Modify/Create Element Set

This form opens.

There are three ways in which you can modify the element set. But, they all only change the time of the element set and adjust the Right Ascension of the Ascending Node to match that change.

Lets say you know Falconsat is going to launch 10 minutes late. 

You could on the far left, enter the date and time of the original scheduled launch time, then enter the new date and time of the actual launch time. Press the accept key and the program will calculate the difference in time and come up with a 10 minute delay and create an element set with this change incorporated. This part of the form is perhaps better for longer delays of days or weeks. The dates and times initially loaded into this box are the computer's current system time.

In the middle, you could adjust the epoch time of the element set directly. The date and time in this box is that of the element set as it appears above in the "current element set" box. Just add 10 minutes to the time and make that change (in this case change 19:12:02 to 19:22:02. Press the accept key and as before the program will create an element set with this change incorporated.

Finally, the part of the form on the right allows you to enter the number of days, hours, minutes, and seconds you wish to offset the launch time. In this scenario, just enter 10 in the minutes box. If the satellite launched 10 minutes early press subtract. If it is launched 10 minutes late press add. Then, the program will create an element set with this change incorporated.

Once the new/modified element set has been generated, you must press the "Create New Elset" button at the bottom of the form to save it back to your active list of satellites.

Suppose you have NO orbital elements for a launch. Click on the Create New Element Set tab.

The form changes.

Here you can input the necessary information to create a new element set. Many times most of this information is available but no element set has been generated. For instance, many shuttle launches are described in the Press Kits long before a firm date for launch is set.

Fill out the fields  in the orbital data box. Minimal error checking takes place. For instance, you can't enter an inclination that is less than the latitude of the current satellite position.

You might know what inclination, and perigee (or mean orbital altitude) the shuttle will take on orbit. 

For eccentricity, (generally) you can enter a very low value or enter zero and the program will enter the minimum value. This will create a nearly circular orbit. If you  are calculating a two line element for satellites in eccentric orbits, you'll need to know both the intended eccentricity and the Argument of Perigee to generate an accurate elset.

For the argument of perigee, enter anything. This term denotes the point along the orbital path where the satellite achieves it's closest approach to Earth. And in this case, it's not too important. If you are trying to create an element set for a satellite with a significantly eccentric orbit, as noted above, you will NEED to know where the planned argument of perigee is to be. Although the absolute location of this term may not be that relevant to a satellite in a nearly circular orbit, it is still important as the satellite's position at the epoch time in a 2 line element set is calculated relative tothis point using the mean anomaly.

You can enter any value for the 1st time derivative of mean motion, but you might want to research past element sets of satellites in orbits similar to your satellite and fill in a value that matches a previous mission. If not, enter zero and the program will enter a minimum value. I would recommend you always set this to the minimum value by entering a zero unless you KNOW what the planned value will be.

Next you have to place the satellite at the correct position along its orbit. Do this by filling in the latitude and longitude where the satellite will be at a given time (which will be the epoch date/time of this element set).

Next you have to specify that time. This will set the plane of the orbit in relation to the celestial sphere. Enter the time the satellite will appear at the previously entered  latitude and longitude in UTC time. You also need to specify whether the satellite will be in the ascending (south to north) or descending (north to south) phase of its orbit.

That's it. When you press the accept key, the element set is created BUT only on this form. You can look it over and decide if it looks right. If you are satisfied, press Create New Element Set and the program will write the element set to the currently active list of satellites at the end of the file.

A proviso. You can't just enter the launch time for a satellite when creating a new element set. After all, at that time the satellite is NOT in orbit. Usually, you need to research a previous mission with similar parameters and come up with some kind of fudge factor.  Once you have this fudge factor, keep it handy for future flights. For instance, to create this fudge factor for the shuttle you need a set of orbital elements for the orbit of the shuttle after it has entered its initial circularized orbit. Back these element up to the point where the shuttle is DIRECTLY over the Cape. You'll notice the time is several minutes later than the launch time. This is a good fudge factor to use. For the shuttle in a pretty low orbit try 5 minutes.

When the shuttle is launched it isn't in orbit until 8 minutes after the take off. Even then, it's in a preliminary orbit usually with a very low perigee and an apogee about equal to it's intended orbital altitude. The shuttle then orbits half way around the world as it ascends to this apogee altitude. Then, the orbital maneuvering engines fire to circularize the orbit at that altitude. Only then is the shuttle in a (semi) permanent orbit. Later refinements may be made depending on the type of mission the shuttle is flying.