

[Ohreally_factor]

One wonders if this failure is due to a design philosophy similar to the top down design that has doomed the shuttle.

From the Feynman report:

The usual way that such engines are designed (for military or civilian aircraft) may be called the component system, or bottom-up design. First it is necessary to thoroughly understand the properties and limitations of the materials to be used (for turbine blades, for example), and tests are begun in experimental rigs to determine those. With this knowledge larger component parts (such as bearings) are designed and tested individually. As deficiencies and design errors are noted they are corrected and verified with further testing. Since one tests only parts at a time these tests and modifications are not overly expensive. Finally one works up to the final design of the entire engine, to the necessary specifications. There is a good chance, by this time that the engine will generally succeed, or that any failures are easily isolated and analyzed because the failure modes, limitations of materials, etc., are so well understood. There is a very good chance that the modifications to the engine to get around the final difficulties are not very hard to make, for most of the serious problems have already been discovered and dealt with in the earlier, less expensive, stages of the process.

The Space Shuttle Main Engine was handled in a different manner, top down, we might say. The engine was designed and put together all at once with relatively little detailed preliminary study of the material and components. Then when troubles are found in the bearings, turbine blades, coolant pipes, etc., it is more expensive and difficult to discover the causes and make changes. For example, cracks have been found in the turbine blades of the high pressure oxygen turbopump. Are they caused by flaws in the material, the effect of the oxygen atmosphere on the properties of the material, the thermal stresses of startup or shutdown, the vibration and stresses of steady running, or mainly at some resonance at certain speeds, etc.? How long can we run from crack initiation to crack failure, and how does this depend on power level? Using the completed engine as a test bed to resolve such questions is extremely expensive. One does not wish to lose an entire engine in order to find out where and how failure occurs. Yet, an accurate knowledge of this information is essential to acquire a confidence in the engine reliability in use. Without detailed understanding, confidence can not be attained.

A further disadvantage of the top-down method is that, if an understanding of a fault is obtained, a simple fix, such as a new shape for the turbine housing, may be impossible to implement without a redesign of the entire engine.

Re:Disband NASA

[Ohreally_factor]

Unfortunately, the faulty design was due to the screw ups of a private contractor, so there goes your "private sector" argument.

Re:Disband NASA

[xoyoyo]

Snore. And out come the free enterprise loonies. The only trouble with your argument is that free enterprise is already perfectly able to indulge in space exploration and, well, hasn't. You can rent time on a launch pad, you can rent space in a rocket. There are many excellent engineering companies who can build more or less any satellite or other space craft you want. But there's no return on doing anything more ambitious than communications satellite. What exactly is the private sector going to do with a Mars probe, say? Sell ad hoardings on the side? (Didn't Beagle II do this?) It's better to regard what NASA and ESA do as a public infrastructure project rather than as competition for private enterprise. The work NASA is doing (mostly competently) is more like building the channel tunnel than a profit-based business. We tried building the tunnel through the private sector, but Eurotunnel has been bailed out by the giovernment and the banks so many times that it's actually ended up costing us far more than it would have done if we'd done it the old fashioned way, even assuming the usual obscene project over-run costs of a public project.