The Jovian Sweep (Asteroid Scrabble Book 1)

by Martin Bourne

  And yet he still felt his heart pumping, his stomach broiling, and a desert-like dryness in his mouth. It was illogical and irrational, but he felt it all nonetheless. It was unfortunate that what the mind knew the body did not necessarily feel. It was ironic that only now, when he had the time to rest, he found he no longer had the inclination or the ability to do so.

  In the next few hours the tactical conclusion of this campaign would start to happen. The next few days would decide things, one way or another. Historians and pundits would concentrate almost solely on these upcoming hours and days. All the planning and hard work beforehand would get a cursory mention from them at best, unless of course something went terribly wrong.

  He breathed in and out deeply to steady himself, trying to enjoy the unusual luxury of being able to concentrate on a single routine sensation. Out of the corner of his eye he saw his aides whispering, pointing, puzzling - occasionally glancing in his direction. Snatches of conversation reached him – nothing but indistinct sounds - but he could guess what they were saying. He admitted it - he did so enjoy mystifying them. It really was a very bad habit, but he consoled himself with the thought that he didn’t have too many. Besides, he had been working over hard. He was entitled to indulge himself a little. Anyway, it was all ultimately for their benefit.

  It was amazing how you could justify almost anything if you tried hard enough.

  He yawned and made a very obvious stretch, before folding his arms and letting his eyelids droop. Through the blurred sieve of his own lashes he made out faces turning, examining him, then turning back, apparently satisfied. He saw Commander Prince making some kind of point. He could make out that Cromarty was arguing with him, either countering with another argument, or expressing – disagreement…caution? It was hard to tell. Eventually, Prince detached himself and sauntered over to the holotank. Courage saw him staring, and then tapping into his perscomp. Images appeared in the holotank. They expanded, they contracted; they moved this way and that. Courage recognised the pattern. Prince was setting up a scenario. Amused, Courage saw Jupiter appear in the holotank, huge and yet fast rotating. The green emblems of Virtue Confederation ships became lines as Prince plotted projected changes of course. They veered close to the storm-wracked gas giant, were caught in its massive gravitational embrace, and then veered around it in a vast arc, their velocity increased by the planet’s immense angular momentum.

  His new aide was quick on the uptake, no doubt about it. He had examined and extrapolated his orders, not simply obeyed them. That was impressive. Now, had he spotted the twist? A lot hinged on that. Courage quickly veiled his eyes even further as Prince turned to stare at him, and then closed them fully as he saw his aide begin to walk towards him. He felt the presence of the Commander before he heard the discrete cough.

  “Excuse me Admiral.”

  It was very hard to affect nonchalance. “Is something the matter Commander?”

  “No sir. I just wanted to ask you a question.”

  It was very hard not to be smug either. “Please go on.”

  “Sir, I have been running simulations of our course, and it seems to me that you are planning a slingshot manoeuvre around Jupiter. Would I be correct in that conclusion Admiral?”

  So Prince had picked up the first part of his grand plan. He was smart alright. He had also been bold enough to approach him about it, so he had courage too.

  Of course every spacefarer would know about slingshotting, even if they never used it. The technique, sometimes called swing-by, was very old. It was a method of increasing the velocity of a spaceship without having to waste precious propellant. It worked by drawing on the motion of the gravitating body as it pulled on the spaceship, and siphoning some of the attraction into extra motion.

  He was counting on the fact that most Belters would not be very familiar with slingshotting. It was, after all, of minimal use in the Belts. The average asteroid didn’t have much mass and therefore a pretty negligible natural gravity to draw upon. The large merchantmen that plied their trade in the inner solar system, with its large and massive planets, and in the outer system around the larger satellites of Jupiter and Saturn, did use slingshots fairly often, but they were the exception. Most merchant vessels were small and involved only in local trading. And because most navy vessels spent most of their time protecting the merchant fleet, even fewer naval officers came into regular contact with the practice.

