Trappist-1, page 8
part #3 of Mark Noble Space Adventures Series
‘Yes, and the tethers will no longer be steadying the tank when we dock,’ I said.
Anna spent the next ten minutes reporting the problem to Bill, Chi and NASA. NASA’s suggestion was that we bring forward departure to that afternoon instead of the next day. They told us that Opportunity’s cameras were swivelled around to watch us lift off. It was part of the plan that if the rover could be revived, it could film the event.
‘Okay,’ said Anna. ‘Let’s trim the craft ready for docking and lift-off.’
‘Chi, how are we in relation to orbit requirements?’ asked Mary.
‘Any time in the next four hours will do. We’ll come and get you in orbit if necessary,’ said Chi.
Mary said, ‘You know, it would be better if we could release the tethers remotely once we are attached to the tank. I’ll ask SpaceX to look at that when we get back.’
‘Sounds like a plan,’ I said. ‘There might need to be more on the side opposite docking though. Don’t like the idea of trying to dock with cables in the way.’
‘No. Good point,’ said Mary.
Fifteen minutes later, Tosh reported that all external lockers were empty, save those which contained rock and regolith samples. Anything not required had been put into the storage tent and we were ready to leave. Anna, Tosh and Mary climbed aboard.
Still standing on the surface, I pressed a button on my tablet and watched the tethers disconnect from the top of the tank and tumble slowly under the weak Mars gravity to the desert below. I tried to envisage any problem with Mary’s suggestion for doing this from inside the Rimor.
‘Tethers released,’ I said.
‘Copy that,’ said Anna, who was already in her pilot’s seat.
We climbed aboard, quickly donned our flight suits, and strapped ourselves into the seats. This was to be the most critical part of the mission and, potentially, with the ground not being as firm as we would have liked, the most dangerous.
12 Emergency
‘Everyone secure?’ I asked and got three affirmatives. ‘Okay, Anna. Take command.’
The engines started and Rimor lifted off vertically. It swung around and we could see the tank standing before us. Now the Rimor was manoeuvred into a vertical position. Anna could no longer see the tank and she activated the automatic dock system. Although it could be done manually, the automatic system was faster.
The Rimor approached the tank. My nerves tensed as I worried about the force of the engines causing more land slippage beneath us.
‘Warning. Tank no longer vertical,’ said the computer.
Anna made no comment, watching the external cameras intently as the Rimor came up against the tank and slid downwards into its docking brackets.
‘Warning. Tank no longer vertical,’ repeated the computer.
‘Angle, computer?’ asked Anna.
‘One point seven degrees,’ said the computer.
‘Docking brackets locked,’ said the computer, then after about fifteen seconds it added, ‘Fuel hoses connected.’
‘Computer, begin fuel pumping,’ said Anna.
‘Pumping commencing.’
The Rimor’s tanks were now filling with fuel from the main tank. We could not lift off until they were at least partially replenished, otherwise we’d have no manoeuvring capability in orbit.
‘Warning. Tank angle increasing. Now two point two degrees,’ said the computer.
‘Computer, how much fuel in the Rimor?’ asked Anna.
‘Sixty per cent. Tank now at three point six degrees and increasing,’ warned the computer.
‘We’re toppling,’ said Anna. ‘Prepare for lift-off. Computer, seal tank valves and disconnect the hoses.’
All of a sudden, the movement of the tank became obvious. I gripped my armrests. The entire assembly was falling and we’d be underneath it. I heard a gasp from Bill, but Anna was as cool as ever. Nothing fazed her. When the whole stack hit the desert, the lightweight tank would rupture. The oxygen and hydrogen would meet in our exhaust and we’d be consumed in the fireball. We’d certainly not survive. A childhood fear of fire passed through me. Would it be quick? I gripped the seat tighter.
‘Tank valves disconnected. Tank now in continual motion. Currently eight degrees,’ said the computer.
‘I’m firing,’ said Anna.
I saw her finger jab the red button on the screen before her and we felt the ignition and power of the tank’s motors joining our own. Lift-off began.
