I am born in Sagittarius Ascendant with Jupiter,Mercury and venus in the ascendant(1st house),saturn exalted?

Saturn is well placed in Libra whereas Mars isn't. Saturn is more powerful by house position than aspect. So he won't affect the ascendant as much as it will affect 11th house matters regarding friendship and your aspirations. Any asepects he makes to the ascendant will make you more serious and add more depth to your character. As far as saying he is a malefic. That's old school. Saturn is a tester and will test you along the way and it is up to you to make the most of it and reap the rewards later on. They say the MIND is more dangerous to cope with than the SENSES. The conjunction Saturn/Mars is not an easy one but if he is handled constructively, the rewards will follow eventually. On a positive note, this conjunction is good in that it will help you balance the impulse of Mars. This means that their is less energy wasted. On the negative side, frustrations can easily set in especially when you are challenged. This can lead to extremes if let uncontrolled.