by Jeff Pollard
“Talk to me, what do you guys see?” K says more insistently. The telescopes view was now the focus of the watching world. What would they see? A splattered spacecraft and body parts strewn across the crater? Or just a crumpled lander and no real new information?
“The lander is on its side,” Tim says. “It looks like it landed on a slope and rolled on impact. Pretty bad shape. Definitely lost cabin pressure. One of the landing legs snapped off and is laying a few meters away.”
Caroline switches her radio so she's just talking to Kingsley. “You think this could have been a hacker?” Caroline asks. Kingsley's eyes go wide as he has a realization: if it was a hacker, then it's possible that the Pegasus is a ticking time bomb, waiting to kill them when they try to take off.
“I don't know,” K says. “They did race to beat us by going on the first landing rather than doing a test. It might just be one of those first-time bugs that they didn't work out.”
“Or maybe there's a Russian psychopath hacker,” Caroline replies.
“Wait a minute,” Tim says. “I think I see...Yes. There!”
“What?” K asks.
“Absolutely, clear as day,” Tim says, talking to Mission Control.
“What!?”
“Survivors, at least two of them. They're outside the ship, standing about twenty meters to the west of the ship.”
“Just two?” K asks.
“That I can see right now,” Tim replies.
“Hawthorne,” K says.
“Go ahead,” Josh says.
“What's going on in the simulator?” K asks.
“They're working on it,” Josh replies.
“You drive,” K says to Caroline and she takes over the joystick. K starts punching numbers on a simple calculator on his wrist.
“What are you doing?” Caroline asks.
“Natural logs of mass-fractions,” K replies.
Sylvia Probst and Gary Ross, pilot and flight engineer, are in one of the Pegasus simulators at SpacEx headquarters. They've loaded up the virtual Moon and are now attempting the rescue maneuver of lifting off, heading about fifty kilometers south, landing four kilometers down inside Tycho Crater near a simple way-point, looking like a big red monolith placed in the best approximation they have of the crashed Boeing Lunar Lander. The maneuver itself isn't inherently difficult or taxing, assuming there's a decently clear and flat area close to the Armstrong to set down. But point-to-point travel is not something they practice. The real purpose of the simulation is to determine the amount of fuel that will be consumed in performing the maneuver Sylvia is at the controls while Gary reads off altitude, horizontal and vertical velocities, as well as fuel consumption.
She begins by doing the traverse in a baseline safe manner. Taking off and gaining a fair amount of altitude before pitching over, then pitching back so the lander is pointed straight up, the engine thrust keeps the lander from falling out of they sky and killing time while the horizontal velocity sends them toward their target. She pitches back to kill the horizontal velocity before a nice soft touchdown. They note the amount of fuel consumed. They did the first maneuver with the Pegasus at full capacity with the mass of surface samples and everything still aboard. The answer comes back immediately from a controller. Too much fuel consumed. And it's not even close.
“So much for not having to ditch weight,” Sylvia says. The screens flicker and the ship is back at its original spot outside Tycho Crater.
“This is reduced mass,” a controller says and Sylvia and Gary begin their second attempt.
Typically the dry mass of the Pegasus (dry meaning the fuel tank is empty) will be about 6 tonnes. That includes roughly a full tonne of margin for the mass of astronauts, supplies, and returning surface samples. In order to push that 6 tonnes of mass through 2.2 km/s of delta-v, they need right about 5 tonnes of fuel (making the wet mass 11 tonnes). As the Pegasus sits on the edge of Tycho Crater, it has a wet mass of 11.8 tonnes, or about 5.8 tonnes of fuel. Thus, if they could take off, head over to the crash site and land, all while using less than 800 kg of fuel (.8 tonnes), then they would just have enough fuel remaining to get to orbit.
In the first simulation, they tried with the full Pegasus dry mass of 6 tonnes, and ended up using 1.7 tonnes of fuel, leaving only 4.1 tonnes in the tanks, well short of the 5 tonnes they need.
