|
|
Thread Tools | Display Modes |
#41
|
|||
|
|||
Pegasus/SciSat Launch Cost
Kim Keller wrote:
"Henry Spencer" wrote in message ... Uh, no, that's ridiculous. Launchers operate for only a few minutes between leaving the atmosphere and finishing their job; the chances of a radiation upset during that time are minimal. This is not true. Most launchers that access GTO use multiple burns of the second stage. Some missions last for six hours before spacecraft sep. During that time, their trajectory takes them through the lower edges of the Van Allen Belt. Since the "brains" for the whole launcher are carried in the second stage, they'd better be SEU-resistant. SEU-resistant is a *system* requirement, not a individual parts requirement. You could achieve the exact same results of a rad-hardened chip by a slightly different avionics package design. Calculate out the radiation protection requirement for the chips, then seal them in a box that meets those requirements. Non-rad-hard computers have operated in LEO for years without any difficulties, on the amateur-radio satellites. The requirements in this area are ridiculously inflated; the launcher companies inherited them from the missile business, and stick with them because they're traditional, not because they're needed to complete the mission. Again, the difference is the altitude of the operating environment. LEO altitude does greatly reduce the incidence of SEUs, but it does not eliminate them, particularly around the South Atlantic Anomaly. Except that much of that effort is no longer necessary. It's an artifact of trying to build high-reliability hardware with 1950s electronic parts. Modern parts are so much better -- often *superior* to the mil-spec ones when you look at the actual numbers -- that the old design practices are now in the "nobody ever got fired for doing it this way" category. That's an opinion, not a fact. Given the cost of qualification testing, one must wonder why a launcher constructor would willingly spend that much money to get their vehicle ready for flight, particularly if they're paying the tab, not a subsidizing government agency. The reason is the testing philosophy works and booster reliability increases as a result. Out of curiousity, what would the differences be in testing a Mil-spec vs non-Mil-Spec systems? Seems to me that the test program is the same for the vehicle no matter it's individual parts. The test hardware is the same either way. The tests are the same. The costs are the same. |
#42
|
|||
|
|||
Pegasus/SciSat Launch Cost
Henry Spencer wrote: In article , John Schilling wrote: Believe me, some of us have thought about it. :-) Really hard to get the Canadian government to fund it, however. Partly there's an ingrained inferiority complex, a belief that Canada couldn't *possibly* do something that daring all by itself, And this from the country that built the Arrow? Oh, how the mighty have fallen. The Arrow fell partly for the same reason, alas -- it was inconceivable for Canada to succeed in something so ambitious, so the program *must* somehow be headed for disaster, and the sooner it was terminated, the better. Being unspoken and implicit made this belief all the stronger, since there was no way to openly challenge it. The people who built the Arrow built a "Jetliner" for airline use several years earlier. It was advanced enough to get orders in the US years before Boeing got into jets, but the Canadian government shut it down because they wanted the company to focus on fighters. John Halpenny |
#43
|
|||
|
|||
Pegasus/SciSat Launch Cost
"Charles Buckley" wrote in message ... SEU-resistant is a *system* requirement, not a individual parts requirement. You could achieve the exact same results of a rad-hardened chip by a slightly different avionics package design. Calculate out the radiation protection requirement for the chips, then seal them in a box that meets those requirements. Okay, works for me. Out of curiousity, what would the differences be in testing a Mil-spec vs non-Mil-Spec systems? Seems to me that the test program is the same for the vehicle no matter it's individual parts. The test hardware is the same either way. The tests are the same. The costs are the same. The differences would depend on the manufacturer or his customer: what levels do they want their parts tested to? The tests would be basically the same in set-up, but the key question is, do they envelope the components' expected operational environment plus a satisfactory safety factor? That would be called out by the customer's spec. -Kim- |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
cheap access to space - majority opinion | Cameron Dorrough | Technology | 15 | June 27th 04 03:35 AM |
Unofficial Space Shuttle Launch Guide | Steven S. Pietrobon | Space Shuttle | 0 | April 2nd 04 12:01 AM |
Unofficial Space Shuttle Launch Guide | Steven S. Pietrobon | Space Shuttle | 0 | February 2nd 04 03:33 AM |
Unofficial Space Shuttle Launch Guide | Steven S. Pietrobon | Space Shuttle | 0 | September 12th 03 01:37 AM |
Cost of launch and laws of physics | Greg Kuperberg | Policy | 235 | August 30th 03 10:20 PM |