‘Warning,’ said the computer. ‘Lift-off not vertical. Assembly at seventeen degrees.’
We had left the ground. Seventeen degrees was certainly enough for us to feel as the ship started to gain velocity. I could see the Martian desert through the windows as we were now on our backs. We should be vertical. Automatic engine controls tried to bring us back to vertical. Not a word from Anna who I could see hitting buttons, bringing up displays, looking for solutions for problems yet to materialise. This was not a normal lift-off.
‘Assembly at fifteen degrees,’ said the computer, meaning that the gimballing engines had created some recovery. Could we regain the correct angle of ascent? My grip on the seat didn’t lessen.
Anna broke her silence. ‘Altitude one thousand metres. The problem is that the angle is changing our trajectory. We won’t be able to achieve the planned orbit,’ said Anna, as if it was no more important than being late for lunch.
I sensed the force of the acceleration. ‘Make any good orbit, Anna, and Spirit will come and get us,’ I managed to say more coolly than I felt.
‘Assembly at eighteen degrees,’ said the computer.
‘We’re losing it,’ said Anna. ‘The angle is too great for the engines to compensate. Be prepared for emergency separation.’
I could see it was all wrong. The desert almost filled the scene above my head. We weren’t going to make it.
‘Assembly at thirty degrees. Danger. Danger!’ said the computer. I guessed I wasn’t the only one hanging onto my seat with both hands.
‘Revolve us, computer,’ said Anna, still the epitome of the test pilot.
I watched the live schematic on the upper screen in the control panel. The ship was revolving, bringing the Rimor around to the top side of the tank from its previous position hanging beneath.
As commander, I was in an unenviable situation. Anna was without doubt in trouble. I couldn’t help her. The fear was tangible. I saw Tosh snap his visor shut. We weren’t getting to orbit. Anna was using the tank to gain as much height as she could, but at an angle of over thirty degrees the ratio of downrange to altitude was slipping and fuel must be running low by now. The tank jets were designed to maintain a fixed flight plan, but this was way off. Anna shut her visor, and that did worry me. I heard Mary close hers and snapped mine shut too.
When the rotation completed, the computer warned of fifty degrees and Anna shouted, ‘Brace for emergency separation.’ Still professional, as in control as it was possible to be. I wondered how often she had practiced this in simulation.
Crunch time. My heart rate was through the roof. This was it. Anna must disconnect before we’d reached a sufficient altitude to achieve orbit. Perhaps she had enough left in the Rimor to see us through the crisis. I didn’t know. This was not a scenario I’d been involved in during simulation. I’d have aborted a couple of minutes after lift-off.
‘Assembly at sixty degrees. Tank fuel at ten per cent,’ said the computer.
‘Emergency undock!’ said Anna. If it was possible, the rest of us gripped our seats even more tightly.
She hit the button which would separate us from the tank. A loud clunk sounded from outside, the Rimor shook, and we felt it accelerate now it was free of the external tank.
‘Computer, fuel?’ she said.
‘Fifty-four per cent,’ said the computer.
‘Computer, what orbit can we achieve with that?’ Anna asked.
‘Between forty-eight and fifty-five miles, Anna,’ replied the computer.
‘Chi. Do you have a fix on us?’ asked Anna.
‘Copy that. We do. Have been keeping our noses out of your problems, but monitoring them,’ said Chi over the radio.
‘Can you rendezvous at forty-eight miles?’ asked Anna.
‘Bit low. Add ten and we’d be fairly certain,’ said Chi.
‘Can’t be more specific,’ said Anna. ‘Either you can rendezvous at forty-eight miles or I’ll have to abort and return to the surface.’
‘What does Mary think?’ asked Chi. ‘I’m dubious of any rendezvous under fifty-eight miles.’
‘I’m with Chi,’ said Mary. ‘If Spirit descends to forty-eight miles, it might not have the manoeuvring power to get back into orbit.
‘Computer, fuel?’ asked Anna.
‘Forty per cent and falling at ten per cent per minute,’ said the computer.
