Sorry. I did use plot3d.   Anyway, my problem is not with the plot3d command  but with the numerical  integration command.

Thanks for the comments.   I also found that  I can get a background plot without using the animate command by calling

> trajpl := seq(plot([seq(traj[j], j = 1 .. k)] ), k = 2 .. maxpt);
> display(fpl, display(trajpl, insequence = true));