Adding seconds to get new date

I have some dates and then I have an ellapsed time for a transfer orbit (in seconds). I need to add the seconds (t.trans.trans12) to a date (DateString.launch) and want it to output the new date in the format 'yyyy-mm-dd HH:mm:ss'. I'm not really sure why its not working. I've tried everything I can find and isn't working quite how I want it.

So I need the new date (DateString.afterTrans12) so I can plug it into juliandate() so I can find the position of Mars and Earth at DateString.afterTrans12

If anybody has an easier way to do all of what I have below please share :)

%% Format Specifiers
epochValue = '2000-01-01';
formatIn = 'yyyy-MM-dd hh:mm:ss';

%% Transfer Time
t.trans.trans12 = seconds(2.236376148291764e+07);	% seconds

%% DateStrings
DateString.epoch = datevec(datetime('2000-01-01 12:00:00','format',formatIn,'ConvertFrom','epochtime','Epoch',epochValue));    % J2000 epoch
DateString.start = datevec(datetime('2032-04-17 12:00:00','format',formatIn,'ConvertFrom','epochtime','Epoch',epochValue));    % mission start date
DateString.emergency = datevec(datetime('2039-11-03 12:00:00','format',formatIn,'ConvertFrom','epochtime','Epoch',epochValue));    % emergency date
DateString.launch = datevec(datetime('2040-04-17 12:00:00','format',formatIn,'ConvertFrom','epochtime','Epoch',epochValue));    % launch to planet date

DateString.afterTrans12 = [];	% Need output in 'yyyy-mm-dd HH:mm:ss' for input of seconds;    

%% Elapsed Time Data
T.launch = etime(DateString.launch,DateString.epoch);    % between epoch and launch
T.emergency = etime(DateString.emergency,DateString.epoch);    % between epoch and emergency
T.start = etime(DateString.start,DateString.epoch);    % between epoch and start

%% Position Data
% ignore or erase this if you copy+paste to your computer and don't have the planet ephemeris package
position.earth.launch = planetEphemeris(juliandate(DateString.launch),'Sun','Earth');
position.earth.start = planetEphemeris(juliandate(DateString.start),'Sun','Earth');
position.earth.emergency = planetEphemeris(juliandate(DateString.emergency),'Sun','Earth');
position.mars.launch = planetEphemeris(juliandate(DateString.launch),'Sun','Mars');
position.mars.start = planetEphemeris(juliandate(DateString.start),'Sun','Mars');
position.mars.emergency = planetEphemeris(juliandate(DateString.emergency),'Sun','Mars');

Answer 1

[Peter Perkins]

Andrew, it's not clear to me why you are converting datetimes to datevecs and then using etime. Not sure I've followed what you want to do, but this seems much simpler:

>> epoch = datetime('2000-01-01 12:00:00')
epoch = 
  datetime
   01-Jan-2000 12:00:00
>> launch = datetime('2040-04-17 12:00:00')
launch = 
  datetime
   17-Apr-2040 12:00:00
>> Tlaunch = launch - epoch % as hh:mm:ss
Tlaunch = 
  duration
   353208:00:00
>> Tlaunch.Format = 'd' % as 24hr days
Tlaunch = 
  duration
   14717 days
   

Here's how you add the seconds

>> afterTrans12 = seconds(123456)
afterTrans12 = 
  duration
   123456 sec
>> launch = launch + afterTrans12
launch = 
  datetime
   18-Apr-2040 22:17:36
>> JDLaunch = juliandate(launch)
JDLaunch =
          2466263.42888889
>> %position.earth.launch = planetEphemeris(JDLaunch,'Sun','Earth');