The NEAR spacecraft

Progress Report: 21Jul99


We only know Eros's mass to within about 10%. If Eros weighs significantly less or significantly more that predicted, NEAR will enter a 100 km orbit different from the one it will enter if the mass is what we expect. Therefore, we need to run simulations of what will happen if the mass is not nominal


The first thing we did was to modify our REQ files; since the spacecraft goes into orbit at a different time, the orbit has to be broken into different five-and-a-half hour chunks.

Jessica: I made a sequence for the high mass case. My .REQ files for the high mass case can be found in To see a model of the asteroid using all the unaltertered 5.5 hour periods, click here. (the colors on the model describe the emission angle -- purple is 0, green is about 45, and red is 90) I made plate models of the whole asteroid using all but one 5.5 hr orbit (these models can be found in, so that I could see if altering any one period would significantly worsen any part of the image. Notes on observations of these missing periods are in
Then I took each of the periods that did NOT significantly affect the image, and altered each of their aimpoints to get good emission angle on problem areas. I made plate models of the whole asteroid with just the one period altered (these plate models, as well as individual off-nadir .REQ files, are found /work2/jedmonds/orbit/100k/high_mass/off_nadir_5.5s). Notes on observations of these altered periods are in a To see an example of one altered orbit, click here.
I combined two and then three of these periods in many combinations, and noted my results. There are notes about the two 5.5 hr off-nadir period runs at, and notes about the three 5.5 hr off-nadir period runs at To see a picure of the best three period alteration, click here.
Finally, I combined seven, then nine, then eleven 5.5 hour periods to see what kind of coverage I could get using these minimumu numbers. These plate models, as well as descriptive README files to explain how I reasoned these models, can be found in,, and To see a picture of the image in which nine periods was used, click here.

Emily: I did almost exactly what Jessica did, except that I did it for the low mass case. Also, I only did one sequence off-nadir and three sequences off nadir. All of my files are in or All the REQ files are in the first one; all the plate models and frames are in the second one. My README file is at


Jessica: I found that it was best to point off-nadir for the periods of 113:08:00 (aimpoint: 6/30/0), 098:19:00 (aimpoint: 4/220/0), and 106:08:00 (aimpoint: 4/330/0). There is a useful file describing why this is the best sequence located at

Emily: I found that it was best to point off-nadir for the periods of 104:19(5/330/0), 101:13(4/330/0) and 105:08(3/150/0). Information about how I did this is in the aformentioned README file.

(Emily Peters and Jessica Edmonds, 7-21-99)