Parkinson's disease didn't stop Rich Clifford from walking in space...

(Rich Clifford in his own words...)

(CNN) -- It had been a little more than four months since completing my second space shuttle mission, STS-59, on the shuttle Endeavour.

I was finishing my annual flight physical at the Johnson Space Center Flight Medicine Clinic. The words from the flight surgeon were as expected: I was in great condition with nothing of note. Then I asked the doctor to look at my right shoulder because my racquetball game was suffering.

He asked if I had pain. I told him I wasn't in pain, but my right arm did not swing naturally when I walked. This comment must have set off some alarm, because he observed my walk down the hall and quickly said he would take me downtown to the Texas Medical Center the next day.

I remember saying, "I don't believe we can see an orthopedic surgeon that quickly." He merely noted that we were going to a neurologist.

Little did I know that next day would change my life so quickly. The neurologist spent five minutes with me before saying that I had Parkinson's disease. He added I would have to undergo several separate tests to prove that I didn't have some other neurological disorder. Parkinson's disease is diagnosed by the process of eliminating other possible diseases.

After several tests, the diagnosis was confirmed. This was December 1995.

To their credit, the flight surgeons asked me what I wanted to do about flying. I quickly said I wanted to continue with all activities, including standing in line for another space shuttle mission.

I kept my condition a secret to all, except my wife and my children. I assumed senior NASA management were told, but no one ever spoke to me about the disease. They protected my privacy.

I continued my normal duties and was subsequently offered my third shuttle mission -- STS-76, which included a planned space walk. The mission was highly successful. One year after that mission, I left NASA for a job in the private sector supporting human space flight.

With the exception of my closest friends and family, I kept my condition a secret for almost 15 years. My reason for secrecy was simple: People did not need to know.

Now I'm an advocate for Parkinson's disease awareness. Having Parkinson's disease is no reason to stop living life to its fullest extent. Yes, as the disease progresses I have had to change the way I do certain activities, but I continue to do them.

I have a keen awareness now of the stress my disease places on my loved ones who provide me encouragement and tender loving care. The caregivers to a person with Parkinson's are the people who give so much of their lives to care for a loved one. My wife is my caregiver and I am acutely aware of her sacrifices. Parkinson's disease affects more than just the patient. The patient needs to understand the caregiver is there to help.

So do not let Parkinson's disease control your life. You may do things slower, or you may not be able to do things you once did as easily. It is not the end of the world. Do not give up trying.