I could imagine the calculations flying through Anna’s and Chi’s minds. I felt helpless. I couldn’t help with this and Mary was agreeing with Chi. Anna must make a decision before fuel reached twenty per cent. One minute had gone. Anna had less than sixty seconds to decide whether to abort or try a rendezvous which was likely to endanger both craft. Should I step in and call for the abort?
Five seconds later, Anna said, ‘Aborting!’
The power ceased and the Rimor was suddenly in a version of free fall that we all recognised from the vomit-comet back on Earth.
‘Ah, wings biting,’ she said.
The stomach-sinking sensation passed and we were now heading down towards the surface once more with the engines off.
‘Twenty thousand metres,’ said Anna.
‘Where are we headed?’ I asked.
‘We’re going in the general direction of Gusev crater. There’s plenty of flat terrain there,’ said Anna, as if she was just avoiding congestion on the journey home.
‘Ten thousand metres,’ said Anna. ‘Prepare for engine re-ignition.’
We were still coasting, but, unlike the space shuttle, we had no perfectly flat runway to aim for, so the engines would fire at about five thousand metres and we’d land as if returning from one of our excursion trips. This time, however, we had no way to leave the planet and our lives would be in the hands of Chi who would land a second tank close to our location.
I felt the thrust of the engines as they fired up and breathed a sigh of relief. At least Anna was in control of our fate again.
‘Under power,’ said Anna.
The next ten minutes were less stressful. We’d done this before. Anna chose the flattest area within Gusev crater that she could find and Rimor settled gently back onto the surface of Mars.
‘Engines cut,’ said Anna.
‘Copy that,’ said Chi.
‘Venting engines. Stable landing. Rimor has landed,’ said Anna. ‘Computer, fuel?’
‘Seven per cent, Anna,’ said the computer.
We all knew that five per cent was the bare minimum to fire up the engines to approach and dock with a tank, so we were close to minimums. No room for error. We’d only get one shot at it.
‘Well done, Anna,’ said Tosh. A rare compliment indeed from the usually belligerent and stern doctor, perhaps showing that he wasn’t immune to apprehension and fear after all.
I breathed a sigh of relief and seconded the praise, as did Mary.
‘We’d better get some rest,’ I said. ‘No point getting suited up for the surface this late in the day.’
‘No, but I’ll stay on duty,’ said Mary, ‘in case Chi needs us.
13 Anxious Times
I awoke as the weak dawn sunshine illuminated the inside of the Rimor. I was immediately anxious about our unexpected isolation. The landing systems required a method of lifting off to be available before the Rimor touched down. Our method of returning to orbit was now lying somewhere in the Martian desert, almost certainly having exploded on impact if the tank had ruptured. Fortunately, there were a number of plans to deal with this eventuality, but they were all less than ideal.
The computer told us that we had enough fuel to dock with the next tank when it arrived. Two external tanks were still attached to Spirit and also a spare Rimor. If we hadn’t enough fuel to dock, the other Rimor could come to our rescue, but that would reduce the backups to zero. First things first. Chi would have to pilot the second tank down to our location. All her calculations were being checked by NASA. Our fuel was sufficiently tight that we could not afford a lengthy journey to rendezvous with the tank.
‘Rimor, come in, over,’ said Chi over the radio.
‘Copy you,’ said Anna.
‘This is a little more complicated than we expected,’ said Chi. ‘Your location requires Spirit to change to a polar orbit in order to get the tank close to your location. NASA are currently checking my calculations.’
‘Send me a copy, please,’ said Mary.
‘On its way,’ said Chi. ‘Can you do an EVA and check that the ground is strong enough to take the weight of the tank? Find a section of granite bedrock rather than sandstone if you can, and send me the coordinates.’
‘We left the drill at Perseverance Valley,’ said Tosh. ‘We will only be able to make a visual judgement call.’
‘Did you hear that, Chi?’ I said.
‘Will have to do,’ she replied.
I said, ‘Let’s get suited up guys.’
Forty minutes later, we were ready to descend to the surface. Mary had her head buried in calculations, so it was Anna, Tosh and me who climbed down into Gusev crater.
