 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
| HomeDiscussion Groups General ModelsRailroadsRocketsRadio Controlled Air ModelsHelicoptersLand ModelsWater ModelsModelGeeks.com Contact UsLink To UsSearch & Site Map |
Model Forum / General / Rockets / February 2008How hard was it to hit the satellite?
I am not a rocket scientist, but it occurred to me that it must be extremely difficult to make sufficiently accurate course corrections on such a fast moving missile. Besides continuously acquiring the position of the target with the necessary accuracy and then computing the heading and velocity of the missile, it must also compute how long to fire which steering jets. And the jets must be very powerful but at the same time very precise. It just seems to a relatively uninformed person like myself to be a near impossible task at the speed involved and given the size of the fuel tank they were trying to hit. As I understand it, the closing velocity of the missile that shot down the satellite was 22,000 mph, so at one second before impact, the missile was still 6.11 miles away, which means that a course correction even at that late stage had to be about 0.108 degrees per 10 feet of accuracy. There must be a point at which you must make the final correction with the greatest accuracy. The timing of that point depends on how long it takes to do all the acquisition and computation, and then take into account the response time of the control system. So, I wonder what is the last time a useful correction can be made at that speed. T minus one second? A tenth of a second? And what kind of force does it take to steer a heavy very fast-moving missile? So, like I said, I am not a rocket scientist, but some of you might be. Has anyone made a serious attempt to compute what it took to do this? Was it as incredible a feat as it seems to me? It almost makes me think that they really didn't do it, but it is probably just my ignorance and natural distrust of the government to blame for that. silverfox <dcfrench@gmail.com> wrote in news:2053ef2b-8b00-41ea-8c1d- bb71c8b756f5@n75g2000hsh.googlegroups.com: > So, like I said, I am not a rocket scientist, but some of you might > be. Has anyone made a serious attempt to compute what it took to do > this? Was it as incredible a feat as it seems to me? Well, yes it was almost incredible (meaning beyond belief). The math and physics, however are rather straightforeward. Almost all the factors are "knowns". The orbital elements were well known. The performancce of the missile is well known. This simplifies things greatly. From wikipedia article on the RIM-161: Radar finds the ballistic missile target and the Aegis weapon system calculates a solution on the target. When the missile is ordered to launch, the Aerojet MK 72 solid-fuel rocket booster launches the SM-3 out of the ship's Mark 41 vertical launching system (VLS). The missile then establishes communication with the launching ship. Once the booster burns out, it detaches, and the Aerojet MK 104 solid-fuel dual thrust rocket motor (DTRM) takes over propulsion through the atmosphere. The missile continues to receive mid-course guidance information from the launching ship and is aided by GPS data. The ATK MK 136 solid-fueled third stage rocket motor (TSRM) fires after the second stage burns out, and it takes the missile above the atmosphere (if needed). The TSRM is pulse fired and provides propulsion for the SM-3 until 30 seconds to intercept. At that point the third stage separates, and the Lightweight Exo-Atmospheric Projectile (LEAP) kinetic warhead begins to search for the target using pointing data from the launching ship. The ATK solid divert and attitude control system (SDACS) allows the kinetic warhead to maneuver in the final phase of the engagement. The KW's sensors identify the target and attempt to identify the most lethal part of the target and aim the KW at that point. If the KW intercepts the target, it provides 130 megajoules of kinetic energy at the point of impact. The KW actually "spins" at a low revolution along its path of flight. The tracking software tries to keep the target centered in the sensor. You're right, everything does happen at an extremely high rate of closure, but in this case the target is on a "fixed" course and not evading. The target is not going to vary in its path. Other variances might include weather (winds, atmospheric density, etc), propellent and flight variances in any of the booster phases, targeting misalignments from ground stations, acts of God. This is a self-correcting system with a high rate of sampling in the feedback loop. Check out the picture of the KW on the binaries group. The kill vehicle in the ASAT used dual 1802 micro-processors. These have never been the fastest computers around. 16 clocks for a fetch-execute cycle (no pipelining) and a fast version used a 6.4MHz clock. Their claim to fame is that for a time they were about the only radiation hard micro-processors around. At least if you bought the expensive silicon-on-sapphire version. That should give you some idea as to how hard it really is. Or isn't. http://www.astronautix.com/lvs/asat.htm http://en.wikipedia.org/wiki/RCA_1802  SignatureDavid W. Schultz http://home.earthlink.net/~david.schultz ------ "What you don't know should be a goad to make you try and find out, not an excuse to bliss out and sit drooling into your filet mignon." -- PZ Myers Wow, that IS amazing! That is the same computer they used in the Voyagers. It doesn't make me think that the task was any less difficult, however. But it does suggest that the timing constraints are not as restrictive as I imagined. > The kill vehicle in the ASAT used dual 1802 micro-processors. These have > never been the fastest computers around. 16 clocks for a fetch-execute [quoted text clipped - 12 lines] > "What you don't know should be a goad to make you try and find out, not > an excuse to bliss out and sit drooling into your filet mignon." -- PZ Myers > Wow, that IS amazing! That is the same computer they used in the > Voyagers. It doesn't make me think that the task was any less > difficult, however. But it does suggest that the timing constraints > are not as restrictive as I imagined. I would have sworn they used a 6502 in the Voyager series. >> The kill vehicle in the ASAT used dual 1802 micro-processors. These >> have never been the fastest computers around. 16 clocks for a >> fetch-execute cycle (no pipelining) and a fast version used a 6.4MHz >> clock. Their claim to fame is that for a time they were about the >> only radiation hard micro-processors around. At least if you bought >> the expensive silicon-on-sapphire version. I don't think this is the same missile they used in the recent shoot. The ASAT is different than the RIM-161, a variant of the Standard Missile, see: http://en.wikipedia.org/wiki/RIM-161_Standard_Missile_3 http://en.wikipedia.org/wiki/ASM-135_ASAT 1802 - wow that brings back memories. I built a COSMAC ELF way back when and added a math co-processor. I added a couple of k of memory using Hitachi 6116LP3 static memory chips that would keep programs with battery back-up. What was outstanding about the 1802 was the clock rate - it could be *anything* up to the max. Even single-step pulses. I also had a KIM-1 6502 single-board computer, and an ad-on expansion board. The KIM-1 had 1k of memory, the expansion board added 4k and a PIO chip. With these, I also learned that most of programming is driven by coffee. |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.