As above, send a letter advising the court that you are travelling abroad and therefore are not available. Avoid telling the court that you do not live in the USA. The court should rescind your summons and put you back into the pool of potential jurors for a future case. It would be preferable to have someone hand deliver your request to the court if that is possible. This way, you'll know immediately whether or not your request has been successful. Otherwise, if you do not receive a reply from the court and it is getting close to the date you have been ordered to appear you may need to call to verify that you have been removed from the potential juror list.*
Try not to leave this to the last minute. Not appearing as ordered may affect the status your driver license and possibly result in a warrant that might prove inconvenient the next time you try to fly home.*
If the letter doesn't work for some reason, hire a paralegal (cheaper than a lawyer) or have a family member appear on your behalf to explain to the court why you are not there. Travelling as an excuse should work once, but it might not work the next time, should that day ever arrive.*