  Courage gave a wry smile. “Well, we are being chased by a superior enemy force and need to get away. Gravitational assist from Jupiter would certainly be one way of increasing our acceleration rate.”

  “Yes sir, that is true. But surely sir, they can follow us and increase their acceleration by a slingshot too.”

  Courage crossed his legs. “Yes they can, although there will be a significant time delay before they can get the benefit of the slingshot.”

  Prince still looked perplexed. “That might get us a temporary advantage but they will soon catch up when they get the slingshot, because their acceleration rates are higher than ours.” His eyes widened. “Unless we don’t leave orbit – is that it?"

  Cromarty walked up. "Not leaving orbit would change the equations, but not significantly. They’ve probably at least as much fuel as we do.” Courage looked her a question. "I checked the numbers too."

  Prince alternated looking at them.

  Courage settled. “Tell me Commander. If we were to slingshot around Jupiter, would they be able to catch us if they didn’t do the same?”

  Prince frowned and then tapped at his perscomp, oblivious to the wry grin growing on Cromarty’s face. “Given our current velocity…and the increase in acceleration gained by a slingshot effect on our new course…no, they wouldn’t be able to, not even if they went to maximum acceleration.”

  “So is it theoretically possible for us to escape that way?”

  Prince looked puzzled. “I suppose so sir, if they don’t do the same. But why shouldn’t they? We are well in range of their sensors. They will easily be able to see our change in direction and make the necessary adjustments to their own course.”

  Courage allowed himself a smile. “We’ll get the acceleration first though. If you check carefully you'll see that we’ll pull ahead initially, and as we go around Jupiter we’ll be out of direct sight of them. Just for a while.”

  “But surely not enough to matter,” Prince shot back, proffering his perscomp. “No matter how sharp a turn we might make; we’ll never be able to avoid them. It might give us a temporary reprieve, but the numbers don’t lie. They will definitely have time to adjust course and velocity to compensate for any directional or acceleration changes we might make.”

  Courage studied the display. “This is a very thorough analysis Commander. However, there is a point that you are missing.”

  “Sir?”

  Courage stood up and headed to the holotank. His aides trailed after him. “Every Belter knows about swing-by. It’s mostly used by merchant skippers to minimise their transit times and maximise their profit margins. It’s not so useful in a military situation, for all of the very good reasons you just gave.”

  He exchanged salutes with the Deck officer at the holotank. He took over the controls, nodded at the woman, and waited for her to walk away before bringing up the tactical situation on the holosuite. “The whole of our fleet is now together, here,” he explained, his fingers drew the positions and projected paths. “The whole of the Triangle fleet is here, behind us and closing in. Their current velocity is higher and we know that their acceleration rates are as well. As Commander Cromarty stated, they've probably got more fuel as well, so we can't outlast them. So, to sum up, the only way we can outrun them is if we use a slingshot manoeuvre. So if they want to catch us, if we do use a slingshot they will be forced to do the same.”

  His aides looked puzzled. Courage inwardly revelled in their confusion again. Inevitably it was Prince who raised the obvious objection.

  “But sir,
as I intimated, slingshotting will not alter our relative positions. The velocity gained by swing by is proportional to the amount we start off with. As you said, we know the Trigs can accelerate faster than we can – they are gaining on us steadily now. We might get a temporary edge on them because we will slingshot first, but when they reach Jupiter their higher velocity will get them an even bigger slingshot. So we won’t gain any velocity or distance on them in the long run. We might gain a bit more time, but that’s all.”

  Courage tapped some more numbers into the program. “Everyone may know about slingshotting, but no one, certainly no Belter, thinks about it very much. For a while as we go around Jupiter we will have a higher acceleration than them, because we will get our acceleration by slingshot first, and for a while, a very, very short while, we will be pulling ahead of them, and be out of direct sensor contact for a short time.” He smiled at Prince’s reaction. “Jupiter is a large planet.”

