What are the FAA regulations concerning controlled descent of a light payload?
The FAA FAR says the following on the matter,

Sec. 91.15
Dropping objects.
No pilot in command of a civil aircraft may allow any object to be dropped from that aircraft in flight that creates a hazard to persons or property. However, this section does not prohibit the dropping of any object if reasonable precautions are taken to avoid injury or damage to persons or property.

As long as you take precautions not to hit anything you are ok. All things considered you are somewhat at the mercy of the FAA here, if something were to go wrong it would most likely be considered your fault.
After some looking around there are some other things to consider. Since you are using Magnus Force Cylinders to control the decent depending on how you look at it these can be considered a &quot;Parachute&quot; by the FAA definition

Parachute: means a device used or intended to be used to retard the fall of a body or object through the air.

Likewise what you are doing may also be considered a &quot;Parachute Drop&quot;

Parachute Drop: means the descent of an object to the surface from an aircraft in flight when a parachute is used or intended to be used during all or part of that descent.

Another interesting point is that from 100,000 ft you will be busting through the Class A airspace here in the US (and likely class E). For that you may want to read up on parachuting in controlled airspace.
Again similar to the dropping, parachuting must be done with caution

§105.5   General
No person may conduct a parachute operation, and no pilot in command of an aircraft may allow a parachute operation to be conducted from an aircraft, if that operation creates a hazard to air traffic or to persons or property on the surface.

Again a lot of this is open to interpretation, since you have no (presumed) way of controlling the vehicle on the decent I would say it does not fall under what the FAA considers a UAS/UAV. You may want to reach out to the FAA directly about doing something like this from the kinds of altitudes you intend to.