Gravstar drive is the simplest and slowest form of faster than light travel. For Humans, the process was discovered in 2217 on Terra at CERN by a team of physicists led by Oscar Graveling, but historical records indicate that the Founders employed gravstar vessels one hundred thousand years earlier. Gravstar technology is based on hyper-string theory and the creation and manipulation of pseudo gravity fields. While a standard propulsive hyper-string pseudo-gravity (HSPG) drive provides only reactionless compensated thrust, a series of externally mounted HSPG generators can generate a field that effectively isolates the enclosed volume from classical Einsteinian space, allowing acceleration to theoretically infinite velocities. Instead of undergoing relativistic effects as it approaches the speed of light relative to its external environment, a gravstar vessel instead slows fades away, vanishing from the sight and influence of the external universe as it passes the light barrier. For an internal observer, there is no time dilation, and the universe fades to blackness at superluminal velocity; though ironically, internally calculated travel time is the same as it would be for an equivalent Einsteinian voyage; only the time elapsed at rest velocity is impacted by the gravstar effect. Total velocity is limited only by power available for the gravstar drive units and the ability to dump heat from the vessel at superluminal velocity. Besides the lack of time dilation and the subsequent potential cultural effects on the crew, the greatest benefit of gravstar travel over a conventional HSPG sub-light voyage is the protection afforded from interstellar debris at velocities approaching that of light.
In Human events, gravstar technology occupies niches in the history of interstellar travel. The Terran gravstar ship Pride of Terra, captained by Aaron Timmins was launched in 2219 and arrived at Alpha Centauri after a two and a half year voyage. After returning to the Solar system in 2224, it never flew again, and with the repeal of the Comparative Advantage Amendment in 2233, gravstar travel took a back seat to macrojump technology. Only after the last microjump starships had failed during the Dark Age, did gravstar travel reemerge, with the Alimeen perfecting the technique and launching the Black Horizon to Kalmar in 2461. Exceeding three times the speed of light, it arrived at Kalmar in 2465, starting a process that led to the creation of the Kalmar Pact in 2482. Later vessels, starting with the Vapor of Life, launched in 2493, allowed travel at four times light speed. Twenty-five Kalmaran and seventeen Alimeen gravstar vessels plied interstellar trade routes for over a century, until the reintroduction of macrojump drive to the Pact when Atlantis joined in 2572. Humans soon discontinued gravstar use, though the Alimeen, who where very sensitive to macrojump travel, adapted several vessels to utilize vacuum distillers at sub-light velocities, effectively increasing maximum velocity to 6C. Alimeen gravstar vessels continued to ply their own trade routes until the mid twenty-eighth century.
Historical records indicate that the Founders used gravstar technology for over six thousand years, eventually developing vessels that could exceed 144 times the speed of light. In the late twenty-eighth century a team of Alimeen scientists led by Spray of Hungry Mists constructed a vacuum distiller that could extract energy in the upper dimensional realm of superluminal travel. While this technically allowed for infinite acceleration, heat dissipation was a limiting factor. The Alimeen Industrial Council, in cooperation with the Imperial Ministry of Science, constructed the Infinite Horizon in 2806. This experimental vessel was capable of 15g acceleration and reached a peak velocity of 30C during a test run from Alimeen to Paradise, arriving after four years travel. The Ministry of Science lost interest in funding further experiments as the Autonomist Civil War ensued, but the Alimeen Industrial Council funded the construction of the Fast Vapor in 2823; this vessel achieved 36C with 18g acceleration, and, along with three sister ships, remained in service in the Alimeen sphere until the Heshar War.
The collapse following the War of Disintegration provided another window for gravstar vessels to operate. The Alimeen redeveloped 6C DF gravstar vessels in the 51st century. These gravstar vessels contributed to Central Region trade and maintained linkage between scattered Alimeen worlds. Export licenses allowed DF gravstar behemoths to form the backbone of the Osiris Diaspora three centuries later. After redeveloping upper dimensional vacuum distillers, the Alimeen introduced 36C SD vessels, starting with the prototype Night Vapor in 5732 and these continue to form the backbone of Alimeen travel and commerce, though other races have since abandoned gravstar technology.
A gravstar drive system requires only the perfection of the theories and application of hyper-string pseudo gravity manipulation. Once a practical HSPG drive is available, building a gravstar ship is a fairly straightforward matter.
Gravstar vessels accelerate using a series of externally mounted HSPG thrusters arranged to enclose the vehicle in a weak upper dimensional field. As with a standard HSPG drive, these thrusters convert energy directly into acceleration and like a true gravitational field, impart no acceleration force to the object influenced. As a result, high accelerations are practical. However, unlike standard HSPG drives, the nature of the enveloping field precludes the use of pseudo gravity plating for gravity compensation, and the volume within the gravstar field remains in free fall. Habitat portions of a gravstar vessel are normally spun to provide artificial gravity.
