Case File: Space Motion Sickness on a Short Orbital Flight

What is happening, and how common is it?

Space motion sickness (SMS), also called space adaptation sickness. Most first-time flyers get it, about 70–90% in NASA’s summary, usually in the first 2–3 days, and it typically resolves within about 72 hours [1]. The leading explanation is sensory conflict: without gravity, the inner ear’s otolith organs stop signaling head tilt, which clashes with what the eyes see [2]. Facial puffiness and nasal stuffiness come from the headward fluid shift.

Childhood car sickness does not reliably predict space motion sickness; a previous episode in space does [1].

How severe is it by NASA’s grading?

Moderate (grade 2). NASA’s brief grades mild as a few symptoms with up to one vomiting episode, resolving in 36–48 hours; moderate as persistent malaise with no more than two vomiting episodes, resolving in 72 hours; and severe as more than two vomiting episodes, possibly lasting beyond 72 hours [1].

How is it treated?

• Behavioral measures: limit head movements (pitch, or nodding, movements are the most provocative), keep a consistent sense of “up”, fix the gaze on a task, avoid strong smells and heat, and drink fluids [1].
• Promethazine is NASA’s treatment of choice, given by injection or suppository when vomiting [1]. In Space Shuttle crews, 14 of 15 treated by injection had relief within 1–2 hours [3]. Sedation has not commonly been seen in the first days of flight [1].
• Taking medicine before launch has not shown a clear benefit in NASA data [1].
• The operator’s flight surgeon sets the medicine plan for each participant.

What should she expect after landing?

Similar symptoms can return after landing, along with dizziness and unsteadiness, as the brain readjusts to gravity [1]. Fluid shifts also cause lightheadedness on standing (orthostatic intolerance) [4]. NASA crew are usually advised not to drive during the first week [5].

For short trips the outlook is good. On the 3-day Inspiration4 flight, almost all measured changes in the civilian crew returned to baseline after landing [6].

Red flags: symptoms beyond 72 hours, getting worse rather than better, focal neurological signs, severe headache, fever, or signs of dehydration. Trouble passing urine is also common early in flight, from fluid shifts and anticholinergic drugs [1].