  Cromarty looked suddenly thoughtful. She was smart too, and she had the advantage of having worked with him before. Courage could see she was slowly working it out. Prince was still a step or two behind.

  “But sir, being out of sight for a few minutes isn't going to give us much of an advantage. We won't be able to manoeuvre very far.”

  “There is still a factor you have not considered. A little trick I’ve been keeping in my pocket.” Courage gave a snort of amusement at their expressions. “Don’t be annoyed. I’m deliberately keeping you in the dark for a very good reason. Move and countermove remember? This will only work if they don’t anticipate what we are doing and change what they are going to do to compensate. You two are smart. If you can’t figure it out, then the odds are that your counterparts on the Triangle flagship behind us won’t either.”

  A deck officer approached. Courage acknowledged him with a salute. “Enemy fleet is closing sir. Range now 47 spatials.”

  “Thank you Ensign.”

  The deck officer saluted and moved off. Cromarty waited until he was gone before muttering. “Down to 47 spatials…they’ll be launching drones soon.”

  “They’ll probably wait until we’re clear of Jupiter.”

  Cromarty stared. “That’s a big assumption sir.”

  “They’ve got us outnumbered and outgunned. A straight fight is all to their advantage. Complications like Jupiter will be unwelcome.”

  Prince intervened. “Do you mean the slingshot manoeuvre sir, or the interference from Jupiter’s emissions?”

  “Both really, but the slingshot is of more immediate importance.” He walked back to his chair and made himself comfortable. His aides followed.

  “Slingshotting increases our velocity by using the relative movement and gravity of the planet,” he explained. “Basically we steal momentum from Jupiter. The amount we gain depends on the angle we come in, and how close we get to the planet. The closer we get to Jupiter; the more momentum we can gain from it.”

  “So we get closer to the planet than they do, we pick up more momentum, and then we can out-accelerate and outdistance them!” Cromarty nodded fiercely. “That’s smart admiral, very smart.”

  “Except that it will be almost impossible for us to disguise our change of course,” objected Prince. “Belters may not be very aware of slingshotting, but when they see us moving in closer to Jupiter someone over there is bound to figure out what we are doing. Then they will calculate our potential increase in velocity, and compensate by coming in closer themselves.”

  “Not possible,” said Cromarty. “The admiral has got it right. We are coming in at a steeper angle than them. They’ll never be able to match that.”

  “True…oh but hold on.” Prince tapped furiously at his perscomp. “No. That won’t work either. We get an edge alright, but their higher velocity and their ability to accelerate faster will compensate for almost all of the advantage of our steeper angle.”

  “We must get some gain on them,” exclaimed Cromarty.

  “Yes but not much,” said Prince, shaking his head. “Even if we are out of direct contact with them for twenty minutes, we won’t have enough time to adjust our distance from the planet enough to evade them, whether we go in closer or pull out.” He tapped in numbers into his simulation. “May I show you sir?” Without waiting for an answer he transferred his calculations onto the Bridge holotank simulator. Jupiter was soon spinning in miniature majesty. Changes in the positions of the opposing fleets were soon being updated with a flurry of possibilities.

  Prince swept his hands over the holotank. The projected courses swung to and fro under his commands. Every option led to a point there where the red and blue lines collided. “No combination of moves allows us to escape sir,” he concluded. “All we do by slingshotting is gain a little more time before they catch up to us.”

  “Not quite. If we time it right, we have an opportunity to completely evade them, give them a bloody nose, and force them to retreat.”

  Prince looked very puzzled. Courage took pity.

  “Consider this commander. You are right when you say that the closer we get to Jupiter the more angular momentum we will pick up, and the higher the velocity we will achieve. But, what you have overlooked, what most Belters would overlook, and what I sincerely hope that the Trigs behind us overlook, is that if we come in very close we will actually lose velocity.”

  Prince looked dumbfounded. Cromarty looked puzzled, and then suddenly her face cleared.