Now for the second simulation they are virtually stripping down the Pegasus. Forget about Moon rocks, throw out the food, dump the human waste, get rid of everything extraneous. This gets the dry mass down to 5.3 tonnes. Then their dry mass at liftoff from the crash site will be four people heavier, a not insignificant increase of 320 kilograms. That makes the mass of the rescue ship, including eight people, about 5.6 tonnes
2200 m/s is the delta-v needed for the burn back to lunar orbit. Tsiolkovsky's rocket equation tells us the rest.
Natural Log of the mass fraction (wet/dry) x exhaust velocity = delta-v
ln (X/5.6) x 3734 m/s = 2200 m/s
Solving for X you find that the wet mass needs to be 10.1 tonnes. To get that 5.6 tonnes up to orbital velocity will require at least 4.5 tonnes of fuel.
Thus if Sylvia can take off with 5.8 tonnes of fuel, fly the Pegasus 50 kilometers south, 4 kilometers down into the crater, find a good landing site and bring her in for a soft touchdown and leave at least 4.5 tonnes of fuel still in the tanks, then a rescue mission is possible.
These calculations are done on the backs of napkins all over the world (and on a wrist-mounted calculator on the Moon) almost the instant the crash occurred. This is basic rocket math that could have been done in 1898. You can calculate rocket maneuvers with ease, as long as you know the rocket's basic characteristics like mass and exhaust velocity, but only if you know the delta-v of the maneuver. For launching to lunar orbit, one can simply consult a table of known orbital maneuvers. But there is no experience with point-to-point travel across the Moon and the amount of delta-v for a given maneuver would vary widely based on the distance, the terrain, and the pilot. And this is why Sylvia and Gary are in the simulator.
If Sylvia takes off, gains a lot of altitude, gets a modest and manageable horizontal velocity, hovers her way over, then slowly sets her down, she will use a lot of fuel. If she takes off, pitches over immediately, picks up an immense and dangerous horizontal velocity, then finishes it off with a suicide burn at the crash site, she will not use much fuel at all. The question is how aggressive the flight path needs to be. That's why she began with a safe baseline. Now with a stripped down spacecraft, she goes again, now with a fairly safe approach.
Sylvia lands near the big red monolith placed in the approximate location of the Armstrong. “What was it?” She asks.
“4.3 in the tanks,” Gary replies.
“Burned two hundred kilos too much,” a controller adds.
“Alright, let's get more aggressive,” Sylvia says. That means a faster horizontal velocity, which translates into less time in the air and less thrust needed to keep the ship aloft, and therefore less fuel wasted to gravity losses. She tries again, pitching over almost immediately, scooting along the crater rim at only 100 meters in altitude, maintaining a high rate of speed, waiting till she's almost to the target to kill her horizontal velocity rapidly, then find a safe spot and set her down as quickly as possible.
“Score?” Sylvia asks.
“4.38,” Gary replies. Sylvia looks to Gary, realizing it's unlikely that she'll be able to fly much better than that and still has a lot of ground left to make up. “At least it's progress.”
“Right. Progress,” Sylvia says while trying to pretend that this isn't going to be an impossible task. The screens flicker and they're back at the Pegasus landing site.
“Let's go again,” Gary says.
Kingsley punches in numbers into his calculator on his wrist for fifteen minutes solid while Caroline finishes the drive back to the Pegasus.
“How many numbers are there to crunch?”
Caroline asks.
“I'm working several hypotheticals,” K says.
“Like what?” Caroline asks.
“You don't want to know,” K replies.
“Try me.”
“What if we only bring two passengers,” K says.
“And leave two bodies behind?”
“If they're already dead,” K says. “We might have to pick two to leave behind.”
“Is that a possibility? Are we gonna be picking people to leave behind?”
“We might,” K says simply. “Hawthorne, what's the word from the sim?”
“Last I head, 4.42 tonnes was the best they've done so far,” Josh says.
“Tell her to fly it more aggressively,” K says.
“So what did that number tell you?” Caroline asks.
