|A Science Fiction Fanzine||Summer 2004|
Joe Green has been my friend for thirty years and my father-in-law for three. What an honor to welcome him to Challenger's pages.
THE MISTAKES TECH WRITERS DO
LIVE AFTER THEM, WHILE THE GOOD . . .
In my feckless youth I made a mistake - a technical error. I've lost no sleep over it, and only a few people know, despite the fact a certain incorrect figure I established has become an accepted, world-wide standard. I was reminded of this recently when I saw the term appear in an on-line European magazine, reporting on a recent space launch. The figure they gave for the planned geosynchronous orbit was wrong - and it's all my fault.
It came about this way.
The first 18 of my thirty-one and a half years at the Kennedy Space Center (KSC), before I accepted a serious reduction in salary to join NASA, were spent working as an engineering, or "tech" writer, for various contractors. In 1971 I was working for Boeing, supporting NASA's Unmanned Launch Operations Directorate (ULO) on Cape Canaveral. My title was "Project Writer," and it meant I did all the technical documentation for the NASA branch responsible for Atlas-Centaur vehicles (the data was supplied by NASA engineers, of course). I also manned a console during launches of my vehicle. Two other experienced tech writers supported the Delta and Atlas-Agena, and all of us worked with the spacecraft and telemetry branches. The contractors who built and launched the three vehicles had their own tech writing staffs, and produced different, though sometimes overlapping, launch documentation.
I had worked in ULO for two previous years, 1966 and '67*, in the same position but for a different contractor, before transferring to KSC Headquarters to support the Apollo Program. Though operating in the giant shadow of Apollo, and not drawing that much interest from the general public, ULO had continued to grow while I was away. The major growth area was communications satellites, and the primary emphasis was on those designed to operate in geosynchronous orbit (which would be called "Clark" orbits, if this was a just world). "Geosynchronous" means positioned above the equator and in line with it, at the exact altitude and orbital velocity needed to complete one orbit every 24 hours. Since the equator also rotates once during those 24 hours, the net effect is that the satellite appears to remain motionless in the sky. This is very desirable for people sending data to be retransmitted over a large area, such as television signals. Three correctly located spacecraft transmitting the same signal can cover the entire Earth, except for the polar regions.
One of my duties as Project Writer in the earlier two years was to prepare a little one-page sheet of basic facts on each planned launch of the Atlas-Centaur. It was distributed only "in-house" -- to ULO and contractor employees. When I took it over again, after returning from the Apollo Program, I expanded it to provide a fairly comprehensive overview of the entire mission. I carefully prepared this factsheet in "layman's language," comprehensible to anyone with a high school education. Other employees outside of ULO heard of and wanted it. Distribution expanded, going from an initial figure of about 100 copies eventually up to 2,000. NASA Public Affairs Education and Press branches started giving copies to educators and news media. It became so popular I was asked to prepare ones for Delta launches as well (by then the Atlas-Agena had been discontinued) - though another writer continued to handle the purely technical documentation.
Shortly after I arrived back at ULO, the Atlas-Centaur was scheduled to launch an INTELSAT communications satellite into geosynchronous orbit.** This was not the first NASA attempt at placing satellites there, but it was the first for the Atlas-Centaur. When I did my usual study of the voluminous technical documentation, in preparation for writing the mission fact sheet, I had my first encounter with geosynchronous orbit parameters.
I knew the general operating concepts, of course, but hadn't paid much attention to the exact figures. There they were in front of me, an apogee (highest point) of something over 22,400 statute miles above the Earth's surface, and a perigee (low point) of under 22,100 miles. The Centaur stage would place the spacecraft in that orbit, and over the equator, after which our job was done. INTELSAT operators would make the final height adjustments, using the spacecraft's own small thrusters.
Looking at those figures, I realized that I needed to round off the actual planned final orbital altitude to the nearest hundred. That was as close as most people, and in particular the news media, would ever remember. So I selected 22,300 miles as the figure for the planned altitude, and used that.
My fact sheet sailed through the routine checks by NASA engineering managers without a problem, and was published. The idea of a satellite that could sit apparently motionless in the sky was still very new. INTELSATs, the first satellite system designed to provide communications over the entire world, were receiving a lot of attention. Story after story appeared in the media about the advantages of geosynchrous orbit. And all of them used the figure I had supplied as the final altitude, 22,300 miles. Within a year or two, it had become the established standard. Everyone, from knowledgeable newsmen to devoted space program fans, used it.
ULO continued to launch space vehicles, the only civilian U.S. action around after the last manned flight for Apollo, the Soyuz Test Project, in 1975. Among them were several in the swiftly growing area of spacecraft operating in geosynchronous orbit. And going over the figures for another one a couple of years after my first, I discovered something.
There is an altitude which is perfect for a geosynchronous orbit. Few spacecraft attain it, because exactness isn't that important. A satellite can move slowly up and down in orbit (the only visible effect of not being in a perfect circle) forty or fifty miles, without seriously affecting the received strength of signals from antennas on the ground, or the coverage area of its broadcast signal. Spacecraft operators don't waste precious fuel trying to keep a satellite continuously at an exact altitude; here, close is good enough. (They do have to spend fuel keeping a satellite in line with the equator, because the Earth is slightly pear-shaped, and has more weight below its waist than above it; but that's another story.)
But the perfect altitude for a Clark orbit, it turns out, is 22,238 statute miles above mean sea level. (And it is of interest to note that the master visionary, in his famous article "Extra-Terrestrial Relays" in the October 1945 "Wireless World," called for an orbit "with a radius of 42,000 kilometers." That works out to about 22,100 miles above the surface of the sphere; very close.) That meant I should have rounded off geosynchronous altitude as 22,200 miles, the closest hundred. Using 22,300 miles was a mistake.
By the time I recognized my error, everyone was using the 22,300 mile figure, even engineers and others who were experts in orbital mechanics. Not wanting to openly admit my goof, I tried to correct the mistake by using the exact planned apogee and perigee figures on ensuing factsheets. It was too late. The news media ignored the exact figures, as I had known they would when I chose to round off in the first place, and stuck with the 22,300 number.
It's wrong. And it's all my fault.
It's probably also my only real claim to lasting fame (er - infamy?), except that no one but a few people to whom I've spoken - and now, the readers of Challenger - know the real facts.
**The Centaur was the most powerful stage for its weight then in existence, due to using hydrogen as its fuel. The INTELSATS had increased in weight until the less powerful Delta could no longer loft them to geosynchronous orbit. See my article on developing hydrogen as a fuel , written with a NASA engineer, in the January 1968 Analog.