  “Of course! Oh admiral, that is clever! That is really elegant!” Then she paused, looked uncertain. “But do you think they will fall for it?”

  Courage shrugged. “There aren’t too many guarantees in this profession Sally, but neither of you two picked it up, so I guess we have a good chance.”

  Prince was looking from one to the other. “I still don’t get it.”

  Cromarty smiled and put a hand on his shoulder. “No reason you should Thom. You or anyone else born and bred in the Belts.”

  “Eh?”

  Courage grinned. “Unlike every asteroid, and indeed most of the gravity wells in the system, Jupiter has a significant atmosphere.”

  Prince sat down, put his hand to his jaw, and shook his head slowly. “Friction.”

  “The exact term used is aerobraking. If we get in close our ships will start to collide with the gas molecules of Jupiter’s upper atmosphere. Their impact will slow us down. The effect of a single molecule isn’t going to bleed off much velocity, but there are billions of molecules out there. Combined with a sudden sharp deceleration we can make, just for those few minutes we will be out of sight, and the electromagnetic cover provided by Jupiter’s emissions, with any luck they’ll sail right by us before they realise what we have done.”

  “Friction by the atmosphere will give off heat. Lots of it. Won’t they spot that?”

  Courage shrugged. “It’s possible of course, but we will have stopped decelerating and pulled up by the time they are back in direct contact with us, and besides, from their point of view Jupiter will be right behind us. So their sensors will be facing all those nice, powerful, whirling storms.” He leaned forward. “Anyway, we won’t be where they will be concentrating on, and I have another little trick to make sure it stays that way. Commander Prince? Will you transmit order ‘Fire dragon’ to Belofte?”

  Prince looked startled.

  “It’s on page 83, subsection 6 of the battle orders,” Courage expounded.

  Prince gulped and tapped at his perscomp, eyes still wide.

  Cromarty leaned into Courage, lowering her voice. “This is all still very risky sir.”

  “When you are as outnumbered, outgunned and generally outmatched as much as we are Sally, taking risks is pretty much mandatory.”

  “Yes sir, but such risks have to be justifiable. If the Trigs see through this, they will be able to drive at us while we are pinned against Jupiter. We’ll be lucky to get any of the Depot ships away.”

  “I know. But if were to take them on directly we might lose some
Depot ships anyway, and we would certainly lose most of the drones. Risk against certainty Sally.”

  He turned to his other aide. “Commander Prince? Enter in the log that I accept full responsibility for the consequences of the next orders. Commander Cromarty? Captain Raime? I call upon you to witness this entry.”

  He waited while Raime came over, saw what was written, and gave a slight nod.

  “Very well,” said Courage. “Now, I want you to make a general order to the entire fleet. Recall all picket drones, and then turn planetward ten degrees for five minutes, and assume a low orbit.”

  “Yes sir.“

  Prince fumbled with his perscomp. Raime gave a stiff salute and began to bark out orders. In the holotank the welter of green icons descended. After twenty minutes they were in low orbit.

  "Sensor performance is degrading," said a Deck officer.

  Courage ignored the call. His eyes flashed back and forth between the position of his ships in the Holotank, and the increasingly estimated position of the Trigs. You could plan all you liked. Mathematics and computers could give you precise figures, but in the end war was an art. It was necessary to have Human oversight. Finally, it looked right.

  "General order: drop orbit by five microspatials."

  Everyone on the flag bridge bar his aides exchanged surprised looks, but everyone did as they were told. Over the comms links Prince and Cromarty had to field several repeat orders requests from the rest of the fleet. The green icons began to descend, more slowly than before. You could almost sense the reluctance from the ship's movement.

  "Now, general order: full deceleration!"

  Buttons pressed perscomps. In spite of the inertial dampeners, Valiant bucked, and her engines began to wail. On the holotank the mass of green icons began to smear.

  "We're spreading out sir," said Prince urgently. "Our Depot ships have very different deceleration rates."