Certainly the sentence your husband could receive will be governed by either the statutory penalties associated with the offense or the federal sentencing guidelines. Some offenses of this nature carry mandatory time. Without knowing exactly what section of the US Code your husband has been charged it is difficult to provide more information.
However, if the Federal Public Defender indicates a potential sentence of "10 years to life" then more likely than not he is facing a mandatory minimum sentence.
I practice in the Corpus Christi federal system but i must review the Indictment in order to explain the potential sentence exposure that your husband is facing. Feel free to contact me through my Avvo.com contact information to discuss this further.