NEAR spotted; Sunglint & S.Hem. obs. needed

Joan and David Dunham (
Thu, 22 Jan 1998 01:44:40 -0500

                   NEAR Earth Swingby News

1. First 1998 optical sighting of NEAR shows it 2 mags. fainter.
2. Request for timings of NEAR's Sunglints; best chance in southern
    U.S.A.; panel misalignments can cause significant path errors.
3. Request for astrometric observations from Southern Hemisphere 
    observatories soon after the Jan. 23rd flyby.
4. JPL Web site for accurate topocentric positions.

These topics are described in more detail below:

1.  The first optical observation of NEAR reported to me was made 
by Alain Murray at the Observatoire de la Cote d'Azur at Caussols, 
France, at U.T. 1998 Jan. 21, 18h 27m 46s.  NEAR was 19th mag., two 
magnitudes fainter than the prediction I distributed yesterday, and 
was within a few tenths of an arc second (the error of the GSC star 
positions used for the reference frame) of the precision topocentric 
ephemeris computed at JPL's ephemeris generation Web site at

Alain took several more images that he plans to make into a gif-
format movie showing NEAR's motion that we hope to be able to put on 
NEAR's Web site later today.  Probably by then there will be 
observations from some other observatories.  Important information 
about using the JPL site is given in item 4.

2.   Timed observations of tomorrow night's NEAR Sunglints are 
requested by those who can make them.  Unfortunately, the weather 
forecast is poor for most of the Sunglint regions, including 
overcast everywhere east of the Mississippi River except southern 
Florida and the West Coast north of central California.  The weather 
forecast is currently best for southern California, and Arizona and 
New Mexico.  Most of Texas should also be clear at the time, but 
clouds from a retreating front may still cover the southeastern part 
of Texas, including Houston (so observers there who want to see the 
glint should be prepared to travel west).  Partly cloudy skies are 
expected in Utah and Colorado, so the glint might be seen there, but 
conditions deteriorate east of Colorado, with Kansas City expected 
to be mostly cloudy.  Approximately the southern third of the 
Florida peninsula should be mostly clear, with clouds increasing 
towards the north to overcast in Georgia and the Florida panhandle.  
Check your local forecast, since the situation could change.
     To time the Sunglints, use a tape recorder to record WWV 
shortwave time signals and you calls when the Sunglint appears and 
disappears, and any step increases or decreases in brightness.  If 
you have a camcorder, try to record the Sunglint with it, but only 
if you can see at least Mirphak and Algol in the viewfinder; you 
will need to use manual focus rather than the camcorder's autofocus 
to record stars (first, try to record Sirius, then Capella, then 
whatever stars of Perseus you can record).  Record WWV time signals 
at 5 or 10 megahertz for timing.  If you don't have a WWV receiver, 
record the event like IOTA has requested for recent occultations of 
Aldebaran:  Record CNN Headline News before and after the event, 
leaving the camcorder running the whole time (a few IOTA members 
will make a master tape of CNN and WWV to calibrate the tapes that 
use only CNN for timing).  If you have neither a WWV receiver nor 
cable TV, then record, also before and after the Sunglint, the U. S. 
Naval Observatory master clock by telephoning 1-900-410-8463 (it has 
a 50 cent toll), preferably via AT&T to ensure use of land lines.  
Unfortunately, some telephone companies will not allow use of AT&T 
for placing calls to 900 numbers. 
     Keep in mind that the misalignment of the solar panels can 
cause a significant shift of the Sunglint path shown in the maps on 
the NEAR and IOTA Web sites, so observers at least a full path-width 
away should watch for a possible Sunglint.  The Sun's diameter is 
0.5 degree, and the misalignments can be as much as a full degree 
(two path-widths), although I suspect they will be only a few 
tenths, or less than a path width, off.  Also, I have found errors 
in the plotted locations of the Sunglint ellipses on the maps; all 
of them east of the Rocky Mountains should be shifted about a deg. 
of longitude towards the east (the ones west of the Rockies are 
shown in their correct locations).  Hence, all of Massachusetts and 
the whole Florida peninsula are within the predicted Sunglint path.
     We will analyze only a few tapes for measuring the misalignment 
of NEAR's solar panels; we don't need dozens of tapes.  So you 
should send a brief description of what you recorded to me first by 
e-mail, and only send the tape if we request it.  Since most areas 
will be clouded out, your tape could be valuable.  Short glints that 
might be seen from locations near or outside the edges of the 
predicted path would be most valuable for defining the solar panel 
misalignments, and negative observations can also be useful.
     I generated the pointing vectors for the Sunglint sequence, 
but Gene Heyler fine-tuned them with my help, developed the 
spacecraft pointing commands and simulated what the spacecraft would 
really do in response to the commands (the glint path does not bend 
as sharply as shown on the map, but "rounds" the corners slightly).  
Gene generated the Sunglint annimation that is on the NEAR Web site
using the Satellite Tool Kit software.  A little history of the 
Sunglints was published in yesterday's San Francisco Chronicle and 
might be seen on their Web site at

