Why is it unlikely that Irene will travel into space?

Irene's unlikeliness to travel into space is primarily due to her risk of heart failure. Space travel involves exposure to unique physical stresses, including microgravity, which can exacerbate existing health issues. Astronauts are subjected to various physiological changes during their missions, and pre-existing heart conditions can significantly increase the risk during those high-stress environments. Heart failure could jeopardize her ability to handle the physical demands of space travel, making it a critical factor in determining fitness for such missions.

In contrast, while allergies to space, lack of training, and fear of heights may present challenges, they do not pose the same direct life-threatening risks associated with heart health. Training can often be acquired, and fears could potentially be managed, whereas a serious medical condition like heart failure would likely disqualify someone from participating in space missions.