History

Sandy Vincent and her friend "Babs" Bendix were political science majors in college and wanted to change the world, but ultimately had to settle for jobs working for Roxxon Corporation as secretaries.  Wanting more, Sandy was asked to join Roxxon`s research department. She eagerly took the opportunity due to its greater chance to do good, but secretly the scientists only wanted her because her genetic makeup was a good fit to wear an updated version of the Sunturion armor.  (Roxxon had created Sunturion I some time earlier, but he had seemingly died at sea.  They also built the Sunturion II armor but lost it; it was later found by Mike Stone.)
 
The Roxxon scientists there transformed her into Roxxon`s own corporate superhero Stratosfire, just as they had done earlier with Sunturion.  As Stratosfire, she became spokeswoman for Roxxon and improved their tarnished image.  She also met Iron Man, and even upstaged him on the news.  She loved her new job its opportunity to do good, not to mention the fame.  However, Roxxon also had her running on more illicit missions, destroying their competition's facilities.  Sandy rationalized it by saying that you had to destroy in order to create.  But Babs worried about Sandy's new role, and what it was doing to her.  Sandy was no longer the person Babs remembered from their college days; it seemed like the suit was doing something to her mind.  Babs spoke to Anthony Stark, but she was followed by Roxxon operatives and was killed. Angered about what happened to Babs, Stratosfire went on a rampage and partially destroyed Roxxon`s headquarters.  Then she flew off to take her personal mission (to make the world a better place) to the next level.

As an opponent of nuclear power, she decided to destroy a new nuclear facility.  Iron Man tried to stop her, but she defeated him in combat and successfully destroyed the nuclear plant.  Roxxon was worried that she was out of control, and took measures to stop her: they found the armor of Sunturion I and "resurrected" him from dispersed energy.  The U.S. military was also concerned about her, and attacked her with a destroyer ship and some jets.  The navy sortie posed no difficulty to her, and so Iron Man joined them in their attack on Stratosfire.  Once again she was beating him, and almost killed him, when Sunturion showed up.  Sunturion almost managed to drain her energy, but she managed to fly away.
 
Using Sunturion's ability to read computer data, they realized what her next attack would be: a space shuttle launch that carried secret weapons.  Iron Man and Sunturion tried to protect the shuttle, but she evaded them.  A Roxxon operative tried to use a last-ditch destruct mechanism they had built into the suit, but she jammed the frequency.  She was in a position to destroy the shuttle when Sunturion managed to reach inside her using his energy-self, and activated the self-destruct mechanism, killing her.
 

Powers and Abilities

Stratosfire's powers are similar to, although slightly different from, Sunturion's.  Her powers come from her suit, but the suit actually turns the wearer's body into pure energy, thereby actually giving the powers directly to the wearer.
 

Her powers all stemmed from her microwave energy form.  She could shoot powerful energy blasts from her hands.  They were powerful enough to destroy most of the top several stories of a skyscraper.  By placing her hands on an object, she could raise its internal temperature.  She was able to do this to Iron Man's head in such a way that it would have killed him, despite his armor's protection, if she had not been distracted by Sunturion.  She was able to make a large, continuously-burning fireball around herself.  She could transform objects into energy and absorb that energy; this includes objects as large as a nuclear cooling tower.
 
She was also able to manipulate energy to a degree, as she did when she locked onto Iron Man's repulsor blasts, absorbed them, then locked onto them and sent her own energy back along his energy stream.  She was also able to scramble and rewrite the targeting computers in a pair of Sidewinder missles that were fired at her.
 
She could create energy shields around herself or others.
 
She could fly.  She could turn into pure energy and travel through electric wires, such as a phone line.  She could turn into an intangible energy form that could withstand energy and physical attacks.  She could teleport herself.  She could also teleport other people and things, converting them to energy and making them reappear in a new location.  She did this to fairly large objects, like a garbage truck.  She could do both of these teleportation effects quickly and easily, including in combat situations.
 

She could control her appearance, switching instantly from looking like her original human self into her armor.  It is not known whether the armor actually afforded any extra protection once she had been converted into her permanent energy self, or if it was just a visual carry-over from its original purpose.  It is not know if she could take on the appearance of other people.
 
She could control technology to a limited extent: for instance, she could make her face appear on a computer screen, and could scan computer banks for information--even highly secret and encrypted ones.
 
Her power (or perhaps her control of that power) seems to have been slightly lower than that of Sunturion I, who was able to partially drain her energy at one point, and to forcibly start her self-destruct mechanism at another point.