Solar Sailer

by Stephan Besik

  “Uh, Mr. Treble, uh, I just got this assignment. I guess the rep who knows this story is out sick. I apologize if my questions are silly. You mentioned ‘solar sailor’ and ‘solar ship’. Does that mean your spaceship is powered by the Sun?”

  “I didn’t catch your name, sir.”

  “Oh, sorry again, I’m James Adanaya. I’m from Science and Politics.”

  “Well, Mr. Adanaya, I hope your friend recovers soon.

  Concerning your question, you’re right. Edison is the first of what I hope will be a series of solar powered spaceships capable of transporting large cargoes, and eventually people, to the Moon. In addition to Edison we have one more ship in final assembly at the Treble Systems space dock in Earth orbit, and another in parts at our facilities in Taiwan, Costa Rica, and Puerto Rico.”

  A young lady rose immediately and asked the next question. “Cynthia Camallo of Science International, sir. I understand your ship uses ammonia fuel. Did you consider any other options, and if so what were they?”

  The first reporter looked confused and interrupted. “Wait, I thought the ship was solar powered?”

  Arman responded, “It does use ammonia fuel. I understand that other fuels were considered but there were strong arguments for ammonia. As for your confusion, Mr. Adanaya, you have to remember Newton’s Third Law. You know, for every action there is an equal and opposite reaction? Edison uses electricity provided by its solar panel sails to accelerate ammonia ions, which provide thrust to propel the ship.” He grimaced ironically. “And I am afraid you have exhausted my technical knowledge concerning the ship’s propulsion. I will have to refer any technical questions to the head of the Treble Space Unit, Dr. Chaz Delsun, who can also put you in touch with my technical staff for anything really complicated.”

  Another reporter’s hand went up. “I’m Samuel Loo, U.S. correspondent for Taiwan Science. It took roughly three days for Apollo 11 to get from Earth orbit to the Moon. Are you saying your ships will get people to the Moon in less than a day?”

  Aman was beginning to thank his stars for the long briefing Chaz had given him. “That’s right, Sam, we think eighteen to twenty hours from earth orbit to lunar orbit. And we won’t leave anything like boosters behind when the ship returns.” He stopped for a moment to come up with a good way to communicate his next thought. “Speed has never really been an issue in getting to the Moon. It’s always been about the expense. Our solar sailers are going to do their jobs not just quickly, but cost effectively. The biggest problem of getting to the Moon has been solved not by us but by the people who have made inexpensive trips to Earth orbit possible. That’s always been the big cost. We’re going to go faster, but it’s more about cost, reusabililty, and reliability for us. The Moon isn’t going to be our big payoff, either. The real payoff will come when we begin to make trips into interplanetary space, where the continual acceleration of our ships will greatly reduce cost compared to chemical rockets, making human travel to Venus, possibly Mercury, and perhaps even Mars truly practical.”

  A hand in the cluster of politicians went up. “I am Serafina Delgado, representing Mexico. As signatories to your Lunar Compact, will there be any benefit to us as you begin interplanetary space travel?”

  This was another question that Aman wanted to answer in exactly the right way. He smiled. “That depends. As a signatory, we hope you will take advantage of the intent of the Compact and give serious consideration to sending not just scientists, but other skilled workers as well to the Moon to help establish human habitats there. If you’ll forgive a theft of an old company saying, we would also like you to consider buying a piece of our rock. Your country and the others that have joined the Compact will be given priority as you help us build places for the first space settlers to live and work. The Compact contains rules for establishing ownership of portions of the Moon’s surface, so the legal wrangling over who owns the Moon can be kept to a minimum. We believe this will benefit both your nations and our project by showing your citizens what you have obtained for their tax dollars and enabling the development of a group of skilled citizens in space. Their discoveries will contribute to the welfare of your people, and these citizens of your countries will be in great demand as space becomes the next frontier for all of humanity.”

