WASHINGTON (AP) - NASA's future plans to explore Mars may end up using astronauts as space messengers. A special team has been looking for a new Mars plan since budget cuts earlier this year killed two future robotic flights. A preliminary report released Tuesday gives NASA several options. A decision won't be announced until next year. Mars exploration so far has been done with orbiters and robots, like the rover Curiosity that landed last month. None of the options would put astronauts on the red planet. But one plan calls for a robotic explorer to grab Martian rocks and take them back into space. Then astronauts would pick them up and take them home for detailed scientific examination. NASA sciences chief John Grunsfeld said that could help prevent contamination issues.