“That if we go down in that hole we're all as good as dead.”
“4.44 tonnes,” Gary says to Sylvia.
“Dammit!” She smacks the wall of the simulator. She knows she's not going to improve on that last run.
“Let's go again,” Gary says matter-of-factly. Sylvia takes a deep breath and prepares to try to set the most important high score anyone's ever set on a simulator.
“This is the last shot,” Sylvia says. “Total suicide burn.” They blast off and she pitches over so quickly that the Pegasus is barely 15 meters up before it's almost entirely horizontal. She scrapes along the lunar surface with so little clearance that a boulder the size of a small house could rip open the side of the ship. They barely clear the lip of Tycho Crater and begin a descent at a very high rate of horizontal speed. She burns vertically, just enough to give them the hang time to last until she starts the suicide burn. They coast in silence above the crater floor, preparing for a last-possible-moment high-thrust burn to bring them to a near stop above their destination. She waits, waits, waits, then hammers the throttle. The Pegasus slows rapidly, the red monolith racing towards them.
The Pegasus crashes into the lunar surface, she waited to start the suicide burn just a moment too long, and they crash into a boulder near the monolith at over 30 meters per second.
“4.46 tonnes,” Gary reads off. Sylvia takes off her headset and walks out. Gary sits down in the passenger seat. They both realize that even when taking just about the most difficult flight path, pushing the limits of the lander, and even going beyond those limits and crashing it, they still burned too much fuel.
Caroline stops Wally a few meters from the Pegasus. Kingsley stares at his calculator but isn't pressing any buttons.
“Let's go,” Caroline says, snapping K out of a trance.
“First, help me with this,” K says, pointing to the massive Selene rock wedged between the two seats on the back half of the rover. The two of them pick it up then drop it off the side of the rover, where it lands in the loose soil. They get down and head for the Pegasus. Kingsley opens up the cargo compartment on the side of the lander. He starts pulling out boxes of samples, setting them down on the lunar surface. Caroline helps, and they silently get rid of all of the samples they so carefully picked out over the past four days.
Back inside, K immediately asks on Sylvia's progress.
“Best score was 4.46,” Tim says to K.
“That's close,” K says optimistically. “Tell her to go more aggressively.”
“That was the best they could do. She's crashed it five times in a row now and they haven't beaten that number,” Tim replies. K closes his eyes and covers them with his hands. “Gary's tried too, and he hasn't done any better.”
“Then it's impossible,” K says.
“That's only 40 kilos short,” Caroline pleads.
“If we try it, we will die in that crater too,” Tim says. “We don't have any option.”
“There is one option,” Jim Lovell speaks up. “You could leave me here and maybe have just enough. I've lived long enough. I die, but you can save maybe four.”
“I hate to ruin your heroic old-timer moment,” Kingsley says. “But leaving one behind isn't gonna cut it. We'd have to leave two people behind.”
“That's not an option,” Tim says. “Leave behind two to try to save two, maybe more, but just two that we know of? That's just not a realistic option.”
“So what, we don't even try, we go back home and leave them?” Caroline asks. “Isn't there something we can do? We take on some of their fuel when we get there?”
“We have no means of transferring fuel, and even if we did, we can't count on their tanks being intact,” Tim replies. “We might as well pack our samples back on board, because there's just no way we can go down in that crater and still get back to orbit. We have no choice.”
“Actually,” K says quietly, looking at his feet. “We do have one other option.”
Chapter 34
“You really think this can work?” Jim Lovell asks Kingsley. K's standing in his EVA suit in the evacuated airlock and Jim on the porch just outside. K passes containers, unnecessary hardware, food bags, etc., to Jim who tosses them overboard.
“I think it can,” K replies. Having dumped all the unnecessary materials possible, they climb down the ladder to the surface. Kingsley gets down on one knee and grabs up all the lunar surface samples, dozens of containers and hundreds of numbered plastic bags, handing them off to Jim Lovell who sets them onto the back of the Wally rover. K places the Selene rock with the rest of the samples. Wally will be able to drive to wherever the next landing takes place and deliver all these samples so they can still be collected and their work from this mission won't have been totally wasted.
