function sat=tle2orb(tlefile)%TLE2ORB  Get Keplerian elements from Two-Line Element data.
%   SAT = TLE2ORB([TLEFILE]), where SAT is an array of struct
%
%      SAT(1:N).oe
%      SAT(1:N).name
%      SAT(1:N).epoch
%
%   as described below. N is the number of satellites.
%%   NAME is the satellite name,
%   EPOCH is in YMDhms format and
%   OE is the Keplerian orbital elements.%%   The orbital elements have the format:%      a [m]   : semi-major axis%      e []    : eccentricity%      i [deg] : inclination%      W [deg] : longitude of the ascending node%      w [deg] : argument of perigee%      M [deg] : mean anomaly at EPOCH% %   The data is extracted from the text file TLEFILE with %   Two-Line Element format of the satellite orbits.
%   To download current satellite data go to:
%
%      http://celestrak.com/NORAD/elements/
%
%   Then put the file(s) in the .../sat/ directory.
%
%   See also MSATTRACK, ORB2CART.% Copyright (c) 2002-12-08, B. Rasmus Anthin% Revision 2002-12-09, 2002-12-30, 2002-12-31,
%          2003-04-03, 2003-04-06, 2003-04-17,
%          2003-06-19.
curr=pwd;path=which(mfilename);
path=path(1:end-length(mfilename)-2);     %additional -2 for the extension.
if nargin
   if ~any(tlefile=='.')
      tlefile=[tlefile '.txt'];
   end
   tlefile=fullfile(path,'sat',tlefile);
else
   currpath=pwd;
   cd(fullfile(path,'sat'))
   [tlefile,tlepath]=uigetfile('*.txt','Load TLE Data');
   cd(curr)   if ~ischar(tlefile)
      sat=[];
      return
   end
   cd(currpath)
   tlefile=fullfile(tlepath,tlefile);
end

fp=fopen(tlefile,'r');line=fgetl(fp);i=0;mu=constant('G')*constant('Me');
Pe=24*3600;while sum(line)>0   i=i+1;   name{i}=line;   line=fgetl(fp);   year=line(19:20);   day=str2num(line(21:32));   if str2num(year(1))>4      year=['19' year];   else      year=['20' year];   end   year=str2num(year);   epoch(i,:)=datevec(datenum(year,0,day));   line=fgetl(fp);   rpd=str2num(line(53:63));   OE(i,1)=(mu*(Pe/rpd/2/pi)^2)^(1/3);   OE(i,2)=str2num(['.' line(27:33)]);   OE(i,3)=str2num(line(9:16));   OE(i,4)=str2num(line(18:25));   OE(i,5)=str2num(line(35:42));   OE(i,6)=str2num(line(44:51));   line=fgetl(fp);endfclose(fp);
for j=1:i
   sat(j).oe=OE(j,:);
   sat(j).name=deblank(name{j});
   sat(j).epoch=epoch(j,:);
end