THE ENTRY FAD: A WORKED EXAMPLE

As was done before all major manoeuvres performed during the flight, and with over four hours remaining to the landing. Capcom read up a PAD to the crew – a large list of numbers and notes that, in this case, defined the parameters of re-entry for the crew and the computer. This list included cheeks to be made of their attitude; and the times, angles and velocities to be expected at various points along their trajectory. Much of the information was to be fed into the computer and the EMS so that this equipment could be properly initialised prior to entry.

In April 1972, rookie astronaut and Capcom Henry Ilartsfield made a call to Casper, the returning CSM of Apollo 16. to pass up a preliminary version of their re-

entry details. They were only 4.5 hours away from splashdown yet they were still 63,000 kilometres out. “Apollo 16, Houston. Have an entry PAD for you.”

“Okay. Go ahead with the PAD,” replied mission commander John Young.

Hartsfield then launched into the long, monotonous, yet precise string of digits and comments that would bring the crew safely to Earth. “Okay, MidPac; 000 153 000 2900632 267; minus 0071, minus 15618…” As with previous PADs, there was no punctuation. Confu­sion was only avoided by the pro forma sheet onto which the informa­tion was copied, along with the crew’s experienced expectation of what each number was likely to be.

Hartsfield continued: “069 36196 650 10458 36276 2902332 0027 Noun 69 is N/A; 400 0202 0016 0333 0743; sextant star 25 1515 262; boresight N/A; lift vector UP. Use non-exit EMS; RET for 90K, 0606; RET mains, 0829; RET landing, 1321; constant-g entry, roll right; Moon – set, 2902026; EMS entry, reverse bank angle at 20,000 feet per sec­

spacecraft to the atmosphere in the attitude it would naturally adopt with its biased centre of mass in their current heads-down attitude.