3.   Astrometrists in the Southern Hemisphere are encouraged to 
obtain astrometric observations of NEAR as soon as possible after 
the Earth flyby, before the distance becomes very large.  
Observations relative to ACT and HIP-catalog stars may be needed, 
that is, hopefully one or more stars from these catalogs will be in 
the CCD frame.  The observations could be of value to define NEAR's 
precise departure direction, important information for designing the 
first post-flyby trajectory correction maneuver for reaching Eros.
The usual radiometric tracking that is already scheduled will 
probably be good enough for this purpose, but for over two months 
after the flyby, NEAR can only be tracked from the Deep Space 
Network (DSN) station in Canberra, the first time an interplanetary 
spacecraft has been in such a situation, trackable from only one 
station, so the real errors could be larger than the expected ones.

4.   The JPL ephemeris Web site given in item 1 is a little more 
difficult to use than the one at the Minor Planet Center (MPC) site 
given in yesterday's message, and is most important for very small 
imaging systems where the errors of just under 1 arc minute common 
to the MPC and my topocentric predictions are important.  It has 
flexibility in using a specifed time interval and increment.  The 
JPL site "requires a table-capable browser".  When you click on the 
object for which an ephemeris is desired, you need to click on the 
box to the right to expand it, then select the NEAR flyby at the 
bottom of that menu.  Then, you must click on the 
"Sun/Planet/Spacecraft" button on the left to "lock" NEAR as the 
selected object; otherwise, it will automatically revert to Mars 
when you back out of that submenu.  When you go to the other 
submenus, you simply need to click on the "use requested .." button 
at the bottom to lock them into place. 
     The JPL ephemeris is full-precision.  The MPC and my 
predictions use the same precision spacecraft trajectory from JPL, 
but at least my predictions neglect the small change in the 
observer's position due to the 2 years of precession from 1998 to 
2000, light-time effects and some other small effects.  Even so, the 
under 1' error that results will not be important for most 
observers.  Note that the azimuths given in the MPC predictions are 
counted from 0 being due south rather than 0 being due north.

Later today, I hope to produce some star charts, showing the 
topocentric paths for several locations during the few hours before 
the Sunglint maneuvers, that can be placed on the NEAR and IOTA Web 
sites.  I will probably make only one more mass mailing like this 
before the flyby, probably around 1h or 2h UT Jan. 23 UT, mainly to 
describe what topocentric star charts might be available.

Below is the ephemeris I distributed yesterday, but with 
magnitudes revised using Alain Murray's observations earlier 
tonight.  Only the date, time, and mag. are given to try to limit 
the size of this message.  During the Sunglint times (6:23 to 6:50 
U.T.) for North American observers, NEAR's unglinted magnitude will 
probably be a little brighter, maybe half a mag. or more, due to the 
smaller phase angle.  Similarly, the mags. after the 7:23 U.T. 
perigee are probably too optimistic by a magnitude or more due to 
the unfavorable departure phase angle. 

Day  h  m Mag.

 21 12:00 19.3
 22  0:00 18.7
 22 12:00 17.6
 22 18:00 16.9
 22 20:00 16.5
 23  0:00 15.6
 23  2:00 14.9
 23  3:00 14.5
 23  4:00 14.0
 23  5:00 13.2
 23  5:30 12.7
 23  6:00 12.0
 23  6:10 11.8
 23  6:20 11.4
 23  6:30 11.0
 23  6:40 10.5
 23  6:50  9.9
 23  7:00  8.9

 23  7:40  8.9
 23  7:50 10.1
 23  8:00 10.8
 23  8:30 12.1
 23  9:00 12.9
 23 10:00 13.9
 23 12:00 15.1
 23 15:00 16.1
 23 18:00 16.8
 24  0:00 17.7

David W. Dunham, NEAR Mission Design, 1998 Jan. 22, 7h U.T.