  Ms. Delgado asked another question. “Can you be more specific about benefits? The major space powers think there is no rationale, other than scientific curiosity, for establishment of permanent habitations on the Moon.”

  Aman knew his briefing had been superficial but he decided to try an answer anyway. “We believe that merely addressing the challenge of survival on the Moon will be of enormous value to humanity over the long run. I understand your concern, though. The dollars needed to fund a Moon colony are immediate, while the scientific benefits are in the future, at best.

  Our intention is to establish the Moon as a waystation on humanity’s journey to the other planets of the solar system. The Moon has all of the materials necessary to build ships that can journey to the planets. Beyond availability of materials, energy is much cheaper than on Earth. In the short run solar energy is available in greater quantity than on Earth. In the long run the Moon has a greater supply of deuterium and tritium, isotopes of hydrogen that will be used to fuel fusion powered space ships. Perhaps even more important, the cost of building and operating spaceships will be considerably reduced if we don’t have to bring fabricated parts up from the bottom of Earth’s gravity well. If we can build and fuel ships on the Moon, getting to the planets will be much more cost effective. The cost of a colony on the Moon will be high, but it may be quite small compared to trying to build and fly ships from the Earth’s surface. And if we’re going to Mars or Venus anyway, why not do it cost effectively?”

  A number of hands went up. Aman knew he was already out of his depth and it would be a good time to hand the session over to Chaz. He smiled again and held up his own hand.

  “I really think it’s time for me to get back to the things I know well and leave questions about planets and spaceships to people who understand these things. My good friend and director of my space unit, Dr. Delsun will take over now. Thank you very much for attending our announcement.”

  Maiden Voyage

  Wallace looked at the screens over Albert’s shoulder. They were both nervous; even though the scaled down prototype had worked well they were scaling up a lot, with more weight, more stress on the sails, and more heat to dissipate. If this worked, though, the world was going to be a different place. Especially in space.

  “How does it look?” he asked.

  Albert scanned the screens and cracked his knuckles. The knuckle-cracking was the tell that Albert was nervous. Suzette stood behind the other workstation, looking over Robbie’s shoulder.

  “Everything looks good. All green; no marginals. Mark One looks good; power to environmental and control systems nominal.”

  Mark One was the first of a series of control points along the sail masts. It was the minimum position of the sails as long as the ship required power. The sail area exposed to the sun at Mark One was just enough to run the ship’s systems and charge the batteries without starting the engines.

  Wallace took a deep breath. “Okay, then. Albert, unlock from the frame. Robbie, push her off with maneuvering jets on Albert’s mark.”

  Almost immediately, Albert announced, “Frame unlocked. All locks clear. Jets on at Five, Four, Three, Two, One, Mark.”

  Everyone looked at the exterior views of Edison on the central screen. A half dozen views of various parts of the ship were displayed, with rotation of two views every thirty seconds. Robbie turned the small control wheel of the maneuvering jets and pushed buttons. The ship moved ever-so-slightly away from the space dock, continuing to drift after the jets were shut down. Once the ship was a few meters away from the frame, Robbie announced, “Ship clear of frame.”

  Wallace spoke into the air. “Alvin, how are you doing?”

  A disembodied
voice filled the control room. “Everything is A-OK, Wally.”

  Wallace wasn’t a fan of the short form of his name, but Alvin stuck with it. Alvin would handle navigation and engineering on the voyage. It was a test not only of the ship, but of Alvin as well. Although Alvin had flown the scale model, that one was never intended to venture out away from the Earth. Alvin was going to take this trip to the Moon and back.

  With a little luck the people in the control room on Earth would have little to do during the trip. The human team on Earth would monitor only the first few hours as Edison’s early acceleration widened her orbit. Alvin would handle most of the remainder of the trip, including insertion into orbit around the Moon. Assuming all went well on this no-cargo “dry run” the human team would exert greater control during the next run, when three fairly expensive automated research stations and six mobile drones would be the cargo. People would be observing and involved as Edison’s cargo was separated and the cargo components landed on the Moon’s surface.