The gravstar drives can utilize any power source, though high efficiency meta-stabilized metallic hydrogen (MSMH) fusion drives were standard for all Human gravstar vessels. As mentioned above, standard vacuum distillers do not function once a vessel has exceeded Einsteinian light speed, and vacuum distiller technology usually does not mature until after macrojump drive is available. The Alimeen modified gravstar vacuum distiller will operate above Einsteinian light speed, but heat dissipation into upper dimensional space is a limiting factor in this technology. The Fast Vapor and Night Vapor classes of vessels achieve 36C after two years acceleration, but need to coast at that velocity until ready to decelerate when 36 light years from the target system. It is not known how the Founders overcame this technological hurdle, but even they eventually abandoned gravstar vessels for faster worm drive travel.
The following table illustrates typical limits for gravstar vessels:
|Class||Fuel source||accel||max C||time to max||dist to max||Year|
The values on the table above indicate typical performance characteristics. Class is the basic type of gravstar vessel, related to fuel sources. The values for acceleration and max C indicate the typical acceleration limit in standard gravities and maximum attainable velocity in multiples of light speed. These values assume a loaded fuel/payload ratio of 3:1 (75% of mass is MSMH at departure) for Class F and DF vessels. Actual operations at higher fuel ratios resulted in slightly better performance; for example, most Pact F3 vessels could reach a max C of 4.2 under normal loads. Class SD vessels are limited by heat dissipation, not power plant fuel, and the value above indicates the best performance of the Alimeen Fast/Night Vapor classes. Note that unlike macrojump fields, gravstar fields do vary in intensity based on the mass they must influence, and mass, not volume, is the limiting factor in acceleration. Time to max indicates the period in standard years of constant acceleration needed to reach max C. Dist to max is the distance traveled in light years before reaching max C. Year is the year of initial introduction of the first vessel of a particular class. Note that an F3 vehicle requires at total of one year and two light years to accelerate to and decelerate from max C. Therefore, a voyage of 18 light years would require 5 years time: 1 for acceleration and deceleration, and 4 at max C coast. A voyage of 58 light years would similarly require 15 years. An SD voyage of 900 light years would require 27 years travel.
Gravstar voyages are normally steady and uneventful. The major consideration for operations is the amount of time a voyage requires. During the Dark Age, the Kalmar Pact operated over forty gravstar vessels. Both Human and Alimeen crews dealt with the log voyage time by running their vessels with a skeleton crew while the rest of the crew remained in hibernation. Human crews typically consisted of twelve teams of five, while the longer lived and more patient Alimeen relied on six crews of five.
Typically a crew would serve for one full round trip, with all crewmembers conscious at the beginning of a journey and all crew members awakened after arrival at the destination system.
Human crew rotation typically obeyed the following schedule:
In this crew rotation, the Command team is responsible for the initiation of a voyage and initial acceleration. The Second team is also awake during the high activity period during the start of a voyage, and remains awake until engine shutdown at max C. Eight sweep teams, responsible mostly for system maintenance during the long dark voyage, supervise the coast phase of a voyage. The ninth or Last sweep team works with the Anchor team to restart engines and begin deceleration and the Anchor team stays on to wake the Command team to prepare for the reentry into Einsteinian space and the end of the voyage. The lengths of periods 1, 2 , 11, 12 correspond to half the time required to reach or slow from max C. The length of periods 3-10 varies depending on the length of the voyage, but correspond to 1/8 of the coast phase. Generally a sweep period ranged in length from under five months for the Delphi run to almost twenty months for the Prometheus run. Very short runs would operate with fewer sweep runs and a smaller overall crew, though all Human Pact gravstar ships could accommodate sixty crewmembers.
Normal crew progression would see a recruit crewmember advance from Sweep crew to Sweep team leader to Last Sweep crew to Anchor, then to Second and Command crews. As the need for crews expanded with the commissioning or more vessels, many crewmembers progress from crew recruit to command crew, and two progressed from Sweep recruit to Captain.
Unlike macrojump travel, gravstar travel is a gentle process. The major risks associated with a gravstar transit are related to the hibernation process. The Kalmar Pact Human vessels mitigated this risk by relying on Sterling Model 8510 and 9500 hibernation chambers, high quality systems that emphasized safety over speed of immersion and emersion from hibernation. Statistically, these Sterling models had a less than 2 in 100,000 fatality rate in normal operation, and during the entire Pact gravstar era, no crew members died from hibernation related causes. With basic medical training a prerequisite for every crew position, even onboard accidents were normally handled by the crew conscious at the time. In the entire Pact gravstar era only three gravstar crewmembers died on duty, all in a riot on Olympus in 2560, with two suffering musket wounds and a third trauma from an axe.
The Human gravstar era ended before the F3 model vessels reached operation limits. Studies based on Alimeen vessels indicated that a vessel could expect an operational lifespan of 500-700 years. Human gravstar travel ended because it proved too slow to compete with other forms of faster than light transportation.
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