Kwangmyongsong 4 Mission Summary

The first concrete information that North Korea was planning a launch came around February 4 when its government dramatically published a copy of its letter to the International Maritime Organisation warning of the drop zones for the launch vehicle's first and second stages and the payload fairing.

In reality, it was window dressing because there are formal communications channels to deal with such matters at administrative level. No letter was published to deal with warning the aviation authorities but South Korea and the Phillipines issued NOTAMs covering the affected areas. The South Korean ones pointedly called it a "missile launch" where the usual convention is to refer to a rocket or satellite launch.

The letter said launch would be between February 8 and February 25 Pyongyang Time toward sun-synchronous orbit like its predecessors. On February 6, North Korea announced that the launch period had been brought forward one day and shortened. The new end date was February 14, meaning the satellite would be in orbit before two upcoming North Korean national days relating to former leader Kim Jong Il.

The NOTAMs

These NOTAMs give drop zone co-ordinates for the first and second stages of the rocket and for the payload fairing. Those for the first stage and the fairing were issued by South Korea and the second stage one came from The Phillipines.



First Stage

A0170/16 - TEMPO PROHIBITED AREA ACT DUE TO MISSILE LAUNCHING BY DPRK : AREA BOUNDED BY 360400N1243000E-360400N1245400E-351900N1245400E-351900N1243000E TO THE BEGINNING. RMK : MISSILE DEBRIS WILL FALL IN THIS AREA. SFC - UNL, 2230-0330, 07 FEB 22:30 2016 UNTIL 25 FEB 03:30 2016. CREATED: 03 FEB 09:46 2016



Payload Fairing

A0171/16 - TEMPO PROHIBITED AREA ACT DUE TO MISSILE LAUNCHING BY DPRK: AREA BOUNDED BY 331600N1241100E-331600N1250900E-322100N1250800E- 322200N1241100E TO THE BEGINNING. RMK : MISSILE DEBRIS WILL FALL IN THIS AREA. SFC - UNL, 2230-0330, 07 FEB 22:30 2016 UNTIL 25 FEB 03:30 2016. CREATED: 03 FEB 09:47 2016



Second Stage

B0521/16 - DUE TO SECOND STAGE OF NORTH KOREA ROCKET LAUCH WI THE AREA BOUNDED BY 1944N12353E 1943N12451E 1700N12448E 1701N12352E THE FLW RTE SEGMENTS ARE CLSD: 1)M501 BTN OMDOB AND BEDIP 2)A590 BTN GURAG AND MUPOB 3)R597 BTN SKATE AND SARSI 4)A582 BTN BISIG AND SARSI ALTN RTE: - MEVIN B462 (INBOUND MANILA FIR) - N884 LEBIX (OUTBOUND MANILA FIR) - OTHER RTE SUBJECT TO ATC APPROVAL. 2130-0400, 07 FEB 21:30 2016 UNTIL 25 FEB 04:00 2016. CREATED: 04 FEB 08:04 2016

Firming-up the Potential Launch Time

The first attempt to launch Kwangmyongsong 3 ended in failure. The second was a success. They occurred:

2012 April 12, 22:38:55 UTC - April 13, 07:38:55 Pyongyang Time

2012 December 12, 00:49:46 UTC - 09:49:46 Pyongyang Time.

The local times of day and later time for the December launch suggested a possible link with sunrise. The two times did not show the same interval after sunrise but the fact that neither lift off was on an exact minute hinted that there was a geographical or astronomical factor at work.

The clue turned out to be the altitude of the Sun above the horizon at the Sohae site at the moment of lift-off. For the April launch it was 16°.8 and for December's it was 16°.4. The values were so similar that coincidence was unlikely.

Using the two altitude values as limits and applying them to the plan for a 2016 February 7 launch suggested a liftoff time between 00:25 and 00:29 UTC. In the event, launch came at 00:30 UTC, exactly on the stroke of the minute. It was 09:00 local time at Sohae and the altitude of the Sun was 17°.1.

The possible coincidence of solar elevation became a hard fact.

Lessons Learned

Existence of a lift-off constraint tells us that launching the rocket has a higher priority than the orbit achieved by the satellite. If it were the other way round then all the launches would have come at the same time of day to ensure a consistent local time beneath the sun-synchronous orbit.

2012 December's launch was accompanied by rumours that the time of launch had been chosen to avoid it being observed by US imaging spy satellites. The existence of the solar elevation figure should have warned the analysts repeating the story that it was highly unlikely to be true. It's tempting to speculate that the tale might have been a piece of disinformation put out by North Korea.

After the successful 2012 launch, the world was treated to images of South Korean vessels pulling the spent first stage from the water and hauling it off for inspection and analysis. On this launch, the first stage exploded after it finished its job. The heavier fragments such as engine components would have sunk in the sea on impact. It may have been unintentional but it could have been a self-destruct mechanism to make sure no-one got their hands on it.

Launch Trajectory

Launch from Sohae to sun-synchronous orbit requires a dog-leg in the ascent ground track. Heading directly there would involve overflight of China and Taiwan and would drop the second stage rocket on The Phillipines.

The map shows the sequence of events during the launch. Impact zones are as specified in the navigation warnings and the final track for the satellite as it entered orbit is based on data fron Space-Track. Positions shown for second and third stage ignition are approximate.

Launch Vehicle Performance

Kwangmyongsong 4's initial orbit shows evidence that the launch vehicle underperformed against expectation. The Zarya.info launch list for 2012 shows that Kwangmyongsong 3 attained an orbit of 498 x 582 km. Its argument of perigee was 167°. Kwangmyongsong 4 on the other hand only reached 465 x 502 km but the argument of perigee was 337°.

Argument of perigee is the angle measured round the orbit from the northbound equator crossing to perigee itself. Satellites tend to be launched so they enter orbit near perigee with sufficient velocity to reach the required apogee. This is what happened with KMS 3. Its perigee of 498 km was at about 13° North latitude, about 20° further round the orbit than the launch site so it fits the normal pattern for a launch.

Kwangmyongsong 4's argument of perigee indicates that it was injected into orbit at APOGEE which is 180° away from perigee. It entered orbit at a height of 502 km at latitude 23° north. The height and location are a close match to those of Kwangmyongsong 3.

The implication is that the launch vehicle third stage imparted 0.5 percent less velocity (36 metres per second) than was intended. If it had been intended to reach an apogee of around 580 km like its predecessor, it fell short by 120 km. Had the underperformance been a little greater (in the region of 120 metres per second), Kwangmyongsong 4 would have not achieved orbit. It would have re-entered the Earth's atmosphere above the northern Atlantic Ocean about half way round its first circuit of the globe.

Orbit Attained

Here is an extract from the Zarya.info satellite launch list for 2016. Note the argument of perigee for both satellite and rocket.