  “Okay, Alvin. We’re going to get moving.” He turned to Robbie. “You’ve got the con, Robbie. Unfurl the sails to Mark Two. Ship’s engines on ten seconds after sails at Mark Two.”

  They all watched as the next portion of the black solar panels unrolled to form more sail area. The process was both slow and tense; some of the sticking points in the first system tests were failures of the small sail motors. The problems had been solved for weeks, but the team still remembered the frustrations.

  “Engines One and Four up and running at low power,” announced Albert. “Fuel consumption matched. Gimbal controls wiggled and operating smoothly. Acceleration at zero point five meters per second-second.”

  Alvin’s voice came on over the speakers. “Confirmed. Moving slow but sure.”

  Wallace rubbed his hands together and smiled. The rub was his nervous tell. “Okay. Unfurl the sails to Mark 4. Let’s give her a shove.”

  Albert smiled. “Aye, Captain.” He turned the control for the sails, watching the motor positions on the masts and the slight increase in fuel consumption. Now everyone was smiling.

  Albert announced, “All systems nominal. Engines Two and Three online and synched. Acceleration at one meter per second-second.”

  Alvin came on the PA system. “Navigation program up and running. Recalculating trajectory to compensate for launch initial conditions.”

  Next came the big question. “How’s the heat in the propulsion system?”

  Alvin responded, “Heat looks good, in nominal range. Looks like I’m not going to get toasted.”

  Wallace smiled broadly. “Okay, guys. Check stress readings as acceleration and steering take effect. Let’s see how she does now that she’s at full power. Alvin, start pulse cycle. One hour of thrust for one hour of drift. We’ll take it easy this trip.”

  “Aye Aye, Captain.”

  “Robbie, Suzette, any concerns on trajectory?”

  Robbie responded, “Nope. We’re off a little bit but barely worth the course correction. Probably should wait until we get to the ellipse to make a correction.”

  Suzette nodded. “Agreed. Trajectory is well within the error envelope at the moment. The recalc hardly changed on launch.”

  Alvin interrupted the silence after the ship went to full power. “Isn’t this where people break out the champagne or something?”

  Wallace kept his smile. “Not yet, Alvin. Not until you get back from the Moon. Then the party will begin.”

  To the Moon and Back

  So far the plan had gone flawlessly. The trip to lunar orbit had gone quickly and the nearly month-long stay above the Moon was over.

  The human crew had been inactive during most of the trip, with the exception of the turnover of the ship to begin the midcourse deceleration. They watched Alvin do his thing for a few seconds as he made sure that the torque of the ship’s hull as it rotated to reverse direction was balanced. The sails stayed pointed toward the Sun while the hull rotated in its gimbal to point the ship’s engines opposite the outbound direction of travel, beginning the task of reducing the ship’s speed as it closed with the Moon.

  Suzette, Lucy, and Robbie had started working with Alvin to develop an observation plan that took advantage of Edison’s ability to maneuver under acceleration shortly after he was awake and fully programmed. There had been refinements in the plan and mods of Alvin’s programming as issues arose. Once Edison reached the transition into lunar orbit Alvin and the computational people began work to execute the plan, collecting new mapping and spectrographic data on Edison’s first cruise to update information required to determine a site for human-inhabited research stations. The stay near the Moon lasted a full thirty days, to enable Edison’s video systems to record a map of the entire lunar surface in daylight.

  In many ways the Moon is a tough customer to produce a comprehensive orbital exploration plan for. The ship had to orbit in a north-south direction because of the importance of the Moon’s poles as possible locations for human habitats, locations where water ice in permanent shadow and energy in the form of nearly constant sunlight were close to one another.