With the samples loaded up, Jim and Kingsley board the rover's front seats and K begins the drive south to the rim of the crater. They leave behind Caroline and Tim in the Pegasus lander, kicking dirt up high as they go.
Before they reach the rim of the crater, the Pegasus zooms nearly directly overhead at an altitude of just a few hundred meters. K and Jim can hear Tim and Caroline over the radio as Tim pilots and Caroline assists him by reading out data.
“Talk about a flyover,” Jim says as they watch the Pegasus until it disappears over the horizon. The radio feed cuts out and Jim and K are back in silence. It takes nearly twenty minutes for them to reach the crater rim, during which they have no contact with the Pegasus. The Wally has contact with Earth, but while driving at a high rate of speed over the lunar surface the reception is intermittent at best. So they drive on in silence until they reach the crater rim, not having any idea of the results of the Pegasus flight.
When they reach rim of the crater, K slides the Wally to a stop. Their earpieces crackle and then pick up on Tim and Caroline's voices.
“How's it going down there?” K asks.
“We're suiting up now,” Tim says as he pulls the port closed behind him, sealing him in the EVA suit. “Rough terrain around the crash site. Closest I could get was about two hundred meters short.”
“Fuel consumption?” K asks on the radio.
“Should be fine,” Tim replies, but with his calm pilot voice you never know if he's actually worried or just trying to keep others from worrying. “Ready?”
“Yeah,” Caroline says as she releases from the port and takes a step out on the porch. Caroline searches the crater rim briefly, not seeing the rover that's up there somewhere. They climb down and then proceed around the Pegasus, revealing the Armstrong up ahead over rough and rocky terrain. Tim leads the way, hopping along from one foot to the other. The rough terrain causes the Armstrong to disappear and reappear as they bob up and down in the undulating terrain.
“We're nearing the lander,” Tim says, speaking both to the world at large and Kingsley and Jim up on the crater rim. “Heavily damaged, with obvious holes in the side. There are footprints surrounding the ship. The hatch is on the other side, going around now.”
Tim discovers two astronauts in pressure suits sitting in the shade, backs against the gold Mylar of the broken lander.
Tim and Ca
roline stand over them, in full sunlight, simply stunning them with the unlikelihood and the brilliance of their appearance.
“I've got Hadara Sharon and Dexter Houston,” Tim says. “They look okay, they must be the two we saw with the scope.” Hadara and Dexter hear nothing at all and quickly come to grips with a new reality after having already given themselves up for dead. They're holding hands. Caroline notices this detail but says nothing of it. Both Dexter and Hadara are married, but it seems to Caroline that she has just entered from stage left in the middle of a dramatic death scene.
They lock eyes, but they cannot communicate. If the ULA astronauts were in their EVA suits they could talk on the radio, but since they lost cabin pressure in the crash it was impossible for them to switch suits. The pressure suits aren't designed for independent operation, they rely on linking to the spacecraft for communication. With the spacecraft totally disabled, the four ULA astronauts have been cut off even from each other. They could only hear each other if they physically pressed their helmets together.
“What about the other two?” K asks. Caroline and Tim help Dexter and Hadar to their feet.
“Where are the others,” Tim says, mouthing the words very deliberately to Dexter as they are face to face. Dexter point to the hatch. Tim gets on his knees and crawls through the sideways hatch, which had to be pried open for Dexter and Hadara to exit a few hours ago.
Tim enters, standing up on the side wall of the crashed lander.
“Sergei is inside,” Tim says. “He's lying on the wall and his eyes are closed.” Tim then sees the fourth member of the crew, Richard Branson, sitting upright with his back to what used to be the floor with his golden visor down, obscuring his face. “I've got Richard, his visor is down, he's not moving either.”
“Are they both dead?” Caroline asks as she joins Tim. Dexter crawls in behind them. Dexter smacks Sergei's arm and his eyes shoot open.