‘Desolate,’ said Tosh, surveying the scene. ‘What’s this material we’re standing on?’
‘Basalt,’ I replied, ‘but there are hollow areas of compressed regolith which would not be so stable. What’s the plan, then?’
‘I’m heading out that way,’ Tosh said, pointing east. ‘Looks flatter than any other direction.’
‘I’m going to stretch my legs and then I’ll join Mary on these calculations,’ said Anna.
Tosh had already set off across the plain and I followed, watching him weave his way through the rocks, gradually catching up with him.
‘Why does the Martian surface have so many scattered rocks covering it?’ he asked.
‘Amazing as it might seem,’ I said, ‘many of these rocks were carried along by ice and dumped here when the ice melted. A long time ago, of course.’
‘The rocks aren’t from around here?’
‘Probably not, but I don’t have the equipment to check.’ I stooped to pick up a pineapple-sized boulder, and examine it. ‘Hmm, this is basalt, so possibly just brought here by wind.’
‘Surely the wind isn’t strong enough for that?’ Tosh said in surprise.
‘If it is that, then it is a slow process. Note how most of the rocks have a build-up of dust behind them on the western side.’
‘But the prevailing wind here is from the east.’
‘Yes,’ I said. ‘The rocks move towards the wind.’
‘How is that possible?’
‘The wind blows away the dust on the east side of the stones. Eventually a hollow is created and the rock slips into it. The pile of dust on the west side is then blown away and starts to build up against the stone once more. It is a really slow process. That might be the mechanism here or the alternative is the rocks being carried on ice. Probably the latter here as with wind effects the stones tend to be more evenly spaced.’
‘I had no idea. Look at this,’ said Tosh, kicking into the surface. ‘It’s a dust-filled crater. We need to avoid these when the tank touches down. But where is the crater rim?’
‘Worn away over millennia. This was almost certainly a lake bed at some time in the past. I’d need to read up on the papers written about it.’
We trudged onwards. Tosh stopped and began to kick away the dust from underfoot. ‘This is good. Solid bedrock. Now, let’s check how large this area is.’
‘Yes, basalt. Perfect,’ I said.
Thirty minutes later, we’d established that the solid basalt here spread at least fifty metres in each direction and was covered with no more than a few centimetres of regolith, which would be blown away by the exhaust from the tank’s landing jets. By eye, it looked pretty flat too. Tosh walked to the centre of the area.
‘Chi, do you copy?’ said Tosh.
‘Copy you,’ said Chi.
‘Mark my position.’
‘Marked,’ Chi said.
‘You have at least fifty metres diameter from here of solid basalt covered with light regolith,’ Tosh said.
‘Brilliant,’ said Chi. ‘I’ll program in the coordinates.’
‘Copy that,’ said Tosh, ‘but you mustn’t miss that spot as there are old hidden craters containing regolith dotted around the plain.’
‘Copy that,’ said Chi. ‘Let me know if you find anything to make it even more complicated!’
Tosh laughed. ‘See you soon,’ he said.
‘Never fear,’ she replied.
‘Can’t believe we’re on Mars,’ I said.
‘No. Amazing.’
In the far east a range of low hills, actually called the East Hills, spread softly across the horizon. Not huge, not jagged, just gentle and undulating. Between us and them, the rock-strewn plain was the floor of Gusev crater. So littered with rocks was it that, when walking, great care had to be taken not to trip and fall. The whole scene was a rusty brownish red colour.
Looking back to the west, there was hardly any raised ground in view, but hills far beyond the horizon were doing their best to peek across the extensive width of Gusev. In the near distance, about eight hundred metres away, the Rimor sat alone, looking for all the world like a child’s toy or some museum diorama.
‘Let’s get back, Tosh. We don’t want to be near here when the tank arrives.’
We walked back towards the Rimor, me occasionally hanging back to collect rocks and place them into a bag I had strung on my waist.
∞∞∞∞∞∞∞
‘That’s the tank separated,’ said Chi. ‘We have a four-minute hold before we start the descent.’