  Then there was the problem of highly variable gravity. The Moon’s gravity changes significantly from place to place due to patches of dense material in some regions of the Moon. In particular some of the large meteor impact basins, which in theory should have a somewhat lower than average gravity, have higher gravity due to the higher density of the material in and under the basins. These areas, ‘mascons’ for short, cause Low Lunar Orbits (LLOs; about sixty kilometers altitude) to be unstable for satellites attempting constant velocity transits, orbits that don’t require power. Alvin had to use information from previous lunar expeditions to help him account for changes in Edison’s altitude as it passed over the dense impact basins. Fortunately for the purpose of polar exploration there are a small number of orbital paths at angles to the Moon’s equator that are fairly stable over the long term. Alvin used this information to establish orbits that were stable during the stay of the moon ship in orbit around the Moon. This minimized the use of fuel while giving Edison an excellent view of the poles for her instrument package.

  Another important aspect of the exploration plan was the long-term operation of the ship on nearly constant velocity (often called “frozen”) orbits with half of the orbit in the dark. The ship ran on batteries during the nighttime phase of an orbit. During the daylight phase the ship had to recharge its batteries, as well as use its plasma engines to compensate for any loss of orbital altitude due to mascons along her orbital trajectory. This meant that the ship’s systems were constantly changing state during each orbit, from charging and acceleration on the daylight side of the Moon to battery supported, constant velocity operation on the night side. While some testing of the expected lunar circumstances were done in Earth orbit the first trip to the Moon was a test of the reliability of the ship’s systems where little help was available.

  Another aspect of the orbital problems was the interaction of the strong gravity of the Earth with the gravity of the Moon. Earth’s gravity was strong enough that circular lunar orbits higher than twelve hundred kilometers were not stable. Fortunately Edison could stay in LLOs to complete its exploratory mission.

  The team reviewed Alvin’s orbital plans every other Earth day based on the data collected by Edison and from prior explorations.

  “Great work, Alvin,” commented Suzette. “We’ve gotten a lot of new data, especially the fine-grained spectrographic, magnetic and electrostatic data that we need.”

  “That’s right,” added Lucy, who was now operating as the drone exploration manager. Her construction duties had been handed off to another in-space drone handler, although she had done much of the training and was still a principal advisor for the drone operators. “The habitat planners have been really happy with the stuff you’ve been sending back. We will be in great shape for the probe deployment on the next trip.”

  “Is that a go for the next run?�
� asked Alvin. “I don’t have an account on the construction computers so it’s hard for me to monitor the progress. Same goes for construction of the new ships.”

  “Well, from what I can tell the probes are making the trip in a container in about three weeks,” the drone manager replied. “That should give you time to get back here, and then give us time to go over you to look for issues arising from this first trip. Once you’re certified ready by the QA team we’ll be loading the drone container into your cargo frame, and you’ll be going back to the Moon.”

  “How will the drone deployment work?” asked the ship.

  “The container is the launch platform for the exploration units,” explained Robbie, who was managing much of the movement of assets in orbit. “There are going to be three stationary units deployed, plus a construction drone to do some preliminary surface grading and testing, and the first three of six mobile drones that will be doing a fair amount of roving near the surface.”

  “Well, it all sounds good. When do I start for Earth orbit?”

  Suzette pulled up a display of the Moon and Edison’s position. “I think you can start for home as soon as you check the thrust plan I’m sending you. It’s based on the assumption you stay in your current polar orbit until you are in the sun to start acceleration. You’ll deploy sails and begin to modify your orbits with declining angles of inclination, plus a spiral out of lunar orbit so you head roughly toward Earth’s equator. The plan is to use point one gees acceleration to get you in full sunlight and away for the trip back. You’ll start decelerating as soon as you clear the Moon’s gravity to get back into Earth orbit. Once in orbit you will make adjustments to match speed and location of the Treble dock. Once you are docked, the drones will climb aboard and start gathering data on your condition. We’ll begin preparation for your second trip as soon as your condition check is completed. Assuming there is nothing significant found, of course.”