‘That makes sense, Hazel, you and Castor work the homing problem; Pol and I will work the Mars vector. First approximations only; we’ll correct when we’re closer. Everyone work independently, then we’ll swap and check. Mind your decimals!’
‘You mind yours.’ Hazel answered.
Castor gave his father a sly grin. ‘You picked the easy one, eh, Dad?’
His father looked at him. ‘Is it too hard for you? Do you want to swap?’
‘Oh, no, Sir! I can do it.’
‘Then get on with it — and bear in mind you are a crew member in space.’
‘Aye aye, sir.’
He had in fact ‘picked the easy one’; the basic tack-around-Earth-for-Mars problem had been solved by the big computers of Luna Pilot Station before they blasted off. To be sure, Luna Pilot’s answer would have to be revised to fit the inevitable errors, or deviations from flight plan, that would show up when they reached perigee rounding Earth — they might be too high, too low, too fast, too slow, or headed somewhat differently from the theoretical curve which had bee computed for them. In fact they could be sure to be wrong in all three factors; the tiniest of errors at blast-off had a quarter of a million miles in which to multiply.
But nothing could be done to compute the corrections for those errors for the next fifteen or twenty hours; the deviations had to be allowed to grow before they could be measured accurately.
But the blast back to shape an ellipsoid home to Luna was a brand-new, unpremeditated problem. Captain Stone had not refused it out of laziness; he intended to do both problems but had kept his intention to himself. In the meantime he had another worry; strung out behind him were several more ships, all headed for Mars. For the next several days there would be frequent departures from the Moon, all ships taking advantage of the one favorable period in every twenty-six months when the passage to Mars was relatively ‘cheap,’ i.e., when the minimum-fuel ellipse tangent to both planet’s orbits would actually make rendezvous with Mars rather than arrive foolishly at some totally untenanted part of Mars’ orbit. Except for military vessels and super expensive passenger-ships, all traffic for Mars left at this one time.
During the four-day period bracketing the ideal instant of departure ships leaving Leyport paid a fancy premium for the privilege over and above the standard service fee. Only a large ship could afford such a fee; the saving in cost of single-H reactive mass had to be greater than the fee. The Rolling Stone had departed just before the premium charge went into effect; consequently she had trailing her like beads on a string a round dozen of ships, all headed down to Earth, to tack around her toward Mars.
If the Rolling Stone vectored back and shaped course for Luna rather than Mars, there was a possibility of traffic trouble.
Collisions between spaceships are almost unheard of; space is very large and ships are very tiny. But they are possible, particularly when many ships are doing much the same thing at the same time in the same region of space. Spacemen won’t forget the Rising Star and the patrol vessel Trygye Lie — four hundred and seven dead, no survivors.
Ships for Mars would be departing Luna for the next three days and more; the Rolling Stone, in rounding Earth and heading back to Luna (toward where Luna would be on her arrival) would cut diagonally across their paths. Besides these hazards, there were Earth’s three radio-satellites and her satellite space station; each ship’s flight plan, as approved by Luna Pilot Station, took into consideration these four orbits, but the possible emergency maneuver of the Rolling Stone had had no such safety check. Roger Stone mentally chewed his nails at the possibility that Traffic Control might refuse permission for the Rolling Stone to change its approved flight plan — which they would do if there was the slightest possibility of collision, sick child or no.
And Captain Stone would ignore their refusal, risk collision and take his child home — there to lose his pilot’s license certainly and to face a stiff sentence from the Admiralty court possibly.