Figure 2 in this paper shows a plot of inclinations necessary for a Sun-sync orbit at various altitudes (assuming zero eccentricity): http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/37900/1/04-0263.pdf Ted, I agree with your overall point about the projected launch Az not right for a SSO orbit at 500 km, but my math is coming out differently. For a latitude of 39.66 and an Az of 192.3 I get an inclination of 99.44 degrees. My excel formula for the inclination is =DEGREES(ACOS(((SIN(RADIANS(B6)))*(COS(RADIANS(B5)))))) where B5 = latitude and B6 = Az I think one of us may have a math error (likely me), so if someone could check my formula I would appreciate it. --------- Brian On Mon, Apr 2, 2012 at 7:51 AM, David Tiller <dtiller@captechconsulting.com>wrote: > Ted, > > Thank you for your (as always) excellent analysis. > > It seems that there are two parameters that are used to compute the > particulars of a sun-synchronous orbit - orbital altitude is used to derive > the correct orbital inclination which then drives the launch azimuth based > on latitude. Your analysis assumes that the stated launch altitude is > correct and the launch azimuth is incorrect. > > What orbital altitude would be correct for a sun-synchronous orbit > assuming that the launch azimuth will be as the DPRK stated? > > -- > David Tiller > Lead Consultant/Architect | CapTech > (804) 304-0638 | dtiller@captechconsulting.com > > ________________________________________ > From: seesat-l-bounces+dtiller=captechconsulting.com@satobs.org[seesat-l-bounces+dtiller= > captechconsulting.com@satobs.org] on behalf of Ted Molczan [ > ssl3molcz@rogers.com] > Sent: Sunday, April 01, 2012 10:46 PM > To: seesat-l@satobs.org > Subject: North Korea satellite: NOTAMs inconsistent with claimed > sun-synchronous orbit > > North Korea claims that its upcoming rocket launch will place a satellite > in a 500 km, sun-synchronous orbit: > > http://www.kcna.co.jp/item/2012/201203/news28/20120328-40ee.html > > "It weighs 100kg and will circle along the solar synchronous orbit at > 500km high altitude." > > The sun-synchronous claim is inconsistent with the NOTAM coordinates North > Korea has issued for the impact zone of the > rocket's two stages: > > NAVAREA NO.12-0174 Date:2012/03/19 12 UTC > > YELLOW SEA AND NORTH PACIFIC, LUZON. > ACCORDING TO INFORMATION FROM NORTH > KOREA VIA IMO, ROCKET LAUNCHING. > IMPACT HOUR 2200Z TO 0300Z COMMENCING > DAILY 11 TO 15 APR. > IMPACT AREAS BOUNDED BY > A. 35-12-25N 124-52-23E > 35-12-13N 124-30-34E > 35-55-20N 124-32-10E > 35-55-10N 124-50-25E. > B. 15-08-19N 124-46-15E > 15-09-35N 123-45-27E > 19-24-32N 123-54-26E > 19-23-08N 124-45-13E. > CANCEL THIS MSG 150400Z APR. > > Stage 1 would impact in zone A; stage 2 in zone B. > > The launch site is located at 39.660107 N, 124.705203 E. > > To be sun-synchronous, a 500 km orbit requires an inclination of 97.42 > deg. At the latitude of the launch site, a > trajectory that directly ascends to that inclination requires a launch > azimuth of approximately 192.3 deg (12.3 deg west > of due south). The azimuth from the launch site through the various impact > zones downrange should agree closely with > this value, typically within a degree or so, absent any significant > yaw-steering (aka dogleg) early in the ascent. > > The azimuth from the launch site to the midpoint of the southern boundary > of the 2nd stage's impact zone (approx. 15.15 > N, 124.26 E) is 181.0 deg, which is far from the required 192.3 deg. > > I considered the possibility of an eastward dogleg early in the ascent, > but the trajectory would have to turn toward > approximately 192 deg azimuth well before the 2nd stage ceased firing, in > which case the 2nd stage's impact zone should > be oriented with its east and west sides pointing roughly toward azimuth > 191 deg, but they do not. The west side points > toward azimuth 181.8 deg, and the east side 179.8 deg - again far from the > required value, and essentially identical to > the azimuth calculated from the launch site. Therefore, there is no > dogleg, which is not surprising, since it would > involve overflying the Korean peninsula, probably including South Korea. > > I do not see how North Korea could reach a sun-synchronous orbit from the > new launch site without risk to populated > areas. Launching directly toward the required 192.3 deg azimuth would > result in a trajectory that skirts China's east > coast near Shanghai. The rocket's second stage would overfly Taiwan, > before impacting in a zone bordering within perhaps > 50 km of the west coast of the northern Philippines. > > To give a *very rough* idea of the effect of launching directly toward > azimuth 192.3 deg, I have adjusted the longitudes > of North Korea's NOTAMs: > > A. 35-12-25N 123-42E > 35-12-13N 123-20E > 35-55-20N 123-33E > 35-55-10N 123-51E > B. 15-08-19N 119-38E > 15-09-35N 118-56E > 19-24-32N 119-43E > 19-23-08N 120-34E > > I very much doubt that North Korea plans for its rocket stages to fall in > the zones I have estimated, but it is for > North Korea to explain the inconsistency between the orbit it claims to be > targeting and the NOTAMs it provided. > > Ted Molczan > > > _______________________________________________ > Seesat-l mailing list > http://mailman.satobs.org/mailman/listinfo/seesat-l > _______________________________________________ > Seesat-l mailing list > http://mailman.satobs.org/mailman/listinfo/seesat-l > -------------- next part -------------- An HTML attachment was scrubbed... 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