I can has flyby?

Today I downloaded the state vectors for New Horizons and MU69 Arrokoth and subtracted their positions. The two new get closer than about 596,000 kilometers.

The New Horizons output header says:

 Revised: Dec 29, 2018        New Horizons Spacecraft                      -98

and the 2014-MU69 output says:

Rec #:  486958 (+COV) Soln.date: 2015-Apr-07_15:31:42      # obs: 58 (118 days)

These suggest to me that the New Horizons state vectors should be quite accurate as they have been revised after the flyby, and that the MU69 state vectors are wrong because 118 days in 2015 is not enough data to predict the position accurately at the end of 2018.

But could it really be off by over a half-million km?

There certainly must be a better solution somewhere for MU69; was it not released to the public?

Have I simply done something wrong?

Here's a sample datapoint just for general reference


2458479.500000000, A.D. 2018-Dec-27 00:00:00.0000,  1.798784534455549E+09, -6.207675388216038E+09,  2.205418932665184E+08,  4.349272029256285E+00,  1.451130097969201E+00, -1.243301247191951E-01,

New Horizons:

2458479.500000000, A.D. 2018-Dec-27 00:00:00.0000,  1.799376676456984E+09, -6.207654742562343E+09,  2.204740238154533E+08,  5.470499469838275E+00, -1.297281585240275E+01,  5.087368672814954E-01,

enter image description here


1 Answer 1


Thanks to Jon. D. Giorgini at NASA JPL for pointing out that there is indeed a much newer solution in Horizons.

The trick is to use the newer, though unofficial designation Ultima Thule when searching for it:

Ultima Thule

Note that the new solution for Ultima Thule has an "MB" or major body designation!

This solution is based on all observational data available to NASA and likely includes those stellar occultations in 2017 and 2018

as well as other checks by ground and space-based telescopes, including Hubble and New Horizons itself:

enter image description here

above: from Strange speck of light in the picture sequence of the approach to 2014 Mu69 (Ultima Thule) Source: Here (German) or here (English), NASA / Johns Hopkins Applied Physics Laboratory / Southwest Research Laboratory / Henry Throop

According to https://ssd.jpl.nasa.gov/?horizons_news

December 29, 2018:
   -- The NH/Ultima Thule trajectories in Horizons have been updated to the 
   latest flight project releases for the 3500 km encounter on 2019-Jan-1 
   at 05:33 UTC.

  The KBO target for the encounter can be looked up using the name 
   "Ultima Thule" and selected as a coordinate origin with "@Ultima" ... 

  The spacecraft ID is -98 or "NH" (for New Horizons).

The situation is also discussed in the Horizons output:

 Revised: Dec 29, 2018            486958 (2014 MU69)                    2486958

 This pre-computed trajectory is consistent with the New Horizons spacecraft
 Kuiper-Belt extended mission, with the planned 3500 km flyby of Ultima Thule
 on 2019-Jan-1 @ 05:33 UTC.

 Trajectories were provided by the New Horizons mission planning team at SWRI 
 and are fits to internal flight-project data that has not been made available 
 outside the flight project.

 To use this official mission trajectory to ...

  A) Generate ephemerides with respect TO the mission target:
      Specify the coordinate center in Horizons as "@2486958" 

  B) Generate ephemerides OF the mission target
      Specify the target in Horizons as "2486958". 

 To instead use the latest JPL ground-based orbit solution (based on the 
 publicly available data) and numerically integrate over an arbitrary 
 time-span with statistical uncertainties of that public dataset, do a 
 look-up in Horizons with syntax "2014 MU69;" or "486958;" or "DES= 2486958;" 
 or "DES= 2014 MU69" or "2486958;" (i.e., with a semi-colon). 

 Note: the object previously had a provisional SPK ID of 3713011.  It was 
 then assigned an IAU number of 486958 such that the primary SPK ID became
 the present 2486958 (2000000 + IAU number).

 Trajectory name                            Start (TDB)         Stop (TDB)
 ---------------------------------------  -----------------  -----------------
 20180601_20250101_od141_tcm30_burn_V0.1  1994-Jan-08 00:00  2033-Dec-21 00:00 

Double checking; yep, Cheezeburger Cat can have FlyBy!

enter image description here


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